Stanford Research Systems SR865 Operation Manual
Operation Manual
SR865
2 MHz DSP Lock-in Amplifier
Revision 1.25
Stanford Research Systems
Certification
Stanford Research Systems certifies that this product met its published specificat ions 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.
Service
For warranty service or repair, this product must be returned to a Stanford Research
Systems authorized service facility. Contact Stanford Research Systems or an authorized
representative before returning this product for repair.
Information in this document is subject to change without notice.
Copyright © Stanford Research Systems, Inc., 2015. All rights reserved.
Stanford Research Systems, Inc.
1290-C Reamwood Avenue
Sunnyvale, California 94089
www.thinkSRS.com
Printed in U.S.A. Document number 9-01707-903
SR865 DSP Lock-in Amplifier
Safety and Preparation For Use i
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.
Line Voltage Selection
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.
The SR865 operates from a 100V, 120V, 220V, or 240V nominal ac power source having
a line frequency of 50 or 60 Hz. Before connecting the power cord, verify that the LINE
VOLTAGE SELECTOR card, located in the rear panel fuse holder, is set so that the
correct ac input voltage value is indicated by the white dot.
Conversion to other ac input voltages requires a change in the voltage selector card
position and fuse value. See Appendix F (page 177) for detailed instructions.
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. See Appendix F
(page 177) for detailed fuse installation instructions.
Line Cord
The SR865 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. 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.
Grounded BNC shields are connected to the chassis ground. Do not apply any voltage to
the grounded shields. The A and B signal input shields are connected to chassis ground
through resistors and can tolerate up to 1 V of applied voltage.
GFCI (Ground Fault Circuit Int errupter)
GFCI protected outlets are often available in production and laboratory environments,
particularly in proximity to water sources. GFCI’s are generally regarded as an important
defense against electrocution. However, the use of GFCI in conjunction with the SR865
SR865 DSP Lock-in Amplifier
ii Safety and Preparation For Use
must not be regarded as a substitute for proper grounding and careful system design.
GFCI’s must also be tested regularly to verify their functionality. Always consult an
electrician when in doubt.
Service
Do not attempt to service this instrument unless another person, capable of providing first
aid or resuscitation, is present.
Do not install substitute parts or perform any unauthorized modifications to this
instrument. Contact the factory for instructions on how to return the instrument for
authorized service and adjustment.
Warning Regarding Use Wi t h Photom ultipliers 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 unterminated, 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 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.
Furnished Accessories
• Power Cord
• Operating Manual
Environmental Conditi ons
Operating
Temperature: +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
SR865 DSP Lock-in Amplifier
Safety and Preparation For Use iii
SR865 DSP Lock-in Amplifier
iv Safety and Preparation For Use
SR865 DSP Lock-in Amplifier
Contents v
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
Sensitivity, Offset and Expand 20
Saving and Recalling Setups 25
Aux Outputs and Inputs 28
Scanning 30
Chapter 2 Lock-in Amplifier Basics 37
What is a Lock-in Amplifier? 37
What Does a Lock-in Measure? 40
Block diagram 41
The Reference Oscillator 42
The Phase Sensitive Detectors 43
Time Constants and Sensitivity 44
Outputs and Scales 46
What is Dynamic Reserve Really? 48
The Input Amplifier 50
Input Connections 51
Intrinsic (Random) Noise Sources 54
External Noise Sources 55
Noise Measurements 58
Chapter 3 Operation 61
Introduction 61
Standard Settings 64
Signal Input 65
CH1 and CH2 Outputs: Offset, Ratio and Expand 71
Reference 74
Display 81
Cursor 83
SR865 DSP Lock-in Amplifier
vi Contents
Functions 85
Interface and Data 87
Setup 88
Rear Panel 96
Chapter 4 Programming 101
Introduction 101
Command Syntax 103
Reference Commands 106
Signal Commands 111
CH1/CH2 Output Commands 114
Aux Input and Output Commands 116
Auto Function Commands 117
Display Commands 118
Strip Chart Commands 120
FFT Screen Commands 125
Scan Commands 128
Data Transfer Commands 132
Data Capture Commands 134
Data Streaming Commands 140
System Commands 143
Interface Commands 146
Status Reporting Commands 148
Status Byte Definitions 151
Appendix A Advanced Filters 155
Appendix B The FFT Display 161
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
Specifications vii
SR865 Specifications
Signal Channel
Voltage Inputs Single-ended (A) or differential (A−B)
Sensitivity (Output Scale) 1 nV to 1 V (voltage input)
1 fA to 1 µA (current input)
Input Impedance 10 MΩ+25 pF, ac (>1 Hz) or dc coupled
Input Range 10 mV to 1 V (peak); max input before overload
Gain Accuracy 1% below 200 kHz and 2% to 2 MHz (signal amplitude <30% of input range)
Input Noise 2.5 nV/√Hz at 1 kHz, 10 mV input range (typical)
CMRR Greater than 90 dB at 1 kHz (dc Coupled)
Harmonic Distortion −80 dB below 100 kHz, −60 dB above 100 kHz
Dynamic Reserve Greater than 120 dB
Current Input Ranges 1 μA or 10 nA
Reference Channel
Frequency Range 1 mHz to 2 MHz specified (operates to 2.5 MHz)
Timebase 10 MHz In/Out phase locks the internal frequency to other SR865 units
Ext TTL Reference Minimum 2 V logic level, rising or falling edge
Ext Sine Reference 400 mV pk–pk minimum signal, ac coupled (>1 Hz)
Ext Reference Input Impedance 1 MΩ or 50 Ω
Acquisition Time (2 cycles + 5 ms) or 40 ms, whichever is greater
Phase Setting Resolution 360/2
Phase Noise Ext TTL reference: <0.001° rms at 1 kHz, (100 ms, 12 dB/oct) (typical)
Internal reference: <0.0001° rms at 1 kHz (100 ms, 12 dB/oct)
Phase Drift Sine Out to Signal In (200 mVrms)
<0.002°/°C below 20 kHz (dc coupled input)
<0.02°/°C below 200 kHz
<0.2°/°C below 2 MHz
Harmonic Detect Detect at N×f
Dual F Reference Detect at f
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
32
deg
where N≤99 and N×f
ref
= | f
− f
dual
|
int
ext
<2 MHz
ref
int
Demodulator
dc Stability Digital output values have no offset drift
Time Constants 1 µs to 30 ks
Low Pass Filters Typical RC type filters or Advanced Gaussian/Linear Phase filters
Filter Slope 6, 12, 18, 24 dB/oct rolloffs
Synchronous Filter Available below 4 kHz
Harmonic Rejection −80 dB
Low Latency Output Rear panel BlazeX output with <2 µs delay (plus low pass filter rise/fall times)
Internal Oscillator
Frequency 1 mHz to 2 MHz specified (operates to 2.5 MHz)
Frequency Accuracy 25 ppm + 30 µHz with internal timebase
External Timebase 10 MHz timebase input/output on rear panel
Frequency Resolution 6 digits or 0.1 mHz, whichever is greater
SR865 DSP Lock-in Amplifier
viii Specifications
Sine Output
Outputs Differential or Single-ended
Output Impedance 50 Ω source
Amplitude 1 nVrms to 2 Vrms (specified amplitude is differential into 50 Ω loads)
Output amplitude is halved when used single-ended
Output amplitude is doubled into a high impedance load
Amplitude Resolution 3 digits or 1 nV, whichever is greater
dc Offset ±5 V, differential or common mode
Offset Resolution 3 digits or 0.1 mV, whichever is greater
Output Limit ±6 V, sum of dc offset and peak amplitude
Sync Logic level sync on rear panel (via BlazeX output)
Data
Data Channels 4 data channels are displayed and graphed (green, blue, yellow, orange)
Data Sources Each data channel can be assigned any of these data sources:
, Y
X, Y, R, θ, Aux In 1–4, Aux Out 1–2, X
DC Level, reference phase, f
int
or f
noise
ext
Data History A ll data sources are continuo u sly stored at all chart display time scales.
The complete stored history of any data source can be displayed at any time.
Offset X, Y and R may be offset up to ±999% of the sensitivity
Ratio X, and Y may be ratioed by Aux In 3; R may be ratioed by Aux In 4
Expand X, Y and R may be expanded by ×10 or ×100
Capture Buffer 1 Mpoints internal data storage. Store (X), (X and Y), (R and θ) or (X, Y, R and θ)
at sample rates up to 1.25 MHz. This is in addition to the data histories for the
chart display.
Data Streaming Realtime streaming of data, either (X), (X and Y), (R and θ) or (X, Y, R and θ) at
sample rates up to 1.25 MHz over Ethernet interface
Scanning One of the following parameters may be scanned:
f
, Sine Out Amplitude, Sine Out DC Level, Aux Out 1 or 2.
int
, Sine Out Amplitude, Sine Out
noise
FFT
Source Input ADC, demodulator output, or filter output
Record length 1024 bins
Averaging exponential rms
Inputs and Outputs
CH 1 Output Proportional to X or R, ±10 V full scale thru 50 Ω
CH 2 Output Proportional to Y or θ, ±10 V full scale thru 50 Ω
X and Y Outputs Proportional to X and Y, ±10 V full scale thru 50 Ω, rear panel
BlazeX Low latency output of X, ±2.0 V full scale or
logic level reference sync output, either thru 50 Ω
Aux Outputs 4 BNC D/A outputs, ±10.5 V thru 50 Ω, 1 mV resolution
Aux Inputs 4 BNC A/D inputs, ±10.5 V, 1 mV resolution, 1 MΩ input
Trigger Input TTL input triggers storage into the internal capture buffer
Monitor Output Analog output of the signal amplifier
HDMI 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
Specifications ix
USB Flash Front panel slot for USB flash storage of screen shots and data, and firmware
upgrades
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
x Commands
Reference Commands
page
description
TBMODE(?) { AUTO | INternal | i }
106
Set the 10 MHz timebase
TBSTAT?
106
Query the current 10 MHz timebase ext (0) or int (1)
PHAS(?) { p } { UDEG | MDEG | DEG | URAD | MRAD | RAD }
106
Set the reference phase to p
APHS
106
Auto Phase
FREQ(?) { f } { HZ | KHZ | MHZ }
106
Set the reference frequency to f
FREQINT(?) { f } { HZ | KHZ | MHZ }
107
Set the internal reference frequency to f
FREQEXT?
107
Query the external reference frequency
FREQDET?
107
Query the detection frequency
HARM(?) { i }
107
Set harmonic detect to i
HARMDUAL(?) { i }
107
Set harmonic for dual reference mode to i
BLADESLOTS(?) {SLT6 | SLT30 | i }
108
Set the chopper blade number of slots
BLADEPHASE(?) { p } { UDEG | MDEG | DEG | URAD | MRAD |
RAD }
108
Set the chopper blade phase to p
SLVL(?) { v } { NV | UV | MV | V }
108
Set sine output amplitude to v
SOFF(?) { v } { NV | UV | MV | V }
108
Set sine output dc level to v
REFM(?) { COMmon | DIFference | i }
109
Set sine output dc mode
RSRC(?) { INT | EXT | DUAL | CHOP | i }
109
Set reference mode
RTRG(?) { SIN | POSttl | NEGttl | i }
109
Set external reference trigger
REFZ(?) { 50ohms | 1Meg | i }
109
Set external reference input impedance
PSTF(?) [ j ] { , f { HZ | KHZ | MHZ } }
110
Set frequency preset j to f
PSTA(?) [ j ] { , v { NV | UV | MV | V } }
110
Set sine amplitude preset j to v
PSTL(?) [ j ] { , v { NV | UV | MV | V } }
110
Set sine dc level preset j to v
Signal Commands
page
description
IVMD(?) { VOLTage | CURRent | i }
111
Set input to voltage/current
ISRC(?) { A | A−B | i }
111
Set voltage input configuration
ICPL(?) { AC | DC | i }
111
Set voltage input coupling
IGND(?) { FLOat | GROund | i }
111
Set voltage input shield grounding
IRNG(?) { 1Volt | 300Mvolt | 100Mvolt | 30Mvolt | 10Mvolt | i }
111
Set voltage input range
ICUR(?) { 1MEG | 100MEG | i }
112
Set current input gain
ILVL?
112
Query the signal strength low to overload (0–4)
SCAL(?) { i }
112
Set sensitivity from 1V (0) to 1 nV (27)
OFLT(?) { i }
113
Set time constant from 1 μs (0) to 30 ks (21)
OFSL(?) { i }
113
Set filter slope from 6 dB (0) to 24 dB (3)
SYNC(?) { OFF | ON | i }
113
Turn synchronous filter off/on
ADVFILT(?) { OFF | ON | i }
113
Turn advanced filtering off/on
ENBW?
113
Query the equivalent noise bandwidth
CH1/CH2 Output Commands
page
description
COUT(?) [ OCH1 | OCH2 | j ] { , XY | RTHeta | i }
114
Set CH1/2 to (X or R)/(Y or θ)
SR865 Command List
SR865 DSP Lock-in Amplifier
Commands xi
CEXP(?) [ X | Y | R | j ] { , OFF | X10 | X100 | i }
114
Set CH1/2 expand
COFA(?) [ X | Y | R | j ] { , OFF | ON | i }
114
Turn CH1/2 output offset off/on
COFP(?) [ X | Y | R | j ] { , x }
114
Set CH1/2 output offset to x percent
OAUT [ X | Y | R | j ]
114
Auto Offset CH1/2
CRAT(?) [ X | Y | R | j ] { , OFF | ON | i }
115
Ratio Ch1/2 with Aux In 3 or 4
Aux Input and Output Commands
page
description
OAUX? [ j ]
116
Query Aux Input j (0–3)
AUXV(?) [ j ] { , v { NV | UV | MV | V } }
116
Set Aux Output j (0–3) voltage to v
Auto Function Commands
page
description
APHS
117
Auto Phase
ARNG
117
Auto Range
ASCL
117
Auto Scale
Display Commands
page
description
DBLK(?) { OFF | ON | i }
118
Turn front panel blanking off/on
DLAY(?) { TREnd | HISTory | BARHist | FFT | BARFft | BAREight | i }
118
Set Screen Layout
DCAP
118
Screen Shot to USB memory stick
CDSP(?) [ DAT1 | DAT2 | DAT3 | DAT4 | j ] { , parameter | i }
118
Assign parameter i to data channel j
CGRF(?) [ DAT1 | DAT2 | DAT3 | DAT4 | j ] { , OFF | ON | i }
119
Turn data channel j strip graph off/on
GETSCREEN?
119
Download screen capture image
Strip Chart Commands
page
description
GSPD(?) { i }
120
Set horizontal scale from 0.5 s (0) to 2 days (16)
GSCL(?) [ DAT1 | DAT2 | DAT3 | DAT4 | j ] { , x }
120
Set channel j vertical scale to x
GOFF(?) [ DAT1 | DAT2 | DAT3 | DAT4 | j ] { , x }
120
Set channel j vertical offset
GAUT [ DAT1 | DAT2 | DAT3 | DAT4 | j ]
121
Auto scale channel j
GACT [ DAT1 | DAT2 | DAT3 | DAT4 | j ]
121
Auto scale with zero center channel j
GAUF [ DAT1 | DAT2 | DAT3 | DAT4 | j ]
121
Auto find for channel j
CGRF(?) [ DAT1 | DAT2 | DAT3 | DAT4 | j ] { , { OFF | ON | i } }
121
Turn channel j graph off/on
GLIV(?) { OFF | ON | i }
122
Turn strip chart off/on (pause/run)
PCUR(?) { i }
122
Move cursor to i (0=right, 639=left)
CURREL(?) {OFF | ON | i}
122
Set cursor relative or absolute mode
CURDISP(?) {i}
122
Set cursor horizontal mode to date/time or interval
CURBUG(?) {AVG | MAX | MIN | i}
122
Set cursor to mean / maximum / minimum
FCRW(?) { LIne | NARrow | WIde | i }
123
Set the cursor width
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
FFT Screen Commands
page
description
SR865 DSP Lock-in Amplifier
xii Commands
FFTR(?) { ADC | MIXer | FILTer | i }
125
Set FFT data source
FFTS(?) { i }
125
Set vertical scale from 1.0 dB (0) to 200 dB (7)
FFTO(?) { x }
125
Set top reference level
FAUT
126
FFT auto scale
FFTMAXSPAN?
126
Query maximum allowed frequency span in Hz/div
FFTSPAN(?) { x }
126
Set frequency span in Hz/div
FFTA(?) { AVG1 | AVG3 | AVG1 0 | AVG30 | AVG100 | i }
126
Set averaging
FFTL(?) { OFF | ON | i }
126
Turn FFT off/on (pause/live)
FCRW(?) { LIne | NARrow | WIde | i }
126
Set the cursor width
FCRX?
127
Query the FFT cursor frequency
FCRY?
127
Query the FFT cursor amplitude
Scan Commands
page
description
SCNPAR(?) { Fint | REFAmp | REFDc | OUT1 | OUT2 | i }
128
Set the scan parameter
SCNLOG(?) { LIN | LOG | i }
128
Set the scan type
SCNEND(?) { ONce | REpeat | UPdown | i }
128
Set the scan end mode
SCNSEC(?) { x }
128
Set the scan time to x seconds
SCNAMPATTN(?) {i}
128
Set the amplitude attenuator mode for scanning
SCNDCATTN(?) {i}
129
Set the dc attenuator mode for scanning
SCNINRVL(?) {i}
129
Set the scan parameter update interval
SCNENBL(?) { OFF | ON | i }
129
Turn the scan off/on
SCNRUN
130
Start or resume the scan
SCNPAUSE
130
Pause the scan
SCNRST
130
Reset the scan
SCNSTATE?
130
Query the scan (off, reset, run, pause or done)(0-4)
SCNFREQ(?) [ BEGin | END | j ] { , f { HZ | KHZ | MHZ } }
130
Set the begin/end frequency
SCNAMP(?) [ BEGin | END | j ] { , v { NV | UV | MV | V } }
130
Set the begin/end reference amplitude
SCNDC(?) [ BEGin | END | j ] { , v { NV | UV | MV | V } }
130
Set the begin/end reference dc level
SCNAUX1(?) [ BEGin | END | j ] { , v { NV | UV | MV | V } }
131
Set the begin/end AuxOut1 value
SCNAUX2(?) [ BEGin | END | j ] { , v { NV | UV | MV | V } }
131
Set the begin/end AuxOut2 value
Data Transfer Commands
page
description
OUTR? [ DAT1 | DAT2 | DAT3 | DAT4 | j ]
132
Query data channel j
OUTP? [ j ]
132
Query lock-in parameter j
SNAP? [ j, k ] { , l }
132
Query multiple lock-in parameters at once
Data Capture Commands
page
description
CAPTURELEN(?) { n }
136
Set the buffer length to n 1 kbyte blocks
CAPTURECFG(?) { X | XY | RT | XYRT | i }
136
Configure capture to X, XY, Rθ or XYRθ (0–3)
CAPTURERATEMAX?
136
Query the maximum capture rate
CAPTURERATE(?) { n }
136
Set the capture rate to (max rate)/2n
CAPTURESTART [ ONEshot | CO NTinuous | i ] , [ OFF | ON | j ]
137
Start capture (OneShot or Cont) (HW trigger off/on)
CAPTURESTOP
137
Stop capture
SR865 DSP Lock-in Amplifier
Commands xiii
CAPTURESTAT?
137
Query the capture buffer state
CAPTUREPROG?
138
Query the length (kB) of captured data (after stop)
CAPTUREVAL? [ n ]
138
Query the nth sample (1, 2 or 4 values) (after stop)
CAPTUREGET? [ i ], [ j ]
138
Download binary capture buffer
Data Streaming Commands
page
description
STREAMCH(?) { X | XY | RT | XYRT | i }
140
Configure streaming to X, XY, Rθ or XYRθ (0–3)
STREAMRATEMAX?
141
Query the maximum streaming rate
STREAMRATE(?) { n }
141
Set the streaming rate to (max rate)/2n
STREAMFMT(?) { i }
141
Set the streaming format to float32 (0) or int16 (1)
STREAMPCKT(?) { i }
141
Set packet size to 1024, 512, 256 or 128 bytes (0–3)
STREAMPORT(?) { i }
142
Sets the Ethernet port to i=1024–65535
STREAMOPTION(?) { i }
142
Sets big/little endianness and integrity checking
STREAM(?) { OFF | ON | i }
142
Turn streaming off/on
System Commands
page description
TIME(?) [ SEConds | MINutes | HOUrs | j ] { , i }
143
Set time
DATE(?) [ DAY | MONth | YEAr | j ] { , i }
143
Set date
TBMODE(?) { AUTO | INternal | i }
143
Set the 10 MHz timebase
TBSTAT?
143
Query the current 10 MHz timebase ext (0) or int (1)
BLAZEX(?) { BLazex | BIsync | UNIsync | i }
143
Select the BlazeX output
KEYC(?) { ON | MUte| i }
144
Turn sounds on or off
PRMD(?) { SCReen | PRNt | MONOchrome | i }
144
Set screen shot mode
SDFM(?) { CSV | MATfile | i }
144
Set data file type
FBAS(?) { s }
144
Set file name prefix
FNUM(?) { i }
144
Set file name suffix
FNXT?
145
Query next file name
DCAP
145
Screen shot
SVDT
145
Save data
Interface Commands
page description
RST
146
Reset the unit to its default configuration
IDN?
146
Query the unit identification string
TST?
146
No-op, returns “0”
*OPC(?)
146
Operation Complete
LOCL(?) { i }
146
Set LOCAL (0), REMOTE (1) or LOCKOUT (2)
OVRM (?) { OFF | ON | i }
147
Set GPIB Overide Remote off (0) or on (1)
Status Reporting Commands
page
description
CLS
148
Clear all status bytes
ESE(?) { j, } { i }
148
Set the standard event enable register
*
*
*
*
*
SR865 DSP Lock-in Amplifier
xiv Commands
ESR? { j }
148
Query the standard event status byte
148
Set the serial poll enable register
STB? { j }
148
Query the serial poll status byte
PSC(?) { i }
149
Set the Power-On Status Clear bit
ERRE(?) { j, } { i }
149
Set the error status enable register
ERRS? { j }
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
*
*SRE(?) { j, } { i }
*
*
SR865 DSP Lock-in Amplifier
Commands xv
Serial Poll Status Byte
bit
name
usage
0
unused
1
unused
2 ERR
An enabled bit in the error status byte has been set
3 LIA
An enabled bit in the LIA status byte has been set
4 MAV
The interface output buffer is non-empty
5 ESB
An enabled bit in the standard status byte has been set
6 SRQ
SRQ (service request) has occurred
7
unused
Standard Event Status Byte
bit
name
usage
0 OPC
Operation complete
1 INP
Input queue overflow
2
unused
3 QRY
Output queue overflow
4 EXE
A command cannot execute correctly or a parameter is out of range
5 CMD
An illegal command is received
6 URQ
Set by any user front panel action
7 PON
Set by power-on
LIA Status Word
bit
name
usage
0 CH1OV
CH1 output overload
1 CH2OV
CH2 output overload
2
unused
3 UNLK
External reference or Chop unlock detected
4 RANGE
Input range overload detected
5 SYNCF
Sync filter frequency out of range
6 SYNCOV
Sync filter overload
7 TRIG
Set when data storage is triggered
8 DAT1OV
Data Channel 1 output overload
9 DAT2OV
Data Channel 2 output overload
10
DAT3OV
Data Channel 3 output overload
11
DAT4OV
Data Channel 4 output overload
12
DCAPFIN
Display capture to USB stick completed
13
SCNST
Scan started
14
SCNFIN
Scan completed
SR865 Status Bytes
SR865 DSP Lock-in Amplifier
xvi Commands
Error Status Byte
bit
name
usage
0 CLK
External 10 MHz clock input error
1 BACKUP
Battery backup failed
2
unused
3
unused
4 VXI
VXI-11 error
5 GPIB
GPIB fast data transfer mode aborted
6 USBDEV
USB device error (interface error)
7 USBHOST
USB host error (memory stick error)
SR865 DSP Lock-in Amplifier
Getting Started 1
Chapter 1
Getting Started
Introduction
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. It is highly recommended that the first
time user step through some or all of these exercises before attempting to perform an
actual experiment.
Keys, Knobs and Touch Buttons
[Key] Front panel keys are referred to in [square] brackets. Some keys have a
second italicized label. Press and hold these keys for 2 seconds to invoke
the italicized function.
<Knob> Knobs are referred to in <angle> brackets. Knobs are used to adjust
parameters which have a wide range of values. Some knobs have a push
button function. Some also have a second italicized label. Press and hold
these knobs for 2 seconds to invoke the italicized function.
{Touch} Touchscreen buttons and icons are referred to in {curly} brackets.
Touchscreen buttons are used to adjust the data display as well as change
certain lock-in parameters.
SR865 DSP Lock-in Amplifier
2 Getting Started Chapter 1
SR865 Front Panel
The SR865’s buttons and knobs are mainly used to configure the lock-in measurement,
while the touchscreen is mainly for data display. The touchscreen display is also used for
keypad entry.
Signal Path
The signal path settings configure input BNC’s, input gain, time constant and filters and
the sensitivity. Unlike previous generation lock-ins, the SR865 does not have a dynamic
reserve setting. The input range setting is simply the largest input signal before overload.
It is best to decrease the input range setting as much as possible without overload. This
increases the gain and utilizes more of the A/D converter’s range as indicated by the
signal strength LEDs.
The sensitivity determines the scale factor for the analog outputs (CH1 and CH2) as well
as the numeric readouts and bar graphs. The sensitivity does not affect the measurem ent
values, it simply determines how much signal corresponds to a full scale 10V output from
CH1 and CH2 outputs and a 100% bar graph. It also sets the scale for the 5 digit numeric
displays. The sensitivity should be viewed as an output function only.
Reference
The reference settings configure the lock-in reference frequency and source. In addition
to internal and external reference, the SR865 includes dual reference (detect at |f
and chop (lock an SR540 chopper TO the SR865 f
) modes.
int
The SR865 can be synchronized to an external 10 MHz frequency refere nce (f ro m
another SR865 or other source). This allows multiple SR865’s to run in phase sync with
each other in internal reference mode.
int
− f
ext
|)
SR865 DSP Lock-in Amplifier
Chapter 1 Getting Started 3
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. Output functions include offset (up to ±999% of the sensitivity),
expand (up to ×100) and ratio. These functions are generally only used when the CH1 or
CH2 outputs are being used to drive other parts of an experiment.
SR865 DSP Lock-in Amplifier
4 Getting Started Chapter 1
SR865 Touchscreen
The SR865 screen displays the lock-in outputs both numerically and graphically. Touch
buttons and icons are used to adjust the data displays as well as enter certain lock-in
parameters.
Screen Layout
Press [Screen Layout] to cycle through the different screen layouts.
Trend Graph Full Screen Strip Chart
Half Screen Strip Chart Full Screen FFT
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
Chapter 1 Getting Started 5
Y, R, θ (detected), f
, f
, phase (setting), Sine Amplitude, DC Level, any Aux Input,
int
ext
Aux Output 1 or 2, Xnoise, or Ynoise.
Displayed parameters can be re-assigned at any time. Data is being stored for all possible
parameters all of the time.
Info Bar and Numeric Entry
Each of the data screens always displays a lock-in info bar across the top.
This bar always shows tiles displaying the phase, frequency, detect harmonic, sine out
amplitude and dc offset of the sine out. Each of these parameters can be adjusted using
the knobs and buttons in the reference settings section of the front panel.
Touching one of these tiles brings up a numeric keypad for direct entry.
Numeric entry is straightforward. {Close} will return to the data screen. The buttons
{F1}, {F2}, {F3} and {F4} are frequency presets. Touching a preset will load the preset
value immediately. Touch and hold a preset button to memorize the current setting. Other
parameters may have slightly different entry screens.
Strip Charts
The most common way to visualize the lock-in outputs is to use the strip chart display.
New data is plotted at the right edge and older data scrolls left. The scrol l rate is
determined by the horizontal scale (time per division). For example, a scale of 1s/div
presents the 10 most recent seconds of data and data points take 10 s to scroll completely
off the left edge. 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
Internal frequency entry screen
6 Getting Started Chapter 1
past. The time interval is determined by the horizontal scale per division and the number
of pixels in the display. There are 640 pixels across 10 divisions of the graph. Thus there
are 64 pixels in each division. At a scale of 0.5 s/div, each pixel represents about 8 ms of
data. 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.
Zooming in and out (changing the horizontal scale) always displays the most recent point
at the right edge. There is no zooming in about a point in the distant past.
All parameters which may be assigned to a data channel are continuously recorded even
when they are not displayed. This means that historical data can be viewed for all
parameters simply by assigning them to a data channel and viewing the strip chart.
Strip charts may be paused. When the graph is paused, the cursor can be used to readout
data values. Data storage continues in the background while the graph is paused. When
live scrolling is resumed, the graph is redrawn so the most recent point is once again at
the right edge.
Graph Scale Bar
Strip Chart displays have a scale bar at the bottom of the screen.
This bar shows tiles indicating the vertical scale per division for the 4 data channels
(green, blue, yellow and orange) and the horizontal time scale per division (white).
Touch a data channel’s scale tile to display a palette of scale functions.
Chart vertical scale palette
SR865 DSP Lock-in Amplifier
Chapter 1 Getting Started 7
Use the palette functions to scale the selected data channel’s graph. Touch the scale tile
again to dismiss the palette.
Vertical Scale Palette Horizontal Scale Palette
Vertical Scale Palette
Vertical scale changes are applied to each data channel separately. {Autoscale} adjusts
the scale and center so the graph occupies as much of the screen as possible. {Autoscale
Zero Center} forces the center of the graph to be zero and then sets the scale to show the
data. The location of zero is indicated by the small triangle on the right edge. It points left
where zero is. It points up or down if zero is above or below the graph.
{Zoom In} and {Zoom Out} change the scale about the center. Use {Center Newest
Point} to bring the current point to the center of the graph before zooming in or out.
{Move Up} and {Move Down} simply move the graph up and down on the screen. The
graph can also be moved simply by touching and dragging on the screen while the
vertical scale palette is displayed.
Each graph can also be turned off. Touch the scale tile to turn the graph back on.
All changes to the graphs are non-destructive. They simply change the way data is
visualized. Stored parameter values are not altered by scale changes.
Horizontal Scale Palette
Horizontal scale changes are applied to the entire strip chart display and all data channels.
{Zoom In} and {Zoom Out} change the horizontal scale and scroll speed.
{Pause} stops the chart scrolling and pauses the graph. When the graph is paused, the
cursor can be used to readout data values. These readouts correspond to the min, max or
mean of the data in the time bin at the cursor location. The time of the cursor location is
displayed in the tile at the left edge of the scale bar below the graph. Touch this tile to
switch between elapsed time from the right edge to absolute time (time and date when the
point was taken). 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
8 Getting Started Chapter 1
The cursor is only displayed when the graph is paused.
Zooming in and out preserves the right hand edge of the graph at the point in time when
the graph was paused.
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
Chapter 1 Getting Started 9
Do This
Explanation
default settings. See the Standard Settings list in
the settings.
should set the values of Y and θ to zero.
The Basic Lock-in
This measurement is designed to use the internal oscillator to explore some of the basic lock-in functions.
Specifically, you will measure the amplitude of the Sine Out at various frequencies, amplitudes, time
constants and phase shifts.
1. Disconnect all cables from the lock-in. Turn the
power on while holding down the [Local] key.
The power switch is on the power entry module
on the rear panel.
2. Connect the Sine Out + on the front panel to the
A input using a BNC cable.
3. Touch {Ampl} in the info bar along the top of
the screen. Then {5}{0}{0}{mV}.
When the power is turned on with [Local]
pressed, the lock-in returns to its standard
the Operation section for a complete listing of
The lock-in defaults to the internal oscillator
reference set at 100.000 kHz. The reference
source is indicated by the
mode, the lock-in generates a synchronous sine
output at the internal reference frequency.
The default data screen is the Trend Graph. The
4 displayed parameters default to X, Y, R and θ.
Each parameter has a numeric display, a bar
graph and a trend graph. The trend graph is a
continuously autoscaling graph of the recent
history of each parameter. This data screen has
no adjustments available.
The default sine amplitude is 0 Vrms. Thus the
data displays will read 0 for X, Y and R. θ will
be just noise.
The lock-in parameters shown in the info bar at
the top of the screen may be entered using a
numeric keypad simply by touching them.
Internal LED. In this
4. Press the [Auto Phase] key. Automatically adjust the reference phase shift
SR865 DSP Lock-in Amplifier
The Sine Out amplitude is specified for
differential output (Sine+) − (Sine−). In this
case, each BNC has an amplitude of 250 mV
(rms) with a 50Ω output. The lock-in input is
high impedance so the output of each BNC is
doubled and the lock-in measures 500 mV.
Since the phase shift of the sine output is very
close to zero, X (green) should read about
0.5000 and Y (blue) should read close to
0.0000 V.
to eliminate any residual phase error. This
10 Getting Started Chapter 1
the magnitude (−0.5000 V).
touchscreen keypad.
adjusted as well.
Range to maximize the signal at the A/D
5. Press the [+90º] key. This adds 90º to the reference phase shift. The
value of X drops to zero and Y becomes minus
Use the <Phase> knob to adjust the phase shift
back to zero (press and hold the <Phase> knob
inward as a short cut). The Phase shift is
displayed in the info bar at the top of the screen.
6. Touch {Fint} in the info bar.
The lock-in parameters shown in the info bar,
Phase, Reference Frequency, Detected
Harmonic, Sine Amplitude and Offset, can all
be adjusted from the front panel as well as via a
Display the numeric entry screen for internal
reference frequency. The 4 buttons labelled
{F1} thru {F4} are frequency presets. Press and
hold them to memorize new frequencies.
Touch {1}{0}{kHz} to enter a new frequency. Change the frequency to 10 kHz.
Use the <Frequency> knob to adjust the
frequency to 1.00000 kHz.
The knob is very useful for making small
adjustments or optimizing a setting. Large
changes are better left to the numeric keypad.
The measured signal amplitude X and R should
stay within 1% of 500 mV and Y and θ should
stay close to zero.
7. Use the <Amplitude> knob to adjust the sine out
to 5.0 mV. The Amplitude is displayed in the
info bar.
As the amplitude is changed, the values of X
and R change to follow.
The yellow LED in the Input Range section
should light. The Input Range is the largest
input signal before overload. The lower the
range, the higher the gain. The signal strength
indicates how much of the A/D converter range
is being used. When the yellow indicator lights,
it means that more gain should be used.
Since the signal has just been reduced by a
factor of 100, the input range should be
8. Press [Auto Range]. The Auto Range function changes the Input
SR865 DSP Lock-in Amplifier
Chapter 1 Getting Started 11
converter without overload. In this case the
Input Range should change to 100 mV.
The Sensitivity is indicated with 3 LEDs. In this
resolution for the smaller signal.
Input Range should change to 10 mV.
The Input Range is the peak allowable voltage
at the input, whether noise or signal. In this
case, the signal is 5 mVrms or 7 mVpk so
10 mV is the best allowed setting.
The signal strength increases from the
minimum (yellow) to something in the middle.
9. Use the <Amplitude> knob to increase the sine
out to 50.0 mV. The Amplitude is displayed in
the info bar.
The peak signal exceeds the input range so the
Input Range
Overload LED lights. Ovld
indicators also appear on the screen when a
displayed value is invalidated by an input
overload.
10. Press [Auto Range]. During Input Range Overload, the Auto Range
function selects the 1 V range.
Press [Auto Range] again. From the 1 V range, the Auto Range function
changes the Input Range to maximize the signal
at the A/D converter without overload. The
10. Press [Input Range Down] to select 30 mV. Settings which have many options, such as
Input Range, Time Constant and Sensitivity, are
changed with up and down keys. The setting is
indicated by LEDs.
The peak signal exceeds the input range so the
Input Range
Overload LED lights. Ovld
indicators also appear on the screen when a
displayed value is invalidated by an input
overload.
Press [Input Range Up] to select 100 mV.
11. Press [Sensitivity Down] multiple times to select
50 mV.
12. Press [Time Constant Down] multiple times to The Time Constant is indicated with 3 LEDs. In
SR865 DSP Lock-in Amplifier
case, the 5, ×10 and mV should be lit.
The Sensitivity sets full scale for the bar graphs
and the resolution for the numeric readouts for
X, Y and R. Sensitivity is also the signal
reading corresponding to 10 V on the CH1 and
CH2 outputs (for X, Y and R).
By decreasing the scale value, the bar graphs
and numeric readings display much more
12 Getting Started Chapter 1
select 300 μs.
this case, the 3, ×100 and μs.
value.
reasonably well and provides steady readings.
noisy for now.
The output values become noisy. This is
because the 2f component of the output (at
2 kHz) is no longer attenuated completely by
the low pass filter.
The red Output Overload LED for CH1 will
light indicating that the output voltage is
clipping. The 50 mV signal outputs 10 V when
the sensitivity is 50 mV. The large additional 2f
component will cause the output to try and
exceed 10 V and results in an output overload.
Output overload does not affect the actual
displayed value, it just indicates that the CH1
(or CH2) output is not following the measured
12. Press [Slope] to select 12 dB/oct. Parameters which have only a few values, such
as Filter Slope and External Source, have only a
single key which cycles through all available
options. Press the key until the desired option is
indicated by an LED.
Press [Slope] twice more to select 24 dB/oct. With 4 poles of low pass filtering, even this
Press [Slope] again to select 6 dB/oct. Let's leave the filtering short and the outputs
13. Press [Sync] to turn on synchronous filtering. This turns on synchronous filtering whenever
The outputs are less noisy with 2 poles of
filtering.
short time constant attenuates the 2f component
the detection frequency is below 4.8 kHz.
Synchronous filtering effectively removes
output components at multiples of the detection
frequency. At low frequencies, this filter is a
very effective way to remove 2f without using
extremely long time constants.
The outputs are now quiet and steady, even
though the time constant is very short. The
response time of the synchronous filte r is equal
to the period of the detection frequency (1 ms in
this case).
This concludes this measurement example. You
SR865 DSP Lock-in Amplifier
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.
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