Stanford Research Systems SR850 User manual

MODEL SR850
DSP Lock-In Amplifier
1290-D Reamwood Avenue
Sunnyvale, California 94089
Phone: [phone] • Fax: [phone]
email: [email protected] • www.thinkSRS.com
Copyright © 1992 by SRS, Inc.
All Rights Reserved.
Revision 2.0 (01/2009)
Stanford Research Systems

TABLE OF CONTENTS
1-1
GENERAL INFORMATION
Safety and Preparation for Use 1-3
Specifications 1-5
Abridged Command List 1-7
GETTING STARTED
Your First Measurements 2-1
The Basic Lock-in 2-3
Displays and Traces 2-7
Outputs, Offsets and Expands 2-13
Scans and Sweeps 2-17
Using the Disk Drive 2-23
Aux Outputs and Inputs 2-31
Trace Math 2-35
SR850 BASICS
What is a Lock-in Amplifier? 3-1
What Does a Lock-in Measure? 3-3
The SR850 Functional Diagram 3-5
Reference Channel 3-7
Phase Sensitive Detectors 3-9
Time Constants and DC Gain 3-11
DC Outputs and Scaling 3-13
Dynamic Reserve 3-17
Signal Input Amplifier and Filters 3-19
Input Connections 3-21
Intrinsic (Random) Noise Sources 3-23
External Noise Sources 3-25
Noise Measurements 3-27
OPERATION
FRONT PANEL 4-1
Power On/Off and Power On Tests 4-1
Video Display 4-1
Soft Keys 4-2
Keypad 4-2
Spin Knob 4-2
Disk Drive 4-2
Front Panel BNC Connectors 4-2
SCREEN DISPLAY 4-5
Default Display 4-5
Data Traces 4-6
Single/Dual Trace Displays 4-7
Bar Graphs 4-9
Polar Graphs 4-10
Strip Charts 4-11
Trace Scans, Sweeps and Aliasing 4-13
Settings and Input/Output Monitor 4-15
Menu Display 4-15
Status Indicators 4-16
KEYPAD 4-19
Normal and Alternate Keys 4-19
Menu Keys 4-19
Additional Menus 4-20
Entry Keys 4-20
START/CONT and PAUSE/RESET 4-20
CURSOR 4-21
ACTIVE DISPLAY 4-21
MARK 4-21
CURSOR MAX/MIN 4-22
AUTO RESERVE 4-22
AUTO GAIN 4-22
AUTO PHASE 4-22
AUTO SETUP 4-22
AUTOSCALE 4-22
PRINT to a PRINTER 4-23
PRINT to a FILE 4-23
HELP 4-23
LOCAL 4-23
REAR PANEL 4-25
Power Entry Module 4-25
IEEE-488 Connector 4-25
RS232 Connector 4-25
Parallel Printer Connector 4-25
PC Keyboard Connector 4-25
Rear Panel BNC Connectors 4-26
Aux Inputs (A/D Inputs) 4-26
Aux Outputs (D/A Outputs) 4-26
X and Y Outputs 4-26
Signal Monitor Output 4-26
Trigger Input 4-27
TTL Sync Output 4-27
Preamp Connector 4-27
USING SRS PREAMPS 4-27
MENUS
Menu Guide 5-1
Default Settings 5-2
Reference and Phase Menu 5-3
Input and Filters Menu 5-7
Gain and Time Constant Menu 5-9
Output and Offset Menu 5-15
Trace and Scan Menu 5-17
Display and Scale Menu 5-21
Aux Outputs Menu 5-25
Cursor Setup Menu 5-29
Edit Mark Menu 5-31
Math Menu 5-33
Disk Menu 5-41
System Setup Menu 5-49
PROGRAMMING
GPIB Communications 6-1
RS232 Communications 6-1
Status Indicators and Queues 6-1
Command Syntax 6-1

Table of Contents
1-2
Interface Ready and Status 6-2
GET (Group Execute Trigger) 6-2
DETAILED COMMAND LIST 6-3
Reference and Phase 6-4
Input and Filter 6-6
Gain and Time Constant 6-7
Output and Offset 6-9
Trace and Scan 6-10
Display and Scale 6-11
Cursor 6-13
Mark 6-14
Aux Input and Output 6-15
Math 6-16
Store and Recall 6-18
Setup 6-19
Print and Plot 6-21
Front Panel and Auto Functions 6-22
Data Transfer 6-23
Interface 6-28
Status Reporting 6-29
STATUS BYTE DEFINITIONS 6-30
Serial Poll Status Byte 6-30
Service Requests 6-31
Standard Event Status Byte 6-31
LIA Status Byte 6-32
Error Status Byte 6-32
PROGRAM EXAMPLES
Microsoft C, Nationall Instr GPIB 6-33
QUICKBASIC, Nationall Instr GPIB 6-39
TESTING
Introduction 7-1
Preset 7-1
Serial Number 7-1
Firmware Revision 7-1
General Installation 7-2
Necessary Equipment 7-3
If A Test Fails 7-3
PERFORMANCE TESTS
Self Tests 7-5
DC Offset 7-7
Common Mode Rejection 7-9
Amplitude Accuracy and Flatness 7-11
Amplitude Linearity 7-13
Frequency Accuracy 7-15
Phase Accuracy 7-17
Sine Output Amplitude 7-19
DC Outputs and Inputs 7-21
Input Noise 7-23
PERFORMANCE TEST RECORD 7-25
SERVICE
Circuit Boards 8-1
Adjusting DC Offset and CMRR 8-3
Adjusting Notch Filters 8-6
CIRCUITRY
Circuit Boards 9-1
Video Driver and CRT 9-1
CPU Board 9-3
Power Supply Board 9-5
DSP Logic Board 9-7
Analog Input Board 9-9
PARTS LISTS
Power Supply Board 9-11
DSP Logic Board 9-13
Analog Input Board 9-20
CPU Board 9-27
Chassis Assembly 9-32
Miscellaneous 9-35
SCHEMATIC DIAGRAMS
CPU Board
Power Supply Board
DSP Logic Board
Analog Input Board

SAFETY AND PREPARATION FOR USE
CAUTION
This instrument may be damaged if operated
with the LINE VOLTAGE SELECTOR set for the
wrong AC line voltage or if the wrong fuse is
installed.
LINE VOLTAGE SELECTION
The SR850 operates from a 100V, 120V, 220V, or
240V nominal AC power source having a line fre-
quency of 50 or 60 Hz. Before connecting the pow-
er cord to a power source, verify that the LINE
VOLTAGE SELECTOR card, located in the rear
panel fuse holder, is set so that the correct AC in-
put voltage value is visible.
Conversion to other AC input voltages requires a
change in the fuse holder voltage card position
and fuse value. Disconnect the power cord, open
the fuse holder cover door and rotate the fuse-pull
lever to remove the fuse. Remove the small print-
ed circuit board and select the operating voltage
by orienting the printed circuit board so that the
desired voltage is visible when pushed firmly into
its slot. Rotate the fuse-pull lever back into its nor-
mal position and insert the correct fuse into the
fuse holder.
LINE FUSE
Verify that the correct line fuse is installed before
connecting the line cord. For 100V/120V, use a 1
Amp fuse and for 220V/240V, use a 1/2 Amp fuse.
LINE CORD
The SR850 has a detachable, three-wire power
cord for connection to the power source and to a
protective ground. The exposed metal parts of the
instrument are connected to the outlet ground to
protect against electrical shock. Always use an
outlet which has a properly connected protective
ground.
SERVICE
Do not attempt to service or adjust this instrument
unless another person, capable of providing first
aid or resuscitation, is present.
Do not install substitute parts or perform any unau-
thorized modifications to this instrument. Contact
the factory for instructions on how to return the in-
strument for authorized service and adjustment.
FURNISHED ACCESSORIES
- Power Cord
- Operating Manual
ENVIRONMENTAL CONDITIONS
OPERATING
Temerpature: +10° C to +40° C
(Specifications apply over +18° C to +28° C)
Relative Humidity: <90% Non-condensing
NON-OPERATING
Temperature: -25° C to 65° C
Humidity: <95% Non-condensing
WARNING REGARDING USE WITH PHOTO-
MULTIPLIERS AND OTHER DETECTORS
The front end amplifier of this instrument is easily
damaged if a photomultiplier is used improperly
with the amplifier. When left completely untermi-
nated, a cable connected to a PMT can charge to
several hundred volts in a relatively short time. If
this cable is connected to the inputs of the SR850
the stored charge may damage the front-end op
amps. To avoid this problem, always discharge the
cable and connect the PMT output to the SR850
input before turning the PMT on.
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.
1-3

1-4

SR850 DSP LOCK-IN AMPLIFIER
1-5
SPECIFICATIONS
SIGNAL CHANNEL
Voltage Inputs Single-ended (A) or differential (A-B).
Current Input 106or 108Volts/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 kΩto 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 at 10 kHz (DC Coupled), decreasing by 6 db/octave above 10 kHz
Dynamic Reserve Greater than 100 dB (with no signal filters).
Harmonic Distortion <-90 dB to 10 kHz, <-80 dB to 100 kHz.
REFERENCE CHANNEL
Frequency Range 1 mHz to 102 kHz
Reference Input TTL (rising or falling edge) or Sine.
Sine input is1 MΩ, AC coupled (>1 Hz). 400 mV pk-pk minimum signal.
Phase Resolution 0.001°
Absolute Phase Error <1°
Relative Phase Error <0.001°
Orthogonality 90° ± 0.001°
Phase Noise External synthesized reference: 0.005° rms at 1 kHz, 100 ms, 12 dB/oct.
Internal reference: crystal synthesized, <0.0001° rms at 1 kHz.
Phase Drift <0.01°/°C below 10 kHz
<0.1°/°C to 100 kHz
Harmonic Detect Detect at Nxf where N<32767 and Nxf<102 kHz.
Acquisition Time (2 cycles + 5 ms) or 40 ms, whichever is greater.
DEMODULATOR
Zero Stability Digital displays have no zero drift on all dynamic reserves.
Analog outputs: <5 ppm/°C for all dynamic reserves.
Time Constants 10 µs to 30 s (reference > 200 Hz). 6, 12, 18, 24 dB/oct rolloff.
up to 30000 s (reference < 200 Hz). 6, 12, 18, 24 dB/oct rolloff.
Synchronous filtering available below 200 Hz.
Harmonic Rejection -90 dB
INTERNAL OSCILLATOR
Frequency 1 mHz to 102 kHz.
Frequency Accuracy 25 ppm + 30 µHz
Frequency Resolution 5 digits or 0.1 mHz, whichever is greater.
Frequency Sweeps Linear and Log.
Distortion f<10 kHz, below -80 dBc. f>10 kHz, below -70 dBc.1 Vrms amplitude.
Output Impedance 50 Ω
Amplitude 4 mVrms to 5 Vrms (into a high impedance load) with 2 mV resolution.
(2 mVrms to 2.5 Vrms into 50Ωload).
Amplitude Accuracy 1%
Amplitude Stability 50 ppm/°C
Outputs Sine output on front panel. TTL sync output on rear panel.
When using an external reference, both outputs are phase locked to the
external reference.

SR850 DSP Lock-In Amplifier
1-6
INPUTS AND OUTPUTS
Channel 1 Output X, R, θ, or Trace 1-4. Traces are defined as A•B/C or A•B/C2where 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.
Channel 2 Output Y, R, θ, or Trace 1-4. Traces are defined as A•B/C or A•B/C2 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.
X and Y Outputs Rear panel outputs of cosine (X) and sine (Y) components.
Output Voltage: ±10 V. 10 mA max output current.
Aux. Outputs 4 BNC Digital to Analog outputs.
±10 V full scale, 1 mV resolution. May be set to a fixed voltage or swept in
amplitude (linear or log). 10 mA max output current.
Aux. Inputs 4 BNC Analog to Digital inputs.
Differential inputs with1 MΩinput impedance on both shield and center
conductor. ±10 V full scale, 1 mV resolution.
Trigger Input TTL trigger input triggers each data sample and/or start of scan.
Monitor Output Analog output of signal amplifiers (before the demodulator).
DISPLAYS
Screen Format Single or dual display.
Displayed Quantities Each display may show one of the traces.
Traces are defined as A•B/C or A•B/C2 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.
Display Types Large numeric readout with bar graph, polar graph, and strip chart.
Chart Data Buffer 64k data points may be stored and displayed on strip charts. The buffer can
be configured as a single trace with 64k points, 2 traces with 32k points
each, or 4 traces with16k points each. The internal data sample rate ranges
from 512 Hz down to 1 point every 16 seconds. Samples can also be
triggered.
ANALYSIS FUNCTIONS
Smoothing 5 - 25 point Savitsky-Golay smoothing of trace regions.
Curve Fits Line, Exponential, and Gaussian fits of trace regions.
Calculator Arithmetic, trigonometric, and logarithmic calculations on trace regions.
Statistics Mean and standard deviation of trace regions.
GENERAL
Monitor Monochrome CRT. 640H by 480V resolution.
Adjustable brightness and screen position.
Interfaces IEEE-488, RS232 and Printer interfaces standard.
All instrument functions can be controlled through the IEEE-488 and RS232
interfaces. A PC keyboard input is provided for additional flexibility.
Preamp Power Power connector for SR550 and SR552 preamplifiers.
Hardcopy Screen dumps to dot matrix and HP LaserJet compatible printers. Data
plots to HP-GL compatible plotters (via RS232 or IEEE-488). Screens can
also be saved to disk as PCX image files.
Disk 3.5 inch DOS compatible format, 720 kbyte capacity.
Storage of data and setups.
Power 60 Watts, 100/120/220/240 VAC, 50/60 Hz.
Dimensions 17"W x 6.25"H x 19.5"D
Weight 40 lbs.
Warranty One year parts and labor on materials and workmanship.

SR850 DSP Lock-In Amplifier
1-7
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 (?) {f} 6-4 Set (Query) the Start Frequency to f Hz.Set only in Internal Sweep mode.
SULM (?) {f} 6-4 Set (Query) the Stop Frequency to f Hz.Set only in Internal Sweep mode.
RSLP (?) {i} 6-4 Set (Query) the External Reference Slope to Sine(0), TTL Rising (1), or TTL Falling (2).
HARM (?) {i} 6-5 Set (Query) the Detection Harmonic to 1 ≤i ≤32767 and i•f ≤102 kHz.
SLVL (?) {x} 6-5 Set (Query) the Sine Output Amplitude to x Vrms. 0.004 ≤x ≤5.000.
INPUT and FILTER page description
ISRC (?) {i} 6-6 Set (Query) the Input Configuration to A (0), A-B (1) , or I (2).
IGAN (?) {i} 6-6 Set (Query) the Current Conversion Gain to 1 MΩ(0) or 100 MΩ(1).
IGND (?) {i} 6-6 Set (Query) the Input Shield Groungind to Float (0) or Ground (1).
ICPL (?) {i} 6-6 Set (Query) the Input Coupling to AC (0) or DC (1).
ILIN (?) {i} 6-6 Set (Query) the Line Notch Filters to Out (0), Line In (1) , 2xLine In (2), or Both In (3).
GAIN and TIME CONSTANT page description
SENS (?) {i} 6-7 Set (Query) the Sensitivity to 2 nV (0) through 1 V (26) rms full scale.
RMOD (?) {i} 6-7 Set (Query) the Dynamic Reserve Mode to Max (0), Manual (1), or Min (2).
RSRV (?) {i} 6-7 Set (Query) the Dynamic Reserve to i th reserve. Set will switch to Manual Reserve Mode.
OFLT (?) {i} 6-7 Set (Query) the Time Constant to 10 µs (0) through 30 ks (19).
OFSL (?) {i} 6-8 Set (Query) the Low Pass Filter Slope to 6 (0), 12 (1), 18 (2) or 24 (3) dB/oct.
SYNC (?) {i} 6-8 Set (Query) the Synchronous Filter to Off (0) or On below 200 Hz (1).
OUTPUT and OFFSET page description
FOUT (?) i {, j} 6-9 Set (Query) the CH1 (i=1) or CH2 (2) Output Source to XY,R,θ,Trace 1, 2, 3, 4 (j=0...6).
OEXP (?) i {, x, j} 6-9 Set (Query) the X, Y, R (i=1,2,3) Offset to x percent and Expand to j. -105.00 ≤x ≤105.00 and
1 ≤j ≤256.
AOFF i 6-9 Auto Offset X, Y, R (i=1,2,3).
TRACE and SCAN page description
TRCD (?) i {, j, k, l, m} 6-10 Set (Query) the Definition of Trace i (1-4) to j•k/l and Store (m=1) or Not Store (0). j, k, l select
1, X, Y, R, q, Xn, Yn, Rn, Aux 1, Aux 2, Aux 3, Aux4, or F (j,k,l = 0...12). l=13-24 selects X2
through F2.
SRAT (?) {i} 6-10 Set (Query) the Sample Rate to 62.5 mHz (0) through 512 Hz (13) or Trigger (14).
SLEN (?) {x} 6-10 Set (Query) the Scan Length to x seconds.
SEND (?) {i} 6-10 Set (Query) the Scan Mode to 1 Shot (0) or Loop (1).
TRIG 6-10 Software trigger command. Same as trigger input.
DISPLAY and SCALE page description
ASCL 6-11 Auto Scale the active display.
ADSP (?) {i} 6-11 Set (Query) the active display to Full (0), Top (1) or Bottom (2). Full screen is always active.
SMOD (?) {i} 6-11 Set (Query) the Screen Format to Single (0) or Up/Down dual (1) display mode.
MNTR (?) {i} 6-11 Set (Query) the Monitor Display to settings (0) or Input/Output (1).
DTYP (?) i {, j} 6-11 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Type to Polar (j=0), Blank (j=1),
Bar (j=2) or Chart (j=3).

SR850 DSP Lock-In Amplifier
1-8
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 at the right edge of the Full (i=0), Top (i=1) or Bottom (i=2) chart display.
CURSOR page description
CSEK (?) {i} 6-13 Set (Query) the active display Cursor Seek mode to Max (0), Min (1) or Mean (2).
CWID (?) {i} 6-13 Set (Query) the active display Cursor Width to Off (0), Narrow (1), Wide (2) or Spot (3).
CDIV (?) {i} 6-13 Set (Query) the active display Chart Divisions to 8 (0), 10 (1) or None (2).
CLNK (?) {i} 6-13 Set (Query) the Cursor Control Mode to Linked (0) or Separate (1).
CDSP (?) {i} 6-13 Set (Query) the active display Cursor Readout to Delay (0), Bin (1), Fsweep (2) or Time (3).
CMAX 6-13 Move active chart cursor to max or min. Same as pressing [CURSOR MAX/MIN] key.
CURS? i 6-13 Query the cursor horz,vert position of Full (0), Top (1) or Bottom (2) chart display.
CBIN (?) {i} 6-13 Set (Query) the center of the cursor region in the active chart display. i is the bin number.
MARK page description
MARK 6-14 Places a mark in the data buffer. Same as pressing [MARK] key.
MDEL 6-14 Delete the nearest mark to the left of the cursor. Same as pressing <Marker Delete> softkey.
CNXT 6-14 Move active chart cursor to next mark to the right.
CPRV 6-14 Move active chart cursor to next mark to the left.
MACT? 6-14 Query the number of active marks. Also returns the active mark numbers.
MBIN? i 6-14 Query the bin number of mark #i.
MTXT (?) i {,s} 6-14 Set (Query) the label text for mark #i.
AUX INPUT/OUTPUT page description
OAUX ? i 6-15 Query the value of Aux Input i (1,2,3,4).
AUXM(?) i{, j} 6-15 Set (Query) the Output Mode of Aux Output i (1,2,3,4). j selects Fixed (0), Log (1) or Linear (2).
AUXV (?) i {, x} 6-15 Set (Query) voltage of Aux Output i (1,2,3,4) to x Volts. -10.500 ≤x ≤10.500. Fixed Output
Mode only.
SAUX (?) i {, x, y, z} 6-15 Set (Query) the Aux Output i (1,2,3,4) Sweep Limits to Start (x), Stop (y) and Offset (z) voltag-
es. 0.001 ≤x,y ≤21.000 and -10.500 ≤z ≤10.500.
TSTR (?) {i} 6-15 Set (Query) the Trigger Starts Scan? mode to No (0) or Yes (1).
MATH page description
SMTH i 6-16 Smooth the data within the active chart using 5 (0), 11 (1), 17 (2), 21 (3), 25 (4) point width.
COPR (?) {i} 6-16 Set (Query) the Calculator Operation to +, -, x, /, sin, cos, tan, √x, x2, log, 10x(i=0...10).
CALC 6-17 Do the Calculation selected by COPR with the argument set by CTRC or CARG.
CAGT (?) {i} 6-17 Set (Query) the Calculation Argument Type to Trace (0) or Constant (1).
CTRC (?) {i} 6-17 Set (Query) the Trace Argument to Trace i (1,2,3,4).
CARG (?) {x} 6-17 Set (Query) the Constant Argument value to x.
FTYP (?) {i} 6-17 Set (Query) the Fit Type to Linear (0), Exponential (1) or Gaussian (2).
FITT i, j 6-17 Fit the data within the chart region between i% and j% from the left edge. 0 ≤i,j ≤100.
PARS ? i 6-17 Query the fit parameters a (0), b (1), c (2) or t0 (3).
STAT i, j 6-17 Statistically analyze the data within the chart region between i% and j% from the left edge.
0 ≤i,j ≤100.
SPAR ? i 6-17 Query the Statistical results mean (0), standard dev (1), total (2) or delta time (3).
STORE AND RECALL FILE page description
FNAM (?) {s} 6-18 Set (Query) the current File Name to string s.
SDAT 6-18 Save the Active Display's Trace Data to the file specified by FNAM.
SASC 6-18 Save the Active Display's Trace Data in ASCII format to the file specified by FNAM.
SSET 6-18 Save the Settings to the file specified by FNAM.

SR850 DSP Lock-In Amplifier
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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 (1).
THRS (?) {i} 6-19 Set (Query) the Hours to 0≤i ≤23.
TMIN (?) {i} 6-19 Set (Query) the Minutes to 0 ≤i ≤59.
TSEC (?) {i} 6-19 Set (Query) the Seconds to 0 ≤i ≤59.
DMTH (?) {i} 6-19 Set (Query) the Month to 1 ≤1 ≤12.
DDAY (?) {i} 6-19 Set (Query) the Day to 1 ≤1 ≤31.
DYRS (?) {i} 6-19 Set (Query) the Year to 0 ≤1 ≤99.
PLTM (?) {i} 6-19 Set (Query) the Plotter Mode to RS232 (0) or GPIB (1).
PLTB (?) {i} 6-19 Set (Query) the Plotter Baud Rate to 300 (0), 1200 (1), 2400 (2), 4800 (3), 9600 (4).
PLTA (?) {i} 6-19 Set (Query) the Plotter GPIB Address to 0 ≤i ≤30.
PLTS (?) {i} 6-19 Set (Query) the Plot Speed to Fast (0) or Slow (1).
PNTR (?) {i} 6-19 Set (Query) the Trace Pen Number to 1 ≤i ≤6.
PNGD (?) {i} 6-20 Set (Query) the Grid Pen Number to 1 ≤i ≤6.
PNAL (?) {i} 6-20 Set (Query) the Alphanumeric Pen Number to 1 ≤i ≤6.
PNCR (?) {i} 6-20 Set (Query) the Cursor Pen Number to 1 ≤i ≤6.
PRNT (?) {i} 6-20 Set (Query) the Printer Type to Epson (0), HP (1) or File (2).
PRINT AND PLOT page description
PRSC 6-21 Print the screen. Same as the [PRINT] key.
PALL 6-21 Plot the display(s).
PTRC 6-21 Plot the trace(s) only.
PCUR 6-21 Plot the cursor(s) only.
FRONT PANEL CONTROLS
AUTO FUNCTIONS page description
STRT 6-22 Start or continue a scan. Same as [START/CONT] key.
PAUS 6-22 Pause a scan. Does not reset a paused or done scan.
REST 6-22 Reset the scan. All stored data is lost.
ASCL 6-11 Auto Scale the active display.
ATRC (?) {i} 6-22 Set (Query) the active display to Top (0) or Bottom (1). Full screen is always active.
AGAN 6-22 Auto Gain function. Same as pressing the [AUTO GAIN] key.
ARSV 6-22 Auto Reserve function. Same as pressing the [AUTO RESERVE] key.
APHS 6-22 Auto Phase function. Same as pressing the [AUTO PHASE] key.
AOFF i 6-22 Auto Offset X,Y or R (i=1,2,3).
CMAX 6-22 Move Cursor to Max or Min. Same as pressing the [CURSOR MAX/MIN] key.
DATA TRANSFER page description
OUTP? i 6-23 Query the value of X (1), Y (2), R (3) or θ(4). Returns ASCII floating point value.
OUTR? i 6-23 Query the value of Trace i (1,2,3,4). Returns ASCII floating point value.
OAUX? i 6-23 Query the value of Aux Input i (1,2,3,4). Returns ASCII floating point value.
SPTS? i 6-23 Query the number of points stored in Trace i (1,2,3,4).
TRCA? i,j,k 6-23 Read k≥1 points starting at bin j≥0 from trace i (1,2,3,4) in ASCII floating point.
TRCB? i,j,k 6-23 Read k≥1 points starting at bin j≥0 from trace i (1,2,3,4) in IEEE binary floating point.
TRCL? i,j,k 6-24 Read k≥1 points starting at bin j≥0 from trace i (1,2,3,4) in non-normalized binary floating point.
FAST (?) {i} 6-25 Set (Query) Fast Data Transfer Mode On (1 or 2) or Off (0).On will transfer binary X and Y eve-
ry sample during a scan over the GPIB interface.
STRD 6-25 Start a scan after 0.5sec delay. Use with Fast Data Transfer Mode.

SR850 DSP Lock-In Amplifier
1-10
SERIAL POLL STATUS BYTE (6-28)
bit name usage
0 SCN No data is being acquired
1 IFC No command execution in progress
2 ERR Unmasked bit in error status byte set
3 LIA Unmasked bit in LIA status byte set
4 MAV The interface output buffer is non-empty
5 ESB Unmasked bit in standard status byte set
6 SRQ SRQ (service request) has occurred
7 Unused
STANDARD EVENT STATUS BYTE (6-29)
bit name usage
0 INP Set on input queue overflow
1 Unused
2 QRY Set on output queue overflow
3 Unused
4 EXE Set when command execution error occurs
5 CMD Set when an illegal command is received
6 URQ Set by any key press or knob rotation
7 PON Set by power-on
LIA STATUS BYTE (6-29)
bit name usage
0 RESRV Set when a RESRV overload is detected
1 FILTR Set when a FILTR overload is detected
2 OUTPT Set when a OUTPT overload is detected
3 UNLK Set when reference unlock is detected
4 RANGE Set when detection freq crosses 200 Hz
5 TC Set when time constant is changed
6 TRIG Set when unit is triggered
7 PLOT Set when a plot is completed
ERROR STATUS BYTE (6-30)
bit name usage
0 Prn/Plt Err Set when an printing or plotting error occurs
1 Backup Error Set when battery backup fails
2 RAM Error Set when RAM Memory test finds an error
3 Disk Error Set when a disk error occurs
4 ROM Error Set when ROM Memory test finds an error
5 GPIB Error Set when GPIB binary data transfer aborts
6 DSP Error Set when DSP test finds an error
7 Math Error Set when an internal math error occurs
STATUS BYTE DEFINITIONS
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) the Standard Event Status Byte Enable Register to the decimal value i (0-255).
*ESE i,j sets bit i (0-7) to j (0 or 1). *ESE? queries the byte. *ESE?i queries only bit i.
*ESR? {i} 6-27 Query the Standard Event Status Byte. If i is included, only bit i is queried.
*SRE (?) {i} {,j} 6-27 Set (Query) the Serial Poll Enable Register to the decimal value i (0-255). *SRE i,j sets bit i (0-
7) to j (0 or 1). *SRE? queries the byte, *SRE?i queries only bit i.
*STB? {i} 6-27 Query the Serial Poll Status Byte. If i is included, only bit i is queried.
*PSC (?) {i} 6-27 Set (Query) the Power On Status Clear bit to Set (1) or Clear (0).
ERRE (?) {i} {,j} 6-27 Set (Query) the Error Status Enable Register to the decimal value i (0-255). ERRE i,j sets bit i
(0-7) to j (0 or 1). ERRE? queries the byte, ERRE?i queries only bit i.
ERRS? {i} 6-27 Query the Error Status Byte. If i is included, only bit i is queried.
LIAE (?) {i} {,j} 6-27 Set (Query) the LIA Status Enable Register to the decimal value i (0-255). LIAE i,j sets
bit i (0-7) to j (0 or 1). LIAE? queries the byte, LIAE?i queries only bit i.
LIAS? {i} 6-27 Query the LIA Status Byte. If i is included, only bit i is queried.

GETTING STARTED
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 procedures are detailed in two columns. The left column lists the actual steps in the experi-
ment. The right column is an explanation of each step.
Key Types There are two types of front panel keys which will be referred to in this
manual. Hardkeys are those keys with labels printed on them. Their func-
tion is determined by the label and does not change. Hardkeys are refer-
enced by brackets like this - [HARDKEY]. The softkeys are the six gray
keys along the right edge of the screen. Their function is labelled by a
menu box displayed on the screen next to the key. Softkey functions
change depending upon the situation. Softkeys will be referred to as the
<Soft Key> or simply the Soft Key.
Hardkeys The keypad consists of five groups of hardkeys. The ENTRY keys are
used to enter numeric parameters which have been highlighted by a soft-
key. The MENU keys select a menu of softkeys. Pressing a menu key
will change the menu boxes which are displayed next to the softkeys.
Each menu groups together similar parameters and functions. The
CONTROL keys start and stop actual data acquisition, select the cursor
and toggle the active display. These keys are not in a menu since they
are used frequently and while displaying any menu. The SYSTEM keys
output the screen to a printer and display help messages. These keys
can also be accessed from any menu. The AUTO keys perform auto
functions such as Auto Gain and Auto Phase.
Softkeys The SR850 has a menu driven user interface. The 6 softkeys to the right
of the video display have different functions depending upon the informa-
tion displayed in the menu boxes at the right of the video display. In gen-
eral, the softkeys have two uses. The first is to toggle a feature on and
off or to choose between settings. The second is to highlight a parameter
which is then changed using the knob or numeric keypad. In both cases,
the softkey selects the parameter which is displayed adjacent to it.
Knob The knob is used to adjust parameters which have been highlighted by a
softkey. Many numeric entry fields may be adjusted with the knob. In
addition, many parameters are adjusted only with the knob. These are
typically parameters with a limited set of values, such as sensitivity or
time constant. In these cases, the parameter is selected by a softkey.
The [CURSOR] key will set the knob function to scrolling the cursor
within the active chart display.
2-1
YOUR FIRST MEASUREMENTS

2-2
Getting Started

2-3
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
the power on while holding down the [←]
(backspace) key. Wait until the power-on tests
are completed.
2. Connect the Sine Out on the front panel to the
A input using a BNC cable.
3. Press [AUTO PHASE]
4. Press [REF/PHASE]
When the power is turned on with the backspace
key depressed, the lock-in returns to its default
settings. See the Default Settings list in the Menu
section for a complete listing of the settings.
The display is the "normal" lock-in display. The
lock-in setup is displayed across the top of the
screen. The sensitivity, reserve, time constant,
prefilters and input configuration are all easily visi-
ble. Watch how these indicators change as you
change parameters. The upper numeric readout
and bar graph shows the value of X (Rcosθ) and
the lower graph shows the the value of Y (Rsinθ).
The input impedance of the lock-in is 10 MΩ. The
Sine Out has an output impedance of 50Ω. Since
the Sine Output amplitude is specified into a high
impedance load, the output impedance does not
affect the amplitude.
The lock-in defaults to the internal oscillator refer-
ence set at 1.000 kHz. The reference mode (Intrnl)
and frequency are displayed at the bottom of the
screen. In this mode, the lock-in generates a syn-
chronous sine output at the internal reference
frequency.
The sine amplitude is 1.000 Vrms and the
sensitivity is 1 V(rms). Since the phase shift of the
sine output is very close to zero, the upper display
(X) should read close to 1.000 V and the lower dis-
play (Y) should read close to 0.000 V.
Automatically adjust the reference phase shift to
eliminate any residual phase error. This should set
the value of Y to zero.
Display the Reference and Phase menu. The
phase shift (displayed in the top menu box) should
be close to zero.
The Basic Lock-in

2-4
5. Press the <Rotate 90 deg> softkey.
Press the <deg.> softkey.
Use the knob to adjust the phase shift until Y
is zero and X is equal to the positive
amplitude.
Press [9] [0] [ENTER]
Press [AUTO PHASE]
6. Press <Ref. Frequency>
Press [1] [2] [.] [3] [4] [5] [EXP] [3] [ENTER]
Press [1] [0] [0] [0] [ENTER]
7. Press <Sine Output>
Use the knob to adjust the amplitude.
Press [.] [0] [1] [ENTER]
8. Press [GAIN/TC]
Press [AUTO GAIN]
This adds 90° to the reference phase shift. The
value of X drops to zero and Y becomes minus the
magnitude (-1.000 V).
Highlight the phase shift.
The knob can be used to adjust parameters which
are continuous, such as phase, amplitude and fre-
quency. The final phase value should be close to
zero again.
Phase shifts can also be entered numerically.
The knob is useful for small adjustments while
numeric entry is easier when changing to a pre-
cise value or by a large amount.
Use the Auto Phase function to return Y to zero
and X to the amplitude.
Highlight the internal reference frequency menu.
Enter 12.345 kHz in exponential form. The meas-
ured signal amplitude should stay within 1% of 1 V
and the phase shift should stay close to zero (the
value of Y should stay close to zero).
Parameters can be entered in real or integer form
as well. In this case, the frequency is changed to
1.000 kHz.
The internal oscillator is crystal synthesized with
25 ppm of frequency error. The frequency can be
set with 5 digit or 0.1 mHz resolution, whichever is
greater.
Highlight the sine output amplitude.
As the amplitude is changed, the measured value
of X should equal the sine output amplitude.
The amplitude may be entered numerically also.
The sine amplitude can be set from 4 mV to 5 V
rms into high impedance (half the amplitude into a
50 Ωload).
Display the Gain and Time Constant menu.
The Auto Gain function will adjust the sensitivity so
The Basic Lock-in

2-5
9. Press <Sensitivity>
Use the knob to change the sensitivity to
50 mV.
Change the sensitivity back to 20 mV.
10. Press <Time Constant>
Use the knob to change the time constant to
300 µs.
Change the time constant to 3 ms.
11. Press the <Filter db/oct.> softkey until 6 dB/oct
is selected.
Press <Filter db/oct.> again to select
12 dB/oct.
Press <Filter db/oct.> twice to select
24 db/oct.
Press <Filter db/oct> again to select 6 db/oct.
12. Press [REF/PHASE]
Press <Ref. Frequency>
Press [5] [0] [ENTER]
that the measured magnitude (R) is a sizable per-
centage of full scale.
Highlight the full scale sensitivity.
Parameters which are discrete values, such as
sensitivity and time constant, can only be changed
with the knob. Numeric entry is not allowed for
these parameters.
Highlight the time constant.
The values of X and Y become noisy. This is
because the 2f component of the output (at 2 kHz)
is no longer attenuated completely by the low pass
filters.
Let's leave the time constant short and change the
filter slope.
Parameters which have their available options dis-
played within the menu box are selected by press-
ing the corresponding softkey until the desired
option is chosen.
The X and Y outputs are somewhat noisy at this
short time constant and only 1 pole of low pass
filtering.
The outputs are less noisy with 2 poles of filtering.
With 4 poles of low pass filtering, even this short
time constant attenuates the 2f component rea-
sonably well and provides steady readings.
Let's leave the filtering short and the outputs noisy
for now.
Display the Reference and Phase menu.
Highlight the internal reference frequency.
Enter 50 Hz for the reference frequency. With a
3 ms time constant and only 6 db/oct of filtering,
the output is totally dominated by the 2f compo-
nent at 50 Hz.
The Basic Lock-in

2-6
13. Press [GAIN/TC]
Press <Synchronous> to select <200 Hz. Display the Gain and Time Constant menu again. 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 constant is very short. The
response time of the synchronous filter is equal to
the period of the detection frequency (20 ms in this
case).
This concludes this measurement example. You
should have a feeling for the basic operation of the
menus, knob and numeric entry. Basic lock-in
parameters have been introduced and you should
be able to perform simple measurements.
The Basic Lock-in

2-7
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-
nal reference frequency. This setup ensures changing outputs which are more illustrative than steady outputs.
The displays will be configured to show X, Y, R and θin bar graph and polar formats. The example Scans and
Sweeps demonstrates the use of the chart graph.
1. Disconnect all cables from the lock-in. Turn
the power on while holding down the [←]
(backspace) key. Wait until the power-on tests
are completed.
2. Turn on the function generator, set the fre-
quency to 1.0000 kHz (exactly) and the ampli-
tude to 500 mVrms.
Connect the function output (sine wave) from
the synthesized function generator to the A
input using a BNC cable and appropriate
terminator.
3. Press [REF/PHASE]
When the power is turned on with the backspace
key depressed, the lock-in returns to its default
settings. See the Default Settings list in the Menu
section for a complete listing of the settings.
The display is the "normal" lock-in display. The
lock-in setup is displayed across the top of the
screen. The sensitivity, reserve, time constant,
prefilters and input configuration are all easily visi-
ble. Watch how these indicators change as you
change parameters. The upper numeric readout
and bar graph shows the value of X (Rcosθ) and
the lower graph shows the the value of Y (Rsinθ).
The input impedance of the lock-in is 10 MΩ. The
generator may require a terminator. Many genera-
tors have either a 50Ωor 600Ωoutput impedance.
Use the appropriate feedthrough or T termination if
necessary. In general, not using a terminator
means that the function output amplitude will not
agree with the generator setting.
The lock-in defaults to the internal oscillator refer-
ence set at 1.000 kHz. The reference mode (Intrnl)
and frequency are displayed at the bottom of the
screen. In this mode, the internal oscillator sets
the detection frequency.
The internal oscillator is crystal synthesized so
that the actual reference frequency should be very
close to the actual generator frequency. The X and
Y displays should read values which change very
slowly. The lock-in and the generator are not
phase locked but they are at the same frequency
with some slowly changing phase.
Display the Reference and Phase menu.
Displays and Traces

2-8
Displays and Traces
Highlight the internal oscillator frequency.
By setting the lock-in reference 0.2 Hz away from
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).
Display the Display and Scale menu.
The SR850 collects data in the form of traces.
There are 4 definable traces and only these trace
quantities may be displayed. The default definition
of these traces is X, Y, R and θfor traces 1, 2, 3
and 4.
The Display Scale menu box shows the display
parameters for the Full (screen), Top or Bottom
(split screen) displays. In this case, the Top dis-
play parameters are shown.
Each display shows one of the data traces. The
Top display defaults to showing trace 1 which has
a default definition of X. Thus the top bar graph
shows the X output.
Trace 3 has a default definition of R so showing
trace 3 on the top graph will display the quantity R.
R is phase independent so it shows a steady value
(close to 0.500 V).
[AUTO SCALE] automatically scales the active
display. The top display is the active display (as
indicated by the inverse trace identifier at the
upper left of the display).
To modify the bottom graph, you must display the
bottom graph's parameters in the Display Scale
menu box. This also makes the bottom display the
active display (for autoscaling). The trace indicator
(at the upper left of each display) is highlighted on
the active display.
The bottom display defaults to trace 2 (Y).
Trace 4 is θ. The phase between the reference
and the signal changes by 360° every 5 sec
(0.2 Hz difference frequency).
Press <Ref. Frequency>
Use the knob to change the frequency to
999.80 Hz.
4. Press [DISPLAY/SCALE]
Press <Type/Trace> twice to highlight the dis-
played trace number.
Use the knob to change the trace number to 3.
Press [AUTO SCALE]
5. Press <Full, Top or Bottom> to select Bottom.
Press <Type/Trace> twice to highlight the dis-
played trace number.
Use the knob to change the trace number to 4.