DSP TP104-plus Specifications

MODEL SR850 DSP Lock-In Amplifier 1290-D Reamwood Avenue Sunnyvale, California 94089 Phone: (408) 744-9040 • Fax: (408)

SR850 DSP Lock-In Amplifier1-8DTRC (?) i {, j} 6-11 Set (Query) theFull (i=0), Top (i=1) or Bottom (i=2) Display Trace to trace j (1,2,3,4).DSCL (?) {

4-18Screen Display

SR850 DSP Lock-In Amplifier1-9RDAT 6-18 Recall the Trace Data from the file specified by FNAM to the active display's trace buffer.RSET 6-18 Reca

SR850 DSP Lock-In Amplifier1-10SERIAL POLL STATUS BYTE (6-28)bit name usage0 SCN No data is being acquired1 IFC No command execution in progress2 ERR

GETTING STARTEDThe sample measurements described in this section are designed to acquaint the first time user with theSR850 DSP Lock-In Amplifier. Do

2-2Getting Started

2-3THE BASIC LOCK-INThis measurement is designed to use the internal oscillator to explore some of the basic lock-in functions.You will need BNC cable

2-45. Press the <Rotate 90 deg> softkey.Press the <deg.> softkey. Use the knob to adjust the phase shift until Yis zero and X is equal to

2-59. Press <Sensitivity>Use the knob to change the sensitivity to50 mV.Change the sensitivity back to 20 mV.10. Press <Time Constant>Use

2-613. Press [GAIN/TC]Press <Synchronous> to select <200 Hz. Display the Gain and Time Constant menu again.This turns on synchronous filterin

2-7DISPLAYS and TRACES This measurement is designed to use the internal oscillator and an external signal source to explore some ofthe display types.

2-8Displays and TracesHighlight the internal oscillator frequency.By setting the lock-in reference 0.2 Hz away fromthe signal frequency, the X and Y o

2-9Displays and Traces[AUTO SCALE] automatically scales the activedisplay. In this case, the trace data is moving andautoscaling may not do a very sat

2-10Displays and TracesWith a TTL reference signal, the slope needs to beset to either rising or falling edge.The signal vector on the polar graph wil

2-11Displays and TracesUsing the keypad, enter a phase shift which is45° greater than the displayed phase shift.At a measured phase shift of 45°, trac

2-12Displays and Traces

2-13OUTPUTS, OFFSETS and EXPANDSThis measurement is designed to use the internal oscillator to explore some of the basic lock-in outputs. Youwill need

2-144. Press [REF/PHASE]Press <Sine Output>Press [.] [5] [ENTER]5. Press [OUTPUT/OFFSET]Press <Auto Offset>Press <Offset>Press [4] [

2-156. Connect the DVM to the X output on the rearpanel.7. Connect the DVM to the CH1 output on thefront panel again.Press <Expand>Press [1] [EN

2-16Press <Source>Use the knob to select Trace1.8. Press [TRACE/SCAN]Press the second softkey, next to the tracedefinition, to highlight the X.U

2-17SCANS and SWEEPSThis measurement is designed to use the internal oscillator to explore some of the basic lock-in functions.You will need BNC cable

TABLE OF CONTENTS 1-1 GENERAL INFORMATION Safety and Preparation for Use 1-3 Specifications 1-5 Abridged Command List 1-7 GETTING STA

2-184. Press [DISPLAY/SCALE]Press the <Type/Trace> softkey to select theTrace number.Use the knob to select Trace 3.5. Press [REF/PHASE]Press &l

2-19Press <Sample Rate>Use the knob to select 32 Hz.Press <Scan Length>Press [1] [0] [0] [ENTER]Press <1 Shot/Loop> to select 1 Shot

2-2010. Press [DISPLAY/SCALE]Press <Format> to select Single.Press <Type> Use the knob to select Chart.Press <Type> again to highlig

2-21Press <Cursor Seek> to select Min.Use the knob to read the frequencies of thenotch filter zeroes or minimums.13. Press [DISPLAY/SCALE]Press

2-22Scans and Sweeps16. When the scan is complete, press[TRACE/SCAN].Press <1 Shot/Loop> to select Loop.Press [PAUSE/RESET]Press [START/CONT] to

2-23USING THE DISK DRIVEThe disk drive on the SR850 may be used to store 3 types of files.1. Data FileThis includes the data in the active display tra

2-243. Press [AUTO PHASE]4. Press [DISPLAY/SCALE]Press <Format> to select Single display.Press <Type> Use the knob to adjust the display t

2-258. Press [DISK]Press <Disk Utils>Press <Disk Format>Press <Return>Press <Data Save>Press <File Name>Press [ALT] Pres

2-26The Disk DrivePress <Data Save>11. Press <Catalog> to select On.Press <Return>12. Press [PAUSE RESET]13. Press <Data Recall&g

2-27Use the knob to select the Chart display.Press <Full, Top or Bottom> to select Bottom.Use the knob to select the Chart display forthe bottom

Table of Contents 1-2 Interface Ready and Status 6-2 GET (Group Execute Trigger) 6-2 DETAILED COMMAND LIST 6-3 Reference and Phase

2-28Press <Data Recall>Press [AUTO SCALE]This recalls the data file from disk and stores it inthe active display trace. The active display trace

2-29STORING AND RECALLING SETTINGS1. Turn the lock-in on while holding down the [←](backspace) key. Wait until the power-on testsare completed. Discon

2-30Press <Catalog>Use the knob to select the settings file whichyou just saved.6. Press <Settings Recall>Press [GAIN/TC]Display the disk

2-31AUX OUTPUTS and INPUTSThis measurement is designed to illustrate the use of the Aux Outputs and Inputs on the rear panel. You willneed BNC cables

2-325. Disconnect the DVM from Aux Out 1. ConnectAux Out 1 to Aux In 1 on the rear panel. 6. Press [TRACE/SCAN]Press the second softkey, next to the t

2-3310. Press [DISPLAY/SCALE]Press <Type / Trace> to highlight the type ofthe top display.Use the knob to change the display type toChart.1 V to

2-34Aux Outputs and Inputs

2-35TRACE MATHThis example is designed to familiarize the user with the trace math functions in the lock-in. You will needBNC cables and a 50Ω termina

2-36Use the knob to select 50 nV.4. Press [TRACE/SCAN]Press <Sample Rate>Use the knob to change the sample rate to16 Hz.5. Press [DISPLAY/SCALE]

2-37Press <Return> twice.8. Press <Smooth>Press <17 point>Press [CURSOR]Use the knob to move the cursor past the leftedge of the gra

SAFETY AND PREPARATION FOR USECAUTIONThis instrument may be damaged if operatedwith the LINE VOLTAGE SELECTOR set for thewrong AC line voltage or if t

2-38Press <Do Calc.>Press [AUTO SCALE]Use the knob to select log10.Press <Do Calc.>Use the knob to select ❊.Press <Argument Type> to

2-39Trace MathPress <1 Shot/Loop> to select 1 Shot.13. Connect the Sine Out to the A input using aBNC cable.Wait until the value of X reaches 1

2-40Trace MathPress <Left Limit>Use the knob to position the cursor 3 divisionsto the right of the left limit.Press <Right Limit>Move the

2-41Trace MathMove the cursor past the left edge of thegraph to pan the data window until the signaldecay becomes visible again.20. Press [MATH]Press

2-42Trace Math

SR850 BASICSLock-in amplifiers are used to detect and measurevery small AC signals - all the way down to a fewnanovolts! Accurate measurements may be

3-2SR850 BasicsThis is a very nice signal - it is a DC signal propor-tional to the signal amplitude. Narrow band detectionNow suppose the input is mad

3-3SR850 BasicsSo what exactly does the SR850 meas-ure?Fourier's theorem basically states that anyinput signal can be represented as the sum ofma

3-4SR850 Basics

3-5SR850 BasicsThe functional block diagram of the SR850 DSPLock-In Amplifier is shown below. The functions inthe gray area are handled by the digital

1-4

3-6SR850 Basics

3-7SR850 BasicsA lock-in amplifier requires a reference oscillatorphase-locked to the signal frequency. In general,this is accomplished by phase-locki

3-8SR850 Basicsdegrees of noise. This shows up at the output asnoise in phase or quadrature measurements.Phase noise can also cause noise to appear at

3-9SR850 BasicsThe SR850 multiplies the signal with the referencesine waves digitally. The amplified signal is con-verted to digital form using a 16 b

3-10SR850 Basics

3-11SR850 BasicsRemember, the output of the PSD contains manysignals. Most of the output signals have frequen-cies which are either the sum or differe

3-12SR850 Basicsneed to be at 0.001 Hz!In the SR850, synchronous filters are available atdetection frequencies below 200 Hz. At higher fre-quencies, t

3-13SR850 BasicsThe SR850 has X and Y outputs on the rear paneland Channel 1 and 2 (CH1 and CH2) outputs onthe front panel. X and YThe X and Y rear pa

3-14SR850 Basicsdeviations can be expanded up to 100 timesbefore they exceed full scale (at 1 mV sensitivity).The analog output with offset and expand

3-15SR850 Basicsoutput voltages of X, Y or R in trace output calcu-lations. For example, a trace which is defined as Xand output through CH1 or CH2 in

SR850 DSP LOCK-IN AMPLIFIER1-5SPECIFICATIONSSIGNAL CHANNELVoltage Inputs Single-ended (A) or differential (A-B).Current Input 106 or 108 Volts/Amp.Ful

3-16SR850 Basics

3-17SR850 BasicsWe've mentioned dynamic reserve quite a bit inthe preceding discussions. It's time to clarifydynamic reserve a bit.What is d

3-18SR850 Basicsfrequencies than within the operating range. Whilethis may be a nice specification, removing noise atfrequencies very far from the ref

3-19SR850 BasicsA lock-in can measure signals as small as a fewnanovolts. A low noise signal amplifier is requiredto boost the signal to a level where

3-20SR850 Basicsmeasurements in the vicinity of the notch frequen-cies. These filters have a finite range of attenua-tion, generally 10 Hz or so. Thus

3-21SR850 BasicsIn order to achieve the best accuracy for a givenmeasurement, care must be taken to minimize thevarious noise sources which can be fou

3-22SR850 BasicsCurrent Input (I)The current input on the SR850 uses the A inputBNC. Voltage or current input is chosen in theINPUT menu. The current

3-23SR850 BasicsRandom noise finds its way into experiments in avariety of ways. Good experimental design canreduce these noise sources and improve th

3-24SR850 Basics

3-25SR850 BasicsIn addition to the intrinsic noise sources discussedin the previously, there are a variety of externalnoise sources within the laborat

SR850 DSP Lock-In Amplifier1-6INPUTS AND OUTPUTSChannel 1 Output X, R, θ, or Trace 1-4. Traces are defined as A•B/C or A•B/C2 where A, B,and C are sel

3-26SR850 BasicsCures for inductively coupled noise include:1) Removing or turning off the interferingnoise source.2) Reduce the area of the pick-up l

3-27SR850 BasicsLock-in amplifiers can be used to measure noise.Noise measurements are generally used to char-acterize components and detectors.The SR

3-28SR850 BasicsWhich method you use depends upon the require-ments of the experiment.R noiseThe quantity Rn can be somewhat hard to under-stand. For

POWER BUTTONThe SR850 is turned on by pushing in the powerbutton. The video display may take a few secondsto warm up and become visible. Adjust the br

4-2The main area of the display is occupied by theoutput display(s). Both single and dual trace dis-plays are available. In addition, each display can

4-3Front PanelCh1 & Ch2 OutputsThe Channel 1 and Channel 2 outputs can be con-figured to output a voltage from -10 V to +10 Vproportional to X, Y,

4-4Front Panel

4-5Lock-in ParametersMaxFr= 100.00 HzFull Scale = 10 mVTrace 1Dyn Reserve = 0 dB100 mS12 dB/oct Line 2xLin AC AXX = 9.7284 mV± 10.000 e-3 0.0

4-6Screen DisplayDATA TRACESThe SR850 collects and displays data in the formof traces. There are four data traces which may bedefined. Each trace is d

4-7Up/DownSingleMonitorTrace 2Display ScaleFormatXX = 9.7284 mV± 10.000 e-3 0.0 VYcenter = 0.0 ± 50.00 e-3 VTrace 1SettingsInput/Outpu

SR850 DSP Lock-In Amplifier1-7COMMAND LISTVARIABLES i,j,k,l,m Integersf Frequency (real)x,y,z Real Numberss StringREFERENCE and PHASE page description

4-8Screen Display

4-9Center value and Trace UnitsTrace Offset and Expand IndicatorsXX = 9.7284 mV± 10.000 e-3 0.0 VTrace 1Trace Identifier Trace DefinitionFull sc

4-10X Axis (0°)Y Axis (90°)Signal VectorTrace Offset and Expand IndicatorsPOLAR GRAPHSThe polar graph is a convenient way to view magnitude and phase.

4-11center = 0.0 ± 50.00 e-3 V10 S /divY 36.000 S 58.332 e-30.000 STrace Identifier Trace Definition Cursor ReadoutVertical rangeVer

4-12Data ScrollingThe chart display acts like a strip chart recorderwhere the pen is drawing the most recent data.For example, if the sample rate is 1

4-13Screen DisplayTRACE SCANS, SWEEPS & ALIASINGTrace and Scan parameters are selected in theTRACE/SCAN menu.Trace StorageHaving defined up to fou

4-14Screen Displaythe scan length is only meaningful is parametersare being swept. Once the trace buffer has loopedaround, the oldest point (at any ti

4-15SETTINGS & INPUT/OUTPUT MONITORThe upper two lines of the screen are the monitordisplay (see the screen on pg. 4-5). The lock-insettings (sens

4-16STATUS INDICATORSThere are a number of status indicators which aredisplayed at the bottom of the screen. Theseinclude the scan, unlock, and overlo

4-17allowed), press the [HELP] key. LOC is on when-ever local front panel control is allowed (usuallyon).SRQThis indicator is on whenever a GPIB Servi