TABLE OF CONTENTS Additional Menus 4-20 GENERAL INFORMATION Entry Keys 4-20 Safety and Preparation for Use 1-3 START/CONT and PAUSE/RESET 4-20 Specifications 1-5 CURSOR 4-21 Abridged Command List 1-7 ACTIVE DISPLAY 4-21 MARK 4-21 GETTING STARTED CURSOR MAX/MIN 4-22 Your First Measurements 2-1 AUTO RESERVE 4-22 The Basic Lock-in 2-3 AUTO GAIN 4-22 Displays and Traces 2-7 AUTO PHASE 4-22 Outputs, Offsets and Expands 2-13 AUTO SETUP 4-22 Scans and Sweeps
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Table of Contents Interface Ready and Status 6-2 SERVICE GET (Group Execute Trigger) 6-2 Circuit Boards 8-1 Adjusting DC Offset and CMRR 8-3 DETAILED COMMAND LIST 6-3 Adjusting Notch Filters 8-6 Reference and Phase 6-4 Input and Filter 6-6 CIRCUITRY Gain and Time Constant 6-7 Circuit Boards 9-1 Output and Offset 6-9 Video Driver and CRT 9-1 Trace and Scan 6-10 CPU Board 9-3 Display and Scale 6-
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SAFETY AND PREPARATION FOR USE WARNING Dangerous voltages, capable of causing injury or death, are present in this instrument. Use extreme caution whenever the instrument covers are removed. Do not remove the covers while the unit is plugged into a live outlet. CAUTION outlet which has a properly connected protective ground. This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the SERVICE wrong AC line voltage or if the wrong fuse is installed. Do not attempt to ser
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1-4
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SR850 DSP LOCK-IN AMPLIFIER SPECIFICATIONS SIGNAL CHANNEL Voltage Inputs Single-ended (A) or differential (A-B). 6 8 Current Input 10 or 10 Volts/Amp. Full Scale Sensitivity 2 nV to 1 V in a 1-2-5-10 sequence (expand off). Input Impedance Voltage: 10 MΩ+25 pF, AC or DC coupled. Current: 1 kΩ to virtual ground. Gain Accuracy ±1% from 20°C to 30°C (notch filters off), ±0.2% typical. Input Noise 6 nV/√Hz at 1 kHz (typical). Signal Filters 60 (50) Hz and 120(100) Hz notch filters (Q=4). CMRR 100 dB
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SR850 DSP Lock-In Amplifier INPUTS AND OUTPUTS 2 Channel 1 Output X, R, θ, or Trace 1-4. Traces are defined as A•B/C or A•B/C where A, B, and C are selected from the quantities Unity, X, Y, R, θ, Xnoise, Ynoise, Rnoise, Aux Inputs 1 through 4, or Frequency. Output Voltage: ±10 V full scale. 10 mA max output current. 2 Channel 2 Output Y, R, θ, or Trace 1-4. Traces are defined as A•B/C or A•B/C where A, B, and C are selected from the quantities Unity, X, Y, R, θ, Xnoise, Ynoise, Rnoise, Aux Inpu
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SR850 DSP Lock-In Amplifier COMMAND LIST VARIABLES i,j,k,l,m Integers f Frequency (real) x,y,z Real Numbers s String REFERENCE and PHASE page description PHAS (?) {x} 6-4 Set (Query) the Phase Shift to x degrees. FMOD (?) {i} 6-4 Set (Query) the Reference Source to Internal (0), Sweep (1) , or External (2). FREQ (?) {f} 6-4 Set (Query) the Reference Frequency to f Hz.Set only in Internal reference mode. SWPT (?) {i} 6-4 Set (Query) the Internal Sweep Type to Linear (0) or logarithmic (1). SLLM
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SR850 DSP Lock-In Amplifier DTRC (?) i {, j} 6-11 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Trace to trace j (1,2,3,4). DSCL (?) {x} 6-11 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Range to x. DOFF (?) {x} 6-11 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Center value to x. DHZS (?) {i} 6-12 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Horizontal Scale to 2 ms (0) through 200 ks (32) per div. RBIN? i 6-12 Query the bin number a
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SR850 DSP Lock-In Amplifier RDAT 6-18 Recall the Trace Data from the file specified by FNAM to the active display's trace buffer. RSET 6-18 Recall the Settings from the file specified by FNAM. SETUP page description OUTX (?) {i} 6-19 Set (Query) the Output Interface to RS232 (0) or GPIB (1). OVRM (?) {i} 6-19 Set (Query) the GPIB Overide Remote state to Off (0) or On (1). KCLK (?) {i} 6-19 Set (Query) the Key Click to Off (0) or On (1). ALRM (?) {i} 6-19 Set (Query) the Alarms to Off (0) or On (
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SR850 DSP Lock-In Amplifier INTERFACE page description *RST 6-26 Reset the unit to its default configurations. *IDN? 6-26 Read the SR850 device identification string. LOCL(?) {i} 6-26 Set (Query) the Local/Remote state to LOCAL (0), REMOTE (1), or LOCAL LOCKOUT (2). OVRM (?) {i} 6-26 Set (Query) the GPIB Overide Remote state to Off (0) or On (1). TRIG 6-26 Software trigger command. Same as trigger input. STATUS page description *CLS 6-27 Clear all status bytes. *ESE (?) {i} {,j} 6-27 Set (Query)
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GETTING STARTED YOUR FIRST MEASUREMENTS The sample measurements described in this section are designed to acquaint the first time user with the SR850 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. It is highly recommended that the first time user step through some or all of these exercises before attempting to perform an actual experiment. The experimental
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Getting Started 2-2
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The Basic Lock-in THE BASIC LOCK-IN This measurement is designed to use the internal oscillator to explore some of the basic lock-in functions. You will need BNC cables. Specifically, you will measure the amplitude of the Sine Out at various frequencies, sensitivities, time con- stants and phase shifts. The "normal" lock-in display will be used throughout this exercise. 1. Disconnect all cables from the lock-in. Turn When the power is turned on with the backspace the power on while holding down
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The Basic Lock-in 5. Press the softkey. This adds 90° to the reference phase shift. The value of X drops to zero and Y becomes minus the magnitude (-1.000 V). Press the softkey. Highlight the phase shift. Use the knob to adjust the phase shift until Y The knob can be used to adjust parameters which is zero and X is equal to the positive are continuous, such as phase, amplitude and fre- amplitude. quency. The final phase value should be close to zero again. Press [9] [0] [
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The Basic Lock-in that the measured magnitude (R) is a sizable per- centage of full scale. 9. Press Highlight the full scale sensitivity. Use the knob to change the sensitivity to Parameters which are discrete values, such as 50 mV. sensitivity and time constant, can only be changed with the knob. Numeric entry is not allowed for Change the sensitivity back to 20 mV. these parameters. 10. Press
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The Basic Lock-in 13. Press [GAIN/TC] Display the Gain and Time Constant menu again. Press to select <200 Hz. This turns on synchronous filtering whenever the detection frequency is below 200 Hz. Synchronous filtering effectively removes output components at multiples of the detection frequen- cy. At low frequencies, this filter is a very effective way to remove 2f without requiring extremely long time constants. The outputs are now very quiet and steady, even though the time cons
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Displays and Traces DISPLAYS and TRACES This measurement is designed to use the internal oscillator and an external signal source to explore some of the display types. You will need a synthesized function generator capable of providing a 100 mVrms sine wave at 1.000 kHz (the DS345 from SRS will suffice), BNC cables and a terminator appropriate for the gener- ator function output. Specifically, you will display the lock-in outputs when measuring a signal close to, but not equal to, the inter- na
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Displays and Traces Press Highlight the internal oscillator frequency. Use the knob to change the frequency to By setting the lock-in reference 0.2 Hz away from 999.80 Hz. the signal frequency, the X and Y outputs are 0.2 Hz sine waves (difference between reference and signal frequency). The X and Y output dis- plays should now oscillate at about 0.2 Hz (the accuracy is determined by the crystals of the gen- erator and the lock-in). 4. Press [DISPLAY/SCALE] Display the Display a
