Stanford Research Systems SR510 User Manual

MODEL SR510

LOCK-IN AMPLIFIER

1290- D Reamwood Av enue

Sunnyvale, CA 940 89 U.S.A.
Phone: ( 408) 744- 9040 • Fax: [phone]
Email: [e-mail] • www.thinkSRS.com

Copyright © 1985, 1987, 198 9

Stanford Resear c h S y s tems, I nc .

All Rights Reserved

Revision: 3.3 (11/2003)

TABLE OF CONTENTS

Condensed Information

SAFETY and Preparation for use 1
Symbols 2
Specifications 3
Front Panel Summary 5
Abridged Command List 6
Status Byte Definition 7
Configuration Switches 7

Guide to Operation

Front Panel 8
Signal Inputs 8
Signal Filters 8
Sensitivity 8
Dynamic Reserve 9
Status Indicators 9
Display Select 9
Output 9
Expand Function 9
Rel Function 9
Offset 10
Time Constants 10
Noise Measurements 10
Reference Input and Trigger Levels 11
Phase Controls 11
Power Switch 12
Local/Remote Operation 12
Default Settings 12

Rear Panel 13
AC Power 13
GPIB (IEEE-488) Connector 13
RS232 Interface 13
Signal Monitor Output 13
Pre-Amp Connector 13
A/D Inputs and D/A Outputs 13
Ratio Feature 13
Internal Oscillator 13

Guide to Programming

Communications 15
Command Syntax 15
Status LED's 15
RS232 Echo Feature 16
Try-out with an ASCII Terminal 16

Command List 17
Status Byte 20
Errors 20
Reset Command 20
Trouble-Shooting Interface Problems 21
Common Hardware Problems 21
Common Software Problems 21

RS232 Interface

Introduction to the RS232 21
Data Communications Equipment 22
Wait Command 22
Termination Sequence 22

GPIB (IEEE-488) Interface

Introduction to the GPIB 22
GPIB Capabilities 22
Response to Special GPIB commands 22
Serial Polls and SRQ's 23
Echo Mode using the RS232 23
Using Both the RS232 & GPIB 23

Lock-in Technique

Introduction to Lock-in Amplifiers 24
Measurement Example 24
Understanding the Specifications 25
Shielding and Ground Loops 25
Dynamic Reserve 26
Current Input 26
Auto-Tracking Bandpass Filter 26
Notch Filters 27
Frequency Range 27
Noise Measurements 27
Output Filters 27
Ratio Capability 27
Computer Interface 27
Internal Oscillator 27

SR510 Block Diagram

Block Diagram 28
Signal Channel 29
Reference Channel 29
Phase-Sensitive Detector 29
DC Amplifier and System Gain 29
Microprocessor System 29

Circuit Description

Introduction 30
Signal Amplifier 30
Current Amplifier 30
Notch Filters 30
Bandpass Filter 30
Reference Oscillator 31
PSD, LP Filters and DC Amplifier 31
Analog Output 31
A/D's 31
D/A's 32
Expand 32
Front Panel 32
Microprocessor Control 32

i

RS232 Interface 32
GPIB Interface 32
Power Supplies 33
Internal Oscillator 33

Calibration and Repair

Introduction 34
Multiplier Adjustments 34
Amplifier and Filter Adjustments 34
CMRR Adjustment 34
Line Notch Filter Adjustment 35
2xLine Notch Filter Adjustment 35
Repairing Damaged Front-End 35

Appendix A: Noise Sources and Cures

Johnson Noise 36
'1/f' Noise 36
Noise Spectrum 36
Capacitive Coupling 37
Inductive Coupling 37
Ground Loops 38
Microphonics 38
Thermocouple Effect 38

Appendix B: RS232

Simplest Case Using the RS232 39
Using Control Lines 39
Baud Rates 39
Stop Bits 40
Parity 40
Voltage Levels 40
'Eavesdropping' 40

Appendix C: GPIB

Introduction to the GPIB 41
Bus Description 41

Appendix D: Program Examples

IBM PC, Microsoft Basic, via RS232 42
IBM PC, Microsoft Fortran, via RS232 43
IBM PC, Microsoft C, via RS232 45
IBM PC, Microsoft Basic, via GPIB 47
HP-85, HP Basic, via HPIB 49

Documentation

Part Numbering and Locations 50
Parts List, Main Assembly 51
Parts List, Internal Oscillator 65
Parts List, Miscellaneous 66
Parts List, Front Panel 67
Schematic Diagrams 71

ii

Safety and Preparation for Use

***CAUTION***: This instr um ent m ay be damaged if oper at ed with the LINE VOLTAG E SELECTOR set f or
the wrong applied ac input-sour ce volt age or if the wrong f use is installed.

LINE VOLTAGE SELECTION

The SR510 operates fr om a 100V, 120V, 220V, or
240V nominal ac power source having a line
frequency of 50 or 60 Hz. Before connecting the
power cord to a power source, v erify that the LINE
VOLTAGE SELECTOR car d, located in the rear
panel fuse holder, is set so that the correct ac input
voltage value is visible.

Conversion to other ac input volt ages requires a
change in the fuse holder volt age car d pos ition and
fuse value. Disconnect the power cord, open the
fuse holder cover door and rotat e the fuse-pull lever
to rem ove the fuse. Remove the small printed circuit
board and select t he oper at ing voltage by orienting
the printed c ircuit boar d to position the desir ed
voltage to be visible when pushed firmly into it s slot .
Rotate the fuse-pull lever back into its normal
position and insert t he cor r ect fuse into the fuse
holder.

LINE FUS E

Verify that the correct line fuse is installed befor e
connecting the line cord. For 100V and 120V, use a
½ Amp fuse and for 220V and 240V, use a 1/4 Amp
fuse.

OPERATE WITH COVERS IN

PLACE

To avoid personal injury, do not remov e the
product cov er s or panels. Do not operate the
product without all covers and panels in place.

WARNING REGARDING USE

WITH PH OTOMULTIPLIERS

It is relatively easy to dam age t he signal inputs if
a photomultiplier is used improper ly with t he
lock-in amplifier. W hen left c ompletely
unt erminated, a PMT will charge a c ab le t o a
few hundred volts in a ver y short time. If this
cable is connected to t he lockin, the stored
charge may dam age the front-end transist or s.
To avoid this problem, pr ovide a leakage path of
about 100 KΩ to ground inside the base of the
PMT to prev ent charge acc um ulation.

LINE CORD

This instrument has a det achable, three- wire power
cord with a thr ee- contact plug for connect ion to both
the power sourc e and pr otective gr ound. The
protect ive gr ound cont ac t connect s to the accessible
metal part s of the instr um ent. To prevent electrical
shock, always use a power sour ce out let that has a
properly grounded pr ot ec t ive- gr ound cont act.

1

2

SR510 Specification Summary

General

Power 100, 120, 220, 240 VAC (50/60 Hz); 35 Watts Max
Mechanical 17" x 17" x 3.5" (Rack Mount Included) 12 lbs.
Warranty Two years parts and labor.

Signal Channel

Inputs Voltage: Single-ended or True Differential
Current: 10
Impedance Voltage: 100 MΩ + 25 pF, ac coupled
Current: 1 kΩ to virtual ground
Full Scale Voltage: 100 nV (10 nV on expand) to 500 mV
Sensitivity Current: 100 fA to 0.5 µA
Maximum Voltage: 100 VDC, 10 VAC damage threshold
Inputs 2 VAC peak-to-peak saturation
Current: 10 µA damage threshold
1 µA ac peak-to-peak saturation
Noise Voltage: 7 nV/√Hz at 1 kHz
Current: 0.13 pA/√Hz at 1 kHz
Common Mode Range: 1 Volt peak; Rejection: 100 dB dc to 1KHz
Above 1KHz the CMRR degrades by 6 dB/Octave
Gain Accuracy 1% (2 Hz to 100KHz)
Gain Stability 200 ppm/°C
Signal Filters 60 Hz notch, -50 dB (Q=10, adjustable from 45 to 65 Hz)
120 Hz notch, -50 dB (Q=10, adjustable from 100 to 130 Hz))
Tracking bandpass set to within 1% of ref freq (Q=5)
Dynamic Reserve 20 dB LOW (1 µV to 500 mV sensitivity)
40 dB NORM (100 nV to 50 mV sensitivity)
60 dB HIGH (100 nV to 5 mV sensitivity)
Bandpass filter adds 20 dB to dynamic reserve
Line Notch filters increase dynamic reserve to 100 dB

6

Volts/Amp

Reference Channel

Frequency 0.5 Hz to 100 kHz
Input Impedance 1 MΩ, ac coupled
Trigger SINE: 100 mV minimum, 1Vrms nominal
PULSE: ±1 Volt, 1 µsec minimum width
Mode Fundamental (f) or 2nd Harmonic (2f)

3

Acquisition Time 25 Sec at 1 Hz

6 Sec at 10 Hz

2 Sec at 10 kHz
Slew Rate 1 decade per 10 S at 1 kHz
Phase Control 90° shifts

Fine shifts in 0.025° s t eps
Phase Noise 0.01° r m s at 1 kHz, 100 msec, 12 dB TC
Phase Drift 0.1°/°C
Phase Error Less than 1° above 10Hz

Demodulator

Stab ility 5 ppm /°C on LOW dynamic reserv e

50 ppm/°C on NORM dynamic reserve

500 ppm/°C on HIG H dynam ic reserve
Time Constants Pre: 1msec to 100 s ec (6 dB/Octav e)

Post: 1sec, 0. 1 sec, none (6 dB/Octave) or none
Offset Up to 1X full scale (10X on expand)
Harmonic Rej -55 dB (bandpass f ilter in)

Outputs & Interfaces

Outputs X (RcosØ), X Offset, Noise
Output Meter 2% Precision mirror ed analog m et er
Output LCD Four digit aut o- r anging LCD display shows same values as t he analog m et er s
Output BNC ±10 V output corresponds to full scale input

<1Ω output impedance
Reference LCD Four digit LCD display for r eference phase shift or frequency
RS232 Int er f ace contr ols all funct ions. Baud rates from 300 to 19.2 K
GPI B Inter face cont r o ls a ll f u n c tions. (I EEE-488 Std)
A/D 4 BNC inputs with 13 bit resolution ( ± 10. 24 V)
D/A 2 BNC outputs with 13 bit r esolution ( ± 10. 24 V)
Ratio Ratio output equals 10X output divided by the Denom inator input .
Interna l Oscillat o r Range: 1 Hz to 100 kHz, 1% accuracy

Stability: 150 ppm/°C

Distortion: 2% THD

Amplitude: 1% accurac y, 500 ppm/°C st ability

4

Front Panel Summary

Signal Inputs Single Ended (A), Tr ue Diff erential (A-B), or Current (I)
Signal Filters Bandpass: Q-of- 5 Auto-tracking f ilter (In or Out)

Line Notch: Q- of - 10 Notch Filter at line frequency ( I n or Out)
2XLine Notch: Q-of - 10 Notch Filter at twice line frequency ( I n or Out)

Sensitivity Full scale sensitivity f r om 100 nV to 500 mV RMS for voltage inputs

or fr om 100 fA to 500 nA RMS for current inputs.

Dynamic Reserve Select Dynam ic Reserve Stability Sensitivity Rang es

LOW 20 dB 5 ppm 1 µV to 500 mV
NORM 40 dB 50 ppm 100 nV to 50 mV
HIGH 60 dB 500 ppm 100 nV t o 5 mV

Status I ndicat or s OVLD Signal O ver load

UNLK PLL is not locked to the referenc e input
ERR I llegal or Unrecognized command
ACT RS232 or GPIB interface Activity
REM Remot e m ode: front panel has been locked-out

Display Select X Signal Amplitude at t he select ed phase ( AcosØ )

OFST Display the off set which is being added to the signal output

NOISE Compute and display t he noise on t he signal
Analog Meters Displays Signal, Offset, or Noise as a fraction of full scale
Output LCD's Displays Signal, Offset, or Noise in absolute units
Output BNC's Output follows Analog Meter, ± 10 V for ± full scale
Expand Multiplies the Analog Met er and Out put voltage by a factor X1 or X10.
REL Set the Offset to null the output: subsequent readings are relat ive readings.
Offset Enables or Disables Offset, and allows any offset (up to full scale) to be enter ed.
Time Constants Pre-filter has time const ant s from 1 mS to 100 S (6 dB/Octave)

Post-f ilter has time const ant s of 0, 0.1 or 1.0 S (6 dB/Octave)
ENBW Equivalent Noise Bandwidth. Specifies t he bandwidth when making Noise

measurem ent s. (1Hz or 10 Hz ENBW)
Reference I nput 1 MΩ Input, 0. 5 Hz to 100 KHz, 100 mV minimum
Reference Tr igger Trigger on r ising edge, z er o cr os sing, or f alling edge
f/2f Mode PLL can lock t o eit her X1 or X2 of the reference input frequency
Phase Controls Adjust phase in smoothly accelerating 0.025° steps , or by

90° steps. Pres s both 90° buttons to zero the phase.
Reference LCD Display refer enc e phase sett ing or r eference frequenc y
Power Switch Instr um ent settings f r om the last use are recalled on power-up

5

Abridged Command List

A Return t he ‘REL’ Status
A0 Turn t he ‘REL’ off
A1 Turn t he ‘REL’ on

B Return Bandpass Filter St at us
B0 Take out t he Bandpass Filter
B1 Put in the Bandpass Filter

C Retur n the Reference LCD Status
C0 Display the Reference Fr equency
C1 Display t he Ref er ence Phase Shift

N Retur n the ENBW sett ing
N0 Select 1 Hz ENBW
N1 Select 1 0 Hz ENBW

O Ret ur n O ffs et Stat us
O0 Turn off Offset
O1,v Turn on Offset, v = offset

P Return t he Phase Set t ing
Pv Set the Phase to v. Abs(v) < 999 deg

D Retur n Dynam ic Reserve Set t ing
D0 Set DR to LOW range
D1 Set DR to NORM range
D2 Set DR to HIGH range

En Return Expand St at us
En,0 Turn Expand off
En,1 Turn Expand on

F Return the Ref er ence Fr equenc y
G Ret ur n t he Sensit ivity Set t ing

G1 Select 10 nV Full-Scale
... (G 1- G3 with SRS preamp only)
G24 Select 500 mV Full-Scale

H Retur n Pr eam p St at us (1=inst alled)
I Ret ur n t he Rem ot e/ Local Status

I0 Select Local: Fr ont panel act ive
I1 Select Remote: Front panel inactive
I2 Sele c t Remote with f u ll lo c k -out

J Set RS232 End-of-Record to <cr>
Jn,m,o,p Set End-of-record to n,m,o,p

K1 Simulates Key-pr ess of button #1
... (see un- abr idged comm and list)
K32 Simulates Key- pr ess of but t on #32

Q Ret ur n t he value shown on t he Output

LCD

R Retur n the trigger mode
R0 Set the trigger for rising edge
R1 Set the trigger for + zero crossing
R2 Set the trigger for falling edge

S Return t he display st at us
S0 Disp lay X = Aco s Ø
S1 Display Offset setting
S2 Dis play Noise

T1 Return pre-filter setting
T1,1 Set the pre-filter TC to 1 mS
...
T1,11 Set the pre-filter TC to 100 S

T2 Return the post-filter sett ing
T2,0 Remove post filter
T2,1 Set the post filter TC to 0.1 S
T2,2 Set the post filter TC to 1.0 S

V Return t he value of the SRQ mask
Vn Set the SRQ Mask to the value n

(See the Stat us Byte def inition)

W Return the RS232 wait inter val
Wn Set RS232 wait interval to nX4mS

L1 Return Stat us of Line Notch Filter
L1,0 Remove Line Notch Filter
L1,1 Insert Line Notc h Filter

L2 Return Stat us of 2XLine Filter
L2,0 Remove 2XLine Notch Filter
L2,1 Insert 2XLine Notch Filter

M Return t he f/2f Stat us
M0 Set refer enc e mode to f
M1 Set refer enc e mode to 2f

Xn Return t he v oltage at the rear panel

analog port n. ( n from 1 to 6)

X5,v Set analog port 5 to voltage v
X6,v Set analog port 6 to voltage v

Y Return t he St at us Byte value
Yn Test bit n of the Status Byte

Z Reset to def ault s ettings and cancel

all pending command

6

Status Byte Definition

Bit Meaning
0 Magnitude too small to calculat e

phase
1 Command Parameter is out-of -range
2 No detectable refer ence input
3 PLL is not locked to the reference
4 Signal Overload
5 Auto-off set failed: signal too large
6 SRQ generated
7 Unrecognized or illegal command

Configuration S witches

There are t wo banks of 8 switches, SW1 and
SW2, located on t he rear panel. SW1 sets the
GPIB address and SW2 set s the RS232
paramet er s. The conf igurat ion switches ar e read
continuously and any changes will b e e ffective
immediately.

SW1:GPIB Mode Switches

Bit Example Function
1 } up GPIB Address Switches

2 } up Address 0 to 30 allowed
3 } up 'up' for bit = 1
4 } down 'down' f or bit = 0
5 } up (Most Significant Bit)

6 down 'down' t o echo on RS232

(norm ally 'up')

7 up Not Used
8 up Not Used

If the GPIB mode switches ar e set as shown in the
example column above, t hen the lockin will be
addressed as G PIB device #23, and all GPI B
commands and dat a will b e e c hoed over t he
RS232 for de-bugging purposes.

SW2:RS232 Mode Swi t ches

Bit 1 Bit 2 Bit 3 Baud Rate
up up up 19200

down up up 9600
up down up 4800
down down up 2400
up up down 1200
down up down 600
up down down 300

Bit Setting Explanation
4 up Odd parity

down Even parit y

5 up No par ity

down Parit y enabled

6 up No echo ( f or comput er )

down Echo mode ( for terminal)

7 up Two st op bits

down O ne st op bit
8 unused
Eight data bits ar e always sent, regar dless of the

parity set t ing. The most significant bit is always
zero.

Example: Bit 1 'down' and all others 'up' for
RS232 communication at 9600 baud, no par it y,
two stop bits, and no echo or prom pt s by the
SR510.

7

SR510 Guide to Operation
Front Panel

The front panel has been designed to be almost
self-explanator y . The effec t of each key press is
usually reflected in the c hange of a near by LED
indicator or by a change in t he quant it y shown on
a digital display. This discussion explains each
section of t he front panel, pr oceeding left to right .

Signal Inputs

There are t hr ee input connector s locat ed in the
SIGNAL INPUT section of the front panel. The

rocker switch locat ed abov e t he B input selects
the input mode, either single-ended, A, differential,
A-B, or current , I.

The A and B inputs are voltage inputs with 100
MΩ, 25 pF input impedance. Their connector
shields are isolated from t he c hassis gr ound by
10Ω. These inputs are pr otect ed to 100V dc but
the ac input should never ex ceed 10V peak. The

maximum ac input bef ore overload is 1V peak.
The I input is a current input with an input

impedance of 1 KΩ to a virtual ground. The
largest allowable dc curr ent before overload is 1

µA. No current larger than 10 mA should ever be
applied to t his input. The conver sion ratio is 10

V/A, thus , the full scale current sensit ivities r ange
from 100 fA to 500 nA with a max ac input before
overload of 1 µA peak. You should use short
cables when using the cur r ent input.

6

allowable signals at t he inputs . The notch
frequencies ar e set at the factory to either 50 Hz
or 60 Hz. The user can adjust these frequencies.
(See the Maint enance and Repair section for
alignment details.) These f ilter s pr ecede the
bandpass filter in t he signal amplifier.

The bandpass filter has a Q of 5 and a 6 dB roll off
in either direction. Thus, the pass band (between
70% pass points) is always equal to 1/5t h of the
center frequency . The center frequenc y is
continually adjusted t o be equal t o t he internal
demodulator f r equenc y. When the refer ence
mode is f, the filter tracks the reference. When the
mode is 2f, the filter frequency is t wice the
refer ence input frequency. The center frequency
tracks as fast as the reference oscillator c a n s lew
and may be used during frequency sc ans. The
bandpass filter adds up to 20 dB of dynamic
reserve f or noise signals outside the pass band,
and increases the har m onic r ejection by at least
13dB. (2nd harm onic attenuat ed by 13 dB, higher
harmonics at t enuat ed 6dB/ octave more.) If not
needed to improve the dynamic reserve or the
harmonic reject ion t hen t he filter should be left

OUT.

Sensitivity

The sensitivity is displayed as a v alue (1- 500) and
a scale (nV, µV, mV). When using the current

input, which has a gain of 106 V/A, these scales
read fA, pA, and nA. The two keys in the
SENSITIVITY section mov e t he sensit ivity up and

down. If eit he r key is held d o wn, the s en s itivity will
continue to change in the des ired direc t ion four
times a second.

Signal Filters

There are t hr ee user selectable signal filters
available; a line frequency not ch, a 2X line
frequency notch, and an auto-tracking bandpass.
Each of the filters has a pair of indicator LED's and
a function key locat ed in the SIG NAL FILTERS

section of t he front panel. Pres sing a key will
toggle the st at us of the appropr iate filter. The
status of each filter is displayed as IN, filter active,
or OUT, fi l te r in a c tive .

The notch filter s have a Q of 10 and a depth of at
least 50 dB. Thus, the line fr equency not c h is 6
Hz wide and the 2X line notch has a width of 12
Hz. Both of these filters can incr ease the dynamic
reserve up t o 50 dB at the notch frequencies. The
achievable reser ve is limited by the maximum

The full scale sensitivit y can r ange from 100 nV to
500 mV. The sensitivit y indication is not changed
by the EXPAND func t ion. The EXPAND function

increases the out put s ensit ivity ( Volts out / volts in)
as well as the resolution of t he digital output
display.

Not all dynamic reserves ar e av ailable at all
sensitivities. I f the sensitivity is changed to a
setting f or which the dynamic r eser ve is not
allo we d , the dy n a mic res e r v e will c hange t o the
next setting which is allo we d. Sensitivity takes
precedence over the dynamic reserve. The
sensitivity range of eac h dynam ic res er ve is
shown below.

8

Dynamic Reserve Sensitivity Ran ge
LOW 1 µV through 500 mV

NORM 100 nV t hr ough 50 m V
HIGH 100 nV thr ough 5 m V

Dynam ic Reserve

REM indicates t hat t he unit is in the remote state

and that the front panel cont r ols ar e not operative.
There are t wo remote stat es. The Remot e-With­Lock o ut will not a llow any inputs from the front
panel. The Remote- Wit hout - Lock out comm and
allows you to return the front panel to operation by
pressing the DI SPL AY UP key.

The dynamic reser ve ( DR) is set using the keys in
the DYNAMIC RES ERVE section. The r eser v e is

displayed by the three indicator LED's, HIGH,
NORM, LOW. Only those dynamic reserve
settings available for the sensitivity are allowed
(see above table) . For example, when the

sensitivity is 500 mV, the DR will always b e LOW.
The dynamic reser ve and out put st ability of e a c h

setting ar e shown below.
Setting Dy n amic Reserve Ou tput Sta bility

(ppm/°C)
LOW 20 dB 5
NORM 40 dB 50
HIGH 60 dB 500

Since a higher DR results in degraded output
sta b ility, y ou s hould use t he lowest DR sett ing f or
which there is no overload indication. Note t hat
using the Bandpass Filter prov ides about 20dB of
additional DR and so allows you to oper at e with a
lower DR s etting .

Status

Dip lay Sel ect

The keys in the DISPLAY section select the
paramet er to be displayed on the out put meters

and the output on the OUT PUT BNC connector.
The displayed param et er is indicated by one of t he

three LED’s and can be either t he demodulator
output ( X), the offset (OFST), or the rm s noise

(NOISE). When displaying NOISE, the equivalent
noise bandwidth (ENBW) is se lec ted in t h e TIME

CONSTANT section.

Output

The analog output is available at t he OUTPUT
BNC. The input signal equal t o t he s elected full

scale sensitivity will generate a ± 10V out put when
the EXPAND function is off. With the EXPAND on,

the output is multiplied by 10, eff ectively
increasing the full scale sensitivity by 10. The
ouptut impedanc e is <1Ω and t he output current is
limited to 20 mA.

The analog meter always displays the OUTPUT
voltage. Accur acy is 2% of full scale.

There are f ive STATUS LED's.
OVLD indicates a signa l over load. This condition

can occur when the signal is too large, the
sensitivity is too high, the dynamic reserve is too
low, the off set is on, the expand is on, the time
constant is not lar ge enough, or the ENBW is too
large.

UNLK in d ic ates t h at the referen c e o s c illator is n o t
phase locked to the external refer enc e input. This
can occur if the ref erence amplitude is t oo low, t he

frequency is out of range, or the trigger m ode is
incorrect f or the refer ence s ignal waveform .

ERR flashes when an er r or occ ur s on one of the
computer int erfaces, such as an incorrect

command, invalid parameter, etc.
ACT indicates act ivity on t he com put er interfaces.

This LED blinks every tim e a char act er is received
by the SR510 or transmit t ed by the SR510.

The OUTPUT LC D disp lay pr ovides a r ead- out of
the displayed paramet er in r eal units. The scale of

the displayed quantity is indicated by t he t hr ee
scale LED's to the r ight of the display. This read­out auto r anges and will re flect the sens itivity
added when the EXPAND f unc t ion is on.

Expand

The output EXPAND is toggled by pressing the
key in the EXPAND section. The expand status is
indicated by the X10, ex pand on, and the X1,

expand off, LED's.

REL Function

The relative (aut o- zer o) func t ion is toggled by the
key in the REL section. Every time t he rel stat us

LED is turned ON the offset value is set to minus
the value of t he X output, thus zeroing the X
out p ut. This function will work e v en if X is not the

9

current ly displayed param et er . If the output is
greater than 1.024 t im es full scale, the REL

fun c tion will not b e a ble to zer o the output and the
ON LED will blink . The of fset v a lue will then be set

to its max value. If NOISE is being displayed when
the REL function is turned on, the noise ouptut will

require a sew seconds to s ettle again.
If the manual OFFSET in ON when the REL

function is tur ned on, t he manual OFFSET will be
turned OFF before the auto zero is done.

The REL func t ion and t he m anual OFFSET are
both ways to ent er the offs et value. When the REL
function is tur ned off using t he REL key the offset

is turned of f but the value is not lost. If the manual
OFFSET is now tur ned ON, the off s et will b e that

set by the REL funct ion.

Offset

The OFFSET section controls the manual
OFFSET. The offset is turned ON and OFF using

the upper key in the OFFSET section. When the
offset is ON, the lower two keys are used to set
the amount of offset. A single key press will
advance the of f set by 0.025% of full scale. If the
key is held down, the off set advances in larger and
larger increments, the largest increment being

10% of full scale. When the offs et is turned OFF
the applied offset r eturns to zero but the offset

value is not lost. The next pres s of the upper
offset key (ret ur ns to ON) sets the offset to the

previously entered value.
If an attempt is made to advance the offset v alue

beyond full scale, the OFFSET ON LED will blin k .
An offset up to 1.024 tim es the full scale sensitivity

may be enter ed. When the expand is on, this is
10X the full scale output.

If the REL function is ON when the manual

OFFSET is t ur ned ON, the REL funct ion is tur ned
OFF but the off set value rem ains the same. The
OFFSET key s m ay now be used t o adjust this

offset value.
Note that the offsets (either manual off set or those

generated by t he REL function) represent a
fract ion of the full scale reading, and so their

absolute value will change when the s ensitivity
scale is changed. A signal which has been nulled
by an offset will n o t be nulled when t he sens itivity
scale is changed. The analog meter and the
output BNC indicate the sam e value given by the
equation:

V

= 10Ae(AvVicosØ+Vos)

out
where...
Ae= 1 or 10 per the Expand setting

Av= 1/Sensitivity
Vi= m agnitude of the signal
Ø = phase between signal & reference

Vos= of f s et (fract ion of FS < 1.024)

Time Constant

There are t wo post demodulator low pass f ilters ,
labeled PRE and POST. The PRE filter precedes

the POST filter in the output amplifier. Each filter
provides 6 dB/oct attenuat ion.

The PRE filter t im e const ant ranges from 1 mS to

100 S and is selected by the two keys below the
PRE filter indicator LED's. Holding down either

key will a d v ance the time constant twic e a s ec o n d
in the desired direction.

The POST filter time constant can be set to 1 S or

0.1 S, or can be removed altogether, NONE, using
the two keys below the ENBW indicators. When
set to NONE, the total attenuat ion is that of the

PRE filter, or 6 dB/ oct. When the POST filter is 1
S or 0.1S, the total attenuation is 12 dB/oct for

frequency c om ponent s beyond the larger of the
POST and PRE f ilter bandwidths ( r ecipr ocal tim e

constant).

Noise

When the DISPLAY is set to NOISE, none of the
PRE and POST ind icat or LED's ar e on. Inst ead,

one of the two ENBW indicator s will be on,
showing the Equivalent Noise Bandwidth of the

rms noise calculation. The ENBW is set using the
keys below the ENBW indicator LED's (same keys
as used to set the POST f ilter ). The PRE filter
keys do nothing in this case. Pressing the upper

key when the bandwidth is already 1 Hz will reset
the rm s noise average (out put) to zero, res t arting

the calculation. Likewise with pr ess ing the lower
key when 10 Hz is already selected.

The noise is the rms dev iation of the out put within
a 1 or 10 Hz equivalent noise bandwidth about the
refer ence frequency . A dc output does not
contribut e t o the noise, the noise is determ ined

10

only by the ac 'wiggles' at t he output. By
measuring the noise at dif f erent frequencies, t he
frequency dependenc e of t he noise densit y can be
found. This usually has the form of v

The noise computat ion assum es t hat t he noise
has a Gaussian distr ibution ( such as J ohnson
noise). Since the com put ation takes m any time
constant s (reciproc al bandwidt h) , t he noise output
should be allowed to approach a st eady value
before a r eading is taken. For the 1 Hz ENBW,
this time is on the order of 15 to 30 seconds; for
the 10 Hz ENBW , the o utp ut stabilizes much
fas ter. The n ois e o u tput will var y s lig htly sinc e
the re will alwa y s b e n o is e v a riation s that a r e s lo w
compared t o the bandwidth. Any DC component
in th e ou tput will n o t cont ribute to the noise.
Howeve r , a larg e DC ou tput will c a u s e the nois e
computat ion t o initially rise to a large value bef or e
approaching the f inal answer. As a r esult, t he
com p utatio n will take longer to settle.

To obtain a value for the noise density, t he noise
reading should be divided by the squar e r oot of
the ENBW. Thus, when the ENBW is 1 Hz, the
noise output is the noise densit y, and when t he
ENBW is 10 Hz, the noise density is the noise
output divided by √10. For exam ple, if the input
noise is measured to be 7 nV with the ENBW set
to 1 Hz, the noise density is 7 nV/√Hz . Swit c h in g
the ENBW to 10 Hz results in a faster
measurem ent and a reading of 22 nV on the
output. The noise density is 22 nV/√10 Hz or 7

nV/√Hz. At frequencies » 10 Hz, the noise
density should be independent of t he ENBW.

noise ~

1/f.

Reference and Trigger Level

The REFERENCE I NPUT BNC is lo c a ted in t his
section. The input is ac c oupled and the

impedance is 1 MΩ. The dc voltage at this input
should not exceed 100 V and the largest ac signal
should be less than 10 V peak. The t hree
indicators above the input BNC display t he

TRIGGER MODE. The single key above the input
BNC is used to select the TRIGGER MODE.

If the center TRIGGER MODE LED is on, the
mode is SYMMETRIC and the reference oscillator
will lock to the positive zer o cr oss ings of the ac
refer ence input . The ac signal must be symmetric
(e.g. sine wave, s quar e wave, etc.) and have a
peak to peak amplitude gr eat er t han 100 mV. A
signal with 1 Vrms am plitude is r ecommended.
The phase accuracy of the reference channel is
specified for a 1Vr m s sinewave in the symmetric
trigger m ode.

If the upper TRIGGER MODE LED is on, the
mode is POSITIVE. The trigger threshold is +1V
and the ref erence oscillator will lock t o the positive
going transitions of t he refer ence input . This
mode tr iggers on the rising edges of a TTL type
pulse train. The pulse width mus t be great er than
1 µS.

If the lo w e r TRIGGER MODE LED is on, the mode
is NEGATIVE. The trigger threshold is -1V and

the referen c e o s c illa tor wil l lo c k to the negative
going transitions of t he refer ence input . This
mode tr iggers on a negative pulse tr ain or on the
falling edges of a TTL type pulse t r ain
(rem em ber ing that t he input is ac coupled). The
pulse width must be greater than 1 µS.
Above the TRIGGER MODE indicators are the

REFERENCE MO DE LED's. The key below the
REFERENCE MO DE indicators toggles bet ween f

and 2f. When the MODE is f, the lock-in will
detect s ignals at t he refer ence input fr equency.
When the MODE is 2f, the lock-in det ect s signals
at twice the refer ence input frequency . In either
case , the referen c e os c illa tor ha s a ma x im u m
frequency of 100 KHz, thus, when in the 2f mode,
the ref erence input f r equency may not exceed 50
KHz.

The REFERENCE DIGITAL DISPLAY shows
eith e r the ref erence o s c illa tor f r equenc y or

phaseshift. The displayed parameter toggles
between the t wo whenever t he SELECT key is

pressed. The appr opr iat e sc ale indicator below
the display will be on. It is useful to check the
frequency display t o ver if y that the lock-in has
correct ly locked t o y our ref erence. The reference
frequency is m easur ed to 1 part in 256 resolution.

Phase Controls

The phase shift bet ween t he refer ence osc illator
and the ref erence input is set using the f our keys
in the PHASE section. The t wo keys below the
FINE label increment t he phase setting in small

amounts. A single key press will change t he
phase by 0.025 degrees in the desir ed direction.
Holding the key down will continue to change the
phase with larger and larger s t eps with t he largest
step being 10 degrees. The two 90° keys are
used to change t he phase by 90 degree
increments . The upper key will add 90 degrees
and the lower key will su btract 90 degrees.
Holding both keys down at once s et s the phase

shift back to zero. The REFERENCE DIGITAL
DISPLAY automatically displays t he phas e

11

whenever any of t he PHASE key s ar e pr essed.
The phase ranges fr om -180 degr ees to +180

degrees and is the phase delay f r om the refer ence
input signal.

Power

This is the instrume n t's POWER switch. When the
power is turned of f, the front panel settings are

retained so t hat the inst r ument will retur n to the
same settings when the power is next turned on.

When the power is tur ned on, the OUTPUT

DIGITAL DISPLAY will show the SERIAL
NUMBER of the instr ument and REFERENCE
DISPLAY shows the model number of the

instrument. All displays return to normal after 2
seconds.

Local and Remote

When the instr um ent is progr ammed via the
computer int erface t o be in the REMOTE state

WITHO UT LO CK-OUT, the DISPLAY UP key will
return the instrument to LOCAL f ront panel
control. If the instr ument is in the REMOTE WITH
LOCK-OUT state, no front panel key will ret u r n the
status to LOCAL. In this case, a RETURN TO
LOCAL c om m and m ust be s ent over the computer
interfac e or the power must be turned off and back
on.

Defaults

If the REL key is held down when the POWER is
turned on, the instr um ent settings will be s et to the

defaults shown below instead of t he settings in
effect when the power was t ur ned off.

Parameter Setting
BANDPASS OUT

LINE OUT
LINE X 2 OUT
SENSITIVITY 500 mV
DYN RES LOW
DISPLAY X
EXPAND OFF
REL OFF
OFFSET OFF (value=0)
PRE TIME CONSTANT 100 mS
POST TIME CONST ANT 0.1 S
ENBW 1 Hz
REFERENCE MO DE f
TRIGGER MODE SYMMETRIC
REFERENCE DISPLAY FREQUENC Y
PHASE 0°

Whenever def ault values ar e used at power up,
the red ERR LED will turn on f or about 3 seconds.
If the ERR LED is on when the instrument is

powered on without the LOCAL key down, then
the instr um ent is ignoring the ret ained settings.
This can be due to a low battery.

12

SR510 Guide to Operation

Pin Voltage Current Available

Rear Panel

AC Power

The ac line voltage selector car d, line fuse, and
line cord receptacle ar e located in t he f use holder
at the left side of the rear panel. See the section,
Preparati on f or Use at the front of this manual for

instruct ions on set t ing t he ac voltage selector and
choosing the corr ect fuse.

GPIB Connector

The SR530 has an IEEE 488 ( G PI B) int er f ace built
in. The GPIB addr ess is set using SW1 located to

the right of t he interface c onnect or s. Refer to
page 7 for switch sett ing details.

RS232 Connector

The SR530 has an RS232 interf ace. The
connector is conf igur ed as a DCE. The baud rate,

parity, st op bits, and echo mode are select ed
using SW2 locat ed t o t he r ight of the interface

connectors . Refer to Page 7 for switch setting
details.

Signal Monitor O utput

1 + 20 100 mA
2 + 5 10 m A
6 - 20 100 mA

7 Signa l gr ound
8 Digital ground

Gene ral Purpose A/D and D/A

There are f our analog input port s, labeled X1
through X4. These inputs may be digitized and
read via the com put er interfaces. The range is -

10.24 V to +10.24 V and the resolution is 2.5 m V.
The input impedance is 1 MΩ. A digitization can
be perfor m ed in about 3 mS but the result may
take longer t o transm it over the interf ac e being
used.

There are t wo analog output ports, labeled X5 and
X6. The voltages at t hese ports m ay be
program m ed via t he computer interfaces. The
range is -10.24 V to +10. 24 V and the resolution is

2.5 mV. The output impedance is <1Ω and the
output cur r ent is limited to 20 mA.

Ratio

Output X5 is the ratio output when not
program m ed by the computer interface or s et via

the fr ont panel. X5 becom es the ratio output
whenever the unit is t ur ned on.

This BNC provides the buf f er ed output of t he
signal amplifiers and f ilter s . This is the signal just
before t he dem odulat or. The output impedanc e is
<1Ω. When a full scale input is applied, the peak­to-peak am plitude at this output is 20 mV, 200 mV
or 2 V for dynamic reserve settings of high, norm,
and low, respectively.

Preamp Connector

This 9 pin "D" connector provides power and
control signals to ext er nal per ipherals such as pr e­amplifiers. The av ailable power is descr ibed
below.

The voltage at X5 is t he ratio of the det ected
signal output, X, t o the analog voltage at port X1.

An output of 10 V corres ponds to a ratio of 1. The
ratio is comput ed by digitizing the dem odulat or

output and t he voltage at port X1 and then taking
the rat io. The resolution is 0. 0025 V. For best
accuracy, t he sens itivity should be set to provide

at least a 50% full scale signal and the analog
denominator ( X1) should be 5V or greater. The

ratio is updated appr oxim at ely ever y 1. 5 mS. For
the Ratio feat ur e to work, the voltage at the
denominator input m ust ex ceed 40 mV.

Internal Oscillator

The INTERNAL OSCILLATOR is a voltage
controlled oscillat or with a sine wave output . To

use the osc illator as the ref erence s o urce, connect
the REF O UTPUT on the r ear panel to the REF

INPUT on the fr ont panel. The REF OUTPUT is a
1 Vrms sine wave. The SINE OUTPUT may be
used as the st imulus to the experiment . The SINE

13

OUTPUT can be set to three amplitudes, 1 V, 100
mV, and 10 mV (rms) using t he amplitude switch.

The output impedanc e is 600Ω. The AMP CAL
screw adjusts t he am plitude.

The oscillator frequency is controlled by the VCO
INPUT voltage. A voltage f r om 0V to 10V will
adjust the f r equency ac cor ding t o the VCO
RANGE select ed. Thr ee r anges ar e available, 1
Hz/V, 100 Hz/V, and 10 KHz/V. The input
impedance is 10 kΩ. Th e FREQUENC Y CAL
screw adjusts t he frequency.

There are f our ways to set the frequency:

1) Connect X5 or X6 (D/A outputs) to the VCO
INPUT. The fr equency is now cont r ollable via the
computer int erfaces by pr ogr amming X5 or X6.

2) If the VCO INPUT is left open, then the
oscillato r will run at the top of its range (i.e. 10 Hz,

1 KHz, or 100 KHz).

3) A 10 KΩ potentiomet er may be connected from
the VCO INPUT to ground. This pot will then set

the fr equency .

4) Connect t he VCO INPUT to an exter nal voltage
source which can provide 0 to 10V.

In all four cases, if the REF OUTPUT is connected
to the REFERENCE I NPUT on the front panel, the

frequency m ay be read on the front panel
REFERENCE DIGITAL DISPLAY or via the

computer int erfaces.

14

SR510 Guide to
Programming

An example of a multiple comm and is:
G 5; T 1,4; P 45.10 <cr>

The SR510 Lock-in Amplifier is r em ot ely
program m able via both RS232 and GPI B
interfac es. It may be used with laboratory
computer s or simply with a terminal. All front
panel features ( except signal input selection and
power) may be controlled and read via t he
computer int erfaces. The SR510 can also read
the analog output s of other laboratory instr um ents
using its four gener al pur pose analog input por t s.
There are also two pr ogr ammable analog output
ports available to prov ide general purpos e cont r ol
voltages.

Comm unicating with the SR510

Before using either the RS232 or GPIB interface,
the appropr iate c onf iguration switches need t o be

set. There are two banks of 8 switches, SW1 and
SW2, locat ed on t he rear panel. SW1 sets the
GPIB address and SW2 sets the RS232
paramet er s. The conf igurat ion switches ar e read
continuously and any changes w ill be e ffective
immediately. For details on switch settings, s ee
page 7 at the front of this manual.

Command Syntax

Communications with the SR510 use AS CII
character s . Commands to t he SR510 may be in
eith er UPPER or lower cas e .

It is not necessary to wait between comm ands .
The SR510 has a command input buf f er of 256
character s and pr ocess es the commands in the
order r eceived. Likewise, t he SR510 has an
output buf fer (for each interfac e) of 256
characters.

In general, if a command is sent without
paramet er s, it is inter pr eted as a request to read
the status of the associated f unction or setting.
Values returned by t he SR510 are s ent as a string
of ASCII char act ers t erminated usually by car r iage
retur n, line-feed. For example, after the above
command is sent , the following read commands
would generate the r esponses s hown below.

Command Response from t he SR510
G <cr> 5<cr><lf>

T 1 <cr> 4<cr><lf>
P <cr> 45.10< cr > < lf>

The choice of ter m inat ing characters sent by the
SR510 is determined by which interfac e is being
used and whether t he 'ec ho' feat ur e is in use. The
term inating sequence f or the GPIB interf ace is
always <cr>< lf > (with EOI). The default sequenc e
for RS232 is <cr> when the echo mode is off, and
<cr> < lf> when the echo mode is on. The
term inating sequence f or the RS232 interface may
be changed using the J comm and.

A command t o the SR510 consists of one or two
command letters, arguments or parameters if
necessary, and an ASCII carriage ret ur n (<cr>) or
line-feed (<lf > ) or both. The different part s of the
command do not need to be separated by spaces .
If spac es are included, they will b e ignor ed. I f
more t han one paramet er is required by a
command, the param et ers m ust be separated by a
comma. Examples of commands ar e:

G 5 <cr> set the sensitivity to 200 nV
T 1,4 <cr> set the pre filter to 30 mS
F <cr> read the reference frequency
P 45.10 <cr > set phase shift to 45. 10°
X 5,-1. 23E-1 < cr> set por t X5 to -0.123 V

Multiple commands m ay be sent on a single line.
The commands m ust be separ at ed by a semicolon
(;) character. The commands will n o t be exec u ted
until the ter m inating car r iage return is sent.

Note that the terminating char act er s are sent with
each value retur ned by t he SR510. Thus, the
response to the command string G;T1; P< cr > while
using the RS232 non-echo mode would be
5<cr>4<cr>45.10<cr>.

Front Panel S ta tus LED's

The ACT LE D f lashes whenever t he SR510 is
sending or receiving charact er s ov er the comput er

interfaces.
The ERR LED f lashes whenever an er r or has

occurred, s uch as, an illegal command has been
received, a par am et er is out of range, or a
communicat ion buff er has exceeded 240
character s . This LED flashes for about thr ee
seconds on power-up if t he batt er y voltage is
insufficient t o r et ain pr evious instr um ent settings.

15

The REM LED is on whenever t he SR510 is
program m ed to be in the remote state.

RS232 Echo and No Echo
Operation

In order to allow the SR510 to be operat ed from a
term inal, an echo f eature has been included which
causes the unit t o echo back commands rec eived
over the RS232 port . This feature is enabled by
setting switch 6 on SW2 to the DOWN position. In

this mode, the SR510 will send line-feeds in
addition to carr iage returns with each value
retur ned and will a ls o s end the prompts 'OK>' and
'?>' t o indicate that the pr evious com m and line
was either processed or contained an error.
Operat ing t he SR510 fr om a terminal is an ideal
way to learn the commands and r es ponses bef ore
attem pt ing t o program a computer to contr ol the
SR510. When the unit is controlled by a
computer , the ec ho featur e should be turned off t o
prevent t he s ending of spurious characters which
the comput er is not expecting.

Try-Out with an ASCII Terminal

Before at t em pting any detailed program m ing with
the SR510, it is best to try out the commands
using a terminal. Connect a term inal with an
RS232 port to t he RS232 connector on t he rear
panel of the SR510. Set the baud rat e, parit y, and

stop bits t o match the term inal by setting SW2 per
the switch set t ing t able given on page 7. The
echo mode should be enabled (switch 6 DOWN).

After setting SW2 and connecting the term inal,
hold down the REL key whi le turning the unit on.
This causes the SR510 to assum e its def ault
settings so t hat t he following discussion will agree

with the actual re sponses of t he SR510. The ACT
and ERR LED's on t he front panel will f la s h for a
second and the sign-on m essage will appear on
the terminal. Following the m es sage, the prom pt
'O K> ' will be displa y e d. This indicat e s that th e
SR510 is ready to accept commands .

to the terminal.
Now read the gain using the sensitivity r ead

command, G<cr>. The response should be 24
meaning that the sensitivity is at the 24th setting or
500 mV. Change the sensit ivity by typing
G19<cr >. The sensitivity should now be 10 mV.
Check the fr ont panel to mak e sure this is so.

The output of the lock- in is read by typing the
command, Q1<c r >. The response is a signed
floating point number with up t o 5 significant digits
plus a signed exponent. Change the gain to 10 uV
using the G10 com m and. The response to the Q1
command will now be sim ilar to the pre v iou s o n e
except t hat the exponent is differ ent.

Attach a DC voltmeter to the X6 output on the rear
panel. The range should allow for 10V readings.

The voltage at t he X6 output can be set using the
X6 command. Type X6,5.0<cr> and the X6 output

will change to 5.0V. To read this back to the
terminal, just type X6<cr>. When setting the X6

voltage, t he volt age m ay be sent as an integer (5),
real (5.000) , or floating point ( 0. 500E1) num ber.

Now connect the X6 out put to the X1 input (also
on the rear panel). X1 through X4 ar e analog
input ports . To read the voltage on X1, si mply
type X1<cr>. The response 5.000 should appear
on the terminal. The analog port s X1 through X6
can be used by your computer to read outputs of
other inst r um ent s as well as to control other
laboratory par am eters.

At this point, the user should experiment with a
few of the comm ands. A detailed command list
follows.

Type the lett er 'P' followed by a carriage ret ur n
(P<cr> ). The SR510 responds by sending to t he
term inal the char acters 0.00 indicating that t he
phase is set to 0 degrees. In general, a command
with no argument s or param et ers reads a sett ing
of the unit. To set the phase to 45 degrees, type
the comm and, P45<cr >. To see that the phase
did change, use the SELECT k ey on t he front
panel to display the phase on the REFERENCE
DIGITAL DISPLAY. Typing the phase read

command, P< cr>, will now return the s tr in g 45 .00

16

SR510 Command List

The first letter in each command sequenc e is the
command. The rest of the sequence consists of
paramet er s. Multiple parameter s ar e separated by
a comma. Those param eters shown in {} are
optional while those without { } ar e required.
Variables m and n represent integer parameters
while v represent s a real number. Parameter s m
and n must be expressed in integer f ormat while v
may be in integer, real, or floating point f ormat .

F

The F command r eads the refer ence frequency.
For example, if the ref erence frequency is 100 Hz,

the F comm and retur ns the string "100. 0". If the
refer ence frequency is 100. 0 kHz, the string
"100.0E+3" is ret ur ned. The F command is a read
only command.

G {n}

If n is included, the G command sets t he gain
(sensitivity) . If n is absent, the gain setting is
returned.

A {n}

If n is "1", the A command causes the auto offset
routine to r un. Every time an "A 1" command is

received, t he aut o offs et function is executed. If n
is "0", then the auto offset is tur ned off. If n is
absent, then the auto offset st atus is returned.
Note that if the manual offset is on, an "A 1"
command will turn o ff the m anual offset befor e
executing the aut o offs et funct ion.

B {n}

If n is "1", the B command sets the bandpass filter
in. If n is "0", the bandpass filter is taken out. If n

is absent, t hen the bandpass f ilter status is
returned.

C {n}
If n is "1", the C command sets the reference LCD
display to show the phase setting. If n is "0", the

LCD will display the refer enc e frequency. If n is
absent, the paramet er being displayed (frequency
or phase) is returned. Note that the P and F
commands ar e used to read the act ual values of
the phase and fr equenc y.

D {n}
If n is included, the D command s ets the dynamic
reserve. If n is absent, the dynamic reserve

setting is ret ur ned.

n Sensitivity
1 10 nV
2 20 nV
3 50 nV
4 100 nV
5 200 nV
6 500 nV
71 µV

82 µV
95 µV
10 10 µV
11 20 µV
12 50 µV
13 100 µV
14 200 µV
15 500 µV
16 1 mV
17 2 mV
18 5 mV
19 10 mV
20 20 mV
21 50 mV
22 100 mV
23 200 mV
24 500 mV

Note that sensit ivity sett ings below 100 nV are
allowed only when a pre-amplifier is connect ed.

n Dyn Res
0LOW
1NORM
2 HIGH

Note that not all dynamic reserv e settings ar e
allowed at every s ensit ivity.

E {n}

If n is "1", the E command turns the output expand
on. If n is "0", the expand is turned off. If n is

absent, the expand status is returned.

H

The H command reads t he pre-ampli f i er stat us.
If a pre-am plifier is connect ed, a "1" is returned,

otherwise, a "0" is r et urned. The H command is a
read only command.

I {n}
If n is included, the I command sets t he remote­local st atus. If n is absent, the remote-local stat us

is returned.

17

n Status
0 Local: all front panel keys ar e oper ative
1 Remote: front panel keys ar e not

operative. The display up key re t urns the
status to local.

20 Quad Down
21 Select Display (f/ phase)
22 Sensitivity Up
23 Sensitivity Down
24 Dyn Res Up
25 Dyn Res Do wn
26 Display Up
27 Display Down

2 Lock-out: front panel keys are not

operative. No key retur ns the status to
local. Another I command is needed t o
return to loc a l.

When using the GPI B interface, the REN, LLO,
and GTL comm ands ar e not implement ed. The I
command is used by bot h interf aces to set the
remot e- local status.

J {n1,n2, n3, n4}

The J command sets the RS232 end-of-record
character s sent by the SR510 to those specif ied

by the ASCII codes n1- n4. If no argument is
included, t he end- of-r ec or d sequence r eturns to
the default ( a carriage return) , other wise, up to
four char acters may be specified. The end- of­record r equired by the SR510 when receiving
commands is not affected.

K n
The K command simulat es a front panel key
press. The effect is exactly the same as press ing

the selected key onc e. The paramet er n is
required.

nKey
1 Post Time Constant Up
2 Post Time Constant Down
3 Pre Time Constant Up
4 Pre Time Constant Down
5 Offset Up
6 Offset Down
7 Zero Phase (Simultaneous 90¡ Up and

Down)
8 Line Notch Filter
9 Bandpass Filter
10 Line X 2 Notch Filter
11 Relative (Auto Offset)
12 Offset (On/Off)
13 Expand
14 Local (Display Up when REMOTE)
15 Reference Trigger M ode
16 Reference Mode (f/2f)
17 Degrees Up
18 Degrees Down
19 Quad Up

L m {,n}

The L command set s and reads the status of the
line notch filters. If m is "1", then the 1X line

notch is selected, if m is "2", the 2X line notch is
selected. The par am et er m is required. If n is "1",
the L command sets the selected f ilter in. If n is
"0", the select ed filter is t aken out. If n is absent,
the status of the selected filter is ret urned.

M {n}
If n is "1", the M command sets the reference
mode to 2f. If n is "0", the reference mode is set

to f. If n is absent, the reference mode is returned.

N {m}

If m is "1", the N command sets the ENBW to 10
Hz. If m is "0", the ENBW is set to 1 Hz. If m is

absent, the ENBW setting is retur ned.

O {n} {,v}

If n is "1", the O command turns the offset on. If n
is "0", the offset is tur ned off. If n is absent, the

offset st at us (on or off) is returned. (The value of
the off s et is read using the S and Q commands.)
If n is included, then v may also be sent. v is the
offset value up to plus or minus full scale in units
of volts. For example, to offset half of full scale on
the 100 µV sensitivity, v should be "50. 0E-6" or an
equivalent value. However, if the sensitivit y is
then changed to 200 µV, the off s et is now half of
the new full scale or 100 µV. When the sensitivity
is changed, the offset is retained as a const ant
fract ion of full scale rat her than as a voltage
refer r ed to the input. The expand funct ion will, o n
the other hand, preser v e the value of the offset as
an input refer r ed voltage. Once a value of v is
sent, the of f set may be turned off and on without
losing the offset value by using the O command
without the v par am eter. Note that if the auto
offset is on, an "O 1" command will t u rn the au to
offset of f and tur n the manual offset on without
changing the actual offset value.

P {v}

If v is absent, the P command returns the phase
setting f r om -180 to +180 degrees. When v is

included, t he phase is set to the value of v up to
±999 degrees.

18