Stanford Research Systems SR785 Operating Manual And Programming Reference
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Stanford Research Systems SR785 Operating Manual And Programming Reference

Dynamic signal analyzer
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Operating Manual and
Programming Reference
Model SR785
Dynamic Signal Analyzer
1290-D Reamwood Avenue
Sunnyvale, CA 94089 U.S.A.
Phone: (408) 744-9040 • Fax: (408) 744-9049
Email: info@thinkSRS.com • www.thinkSRS.com
Copyright © 1995, 1996, 1998
Stanford Research Systems, Inc.
All Rights Reserved
Revision 1.4 (December, 2006)

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Summary of Contents for Stanford Research Systems SR785

  • Page 1 Programming Reference Model SR785 Dynamic Signal Analyzer 1290-D Reamwood Avenue Sunnyvale, CA 94089 U.S.A. Phone: (408) 744-9040 • Fax: (408) 744-9049 Email: info@thinkSRS.com • www.thinkSRS.com Copyright © 1995, 1996, 1998 Stanford Research Systems, Inc. All Rights Reserved Revision 1.4 (December, 2006)
  • Page 2 (1) year from the date of shipment. Service For warranty service or repair, this product must be returned to a Stanford Research Systems authorized service facility. Contact Stanford Research Systems or an authorized representative before returning this product for repair.

  • Page 3: Safety And Preparation For Use

    Contact the factory for instructions on how to return the instrument for authorized service and adjustment. The fans in the SR785 are required to maintain proper operation. Do not block the vents in the chassis or the unit may not operate properly.

  • Page 5: Table Of Contents

    2-27 Waterfall Display 2-30 Capture Buffer 2-33 The Source 2-36 Correlation Analysis 2-38 Octave Analysis 2-41 Swept Sine Measurements 2-47 Order Analysis 2-55 Time/Histogram Measurements 2-58 Trace Storage 2-60 User Math Functions 2-61 Signal Inputs 2-65 SR785 Dynamic Signal Analyzer...
  • Page 6 Contents Input Connections 2-68 Intrinsic Noise Sources 2-70 External Noise Sources 2-71 Curve Fitting and Synthesis 2-75 Chapter 3 Operation Overview Front Panel Connectors Rear Panel Connectors Screen Display 3-11 Status Indicators 3-18 Keypad 3-23 Normal and Alternate Keys 3-23 Menu Keys 3-24 Entry Keys...
  • Page 7 Contents Trigger Menu 4-100 Average Menus 4-107 FFT, Correlation, and Order Average Menu 4-107 Octave Average Menu 4-115 Swept Sine Average Menu 4-119 User Math Menu 4-122 Window Menu 4-131 Waterfall Menu 4-135 Capture Menu 4-143 Analysis Menu 4-147 Data Table Analysis Menu 4-150 Limit Testing Analysis Menu 4-152...
  • Page 8 Data Transfer Commands 5-107 Interface Commands 5-117 Nodal Degree-of-Freedom Commands 5-118 Status Reporting Commands 5-120 Status Word Definitions 5-124 Example Program 5-129 Chapter 6 File Conversion Why File Conversion? SR785 File Types Supported External File Types Using the File Conversion Utility...

  • Page 9: Table Of Figures

    3-12 Figure 3-5 Vertical Scale Bar 3-13 Figure 3-6 Horizontal Scale Bar 3-14 Figure 3-7 Marker Region 3-15 Figure 3-8 Marker Position Bar 3-15 Figure 3-9 Status Indicator Panel 3-18 Figure 3-10 Front Panel Keypad 3-23 SR785 Dynamic Signal Analyzer...
  • Page 10 viii...

  • Page 11: Features

    Peak Finding THD/THD+N Limit Testing Data Table Exceedance (L Statistics Waterfall Slice Curve Fitting Curve Synthesis User Math +, -, *, / Conjugate Magnitude/Phase Real/Imaginary Sqrt FFT/Inverse FFT ω Log/Exp d/dx Group Delay A, B, C Wt SR785 Dynamic Signal Analyzer...
  • Page 12 GIF, EPS and PCX graphic formats available for disk output. ® File Translation Native SR785 binary files can be converted to: ASCII, MATLAB .MAT Files, Universal File Format, and HP SDF v3 Files.SDF and SR780 files can be converted to native SR785 binary format.

  • Page 13: Specifications

    Cross Channel ± 0.5 deg (dc to 51.2 kHz) ± 1.0 deg (dc to 102.4 kHz) (Transfer Function measurement, both inputs on the same Input Range, Vector averaged.) SR785 Dynamic Signal Analyzer...
  • Page 14 Specifications Signal Inputs Number of Inputs Full Scale Input Range -50 dBV (3.16 mVpk) to +34 dBV (50 Vpk) in 2 dB steps. Maximum Input Level 57 Vpk Input Configuration Single-ended (A) or True Differential (A-B). Ω Input Impedance + 50 pF + 0.01 Ω...
  • Page 15 Specifications xiii Maximum Capture Length 2M samples standard, 8M samples optional. Octave Analysis Standards Conforms to ANSI S1.11-1986, Order 3, Type 1-D. Frequency Range Band centers: Single Channel 1/1 Octave 0.125 Hz - 32 kHz 1/3 Octaves 0.100 Hz - 40 kHz 1/12 Octaves 0.091 Hz - 12.34 kHz Two Channels...
  • Page 16 Specifications (5000 rms averages). Pink Noise Time Record Continuous or Burst Bandwidth DC to 102.4 kHz Flatness <2.0 dB pk-pk, 20 Hz - 20 kHz, (measured using averaged 1/3 Octave Analysis). Chirp Time Record Continuous or Burst Output Sine sweep across the FFT span. Flatness ±0.25 dB pk-pk, Amplitude = 1.0 Vpk.

  • Page 17: Getting Started

    These example measurements are designed to acquaint the first time user with the SR785 Dynamic Signal Analyzer. They provide a foundation for understanding how to use the SR785. For a more complete overview of the instrument and its capabilities, refer to the ‘Analyzer Basics’ and ‘Operation’...

  • Page 18: General Installation

    Dimmer buttons below the softkeys (below right of the display). Do not set the brightness higher than necessary. The fans in the SR785 are required to maintain proper operation. Do not block the vents in the chassis or the unit may not operate properly.

  • Page 19: Front Panel Quick Start

    <Softkeys> The SR785 has a menu driven user interface. The Menu keys each display a menu of softkeys. The softkeys are at the right of the video display and have different functions depending upon the displayed menu.
  • Page 20 Enter the on screen help system by pressing [Help/Local]. Help on any hardkey or softkey is available simply by pressing the key. Press [1] for the Help Index. Press [0] to exit the help system and return to normal operation. SR785 Dynamic Signal Analyzer...

  • Page 21: Things To Watch Out For

    If the measurement is not meant to be triggered, make sure the Trigger Mode is Auto Arm and the Trigger Source continuous. If the measurement is meant to be triggered, make sure that the correct Trigger Source is selected and the Trigger Level is appropriate for the trigger signal. SR785 Dynamic Signal Analyzer...
  • Page 22 If the analyzer still seems to function improperly, turn the power off and turn it back on while holding down the [<-] (backspace) key. This will reset the analyzer into the default configuration. The analyzer should power on running and taking measurements. SR785 Dynamic Signal Analyzer...

  • Page 23: Analyzing A Sine Wave

    Analyzing a Sine Wave This measurement investigates the spectrum of a 1.024 kHz sine wave. You will use the SR785 source to provide the sine signal (or you can use a function generator capable of providing a 1.024 kHz sine wave at a level of 100 mV to 1 V, such as the SRS DS345).
  • Page 24 1.6 kHz. noticeable time to settle at this last span. This is because the time record is 250 ms long. Press [Marker Max] Move the Marker to the peak. SR785 Dynamic Signal Analyzer...
  • Page 25 Press [Marker Ref] Pressing [Marker Ref] again removes the Marker Offset and returns the Marker to absolute readings. 12. Let's have the analyzer measure the distortion. Press [Marker] Select the Marker menu. Press <Mode> Adjust the Marker Mode. SR785 Dynamic Signal Analyzer...
  • Page 26 Harmonic power is an absolute measurement of the harmonic power level. This concludes this measurement example. You should have a feeling for the basic operation of the menus, knob and numeric entry, marker movement and some function keys. SR785 Dynamic Signal Analyzer...

  • Page 27: Measuring A Frequency Response Function

    This example investigates the frequency response of the test filter (enclosed with this manual) using FFT measurements. You will use the SR785 source to provide a broad band chirp and both input channels to measure the input to and output from the device under test.
  • Page 28 Press <Link> The <Link> key lets you make a choice for both displays. We want both displays on a log x- axis.Note that the linkage indicator at the top of the screen changes from DispA to Link. SR785 Dynamic Signal Analyzer...
  • Page 29 11. Press [Link] and use the knob to move the The [Link] key links the two display markers marker. together. This allows simultaneous readout of Transfer Function Magnitude (top) and Phase (bottom). Press [Enter] Pressing any key removes the linkage between the markers. SR785 Dynamic Signal Analyzer...
  • Page 30 DisplayA Marker. To do this, change the DisplayB Marker Type to Linked also. This concludes this measurement example. You should have a feeling for the basic operation of two channel measurements and the use of [Active Display]. SR785 Dynamic Signal Analyzer...

  • Page 31: Linking (Advanced Operation)

    This example investigates the test filter (enclosed with this manual) using FFT measurements. You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test. Display parameter linking and function linking will be explored in greater detail.
  • Page 32 Use the knob to adjust the Span to 3.2 kHz and Change the Span of DisplayA to 3.2 kHz. The Span press [Enter]. of DisplayB remains at 12.8 kHz. The SR785 allows the two displays to have differing Spans and Start frequencies in the Independent Channels mode.
  • Page 33 Select (rms) with the knob and press [Enter]. Both displays’ Units become dBVrms with a single parameter entry. The Pk Units remain linked until unlinked with the [Link] key. 11. Press <Return> Return to the Display Setup Menu. SR785 Dynamic Signal Analyzer...
  • Page 34 [Link] [Auto Scale] matches the active display. [Span Up] and [Span Down] are always linked. This concludes this measurement example. You should have a feeling for linking and unlinking and the flexibility of unlinked measurements. SR785 Dynamic Signal Analyzer...

  • Page 35: Triggering And The Time Record

    4. Press [Active Display] Let’s change the Measurement for DisplayB. Make DisplayB the active display. Press [Display Setup] Select the Display Setup menu. Press <Measurement> Change the Measurement of the active display (B). SR785 Dynamic Signal Analyzer...
  • Page 36 10 kHz.) 7. Press <Window> Choose a non-optimum window. Select (Hanning) with the knob and press Choose the Hanning window. Notice how the [Enter]. spectrum in DisplayA goes away. Press [Display Setup] Select the Display Setup menu. SR785 Dynamic Signal Analyzer...
  • Page 37 They are used for signals which last the entire time record and normalized as such. The Uniform (and Force) windows have no gain and should be used with pulsed signals such as this. SR785 Dynamic Signal Analyzer...
  • Page 38 If the generator is set to 256 Hz pulse rate, the signal will drift slowly in the time record. This is because the SR785 time records are exactly 1/256 Hz (3.90625 ms) long (400 lines at full span) and the analyzer is running in real time (no missed data).

  • Page 39: Octave Analysis

    Octave Analysis This example investigates the test filter (enclosed with this manual) using Octave measurements. You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test. Refer to ‘Octave Analysis’ in Chapter 2 for more about Octave Analysis measurements.
  • Page 40 Change the number of bands per octave. Use the knob to select (Full) and press [Enter]. Choose Full octave bands. Each band represents a full octave with very poor frequency resolution. Press <Octave Resolution> Change the number of bands per octave again. SR785 Dynamic Signal Analyzer...
  • Page 41 Use the knob to select 40 kHz and press [Enter]. Set the highest band to 40 kHz. This is the highest allowed band for 1 channel, 1/3 octave analysis. 8. Press [Display Setup] Select the Display Setup menu. SR785 Dynamic Signal Analyzer...
  • Page 42 Press [Link] [Auto Scale A] The A-Weighted spectrum is a bandpass centered around 2 kHz. This concludes this measurement example. You should have a feeling for Octave measurements and how they are setup. SR785 Dynamic Signal Analyzer...

  • Page 43: Capture

    Capture 1-27 Capture This example investigates the Capture buffer using FFT measurements. You will use the SR785 to capture a signal and then analyze it from memory. 1. Press [System] Display the System menu. Press <Preset> Preset returns the unit to its default settings.
  • Page 44 Make DisplayB (bottom) the active display. Press [Display Setup] Select the Display Setup menu. Press <Measurement> Change the measurement of DisplayB. Use the knob to select (Capture1) and press Choose Capture1 to show the contents of the Ch1 [Enter]. Capture buffer. SR785 Dynamic Signal Analyzer...
  • Page 45 Choose circular playback. The % indicator at the [Enter]. top of the display shows the current progress through the playback buffer. uffer during playback. DisplayB automatically pans to show the portion of the Capture buffer at the current playback position. SR785 Dynamic Signal Analyzer...
  • Page 46 Capture Progress indicator to reach 100%. 10. Disconnect the signal from both inputs. The signal should disappear from the spectrum in both displays. Press [Input] Select the Input menu. Press <Input Source> Change the Input Source. SR785 Dynamic Signal Analyzer...
  • Page 47 Every Time Record playback is not limited by real time considerations. Press [Trigger] Select the trigger menu. Press <Trigger Source> We'll use manual trigger to show how you can step through each time record in the capture buffer. SR785 Dynamic Signal Analyzer...
  • Page 48 8 kPoints. 112 time records uses 896 kPoints and is close to the full capture length. Press [8] [9] [6] and [Enter]. Change the Playback Length to an exact number of time records. Press [Start/Reset] Start the playback again. SR785 Dynamic Signal Analyzer...
  • Page 49 Capture 1-33 This concludes this example. Capture and Playback is a way to record a signal and re-analyze it over and over. SR785 Dynamic Signal Analyzer...

  • Page 50: Waterfall Display

    In this example, we will simulate a reverberation measurement measuring the SR785 source. To perform a real measurement, you would use the source to drive a power amplifier and a microphone to receive the signal.
  • Page 51 Use the knob to select (8 ms) and press [Enter]. Choose the minimum time for the best resolution. Press <Linear Avg Trig> Change the Linear Average Trig. This determines how measurements behave when triggering is enabled (not Free Run). SR785 Dynamic Signal Analyzer...
  • Page 52 (Trigd Source Mode=One Shot). The display starts a continuous stream of octave measurements, each linear averaged for 8 ms and each starting when the previous average is complete (Linear Avg Mode=Continuous). SR785 Dynamic Signal Analyzer...
  • Page 53 Entering 50 changes the total count for both displays to 50. 10. Press [Trigger] Select the Trigger menu again. Press [Start/Reset] [Start/Reset] starts the measurement. Since the measurement is triggered (not Free Run), nothing happens until the first trigger is received. SR785 Dynamic Signal Analyzer...
  • Page 54 Pressing [Alt] removes the keypad and knob from the alternate mode. Turn the knob clockwise to move the marker The normal knob function moves the marker along along the frequency axis of a single record. the X axis of a single record. SR785 Dynamic Signal Analyzer...
  • Page 55 Change the View Count. This is the number of records which are displayed. Press [5] [0] [Enter]. Enter 50 to show the entire waterfall buffer. Press <Marker Z to> Move the marker to a specific record number. SR785 Dynamic Signal Analyzer...
  • Page 56 Waterfall menu which you should familiarize yourself with. The transient response of any FFT or Octave measurement may be recorded in a waterfall buffer. Using a slice will give a time evolution of a single X axis bin. SR785 Dynamic Signal Analyzer...

  • Page 57: Swept Sine Measurement

    This example investigates the test filter (enclosed with this manual) using Swept Sine measurements. You will use the SR785 source to provide a sweeping sine source and both inputs to measure the input to and output from the device under test.
  • Page 58 Scale the display to show the Frequency Response. 7. Press [Marker] Select the Marker menu. Press <Width> Change the Marker Region width. Select (Normal) with the knob and press [Enter]. Choose Normal Width (1/2 division). Press <Seeks> Change the Marker Seeks function. SR785 Dynamic Signal Analyzer...
  • Page 59 Let’s change these to optimize both the measurement and the measurement time. Press [Auto Range Ch1] and [Auto Range Ch2] Change both inputs to Auto Range (the Input Range indicators at the top of the screen are highlighted). SR785 Dynamic Signal Analyzer...
  • Page 60 Each successive time this threshold is met, the number of points skipped is increased until the Max # of Skips is reached. This speeds up the sweep in regions where the response is slowly changing. SR785 Dynamic Signal Analyzer...
  • Page 61 (usually input or output). In this case, Auto Level is not really required but illustrates its use. Press [Active Display] Change the active display to DisplayB (which is still measuring the spectrum of Ch2). SR785 Dynamic Signal Analyzer...
  • Page 62 This concludes this measurement example. You should have a basic understanding of Swept Sine measurements. The Input Range, Resolution and Source Level optimizations greatly extend the dynamic range of the measurement while minimizing the measurement times. SR785 Dynamic Signal Analyzer...

  • Page 63: Saving And Recalling

    The marker can also be set to read the current data relative to the reference graph. The reference graph can be loaded by copying the current live data or by copying a stored trace. SR785 Dynamic Signal Analyzer...
  • Page 64 Press [Span Up] twice to return to full span. Change the live measurement. Press [Active Display] Make DisplayB (bottom) active. Press [Alt] [Help/Local] Trace to Display is an alternate function. This function recalls trace data to the active display. SR785 Dynamic Signal Analyzer...
  • Page 65 Make DisplayB (bottom) the active display again. Press [Display Options] Select the Display Options menu. Press <Display> Make DisplayB live again. Use the knob to select (Live) and press [Enter]. Choose Live to return the live measurement to DisplayB. SR785 Dynamic Signal Analyzer...
  • Page 66 The extension .78D is appended automatically. Press <Display to Disk> Save the measurement again. Notice that the <File Name> ahs been changed to DATA2. The SR785 will try to autoincrement any filename containing a number. 8. Press [Active Display] Make DisplayB (bottom) the active display.
  • Page 67 Choose Live to return the live measurement to DisplayB. This concludes this example. Remember, ‘Off- Line’ displays are showing stored data, not live measurement results. Many measurement parameters can not be adjusted for an ‘Off-Line’ display. SR785 Dynamic Signal Analyzer...

  • Page 68: User Math Functions

    This example measures the group delay of the test filter (enclosed with this manual) using User Math Functions. You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test.
  • Page 69 Choose the divide operation next. [Enter]. The display switches back to operands. You can choose another operation instead by pressing <Operations>. Use the knob to highlight FFT(1) and press Choose FFT(1) as the denominator of the transfer [Enter]. function. SR785 Dynamic Signal Analyzer...
  • Page 70 Most points are in the µ neighborhood of 10 to 600 At the 1 kHz notch, the group delay has a singularity. Remember, the notch filter has a phase discontinuity at the notch frequency. SR785 Dynamic Signal Analyzer...
  • Page 71 This concludes this example. User Functions allow you to define your own measurements starting with the basic SR785 measurements. User Functions can also use stored trace data (for calibrations and normalizations) and user constants. SR785 Dynamic Signal Analyzer...

  • Page 72: Limit Testing

    1-56 Limit Testing Limit Testing This example is intended to familiarize the user with limit testing. Limit Testing tests the measurement data against a set of defined Limit Segments. When measurement data exceeds a Limit Segment at any point, the test fails. Each display has its own set of Limit Segments. A Limit Segment is defined as the line between the pair of points (X0,Y0) and (X1,Y1).
  • Page 73 Limit Testing 1-57 Press <New Segment> This function adds a new segment. The new segment has a default position and length. The segment is defined by its endpoints, (X0,Y0) and (X1,Y1). These values are specified for the current view and units, in this case, Hz for the x values and dBVpk for the y values.
  • Page 74 1-58 Limit Testing Press <Shift All> Select Shift All limit segments. This moves all of the segments together. In this case, there is only one segment. Press [7] [Enter] Enter 7 to move the segment up by 7 dBVpk. The new segment is above the signal peak and the limit test passes.
  • Page 75 This concludes this example. Limit testing is a powerful tool for repetitive tests. In an automated test environment, limit segments are usually downloaded from a host computer. The SR785 performs the limit testing in real-time and the results are queried by the host computer.

  • Page 76: Exceedance Statistics

    This example is intended to familiarize the user with calculating exceedance centile statistics (L ). L calculated from measurements stored in the waterfall buffer. is the amplitude at each bin which is exceeded by n% of the records in the waterfall. The SR785 simultaneously calculates L at all frequencies in the spectrum. L is commonly used to characterize environmental noise levels.
  • Page 77 Storage Interval so 100 measurements will take 10 s to complete. Press <Save Option> The SR785 has two waterfall storage options for saving measurements. (All) Means that all possible measurements for the currently selected measruement group will be stored in the waterfall buffer.
  • Page 78 1-62 Exceedance Statistics Press [Start/Reset] Start the measurement. This resets the waterfall buffer. New measurements are added to the waterfall buffer every 100 ms. The number of records stored in the waterfall is shown in the Vertical Scale Bar and increments to 100. Because the waterfall storage is One Shot, the waterfall buffer fills once (100 records).
  • Page 79 Exceedance Statistics 1-63 Press [Pause/Cont] Continue the live measurement. Note that the live measurement data rarely exceeds the reference graph. 9. Press [Pause/Cont] Pause the live measurement again. Press <Exceedance Pct> Change the Exceedance Percentage. Press [9] [9] [Enter]. Enter 99%. This level is exceeded 99% of the time. Press <Calculate Excd>, choose (Trace 2) with The exceedance results are stored in Trace 2.
  • Page 80 1-64 Exceedance Statistics...
  • Page 81 Input Sampling 2-33 Windowed Time Record 2-17 Capture Fill 2-33 Orbit 2-18 Capture Playback 2-34 Cross Spectrum 2-18 Capture as the Arbitrary Source 2-35 Frequency response 2-18 The Source 2-36 Coherence 2-19 Capture Buffer 2-19 Sine 2-36 SR785 Network Signal Analyzer...
  • Page 82 Inductive Coupling 2-72 What is Order Analysis? 2-55 Resistive Coupling (Ground Loops) 2-73 Order Spectra and Order Tracking 2-55 Microphonics 2-73 Order Measurement Setup 2-55 Thermocouple Effects 2-74 Order Measurements 2-56 Linear Spectrum 2-56 Power Spectrum 2-56 SR785 Dynamic Signal Analyzer...
  • Page 83 Analyzer Basics Curve Fitting and Synthesis 2-75 Curve Tables 2-75 Polynomial 2-75 Pole-Zero 2-75 Pole Residue 2-75 Frequency Scale 2-76 Delay 2-76 Trace 2-76 Curve Fitting 2-76 Weighting 2-77 Curve Synthesis 2-77 SR785 Dynamic Signal Analyzer...

  • Page 84: Measurement Groups

    Some measurements made by the SR785 are intrinsically two channel measurements, for instance frequency response, or cross-correlation. Other measurements, such as Autocorrelation or FFT1, only involve a single input channel. The SR785 has a uniquely flexible architecture with regard to processing single and dual channel measurements which is set by the [Input]<Analyzer Coniig>...
  • Page 85 Measurement Groups If two-channel measurements aren't required however, the SR785 allows selection of the Independent Channel configuration. In this mode, each display of the SR785 functions as a completely separate single channel analyzer with an independent set of operating parameters. For instance in the Independent Channel mode display A could be configured to show a broadband measurement of channel 1 with linear averaging while display B could show a narrowband detail of the same input with exponential averaging.

  • Page 86: What Is An Fft

    (in the frequency domain). In the SR785, sampling occurs at 262 kHz. To make sure that Nyquist's theorem is satisfied, the input signal passes through an analog anti-aliasing filter that removes all frequency components above 102.4 kHz.
  • Page 87 (which you haven't measured yet). This is not a practical solution. Instead, the way to measure the signal accurately is to lengthen the time record and change the span of the spectrum. SR785 Dynamic Signal Analyzer...

  • Page 88: Fft Frequency Spans

    Full span is the widest frequency span corresponding to the fastest available sampling rate. In the SR785, this is DC to 131 kHz using a sampling rate of 262 kHz. Because the signal passes through an anti-aliasing filter at the input, the entire frequency span is not useable.
  • Page 89 The sampling rate is the number of points in the time record divided by the duration of the time record. The SR785 allows FFT resolutions of 100, 200, 400 or 800 bins (not counting DC). Changing the resolution does not change the span, instead the time record length is changed.

  • Page 90: Fft Time Record

    The new time record must have twice the original duration and thus, half of the original span. This results in a 51.2 kHz (±25.6 kHz) span centered at 51.2 kHz. The time record SR785 Dynamic Signal Analyzer...
  • Page 91 Watch Out For Windowing! The SR785 can display both the time record and the windowed time record. Most window functions taper off to zero at the start and end of the time record. If a transient signal occurs at the start of the time record, the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero.

  • Page 92: Fft Windowing

    Windowing allows the FFT to accurately measure signals at frequencies which are not exact frequency bins. The different types of windows trade off selectivity, amplitude accuracy, and noise floor. The SR785 offers many types of window functions - Uniform (no windowing), Flattop, Hanning, Blackman-Harris (BMH), Kaiser, Force-Exponential, and User Defined windows.
  • Page 93 The BMH window has much lower side-lobes than the Hanning window and very little broadening of non-bin frequencies. The BMH window is a good window to use for measurements requiring a large dynamic range. The BMH window function is SR785 Dynamic Signal Analyzer...
  • Page 94 Force-Exponential Many impact measurements require a Force window for excitation channel and an Exponential window for the response channel. With the SR785, this is accomplished by selecting the Force/Exponential Window. The Force/Exponential window is actually two windows, either of which can be applied to either input channel.
  • Page 95 FFT Windowing 2-15 Remember, window functions have a great deal of impact on the resulting FFT spectrum. A poorly designed window can result in significant measurement errors. SR785 Dynamic Signal Analyzer...

  • Page 96: Fft Measurements

    The power spectrum is a real quantity and contains no phase information. The precise definition of the Power Spectrum measurement for all averaging modes is as follows: No Average Power Spectrum = FFT1*• FFT1 Vector Average Power Spectrum = <FFT1>*• <FFT1> SR785 Dynamic Signal Analyzer...
  • Page 97 If a transient signal occurs at the start of the time record, the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero. SR785 Dynamic Signal Analyzer...
  • Page 98 A broadband source (such as chirp or noise) should be used to measure frequency response. The definition of frequency response depends on the type of averaging which is displayed. No Average Freq. Response = FFT2 / FFT1 SR785 Dynamic Signal Analyzer...
  • Page 99 This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur. Once capture is complete, the display is redrawn showing the envelope of all points, eliminating any visual aliasing effects. SR785 Dynamic Signal Analyzer...
  • Page 100 A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group. See ‘User Math’ later in this section for more. SR785 Dynamic Signal Analyzer...

  • Page 101: Views

    If y is negative, the phase is negated. Phase is graphed linearly from - 180 (-π) to +180 (π) degrees (radians). To show unwrapped phase, choose the Unwrapped Phase view. Real measurement data, such as baseband time record, have zero imaginary part. The phase is zero for all points. SR785 Dynamic Signal Analyzer...
  • Page 102 FFT frequency bins, the filters cause phase errors. Because these filters are very steep and selective, they introduce very large phase shifts for signals not exactly on a frequency bin. Use the SR785 source to generate exact bin frequencies whenever possible.
  • Page 103 The marker moves sequentially through the frequency (time) points and can be linked to the frequency of the other display. Real measurement data, such as baseband time record, have zero phase. This view is entirely along the Y axis. SR785 Dynamic Signal Analyzer...

  • Page 104: Fft Averaging

    You can control whether the SR785 calculates averaged quantities for measurements with the <Compute Avgs> Softkey. If <Compute Avgs> is set to "Yes," the SR785 will compute averages for all measurements. If <Compute Avgs> is "No" the SR785 will not compute any averages and all quantities diplayed will be instantaneous values.
  • Page 105 N is the number of averages. While Exponential averaging is in progress, the number of averages completed is shown in the Horizontal Scale Bar below the graph. The displayed number stops incrementing at the Number of Averages while the averaging continues. SR785 Dynamic Signal Analyzer...
  • Page 106 Once in steady state, further changes in the average are detected only if they last for a sufficient number of measurements. Make sure that the number of averages is not so large as to eliminate changes in the data which might be important. SR785 Dynamic Signal Analyzer...

  • Page 107: Real Time Bandwidth And Overlap

    500 averages. The SR785, on the other hand, can make real time measurements at full span (102.4 kHz). This results in 256 measurements per second (on each display!). In fact, this is so fast, that the display can not be updated for each new measurement.
  • Page 108 These first 3 measurements have time records which contain data from before AND after the measurement was unsettled. These unsettled measurements are displayed in half intensity indicating that the SR785 Dynamic Signal Analyzer...
  • Page 109 Triggering If the measurement is triggered, then Time Record Increment is ignored. Time records always start with the trigger (with the specified Trigger Delays). The analyzer must use the Continuous Trigger Source to use overlap processing. SR785 Dynamic Signal Analyzer...

  • Page 110: Waterfall Display

    Waterfall records are stored in waterfall memory. This memory is not retained when the power is off. Use the [Waterfall] <Memory Allocation> menu to allocate memory between the capture buffer, waterfall storage and the arbitrary source waveform. Waterfall memory must be allocated before waterfall storage may be used. SR785 Dynamic Signal Analyzer...
  • Page 111 Waterfall Display 2-31 The SR785 can store waterfall measurements in the waterfall buffer in one of two ways depending on the setting of the <Save Option> softkey. If <Save Option> is set to "All," each time the SR785 stores a record it stores enough information to recreate every measurement in the current measurement group.
  • Page 112 (back). This is reversed from how the display is scrolled while the measurement is running. A single record can be saved to a trace. A time slice ( history of a single X from all stored records) can also be saved to a trace. SR785 Dynamic Signal Analyzer...

  • Page 113: Capture Buffer

    If the Capture Mode is Continuous, once capture is started, it continues indefinitely and fills the capture buffer in a circular fashion. In this case, press [Stop Capture] to halt SR785 Dynamic Signal Analyzer...
  • Page 114 There is often a discontinuity in the playback measurement when the playback jumps from the end to the start of the buffer. In either mode, press [Start/Reset] to restart playback at the start again. SR785 Dynamic Signal Analyzer...
  • Page 115 The amplitude of the arbitrary output depends upon the amplitude of the captured data relative to the Input Range during capture. If the captured data was 100% of the Input Range, then an output amplitude of 100% will be 1 Vpk. SR785 Dynamic Signal Analyzer...

  • Page 116: The Source

    2-36 The Source The Source The SR785 source provides a variety of test signals which allow the SR785 to measure the response of electronic, mechanical and acoustic devices, without the need for an external generator. In many cases, the SR785 source is better than an external source since it is synchronous with the input sampling.
  • Page 117 For Chirp, Burst Chirp, Burst Noise and Arbitrary, the External trigger can trigger the source output. The source can trigger on only the first trigger or on every trigger after a measurement is started as selected in the [Trigger] menu. The measurements are triggered normally in either case. SR785 Dynamic Signal Analyzer...

  • Page 118: Correlation Analysis

    Correlation is a time domain measurement which reveals similarities and periodicities within a signal (autocorrelation) or between two signals (cross-correlation). Although a time domain measurement, the SR785 computes correlation measurements by transforming input data into the frequency domain, processing it, and retransforming back to the time domain.
  • Page 119 Correlation uses a different set of windows than the FFT measurement group. The Correlation windows, which are described above, are designed to zero half of the time record in order to eliminate "wrap-around" error. SR785 Dynamic Signal Analyzer...
  • Page 120 User Function User Function displays the results of a user defined math function. User Functions defined within the Correlation Analysis Measurement Group may include correlation measurement results. Use the [User Math] menu to define a math function. SR785 Dynamic Signal Analyzer...

  • Page 121: Octave Analysis

    = -10 .. 46 1/12 Octave Bands 1/12 octave bands are defined ranging from 100 mHz to 12.34 kHz. Up to 11 octaves (132 bands) may be measured at one time. The exact centers are given by SR785 Dynamic Signal Analyzer...
  • Page 122 Signals at frequencies above the sample rate/2.56 have been filtered out. The capture buffer is not a continuous representation of the input signal. The data is sampled and has a time resolution of 1/(sample rate). High frequency signals will appear SR785 Dynamic Signal Analyzer...
  • Page 123 Horizontal Scale Bar below the graph. The displayed time stops incrementing at the Integration Time while the averaging continues. Exponential weighting reaches a steady state after approximately an integration time. Once in steady state, further changes in the average are detected only if they last for a SR785 Dynamic Signal Analyzer...
  • Page 124 Broadband Impulse sound level (I) is computed according to IEC 651-1979, Type 0. It is computed from real-time low-pass filtered input data, not from the octave band outputs. The Impulse bandwidth is DC-100kHz for 1 octave channel and DC-50kHz for 2 channels. SR785 Dynamic Signal Analyzer...
  • Page 125 Averaging Types. The last bin in the measurement displays the Total Power. The last bin is labeled as follows. Label Frequency Weighting uniform weighting A-Wt (input filter) A-Wt (User Math) B-Wt (User Math) C-Wt (User Math) undefined SR785 Dynamic Signal Analyzer...
  • Page 126 ‘Settle’ is shown below the graph while settling takes place. Bands which are un-settled are displayed at half intensity in the graph. When Waterfall Storage is selected, records are not added to the waterfall buffer while octavebands are still settling. SR785 Dynamic Signal Analyzer...

  • Page 127: Swept Sine Measurements

    10 seconds to complete. The swept sine also took 400 points. Each point was averaged for 16 ms or 10 cycles, whichever was longer. The entire sweep also takes about 12 seconds. SR785 Dynamic Signal Analyzer...
  • Page 128 Channel 2 is -80 dBV (or less). The input range of Channel 2 is adjusted to -50 dBV for these frequencies eliminating the noise floor limitation. The depth of the zero in the response as well as the shape of the stop band are clearly resolved. SR785 Dynamic Signal Analyzer...
  • Page 129 Ranging. Auto Ranging always tracks the input signals during a swept sine measurement. The signal connections are the same as for an FFT frequency response. The SR785 measures Channel 2 response divided by Channel 1 as the frequency response. The input to the device under test is measured by Channel 1 (typically this is the source output) and the device output is measured by Channel 2.
  • Page 130 This is done by multiplying the input data by sin( t) and ω cos( t) and averaging the results over an Integration Time. As with the FFT, real (in- phase) and imaginary (quadrature) signals are measured yielding both magnitude and phase frequency responses. SR785 Dynamic Signal Analyzer...
  • Page 131 The span of a swept sine sweep is determined by the Start and Stop frequencies. The entire 102.4 kHz frequency range of the SR785 is available for swept sine measurements. Note that starting a sweep at DC is not possible. In fact, beware of starting at any frequency much less than 1 Hz since the Settle and Integration times are always a minimum of 1 cycle.
  • Page 132 Auto Ranging increases the measurement times whenever an input range is changed. This is especially true when the signal drops below -6 dBfs. In order to detect this under- range condition, the measurement must be made for the entire integration time. At low SR785 Dynamic Signal Analyzer...
  • Page 133 The Maximum Source Level is the largest allowed source amplitude. This is limited by the SR785 source output or the device under test input range. The Reference Upper and Lower limits are the allowable tolerances for the Reference Channel.
  • Page 134 The source ramps off whenever there are no measurements being made. This occurs before the start of a sweep, at the end of a single sweep or while a sweep is paused (by the user). If Ramping is Off, the source shuts off instantly in these situations. SR785 Dynamic Signal Analyzer...

  • Page 135: Order Analysis

    This is provided by a tachometer input, which provides a signal at fixed positions relative to the shaft rotation. With the SR785, all the traditional measurements of rotating machinery analysis including order maps, rpm profiles, run-up and run-down plots, can be easily made without any additional equpment.
  • Page 136 The windowed time record shows the Time Record multiplied by the Window function. Remember that in the order measurement group you should use the uniform window if the expected harmonics are integer multiples (orders) of the rotating machine speed. SR785 Dynamic Signal Analyzer...
  • Page 137 Use the [User Math] menu to define a math function. A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group. SR785 Dynamic Signal Analyzer...

  • Page 138: Time/Histogram Measurements

    The x-axis of the histogram represents the input amplitude range of the SR785, from negative full scale (plus an overhead factor of 1.25) to positive full scale (plus an overhead factor of 1.25) divided into a number of histogram "bins"...
  • Page 139 User Function User Function displays the results of a user defined math function. User Functions defined within the Time/Histogram Measurement Group may include time/histogram measurement results. Use the [User Math] menu to define a math function. SR785 Dynamic Signal Analyzer...

  • Page 140: Trace Storage

    Trace in its equation, then that Trace cannot be changed to data from a different Measurement Group. For example, if an FFT User Function using Trace1 is being displayed, you cannot recall octave data from disk to Trace1. SR785 Dynamic Signal Analyzer...

  • Page 141: User Math Functions

    Trace length (length of the data which is stored in the Trace). Constants assume the length of the user function. Operands which are measurement results enclosed in angle brackets, such as <Freq. Resp.> or <Spec(1)>, are exactly the same as the normal measurements. They are SR785 Dynamic Signal Analyzer...
  • Page 142 A frequency domain operand (FFT(1)) can be added to a time domain operand (Time(1)) point by point even though the result is meaningless. The X axis type of a User Function is determined by examining its equation from left to right SR785 Dynamic Signal Analyzer...
  • Page 143 FFTu( ) is the un-windowed FFT operator. The uniform window is always used. The FFT( ) and FFTu( ) operators do not calibrate their results since their operands are not necessarily input time records. To use a calibrated FFT, use the measurement operand FFT(1) or FFT(2). SR785 Dynamic Signal Analyzer...
  • Page 144 Editing a function which is currently being displayed is allowed. In this case, Traces which do not contain compatible measurements are not allowed as operands. User Functions have a maximum length of 31 operators plus operands. User Functions cannot use another User Function as an operand. SR785 Dynamic Signal Analyzer...

  • Page 145: Signal Inputs

    Signal Inputs 2-65 Signal Inputs The Input Range on the SR785 varies from a maximum of 34 dBV full scale to a minimum of -50 dBV full scale. A signal which exceeds the current input range will cause the OverLoad indicator to appear at the top of the screen. A signal which exceeds the maximum safe range (35 dBVpk) will turn on the Hi V indicator and set the range to 34 dBV.
  • Page 146 Hz of noise! A signal source impedance of 6 k has a Johnson noise equal to the SR785’s input noise. To determine the overall noise of multiple noise sources, take the square root of the sum of the squares of the individual Ω...
  • Page 147 Transducer Units require a transducer which is linear over the frequency range of interest. Measurements of inputs which are assigned units of acceleration, velocity or displacement may be displayed with any of these three units using Transducer Convert in the [Display Options] menu. SR785 Dynamic Signal Analyzer...

  • Page 148: Input Connections

    The common mode rejection ratio (CMRR) specifies the degree of cancellation. For low frequencies, the CMRR of 90 dB indicates that the common mode signal is canceled to 1 part in 30,000. Even with a CMRR of 90 dB, a 1 V common mode SR785 Dynamic Signal Analyzer...
  • Page 149 AC signal of interest. In this case, the input range may be limited to accommodate the large DC offset while sacrificing signal to noise in the measurement of the AC signal. If the signal frequency exceeds 0.16 Hz, use AC coupling if possible. SR785 Dynamic Signal Analyzer...

  • Page 150: 2-70 Intrinsic Noise Sources

    All of these noise sources are incoherent. The total random noise is the square root of the sum of the squares of all the incoherent noise sources. Thus, the largest noise source easily dominates all others in determining the noise floor of the measurement. SR785 Dynamic Signal Analyzer...

  • Page 151: External Noise Sources

    1 cm separated by 10 cm, then C is 0.009 pF. The resulting noise stray current will be 400 pA (at 60 Hz). This small noise current can be larger than the signal SR785 Dynamic Signal Analyzer...
  • Page 152 2 coaxial cables used in differential connections. 3) Using magnetic shielding to prevent the magnetic field from crossing the area of the signal path. 4) Measuring currents, not voltages, from high impedance sources. SR785 Dynamic Signal Analyzer...
  • Page 153 C dV/dt + V dC/dt = dQ/dt = i Mechanical vibrations in the cable which cause a dC/dt will give rise to a current in the cable. This current affects the measured signal. Some ways to minimize microphonic signals are: SR785 Dynamic Signal Analyzer...
  • Page 154 2) Use a compensation junction, i.e. a second junction in reverse polarity which generates an emf to cancel the thermal potential of the first junction. This second junction should be held at the same temperature as the first junction. SR785 Dynamic Signal Analyzer...

  • Page 155: Curve Fitting And Synthesis

    Curve Tables Both curve fitting and curve synthesis use the SR785's two Curve Tables. The curve tables allow entry and editing of frequency response parameters in one of three formats: polynomial, pole-zero, and pole residue. Once parameters have been entered into the curve tables the corresponding frequency response function can be synthesized into a trace for comparison with measured data.
  • Page 156 The SR785 will convert curve parameters between any of these three formats. Results of curve fits are always initially presented in pole-zero format although they can always be subsequently converted to any format.
  • Page 157 The curve table is synthesized when the user presses the Synthesize Table 1 or Synthesize Table 2 softkeys. The analyzer first looks at the active display to determine the frequency range over which the synthesis occurs. Then the SR785 calculates the complex frequency response function corresponding the curve parameters, frequency scale, delay and gain settings contained in the curve table.
  • Page 158 2-78 Curve Fitting and Synthesis SR785 Dynamic Signal Analyzer...
  • Page 159 [Alt] [Control Key] 3-31 Status Indicators 3-18 Play Macro ([Alt] [Start/Reset]) 3-31 Input Ranges 3-18 Macro Rec ([Alt] [Pause/Cont]) 3-31 Overloads 3-18 End Rec ([Alt] [Stop Capture]) 3-32 Input Configurations 3-18 Snap Ref ([Alt] [Start Capture]) 3-32 SR785 Dynamic Signal Analyzer...
  • Page 160 3-35 [Span Up] 3-35 [Span Down] 3-35 [Marker Ref] 3-36 [Display Ref] 3-36 [Marker Center] 3-37 [Marker Max] 3-37 [Marker Min] 3-37 [Show Setup] 3-37 Macros 3-38 Keypad Macros 3-38 Choosing From Lists 3-38 Menus 3-38 SR785 Dynamic Signal Analyzer...

  • Page 161: Overview

    Figure Chapter 3 -1 Front Panel Power Switch The power switch is located on the rear panel. The SR785 is turned on by depressing the upper half of the power switch. The green power LED on the front panel indicates that the unit is powered.
  • Page 162 A complete description of the keys follows. Softkeys The SR785 has a menu driven user interface. The MENU keys each display a menu of softkeys. The softkeys are at the right of the video display and have different functions depending upon the displayed menu.
  • Page 163 (DS/HD) have a capacity of 1.44M bytes and double sided, double density disks (DS/DD) have a capacity of 720k bytes. The disk format is DOS compatible. Use the [Disk] menu to format a disk or access disk files. SR785 Dynamic Signal Analyzer...

  • Page 164: Front Panel Connectors

    An IBM PC or XT compatible keyboard may be attached to the keyboard connector. Most keyboards have a switch on the back to select PC/XT or 8088 mode. The SR785 can be controlled from this keyboard according to the table below.
  • Page 165 Alt-5 through Alt-8 (bottom row) Number Keys 0 through 9 Knob (slow) Left and Right arrow Knob (fast) Up and Down arrow Escape Enter Enter or Return The keyboard should only be connected when the power is off. SR785 Dynamic Signal Analyzer...

  • Page 166: Rear Panel Connectors

    Do not attempt to service or adjust this instrument while it is plugged into a live outlet. Line Voltage Selection The SR785 operates from a 100V, 120V, 220V, or 240V nominal AC power source having a line frequency of 50 or 60 Hz. Before connecting the power cord to a power...
  • Page 167 The RS232 interface connector is configured as a DCE (transmit on pin 3, receive on pin 2). The Baud Rate, Parity, and Word Length are set in the [Setup] <Remote> menu. To connect the SR785 to a PC serial adapter, which is usually a DTE, use a straight through serial cable.
  • Page 168 B output from the preamp (preamp ground) may be connected to the B input on the SR785. In this case, use A-B as the Input Mode. Be sure to twist the A and B cables together to reduce noise pick-up.

  • Page 169: Screen Display

    Many instrument parameters are set independently for each display. The display format is selected in the [Display Options] menu. The display shown above is the Dual display format. The [Active Display] key toggles between the two displays. Display A is always on top. SR785 Dynamic Signal Analyzer...
  • Page 170 FFT’s, a complete new time record has been acquired. FFT measurements running with a Time Record Increment less than 100% (overlapped time records) display unsettled measurements in half intensity. SR785 Dynamic Signal Analyzer...
  • Page 171 The Limit Test Result, either ‘Pass’ or ‘Fail’ is displayed if limit testing is on for this display. The Waterfall Storage Count shows how many measurement records are currently stored in the waterfall buffer. This count is not displayed when Waterfall Storage is Off. SR785 Dynamic Signal Analyzer...
  • Page 172 To horizontally expand a graph, use <Pan> and <Zoom> in the [Display Setup] menu. When the display is expanded on the horizontal axis, the graph labels reflect the displayed data, not the actual measurement span or time. Expanded displays show the ‘Expand’ indicator. SR785 Dynamic Signal Analyzer...
  • Page 173 Figure Chapter 3 -8 Marker Position Bar The Marker Position Bar is displayed above each graph. The first value is the marker frequency, time or bin number. If the display is a waterfall, the waterfall record number is also shown. SR785 Dynamic Signal Analyzer...
  • Page 174 Enter a new value with the entry keys and press [Enter]. <Start Freq> is an example of a numeric value. Menus which show parameters specific to a single display show the parameters for the active display. Use [Active Display] to change the active display. SR785 Dynamic Signal Analyzer...
  • Page 175 A softkey menu box which is shown in gray is not available in the current measurement. Also, the measurement softkeys for an ‘Off-Line’ display are shown in gray indicating that they may not be changed. Each menu is described at length in Chapter 4. SR785 Dynamic Signal Analyzer...

  • Page 176: Status Indicators

    ON, then ‘AWt’ is displayed on a highlighted background. ArmWait/Trig-wait/Trig/Acquire This indicator reads ‘Trig-wait’ while waiting for a trigger. Once triggered, the indicator flashes ‘Trig’ and then displays ‘Acquire’ while the time record is being acquired. If the SR785 Dynamic Signal Analyzer...
  • Page 177 Factors which affect the processor’s ability to run real time include the measurement type, averaging and source type. See also Real Time Bandwidth and Overlap. SR785 Dynamic Signal Analyzer...
  • Page 178 To link or unlink a parameter, highlight the parameter softkey and press the [Link] key. If the Link indicator is shown in gray, then the parameter linking may not be changed. SR785 Dynamic Signal Analyzer...
  • Page 179 ‘ERR’ flashes whenever a computer interface error occurs, such as illegal command or out of range parameter is received. This indicator is on whenever a GPIB Service Request is generated by the SR785. SRQ stays on until a serial poll is completed.
  • Page 180 ‘Record’ indicates that a keypad macro is being recorded. Use [Macro Rec] to start recording. ‘Play’ indicates that a macro is being played. Use [Play Macro] to playback a stored macro. See ‘Macros’ later in this chapter for more. SR785 Dynamic Signal Analyzer...

  • Page 181: Keypad

    Use the alternate keys to enter alphabetic characters and to access secondary functions. The [0]...[9], [.], [-], [<-], [Exp] and [Alt] keys have the same definition in both modes. Press [Alt] again to return to the normal keypad if necessary. SR785 Dynamic Signal Analyzer...

  • Page 182: Menu Keys

    3-24 Status Indicators Menu Keys All operating parameters of the SR785 are grouped into sixteen function menus. The menu keys select a menu of parameters to display next to the ten softkeys. The softkeys either choose a submenu or select a parameter and place it in the entry field at the top of the screen (for numeric entry or knob adjustment).

  • Page 183: Entry Keys

    Some parameters do not require the [Enter] key to make the new selection valid. <Window> is an example. In this case, moving through the list of windows with the knob changes the Window immediately and displays the selection in the highlighted menu SR785 Dynamic Signal Analyzer...

  • Page 184: Numeric Values

    If no menu box is highlighted, pressing a numeric entry key automatically selects the most recently modified parameter within the menu and begins numeric entry. This is convenient when a measurement requires a single parameter within a menu (or menus) to be modified repeatedly. SR785 Dynamic Signal Analyzer...
  • Page 185 Changes are effective immediately while the value is being adjusted. Press [Enter], the same softkey, another softkey or a menu key to un-highlight the menu box when finished. Some entry fields allow only knob adjustment or only numeric entry. SR785 Dynamic Signal Analyzer...

  • Page 186: Control Keys

    If measurement related parameters are changed while the unit is paused, the measurement cannot be resumed. The SR785 will display the message "Can't continue, Measurement has Changed." In this case it is necessary to press [Start/Reset] to restart the measurement.
  • Page 187 Display A. Pressing [Active Display] once makes Display B active and allows you to select the measurement for Display B using the same menu. Only those parameters which are associated with an individual display have differing values SR785 Dynamic Signal Analyzer...
  • Page 188 [Link] only affects the next key pressed. If the next key is not a function key then it has no affect. Linking affects each function differently. See the function key definitions for more information. SR785 Dynamic Signal Analyzer...
  • Page 189 Use [Alt] and the numeric keys to choose the units of a numeric parameter while recording a macro. The units choices are numbered starting with 0 as the first (leftmost) units. To play a recorded macro, press [Play Macro] ([Alt] [Start/Reset]) and choose the desired macro with the knob. SR785 Dynamic Signal Analyzer...
  • Page 190 Select a Trace # (1..5) with the knob and press [Enter] to save the display data to the Trace. A stored trace can be recalled to a Display or Reference Display, used in a User Math Function, saved to disk, or copied to the Arbitrary Waveform buffer. SR785 Dynamic Signal Analyzer...
  • Page 191 When the Display is returned to Live, the measurement, frequency span, averaging and window all return to the settings in effect before the data was recalled and the live measurement returns to the display. Command: RCTR d, i SR785 Dynamic Signal Analyzer...

  • Page 192: Function Keys

    Auto Range responds to all frequencies present at the input (except those attenuated by AC coupling), not just those within the measurement span. [Link] [Auto Range Ch1] toggles the Input Ranging of both channels. Command: A1RG (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 193 The Span is adjusted with either a fixed Start, Center or End frequency depending upon which frequency was most recently anchored in the [Frequency] menu. In Correlation group, [Span Down] inreases the time window over which the correlation is computed, but decreases the time resolution. SR785 Dynamic Signal Analyzer...
  • Page 194 Ymid or Ymin in the [Display Setup] menu. To graph the Reference Display in the new display scale, press [Alt] [Snap Ref]. [Link] [Display Ref] toggles the Reference Display of both displays. Command: DREF d, i SR785 Dynamic Signal Analyzer...
  • Page 195 [Link] [Marker Min] moves the marker to the location of the minimum within both displays. Command: MKMN d [Show Setup] [Show Setup] enters the Help system and displays the measurement setup and system settings. Press [0] to exit Help and return to the measurement displays. SR785 Dynamic Signal Analyzer...

  • Page 196: Macros

    Thus, do not start a macro with a softkey press since the menu which is displayed at playback may not be the one displayed when the macro was recorded. Always start a macro with a menu key press if you want to change parameters within a menu. SR785 Dynamic Signal Analyzer...
  • Page 197 Chapter 4 Menus The SR785 has a menu driven user interface. All operating parameters of the SR785 are grouped into sixteen menus. The Menu keys each display a menu of softkeys. The softkeys at the right of the display change depending upon the displayed menu.
  • Page 198 Tone 2 4-72 Nyquist Grid 4-48 Frequency 2 4-72 Phase Suppress 4-48 Amplitude 2 4-72 d/dx Window 4-49 Chirp Source Menu 4-73 Marker Menu 4-50 Amplitude 4-73 Marker 4-50 Burst 4-73 Mode 4-50 Source Display 4-74 SR785 Dynamic Signal Analyzer...
  • Page 199 Transducer Convert 4-94 Power Bin 4-117 Linear Average Trigger 4-117 Tachometer Input Submenu 4-95 Swept Sine Average Menu 4-119 Pulses per Rev 4-95 Tach Trigger Range 4-95 Settle Time 4-119 Tach Level 4-95 Settle Cycles 4-119 SR785 Dynamic Signal Analyzer...
  • Page 200 Slice to Trace 4-142 Exceedance Statistics Menu 4-159 Capture Menu 4-143 Start Index 4-159 Capture Channels 4-143 Stop Index 4-159 Capture Mode 4-143 Exceedance Pct 4-160 Capture Length 4-144 Calculate Excd 4-160 Sampling Rate 4-144 Allocate Memory 4-145 SR785 Dynamic Signal Analyzer...
  • Page 201 4-176 Macros 4-176 System Remote Menu 4-194 Recall from Disk 4-176 Output To 4-194 Disk Buffers Menu 4-177 GPIB Address 4-194 Overide REM? 4-194 File Name 4-177 Baud Rate 4-194 Current Directory 4-177 Word Length 4-195 SR785 Dynamic Signal Analyzer...
  • Page 202 Date 4-199 Dec. Knob Count 4-204 System Diagnostics Menu 4-200 Delete 4-204 Clear Macro 4-204 Keypad Test 4-200 Cancel 4-204 Keyboard Test 4-200 Knob Test 4-200 Enter Macro 4-204 RS232/Printer Test 4-200 String to RS232 4-201 SR785 Dynamic Signal Analyzer...

  • Page 203: Frequency Menus

    Independent Channels. In this configuration, no two channel measurements are allowed (frequency response, cross-spectrum, etc.), but the entry field can be linked to both displays using the [Link] key. If Analyzer Configuration is set to Dual Channel the field is automatically linked to both displays. SR785 Dynamic Signal Analyzer...
  • Page 204 Set the FFT Span of both displays to the FFT Base Frequency 102.4 (100.0) kHz. The Linewidth, Acquisition Time, Start frequency and Center frequency are set to 256 (250) Hz, 3.906 (4.00) ms, 0.0 Hz, and 51.2 (50.0) kHz respectively. SR785 Dynamic Signal Analyzer...
  • Page 205 Command: FBAS (?) d {, i} Start Frequency Set the Start frequency of the active display FFT span. The Start frequency is the lowest frequency in the measurement span. The knob adjusts the Start frequency in steps equal SR785 Dynamic Signal Analyzer...
  • Page 206 The knob adjusts the End frequency in steps equal to the Linewidth. If an entered End frequency is incompatible with the Span, then it will be set to the closest allowed value. SR785 Dynamic Signal Analyzer...
  • Page 207 (frequency response, cross-spectrum, etc.), but the entry field can be linked or unlinked using the [Link] key. If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays. Command: FEND (?) d {, f} SR785 Dynamic Signal Analyzer...

  • Page 208: Octave Frequency Menu

    The two displays can have different Highest Bands if the Analyzer Configuration is set to Independent Channels. If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays. Command: OHIB (?) d {, f} SR785 Dynamic Signal Analyzer...
  • Page 209 The two displays can have different Octave Resolution if the Analyzer Configuration is set to Independent Channels. If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays. Command: ORES (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 210 Measurement or input of the other display if necessary. User Functions which use both inputs may not be measured. Choosing 1 Octave Channel may change the current Measurements so that both displays use the same input. Command: OCHN (?) d {i} SR785 Dynamic Signal Analyzer...

  • Page 211: Swept Sine Frequency Menu

    The Stop frequency is usually greater than the Start frequency. If the Stop frequency is less than the Start frequency, then the sweep is downward from the Start frequency. If the Stop frequency is changed during a sweep, the sweep will be reset. Command: SSTP (?) d {, f} SR785 Dynamic Signal Analyzer...
  • Page 212 (with no skipping). The sweep continues from this point, speeding up if allowed and slowing down when required. This ‘fills’ in skips in the sweep which vary by more than the Slower Threshold. SR785 Dynamic Signal Analyzer...
  • Page 213 Size is reached. This speeds up the sweep in regions where the response is flat (varies less than the Faster Threshold). Measurements which differ by more than the Faster Threshold on EITHER channel, but less than the Slower Threshold on BOTH channels, maintain the present sweep speed. SR785 Dynamic Signal Analyzer...
  • Page 214 Generally, the Slower Threshold should be set to less than half of the smallest desired feature size (relative to the region before the feature). A good rule is to set the Slower Threshold at twice the Faster Threshold. Command: SSLO (?) d {, i} SR785 Dynamic Signal Analyzer...

  • Page 215: Order Frequency Menu

    Max Order Specifies the maximum order, i.e. multiple of the rotational speed, calculated by the SR785. Allowed values are between 3 and 200. Choosing a higher Max Order will limit the allowed range of Max RPM. Command: OMAX (?) d {, f}...
  • Page 216 A track measurement is a two-dimensional plot of the amplitude of a particular order vs. rpm with time as the parameter. Individual points in the measurement can be taken continuously, or at specified time or rpm intervals using Time arming and RPM Arming. Command: ONPT (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 217 Track 1 Order Specifies the order associated with the Track 1 measurement. If the entered value is not an integer multiple of delta order, the SR785 will display the closest available order to the entered value. Regardless of the order specified, the SR785 always tracks all orders specified by the max order and delta order softkeys.
  • Page 218 Input Channel (Track 2) Specifies the input channel associated with the Track 2 measurement. Regardless of the input channel specified, the SR785 always tracks all orders specified by the max order and delta order softkeys for both input channels. The Input Channel (Track 2) softkey merely selects which channel will be displayed.

  • Page 219: Time/Histogram Frequency Menu

    (each record is 1024 samples), or in seconds.When the specified number of samples, records, or seconds, has been reached, the histogram will update. If repeat is on the SR785 will begin accumulating a new histogram at the end of the prior histogram.
  • Page 220 Command: FBAS (?) d {, i} Repeat When repeat is set 'off', the SR785 computes a single histogram and stops. If repeat is on, the analyzer will automatically acquire new histograms continually as each one is finished. This can be useful for analyzing signals which change slowly with time.

  • Page 221: Display Setup Menu

    The Order Measurement Group makes spectrum and time measurements which are synchronized to the rotation of a rotating machine. The Time/Histogram Measurement Group calculates histograms and statistical parameters of the input signal. SR785 Dynamic Signal Analyzer...
  • Page 222 √ FFT 1 = MAX(FFT1*• FFT1) Power Spectrum The Power Spectrum is derived from the FFT spectrum by multiplying the spectrum by its complex conjugate. The averaged power spectrum is a good approximation to the rms SR785 Dynamic Signal Analyzer...
  • Page 223 If a transient signal occurs at the start of the time record, the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero. SR785 Dynamic Signal Analyzer...
  • Page 224 The definition of frequency response depends on the type of averaging which is displayed. No Average Freq. Response = FFT2 / FFT1 Vector Average Freq. Response = <FFT2> / <FFT1> RMS Average Freq. Response = (RMSAvg cross spectrum)/power spectrum 1 SR785 Dynamic Signal Analyzer...
  • Page 225 The capture data is filtered and down-sampled according to the capture Sample Rate. Only baseband data (data bandwidth starts at DC) are captured. The capture buffer resembles a digital oscilloscope display. Signals at frequencies above 1/2.56 times the sample rate have been filtered out. SR785 Dynamic Signal Analyzer...
  • Page 226 Vector Averaging On Auto Correlation = invFFT( <FFTuN> • <FFTN*> ) where N is Channel 1 or 2. FFT is a windowed FFT, FFTu is an un-windowed FFT (uniform window) and invFFT is an inverse FFT. SR785 Dynamic Signal Analyzer...
  • Page 227 [-T/4..T/4] window zeroes the first and last quarter of the time record. The [-T/2..T/2] is a uniform window which should only be used on data which is self windowing (lasts less than half of the time record). SR785 Dynamic Signal Analyzer...
  • Page 228 Measurement (Octave Analysis) Select the Measurement of the active display when the Measurement Group is Octave Analysis. Each Measurement has an associated View. Changing the Measurement changes the View to the View last used with the new Measurement. SR785 Dynamic Signal Analyzer...
  • Page 229 Use the [User Math] menu to define a function. A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group. SR785 Dynamic Signal Analyzer...
  • Page 230 The swept sine Frequency Response (sometimes called frequency response) is a two channel measurement defined as Frequency Response = Spec2 / Spec1 The Frequency Response contains both magnitude and phase information. The phase is the relative phase (at each frequency) between the two channels. SR785 Dynamic Signal Analyzer...
  • Page 231 If this happens, use a uniform window, or adjust the trigger to move the event to the center of the time record. SR785 Dynamic Signal Analyzer...
  • Page 232 User Functions A User Function displays the results of a user defined math function. User Functions defined within the Order Measurement Group may include order measurement results. Use the [User Math] menu to define a function. SR785 Dynamic Signal Analyzer...
  • Page 233 User Functions A User Function displays the results of a user defined math function. User Functions defined within the Histogram Measurement Group may include histogram measurement results. Use the [User Math] menu to define a function. SR785 Dynamic Signal Analyzer...
  • Page 234 Imag Part view graphs the imaginary part of the measurement data. The Y axis of the display is linear in scaling. Real measurement data, such as baseband time record, have zero imaginary part. This view is zero for all points. SR785 Dynamic Signal Analyzer...
  • Page 235 Because these filters are very steep and selective, they introduce very large phase shifts for signals not exactly on a frequency bin. Use the SR785 source to generate exact bin frequencies whenever possible.
  • Page 236 Measurement and View. For instance, dB units may not be selected when the view is Real Part. Settings in the units submenu are associated with the Measurement and View. Changing Measurements or Views may change the settings within the Units submenu SR785 Dynamic Signal Analyzer...
  • Page 237 Pk Units Determines whether the active display units will be peak, peak to peak, or rms. This softkey is inactive if the underlying measurement and view is unitless, e.g. frequency response. Command: UNPK (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 238 The two displays can have different center reference values. This entry field can be linked to both displays using the [Link] key. When Y Mid is changed, the value of Y/Div is kept fixed and Y-Max and Y-Min are adjusted. SR785 Dynamic Signal Analyzer...
  • Page 239 Center is the X axis value at the center of the graph. The X Center has the same units as the display. The two displays can have different X Center values. This entry field can be linked to both displays using the [Link] key. Command: XCEN (?) d {, x} SR785 Dynamic Signal Analyzer...
  • Page 240 Set the Pan (translation) of the active display. This value is the left most displayed bin when the X axis is Zoomed (expanded). The two displays can have different translations when expanded. This entry field can be linked to both displays using the [Link] key. Command: XPAN (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 241 Zoom is not allowed when the X axis is logarithmic or when the View is polar (Nyquist or Nichols plot). The two displays can have different Zoom values when expanded. This entry field can be linked to both displays using the [Link] key. Command: XZOM (?) d {,i} SR785 Dynamic Signal Analyzer...

  • Page 242: Display Options Menu

    A single display may be taken Off-Line while the other display is still Live. This allows comparison of live results with a previous result. This is unlike the [Pause/Cont] key which pauses ALL measurements. Command: DISP (?) d {, i} Format Select the screen Display Format [Single, Dual, or Overlay]. SR785 Dynamic Signal Analyzer...
  • Page 243 Off, the values are displayed in Hz. Command: RPMF(?) {i} Grid Select the Grid for the active display [On, Off]. The grid is the set of dotted lines on the display which mark each scale division. SR785 Dynamic Signal Analyzer...
  • Page 244 To suppress the phase of signals below -60 dBV (1.0E-3 V), set the threshold to 1.0E- (magnitude squared). The two displays have their own Phase Suppress Threshold. This entry field can be linked to both displays using the [Link] key. Command: PHSL (?) d {, x} SR785 Dynamic Signal Analyzer...
  • Page 245 The two displays have their own d/dx Window. The same function may viewed in the two displays with different d/dx windows. This entry field can be linked to both displays using the [Link] key. Command: DDXW (?) d {, x} SR785 Dynamic Signal Analyzer...

  • Page 246: Marker Menu

    Correlation, Swept Sine, and Time/Histogram measurement groups can only use Normal mode. Each display has its own Marker Mode. This entry field can be linked to both displays using the [Link] key. Command: MKMD (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 247 Harmonic Marker is not available for Correlation, Octave, Swept Sine, or Time/Histogram measurement groups. Sideband The Sideband Marker Mode defines a Fundamental (carrier) Marker with a solid vertical line. In addition to the Fundamental Marker, a number of sidebands (discrete SR785 Dynamic Signal Analyzer...
  • Page 248 Choose the 2/(1+2) ratio mode to measure THD+N (power with fundamental notched out/total power including fundamental). Band Marker is only available for frequency domain FFT, Order, and Octave measurements. Band Marker is not available for the Swept Sine, Correlation, or Time/Histogram measurement groups. SR785 Dynamic Signal Analyzer...
  • Page 249 The fit area is moved using the knob. Use [Alt] knob to re-size the fit region. The Frequency/Damping cursor should only be used with frequency response data.. The Frequency/Damping Cursor is only available in the FFT and Swept Sine measurement groups. SR785 Dynamic Signal Analyzer...

  • Page 250: Normal Marker Menu

    Marker is the small square which Seeks the Max, Min or Mean of the data within the Marker Region. Each display has its own Normal Marker Width. This entry field can be linked to both displays using the [Link] key. SR785 Dynamic Signal Analyzer...
  • Page 251 Marker Offset (in the display units) from the absolute marker position. Changing the display units invalidates the Marker Offset. Re-enter the Marker Offset or use [Marker Ref] to reset the Marker Offset in the new units. SR785 Dynamic Signal Analyzer...
  • Page 252 X position in absolute units. Each display has its own X Rel Mode. This entry field can be linked to both displays using the [Link] key. Command: MXRL (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 253 Specifies the X position the marker will be sent to with the Marker X to button. The target is entered in the current units of the x-aaxis. If the exact x value specified is not available, the marker will be sent to the closest available X value. SR785 Dynamic Signal Analyzer...

  • Page 254: Harmonic Marker Menu

    Select the Harmonic and Sideband Display for the active display. The Marker Position can display the Fundamental or any identified Harmonic or Sideband. For Harmonic Marker, the minimum is 0 (Fundamental) and the maximum is the Number Of Harmonics. The second harmonic (2xfundamental) is identified as #1, etc. SR785 Dynamic Signal Analyzer...
  • Page 255 Command: HTHD ? d , i Harmonic Power This menu box displays the Total Harmonic Power of the active display. The harmonic power is the sum of the squared magnitudes of the harmonics identified with a Harmonic SR785 Dynamic Signal Analyzer...
  • Page 256 4-60 Harmonic Marker Menu Marker. The result is shown in Vrms, or dBVrms depending on the setting of dB Units. To convert a value in Vrms to power, square the result. Command: HPWR ? d SR785 Dynamic Signal Analyzer...

  • Page 257: Sideband Marker Menu

    The Sideband Marker identifies the carrier frequency with the Fundamental Marker (solid vertical line) and the number of sidebands with small triangular Sideband Markers. The Sideband Separation determines the location of these Sideband Markers relative to the fundamental. SR785 Dynamic Signal Analyzer...
  • Page 258 Command: HRDO (?) d {, i} Sideband Ratio This menu box displays the Sideband Ratio of the active display. The sideband power is the sum of the squared magnitudes of the sidebands. Only those sidebands within the SR785 Dynamic Signal Analyzer...
  • Page 259 Sideband Markers contribute to the calculation. The result is shown in Vrms, or dBVrms depending on the setting of dB Units. To convert a value in Vrms to power, square the result Command: SPWR ? d , i SR785 Dynamic Signal Analyzer...

  • Page 260: Band Marker Menu

    The region where the two bands overlap is not included in band 1 (Lower). For example, to measure THD+N, use the Lower (1) band to define a small region around the fundamental and the Upper (2) band to define the total bandwidth of interest. SR785 Dynamic Signal Analyzer...
  • Page 261 Band Ratio This menu box displays the band ratio, either 2/1 or 2/(1+2) as selected by the Band Ratio Mode, for the active display. The result is shown in % and dB. Command: BRAT (?) d, i SR785 Dynamic Signal Analyzer...

  • Page 262: Frequency/Damping Marker Menu

    Displays the damping ratio of the data in the cursor area. The damping ratio frequency is calculated by fitting a single-pole frequency response function to the data. The damping ratio is negative the ratio of the real part of the pole to the magnitude of the pole. Command: MMCA? d SR785 Dynamic Signal Analyzer...

  • Page 263: Source Menus

    The output is the sum of two tones (sine waves) plus the offset. To generate a single tone, set the amplitude of one of the tones to zero. The frequencies should be exact bin frequencies of the FFT. This eliminates windowing effects in the measured amplitude and phase. SR785 Dynamic Signal Analyzer...
  • Page 264 In FFT group, the noise bandwidth and burst time record is linked to either DisplayA or DisplayB. If the other display has a different span, the source may not be appropriate for that display. Since the signal is random, windows are always required when making FFT measurements using the noise source. SR785 Dynamic Signal Analyzer...
  • Page 265 Source trigger outputs the source continuously over and over. The FFT time records are synchronized to the source start. Continuous Trigger outputs the source continuously over and over. Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received. SR785 Dynamic Signal Analyzer...
  • Page 266 If the Arbitrary source is selected, the triggered FFT measurement phase is stable only if the input signals are derived from the triggered source output. Turn the source off (or set it to Sine) when making triggered measurements of external signals (not the source). Command: STYP (?) {i} SR785 Dynamic Signal Analyzer...

  • Page 267: Sine Source Menu

    Note that the sum of the amplitudes of Tone 1, Tone 2 and the absolute value of the offset cannot exceed 5 V. Command: S1AM (?) {x} SR785 Dynamic Signal Analyzer...
  • Page 268 Note that the sum of the amplitudes of Tone 1, Tone 2 and the absolute value of the offset cannot exceed 5 V. Command: S2AM (?) {x} SR785 Dynamic Signal Analyzer...

  • Page 269: Chirp Source Menu

    FFT time record of the display selected as the Source Display. Burst is only available for the FFT Measurement Group. For a continuous output, use 100% burst with continuous Trigger Source or Source Trigger. Source Trigger will synchronize the FFT time record with the chirp waveform. SR785 Dynamic Signal Analyzer...
  • Page 270 Select which display sets the time record and frequency span of the chirp. If the other display has a different span, the chirp will not be appropriate for that span. Burst Chirp is a percentage of the Source Display FFT time record length. Command: CSRC (?) {i} SR785 Dynamic Signal Analyzer...

  • Page 271: Noise Source Menu

    FFT spectrum. The power spectral density (PSD) remains constant at all spans. Pink Noise Pink noise rolls off at 3 dB/oct providing equal energy per octave and extends beyond 102 kHz. The spectrum of pink noise appears flat in octave analysis. SR785 Dynamic Signal Analyzer...
  • Page 272 Changing this entry for one type of source also changes it for the other. Select which display sets the bandwidth for bandlimited noise. Burst Noise is a percentage of the Source Display FFT time record length. SR785 Dynamic Signal Analyzer...
  • Page 273 Source trigger outputs a noise burst every source period. Free Run Trigger Mode outputs a noise burst every source period. Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received. Command: NPER (?) {x} SR785 Dynamic Signal Analyzer...

  • Page 274: Arbitrary Source Menu

    Select the Arbitrary Source Play Rate. The Play Rate can be 1, 1/2, 1/4, 1/8, ... times the maximum sampling rate. The maximum sampling rate is 262.1 kHz when the FFT Base Frequency is 102.4 kHz and 256 kHz when the FFT Base Frequency is 100.0 kHz OR the Measurement Group is Octave. SR785 Dynamic Signal Analyzer...
  • Page 275 The Arbitrary waveform memory can be loaded from a stored trace, via the computer interfaces or from a disk file. The Capture buffer is filled by capturing an input signal. Command: ASRC (?) {i} More Display the Arbitrary Source Settings menu. Press <Return> for the main [Source] menu. SR785 Dynamic Signal Analyzer...
  • Page 276 The Source Length is always set to a 2 kPoint (2048 points) increment. If the marker position is to the left of the Source Start, then the Source Length is set to the minimum (2 kPts). SR785 Dynamic Signal Analyzer...
  • Page 277 2 kPoints is reached. This can cause discontinuities if the trace is not continuous from its end to its beginning. If this source is measured with an FFT time record equal to the trace length (in time), then windowing should solve this problem. SR785 Dynamic Signal Analyzer...
  • Page 278 The amplitude of the Arbitrary Waveform is normalized to the maximum value in the Trace. The largest trace value is considered full scale (100% amplitude = 1V). Be sure to set the Play Rate to the appropriate value to reproduce the frequencies in the trace correctly. Command: TARB i SR785 Dynamic Signal Analyzer...

  • Page 279: Swept Sine Source Menu

    Level Reference is Off. The swept sine source turns off whenever there are no measurements being made. This is before the sweep is started, at the end of a single sweep or while a sweep is paused. If SR785 Dynamic Signal Analyzer...
  • Page 280 Set the Source Ramp Rate [0.001 V/s .. 500 V/s]. The Source Ramp Rate is the rate at which the source amplitude changes when Source Ramping is On. If Source Ramping is Off, source amplitude changes are made instantly. SR785 Dynamic Signal Analyzer...
  • Page 281 The Reference Lower Limit may be changed during a sweep. Command: SSLL (?) {x} Maximum Source Level Set the Maximum Source Level [0 mV .. 5000 mV]. This parameter is adjustable only if Auto Level Reference is set to Channel 1 or Channel 2. SR785 Dynamic Signal Analyzer...
  • Page 282 The Maximum Source Level is the largest allowed source amplitude. This is limited by the SR785 source output or the device under test input range. If the Reference Lower Limit requires a source amplitude greater than the Maximum Source Level, then the source amplitude is set to the Maximum Source Level.

  • Page 283: Input Menu

    Dual channel measurements, such as frequency response, or orbit, cannot be selected. Dual Channel allows selection of all measurements, both single and dual channel. However, in Dual Channel mode the two displays always have the same frequency parameters. SR785 Dynamic Signal Anaylzer...
  • Page 284 To avoid disrupting a lengthy measurement, turn Auto Offset Off. A warning message is displayed 15 seconds before an Auto Offset calibration is performed. Pressing [<-] (backspace) will abort the scheduled calibration. Command: IAOM (?) {i} SR785 Dynamic Signal Anaylzer...

  • Page 285: Input Configuration Menu

    Select the Input Grounding for the selected input shields [Float, Ground]. The shields of A and B are connected. Float connects the shields to chassis ground through 1 MΩ + 0.01 µF. This allows the shield of a single ended input to ‘float’. SR785 Dynamic Signal Anaylzer...
  • Page 286 The actual underlying Input Range of the SR785 varies by 2 dB steps from -50 dBVpk to +34 dBVpk. The input range can be set in units of dBVpk, dBVrms, dBVpp, Vpk, Vrms, dBEUpk, dBEUrms, dBEUpp, EUpk, EUrms, or EUpp.
  • Page 287 Range to oscillate. Do not use Tracking Mode in these cases. Auto Range responds to all frequencies present at the input (except those attenuated by AC coupling or the anti-aliasing filter), not just those within the measurement span. Command: I1AR (?) {i} Command: I2AR (?) {i} SR785 Dynamic Signal Anaylzer...

  • Page 288: 4-92 Transducer Parameter Menu

    Pascals/Volt. Note that this softkey applies to an input channel, unlike most softkeys which apply to a specific display. Command: EU1M (?) {i} EU2M (?) {i} SR785 Dynamic Signal Anaylzer...
  • Page 289 The active display measurement must be a single channel measurement and Engineering Units must be On. This feature is normally used for the input channel which is being measured in the active display. In this case, the active display marker reading changes to the calibrated value. SR785 Dynamic Signal Anaylzer...
  • Page 290 The two input channels may have different transducer conversions. Command: TD1C (?) {s} EU2U (?) {s} SR785 Dynamic Signal Anaylzer...

  • Page 291: Tachometer Input Menu

    The tachometer will trigger when the input passes through the specified level in the direction specified by the tach slope softkey. If the tachometer signal is noisy near the specified tach trigger level, use the hold off to increase the noise immunity of the tach input. SR785 Dynamic Signal Anaylzer...
  • Page 292 When the measurement group is Order, Show Tach is always On. Likewise, if the trigger mode is RPM Arm , Show Tach is always on. If Show Tach is off, the indicator is displayed in the same position as the RPM indicator. Command: TASH(?) {i} SR785 Dynamic Signal Anaylzer...

  • Page 293: Playback Input Menu

    The corresponding playback time is displayed as well. Both channels playback the same Playback Length. Command: ILEN (?) {i} Set Left Edge The active display must be a Capture Buffer measurement for this key to be active. SR785 Dynamic Signal Anaylzer...
  • Page 294 Normal playback is limited to the real time limitations of the equivalent real time analog input measurement. Not all time records are displayed during Normal playback though all time records contribute to averaged measurements. For example, 1 second of capture contains 256 full SR785 Dynamic Signal Anaylzer...
  • Page 295 When the playback is in Octave Group, playback is always Normal Speed. The Capture Progress indicator at the top of the screen shows the playback progress through the buffer. Both channels playback with the same Playback Speed. Command: ISPD (?) {i} SR785 Dynamic Signal Anaylzer...

  • Page 296: Trigger Menu

    In RPM Arming, the trigger is armed when the RPM passes through a start threshold and at fixed rpm increments thereafter. In Time Arming, the trigger is armed after a specified amount of time has elapsed. The time interval is specified with the Time Arm Step softkey. SR785 Dynamic Signal Analyzer...
  • Page 297 For Order measurements, the phase is measured relative to the trigger rather than the tachometer pulse if a non continuous trigger source is used. The Trigger Source applies to both displays. Command: TSRC (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 298 (time record length plus trigger delay) is noticeably long. Command: TDLA (?) {i} Delay B Set the Trigger Delay for Ch1, or Display A. depending on the Analyzer Configuration. The Trigger Delay applies only to FFT and Correlation measurements. SR785 Dynamic Signal Analyzer...
  • Page 299 Watch Out For Triggered Sources If a triggered source is selected (Chirp, Burst Chirp, Burst Noise or Arbitrary), the triggered FFT measurement phase is stable only if the input signals are derived from the SR785 Dynamic Signal Analyzer...
  • Page 300 Delta RPM Set the RPM increments for which the trigger will be armed. Once the Start RPM condition, if any, has been met. The trigger will arm each time the rpm changes by the specified amount. SR785 Dynamic Signal Analyzer...
  • Page 301 Trigger the measurements (and burst Chirp & Noise sources) regardless of Trigger Source. Manual Trigger Source requires <Manual Trigger> or an interface command to trigger. Use Auto Arm Trigger Mode with Manual Trigger Source since unwanted triggers are not a problem. SR785 Dynamic Signal Analyzer...
  • Page 302 For FFT, correlation, and Time Histogram measurements each time record requires the trigger to be re-armed. For octave and swept sine measurements, the first trigger after arming starts the measurement and subsequent triggers are ignored. Command: TMAN SR785 Dynamic Signal Analyzer...

  • Page 303: Average Menus

    Compute Averages should be left On. Some FFT measurements, such as coherence, have averaging as part of their definition. If one of these measurements is selected, Compute Averages will be forced On. Command: FAVG (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 304 Once in steady state, further changes in the average are detected only if they last for a sufficient number of measurements. Make sure that the number of averages is not so large as to eliminate changes in the data which might be important. SR785 Dynamic Signal Analyzer...
  • Page 305 Display Average Select the type of averaging for the measurement displayed on the active display [None, RMS, Vector, Peak Hold]. Note that when Compute Averages is On, the SR785 always computes the non-averaged, rms averaged, vector averaged, and peak-hold averaged version of all measurements simultaneously.
  • Page 306 As long as the signals of interest have stable relative phases, triggering is not required for vector averaging. Triggering is still required to isolate time records which contain the signals of interest. The Time Record Increment should be set to 100% when vector averaged measurements are being used. SR785 Dynamic Signal Analyzer...
  • Page 307 Settling When the frequency span or input signal path (gain, filtering, etc.) is changed, a settling time is required before the FFT measurement is considered settled or valid. The SR785 Dynamic Signal Analyzer...
  • Page 308 Whenever a time record is rejected, the ‘Reject’ indicator below the graph (next to the average type and number) turns on briefly. This has no effect if Averaging is Off. SR785 Dynamic Signal Analyzer...
  • Page 309 DisplayB shows Ch2 time record. In this case, use the dual display format to view both time records. While the preview time records are displayed, the displays are labeled ‘Preview’ instead of ‘Live’ (in the Vertical Scale Bar). While previewing the time record, the measurement SR785 Dynamic Signal Analyzer...
  • Page 310 Average Preview allows each individual measurement to be accepted (added to the average) or rejected (not added to the average) based upon the input time records. This is useful for rejecting bad time records from corrupting an averaged measurement. Command: PAVR SR785 Dynamic Signal Analyzer...

  • Page 311: Octave Average Menu

    When the measurement is free running (Auto Arm, Continuous Trigger), each time the linear average is done, the result is stored in the waterfall buffer and the average is reset and started over (instead of stopping). Each completed average counts as a single waterfall record. SR785 Dynamic Signal Analyzer...
  • Page 312 Decreasing the Lowest Band below 100 Hz increases the minimum value of the Integration Time. The [Start/Reset] key resets the current averages and starts the measurement over. The [Pause/Cont] key pauses the measurement. Pressing [Pause/Cont] again resets the averages and starts the measurement over. SR785 Dynamic Signal Analyzer...
  • Page 313 Mode and Trigger Source are not Auto Arm and Continuous, respectively. When the measurement is triggered the Linear Average Mode determines how the measurement restarts. One Linear Average means that each trigger starts a new measurement. SR785 Dynamic Signal Analyzer...
  • Page 314 (use the Burst Noise source with 1-Shot Trigd Source Mode) and subsequent measurements follow continuously. All complete averages are stored to a waterfall to examine the sound level decay. Both displays always have the same Linear Average Trigger. Command: OLAT (?) d {, i} SR785 Dynamic Signal Analyzer...

  • Page 315: Swept Sine Average Menu

    The estimated sweep time is displayed in the Horizontal Scale Bar. This time is simply the sum of the Settle and Integrate times for all points in the sweep. Auto functions (Source Auto Level, Auto Range, Auto Resolution) will change the actual sweep time. SR785 Dynamic Signal Analyzer...
  • Page 316 1 cycle or 15.625 ms. To measure each point for a time inversely proportional to the frequency, set the Integration Time to 15.625 ms (minimum) and the Integration Cycles to the desired SR785 Dynamic Signal Analyzer...
  • Page 317 The estimated sweep time is displayed in the Horizontal Scale Bar. This time is simply the sum of the Settle and Integrate times for all points in the sweep. Auto functions (Source Auto Level, Auto Range, Auto Resolution) will change the actual sweep time. Command: SSCY (?) d {, i} SR785 Dynamic Signal Analyzer...

  • Page 318: User Math Menu

    Command: USRS (?) i {, j, k, l, m, ...} (Swept Sine Group) Command: USRT (?) i {, j, k, l, m, ...} (Order Group) Command: USRH (?) i {, j, k, l, m, ...} (Time/Histogram Group) SR785 Dynamic Signal Analyzer...
  • Page 319 Use the knob to pick one of the displayed Operands and press [Enter] to place it in the equation at the cursor location. The display then automatically switches to the Operations display. To enter another operand instead, press <Operands> again. The available measurement operands depend upon the current Measurement Group. FFT Measurement Group SR785 Dynamic Signal Analyzer...
  • Page 320 4-124 User Math Menu Correlation Measurement Group Octave Measurement Group Swept Sine Measurement Group Order Measurement Group SR785 Dynamic Signal Analyzer...
  • Page 321 Trace operands are simply the data stored in the Traces. For example, Traces can hold reference data used for normalization or calibration. There are 5 Traces which can be stored. These Traces are shared by all 3 Measurement Groups. SR785 Dynamic Signal Analyzer...
  • Page 322 The display then automatically switches to the Operands display. To enter another operation instead, press <Operations> again. The available operations depend upon the current Measurement Group. FFT Measurement Group Correlation Measurement Group Octave Measurement Group SR785 Dynamic Signal Analyzer...
  • Page 323 Ln(x + jy) = ln(r) + jθ Exp(x + jy) = exp(x) • ( cos(y) + jsin(y) ) √ r • ( cos(θ/2) + jsin(θ/2) ) Sqrt(x + jy) = [X/(1-X)] = (x + jy)/(1 - x - jy) SR785 Dynamic Signal Analyzer...
  • Page 324 Insert/Replace Toggle between insert and replace mode while editing a User Function equation. If editing in insert mode, ‘Ins’ appears in the upper right corner of the edit window. If editing in replace mode, ‘Rep’ appears. SR785 Dynamic Signal Analyzer...
  • Page 325 Display the Edit Constant menu. Press <Return> or [User Math] for the main [User Math] menu . Constants may be used as operands in a User Function. There are 5 constants which may be defined and are shared by all Measurement Groups. Command: USRC (?) i {, x, y} SR785 Dynamic Signal Analyzer...
  • Page 326 Copy the marker reading (exactly as shown in the Marker Position Bar) of the active display to the magnitude of the selected Constant. No unit translation takes place. Make sure that the units of the active display are correct before using this feature. SR785 Dynamic Signal Analyzer...

  • Page 327: Window Menu

    The Hanning window is the most commonly used window. However, it has an amplitude variation of about 1.5 dB for off-bin signals and provides only reasonable selectivity. Its side-lobes are very high and broad for off-bin frequencies. As a result, the Hanning SR785 Dynamic Signal Analyzer...
  • Page 328 <Trace to Window>. The trace may contain stored data or may be loaded from disk or via the computer interface. Remember, window functions have a great deal of impact on the resulting FFT spectrum. A poorly designed window can result in significant measurement errors. SR785 Dynamic Signal Analyzer...
  • Page 329 Set the Expo Window Time Constant as a percentage of the FFT time record [5%..1000%]. This is the point where the window function reaches 1/e. Choose Force/Exponential as the window before setting the Expo Time Constant. Command: FWTC (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 330 BMH and Kaiser windows are all symmetric. Use Non-Symmetric if the User window is non-symmetric. Phase will be measured relative to the start of the time record. Force and Exponential windows are non- symmetric. Command: WSYM (?) d {, i} SR785 Dynamic Signal Analyzer...

  • Page 331: Waterfall Menu

    Vertical Scale Bar when storage is on. A waterfall display may not be taken Off-Line. Moving the Marker The marker may be moved to a record other than 0 only if storage is on. SR785 Dynamic Signal Analyzer...
  • Page 332 Each completed average counts as a single waterfall record. Command: WSTO (?) d {, i} Save Option Select whether the analyzer should store all the measurements in the current measurement group, or only the currently displayed measurements. SR785 Dynamic Signal Analyzer...
  • Page 333 Waterfall Menu 4-137 When All is selected the SR785 stores all the measurements in the current measurement group to the waterfall buffer. This allows later viewing of any measurement, but uses up more space in the waterfall buffer. When Active Measurement Only is selected, the SR785 stores only the currently selected measurement for each display.
  • Page 334 When the Scroll Angle is 0, the older records scroll straight down. When the Scroll Angle is negative, the older records shift left as they scroll down. When the Scroll Angle is positive, they shift right as they scroll down. SR785 Dynamic Signal Analyzer...
  • Page 335 Command: MMEM ? Capture Memory Allocates memory blocks for the capture buffer. The allocated Capture Memory sets the limit for the Capture Length. Capture memory must be allocated before the capture buffer may be used. SR785 Dynamic Signal Analyzer...
  • Page 336 The View Count and the Trace Height determine the available scroll Angles. Each display has its own Waterfall Trace Height. This entry field can be linked to both displays by using the [Link] key. Command: WHIT (?) d {, i} SR785 Dynamic Signal Analyzer...
  • Page 337 Set the waterfall display direction for a paused measurement [Normal, Oldest at Top]. While the measurement is running, the waterfall display scrolls down and the newest record is added to the top (back) of the waterfall. SR785 Dynamic Signal Analyzer...
  • Page 338 A stored slice trace can be recalled to a Display or Reference Display, used in a User Math Function or saved to disk. A slice can not be copied to the Arbitrary Waveform buffer. Command: WSLC (?) d, i, j SR785 Dynamic Signal Analyzer...

  • Page 339: Capture Menu

    If the Capture Mode is Continuous, once capture is started, it continues indefinitely and fills the capture buffer in a circular fashion. In this case, press [Stop Capture] to halt capture with the most recent data in the buffer. Continuous capture is not allowed in the order measurement group. SR785 Dynamic Signal Analyzer...
  • Page 340 Instead the analyzer calculates the sampling rate based on the Max Order and Delta Order. Based on the computed sample rate and the capture length, the analyzer will display the length of the capture buffer in seconds. Command: CRAT (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 341 Waterfall Memory allocates memory blocks for waterfall storage. Command: MALC i, j, k Arb Memory Arb. Memory allocates memory blocks for the Arbitrary Source waveform. The Arbitrary Source can also use the capture buffer as the output waveform. Command: MALC i, j, k SR785 Dynamic Signal Analyzer...
  • Page 342 During playback, this keeps the capture display showing the points which are currently being measured. Off leaves the display Pan to that set in the [Display Setup] menu. Command: CPAN (?) {i} SR785 Dynamic Signal Analyzer...

  • Page 343: Analysis Menu

    Upper limit or less than a Lower limit cause the test to fail. Limit Segments are defined for the current View. Changing the View invalidates the Limit Segments and limit testing is not available in the new View. Either return to the SR785 Dynamic Signal Analyzer...
  • Page 344 Press <Calculate Excd> to start the calculation. The result is stored in a data trace and has the same measurement type as the waterfall measurements. To view the result, recall the trace to a display or reference graph. Curve Fit Display the Curve Fit/Synthesis menu. SR785 Dynamic Signal Analyzer...
  • Page 345 The SR785 does curve fitting and synthesis in two curve tables. Each table contains a model of frequency response function containing up to 20 poles and zeros. The model can be expressed in pole-zero format, pole residue format, or polynomial format.

  • Page 346: Data Table Analysis Menu

    Data Table. To select an entry in the table, use the backspace key [<-] or press [Alt] and turn the knob. Press [Alt] again to return the keypad to normal mode. Command: DMOD d, i, x SR785 Dynamic Signal Analyzer...
  • Page 347 You can not delete all of the entries in the table. Command: DDLT d, i Clear Table Clear the Data Table for the active display. The table is left with a single entry for the first bin in the display. Command: DCLR d SR785 Dynamic Signal Analyzer...

  • Page 348: Limit Testing Analysis Menu

    Command: LTST (?) d {, i} Limit Beep Turn the audible Limit Alarm for the active display On or Off. Off turns off the alarm. On turns on the alarm. Limit tests which fail will sound an audible alarm. SR785 Dynamic Signal Analyzer...
  • Page 349 Select the Limit Type for the Current Segment [Upper, Lower]. Each segment is identified by small triangular arrow markers at the segment end points. These markers are above the segment and point downwards for Upper limits. They are below the segment and point upwards for Lower limits. SR785 Dynamic Signal Analyzer...
  • Page 350 Enter or adjust the Y coordinate for the Current Segment End point. The Y coordinates are assumed to be in the display units. Use Zoom and Pan to expand the display when drawing small segments. Command: LSEG (?) d, i {, j, x0, y0, x1, y1} SR785 Dynamic Signal Analyzer...
  • Page 351 Use the Current Segment markers to identify the correct segment before editing. Command: LDLT d, i Shift All Shift all of the Limit Segments up or down together. Enter a value or use the knob to shift by 1/10’s of a division. Command: LSFT d, x SR785 Dynamic Signal Analyzer...

  • Page 352: Marker Statistics Analysis Menu

    Reset and start the accumulation of marker statistics. The various quantities are reset to zero and the accumulation of marker statistics begins. Use this key whenever the marker position is changed to avoid mixing data from different marker positions. Command: MSRS SR785 Dynamic Signal Analyzer...
  • Page 353 Display A is not visible. Command: MSSA ? Max (Display B) This menu box displays the maximum value of the marker Y value for display B since Marker Stats was turned On or Reset. SR785 Dynamic Signal Analyzer...
  • Page 354 This menu box displays the standard deviation of the marker Y value for display B since Marker Stats was turned On or Reset. This standard deviation is updated whenever new data is available for Display B and does not update if Display B is not visible. Command: MSSB ? SR785 Dynamic Signal Analyzer...

  • Page 355: Exceedance Statistics Analysis Menu

    The total number of records currently stored and available in the waterfall buffer is displayed in the Vertical Scale Bar. The Stop Index should not exceed the total number of records in the buffer. Both displays use the same Stop Index. Command: ESTP (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 356 The save option must be set to Active Measurement Only. The result is stored in a data trace and has the same measurement type as the waterfall measurements. To view the result, recall the trace to a display or reference graph. Command: EXCE d, i SR785 Dynamic Signal Analyzer...

  • Page 357: Curve Fit Menu

    Synthesis of user entered curve parameters is also provided. Start Fit When start fit is pressed the analyzer begins the curve fitting process. The SR785 will determine a fit to the data in the active display, which must be part of the FFT or swept- sine measurement group.
  • Page 358 Table Turns the curve table display on and off. When the curve table display is on you can use the edit table menu to modify poles, zeros, residues, polynomial coefficients, overall gain, delay, or frequency scaling. SR785 Dynamic Signal Analyzer...
  • Page 359 Weighting Trace softkey. The length of the trace being used must match the length of the display being fit. Only the real part of the trace data is used SR785 Dynamic Signal Analyzer...
  • Page 360 When the fit parameters are calculated the fit curve will be synthesized only inside the fit region. Outside of the fit region, the data in the fit trace will be zero. Command: ERNG (?) d, {i,j} SR785 Dynamic Signal Analyzer...
  • Page 361 Deletes the highlighted item in the curve table. This option is only available when the highlighted item is a pole, zero, residue, or polynomial coefficient. Table Format Changes the representation of the curve in the curve fit table [polynomial, pole zero, or pole residue]. SR785 Dynamic Signal Analyzer...
  • Page 362 Complex poles, zeros, or residues only occur as part of complex conjugate pairs. Thus, if the string 3 j 7 is entered for a pole, for instance, it corresponds to the term (s-(3+j7))*(s-(3-j7)) in the frequency response. SR785 Dynamic Signal Analyzer...

  • Page 363: Disk Menu

    Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension .78? (SR785 files). Press [Exp] to display all files in the directory (*.*). Choose a file name with the knob and press [Enter] to make it the Current File Name.
  • Page 364 These menus are shown in gray and reflect the settings or values for the last Live measurement. Parameters which pertain to the display of the data, such as scale and view, may be changed in the [Display Setup] and [Display Options] menus. SR785 Dynamic Signal Analyzer...
  • Page 365 Trace. The recalled data will replace any data presently stored in the Trace. A stored trace can be recalled to a Display or Reference Display, used in a User Math Function or saved to disk. Command: TRCL i SR785 Dynamic Signal Analyzer...
  • Page 366 Disk Upkeep Display the Disk Upkeep menu. Press <Return> or [Disk] for the main Disk menu. The Disk Upkeep menu allows files to be deleted, directories to be created and removed and disks to be formatted. SR785 Dynamic Signal Analyzer...

  • Page 367: Nodal Degree-Of-Freedom Menu

    The SR780 does not use the nodal degree-of-freedom information itself. The information is stored with the .78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs. Command: RFNU (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 368 The SR780 does not use the nodal degree-of-freedom information itself. The information is stored with the .78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs. Command: RSDR (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 369 Nodal DOF Menu 4-173 Abort Save Press to abort the selected disk operation while in the nodal DOF information menu. Continue Save Press when finished entering nodal DOF information to continue the selected disk operation. SR785 Dynamic Signal Analyzer...

  • Page 370: Recall Settings Menu

    Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension .78? (SR785 files). Press [Exp] to display all files in the directory (*.*). Choose a file name with the knob and press [Enter] to make it the Current File Name.
  • Page 371 Spans and Views. Command: SRCL i Inputs/Triggers Include the [Input] and [Trigger] menu settings in the recall. Command: SRCL i DRAM settings Include the memory allocation (Capture, Arbitrary Source, or Waterfall) settings in the recall. Command: SRCL i SR785 Dynamic Signal Analyzer...
  • Page 372 Command: SRCL i Macros Include stored macros in the recall. Command: SRCL i Recall from Disk Recall the selected instrument settings from the Current File in the Current Directory. The recalled settings become effective immediately. Command: SRCL i SR785 Dynamic Signal Analyzer...

  • Page 373: Disk Buffers Menu

    Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension .78? (SR785 files). Press [Exp] to display all files in the directory (*.*). Choose a file name with the knob and press [Enter] to make it the Current File Name.
  • Page 374 For example, the ASCII file for a 400 line FFT might be 0.000, 0.500 1.000, 1.500 2.000, 2.500 399.000, 399.500 where (0.000, 0.500) is the first complex data point and (399.000, 399.500) is the 400th data point. SR785 Dynamic Signal Analyzer...
  • Page 375 Buffers which have no allocation may not be chosen. Only the capture buffers specified by <Capture Channels> may be chosen. Ch1 capture and Ch2 capture are saved and recalled separately. Both can be recalled into a buffer configured for Ch1+Ch2capture channels. SR785 Dynamic Signal Analyzer...
  • Page 376 <Buffer> to choose the other channel and load the other disk file to the buffer. Since the existing Capture Length and Sampling Rate are already compatible, this operation does not zero the first capture buffer. Load the Waterfall Buffer A saved Waterfall file may be loaded into the Waterfall buffer. SR785 Dynamic Signal Analyzer...
  • Page 377 Save binary data from the selected data buffer to the Current File in the Current Directory. Use <Interval> to select the playback portion or entire buffer. Command: AGET ? i Command: CGET ? i Command: WGET ? Command: TGET ? i SR785 Dynamic Signal Analyzer...

  • Page 378: Disk Upkeep Menu

    Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension .78? (SR785 files). Press [Exp] to display all files in the directory (*.*). Choose a file name with the knob and press [Enter] to make it the Upkeep File Name.
  • Page 379 Format the disk. The disk capacity is 720k for DS/DD disks and 1.44M for DS/HD disks. A disk must be formatted before files can be stored on it. Formatting a disk involves erasing all information from the disk and rewriting the directory. Formatting a disk destroys all data presently on disk! SR785 Dynamic Signal Analyzer...

  • Page 380: Output Menu

    Command: PRNT Vector/Plot Plot the screen using the selected Vector Plotter to the selected Destination (Interface or Disk). Other front panel operations are disabled until plotting is completed. Pressing backspace will abort the operation. Command: PLOT SR785 Dynamic Signal Analyzer...
  • Page 381 Indicators prints the status indicators at the top of the screen. All prints the entire screen image including the menu softkeys and status area. Command: PSCR (?) {i} Vector/Plotter Select the Vector/Plotter type for the Vector/Plot operation [HPGL, Postscript]. Vector/Plot only plots the displayed graphs. SR785 Dynamic Signal Analyzer...
  • Page 382 SR785 and the plotter are controlled by a host computer. The host is responsible for issuing the PLOT command to the SR785, and then making the plotter a listener and the SR785 a talker. The plotter commands will then be transferred from the SR785 to the...
  • Page 383 Output Menu 4-187 plotter. The host can periodically untalk the SR785 and serial poll the SR785 (via the Instrument Status) to determine when the plot is finished. Command: PCIC (?) {i} GPIB Address Enter the GPIB Address for a GPIB plotter or printer [0..30].
  • Page 384 Files are written to the Current Directory specified in the [Disk] menu. Files are named SCRNXXXX.EXT where XXXX is a 4 digit number which automatically increments starting at the File Start Number. Command: PFIL (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 385 Command: PDIM (?) {i} Print Black Select the print density for black text [Black, White (none on white paper)]. Use White only if the Print Bright and Print Dim are both black or gray. Command: PBLK (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 386 Assign a plotter pen number to the graph data trace [1 to 8]. Command: PLTR (?) {i} Plotter Marker Pen Assign a plotter pen number to the graph marker [1 to 8]. Turn the marker off to avoid plotting it. Command: PLMK (?) {i} SR785 Dynamic Signal Analyzer...

  • Page 387: System Menu

    Display the [System] <Remote> interface menu. Remote interface parameters should not be altered while the computer interface is active. Press <Return> or [System] for the [System] menu. Preferences Display the [System] <Preferences> menu. Press <Return> or [System] for the [System] menu. SR785 Dynamic Signal Analyzer...
  • Page 388 <Cancel> will discard any changes made in this menu and exit this menu. <Enter Macro> will enter the new macro and exit this menu. Pressing [Enter] while the cursor is in the macro string display also enters the macro and exits this menu. SR785 Dynamic Signal Analyzer...
  • Page 389 Show the power on screen. This screen shows the version number as well as the results of the power on tests. The size of the installed data memory is also displayed (2 Ms, 4 Ms or 8Ms). SR785 Dynamic Signal Analyzer...

  • Page 390: System Remote Menu

    To return from REMOTE to LOCAL (front panel enabled), press [Help/Local]. Command: OVRM (?) {i} Baud Rate Select the RS232 (Serial) interface Baud Rate [300, 1200, 2400, 4800, 9600, 19.2k]. Most PC’s use 9600 as a default. SR785 Dynamic Signal Analyzer...
  • Page 391 The upper half of the screen is the Receive Queue. These are the most recent characters which have been received by the SR785. Commands which have already been executed are shown in normal text. Commands which have not yet been executed are shown with a bright background.

  • Page 392: System Preferences Menu

    Done Volume If Done Volume is set to Noisy, an audible alarm is sounded when a measurement is done or completed. For example, when linear averaging is complete, an alarm is sounded. Command: ADON (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 393 For example, for a 400 line FFT on 100.0 kHz base with a span of 97.66 Hz, the first frequency bin is shown as 244.140625 mHz (Exact Bin) or 244.1 mHz (Rounded). The second bin is 488.28125 mHz (Exact Bin) and 488.3 mHz (Rounded). Command: FFMT (?) {i} SR785 Dynamic Signal Analyzer...
  • Page 394 (transfer function) be associated with information regarding the nodal degrees of freedom (DOF). When Node Info Prompt is set on, the SR785 allows enty of DOF parameters when saving data using Trace to Disk or Display to Disk. When the <Trace to Disk>...

  • Page 395: System Date/Time Menu

    Set the System Date [mm:dd:yy]. The System Date is entered as month:day:year and all entries are 6 digits. [Enter] sets the new date or press this softkey again to abort the entry. Command: DATE (?) {i} SR785 Dynamic Signal Analyzer...

  • Page 396: System Diagnostics Menu

    [Snail, Human Baby, Adult, Lunatic]. Turning the knob will move the marker around the circle, verifying knob action and direction. Press <Return> for the <Diagnostics> menu. RS232/Printer Test Display the RS232/Printer Test screen. SR785 Dynamic Signal Analyzer...
  • Page 397 The entire test takes about 2 minutes. Press <Begin> to start the test. When the test reaches the Disk Changed Sensor Out phase, remove the disk and then insert it again. SR785 Dynamic Signal Analyzer...
  • Page 398 Do not use this function unless you are making input offset or CMR adjustments to an analog input board. See the Service Manual for more information. The unit must be turned off and back on after using this function to restore the input calibrations! SR785 Dynamic Signal Analyzer...

  • Page 399: Edit Macro Menu

    [<-] (Backspace) deletes the term before the cursor. Insert/Replace Toggle between insert and replace mode while editing a macro string. If editing in insert mode, ‘Ins’ appears in the upper right corner of the edit window. If editing in replace mode, ‘Rep’ appears. SR785 Dynamic Signal Analyzer...
  • Page 400 Clear the entire macro string. Cancel Discard any changes made in this menu and exit this menu. Enter Macro Enter the displayed string as the new macro and exit this menu. Use [Play Macro] to playback the macro string. SR785 Dynamic Signal Analyzer...

  • Page 401: Remote Programming

    5-47 Example Program 5-129 Marker Commands (Harmonic) 5-49 Marker Commands (Sideband) 5-50 Marker Commands (Band) 5-51 Marker Commands (Frequency/ Damping) 5-52 Source Commands 5-53 Sine Source Commands 5-54 Chirp Source Commands 5-55 Noise Source Commands 5-56 SR785 Dynamic Signal Analyzer...

  • Page 402: Index Of Commands

    O1BN (?) d {, i} 5-35 Track 1 BNC O2TK (?) d {, f} 5-35 Track 2 Order O2BN (?) d {, i} 5-35 Track 2 BNC Frequency (Time/Histogram Measurement Group) FSPN (?) d {, i} 5-28 Sampling Time SR785 Dynamic Signal Analyzer...
  • Page 403 Query the Marker Y Position MRKZ ? d 5-46 Marker Z Read MKMX d 5-46 Move the Marker to the Maximum MKMN d 5-46 Move the Marker to the Minimum MKCN d 5-46 Center of FFT Span to Marker SR785 Dynamic Signal Analyzer...
  • Page 404 Sine Offset Chirp Source CAMP (?) {x} 5-55 Chirp Amplitude CBUR (?) {x} 5-55 Chirp Burst Percentage CSRC (?) {i} 5-55 Source Display Noise Source NAMP (?) {x} 5-56 Noise Amplitude NTYP (?) {i} 5-56 Noise Type SR785 Dynamic Signal Analyzer...
  • Page 405 5-62 Ch1 Engineering Units Off/On EU1L (?) d {,i} 5-62 Ch1 EU Label EU1V (?) d {,x} 5-62 Ch1 EU/Volt EU1U (?) d {,s} 5-62 Ch1 User Label TD1C (?) d {,i} 5-62 Ch1 Transducer Convert SR785 Dynamic Signal Analyzer...
  • Page 406 5-69 FFT Overload Reject TAVM (?) { i} 5-69 Trigger Average Mode PAVO (?) d {, i} 5-69 Average Preview PAVT (?) d {, x} 5-69 Preview Time PAVA 5-69 Accept Preview PAVR 5-69 Reject Preview SR785 Dynamic Signal Analyzer...
  • Page 407 Waterfall Record to Trace WSLC d, i, j 5-82 Waterfall Slice to Trace WGET ? 5-114 Upload Waterfall Buffer WPUT ? 5-115 Download Waterfall Buffer Capture CCHN (?) {i} 5-83 Capture Channels CMOD (?) {i} 5-83 Capture Mode SR785 Dynamic Signal Analyzer...
  • Page 408 Exceed Stop Index EPCT (?) {i} 5-90 Exceed Centile EXCE d, i 5-90 Calculate Exceedance Curve Fit EFIT d 5-91 Start Fit ESYN i,d 5-91 Synthesis ENPL (?) {,i} 5-91 Number Poles ENZE (?) {,i} 5-91 Number Zeros SR785 Dynamic Signal Analyzer...
  • Page 409 5-98 Plotter Text Pen PLGD (?) {i} 5-98 Plotter Grid Pen PLTR (?) {i} 5-98 Plotter Trace Pen PLMK (?) {i} 5-98 Plotter Marker Pen NOTE i, j {, k, l, m, s} 5-99 Display Note SR785 Dynamic Signal Analyzer...
  • Page 410 Disk to Trace i TLOD ? i, n 5-109 Download Trace i Binary TASC ? i, n 5-109 Download Trace i Ascii TGET ? i 5-111 Upload Trace i Buffer TPUT ? i 5-112 Download Trace i Buffer SR785 Dynamic Signal Analyzer...
  • Page 411 SVNI(?) {i} 5-118 Save Nodal Information RFNA(?){s} 5-118 Reference Node Name RFNU(?){i} 5-118 Reference Node Number RFDR(?){i} 5-118 Reference Node Direction RSNA(?){s} 5-119 Response Node Name RSNU(?){i} 5-119 Response Node Number RSDR(?){i} 5-118 Response Node Direction SR785 Dynamic Signal Analyzer...

  • Page 412: Alphabetical List Of Commands

    Continue CPAN (?) {i} 5-83 Capture Auto Pan CPUT ? i, j 5-32 Download Capture Buffer CRAT (?) {i} 5-83 Capture Rate CSRC (?) {i} 5-55 Source Display CSTP 5-83 Capture Stop CSTR 5-83 Capture Start SR785 Dynamic Signal Analyzer...
  • Page 413 EU2M (?) {i} 5-62 Ch2 Engineering Units Off/On EU2U (?) {s} 5-63 Ch2 User Label EU2V (?) {x} 5-63 Ch2 EU/Volt EWTT (?) {,i} 5-91 Weighting Trace EWTU (?) {,i} 5-91 Weighting EXCE d, i 5-90 Calculate Exceedance SR785 Dynamic Signal Analyzer...
  • Page 414 Ch1 AutoRange Mode I1AW (?) {i} 5-61 Ch1 A-Weight Filter I1CP (?) {i} 5-60 Ch1 Input Coupling I1GD (?) {i} 5-60 Ch1 Input Grounding I1MD (?) {i} 5-60 Ch1 Input Mode I1RG (?) {x} 5-60 Ch1 Input Range SR785 Dynamic Signal Analyzer...
  • Page 415 Total Memory Available MREL (?) d {, i} 5-47 Normal Marker Relative Mode MRKB ? d 5-45 Query the Marker Bin MRKR (?) d {, i} 5-45 Marker Tracking MRKX ? d 5-45 Query the Marker X Position SR785 Dynamic Signal Analyzer...
  • Page 416 OTIM (?) d {, x} 5-71 Octave Average Time OTRK (?) d {, i} 5-34 Order Tracking OTYP (?) d {, i} 5-71 Octave Average Type OUTX (?) {i} 5-100 Output Remote Interface OVRM (?) {i} 5-100 Overide Remote SR785 Dynamic Signal Analyzer...
  • Page 417 SBRI (?) {i} 5-100 Screen Brightness SCON (?) {i} 5-104 Screen Contrast SDBN (?) d {, i} 5-50 Number of Sidebands SDLY (?) {i} 5-100 Screen Saver Delay SFST (?) d {, x} 5-33 Swept Sine Faster Threshold SR785 Dynamic Signal Analyzer...
  • Page 418 Time TLOD ? i, n 5-109 Download Trace i Binary TLOD ? i, n 5-109 Download Trace i Binary TLVL (?) {x} 5-66 Trigger Level TMAN 5-66 Manual Trigger TMOD (?) {i} 5-66 Trigger Arming Mode SR785 Dynamic Signal Analyzer...
  • Page 419 Window Form WTHR (?) d {, i} 5-81 Waterfall Threshold WTOT (?) d {, i} 5-80 Waterfall Total Count WTRC d, i, j 5-81 Waterfall Record to Trace WVCT (?) d {, i} 5-81 Waterfall View Count SR785 Dynamic Signal Analyzer...
  • Page 420 YDIV (?) d {, x} 5-41 Y/Division YMAX (?) d {, x} 5-40 Y Maximum YMDX d x,y 5-41 Ymax + Y/Division YMID (?) d {, x} 5-40 Y Midpoint YMIN (?) d {, x} 5-41 Y Minimum SR785 Dynamic Signal Analyzer...

  • Page 421: Introduction

    [System] <Remote> menu. Communicating With RS232 The SR785 is configured as a DCE ( transmit on pin 3, receive on pin 2) device and supports CTS/DTR hardware handshaking. The CTS signal (pin 5) is an output indicating that the SR785 is ready, while the DTR signal (pin 20) is an input that is used to control the SR785's data transmission.
  • Page 422 Start the measurement (same as [Start/Reset] key) Command Synchronization IFC (Interface Ready, bit 7) in the Serial Poll status signals that the SR785 is ready to receive and execute a command. When a command is received, this bit is cleared, indicating that command execution is in progress.
  • Page 423 IFC bit set (since *STB is itself a command). Since the SR785 processes one command at a time, status queries will not be processed until the previous operation is finished. Thus a response to a status query in itself signals that the previous command is finished.
  • Page 424 These set commands are not allowed unless the measurement group is Swept Sine (just like the menu interface). Example Program An example program is included at the end of this chapter. This program is a good reference for writing your own programs to control the SR785. SR785 Dynamic Signal Analyzer...

  • Page 425: Command Syntax

    The rest of the sequence consists of parameters. Parameters shown in { } are not always required. Generally, parameters in { } are required to set a value in the SR785. Multiple parameters are separated by commas. Multiple commands may be sent on one command line by separating them with semicolons (;).
  • Page 426 Hz> Help The detailed command list is available on screen by pressing [Help/Local] to enter the help system. Press [4] to show the command list. Commands are also cross referenced in the help about each key. SR785 Dynamic Signal Analyzer...
  • Page 427 Be careful to send commands in the correct order to avoid context errors. A good practice is to send the commands in the same order as programming the instrument using the softkeys. SR785 Dynamic Signal Analyzer...

  • Page 428: Frequency Commands

    The FCTR command sets (queries) the FFT Center frequency of display d. The parameter f is a frequency (real number of the specified units). Values of f which would cause the span to exceed the 0 to 102.4 (100.0) kHz range cause an error. SR785 Dynamic Signal Analyzer...
  • Page 429 UNST command and wait for settling to finish. This command is valid only when the Measurement Group is FFT or Octave. SR785 Dynamic Signal Analyzer...
  • Page 430 The measurement is unsettled by changing any one of several measurement parameters. For example, changing the input range or FFT span will unsettle the measurement. If the signal comes from an external source and is changed in such SR785 Dynamic Signal Analyzer...
  • Page 431 UNST command and wait for settling to finish. This command is valid only when the Measurement Group is FFT, Correlation or Octave. SR785 Dynamic Signal Analyzer...
  • Page 432 Live. SARS (?) d {, i} The SARS command sets (queries) the swept sine Auto Resolution Mode of display d. The parameter i selects Off (0) or On (1). The set command requires d=2 (both displays). SR785 Dynamic Signal Analyzer...
  • Page 433 The parameter x is a level from 0.05 to 6.0 (dB). The set command requires d=2 (both displays). This command is valid only when the Measurement Group is Swept Sine. The set command requires a display to be Live. SR785 Dynamic Signal Analyzer...
  • Page 434 The parameter i is the number of points. The set command requires d=2 (both displays). This command is valid only when the Measurement Group is Order. The set command requires a display to be Live. SR785 Dynamic Signal Analyzer...
  • Page 435 The parameter i sets the input channel to Channel One (0) or Channel 2 (1). The set command requires d=2 (both displays). This command is valid only when the Measurement Group is Order. The set command requires a display to be Live. SR785 Dynamic Signal Analyzer...
  • Page 436 The HRPT command sets (queries) the histogram repeat mode for display d. The parameter i sets the repeat mode to Off (0) or On (1). This command is valid only when the Measurement Group is Time/Histogram. The set command requires the display d = 2 (both displays).. SR785 Dynamic Signal Analyzer...

  • Page 437: Display Setup Commands

    Windowed Time 1 Windowed Time 2 Orbit Coherence Cross Spectrum Frequency Response Capture Buffer 1 Capture Buffer 2 FFT User Function 1 FFT User Function 2 FFT User Function 3 FFT User Function 4 FFT User Function 5 SR785 Dynamic Signal Analyzer...
  • Page 438 Swept Sine User Function 2 Swept Sine User Function 3 Swept Sine User Function 4 Swept Sine User Function 5 Order Group Measurement Linear Spectrum 1 Linear Spectrum 2 Power Spectrum 1 Power Spectrum 2 Time 1 SR785 Dynamic Signal Analyzer...
  • Page 439 The VIEW command sets (queries) the View of display d. The parameter i selects the view from the list below. Each view has associated units. Changing the View changes the units parameters to the values last used with the new view. SR785 Dynamic Signal Analyzer...
  • Page 440 The YMID command sets (queries) the Y Midpoint (center reference) of display d. The parameter x is a real number in the display units. This command is not valid when the View is Nichols or Nyquist. SR785 Dynamic Signal Analyzer...
  • Page 441 XPAN (?) d {, i} The XPAN command sets (queries) the Pan (translation) of display d. The parameter i is the left most displayed bin. This command is only valid when the display is Zoomed (expanded). SR785 Dynamic Signal Analyzer...
  • Page 442 The XZOM command sets (queries) the Zoom factor (X axis expand) of display d. The parameter i is the zoom factor (1-5). This command is not valid when the X axis is logarithmic or when the View is Nyquist or Nichols. SR785 Dynamic Signal Analyzer...

  • Page 443: Display Options Commands

    Changing the Grid Divisions changes the vertical scaling (Y/div) and horizontal scaling (X/div) (Nyquist and Nichols views). GPOL (?) d {, i} The GPOL command sets (queries) the Nyquist Grid type for display d. The parameter i selects Rectangular Grid (0) or Polar Grid (1). SR785 Dynamic Signal Analyzer...
  • Page 444 The DDXW command sets (queries) the d/dx Window of display d. The parameter x is a percentage of the display width. This affects the calculation of d/dx and group delay for user math functions in display d. SR785 Dynamic Signal Analyzer...

  • Page 445: Marker Commands

    This command is not valid if the Marker of display d is Off. MRKB ? d The MRKB ? command queries the marker bin number of display d. The value returned is the bin number of the marker. Bin 0 is the left most bin in the display. SR785 Dynamic Signal Analyzer...
  • Page 446 (d=2 is not allowed). This command is only valid when the Measurement Group is FFT and display d is Live. This command is not valid if the Marker of display d is Off. SR785 Dynamic Signal Analyzer...
  • Page 447 (d=2 is not allowed). If Marker Rel is Off, MRON d sets the Normal Marker offsets (X and Y) to the current marker position and sets the Marker to Relative to Offset (relative marker readings). SR785 Dynamic Signal Analyzer...
  • Page 448 If Marker Rel is Relative to Offset, MRON d sets the Marker Rel to Off (absolute marker readings). MRON? d returns 0 if Marker Rel is Off and 1 if Marker is Rel to Offset. This command is only valid if the Marker Mode for display d is Normal. SR785 Dynamic Signal Analyzer...
  • Page 449 The HPWR ? command queries the Harmonic Power for display d. The returned value is a real value of Vrms or dBVrms depending on the setting of dB Units>. This command is only valid if the Marker Mode for display d is Harmonic. SR785 Dynamic Signal Analyzer...
  • Page 450 The SPWR ? command queries the Sideband Power for display d. The parameter i selects dB Relative to Fundamental (0) or Vrms or dBVrms (1) and is required. This command is only valid if the Marker Mode for display d is Sideband. SR785 Dynamic Signal Analyzer...
  • Page 451 BRAT ? d, i The BPWR command queries the Band Ratio for display d. The parameter i selects percent (0) or dB (1) band ratio. This command is only valid if the Marker Mode for display d is Band. SR785 Dynamic Signal Analyzer...
  • Page 452 The MMCA command queries the Frequency/Damping marker result. The query returns two values in the form f, g where f is the resonant frequency and g is the damping factor. This command is only valid if the Marker Mode for display d is Frequency/Damping. SR785 Dynamic Signal Analyzer...

  • Page 453: Source Commands

    The STYP command sets (queries) the Source Type. The parameter i selects Sine (0), Chirp (1), Noise (2) or Arbitrary (3). When the Measurement Group is Swept Sine, the Source Type may not be changed and this command is not valid. SR785 Dynamic Signal Analyzer...
  • Page 454 The query returns two numbers of the form y,i where y is a real number and i is an index indicating the units. This command is valid only when the Source Type is Sine. SR785 Dynamic Signal Analyzer...
  • Page 455 The CSRC command sets (queries) the Source Display. The parameter i selects DisplayA (0) or DisplayB (1) This command is valid only when the Source Type is Chirp or Noise and the Measurement Group is FFT or Correlation. SR785 Dynamic Signal Analyzer...
  • Page 456 The CSRC command sets (queries) the Source Display. The parameter i selects DisplayA (0) or DisplayB (1) This command is valid only when the Source Type is Chirp or Noise and the Measurement Group is FFT. SR785 Dynamic Signal Analyzer...
  • Page 457 Arbitrary Length is changed to 2 kPoints and the Arbitrary Source is change to Arb. Buffer. Trace i must contain FFT measurement data (usually a time record). This command is valid only when the Source Type is Arbitrary. SR785 Dynamic Signal Analyzer...
  • Page 458 The SSUL command sets (queries) the Swept Sine Reference Upper Limit. The parameter x is a ratio in dB from 0.1 to 30.0 dB. This command is valid only when the Measurement Group is Swept Sine and Auto Level Reference is Ch1 or Ch2. SR785 Dynamic Signal Analyzer...
  • Page 459 The query returns two numbers of the form y,i where y is a real number and i is an index indicating the units. This command is valid in the swept sine measurement group. SR785 Dynamic Signal Analyzer...

  • Page 460: Input Commands

    The I1AR command sets (queries) the Ch1 AutoRange Mode. The parameter i selects Up Only (0) or Tracking (1). I1AF (?) {i} The I1AF command sets (queries) the Ch1 Anti-Aliasing Filter Off/On. The parameter i selects Off (0) or On (1). SR785 Dynamic Signal Analyzer...
  • Page 461 The I2AW command sets (queries) the Ch2 A-Weighting Filter Off/On. The parameter i selects Off (0) or On (1). IAOM (?) {i} The IAOM command sets (queries) the Input Auto Offset Off/On. The parameter i selects Off (0) or On (1). SR785 Dynamic Signal Analyzer...
  • Page 462 TD1C (?) d {,i} The TD2C command sets (queries) the Ch1 Transducer Conversion. for display d. The set command requires d = 2 (both displays). The parameter i selects the units to be converted to: Label in/s in/s SR785 Dynamic Signal Analyzer...
  • Page 463 TD2C (?) d {,i} The TD2C command sets (queries) the Ch2 Transducer Conversion. for display d. The set command requires d = 2 (both displays). The parameter i selects the units to be converted to: Label in/s in/s SR785 Dynamic Signal Analyzer...
  • Page 464 The TAHD command sets (queries) the Tachometer Holdoff Time. The parameter x is the holdoff time in seconds. TASH (?) {i} The TASH command sets (queries) the Show Tach status. The parameter i selects Off (0) or On (1). SR785 Dynamic Signal Analyzer...
  • Page 465 This command is valid only when the Input Source is Playback. ISPD (?) {i} The ISPD command sets (queries) the Capture Playback Speed. The parameter i selects Normal (0) or Every Frame (1). This command is valid only when the Input Source is Playback. SR785 Dynamic Signal Analyzer...

  • Page 466: Trigger Commands

    STMD (?) {i} The STMD command sets (queries) the Triggered Source Mode. The parameter i selects 1-Shot (0) or Continuous (1). TMAN The TMAN command Manually Triggers if armed. This command may not be queried. SR785 Dynamic Signal Analyzer...
  • Page 467 The TRDM command sets (queries) the RPM Arming Delta RPM sense. The parameter i selects Absolute Change (0), Increasing RPM (1), or Decreasing RPM (2).. TIAS (?) {x} The TIAS command sets (queries) the Time Arming Step. The parameter x is the time increment in seconds.. SR785 Dynamic Signal Analyzer...

  • Page 468: Average Commands

    The FOVL command sets (queries) the FFT Time Record Increment for display d. The parameter x is a percentage up to 300. This command is valid only when the Measurement Group is FFT. The set command requires display d to be Live. SR785 Dynamic Signal Analyzer...
  • Page 469 Poll the NEWA and NEWB (New Data) status bits in the Display Status word to determine when each time record has been acquired. After accepting or rejecting the time record, the display reverts back to showing the actual measurement. SR785 Dynamic Signal Analyzer...
  • Page 470 This change does not set NEWA or NEWB but occurs upon receipt of the accept or reject command (or after a Preview Time). This command is valid only when the Measurement Group is FFT. This command has no effect unless the previewed time records are displayed. SR785 Dynamic Signal Analyzer...
  • Page 471 Total (0), Impulse (1), L (2) or Peak (3). Peak power is not allowed if the Averaging Type is not Peak Hold. Peak power is automatically selected if the Averaging Type is Peak Hold. Use the OTYP command to set Peak Hold averaging. SR785 Dynamic Signal Analyzer...
  • Page 472 The parameter i selects Triggered (0) or Continuous (1). The set command requires d=2 (both displays have the same mode). This command is valid only when the Measurement Group is Octave. The set command requires a display to be Live. SR785 Dynamic Signal Analyzer...
  • Page 473 The parameter i is a number of cycles from 1 to 32767 seconds. The set command requires d=2 (both displays). This command is valid only when the Measurement Group is Swept Sine. The set command requires a display to be Live. SR785 Dynamic Signal Analyzer...

  • Page 474: User Math Commands

    F,C,Or FFTu( -108 F,C,Or IFFT( -109 F,C,Or Sqrt( -110 F,C,O,S,Or jOmega( -113 F,C,S Phase( -114 F,C,O,S,Or,H -115 F,C,O,S,Or,H AWt( -116 F,C,O,S,Or BWt( -117 F,C,O,S,Or CWt( -118 F,C,O,S,Or d/dx( -119 F,C,O,S,Or GrpDly( -120 F,C,O,S [X/(1-X)]( -121 F,C,O,S,Or SR785 Dynamic Signal Analyzer...
  • Page 475 User Math Commands 5-75 F,C,O,S,Or,H F,C,O,S,Or,H F,C,O,S,Or,H F,C,O,S,Or,H F,C,O,S,Or,H F,C,O,S,Or,H FFT Group Operands Time(1) Time(2) FFT(1) FFT(2) <Pwr(1)> <Pwr(2)> <Coherence> <CrossSpec> <Freq.Resp.> Vec<F1> Vec<F2> RMS<F1> RMS<F2> PeakHold<F1> PeakHold<F2> RMS<CrossSpec> Correlation Group Operands Time(1) Time(2) Auto_Corr(1) Auto_Corr(2) X_Corr SR785 Dynamic Signal Analyzer...
  • Page 476 Norm Var(2) Cross Spectrum() Freq. Resp.() Order Operands Time(1) Time(2) <Spec(1)> <Spec(2)> <Pwr(1)> <Pwr(2)> Vec<Time(1)> Vec<Time(2)> Time/Histogram Operands Histo(1) Histo(2) PDF(1) PDF(2) CDF(1) CDF(2) Time(1) Time(2) Operands for All Groups Trace1 Trace2 Trace3 Trace4 Trace5 Const1 SR785 Dynamic Signal Analyzer...
  • Page 477 The USRC command sets (queries) the real and imaginary parts of User Constant i. The parameter i selects a User Constant from 1 to 5. The parameters x and y are floating point values for the real and imaginary parts. SR785 Dynamic Signal Analyzer...

  • Page 478: Window Commands

    FWFL (?) d {, x} <[s], ms, µ µ µ µ s> The FWFL command sets (queries) the FFT Force Window Length for display d. The parameter x is the duration of the force window in the specified units. SR785 Dynamic Signal Analyzer...
  • Page 479 The WSYM sets (queries) User Window Form for display d. The parameter i selects Non-Symmetric (0) or Symmetric (1). This command is valid only when the Measurement Group is FFT or Order and the window of display d is User. SR785 Dynamic Signal Analyzer...

  • Page 480: Waterfall Commands

    Order or Time/Histogram. WOSK (?) d {, x} <ks, [s], ms> The WOSK command sets (queries) the Waterfall Skip count for Octave measurements for display d. The parameter x is a time from .008 to 1000 s. SR785 Dynamic Signal Analyzer...
  • Page 481 This command is not valid when the Measurement Group is Swept Sine. WTRC d, i, j The WTRC command saves waterfall record j [0 is most recent, 1 is next, etc.] from display d to Trace i [1..5]. SR785 Dynamic Signal Analyzer...
  • Page 482 The WSLC command saves the waterfall time slice of bin j [0 is left most on x axis] from display d to Trace i [1..5]. This command is valid only when the measurement is paused with waterfall storage on. If there is no bin j, then an error occurs. SR785 Dynamic Signal Analyzer...

  • Page 483: Capture Commands

    Same as [Start Capture] key. Capture memory must already be allocated. The Input Source cannot be Playback and the Source cannot be Arbitrary playback from Capture. CSTP Same as [Stop Capture] key. This command has no effect if Capture is not in progress. SR785 Dynamic Signal Analyzer...

  • Page 484: Memory Allocation Commands

    The MALC command sets the Memory Allocation to i blocks for Capture, j blocks for Waterfall/Order Track and k blocks for Arbitrary Waveform. The sum of i+j+k cannot exceed the Total Available Memory. The MALC command automatically confirms the allocation. SR785 Dynamic Signal Analyzer...

  • Page 485: Data Table Commands

    This command is valid only if the Data Table for display d is On and display d is the active display. Use the ACTD command to select the active display. Only the Data Table of the active display may be edited or queried. SR785 Dynamic Signal Analyzer...
  • Page 486 This command is valid only if the Data Table for display d is On and display d is the active display. Use the ACTD command to select the active display. Only the Data Table of the active display may be edited or queried. SR785 Dynamic Signal Analyzer...

  • Page 487: Limit Test Commands

    The LSEG command sets (queries) the Endpoints and Type of limit segment i for display d. The parameter i selects the limit segment number from 0 to the last segment. If i exceeds the last segment number (as set by LMAX), an error is reported. SR785 Dynamic Signal Analyzer...
  • Page 488 The LSFT command shifts all Limit Segments for display d. The parameter x is real number. The Y coordinates of all segments are shifted by x (in display units). This command is not valid for d=2 (both displays). This command also sets Limit Segments to Show. SR785 Dynamic Signal Analyzer...

  • Page 489: Marker Statistics Commands

    The MSIB ? command queries Min for the Display B Marker. MSEB ? The MSEB ? command queries Mean for the Display B Marker. MSSB ? The MSSB ? command queries Standard Deviation for the Display B Marker. SR785 Dynamic Signal Analyzer...

  • Page 490: Exceedance Statistics Commands

    The result is stored in a data trace and has the same measurement type as the waterfall measurements. This command is not valid when the measurement group is swept-sine. SR785 Dynamic Signal Analyzer...
  • Page 491 EFSC (?) i {,x} The EFSC command sets (queries) the frequency scaling for one of the curve tables. The parameter i selects curve table 1 (0) or curve table 2 (1) The parameter x is the frequency scaling value. SR785 Dynamic Signal Analyzer...
  • Page 492 The ERES command sets (queries) the residues for one of the curve tables. The parameter i selects curve table 1 (0) or curve table 2 (1). The parameter j selects which residue will be set (queried.) from 0 up to the number of items in the list. SR785 Dynamic Signal Analyzer...
  • Page 493 (if any) of the residue This command will change the specified table format to pole/residue. ECLR i The ECLR command clears one of the curve tables. The parameter i selects curve table 1 (0) or curve table 2 (1) SR785 Dynamic Signal Analyzer...

  • Page 494: Disk Commands

    MYDATA.DAT. DOS file name conventions must be followed, i.e. file names are 8 characters or less with an optional extension of up to 3 characters. If the extension is omitted, the SR785 uses default extensions. File access is to the current directory.
  • Page 495 IS recalled. To determine the value of i, start with i=0. For each bit which is 1, add 2 raised to the bit number. For example, SRCL 127 recalls all groups. SRCL 17 recalls only the Measurements (2 =1) and DRAM Settings (2 =16). SR785 Dynamic Signal Analyzer...
  • Page 496 The DELD command deletes the current directory. The directory must be empty otherwise no action is taken. If the directory is deleted, the current directory is changed to the directory one level closer to the root. The current directory is specified by FDIR. SR785 Dynamic Signal Analyzer...

  • Page 497: Output Commands

    The PSCR command sets (queries) what portion of the screen to print. The parameter i selects Graphs Only (0), Menu Only (1), Status Indicators Only (2) or All (3). This only affects printing. Plotting only plots the display graphs. SR785 Dynamic Signal Analyzer...
  • Page 498 0 to 30 and should agree with the address of the plotter in use. PCIC (?) {i} The PCIC command sets (queries) the GPIB Control mode. The parameter i selects Host (0) or SR785 (1). PLTX (?) {i} The PLTX command sets (queries) the Plotter Text Pen Number. The parameter i is a pen number from 1 to 8.
  • Page 499 The parameter k puts the note in Display A (0) or Display B (1). The parameters l and m are the Text X and Text Y position from 0 to 100. The string s is the note text. The parameters k, l, m and s must always be sent together. SR785 Dynamic Signal Analyzer...

  • Page 500: System Commands

    1 to 59. FFMT (?) {i} The FFMT command sets (queries) the Frequency Format. The parameter i selects Exact Bin (0) or Rounded (1). TIME (?) {i, j, k} The TIME command sets (queries) the System Time. SR785 Dynamic Signal Analyzer...
  • Page 501 The DATE ? command queries the date. A string of the form “MM/DD/YY” is returned. The DATE i, j, k command sets the date to i [1..12] month, j [1..31] day and k [0..99] year. The parameters i, j and k must all be sent. SR785 Dynamic Signal Analyzer...

  • Page 502: Front Panel Commands

    UNST command and wait for settling to finish. This command is valid only when the Measurement Group is FFT or Octave. SVTR d, i The SVTR command saves display d to Trace i. SR785 Dynamic Signal Analyzer...
  • Page 503 Marker Relative to Offset (if Marker Rel was Off). This is similar to the [Marker Ref] key. This command is only valid if the Marker Mode for display d is Normal. SR785 Dynamic Signal Analyzer...
  • Page 504 The SBRI command sets (queries) the Screen Brightness. The parameter i is a brightness level from 150 (dimmest) to 255 (brightest). SCON (?) {i} The SCON command sets (queries) the Screen Contrast. The parameter i is a contrast level from 0 (no contrast) to 90 (most contrast). SR785 Dynamic Signal Analyzer...
  • Page 505 [System] [AutoScale A] [AutoScale B] [Span Up] [Span Down] [AutoRange Ch1] [AutoRange Ch2] [Marker Max] [Marker Min] [Marker Ref] [Display Ref] [Marker Center] [Show Setup] [Start/Reset] [Pause/Cont] [Start Capture] [Stop Capture] [Active Display] [Link] [Print Screen] SR785 Dynamic Signal Analyzer...
  • Page 506 Sequential TONE commands need to be separated by a pause which is at least as long as the preceding tone. PLAY i The PLAY command plays one of the SR785’s pre-programmed sounds. The parameter i selects a sound from 0 to 6 (most recent TONE). For example, PLAY 2 sounds an alert.

  • Page 507: Data Transfer Commands

    Send the command and then make the host computer a listener and the SR785 a talker. Data is returned continuously starting with bin 0 and ending with bin #(length-1). The data points are ASCII real numbers, separated by commas, and the last data point is followed by a terminator.
  • Page 508 IFC will NOT be set until the transfer is complete. Send the command and then make the host computer a listener and the SR785 a talker. The DSPB? d returns 4 bytes per bin starting with bin 0 and continuing to bin #(length-1).
  • Page 509 OK to begin data transfer. A return of 0 indicates that n is too large for Trace i. Host On receipt of 1 (4-byte binary long int), executes a binary transfer to the SR785 of 2n 4-byte IEEE floats. The order is real part of point 0, imag part of point 0, real part of point 1, imag part of point 1, etc.
  • Page 510 OK to begin data transfer. A return of 0 indicates that n is too large for Trace i. Host On receipt of 1 (4-byte binary long int), executes a transfer to the SR785 of 2n ASCII floats. The order is real part of point 0, imag part of point 0, real part of point 1, imag part of point 1, etc.
  • Page 511 Host On receipt of 1 (4-byte binary long int), executes a binary transfer to the SR785 of n 4-byte IEEE floats. The order is point 0, point 1, etc. Each 4-byte float is transmitted least significant byte first. A total of 4n bytes are transferred. Assert EOI with the final byte of the transfer.
  • Page 512 Returns 1 (4-byte binary long int) when OK to begin binary transfer to the SR785. Host On receipt of 1 (4-byte binary long int), executes a binary transfer to the SR785 of n bytes (as uploaded using TGET). Asserts EOI with the final byte of the transfer.
  • Page 513 Data Transfer Commands 5-113 Host On receipt of n (4-byte binary long int), executes a binary read from the SR785 of n bytes. Expect EOI with the final byte of the transfer. Serial Poll until IFC (bit 7) is set in the Serial Poll status before sending another command.
  • Page 514 Capture buffer. Host On receipt of n (4-byte binary long int), executes a binary read from the SR785 of n bytes. Expect EOI with the final byte of the transfer. Serial Poll until IFC (bit 7) is set in the Serial Poll status before sending another command.
  • Page 515 The uploaded data should be saved in its entirety by the host computer. The saved data can be downloaded back to the SR785 at a later time using WPUT. The WGET and WPUT commands allow a host computer to save and reload the Waterfall buffer without using disks.
  • Page 516 Loading the Waterfall buffer loads data into the waterfall buffer and recalls the measurement parameters which were in effect when the waterfall buffer was saved. The recalled parameters include items in the [Frequency], [Display Setup], [Display Options], [Average], [Window], [User Math], and [Waterfall] menus. SR785 Dynamic Signal Analyzer...

  • Page 517: Interface Commands

    In the REMOTE state command execution is allowed but the keyboard and knob are locked out except for the [Help/Local] key which returns the SR785 to the LOCAL state. In the LOCAL LOCKOUT state all front panel operation is locked out, including the [Help/Local] key.

  • Page 518: Nodal Degree-Of-Freedom Commands

    SVNI (?) {i} The SVNI command determines (queries) whether nodal degree-of-freedom information will be stored with SR785 data (.78D) files. If this softkey is set to "on" nodal DOF information will be saved with the files and will be available for use by external programs which convert SR785 files into formats used by modal analysis programs.
  • Page 519 RSNA (?) {s} The RSNA command sets (queries) the name of the reference node. The name may be up to 6 characters long. RSNU (?) {i} The RSNU command sets (queries) the number of the reference node. SR785 Dynamic Signal Analyzer...

  • Page 520: Status Reporting Commands

    Serial Poll status, the condition which causes it to be set must be cleared. For the INST, DISP, INPT, IERR or ESB bits, this is accomplished by clearing the enabled status bits in the Instrument, Display, Input, Error or Standard Event status words (by reading them). SR785 Dynamic Signal Analyzer...
  • Page 521 Instrument status enable register, bit 0 (INST) of the Serial Poll status word is set. This causes an SRQ if bit 0 in the Serial Poll enable register is set. To clear a bit in the Instrument status word, use INST?. SR785 Dynamic Signal Analyzer...
  • Page 522 INPS? clears the entire word while INPS? i clears just bit i. INPC ? i The INPC? command queries the current overload condition of input i. The parameter i selects Ch1 (0) or Ch2 (1). INPC? returns a value from 0 to 3. SR785 Dynamic Signal Analyzer...
  • Page 523 HighV INPC? always returns the current condition. If an overload occurs and goes away, INPC? will not detect it. Use the status words to detect momentary changes in the overload state. SR785 Dynamic Signal Analyzer...

  • Page 524: Status Word Definitions

    A bit stays set as long as the status condition exists. When reading the status using a serial poll, the SRQ bit signals that the SR785 is requesting service. The SRQ bit will be set (1) the first time the SR785 is polled...
  • Page 525 SRQ, performs a serial poll to clear the SRQ, does something in response to the trigger (read data for example) and then clears the TRIGGER status bit by reading the Instrument status register. A subsequent trigger will then generate another SRQ. SR785 Dynamic Signal Analyzer...
  • Page 526 The Instrument status word reports on the overall measurement status of the instrument. These status bits remain set until read by INST?. They are also cleared by the *CLS command. Use INSE to set bits in the Instrument status enable register. SR785 Dynamic Signal Analyzer...
  • Page 527 NOT test the Display status word for both AVGA and AVGB simultaneously. The AVGA and AVGB bits may not be set at the same time. Test for AVGA and AVGB separately and wait until both have occurred. SR785 Dynamic Signal Analyzer...
  • Page 528 The Error status bits stay set until read by ERRS?. They are also cleared by the *CLS command. Use ERRE to set bits in the Error status enable register. Bits 7-12 are set by the power on tests. Bits 3-5 are set in the [System]<Diagnostics>. SR785 Dynamic Signal Analyzer...

  • Page 529: Example Program

    Terminate Read on EOS: Once all the hardware and GPIB drivers are configured, use “IBIC”. Use “IBWRT” and IBRD” to send to and receive from the SR785. If you cannot talk to the SR785 via “IBIC”, then your programs will not run.
  • Page 530 (void); /* ***************************************************** */ void main (void) // **************************************************** // You can see the commands received and responses generated by the SR785 // by using [System]<Remote><View Qs> to display the interface buffers // on the screen. // **************************************************** int i, mode, type, number, nlen;...
  • Page 531 // ****** set the Standard Event enable register to catch EXE and CME // Command errors will set the ESB bit in the Serial Poll status word TxSR785 ("*ESE 48"); //set bits 4 and 5 // ****** Check communication by querying SR785 IDN string GetSR785 ("*IDN?"); printf ("[GPIB IDN] = %s\n\n", recv);...
  • Page 532 ("Loading Arb buffer..."); TxGpib (SR785,"ALOD? 2048"); //use TxGpib so we don't wait for IFC //SR785 will return a binary 1 to acknowledge transmit("mla talk 10",&status); //make SR785 a talker, pc a listener rarray (&ack, 4, &length, &status); //binary read 4 bytes (long int) //return value should be 1 printf ("%d bytes recvd [val=%ld]...",length,ack);...
  • Page 533 // First 33 bins are the spectrum, last bin is the Total Power bin. // All points are complex. // For an octave measurement, the imaginary parts are all zero. transmit("mta listen 10",&status); //make SR785 a listener, pc a talker for (i=0; i<33; i++) { //download 33 octave bins sprintf (cmd,"DATA '%lf, '", octreal);...
  • Page 534 /* ********************************************************************* */ void TxSR785 (char *command) // Send command to the SR785 and wait until IFC (bit7) is set in // the Serial Poll status (indicating that the command is finished). TxGpib (SR785,command); // send command to SR785 address WaitIFC ();...
  • Page 535 // clear the keyboard buffer printf ("\n<Space> to continue, <Q> to quit "); do { ch = (char) getch (); if ((ch == 'q')||(ch =='Q')) exit(0); // exit while (ch!=' '); // continue printf ("\n"); /* ******************************************************************* */ SR785 Dynamic Signal Analyzer...
  • Page 536 5-136 Example Program SR785 Dynamic Signal Analyzer...
  • Page 537 Converting Files to SDF Converting Files to .78D Format Converting Files to MATLAB Format Converting Files to Universal File Format Converting Files to Capture File Format (.78C) 6-10 Converting Files to Arbitrary Waveform Format (.78C) 6-10 SR785 Dynamic Signal Analyzer...

  • Page 538: Why File Conversion

    SR785 for display and comparison. In order to meet both these needs the SR785 is shipped with a file conversion program designed to import and export data as flexibly as possible Stanford Research Systems is committed to supporting as many file formats as possible- as a result we are constantly adding new formats.

  • Page 539: Sr785 File Types

    Buffers: .78C and .78W Files The SR785 uses 4 user-allocable buffers to store large amounts of data. These are the Channel 1 capture buffer, the Channel 2 capture buffer, the waterfall buffer, and the arbitrary waveform buffer.

  • Page 540: Supported External File Types

    The file conversion utility will accept SR780 .78D files anywhere a SR785 .78D file can be used. This allows you to convert your old SR780 files to the SR785 format. The file conversion utility, however will not write SR780 files as output nor will it accept SR780 .78C or .78W files as input.

  • Page 541: Using The File Conversion Utility

    Using the File Conversion Utilities Using the File Conversion Utility The disk supplied with the SR785 contains the conversion utility SRTRANS.EXE. There is no installation required, simply copy to the program to your hard disk. The program has a number of options, some of which are generally applicable, and some of which are specific to certain output file types.
  • Page 542 Convert the 10th through 15th waterfall traces in WATER.78W to an ASCII file with magnitude squared data values only: SRT785 /Oasc /S10 /R6 /Cmag2 WATER.78W An example of a .78D file converted with the default program options is shown below: SR785 Dynamic Signal Analyzer...
  • Page 543 Output Options can be used to change the DOF parameters: /Mrnn Reference node number /Mrdk Reference node direction (see table below) /Msnn Response node number /Msdk Response node direction Node Direction id's -θ -θ -θ Scalar +θ +θ SR785 Dynamic Signal Analyzer...
  • Page 544 Specify firmware version of input file. The firmware version can be found by pressing [System]<Show Version> Example: Convert an SR780 file named OSR780.78D to an SR785 file named NSR785.78D: SRTRANS /O78d OSR780.78D NSR785.78D Converting Files to MATLAB Format Usage: SRT785 /Omat [options] infile [outfile] Allowed Input File Types: .78D Files.
  • Page 545 Reference node name /Mrnn Reference node number /Mrdk Reference node direction (see table below) /Msinodename Response node name /Msnn Response node number /Msdk Response node direction Node Direction id's -θ -θ -θ Scalar +θ +θ +θ SR785 Dynamic Signal Analyzer...
  • Page 546 100%. If the number of values found in the input file is less than the number of points specified with the /Ln option, the output file is zero padded. SR785 Dynamic Signal Analyzer...

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