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National Instruments 4551 User Manual

National Instruments 4551 User Manual

Ni-dsa software for computer-based instruments
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Computer-Based
Instruments
NI-DSA Software
User Manual
Version 1.2
September 2001 Edition
Part Number 370380A-01

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  • Page 1 Computer-Based Instruments NI-DSA Software User Manual Version 1.2 September 2001 Edition Part Number 370380A-01...
  • Page 2 Sweden 08 587 895 00, Switzerland 056 200 51 51, Taiwan 02 2528 7227, United Kingdom 01635 523545 For further support information, see the Technical Support Resources appendix. To comment on the documentation, send e-mail to techpubs@ni.com. Copyright © 2001 National Instruments Corporation. All rights reserved.
  • Page 3 The reader should consult National Instruments if errors are suspected. In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it.
  • Page 4 Conventions The following conventions are used in this manual: <> Angle brackets that contain numbers separated by an ellipsis represent a range of values associated with a bit or signal name—for example, DBIO<3..0>. Square brackets enclose optional items—for example, [ response »...
  • Page 5 jointly refer to LabVIEW VIs and C-language function calls. For example, , when shown in this font, refers both to the Read Measurement LabVIEW NI-DSA Read Measurements VI and to the C function NIDSA_read_measurement...

  • Page 6: Table Of Contents

    Introduction to NI-DSA Getting Started with NI-DSA ..................1-1 Related Documentation ...................1-2 NI-DSA Measurement Modes ..................1-2 FFT Analyzer Mode ..................1-2 Swept-Sine Analyzer Mode (NI 4551 Only)...........1-3 Octave Analyzer Mode (Optional) ..............1-3 Source Mode (NI 4551 Only)................1-4 Chapter 2 Programming with NI-DSA Basic Concepts.......................2-1...
  • Page 7 LabVIEW Example..................4-7 C Example....................... 4-7 Step 4—Control......................4-9 LabVIEW Example..................4-10 C Example....................... 4-10 Source Mode (NI 4551 Only)..................4-11 Step 2—Configure Source..................... 4-11 LabVIEW Examples ..................4-13 C Examples ..................... 4-14 Step 3—Generate Signal ....................4-14 LabVIEW Example..................4-14...
  • Page 8 Sweep Frequency and Auto-Resolution..........6-17 Input Auto-Ranging ................6-18 Source Auto-Level and Ramping............6-19 Swept-Sine Measurements ................6-20 Spectrum ...................6-20 Cross-Spectrum ..............6-20 Frequency Response ............6-20 THD - Total Harmonic Distortion ........6-20 SINAD ................6-21 Swept Harmonics..............6-22 RMS Squared..............6-22 © National Instruments Corporation NI-DSA Software User Manual...
  • Page 9 Contents Octave Analyzer (Add-On) ................... 6-23 Octave and Level Analyzers Software Architecture ......6-24 Architecture of the Fractional-Octave Analyzer....... 6-24 Exact and Preferred Frequencies ............6-26 Summary of NI-DSA Octave Mode Functions ........ 6-29 Level Measurements................. 6-30 Averaging Modes ................6-32 Linear Averaging..............

  • Page 10: Introduction To Ni-Dsa

    Thank you for buying a National Instruments Dynamic Signal Analyzer (DSA), which includes NI-DSA, National Instruments’ driver for its DSA devices. With NI-DSA, you can program your NI 4551 or NI 4552 to analyze time- and frequency-domain data onboard in real time. This manual shows you how to use your application development environment (ADE) with NI-DSA to program your DSA instrument.

  • Page 11: Related Documentation

    Help for LabVIEW VIs is available in the LabVIEW context help. • To learn about the electrical and mechanical aspects and features of your National Instruments DSA hardware, refer to the NI 4551/4552 User Manual. • For the latest versions of drivers, manuals, and example programs, visit for free downloads.

  • Page 12: Swept-Sine Analyzer Mode (Ni 4551 Only)

    • Harmonic analysis—THD, THD+Noise, and SINAD • Time-domain data acquisition Swept-Sine Analyzer Mode (NI 4551 Only) Use swept-sine analyzer mode to make frequency response measurements when you need more accuracy, control, and dynamic range than FFT-based frequency response measurements provide.

  • Page 13: Source Mode (Ni 4551 Only)

    In the optional octave analyzer mode, the data are passed through a parallel bank of filters, averaged if needed, then transferred to the host memory. Source Mode (NI 4551 Only) With your NI 4551 and NI-DSA in source mode, you can generate signals of the following types: •...

  • Page 14: Programming With Ni-Dsa

    In addition to these operations, there are operations performed using utility functions. Utility functions perform auxiliary operations. Examples of Utility functions include: • Reset • Self Test © National Instruments Corporation NI-DSA Software User Manual...

  • Page 15: Notes For C Programmers

    Chapter 2 Programming with NI-DSA • Revision Query • Error Query • Error Message Notes for C Programmers The constants used in the example programs are defined in the NI-DSA header file, . The C code snippets in this manual use these nidsa.h constants for clarity.

  • Page 16: Step 2-Configure

    —sets the parameters for analog triggering. Configure Trigger Refer to the NI 4551/4552 User Manual, Chapter 3, Hardware Overview for more information about configuring your analog input channels. Unless otherwise noted, you can use the functions in this section, and most NI-DSA...

  • Page 17: C Example

    FFT Mode Programming, the Using Capture Mode to Acquire Time-Domain Data section. • If you are using an NI 4551 to generate a signal, refer to Chapter 4, Swept-Sine Mode Programming, the Source Mode (NI 4551 Only) section. • For swept-sine measurements, refer to Chapter 4,...

  • Page 18: Step 4-Control

    Refer to your online help for more information about control functions. Step 5—Close Any application you write with NI-DSA should have a close function. LabVIEW Example Figure 2-3. Close C Example NIDSA_close (DSAsession); © National Instruments Corporation NI-DSA Software User Manual...

  • Page 19: Fft Mode Programming

    Figure 3-1 shows the recommended program flow for baseband FFT analysis. Figure 3-2 shows the recommended program flow for zoom FFT analysis. For a detailed discussion of FFT analysis, refer to the Step 2—Configure the FFT Analyzer section. © National Instruments Corporation NI-DSA Software User Manual...
  • Page 20 Chapter 3 FFT Mode Programming Initialize Configure Mode Set Input Voltage Range Configure Set Input Coupling Hardware Front End Configure Trigger Route Base FFT Configure Base Engine Set Classical Base Band Configure Parameters Configure Base FFT Settings Configure Base FFT Averaging Check New Measurement Get Measurement Length Read Measurement...
  • Page 21 Configure Zoom FFT Span Configure Zoom FFT Configure Zoom Frequencies Parameters Configure Zoom FFT Settings Configure Zoom FFT Averaging Check New Measurement Get Measurement Length Read Measurement Stop? Close Figure 3-2. Zoom FFT Programming Flowchart © National Instruments Corporation NI-DSA Software User Manual...

  • Page 22: Step 2-Configure The Fft Analyzer

    Chapter 3 FFT Mode Programming Step 2—Configure the FFT Analyzer The first step in configuring your FFT measurement is to route the digitized input signal to one or more analyzers using Route Base Route Zoom To configure a baseband FFT, use the following: •...

  • Page 23: Labview Examples

    Figure 3-4. Configuring Zoom FFT C Examples Examples for baseband FFT and zoom FFT are included. Baseband FFT Example //Configure Baseband FFT Analyzer //Route channel i to analyzer 0 NIDSA_route_base_fft (DSASession, "0", InputChannel); © National Instruments Corporation NI-DSA Software User Manual...

  • Page 24: Zoom Fft Example

    Chapter 3 FFT Mode Programming NIDSA_configure_base_fft_engine (gDSASession, "0", VI_FALSE, VI_TRUE, VI_FALSE, VI_FALSE); //Set the frequency span for Baseband FFT analyzer NIDSA_set_classical_baseband_span (DSASession, "0", BaseBandSpan); //Set FFT resolution and windowing NIDSA_configure_base_fft_settings (DSASession, "0", FFTSize, FFTWindow, 100, 0.0); //Configure averaging parameters NIDSA_configure_base_fft_averaging (gDSASession, "0", AvgMode,AvgWeighting, NumberOfAvg,VI_FALSE);...

  • Page 25: Configuring The Fft Engine

    Classical spans are as follows: • Up to 800 lines in 0–80 KHz span for baseband • Up to 1,600 line in 0–80 KHz span for zoom analyzer © National Instruments Corporation NI-DSA Software User Manual...

  • Page 26: Configuring The Fft Settings

    Chapter 3 FFT Mode Programming Acceptable extended spans are: • Up to 800 lines in 0–95 KHz span for baseband • Up to 1,600 line in 0–95 KHz span for zoom analyzer Note NI-DSA automatically sets the hardware sampling rate to optimize antialiasing and real-time performance, based on the span you select.

  • Page 27: Step 3-Read Fft Measurements

    Base FFT 0—reads baseband FFT on analyzer 0 – Base FFT 1—reads baseband FFT on analyzer 1 • Auto-power measurement – Base auto-power 0—reads baseband auto-power from analyzer 0 – Base auto-power 1—reads baseband auto-power from analyzer 1 © National Instruments Corporation NI-DSA Software User Manual...
  • Page 28 Chapter 3 FFT Mode Programming • Cross-power measurement – Base cross-power – Base freq response – Base coherence – Base coherent power – Zoom FFT 0 – Zoom FFT 1 – Zoom auto-power 0 – Zoom auto-power 1 – Zoom cross-power –...
  • Page 29 • Time 2 • Time 3 • Windowed time 2 • Windowed time 3 • Base FFT 2 • Base FFT 3 • Base auto-power 2 • Base auto-power 3 © National Instruments Corporation 3-11 NI-DSA Software User Manual...

  • Page 30: Labview Example

    Chapter 3 FFT Mode Programming LabVIEW Example Figure 3-5. Read FFT Measurements C Example When reading FFT measurements, ideally, you need to use a timer in order to read measurements periodically. //This Function is called periodically (timer tick) int CVICALLBACK TimerCB (int panel, int control, int event,void *callbackData, int eventData1, int eventData2){ ViStatus NewMeasurement;...

  • Page 31: Step 4-Control

    The input level exceeded the maximum voltage allowed. • Wait on trigger—indicates that the DSA instrument is waiting for a trigger condition to be met. Refer to the NI 4551/4552 User Manual, Chapter 3, Hardware Overview for more information about triggering. •...

  • Page 32: Using Capture Mode To Acquire Time-Domain Data

    Chapter 3 FFT Mode Programming • Error message • Reset Using Capture Mode to Acquire Time-Domain Data When you are using the FFT mode of NI-DSA, you can obtain time-domain waveforms from . This function returns time-domain Read Measurement blocks whose size scales with the number of FFT lines you are calculating. For instance, a 400-line classical, or 475-line extended FFT, corresponds to 1,024 time domain data points.

  • Page 33: Using Engineering Units

    0.020 V) and the EU scale to V/EU. With these settings, a 1 V signal from the microphone is presented as a sound pressure of 94 dB, so you set the dB reference to 20 µPa (0.00002 Pa). © National Instruments Corporation 3-15 NI-DSA Software User Manual...

  • Page 34: Labview Example

    Chapter 3 FFT Mode Programming LabVIEW Example Figure 3-6. Configuring Engineering Units C Example //Configuring engineering units //A microphone is connected on Channel 0 (Units = Pa) NIDSA_configure_eu_label (DSASession, "0", EU_LABEL_PA, "EU"); //Microphone sensitivity = 100 mV/Pa NIDSA_configure_eu_scale (DSASession, "0", 0.1, EU_SCALE_V_EU); //Reference level = 20µPa NIDSA_configure_eu_dbref (DSASession, "0", 20e-6);...

  • Page 35: Swept-Sine Mode Programming

    Chapter 6, Advanced Concepts. Note Only the NI 4551 can be programmed in swept-sine mode since this mode requires the instrument to generate stimuli. You can find a swept-sine programming example, 455x Swept Sine , on your NI-DSA CD. Figure shows the recommended program Mode.vi...
  • Page 36 Chapter 4 Swept-Sine Mode Programming Initialize Configure Mode (Swept Sine) Configure Swept Sine Configure Swept Sine Configure Swept Sine Average Parameters Configure Swept Sine Source Start Sweeping Control Swept Sine (Restart) Check New Measurement Get Measurement Length Get Swept Frequencies Read Measurement Get Measurement Length Get Frequency...

  • Page 37: Step 2-Configure The Swept-Sine Analyzer

    Ramping enable—when ramping is enabled (ramping enable = ), the source amplitude changes at the rate specified by Ramping TRUE Rate; if , the source amplitude is allowed to change FALSE instantaneously. © National Instruments Corporation NI-DSA Software User Manual...

  • Page 38: Labview Example

    Chapter 4 Swept-Sine Mode Programming LabVIEW Example Figure 4-2. Configuring the Swept-Sine Analyzer C Example //Configuring Swept sine analyzer NIDSA_configure_dsa_mode (gDSASession, SWPSINE_MODE); NIDSA_configure_swept_sine (gDSASession,startFreq,stopFreq,numberOfSteps, 0, 0, 0, 512, 1.0, 6.0); NIDSA_configure_swept_sine_average (gDSASession, 0.01, 1, 0.01, 1); NIDSA_configure_swept_sine_source (gDSASession, amplitude, 0, "1",1.0, -3.0, 3.0, 10.0, 0, 1.0); Notes on Examples Configuring Harmonics Measurements (Optional) —configure the harmonics used...

  • Page 39: Configuring Custom Frequencies (Optional)

    To read a new measurement, use the following functions: • —returns the number of data points to Get Measurement Length read, based on the type and length of the measurement, and the set of frequency lines you choose with frqLineSelector. © National Instruments Corporation NI-DSA Software User Manual...
  • Page 40 Chapter 4 Swept-Sine Mode Programming Values for frqLineSelector are: – Valid lines—returns alias-free lines only – All lines—returns all FFT lines – Classical lines—returns alias-free classical lines • —reads the measurement from the specified Read Measurement analyzer channel The valid measurement Type settings for Get Measurement Length are limited to the measurements that you specified Read Measurement...

  • Page 41: Labview Example

    //These 2 arrays will be displayed in a XY graph //(Frequency response vs Freq Axis) int CVICALLBACK TimerCB (int panel, int control, int event,void *callbackData, int eventData1, int eventData2) ViStatus sweepStatus; ViStatus NewMeasurement; © National Instruments Corporation NI-DSA Software User Manual...
  • Page 42 Chapter 4 Swept-Sine Mode Programming ViInt32 overload; ViInt32 measError; ViInt32 sweepState; //Variables used for Frequency axis ViInt32 RealOrComplex; ViInt32 Length; ViReal32 dx; ViReal32 x0; //Variables used for Frequency response ViInt32 respRealOrComplex; ViInt32 respLength; ViReal32 respdx; ViReal32 respx0; switch (event) case EVENT_TIMER_TICK: NIDSA_get_swept_sine_status (gDSASession, &sweepState, &measError,&overload);...

  • Page 43: Step 4-Control

    • Wait on trigger—indicates that your DSA instrument is waiting for a trigger condition to be met. Refer to Chapter 3, Hardware Overview, of the NI 4551/4552 User Manual for more information about triggering. © National Instruments Corporation NI-DSA Software User Manual...

  • Page 44: Labview Example

    Chapter 4 Swept-Sine Mode Programming —returns the status of the swept-sine Get Swept Sine Status measurement with the following indicators: • Sweep state—returns the state the current sweep in swept-sine analyzer mode – 0: Sweeping—sweep is in progress – 1: Paused—sweep has been paused –...

  • Page 45: Source Mode (Ni 4551 Only)

    Chapter 4 Swept-Sine Mode Programming Source Mode (NI 4551 Only) Source mode is useful for generating signals for frequency response measurements, and so on. NIDSA_Initialize NIDSA_Set_Output_Voltage_Range 100mV, 1V or 10V NIDSA_Set_Hardware_Update_Range 51200 Max NIDSA_Configure_Source Sine, Chirp, Noise or Arb This Function Will Depend...
  • Page 46 Chapter 4 Swept-Sine Mode Programming – voltageRange—voltage range for the selected output channel • 0: ± 10.0V • 1: ± 1.00V • 2: ± 100mV • 3: OFF (not supported) • —sets the hardware update rate. Set Hardware Update Rate Default Value: 51200.0 S/s;...

  • Page 47: Labview Examples

    51.2 kHz and 102.4 kHz; and one-fourth of the scan rate if it is between 102.4 kHz and 204.8 kHz. Both of the outputs on the NI 4551 work as a single output if the device is used in DSA Instrument Mode through NI-DSA. Output channel 0 generates the specified output, and channel 1 generates the same signal with a 180 degree shift.

  • Page 48: C Examples

    Chapter 4 Swept-Sine Mode Programming C Examples //Set Output voltage range to 10 V NIDSA_set_output_voltage_range (DSASession, "0", OUTVRANGE_10V); //Set update rate to 51.2 kS/s NIDSA_set_hw_sampling_rate (DSASession, 51200); //Turn source ON and select a sine wave output signal NIDSA_configure_source (DSASession, SRC_ON, SINE_SRC); //Configure sine source //Note : This function allows a dual tone generation //To generate a single tone, set Amplitude2 and Freq2 parameters to 0...

  • Page 49: Octave Analysis (Add-On) Mode Programming

    Many research efforts are currently focused on this field of psycho-acoustics, but octave band analysis remains the first choice technique. Figure 5-1 illustrates the recommended programming flow for octave analysis with NI-DSA. © National Instruments Corporation NI-DSA Software User Manual...
  • Page 50 Chapter 5 Octave Analysis (Add-On) Mode Programming Initialize Configure Mode (Octave) Set Input Voltage Range Configure Set Input Coupling Hardware Front End Configure Trigger Configure Weighting Filter Configure Weighting Filter Configure Octave Weighting 25,600 or Set OLM Sampling Rate 51,200 Configure OLM Engine Configure Octave Measurements Configure Octave Averaging...

  • Page 51: Step 2-Configure The Octave Analyzer

    Set the following parameters: – Octave type—1/1, 1/3 or 1/12 – Lo center frequency – Hi center frequency – Compliance ANSI/IEC © National Instruments Corporation NI-DSA Software User Manual...

  • Page 52: Labview Examples

    Chapter 5 Octave Analysis (Add-On) Mode Programming • —sets the averaging mode, time Configure Octave averaging constant, and confidence level – Average Type • 0: None • 1: Linear—band power outputs are equally weighted and averaged over the specified integration time •...

  • Page 53: C Example

    – Octave mode: refer the octave description for further information – Octave power 0 – Octave power 1 – Octave power 2 – Octave power 3 – Level measurements 0 © National Instruments Corporation NI-DSA Software User Manual...
  • Page 54 Chapter 5 Octave Analysis (Add-On) Mode Programming – Level measurements 1 – Level measurements 2 – Level measurements 3 When a new measurement is ready, it needs to be read: • Read octave measurements Returns: – Band power measurements (needed to build the octave graph) –...

  • Page 55: Labview Examples

    Figure 5-4. Reading the Octave Measurement C Examples int CVICALLBACK TimerCB (int panel, int control, int event,void *callbackData, int eventData1, int eventData2) ViStatus NewMeasurement; //NewMeasurement==1 when a new measurement is ready ViInt32 NumberOfBands; ViInt32 FilterSettled; ViReal32 TotalBandPwr; © National Instruments Corporation NI-DSA Software User Manual...
  • Page 56 Chapter 5 Octave Analysis (Add-On) Mode Programming ViReal64 linAvgTime; ViReal64 ElapsedAvgTime; ViString UnitLabel; ViReal32 NominalCenterFreq[120]; ViReal32 ExactCenterFreq[120]; ViReal32 BandPowerMeas[120]; switch (event) case EVENT_TIMER_TICK: //Check if a new measurement is ready NIDSA_check_new_measurement (gDSASession, &NewMeasurement); if (!NewMeasurement) return 0; //Read the new measurement NIDSA_get_octave_number_of_bands (gDSASession, &NumberOfBands);...

  • Page 57: Step 4-Control

    Chapter 5 Octave Analysis (Add-On) Mode Programming return VI_SUCCESS; Step 4—Control Get OLM Status © National Instruments Corporation NI-DSA Software User Manual...

  • Page 58: Advanced Concepts

    The dual-channel zoom analyzer lets you use any starting and ending frequencies for the zoom span. The two channels can have different zoom spans with up to 1,600 lines of frequency resolution, depending on the © National Instruments Corporation NI-DSA Software User Manual...

  • Page 59: Fft Measurements

    Any of the four input channels of the NI 4552, or the two input channels of the NI 4551 can be routed to any analyzer channel, or to multiple analyzer channels. For example, you can have one input channel routed to different analyzer channels with different settings in order to view one part of the frequency spectrum at a higher resolution than the other parts.
  • Page 60 Phase Re X k ( ) X k ( ) 1 – ---------------------- - Im X k ( ) The power spectrum reflects the energy content: X k ( ) Power Spectrum © National Instruments Corporation NI-DSA Software User Manual...
  • Page 61 Chapter 6 Advanced Concepts The power spectrum, normalized to 1 Hz bandwidth, gives the power spectral density (PSD): X k ( ) ⁄ The use of the FFT for frequency analysis implies two important relationships: • The highest frequency that can be analyzed is related to the sampling rate.

  • Page 62: Dual Channel Fft Analysis

    The average cross-power spectrum (S ) is a dual-channel measurement computed by multiplying each FFT component of channel x by the complex conjugate of the corresponding component from channel y: © National Instruments Corporation NI-DSA Software User Manual...
  • Page 63 Chapter 6 Advanced Concepts The complex frequency response function H(f) is calculated from measured spectra using the following formula. Here, channel x represents a stimulus signal sent to the unit under test, while channel y represents the response coming from the test unit. The diagram below illustrates the frequency response H(f) of a system at one particular frequency f.

  • Page 64: Baseband And Zoom Frequency Spans

    /2. For this reason, the alias-free bandwidth of the instrument will be somewhat less than f The oversampling delta-sigma converters used on the NI 4551 and NI 4552 contain integral antialiasing filters that provide an alias-free bandwidth of 46.4% of the sampling frequency. At the maximum sampling rate of 204.8 kS/s, the NI 45XX alias-free bandwidth is 95 kS/s...

  • Page 65: Classical And Extended Fft Size

    Chapter 6 Advanced Concepts Classical and Extended FFT Size Although the superior antialiasing performance of the NI 45XX allows a larger alias-free bandwidth and thus more spectral lines, sometimes a user wants to make measurements at bandwidths that have traditionally been used in spectral analysis.

  • Page 66: Zoom Spans

    In the heterodyning process the input points are multiplied by a complex unit vector (cos(wt) and sin(wt)) to yield a real and imaginary time record. © National Instruments Corporation NI-DSA Software User Manual...
  • Page 67 Chapter 6 Advanced Concepts The original frequency span center is then shifted to DC or heterodyned, this means that the upper half of the span stays positive and the lower half (below the span center) becomes a set of negative frequencies. The result is that a span from 0 to 80kHz becomes a span of –40 to 40 kHz.

  • Page 68: Zoom Span Characteristics

    The zoom span limits have to be within the baseband span, and the maximum extended baseband span is 95 kHz. You can select a zoom FFT of 100, 200, 400, 800, or 1,600 lines. © National Instruments Corporation 6-11 NI-DSA Software User Manual...

  • Page 69: Windowing

    Chapter 6 Advanced Concepts When the selected zoom span is larger than the classical baseband span selected (including the maximum classical baseband span of 80 kHz), the driver will make the zoom analyzer behave as a baseband analyzer and eliminate the modulation and decimation stages. By using the zoom analyzers as baseband analyzers, the two-dual-channel-analyzers architecture lets you perform an FFT analysis in the same frequency span on four channels at the same time.
  • Page 70 Windowing Figure 6-5. Waveform Discontinuity After Windowing Some of the windows available in NI-DSA are: • Uniform • Hanning • Blackman-Harris (standard, 4-term, and 7-term) © National Instruments Corporation 6-13 NI-DSA Software User Manual...

  • Page 71: Fft Averaging

    Chapter 6 Advanced Concepts • Flattop • Kaiser • Low sidelobe • Force • Exponential • Forced-exponential For more information about using windowing functions, refer to NI Application Note 041, The Fundamentals of FFT-Based Signal Analysis and Measurement. FFT Averaging Averaging successive measurements tends to improve measurement accuracy.

  • Page 72: Swept-Sine

    FFT measurements. Instead of using the same settings on all frequency points as in the FFT case, a swept-sine analyzer can optimize the measurement at each individual frequency with auto-ranging and auto-level features. © National Instruments Corporation 6-15 NI-DSA Software User Manual...
  • Page 73 Chapter 6 Advanced Concepts Auto-ranging extends the dynamic range and auto-level increases the signal to noise ratio. If the system’s transfer function has large variations within the measurement span, a swept-sine analysis can often give you greater dynamic range than an FFT analysis. Because the FFT measures all the frequency components at the same time, the source must contain energy at all of the measured frequencies.

  • Page 74: Swept-Sine Controls And Settings

    Start and stop frequencies specify the measurement frequency span and can be specified within the range shown here: 0 < f < f Note Sweeping through very low frequencies—1 Hz, for example—will result in excessive integration times. © National Instruments Corporation 6-17 NI-DSA Software User Manual...

  • Page 75: Input Auto-Ranging

    Chapter 6 Advanced Concepts The number of points results in the minimum frequency resolution of a swept-sine measurement. number of points can be set from 1 to 2,048. The points can be in a linear or logarithmic progression. In some cases, it is desirable to sweep over a wide frequency range while still detecting narrow transition in the frequency response function.

  • Page 76: Source Auto-Level And Ramping

    Ramping on, the source level changes gradually at the ramping rate. The settling time starts after the ramp. Enabling Source Ramping increases the sweep time, but avoids instantaneous source-level changes, which could cause the device under test to respond erratically. © National Instruments Corporation 6-19 NI-DSA Software User Manual...

  • Page 77: Swept-Sine Measurements

    Chapter 6 Advanced Concepts Swept-Sine Measurements Spectrum The spectrum, the measurement of a single channel over a sweep, can be returned for channel 0, channel 1, or both. The spectrum is complex (meaning it contains real and imaginary components), with an amplitude of the measured signal, and phase relative to source.

  • Page 78: Sinad

    Where E = signal amplitude (RMS) = RMS value of the fundamental frequency. NI-DSA computes SINAD on channel 1, which is normally connected to the output of the system under test. © National Instruments Corporation 6-21 NI-DSA Software User Manual...

  • Page 79: Swept Harmonics

    Chapter 6 Advanced Concepts With parameter dB units set to dB on, the SINAD is Read Measurement calculated as shown here: × SINAD -------------- - – Swept Harmonics Up to five individual harmonic distortion measurements can be returned. Each one is calculated as shown in the following formula: ×...

  • Page 80: Octave Analyzer (Add-On)

    In terms of vibration signals, it can be viewed as the destructive ability of the signal. Level measurements return the total amount of energy contained in the signal, and octave measurements return the amount of energy contained in different frequency bands. © National Instruments Corporation 6-23 NI-DSA Software User Manual...

  • Page 81: Octave And Level Analyzers Software Architecture

    Chapter 6 Advanced Concepts Octave and Level Analyzers Software Architecture Figure 6-7 shows the overall architecture for making octave and level measurements. Level Analysis1 Averaging Input Time Level Analysis N Averaging Domain Signal, x [n] Weighting Averaging Octave Analysis Figure 6-7. Octave and Level Measurement Functional Diagram You can perform octave and level measurements on one, two, or four channels simultaneously.
  • Page 82 2. The process is repeated for a maximum of 10 stages of BPF(s), or a maximum of nine stages of lowpass filtering and decimation. © National Instruments Corporation 6-25 NI-DSA Software User Manual...

  • Page 83: Exact And Preferred Frequencies

    Chapter 6 Advanced Concepts The time-domain samples at the output of each BPF are squared, then averaged according to the averaging mode selected, and the averaged output of each BPF is returned as the measurement. Third-octave analysis provides a maximum of 30 results (10 octaves × 3 BPFs/octave). 1/1-octave analysis provides a maximum of 10 results (10 octaves ×...
  • Page 84 198.43 — –6 –2 –5 314.98 — –4 396.85 — –3 –1 –2 629.96 — –1 793.7 — 1,000 1,000 1,259.92 1,250 — 1,587.40 1,600 — 2,000 2,000 2,519.84 2,500 — © National Instruments Corporation 6-27 NI-DSA Software User Manual...
  • Page 85 Chapter 6 Advanced Concepts Table 6-2. Exact and Preferred Octave Analysis Frequencies (Continued) Exact Preferred Frequency Frequency (1/3-octave) (Hz) (Hz) (1/1-octave) 3,174.80 3,150 — 4,000 4,000 5,039.68 5,000 — 6,349.60 6,300 — 8,000 8,000 10,079.37 10,000 — 12,699.21 12,500 — 16,000 16,000 20,158.74...

  • Page 86: Summary Of Ni-Dsa Octave Mode Functions

    However, you can program the operation of the instrument to meet the specific needs of your application. © National Instruments Corporation 6-29 NI-DSA Software User Manual...

  • Page 87: Level Measurements

    Chapter 6 Advanced Concepts The functions can also be classified according to the types of measurements they are used for. In general, a function used for both octave and level measurements has the abbreviation “OLM” in the function name. A function used only for octave measurements has the word “octave”...
  • Page 88 Configure OLM Linear Averaging Peak averaging mode is not truly an averaging operation. Instead, it computes the level by recording the largest instantaneous level measurement since the beginning of the acquisition. © National Instruments Corporation 6-31 NI-DSA Software User Manual...

  • Page 89: Averaging Modes

    Chapter 6 Advanced Concepts When acquiring level values, you should first call Get Level Length get the number of level measurements currently available. Next, make a call to produce an array containing the level Read Level Measurements values. You can also call to generate a string array Get Level Labels containing the corresponding until labels for the level measurements.
  • Page 90 In auto-restart mode, the time duration can only be an integer multiple of 10 milliseconds. If any other duration is specified, it is rounded off to the nearest 10 milliseconds. © National Instruments Corporation 6-33 NI-DSA Software User Manual...

  • Page 91: Exponential Averaging

    Chapter 6 Advanced Concepts For level measurements, the linear average is denoted as Leq (equivalent sound power over the specified time duration). Exponential Averaging Exponential averaging is a continuous averaging process that weighs both current as well as past data. The amount of weight given to past data as compared to current data depends on the exponential time constant.

  • Page 92: Impulse + Linear Averaging

    ) of the Configure Octave Averaging correct mean with a probability of 68%. The probability that the results are within twice the confidence level of the correct mean is 96%. © National Instruments Corporation 6-35 NI-DSA Software User Manual...

  • Page 93: A-, B-, And C-Weighting

    Chapter 6 Advanced Concepts For example, if you specify a confidence level of 1 dB, and the correct mean is 10 dB, there is a 68% confidence that the measured value is between 9–11 dB, and a 96% confidence that the measured value is between 8–12 dB.
  • Page 94 Chapter 6 Advanced Concepts two values: 25.6 kHz or 51.2 kHz. The NI 4551 has two input channels, and the NI 4552 has four input channels. The higher the number of channels used, the more difficult it is for the processor to keep up in real-time.

  • Page 95: Configuration Limits

    NI 4551 Table 6-5 shows different configurations for which real-time processing on the NI 4551 is possible, and illustrates trade-offs that you can make. The table is not exhaustive, but a guide; other configurations are possible. For this table, the following assumptions are made: the sampling rate is the default rate, 51.2 kHz, and both input channels are processed.
  • Page 96 Fast 4,490 Hz (ANSI) 4,621 Hz (IEC) As Table 6-5 shows, the NI 4551 can perform a 1/1-octave analysis in real time while applying the most computationally-intensive averaging and weighting (impulse and A, respectively). In addition, it can simultaneously perform up to eight level measurements with impulse-eq averaging.
  • Page 97 NI 4551. If you configure one or two channels for octave analysis, configurations that allow real-time operation of the NI 4551 generally will for the NI 4552 as well. However, if you configure three or four channels for octave analysis, the additional processing demands reduce the frequency range over which the processor can operate in real-time.

  • Page 98: Frequency Ranges

    = 1/(5 × bandwidth), where the settling time is in seconds and the bandwidth is in hertz (Hz). © National Instruments Corporation 6-41 NI-DSA Software User Manual...

  • Page 99: Overload Detection

    Chapter 6 Advanced Concepts The bandwidth for each band can be calculated by the formula bandwidth = exact center frequency × (2 1/2n –1/2n – 2 ), where n = 1 for full-octave, 3 for 1/3-octave, and 12 for 1/12-octave, and the exact center frequency for each band is returned in the exact center frequencies returned from Get Octave Frequencies...
  • Page 100 1 and 4 1010 2 and 4 1011 1, 2, and 4 1100 3 and 4 1101 1, 3, and 4 1110 2, 3, and 4 1111 1, 2, 3, and 4 © National Instruments Corporation 6-43 NI-DSA Software User Manual...

  • Page 101: Appendix A Common Questions

    Why does a 400-line baseband FFT return an array with 401 data points? By definition, a 400-line FFT contains information on the spectral content of a signal at 400 nonzero frequencies. The analyzer also returns the DC © National Instruments Corporation NI-DSA Software User Manual...
  • Page 102 Appendix A Common Questions content of the signal, providing a total of 401 amplitude values. An x-line FFT always returns an array of length x+1, and the first element of this array is the amplitude of the DC signal component. What is real-time operation for a 455X DSA device? When referring to a NI 455X DSA device, real-time operation simply means that all time-domain data points are used in the frequency-domain...

  • Page 103: Zoom Fft Analysis Questions

    A zoom FFT allows you to examine a frequency starting at a value greater than zero. Using the zoom FFT, you can obtain up to 1,600 frequency resolution from 5,000 Hz to 6,000 Hz. The frequency resolution improves dramatically: 1000 Hz/1600 lines = 0.625 Hz. © National Instruments Corporation NI-DSA Software User Manual...
  • Page 104 Appendix A Common Questions Does the zoom FFT reduce acquisition time? For any given frequency resolution, you must acquire data for the same time interval whether you are using baseband or zoom analysis. If you use either a zoom FFT or a baseband FFT, the time block of data required to perform a single FFT is 1/Df, where Df is the frequency resolution.

  • Page 105: Source Mode

    2. This requirement is because the input and output converters are driven by the same DDS circuitry on the device. The hardware synchronization between input and output is convenient for performing stimulus-response tests. If you make subsequent calls to © National Instruments Corporation NI-DSA Software User Manual...
  • Page 106 Appendix A Common Questions , you will see that the HW Sampling Rate Get HW Update Rate ratio between these two parameters is a power of 2. What is the maximum sine output frequency I can obtain using NI-DSA? The maximum output frequency you can generate with NI-DSA is 23 kHz. This limit is governed by the maximum output sampling rate of 51.2 kS/s.

  • Page 107: Swept-Sine Mode

    Yes. You can obtain up to five harmonics from the swept-sine measurement. To set up the swept-sine harmonic analysis, call Configure Swept Sine . Pass a value of to Enable Harmonic Mapping. The Harmonics © National Instruments Corporation NI-DSA Software User Manual...
  • Page 108 Appendix A Common Questions Harmonic Mapping parameter is an array of five integers defining the harmonics of interest. For example, if the elements of this array are [2,3,5,9,20], the swept-sine harmonic measurements returned are: • Swept-sine harmonic 1—2 harmonic • Swept-sine harmonic 2—3 harmonic •...

  • Page 109: Octave And Level Analyzer Mode (Add-On

    To configure level measurements, use Configure Level . To read the level measurements, first call Measurements Get Level to determine the number of measurements to read, then call Length Read to read the measurements. Level Measurements © National Instruments Corporation NI-DSA Software User Manual...
  • Page 110 Get Hardware Sampling Rate How long does the signal take to propagate through the input section of the NI 4551/4552? The signal delay—the time it takes for a signal entering an analog input channel to become available as digital data at the output of the delta-sigma ADC—is 42 sample periods, regardless of the sample rate, for example—...
  • Page 111 12.05 –76 12.40 12.76 –75 13.14 13.52 –74 13.92 14.33 –73 14.75 15.18 –72 15.625 16.083 –71 16.554 17.039 –70 17.538 18.052 –69 18.581 19.126 –68 19.686 20.263 –67 20.857 21.468 © National Instruments Corporation A-11 NI-DSA Software User Manual...
  • Page 112 Appendix A Common Questions Table A-1. Exact Center Frequencies for 1/12 Octave Analysis (Continued) (1/12 ANSI-Standard Exact IEC-Standard Exact octave) Center Frequencies (Hz) Center Frequencies (Hz) –66 22.097 22.745 –65 23.411 24.097 –64 24.803 25.530 –63 26.278 27.048 –62 27.841 28.656 –61 29.496...
  • Page 113 192.78 –28 198.43 204.24 –27 210.22 216.38 –26 222.72 229.25 –25 235.97 242.88 –24 250.00 257.33 –23 264.87 272.63 –22 280.62 288.84 –21 297.30 306.01 –20 314.98 324.21 –19 333.71 343.49 © National Instruments Corporation A-13 NI-DSA Software User Manual...
  • Page 114 Appendix A Common Questions Table A-1. Exact Center Frequencies for 1/12 Octave Analysis (Continued) (1/12 ANSI-Standard Exact IEC-Standard Exact octave) Center Frequencies (Hz) Center Frequencies (Hz) –18 353.55 363.91 –17 374.58 385.55 –16 396.85 408.48 –15 420.45 432.77 –14 445.45 458.50 –13 471.94...
  • Page 115 2,310.71 2,378.41 2,448.11 2,519.84 2,593.68 2,669.68 2,747.91 2,828.43 2,911.31 2,996.61 3,084.42 3,174.80 3,267.83 3,363.59 3,462.15 3,563.59 3,668.02 3,775.5 3,886.13 4,000 4,117.21 4,237.85 4,362.03 4,489.85 4,621.41 4,756.83 4,896.21 5,039.68 5,187.36 5,339.36 5,495.81 © National Instruments Corporation A-15 NI-DSA Software User Manual...
  • Page 116 Appendix A Common Questions Table A-1. Exact Center Frequencies for 1/12 Octave Analysis (Continued) (1/12 ANSI-Standard Exact IEC-Standard Exact octave) Center Frequencies (Hz) Center Frequencies (Hz) 5,656.85 5,822.61 5,993.23 6,168.84 6,349.60 6,535.66 6,727.17 6,924.29 7,172.19 7,336.03 7,550.99 7,772.26 8,000 8,234.42 8,475.70 8,724.06 8,979.70...

  • Page 117: Technical Support Resources

    Technical Support Resources Web Support National Instruments Web support is your first stop for help in solving installation, configuration, and application problems and questions. Online problem-solving and diagnostic resources include frequently asked questions, knowledge bases, product-specific troubleshooting wizards, manuals, drivers, software updates, and more. Web support is available through the Technical Support section of ni.com...
  • Page 118 Appendix B Technical Support Resources Worldwide Support National Instruments has offices located around the world to help address your support needs. You can access our branch office Web sites from the Worldwide Offices section of . Branch office Web sites provide ni.com...

  • Page 119: Glossary

    – negative of, or minus Ω percent positive of, or plus +5 V +5 VDC source signal amperes alternating current AC coupled allowing the transmission of AC signals while blocking DC signals © National Instruments Corporation NI-DSA Software User Manual...
  • Page 120 Glossary analog input channel signal analog-to-digital analog-to-digital converter—an electronic device, often an integrated circuit, that converts an analog voltage to a digital number ADC resolution the size of the discrete steps in the ADC’s input-to-output transfer function; therefore, the smallest voltage difference an ADC can discriminate with a single measurement AIGND analog input ground signal...
  • Page 121 Examples of PC buses are the ISA and PCI bus. bus master a type of a plug-in board or controller with the ability to read and write devices on the computer bus © National Instruments Corporation NI-DSA Software User Manual...
  • Page 122 Glossary Celsius CalDAC calibration DAC channel pin or wire lead to which you apply or from which you read the analog or digital signal. Analog signals can be single-ended or differential. For digital signals, you group channels to form ports. Ports usually consist of either four or eight digital channels.
  • Page 123 D/A and/or DIO boards in the same computer decibel—the unit for expressing a logarithmic measure of the ratio of two signal levels: dB=20log ), for signals in volts direct current © National Instruments Corporation NI-DSA Software User Manual...
  • Page 124 Glossary DC coupled allowing the transmission of both AC and DC signals direct digital synthesis default setting a default parameter value recorded in the driver. In many cases, the default input of a control is a certain value (often 0) that means use the current default setting.
  • Page 125 EEPROM that may contain device-specific initialization and system boot functionality EXT_TRIG external digital trigger external trigger a voltage pulse from an external source that triggers an event such as A/D conversion © National Instruments Corporation NI-DSA Software User Manual...
  • Page 126 Glossary false triggering triggering that occurs at an unintended time FIFO first-in first-out memory buffer—the first data stored is the first data sent to the acceptor. FIFOs are often used on DAQ devices to temporarily store incoming or outgoing data until that data can be retrieved or output. For example, an analog input FIFO stores the results of A/D conversions until the data can be retrieved into system memory, a process that requires the servicing of interrupts and often the programming of the DMA controller.
  • Page 127 DIN—A 250 Hz sine wave and an 8 kHz sine wave added in a 4:1 amplitude ratio. CCIF—A 14 kHz sine wave and a 15 kHz sine wave added in a 1:1 amplitude ratio. inches © National Instruments Corporation NI-DSA Software User Manual...
  • Page 128 Glossary integral nonlinearity—a measure in LSB of the worst-case deviation from the ideal A/D or D/A transfer characteristic of the analog I/O circuitry input bias current the current that flows into the inputs of a circuit input impedance the measured resistance and reactance between the input terminals of a circuit input offset current the difference in the input bias currents of the two inputs of an...
  • Page 129 AC-coupled circuit, the frequency below which signals are attenuated by at least 3 dB least significant bit © National Instruments Corporation G-11 NI-DSA Software User Manual...
  • Page 130 NI-DAQ National Instruments driver software for DAQ hardware NIST National Institute of Standards and Technology noise an undesirable electrical signal—Noise comes from external sources such...
  • Page 131 Because counters output digital pulses at a constant rate, this means you can generate and retrieve patterns at a constant rate because the handshaked signal is produced at a constant rate. © National Instruments Corporation G-13 NI-DSA Software User Manual...
  • Page 132 Glossary Peripheral Component Interconnect—a high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA. It is achieving widespread acceptance as a standard for PCs and work-stations; it offers a theoretical maximum transfer rate of 132 Mbytes/s. peak to peak a measure of signal amplitude;...
  • Page 133 10% and 90% points of a system’s step response root mean square—the square root of the average value of the square of the instantaneous signal amplitude; a measure of signal amplitude seconds samples © National Instruments Corporation G-15 NI-DSA Software User Manual...
  • Page 134 Glossary sensor a device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal settling time the amount of time required for a voltage to reach its final value within specified limits signal conditioning the manipulation of signals to prepare them for digitizing...
  • Page 135 PC, that has the functionality of a classic stand-alone instrument (2) a LabVIEW software module (VI), which consists of a front panel user interface and a block diagram program © National Instruments Corporation G-17 NI-DSA Software User Manual...
  • Page 136 Glossary waveform multiple voltage readings taken at a specific sampling rate word the standard number of bits that a processor or memory manipulates at one time. Microprocessors typically use 8-, 16-, or 32-bit words. working voltage the highest voltage that should be applied to a product in normal use, normally well under the breakdown voltage for safety margin.

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