Stanford Research Systems SR865 Operation Manual
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Stanford Research Systems SR865 Operation Manual

2 mhz dsp lock-in amplifier
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Operation Manual
SR865
2 MHz DSP Lock-in Amplifier
Revision 1.25

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Summary of Contents for Stanford Research Systems SR865

  • Page 1 Operation Manual SR865 2 MHz DSP Lock-in Amplifier Revision 1.25...
  • Page 2 Certification Stanford Research Systems certifies that this product met its published specifications at the time of shipment. Warranty This Stanford Research Systems product is warranted against defects in materials and workmanship for a period of one (1) year from the date of shipment.

  • Page 3: Safety And Preparation For Use I

    Power Cord Grounding A chassis grounding lug is available on the back panel of the SR865. Connect a heavy duty ground wire, #12AWG or larger, from the CHASSIS GROUND lug directly to a facility earth ground to provide additional protection against electrical shock.

  • Page 4: Environmental Conditions

    PMT can charge to several hundred volts in a relatively short time. If this cable is connected to the inputs of the SR865 the stored charge may damage the front-end amplifier. To avoid this problem, always discharge the cable and connect the PMT output to the SR865 input before turning the PMT on.
  • Page 5 Safety and Preparation For Use SR865 DSP Lock-in Amplifier...
  • Page 6 Safety and Preparation For Use SR865 DSP Lock-in Amplifier...

  • Page 7: Table Of Contents

    Contents Contents Safety and Preparation for Use i Contents v SR865 Specifications vii SR865 Command List x SR865 Status Bytes xv Chapter 1 Getting Started 1 Introduction 1 SR865 Front Panel 2 SR865 Touchscreen 4 The Basic Lock-in 9 Using Displays 13...
  • Page 8 Appendix C Using the Webserver 169 Appendix D Data Streaming and Capture 171 Appendix E Dual Reference Detection 175 Appendix F Fuse Installation and ac Line Select 177 Appendix G Performance Tests 181 Appendix H Circuit Description 201 SR865 DSP Lock-in Amplifier...

  • Page 9: Sr865 Specifications

    All frequencies less than 2 MHz for specified performance (operates to 2.5 MHz) Chopper Reference SR865 drives SR540 Chopper (via Aux Out 4) to lock the chopper to f Demodulator dc Stability Digital output values have no offset drift Time Constants 1 µs to 30 ks...

  • Page 10: Inputs And Outputs

    Video output to external monitor or TV, 640x480/60 Hz. Timebase Input/Output 1 Vrms 10 MHz clock to synchronize internal reference frequency to other units General Interfaces IEEE488, RS-232, USB device (Test and Measurement Class) and Ethernet (VXI-11 and telnet) SR865 DSP Lock-in Amplifier...
  • Page 11 Preamp Power 9 pin D connector to power SRS preamps Power 60 Watts, 100/120/220/240 VAC, 50/60 Hz Dimensions 17"W × 5.25"H × 17"D Weight 22 lbs Warranty One year parts and labor on materials and workmanship SR865 DSP Lock-in Amplifier...

  • Page 12: Sr865 Command List

    113 Query the equivalent noise bandwidth page description CH1/CH2 Output Commands COUT(?) [ OCH1 | OCH2 | j ] { , XY | RTHeta | i } 114 Set CH1/2 to (X or R)/(Y or θ) SR865 DSP Lock-in Amplifier...
  • Page 13 SCRY? [ DAT1 | DAT2 | DAT3 | DAT4 | STATus | j ] 123 Query the cursor data values CURDATTIM? 123 Query the cursor horizontal position as date/time CURINTERVAL? 124 Query the cursor horizontal position as interval page description FFT Screen Commands SR865 DSP Lock-in Amplifier...

  • Page 14: Data Transfer Commands

    136 Set the capture rate to (max rate)/2 CAPTURESTART [ ONEshot | CONTinuous | i ] , [ OFF | ON | j ] 137 Start capture (OneShot or Cont) (HW trigger off/on) CAPTURESTOP 137 Stop capture SR865 DSP Lock-in Amplifier...

  • Page 15: System Commands

    OVRM (?) { OFF | ON | i } 147 Set GPIB Overide Remote off (0) or on (1) page description Status Reporting Commands 148 Clear all status bytes *CLS 148 Set the standard event enable register *ESE(?) { j, } { i } SR865 DSP Lock-in Amplifier...
  • Page 16 149 Query the error status byte LIAE(?) { j, } { i } 149 Set LIA status enable register LIAS? { j } 150 Query the LIA status word CUROVLDSTAT? 150 Query the present overload states SR865 DSP Lock-in Amplifier...

  • Page 17: Sr865 Status Bytes

    Data Channel 1 output overload DAT2OV Data Channel 2 output overload DAT3OV Data Channel 3 output overload DAT4OV Data Channel 4 output overload DCAPFIN Display capture to USB stick completed SCNST Scan started SCNFIN Scan completed SR865 DSP Lock-in Amplifier...
  • Page 18 External 10 MHz clock input error BACKUP Battery backup failed unused unused VXI-11 error GPIB GPIB fast data transfer mode aborted USBDEV USB device error (interface error) USBHOST USB host error (memory stick error) SR865 DSP Lock-in Amplifier...

  • Page 19: Chapter 1 Getting Started

    The sample measurements described in this section are designed to acquaint the first time user with the SR865 DSP Lock-In Amplifier. Do not be concerned that your measurements do not exactly agree with these exercises. The focus of these measurement exercises is to learn how to use the instrument.

  • Page 20: Sr865 Front Panel

    ) modes. The SR865 can be synchronized to an external 10 MHz frequency reference (from another SR865 or other source). This allows multiple SR865’s to run in phase sync with each other in internal reference mode. SR865 DSP Lock-in Amplifier...

  • Page 21: Getting Started

    Chapter 1 Getting Started The sine output from the SR865 is differential. This provides improved performance at low amplitudes. A variable dc offset is provided in both differential and common mode. Use either sine out for single ended excitation. Outputs The CH1 output can be proportional to either X or R, while the CH2 output can be proportional to Y or θ.

  • Page 22: Sr865 Touchscreen

    Half Screen FFT Big Numbers The SR865 displays up to 4 channels at a time, in green, blue, yellow and orange. Each channel is assigned a parameter using the [Config] key. Parameters are chosen from X, SR865 DSP Lock-in Amplifier...
  • Page 23 Horizontal scales range from 0.5 s to 2 days per division. At each point along the horizontal axis, the graph displays the maximum to minimum excursion of each data channel during a time interval corresponding to that point in the SR865 DSP Lock-in Amplifier...
  • Page 24 At a scale of 1 min/div, each pixel represents about 1s of data. This ‘binning’ is fundamental to the SR865 strip chart display. All time scales are stored all of the time. This allows the horizontal scale to change without re-acquiring any data. The caveat is that all graphs are drawn with the most recent point at the right hand edge.
  • Page 25 Use {Cursor MinMaxMean} and {Cursor Width} to change the cursor. Note that the cursor marker may not lie on the data graph for wide cursors since the marker shows the min, max or mean of all the data within the cursor width. SR865 DSP Lock-in Amplifier...
  • Page 26 Data storage continues in the background while the graph is paused. When live scrolling is resumed with {Resume}, the graph is redrawn so the current point is once again at the right edge. SR865 DSP Lock-in Amplifier...

  • Page 27: The Basic Lock-In

    0.5000 and Y (blue) should read close to 0.0000 V. Press the [Auto Phase] key. Automatically adjust the reference phase shift to eliminate any residual phase error. This should set the values of Y and θ to zero. SR865 DSP Lock-in Amplifier...
  • Page 28 Since the signal has just been reduced by a factor of 100, the input range should be adjusted as well. Press [Auto Range]. The Auto Range function changes the Input Range to maximize the signal at the A/D SR865 DSP Lock-in Amplifier...
  • Page 29 By decreasing the scale value, the bar graphs and numeric readings display much more resolution for the smaller signal. 12. Press [Time Constant Down] multiple times to The Time Constant is indicated with 3 LEDs. In SR865 DSP Lock-in Amplifier...
  • Page 30 (1 ms in this case). This concludes this measurement example. You should have a feeling for the basic operation of the front panel. Basic lock-in parameters have been introduced and you should be able to perform simple measurements. SR865 DSP Lock-in Amplifier...

  • Page 31: Using Displays

    The lock-in and the generator are not phase locked but they are at (nearly) the same frequency with a slowly changing θ (orange). The signal magnitude R (yellow) is phase independent and does not change. SR865 DSP Lock-in Amplifier...
  • Page 32 Touch the scale tile again to dismiss the palette. The trace may be moved up and down, auto scaled, zoomed in and out and dismissed entirely. SR865 DSP Lock-in Amplifier...
  • Page 33 Keep zooming in until the yellow trace moves the zero for R below the graph as shows some noise. The scale will probably end indicated by the downward facing yellow up less than 1 mV. triangle at the bottom right edge. SR865 DSP Lock-in Amplifier...
  • Page 34 12. Increase the amplitude of the function generator The signal now exceeds the input range of 1 V to 1.5 Vrms. (peak) so the Input Range Overload LED is on. ‘Ovld’ indicators are displayed for X, Y, R and SR865 DSP Lock-in Amplifier...
  • Page 35 14. Press [Screen Layout] once to change the display The half screen strip chart behaves the same as to the half screen strip chart. the full screen version. The only difference is that the numeric and bar graphs are full sized. SR865 DSP Lock-in Amplifier...
  • Page 36 4 aux inputs on the rear panel. The 4 aux outputs are shown in tiles across the bottom. Touching an output tile displays a keypad to set the aux output. SR865 DSP Lock-in Amplifier...
  • Page 37 18. Press [Screen Layout] again to cycle back to the Use [Screen Layout] to cycle through the trend graph. various display screens. This concludes the measurement example. You should have a feeling for the basic operation of the display screens. SR865 DSP Lock-in Amplifier...

  • Page 38: Sensitivity, Offset And Expand

    BNC is doubled and the lock-in measures 100 mV. Since the phase shift of the sine output is very close to zero, X (green) should read about 0.1000 and Y (blue) should read close to 0.0000 V. SR865 DSP Lock-in Amplifier...
  • Page 39 The DVM should now read 2 V. This is because X (100 mV) is now 20% of the sensitivity (500 mV). This also increases the bar graph to +20% and increases the resolution of the numeric readout. SR865 DSP Lock-in Amplifier...
  • Page 40 Auto Offset automatically adjusts the X offset (or Y or R) such that X (or Y or R) becomes zero. In this case, X is offset to zero. The offset should be about 100%. Offsets are set as a SR865 DSP Lock-in Amplifier...
  • Page 41 Expand increases the resolution of the X display and CH1 output. Note that the trace of X is unaffected by expand. This is because expand does not change the value of X. SR865 DSP Lock-in Amplifier...
  • Page 42 Simply auto scale the data Touch to auto scale the green X trace. channel to graphically offset and expand the chart data. See the Outputs and Scales discussion in the next chapter for more detailed information on output scaling SR865 DSP Lock-in Amplifier...

  • Page 43: Saving And Recalling Setups

    Chapter 1 Getting Started Saving and Recalling Setups The SR865 can store 8 complete instrument setups in non-volatile memory. Do This Explanation Disconnect all cables from the lock-in. Turn the When the power is turned on with [Local] power on while holding down the [Local] key.
  • Page 44 Chapter 1 Press [Filter Slope] once to select 12 dB/oct. Press [Save Recall] to display the Save/Recall The SR865 can store 8 complete setups. In screen. addition the default setup can be recalled. Touch the {Save} button next to the large tile Setups are numbered 1 through 8.
  • Page 45 A summary of settings which will change upon recall is shown. Simply touch {Cancel} to skip recalling this setup. Touch {Confirm} to recall the setup and dismiss The Sensitivity, Time Constant and Filter Slope this screen. should all return to the saved settings. SR865 DSP Lock-in Amplifier...

  • Page 46: Aux Outputs And Inputs

    The <Cursor> knob is used to adjust values 5.000 V. when the Aux Output keypad is shown. The DVM should display 5.00 V. The 4 Aux Outputs are useful for controlling other parameters in an experiment, such as pressure, temperature, wavelength, etc. SR865 DSP Lock-in Amplifier...
  • Page 47 Aux In 1 should now read 5.000 V. The Aux Inputs can be assigned to a data channel and graphed on the strip chart alongside lock-in outputs. Use the [Config] key to change a data channel. SR865 DSP Lock-in Amplifier...

  • Page 48: Scanning

    The longer the update time, the fewer steps. With experiments that take time to settle after a parameter change, it can be beneficial to set the update time long enough to accommodate the settling. SR865 DSP Lock-in Amplifier...
  • Page 49 Touch the white scale tile {Time} to display the horizontal scale palette (bottom right of screen). This scan takes 1m40s or 100 s so a chart span of 100 s will display an entire scan. Touch repeatedly to zoom out to 10 S/div. SR865 DSP Lock-in Amplifier...
  • Page 50 Any data channel can be assigned any of the sources in the keypad. When the Config screen is closed the strip chart does not display a blue trace. This is because we dismissed it previously. Touch {Close} to return to the strip chart. SR865 DSP Lock-in Amplifier...
  • Page 51 Changes to the scan setup do not affect a the scan off, then press [Scan/setup] briefly currently-running scan. We stop the scan and again to re-arm. then start a new one by cycling the [Scan/setup] button; the Ready LED goes off and then on. SR865 DSP Lock-in Amplifier...
  • Page 52 The Done LED turns off. 22. Press [Play Pause/reset] briefly to start the scan This starts the scan again. The LED turns again. on and the frequency ramps upward. SR865 DSP Lock-in Amplifier...
  • Page 53 While the scan is in progress, press [Scan/setup] Turn the scan off before the end and the internal briefly to turn scanning off. frequency returns to its original value (100.000 kHz) as shown in white in the info bar. SR865 DSP Lock-in Amplifier...
  • Page 54 Getting Started Chapter 1 SR865 DSP Lock-in Amplifier...

  • Page 55: Chapter 2 Lock-In Amplifier Basics

    If the sine output from the function generator is used to excite the experiment, the response might be the signal waveform shown below. The signal is sin(ω t + θ ) where ω = 2πf and V is the signal amplitude. SR865 DSP Lock-in Amplifier...
  • Page 56 θ Signal Lock-in Reference θ The SR865 amplifies the signal and then multiplies it by the lock-in reference using a phase-sensitive detector (PSD) or multiplier. The output of the PSD is simply the product of two sine waves. sin(ω t + θ...
  • Page 57 X is called the 'in-phase' component and Y the 'quadrature' component. This is because when θ = 0, X measures the signal while Y is zero. By computing the magnitude (R) of the signal vector, the phase dependency is removed. R = (X SR865 DSP Lock-in Amplifier...

  • Page 58: What Does A Lock-In Measure

    S(t) = 1.273 sin(ωt) + 0.4244 sin(3ωt) + 0.2546 sin(5ωt) + … where ω = 2πf. The SR865, locked to f will single out the first component. The measured signal will be 1.273 sin(ωt), not the 2V pk–pk that you'd measure on a scope.

  • Page 59: Block Diagram

    Chapter 2 Basics Thus, in the previous example with a 2 V pk–pk square wave input, the SR865 would detect the first sine component, 1.273 sin(ωt). The measured and displayed magnitude would be 0.90 V (rms), e.g. 1.273/√2. Degrees or Radians? In this discussion, frequencies have been referred to as f (Hz) and ω...

  • Page 60: The Reference Oscillator

    Reference Input The SR865 reference input can trigger on an analog signal (like a sine wave) or a TTL logic signal. The first case is called External Sine. The input is ac coupled (above 1 Hz) and the input impedance is 1 MΩ.

  • Page 61: The Phase Sensitive Detectors

    Chapter 2 Basics The input to the Y PSD is a third sine wave, computed by the SR865, shifted by 90° from the second sine wave. This waveform is sin(ω t + θ + 90°). The phase shifts (θ and the 90° shift) are exact numbers and accurate to better than 0.000001°.

  • Page 62: Time Constants And Sensitivity

    The ENBW is not the filter −3 dB pole, it is the effective bandwidth for Gaussian noise. More about this later. The digital signal processing in the SR865 handles all of the low pass filtering. Each PSD can be followed by up to four filter stages for up to 24 dB/oct of roll off.
  • Page 63 Sync filter (described below) is performed using floating point math. The SR865 plots these floating point outputs in the strip chart displays in units of Volts (or Amps) referred to the signal inputs. These values have no real limit in size (either too small or too large) and do not overload.

  • Page 64: Outputs And Scales

    If the Sync filters are overloaded, the Sync error indicators on the display will light. Outputs and Scales The SR865 has X and Y outputs on the rear panel and Channel 1 and 2 (CH1 and CH2) outputs on the front panel. X and Y Rear Panel Outputs The X and Y rear panel outputs are the outputs from the two phase sensitive detectors with low pass filtering, offset and expand.
  • Page 65 X, Y and R Output Offset, Ratio and Expand The SR865 has the ability to offset the X, Y and R outputs. This is useful when measuring deviations in the signal around some nominal value. The offset can be set so that the output is offset to zero.

  • Page 66: What Is Dynamic Reserve Really

    Basics Chapter 2 The X and Y offset, ratio and expand functions in the SR865 are output functions and do not affect the calculation of R or θ. R has its own output offset, ratio and expand. θ has no offset or ratio or expand capability.
  • Page 67 Chapter 2 Basics In the SR865 the only real gain is in the input amplifier, which amplifies the signal before it reaches the A/D converter. After this point, the signal is processed digitally so there’s no further gain. Therefore, the only question is how to set the gain of the input amplifier.

  • Page 68: The Input Amplifier

    The input noise of the SR865 signal amplifier is about 2.5 nVrms/√Hz. What does this noise figure mean? Let's set up an experiment. If the SR865’s Input Range is set to 10 mV then the input gain is sufficient that the noise floor of the measurement is determined by the input noise.

  • Page 69: Input Connections

    This filter is transparent to the user. Input Impedance The input impedance of the SR865 is 10 MΩ. If a higher input impedance is desired, then a preamplifier such as the SR550 must be used. The SR550 has an input impedance of 100 MΩ...
  • Page 70 . Even with a CMRR of 100 dB, a 100 mV common mode signal behaves like a 1 µV differential signal! This is especially bad if the common mode signal is at the reference frequency (this often happens due to SR865 DSP Lock-in Amplifier...
  • Page 71 160 mHz. Current Input (I) The current input on the SR865 uses a separate input BNC. The current input has a gain Volts/Amp (1 μA or 10 nA range). The input burden resistance is...

  • Page 72: Intrinsic (Random) Noise Sources

    300 K), R is the resistance in ohms, and ∆f is the bandwidth in hertz. ∆f is the equivalent noise bandwidth of the measurement. Since the input signal amplifier in the SR865 has a bandwidth of approximately 3 MHz, = 220√R nVrms or 1.1√R μV pk–pk.

  • Page 73: External Noise Sources

    Typical sources of synchronous noise are ground loops between the experiment, detector and lock-in, and electronic pick up from the reference oscillator or experimental apparatus. SR865 DSP Lock-in Amplifier...
  • Page 74 3) Designing the experiment to measure voltages with low impedance (noise current generates very little voltage). 4) Installing capacitive shielding by placing both the experiment and detector in a grounded metal box. SR865 DSP Lock-in Amplifier...

  • Page 75: Inductive Coupling

    The detector and the experiment are grounded at different places which, in this case, are at different potentials. Cures for ground loop problems include: 1) Grounding everything to the same physical point. SR865 DSP Lock-in Amplifier...

  • Page 76: Noise Measurements

    This second junction should be held at the same temperature as the first junction. Noise Measurements Lock-in amplifiers can be used to measure noise. Noise measurements are generally used to characterize components and detectors. SR865 DSP Lock-in Amplifier...
  • Page 77 To display a noise measurement, choose X or Y noise (Xn or Yn) as one of the displayed parameters in the [Config] screen. The SR865 is calculating the noise all of the time, whether or not X or Y noise are being displayed. Thus, as soon as noise is displayed, the value shown is up to date and no settling time is required.
  • Page 78 Basics Chapter 2 X and Y noise are displayed in units of V(rms). The ENBW of the time constant is NOT factored into the calculation. To convert to spectral noise density, divide the reading by √ENBW. SR865 DSP Lock-in Amplifier...

  • Page 79: Chapter 3 Operation

    Operation Introduction Power The power switch is on the rear panel. The SR865 is turned on by pushing the switch up. Keys The keys are grouped and labeled according to function. This manual will refer to a key with square brackets such as [Key]. A complete description of the keys follows in this section.

  • Page 80: Reference Input

    A 2.5 V sync logic output is provided on the rear panel via the configurable BlazeX output. This output is useful for triggering scopes and other equipment at the reference frequency. The sync output is a square wave derived from the zero crossings of the sine output. SR865 DSP Lock-in Amplifier...

  • Page 81: Signal Inputs

    Display Off Operation Press the [Blank] key to operate with the front panel display and LEDs off. The SR865 is still operating, the outputs are active, data collection continues and the unit responds to interface commands.

  • Page 82: Standard Settings

    0.00% All Expands All Ratios None All Aux Outputs 0.000 V Display Green Channel X, Graph On Blue Channel Y, Graph On Yellow Channel R, Graph On θ, Graph On Orange Channel Screen Layout Trend Blank SR865 DSP Lock-in Amplifier...

  • Page 83: Signal Input

    The ac coupling option uses a high pass filter to pass signals above 160 mHz and attenuate signals at lower frequencies. ac coupling should be used at frequencies above 160 mHz whenever possible. At lower frequencies, dc coupling is required. ac SR865 DSP Lock-in Amplifier...
  • Page 84 The signal strength LEDs indicate how much of the A/D range is being used. The Signal Monitor on the rear panel is the amplifier output. The current range setting has no effect when the voltage input is selected. SR865 DSP Lock-in Amplifier...

  • Page 85: Input Overload

    The normal low pass filter is an RC filter. This is equivalent to the traditional filter found in analog lock-ins. To use advanced filters in place of the RC filters press and hold the [Slope/adv] key until LED turns on. Brief presses of [Slope/adv] cycles the number of poles Advanced SR865 DSP Lock-in Amplifier...
  • Page 86 In general, setting the sensitivity to display a reasonable amount of bar graph is sufficient for accurate synchronous filtering. If the synchronous filter overloads because of the sensitivity, the Sync warning is displayed with displays of X, Y, R or θ. SR865 DSP Lock-in Amplifier...
  • Page 87 (≥ period) will increase the settling time far beyond a period. [Sensitivity] The Sensitivity setting of the SR865 determines what input signal corresponds to 10 V full scale output for X, Y and R. For example, a Sensitivity of 100 mV means that a signal at f of 100 mVrms will result in a 10 V output of R.
  • Page 88 If the Sensitivity is set too low, the values will be overloaded (pinned) and no noise will be measured. In general, setting the Sensitivity to display a reasonable amount of bar graph is sufficient. SR865 DSP Lock-in Amplifier...

  • Page 89: Ch1 And Ch2 Outputs: Offset, Ratio And Expand

    CH1 and CH2 Outputs: Offset, Ratio and Expand Analog Outputs Analog voltages proportional to X, Y, R and θ can be output from the SR865. The X and Y rear panel outputs always output X and Y. The CH1 output voltage is proportional to either X or R.
  • Page 90 The strip charts do reflect the offsets however. See the SR865 Basics section for more information. Output [Select] This key selects the source for the CH1 (CH2) output BNC. CH1 can select either X or R.
  • Page 91 LED will light. Any corresponding displayed numeric value/bar graph will indicate ‘Scale’ in the display. The actual measurement is unaffected since it is done in floating point and has no overload. Data displayed in the strip chart will still be accurate. SR865 DSP Lock-in Amplifier...

  • Page 92: Reference

    Each of these parameters can be adjusted using the knobs and buttons in this section of the front panel. Touching one of these tiles brings up a numeric keypad for direct entry. SR865 DSP Lock-in Amplifier...
  • Page 93 When the source is External, the SR865 will phase lock to the external reference provided at the Ref In BNC. The SR865 will lock to frequencies between 0.001 Hz and 2.5 MHz. The external frequency is shown in the info bar. The <Frequency> knob has no effect on the external frequency.
  • Page 94 SR865’s internal reference frequency. This is achieved by connecting the f Reference output from the SR540 to the Ref In of the SR865. But instead of using this input as the external reference, the SR865 will servo the SR540 to lock the SR540 to the SR865 internal frequency.
  • Page 95 Chapter 3 Operation Make sure that the SR865 External Trig is set to Pos TTL and the Input is 1 MΩ. Adjust the SR865 internal frequency to a value that the SR540 can reach with the selected blade. The Phase setting in this screen is the ‘blade’ phase. This is the phase of the blade opening relative to the optical detector at the base of the chopper head.
  • Page 96 The SR865 has a 10 MHz TIMEBASE input and output on the rear panel. Apply a 10 MHz sine signal (1 Vrms) to the TIMEBASE input to lock the SR865’s timebase to an external 10 MHz timebase. The internal reference frequency of the SR865 is derived from this timebase.
  • Page 97 The harmonic number is shown in the info bar at the top of the screen. Touch this {Harm} tile to show the numeric entry screen. The SR865 can detect signals at harmonics of the reference frequency. The SR865 multiplies the input signal with digital sine waves at N×f .
  • Page 98 When the reference source is Internal or Dual, this is the excitation source provided by the SR865. When an external reference is used (or in Chop mode), this sine output provides a sine wave phase locked to the external reference.

  • Page 99: Display

    Big Numbers [Screen Shot] Pressing [Screen Shot] saves a screen shot to the USB memory stick as a .BMP file. Set the Print Mode in the system menu. Screen is an exact screen shot, Print replaces the SR865 DSP Lock-in Amplifier...
  • Page 100 Busy [Blank] Press the [Blank] key to operate with the front panel display and LEDs off. The SR865 is still operating, the outputs are active, data collection continues and the unit responds to interface commands. To change a setting, press [Blank] to return to normal operation, change the desired parameter, then press [Blank] again.

  • Page 101: Cursor

    The cursor is always active in the FFT screens. The amplitude and frequency readout is at the upper right of the graph. Use the <Cursor> knob to position the cursor. There is no relative cursor function SR865 DSP Lock-in Amplifier...
  • Page 102 Chapter 3 Touch in the vertical scale paleete to change the width of the cursor. In the FFT display, the wide cursors always find the peak within the cursor region. This makes reading an FFT much easier. SR865 DSP Lock-in Amplifier...

  • Page 103: Functions

    Note that the Sensitivity will affect analog outputs proportional to X, Y and R. not use [Auto Scale] if changes to the analog output scales cannot be tolerated in the experiment. [Save Recall] Press [Save Recall] to display the Save/Recall screen. SR865 DSP Lock-in Amplifier...
  • Page 104 Operation Chapter 3 The SR865 can store 8 complete setups. In addition the default setup can be recalled. Touch one of the 8 {Save} buttons to save a setup. Enter a name for this setup using the keypad. Touch {Confirm} to commit the current setup or {Cancel} to quit the operation.

  • Page 105: Interface And Data

    This does not affect the computer interface settings. [Save] The SR865 can save data files to a USB memory stick inserted into the front panel USB slot. Press [Save] to save the data points in the current strip chart to the memory stick. This file can be .CSV or .MAT file as selected in the system menu.

  • Page 106: Setup

    Set the End Mode to Once, and the scan stops at the end value and the strip chart is automatically paused. SR865 DSP Lock-in Amplifier...

  • Page 107: Aux Output

    LED back on. Alternatively, press and hold [Play Pause/reset] to return to the LED on state; this will also put newly changed scan parameters into effect. Ready [Aux Output] Press [Aux Output] to display the Aux Output screen. SR865 DSP Lock-in Amplifier...

  • Page 108: System Menu

    Operation Chapter 3 The SR865 has 4 Aux Outputs on the rear panel. Use this screen to set their levels. Touch one of the {Out n} buttons to select an aux output, then use the keypad to enter a value. The <Cursor> knob will also adjust the output value in this screen.

  • Page 109: General Settings

    The time and date are used to label data files and screen shots as well as saved settings. 10MHz Timebase The SR865 can accept an external 10 MHz timebase input on the rear panel. This allows the internal reference frequency of the SR865 to remain frequency and phase stable with other SR865 units on the same timebase.
  • Page 110 Determines the format of the data files that are produced when the [Save] button is pressed. Has no effect on screenshots. Format can be set to .CSV (comma-delimited ASCII text file) or .MAT (Matlab binary file). SR865 DSP Lock-in Amplifier...

  • Page 111: Ethernet Settings

    VXI-11 and Web Settings The SR865 allows computers to connect via VXI-11 from a range of Trusted IP addresses or Disabled altogether. Set the Trusted IP address using ‘*’ as a wildcard. This allows any computer on a specified subnet VXI-11 access.
  • Page 112 Choose Echo On/Off and the Receive/Transmit Terminators depending upon your host software requirements. Streaming Settings The SR865 can stream output values continuously over the ethernet interface to a host computer. It is the host computer’s responsibility to keep up, there is no retry on dropped packets.
  • Page 113 Chapter 3 Operation The SR865’s firmware can be updated via the USB memory stick. Follow the directions that accompany the update to prepare the memory stick. Insert the memory stick into the front panel and press {Update} to start the process.

  • Page 114: Rear Panel

    The RS-232 interface port is configured as a DCE. The baud rate and parity are set in the system menu (hold the [Calc/system] key). The number of data bits is always 8. USB Port The USB port allows a computer to control the SR865 via USB. The SR865 is a Test and Measurement Class instrument. Ethernet Port The Ethernet port allows a computer to control the SR865 via an ethernet network connection.

  • Page 115: Signal Monitor Output

    Operation Timebase In/Out Apply a 10 MHz sine signal (1 Vrms) to the TIMEBASE input to lock the SR865’s timebase to an external timebase. The internal reference frequency of the SR865 is derived from this timebase. When multiple SR865’s are locked to the same 10 MHz timebase, then harmonically related internal frequencies on different units will stay in phase indefinitely.

  • Page 116: Preamp Connector

    SR865 within the loop. The BlazeX output is always an RC filter (1 to 4 poles) regardless of the front panel Advanced Filter setting, and its maximum time constant is 10 ms.
  • Page 117 Chapter 3 Operation cables to connect the A output from the preamp to the A input of the SR865 and the B output from the preamp (preamp ground) to the B input of the SR865. Use A−B as the input configuration. Be sure to twist the A and B cables so that there is no differential noise pickup between the cables.

  • Page 119: Chapter 4 Programming

    (IEEE-488), USB or ethernet interfaces. Any computer supporting one of these interfaces may be used to program the SR865. All interfaces can receive commands at all times and the SR865 will send responses to the querying interface only. A few specialized commands such as interface status and data streaming are interface specific.
  • Page 120 Chapter 4 GPIB Interface Ready And Status The Interface Ready bit (bit 1) in the Serial Poll Status Byte signals that the SR865 is ready to receive and execute a command. When a command is received, this bit is cleared indicating that an operation is in progress.

  • Page 121: Command Syntax

    No space is allowed between the command and the ‘?’. Values returned by the SR865 are sent as a string of ASCII characters. If multiple queries are sent on one command line (separated by semicolons, of course) the responses will be returned as semicolon-separated strings.
  • Page 122 IVMD VOLT IVMD VOLTAGE These commands are all equivalent ways to set the input to current. IVMD 1 IVMD CURR IVMD CURRENT query always returns the setting index i (0 or 1 in this case). IVMD? SR865 DSP Lock-in Amplifier...
  • Page 123 Example Commands Set reference source to external RSRC 1 RSRC EXT Query the reference source RSRC ? Set the internal reference frequency to 10000 Hz FREQ 10E3 FREQ 10 KHZ FREQ 10000.0 Execute Auto Phase APHS SR865 DSP Lock-in Amplifier...

  • Page 124: Reference Commands

    , returns the internal reference frequency whenever the reference mode is either Internal, Dual, or Chop. The query returns the external frequency when operating in External mode. This behavior mirrors the value displayed in the info bar at the top of the display. SR865 DSP Lock-in Amplifier...
  • Page 125 The value of i is limited to 1 ≤ i ≤ 99. The actual detection frequency, when operating in dual reference mode, is × − × detect HARM HARMDUAL SR865 DSP Lock-in Amplifier...
  • Page 126 BLADEPHASE(?) { p } { UDEG | MDEG | DEG | URAD | MRAD | RAD } command sets the phase of the SR540 chopper blade. When BLADEPHASE p operating a single chopper, this has little effect since the SR865 will follow the chopper. If multiple SR865/SR540 systems are being used in a single experiment, BLADEPHASE can be used to modify the relative phase of the choppers.
  • Page 127 1 MΩ (i=1). Example Set the external reference input to 50 Ω REFZ 50 REFZ 50OHMS REFZ 0 Set the external reference input to 1 MΩ REFZ 1M REFZ 1MEG REFZ? Returns the external reference input i SR865 DSP Lock-in Amplifier...
  • Page 128 The levels may be programmed from −5.00 V to +5.00 V. Example PSTL 0, 1.23 V Set dc level preset L1 to 1.23 V PSTL 0, 1230 MV PSTL? 0 Returns the dc level preset L1 in Volts SR865 DSP Lock-in Amplifier...

  • Page 129: Signal Commands

    1 V (i=0), 300 mV (i=1), IRNG i 100 mV (i=2), 30 mV (i=3) or 10 mV (i=4). Example IRNG 1V Set the voltage input range to 1 V IRNG 1VOLT IRNG 0 IRNG? Returns the voltage input range i SR865 DSP Lock-in Amplifier...
  • Page 130 5 nV [fA] 200 μV [pA] 2 nV [fA] 100 μV [pA] 1 nV [fA] 50 μV [pA] 20 μV [pA] Example SCAL 6 Set the sensitivity to 10 mV [nA] SCAL? Returns the sensitivity i SR865 DSP Lock-in Amplifier...
  • Page 131 Returns the state of the advanced filter i ENBW? ENBW? query returns the equivalent noise bandwidth of the output filter, in hertz. Note that the effect of the filter is neglected by SYNC ENBW? Example ENBW? Returns the equivalent noise bandwidth, in hertz. SR865 DSP Lock-in Amplifier...

  • Page 132: Ch1/Ch2 Output Commands

    COFP? X OAUT [ X | Y | R | j ] command auto offsets X (j=0), Y (j=1), or R (j=2). This is the same as Auto OAUT j Offset in the offset keypad display. SR865 DSP Lock-in Amplifier...
  • Page 133 Expand             1.000 Example CRAT X, ON Set X ratio mode to on CRAT 0, 1 CRAT? 0 Returns the X ratio mode CRAT? X SR865 DSP Lock-in Amplifier...

  • Page 134: Aux Input And Output Commands

    1–4 on the rear panel. The voltage v can be set from –10.5 V to +10.5 V. Example AUXV 2, 678.9 MV Set aux out3 to 678.9 mV AUXV 2, 6.789E-1 AUXV 2, 0.6789 AUXV? 2 Returns the aux out3 voltage setting in Volts SR865 DSP Lock-in Amplifier...

  • Page 135: Auto Function Commands

    Auto Scale function. This command is the same as ASCL pressing the [Auto Scale] key. This automatically sets the sensitivity. Measurements with the synchronous filter on or measurements of Xnoise or Ynoise may take many time constants to return to their steady state values. SR865 DSP Lock-in Amplifier...

  • Page 136: Display Commands

    CDSP DAT2, IN2 Assign Aux In2 to data channel 2 (blue) CDSP 3, 15 Assign the Reference Frequency to data channel 4 (orange) CDSP DAT1, SAM Assign the Sine Out Amplitude to data channel 1 (green) SR865 DSP Lock-in Amplifier...
  • Page 137 “xxxxxxx” is the ccccc–byte binary image file itself. This binary image should be saved as a .BMP format file. Example GETSCREEN? Request a screen capture file The SR865 responds with #535219xxxxxxx corresponding to a 35219-byte .BMP file image (the “ xxxxxxx ” data).

  • Page 138: Strip Chart Commands

    DAT3 (orange) data channels. DAT4 Example GOFF DAT3, 0.1 Set the vertical offset for data channel 3 (yellow) to 0.1 GOFF 2, 0.1 GOFF? 2 Returns the vertical offset for data channel 3 (yellow) GOFF? DAT3 SR865 DSP Lock-in Amplifier...
  • Page 139 CGRF DAT2, ON Turn graphing on for data channel 2 (blue) CGRF 1, 1 CGRF 0, OFF Turn graphing off for data channel 1 (green) CGRF? 1 Returns data channel 2 (blue) graphing state i CGRF? DAT2 SR865 DSP Lock-in Amplifier...
  • Page 140 Each pixel represents data collected over the time elapsed for one pixel of horizontal scrolling (set by the GSPD command). CURBUG determines whether the cursor readout shows the mean, maximum, or minimum value of the data from within each pixel. SR865 DSP Lock-in Amplifier...
  • Page 141 This string is in the format 28Apr14,14:25:35.96 In this example, the date is 28 April 2014, and the time is 14:25:35.96 (2:25 PM). Performing the query when the display is not paused generates a CURDATTIM? parameter range error. SR865 DSP Lock-in Amplifier...
  • Page 142 GSPD chart). When the cursor is in relative mode, returns the interval between the CURINTERVAL? cursor position and the marker position. Performing the CURINTERVAL? query when the display is not paused generates a parameter range error. SR865 DSP Lock-in Amplifier...

  • Page 143: Fft Screen Commands

    Chapter 4 Programming FFT Screen Commands The SR865 has a basic FFT function accessable from the front panel by selecting the appropriate [Screen Layout] display (remotely, by setting ). A more complete discussion of FFT DLAY FFT DLAY BARFFT mode can be found in Appendix B .
  • Page 144 FCRW(?) { LIne | NARrow | WIde | i } FCRW i command sets the cursor width to line (i=0), narrow (i=1) or wide (i=2). Example FCRW NAR Set the cursor to narrow FCRW 1 FCRW? Returns the cursor width i SR865 DSP Lock-in Amplifier...
  • Page 145 FFT cursor readout (in dB). FCRY? FCRY? is a query only command. Note that only returns valid data when the SR865 display is set to FFT mode. FCRY? Example FCRY? Returns the FFT cursor amplitude value...

  • Page 146: Scan Commands

    During scans, however, it can be helpful to force the attenuators to remain in a fixed configuration, inhibiting the relay switching that would otherwise introduce transients in the sine output. SR865 DSP Lock-in Amplifier...
  • Page 147 SCNENBL(?) { OFF | ON | i } command turns scanning off (i=0) or on (i=1). This sets the scan SCNENBL i parameter to its begin value but does not start a scan. Example SCNENBL ON Turn scanning on SR865 DSP Lock-in Amplifier...
  • Page 148 3 digits or 0.1 mV, whichever is greater. The levels may be programmed from −5.00 V to +5.00 V. Example Set the begin reference dc level to −1.23 V SCNDC BEGIN, -1.23 SCNDC 0, -1230 MV SR865 DSP Lock-in Amplifier...
  • Page 149 −10.5 V to +10.5 V with 1 mV resolution. Example SCNAUX2 END, 4.567 Set the end AuxOut2 value to 4.567 V SCNAUX2 1, 4567 MV SCNAUX2? 1 Returns the end AuxOut2 value SR865 DSP Lock-in Amplifier...

  • Page 150: Data Transfer Commands

    (see ). The enumeration strings OUTP? may be used instead of the integer values for j, k, l. Example SNAP? 0,1,4 Returns the values of X, Y and Aux In1 SNAP? X, Y, IN1 SR865 DSP Lock-in Amplifier...
  • Page 151 The first value is X, the second is Y and the third is Aux In1. Not all parameters are measured at the same rate within the SR865. The external frequency, for example, is only measured every reference period (at low frequencies).

  • Page 152: Data Capture Commands

    Data Capture Commands Overview The SR865 can capture data points in an internal capture buffer. This can be up to 1 Mpoints of (X), 512 kpoints of either (X,Y) or (R,θ) or 256 kpoints of (X,Y,R,θ). Data points are stored as floating point values (4 bytes per data point). The capture buffer is made of 2 kbyte blocks (512 total data points per block), but specified in terms of its overall length in kbytes—which must therefore always be an even number of kbytes.
  • Page 153 Hardware Triggering In many situations, it is important to synchronize the beginning of data acquisition to an external event. The SR865 supports this with the rear-panel TRIG IN input BNC. When configured for hardware trigger by the CAPTURESTART command, the lock-in will wait for a falling edge at the BNC input before beginning the capture.
  • Page 154 (78125)/(2 ) = 4882.8125 Hz. Note that if the time constant is modified during a capture, the sampling rate will change mid-capture. query returns the actual capture rate in Hz (not the value n). CAPTURERATE? SR865 DSP Lock-in Amplifier...
  • Page 155 This is a query only CAPTURESTAT? command. The returned integer is a 3-bit binary encoded word Weight Definition Capture currently in progress Capture triggered, either by TTL or remote command Capture wrapped SR865 DSP Lock-in Amplifier...
  • Page 156 The maximum length j is 64 (corresponding to 64 kbytes). Both parameters i and j must be provided. Capture must be stopped when executing CAPTUREGET? or a range error is generated. The binary block query response is in the following format: #nccccxxxxxxx SR865 DSP Lock-in Amplifier...
  • Page 157 “xxxxxxx” is the cccc–byte binary data. Data is packed as 4-byte (32-bit) single precision floating point binary, in little endian format. Example CAPTUREGET? 0,32 returns a binary block with 32 kbytes of capture data SR865 DSP Lock-in Amplifier...

  • Page 158: Data Streaming Commands

    See Appendix D for more detailed information about data streaming. Data Streaming The SR865 can stream data points continuously in real time over its ethernet interface. This stream can be X values, (XY) or (Rθ) values, or (XYRθ) values. Streaming more values uses more ethernet bandwidth.
  • Page 159 (and at the same times).The maximum streaming rate is determined by the time constant of the SR865. Shorter time constants allow faster streaming rates, and if sync filter is on, shorter sync filter periods allow faster streaming rates, up to a limit of 1.25 MHz.
  • Page 160 (i=0) or on (i=1). ). To enable STREAM i streaming, the command must be sent over VXI-11 from the receiving computer. This determines the IP address that the data is sent to. Example STREAM 1 Turn ethernet streaming on STREAM ON SR865 DSP Lock-in Amplifier...

  • Page 161: System Commands

    BlazeX output to blazex (i=0), bipolar sync (i=1) or unipolar (positive) sync (1=2). Example BLAZEX UNI Set the BlazeX output to unipolar sync BLAZEX 2 BLAZEX? Returns the BlazeX output selection i SR865 DSP Lock-in Amplifier...
  • Page 162 8 characters, the suffix will be set to 0. For example, if the file name prefix is “SR865_” (6 characters) then can set the suffix to 0–99 (limited to 2 FNUM i characters). Example FNUM 12 Set the file name suffix to 12 FNUM? Returns the file name suffix SR865 DSP Lock-in Amplifier...
  • Page 163 USB port. SVDT command is the same as pressing the [Data Save] key. The file save will take SVDT some time to complete. A USB memory stick must already be in the front panel USB port. SR865 DSP Lock-in Amplifier...

  • Page 164: Interface Commands

    If i=0 the SR865 is set to LOCAL, if LOCL i=1 the SR865 will go REMOTE, and if i=2 the SR865 will go into LOCAL LOCKOUT. The states duplicate the GPIB local/remote states. In the LOCAL state both command execution and keyboard input are allowed.
  • Page 165 Local state. The default mode is Overide Remote On. To lock-out the front panel, use the OVRM 0 command before local lock-out. Example OVRM 0 Set Overide Remote to No OVRM? Returns the Overide Remote state i SR865 DSP Lock-in Amplifier...

  • Page 166: Status Reporting Commands

    The value is STB? returned as a decimal number from 0 to 255. The * command queries the value STB? j (0 or 1) of bit j (0–7). Reading this byte has no effect on its value. SR865 DSP Lock-in Amplifier...
  • Page 167 Set bits 1 and 8 in the lock-in status enable register LIAE 8, 1 Set bit 8 in the lock-in status enable register LIAE? Returns decimal value of the lock-in status enable register LIAE? 8 Returns bit 8 of the lock-in status enable register SR865 DSP Lock-in Amplifier...
  • Page 168 External reference unlocked Input range unused unused unused Data Channel 1 scale Data Channel 2 scale 1024 Data Channel 3 scale 2048 Data Channel 4 scale Example CUROVLDSTAT? Returns decimal value of the overload status word SR865 DSP Lock-in Amplifier...

  • Page 169: Status Byte Definitions

    When reading the status byte using a GPIB serial poll, the SRQ bit signals that the SR865 is requesting service. The SRQ bit will be set (1) the first time the SR865 is polled following a service request. The GPIB serial poll automatically clears the service request SRQ.
  • Page 170 A command cannot execute correctly or a parameter is out of range. An illegal command is received. Set by any user front panel action. Set by power-on. The bits in this register remain set until cleared by reading them or by the *CLS command. SR865 DSP Lock-in Amplifier...
  • Page 171 VXI-11 error. GPIB GPIB fast data transfer mode aborted. USBDEV USB device error (interface error). USBHOST USB host error (memory stick error). The Error Status bits stay set until cleared by reading or by the command. *CLS SR865 DSP Lock-in Amplifier...

  • Page 173: Appendix A Advanced Filters

    RC filter! The Gaussian filter has better rejection of high frequencies than the RC filter. The Gaussian filter has a constant 11.6 dB more rejection of high frequencies (per stage) than SR865 DSP Lock-in Amplifier...
  • Page 174 50% greater than the RC. This means signals near dc might not be attenuated as much as the RC filter. The SR865 implements multiple poles of FIR filtering by simply adding identical poles in succession. Because the Gaussian filter is computationally intensive it is not available for time constants longer than 3s.
  • Page 175 The chart below summarizes the noise bandwidth of the different filters. Note that for a single stage, all 3 filters are designed with the same noise bandwidth. −1 Equivalent Noise Bandwidth (fraction of f =(2π×time constant) Stages Gaussian Linear Phase 0.79 0.93 0.59 0.94 0.83 0.81 0.78 SR865 DSP Lock-in Amplifier...
  • Page 176 Each stage of the Gaussian filter has the same ENBW as a single stage of the RC filter. Each stage of the Linear Phase filter has the same roll-off as a single stage of the RC filter. SR865 DSP Lock-in Amplifier...
  • Page 177 These graphs illustrate the step response of the different filters at 12 and 24 dB/oct. The advanced filters always settle in less time than the RC filters. Gaussian filters have increasing latency with more stages. Linear Phase filters have ≤ 1% overshoot. SR865 DSP Lock-in Amplifier...
  • Page 178 Advanced Filters Appendix A SR865 DSP Lock-in Amplifier...

  • Page 179: Appendix B The Fft Display

    The FFT display takes a time varying signal, like you would see on an oscilloscope trace, and computes its frequency spectrum. In the SR865, this signal is either the output of the input amplifier (Raw ADC) or the output of the PSD (Post Mixer or Post Filter).
  • Page 180 FFT’s in the SR865 The SR865 FFT display is not a replacement for a full FFT spectrum analyzer instrument. It is intended to give the user an overview of the spectrum of the input signal or the output of the PSD and time constant filters.
  • Page 181 The FFT Display Using the FFT Display This example is designed to use the SR865 internal oscillator and an external signal source to explore some the FFT display. You will need a synthesized function generator capable of providing a 100 mVrms sine wave at 100.000 kHz, BNC cables and a terminator appropriate for the generator function output.
  • Page 182 Touch the {Hz/div} tile along the bottom to The FFT frequency span can be reduced to display the span up/down buttons. provide better frequency resolution. When the FFT source is Raw ADC, the FFT display is SR865 DSP Lock-in Amplifier...
  • Page 183 1 ms. the maximum frequency span is set by the time constant. The shorter the time constant, the higher the maximum frequency span. This is because the PSD output is frequency limited by SR865 DSP Lock-in Amplifier...
  • Page 184 Move the cursor to the signal peak. from its value at 100.000 kHz. The readout is about −36 dB. This is because the lock-in time constant acts like a bandpass filter in the spectrum centered at f (center). SR865 DSP Lock-in Amplifier...
  • Page 185 This is the effect of the steeper time constant filter. At the lock-in output, the 1 kHz output is attenuated further by this filter. This example has provided a quick overview of the FFT display in the SR865. SR865 DSP Lock-in Amplifier...
  • Page 186 The FFT Display Appendix B SR865 DSP Lock-in Amplifier...

  • Page 187: Appendix C Using The Webserver

    Appendix C Using the Webserver The SR865 webserver provides a quick start to interfacing via ethernet. Make sure to set the IP address, subnet mask and gateway address for your network in the system ethernet menu. Be sure to enable the webserver in the VXI-11 & Web settings. Press and hold [Calc/system] to access the system menu.
  • Page 188 Using the Webserver Appendix C Click the Monitor Output tab to display a simple readout of the 4 data channels. SR865 DSP Lock-in Amplifier...

  • Page 189: Appendix D Data Streaming And Capture

    You might want to send fewer data bytes per packet if the sample rate is low and you want packets to arrive with less latency. Otherwise, larger data sizes are recommended as they have less overhead and are more bandwidth-efficient. Header Data 4 bytes 128-1024 bytes Big-endian Big- or little-endian SR865 DSP Lock-in Amplifier...
  • Page 190 XYRθ data is recorded in that order, followed by the next sample of XYRθ. As an example, let's say the packet contains floating-point XYRθ data: Data bytes Byte … θ (0) Data X(0) Y(0) R(0) X(1) … SR865 DSP Lock-in Amplifier...
  • Page 191 Gigabit ethernet to work. Fast (100Mb/s) ethernet is not sufficient to support the maximum data rate. At high data rates, we recommend putting the SR865 and the receiving computer on the same dedicated network. This reduces traffic congestion for other users, and reduces the chance of dropped packets.

  • Page 193: Appendix E Dual Reference Detection

    This signal can be measured using 2 lock-in amplifiers. The signal is input to the first lock-in which is set to detect at ω . The output of this lock-in will contain sum and difference components from both signal components. One of these will be SR865 DSP Lock-in Amplifier...
  • Page 194 The expermental signal could be a fast modulation of a slow carrier or vice versa. The SR865 does not require that one of the frequencies be much greater than the other. The two frequencies can be very close together. The only requirement is that the time constant remove all output components other than dc.

  • Page 195: Appendix F Fuse Installation And Ac Line Select

    Appendix F Fuse Installation and ac Line Select The SR865 operates from 100 V, 120 V, 220 V, or 240 V nominal ac power source having a line frequency of 50 or 60 Hz, and accommodates both North American single- fuse or metric dual-fuse operation.
  • Page 196 Appendix F ac Voltage Selector The SR865 line voltage selection is indicated by the white pin visible at the right hand edge of the power entry module. In the image below, the line voltage selection is showing 120 V. Note that on some units (as pictured below), the 220 V selection can be labeled 230 V;...
  • Page 197 2. Insert a small screwdriver at the point “X” as shown 3. Gently lift the entire door back, away from the rear panel of the SR865. Lift away approximately 0.25" (6 mm). Once lifted, the door will pivot on its hinges to expose the fuse holder.
  • Page 198 6. Replace fuse holder into housing, fuse first. Be sure to align the circular alignment opening on the fuse holder with the orienting pin within the power entry module. 7. Swing and push to snap the door back in place. SR865 DSP Lock-in Amplifier...

  • Page 199: Appendix G Performance Tests

    Throughout this section, it will be necessary to preset the lock-in into a known default state. To do this, press [Save Recall], then touch {Recall default}. Touch {Confirm} to reset the SR865 to its default settings. Each test generally starts with a preset. This procedure will be referred to as {PRESET}.

  • Page 200: Necessary Equipment

    Impedance Test Record Make a copy of the SR865 Performance Test Record at the end of this section. Fill in the results of the tests on this record. This record will allow you to determine whether the tests pass or fail and also to preserve a record of the tests.
  • Page 201 After checking the setup, repeat the test from the beginning to make sure that the test was performed correctly. If the test continues to fail, contact Stanford Research Systems for further instructions. Make sure that you have the unit's serial number and firmware revision code handy. Have the test record on hand as well.
  • Page 202 Select DC coupling. 5) Wait 10 seconds, then record the reading of R (yellow). 6) This completes the dc offset test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...

  • Page 203: Common Mode Rejection

    5) Record the value of R (yellow). 6) This completes the CMRR measurement test. The common mode rejection is 20log(1.0/R) where R is in Volts. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 204 100 mV 30 mV 10.0 mV 0.01 1.00 mV 0.01 a) Use the SR865 front panel to make the following adjustments Touch {Ampl} to display the sine out amplitude keypad Enter the amplitude from the table. SR865 DSP Lock-in Amplifier...

  • Page 205: Performance Tests

    Repeat steps 6a and 6b for all frequencies in the table. 7) This completes the sine output amplitude accuracy and frequency response test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 206 Connect the Sine Out+ to the Voltage A input of the SR865 using a 1 meter BNC cable, with the precision 50Ω terminator at the A input BNC. This test only uses ONE Sine Out BNC. This means that each measurement will nominally be 50% of the programmed sine amplitude.
  • Page 207 Repeat steps 4b and 4c for all of the frequencies listed. 5) This completes the amplitude accuracy and frequency response test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 208 Connect the Sine Out+ to the Voltage A input of the SR865 using a 1 meter BNC cable, with the precision 50Ω terminator at the A input BNC. This test only uses ONE Sine Out BNC. This means that each measurement will nominally be 50% of the programmed sine amplitude.
  • Page 209 (fext), but is more easily read from the large green Fe display. Record the frequency reading. 5) This completes the frequency accuracy test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 210 Sine Out. Setup Connect the Sine Out+ to the Voltage A input of the SR865 using a 24-inch BNC cable, with the precision 50Ω feedthrough terminator at the A input BNC. This test only uses ONE Sine Out BNC.
  • Page 211 Wait for the readings to stabilize. Record the value of θ (orange). c) Repeat steps 4a and 4b for all frequencies in the table. 5) This completes the phase accuracy test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 212 3) For each Aux Output (1, 2, 3 and 4), repeat steps 3a through 3e. a) Connect the Aux Output (on the rear panel) to the DVM. b) Use the front panel to make the following adjustments SR865 DSP Lock-in Amplifier...
  • Page 213 Record the Aux Input (1, 2, 3 or 4) value. 6) This completes the dc outputs and inputs test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 214 3) Wait at least 1 minute for the reading of Xnoise (green) to stabilize. Record the value of Xnoise. 4) This completes the noise test. Enter the results of this test in the test record at the end of this section. SR865 DSP Lock-in Amplifier...
  • Page 215 Performance Test Record SR865 Performance Test Record Serial Number _____________________ Tested By __________________________ Firmware Revision _________________ Date ______________________________ Equipment Used __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ dc Offset Input Coupling Reading Upper Limit _______ 0.500 mV _______ 0.500 mV Common Mode Rejection...
  • Page 216 −100.00 9.90 V _______ 10.10 V −50.00 4.95 V _______ 5.05 V −0.010 V 0.00 _______ 0.010 V −5.05 V −4.95 V 50.00 _______ −10.10 V −9.90 V 100.00 _______ Test Record sheet 2 of 4 SR865 DSP Lock-in Amplifier...
  • Page 217 Reading Upper Limit −10.000 AUX IN 1 -10.10 V _______ -9.90 V −5.000 -5.05 V _______ -4.95 V −0.010 V 0.000 _______ 0.010 V 5.000 4.95 V _______ 5.05 V 10.000 9.90 V _______ 10.10 V SR865 DSP Lock-in Amplifier...
  • Page 218 Frequency Input Range Sensitivity Reading Upper Limit 1 kHz 100 nV 100 nV _______ 5.6 nV (*) (*) noise limit corresponds to 5 nV/√Hz, with time constant filter ENBW=1.25 Hz. Test Record sheet 4 of 4 SR865 DSP Lock-in Amplifier...

  • Page 219: Appendix H Circuit Description

    U204, which also provides CMRR trimming for the voltage preamp front-end. Programmable gain blocks around U402 and U404 implement the SR865 Input Range setting, with U406 driving the rear panel Signal Mon after all programmable gain is added. The main analog signal is driven differentially through R428 and R429 to the shielded twisted pair interconnect J401 leading to the motherboard.
  • Page 220 ±16V to ±5V with linear regulators U207 and U208. Sine Output The SR865 sine output module provides filtering, attenuation, and dc level generation for the differential sine output. A passive 7th order differential Cauer low pass filter is implemented with components L102–L107, C101–C107, C112–C114.
  • Page 221 “drifting away” during testing before connection to their loads. Probing of the output voltage levels is best accomplished from test point array TP1–TP20; these test points are protected through 4.7 kΩ resistors to avoid arcing if accidentally shorted. SR865 DSP Lock-in Amplifier...
  • Page 222 Circuit Description Appendix H Partial schematics follow this page. SR865 DSP Lock-in Amplifier...

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