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5 – 4

Circuits

Figure 5.2: The front-end JFET (Q1101) socket, un-installed.

cover removed. Be sure to have a second person nearby for
safety, and do not proceed if the metal shroud covering the AC
power entry module has been removed.

7. Place a shorting cap or 50

Ω

terminator onto the A

/

I input,

and turn the instrument on.

Press [Recall], and turn the

REFERENCE knob to show “dEFLt”. Press [Recall] a sec-

ond time to restore defaults. Turn the

SENSITIVITY knob to

5 mV

.

8. Attach the voltmeter test leads to Test Points TP1104 and

TP1105 (see Figure 5.3). Slowly adjust trimmer R1102 to null
the voltage between TP1104 and TP1105. You should be able
to reduce the voltage to

<

5 mV.

9. Return the top cover and reinstall all the screws.

5.6

Oscillator

The Oscillator board contains the quadrature sinewave voltage-
controlled oscillator. This board is mounted vertically, at the right-
hand side of the SR124 chassis.

SR124

Analog Lock-In Amplifier

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Summary of Contents for SR124

Page 1: ...Operation and Service Manual Analog Lock In Amplifier SR124 Stanford Research Systems Revision 1 03 July 12 2018...

Page 2: ...e 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 doc...

Page 3: ...scillator external input 1 7 1 9 Reference oscillator output 1 8 2 Introduction 2 1 2 1 Introduction to the instrument 2 2 2 1 1 Clock stopping architecture 2 2 2 1 2 What does the SR124 measure 2 2 2...

Page 4: ...ds 4 7 4 4 1 Command syntax 4 7 4 4 2 Notation 4 8 4 4 3 Examples 4 8 4 4 4 Reference and phase commands 4 9 4 4 5 Input commands 4 11 4 4 6 Filter commands 4 12 4 4 7 Gain and time constant commands...

Page 5: ...Contents iii 5 6 Oscillator 5 4 5 7 Rear outputs 5 5 5 8 Communications 5 5 5 9 Schematics 5 5 SR124 Analog Lock In Amplifier...

Page 6: ...iv Contents SR124 Analog Lock In Amplifier...

Page 7: ...TAGE SELECTOR set for the wrong AC line voltage or if the wrong fuses are installed Verify that the correct line fuses are installed before connecting the line cord Fuse size is 5MF fast blow 5 20 mm...

Page 8: ...nd on SRS Products Symbol Description Alternating current Caution risk of electric shock Frame or chassis terminal Caution refer to accompanying documents Earth ground terminal Battery Fuse On supply...

Page 9: ...this manual are Front panel buttons are set as Button Front panel knobs are set as Knob Front panel indicators are set as Overload Remote command names are set as IDN Literal text other than command...

Page 10: ...ccurancy 1 at 1 kHz Gain stability 100 ppm C flat mode normal reserve Input noise typ 2 8 nV Hz at 1 kHz 0 14 pA Hz at 1 kHz 106 V A 0 014 pA Hz at 100 Hz 108 V A Input filter Tunable from 2 Hz to 100...

Page 11: ...nce 1 M AC coupled 10 s time constant sine DC coupled TTL Phase resolution 0 01 Phase accuracy 5 2 Hz to 20 kHz 10 20 kHz to 210 kHz Harmonic detection F 2 F and 3 F ext ref Reference output Parameter...

Page 12: ...to 10 VDC Quadrant outputs 600 output impedance Four 0 7 Vrms 2 Vpp outputs at 0 90 180 270 Preamp DB 9 connector to power optional remote preamp Status TTL outputs 1 k output 10 k pullup Unlocked lo...

Page 13: ...mplete introduction to the SR124 In This Chapter 1 1 How to use this manual 1 2 1 2 Basic instrument check out 1 2 1 2 1 Equipment needed 1 2 1 3 Preparations before use 1 2 1 4 Signal and input filte...

Page 14: ...RS 232 interface Chapter 5 has a description of the detailed circuit schematics of the SR124 1 2 Basic instrument check out This chapter provides step by step instructions for verifying the basic ope...

Page 15: ...the Type button four times The meter should swing to approximately 0 deviation 5 Turn the Q factor knob clockwise until Q 100 The meter should remain near 0 deviation 6 Press the Mode button in the OU...

Page 16: ...the pause the phase should show a value near 90 deg and the meter should return to near 100 deflection 18 Press the Type button again to select Low Pass filter The meter should swing to near 100 defl...

Page 17: ...right 5 Turn the Quadrant knob one click clockwise The signal is now 90 out of phase with the reference signal as shown in Figure 1 1 6 Turn the Quadrant knob one click clockwise The signal is now at...

Page 18: ...wice to select Normal The OVLD indicator should turn off Manually adjust the phase setting with the REFERENCE knob to null the meter Turn SENSITIVITY 2 more clicks counterclockwise to 1 mV OVLD should...

Page 19: ...Attn OFFSt and the OFFSET annunciator in the REFERENCE display block should blink The sensitivity does not change 8 Press the Ampl button and reduce the amplitude to 90 0 mV The panel meter should sh...

Page 20: ...l again 2 Connect a BNC cable from the rear panel Reference Output 0 to the Channel 1 of the oscilloscope Trigger the scope on the waveform and verify a 1 kHz 0 7 Vrms 2 V peak to peak sine wave 3 Con...

Page 21: ...urn the knob slow counterclockwise to reach 10 0 mV Notice that the SR124 will not allow the Amplitude to decrease below 10 0 mV with the DC Bias enabled and set to 2 V 13 Press DC Bias On Off to disa...

Page 22: ...1 10 Getting Started SR124 Analog Lock In Amplifier...

Page 23: ...1 1 Clock stopping architecture 2 2 2 1 2 What does the SR124 measure 2 2 2 2 Instrument overview 2 3 2 2 1 Reference section 2 3 2 2 2 Signal section 2 6 2 2 3 Input Filter 2 9 2 2 4 Output 2 10 2 3...

Page 24: ...ecture This clock stopping architecture first introduced by SRS in the SR560 Voltage Preamplifier eliminates the inconvenience and relia bility issues associated with mechanical panel controls and mak...

Page 25: ...ts RMS and this is the basis for the SR124 calibration as well For example if the SR124 is configured for 2 mV sensitivity and a 1 mVrms sine wave is input at the reference frequency then the BNC outp...

Page 26: ...cy is controlled with the front panel control knob or remote command 2 2 1 2 Rear panel VCO mode When configured for Rear VCO operation the SR124 oscillator pro gramming voltage is directly controlled...

Page 27: ...rly cause the reference oscillator to operate at three times the external input frequency Note that for harmonic operation the Range setting must correspond to the final frequency for the refer ence o...

Page 28: ...In single ended operation the SR124 internally measures the signal as a voltage on the center pin of the A input referenced to internal ground in the instrument This is indicated as A on the front pan...

Page 29: ...g by the current gain For example if the Sensitivity is set to 20 mV and the input is configured as 108 V A the full scale sensitivity will be 200 fA 20 mV 108 V A In most cases there is little noise...

Page 30: ...determines the dynamic reserve of the lock in Dynamic reserve is traditionally defined as the ratio of the largest interfering signal that can be tolerated to the full scale input signal expressed in...

Page 31: ...signals allowing greater AC gain to be used for better low level signal recovery The input filter is located in the AC signal path between the pream plifier and the programmable AC gain stage The inpu...

Page 32: ...onstant is related to the 3 dB frequency of the filter by the relation f 3dB 1 2 TC where TC is the time constant in seconds The low pass filters are simple 6 dB octave roll off RC type filters A 1 se...

Page 33: ...12dB oct 6dB oct Low Pass fine coarse High Pass Band Pass Float OVLD OVLD On AC Volt Lock In INHIBITED CPU Activity TTL 90 3f 0 2 0k 210k On Square Sine 200 21k 20 2 1k 2 0 210 0 2 21 180 90 270 180...

Page 34: ...ion The left hand section of the instrument comprises the Signal Input See Figure 2 3 for detail Stanford Research Systems RESERVE SENSITIVITY SIGNAL INPUT INPUT FILTER 100 200 500 A A I B Signal Moni...

Page 35: ...type is selected by pressing Type selections cycle from Band Pass High Pass Low Pass Notch and Flat TYPF 4 12 The filter Q factor can be adjusted between 1 and 100 by turning the Q factor knob QFCT 4...

Page 36: ...ode the SR124 should be operated in Low Noise reserve mode 2 3 1 5 10 ENBW The SR124 has an additional setting available for the Input Filter Q factor to set the Equivalent Noise Bandwidth to 10 10 EN...

Page 37: ...Modify Mode Figure 2 4 The SR124 front panel output section The panel meter shows the output signal from the SR124 This is the same signal as appears at the output BNC The meter shows 100 deflection w...

Page 38: ...Figure 2 5 for detail 2 3 3 1 Automatic functions Four built in automatic functions are available in this block Pressing Phase within AUTO starts an auto phase cycle which adjusts the oscillator phas...

Page 39: ...ument config uration into that slot pressing any other key abandons the save request SSET 4 15 The Recall key is used to restore a previously saved configura tion Press Recall once to bring up the rec...

Page 40: ...ne 200 21k 20 2 1k 2 0 210 0 2 21 180 90 270 180 270 360 Unlocked DC Bias Range Hz Mode Ref Out Ext In Quadrant Push to select Hold to null 2f External f Internal Rear VCO PHASE FREQ AMPL BIAS OFFSET...

Page 41: ...uency That frequency is then displayed on the numeric display If the focus is already on FREQ when the instrument changes mode into either Rear VCO or External the display will show pressing Freq agai...

Page 42: ...DC Bias block toggles the bias on and off for the reference output signal BION 4 11 Depending on the current value of the reference amplitude and bias the bias might not be allowed to turn on Full de...

Page 43: ...s Chapter 3 1 Sensitivity and gain 3 2 3 1 1 AC Gain 3 2 3 1 2 Scale normalization 3 3 3 1 3 DC gain 3 4 3 2 Dynamic reserve and overloads 3 4 3 3 Input filter details 3 6 3 4 Attenuators and DC bias...

Page 44: ...5 10 2 5 103 2 5 104 500 nV 5 V 50 V 500 2 10 1 103 1 104 1 V 10 V 100 V 500 1 10 5 102 5 103 2 V 20 V 200 V 500 0 5 10 2 5 102 2 5 103 5 V 50 V 500 V 500 0 2 10 1 102 1 103 10 V 100 V 1 mV 500 1 1 5...

Page 45: ...l Gain 10 V VFS 3 1 where VFS is the full scale sensitivity in volts For example if the sensitivity is set to 200 V the nominal overall gain is 10 V 200 V 50 000 3 1 2 Scale normalization The SR124 is...

Page 46: ...see from Table 3 1 three possible AC gain config urations based on the dynamic reserve setting At Low Noise the total AC gain is 2 5 103 for Normal reserve the total AC gain is 250 while at High Res w...

Page 47: ...10 mV 100 mV 1 28 V 2 mV 20 mV 200 mV 1 28 V 5 mV 50 mV 500 mV 1 28 V 10 mV 100 mV 1 28 V 20 mV 200 mV 1 28 V 50 mV 500 mV 1 28 V 100 mV 1 28 V 200 mV 1 28 V 500 mV 1 28 V be used to optimize out of b...

Page 48: ...00 mV 1 25 V 2 mV 20 mV 200 mV 1 25 V 5 mV 50 mV 500 mV 1 25 V 10 mV 100 mV 1 25 V 20 mV 200 mV 1 25 V 50 mV 500 mV 1 25 V 100 mV 1 25 V 200 mV 1 25 V 500 mV 1 25 V 3 3 Input filter details The input...

Page 49: ...ency f f 0 Filter response dB Q 1 2 5 10 20 50 100 Figure 3 1 The SR124 band pass input filter gain 10 2 10 1 10 0 10 1 10 2 60 50 40 30 20 10 0 10 High Pass Normalized frequency f f0 Filter response...

Page 50: ...sponse dB Low Pass Q 1 2 5 10 20 50 100 Figure 3 3 The SR124 low pass input filter gain 10 0 3 10 0 2 10 0 1 10 0 10 0 1 10 0 2 10 0 3 60 50 40 30 20 10 0 10 Notch Filter Normalized frequency f f 0 Fi...

Page 51: ...of the range 14 5 V DC Table 3 4 Available DC Bias values by Amplitude setting AC Amplitude DC Bias DC Bias RMS Range Resolution 10 mV 10 V 10 V 1 mV 100 V 9 99 mV 100 mV 10 V 1 V 99 9 V 1 mV 100 nV...

Page 52: ...ng back to the point overload was not firing If the SR124 was already in Overload when auto gain is started then the sensitivity is increased gain decreased one step at a time until the overload is cl...

Page 53: ...s pre charged to the correct voltage for the desired frequency The final step in the process is to arm a comparator that waits for the next positive zero crossing of the external frequency reference W...

Page 54: ...3 12 Performance Details SR124 Analog Lock In Amplifier...

Page 55: ...mmand syntax 4 7 4 4 2 Notation 4 8 4 4 3 Examples 4 8 4 4 4 Reference and phase commands 4 9 4 4 5 Input commands 4 11 4 4 6 Filter commands 4 12 4 4 7 Gain and time constant commands 4 13 4 4 8 Outp...

Page 56: ...tude RSLP z 4 10 Reference slope shape FRNG z 4 10 Reference oscillator range BION z 4 11 Reference DC bias enable BIAS g 4 11 Reference DC bias magnitude FORM z 4 11 Reference output waveform Input I...

Page 57: ...ence frequency ASST z 4 17 External lock assist Data transfer OUTR 4 17 Output ORTI 4 17 Output RTI Interface IDN 4 18 Identify TOKN z 4 18 Token Mode OPC 4 18 Operation complete LOCL z 4 19 Local loc...

Page 58: ...4 17 Measure reference frequency ASST z 4 17 External lock assist B BIAS g 4 11 Reference DC bias magnitude BION z 4 11 Reference DC bias enable F FMOD z 4 9 Reference mode FORM z 4 11 Reference outp...

Page 59: ...agnitude OMOD z 4 14 Output mode ORTI 4 17 Output RTI OUTR 4 17 Output OVLD 4 20 Overload P PHAS f 4 9 Reference phase Q QFCT z 4 12 Input filter Q factor QUAD z 4 9 Phase quadrant R RMOD z 4 13 Reser...

Page 60: ...iguration 9600 baud 8 bit with no parity or flow control 4 3 2 Buffers The SR124 stores incoming bytes from the remote interfaces in sepa rate 128 byte input buffers Characters accumulate in the input...

Page 61: ...ers are always required Do not send or or as part of the command Multiple parameters are separated by commas Multiple commands may be sent on one command line by separating them with semi colons so lo...

Page 62: ...meter for both set and query forms 4 4 3 Examples Each command is provided with a simple example illustrating its usage In these examples all data sent by the host computer to the SR124 are set as str...

Page 63: ...Reference mode FMOD z Set query the reference mode to z EXT1F 0 INTERNAL 1 EXT2F 2 EXT3F 3 RVCO 4 FMOD INTERNAL Example Reference oscillator frequency FREQ f Set query the reference oscillator freque...

Page 64: ...TL and CMOS logic RSLP SINE Example Reference oscillator range FRNG z Set query the reference oscillator range to z FRNG P2 0 FRNG 2 1 FRNG 20 2 FRNG 200 3 FRNG 2K 4 In all modes the oscillator range...

Page 65: ...ut commands Input source ISRC z Set query the input source configuration to z A 0 AMINUSB 1 CUR1E6 2 CUR1E8 3 The first two settings ISRC A and ISRC AMINUSB select the voltage input preamp configured...

Page 66: ...Q factor QFCT z Set query the input filter Q factor to z Q1 0 Q2 1 Q5 2 Q10 3 Q20 4 Q50 5 Q100 6 QENBW 7 The 10 ENBW filter mode is set by QFCT QENBW QFCT Q5 Example QFCT 2 Input filter frequency IFF...

Page 67: ...ue Full scale sensitivity sensitivity S100NV 0 100 nV S500UV 11 500 V S200NV 1 200 nV S1MV 12 1 mV S500NV 2 500 nV S2MV 13 2 mV S1UV 3 1 V S5MV 14 5 mV S2UV 4 2 V S10MV 15 10 mV S5UV 5 5 V S20MV 16 20...

Page 68: ...6 300 ms TC1S 7 1 s TC3S 8 3 s TC10S 9 10 s TC30S 10 30 s TC100S 11 100 s TC300S 12 300 s OFLT 7 Example Output filter slope OFSL z Set query the output filter slope rolloff to z SLOPE6DB 0 SLOPE12DB...

Page 69: ...command There is no corresponding front panel methdo to access this command it is exclusive to the remote interface Save user settings SSET z Save query the user settings to non volatile block z USER0...

Page 70: ...iled Auto phase APHS z Set query the auto phase function to z OFF 0 ON 1 Setting APHS with no parameter will initiate an auto phase cycle and is equivalent to APHS 1 The set version of APHS can initia...

Page 71: ...scillator lock assist function to z OFF 0 ON 1 Setting ASST with no parameter will initiate an auto lock assist cycle and is equivalent to ASST 1 The set version of ASST can initiate a lock assist cyc...

Page 72: ...mple ON Operation complete OPC The set form OPC will set the OPC bit in the Standard Event Status register the query form OPC will return the value 1 OPC is useful for pacing streams of remote command...

Page 73: ...ntrol Note however that in LOCL LOCKOUT even the Recall Local button is disabled only a remote command returning the instrument to LOCL LOCAL or a power cycle will restore front panel control Note tha...

Page 74: ...the SR124 reference oscillator is configured for either FMOD INTERNAL or FMOD RVCO then LOCK responds with NOTPLL 2 LOCK Example LOCKED Overload OVLD Reads the current value of the signal overload st...

Page 75: ...ard event status enable ESE i j Set query the Standard Event Status Enable Register bit i to j ESE 6 1 Example ESE 64 Clear status CLS CLS immediately clears the ESR register and the UNLOCK and OVERLO...

Page 76: ...r code so a subsequent LCME will return 0 Valid codes are Value Definition 0 No execution error since last LCME 1 Illegal command 2 Undefined command 3 Illegal query 4 Illegal set 5 Missing parameter...

Page 77: ...egister any set bits within it are cleared These are sometimes known as sticky bits since once set a bit can only be cleared by reading its value Event register names end with SR or EV Enable Register...

Page 78: ...SS Bit 6 of the SRE is undefined setting it has no effect and reading it always returns 0 This register is set and queried with the SRE command At power on this register is cleared 4 5 3 Standard even...

Page 79: ...E Command Error Indicates a command parser detected error 4 5 3 1 Standard event status enable ESE The ESE acts as a bitwise AND with the ESR register to produce the single bit ESB message in the Stat...

Page 80: ...4 26 Remote Operation SR124 Analog Lock In Amplifier...

Page 81: ...it design A complete parts list and circuit schematics are included In This Chapter 5 1 Overview of circuits 5 2 5 2 Power Supply 5 2 5 3 CPU 5 2 5 4 Front Panel 5 2 5 5 Main board 5 2 5 6 Oscillator...

Page 82: ...ront Panel The front panel board contains the LED indicators and button con trols All numeric displays are driven from static shift registers whose values are only updated in response to a user comman...

Page 83: ...directly behind the A I and B inputs about 5 cm back from the edge of the board Q1101 is socketed as shown in Figure 5 1 Using your thumb and forefinger carefully remove the JFET Figure 5 1 The front...

Page 84: ...how dEFLt Press Recall a sec ond time to restore defaults Turn the SENSITIVITY knob to 5 mV 8 Attach the voltmeter test leads to Test Points TP1104 and TP1105 see Figure 5 3 Slowly adjust trimmer R110...

Page 85: ...to receive the oscillator quadrant signals and drive them relative to chassis ground 5 8 Communications The small Communications board located near the power entry module contains the fiber optic tra...

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