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Princeton Applied Research/EG&G Model 124A Lock

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2. pe AC Ie See ee Ret e dio v 3 5 6 Intermediate Amplifier 2 2 Ge Dur Qux MED 0 ee va ee We 5 60 Mixe B s 5 soe koe y ae ae ae eo E SY 4 dome V5 5 6 Mixer Schmitt Triggers re abe tay elas Mota gl 5 SEF 6 5 66 OG Aniplifiers 22222 42 44 2 i ae Bade de 6 57 CHECKS ere Ah We ces Quy m MESA Ba nip We Gao WS VG SCHEMATICS TABLE OF esa ka db ee 575 Viel Jan 29 02 11 44A FIGURES umber Page Modet 124A Lock In 2 2 1 2 1 2 Sync Signal Slewing 1 4 L3 Typical Calibrator Accuracy IP PPP E TAE TET 15 Functional Block Diagram 124A E 1 2 2 Optimum Performance Regions of the Preamplifiers 11 3 1 3 Distortion v Frequency 118 PIRE ura Voltage Rejection Using Differential In ts ue deb 4 11 5 Model 183 Remote Preamplifier Adapter 1 4 1 6 Typical Common Mode 2 2 11 5 Typical Noise Figure Cantours for Model 117 Model 116
3. 1 5 4 5G Final Reference Oscillator Board Adjustments 2 5 45H Signal Board Adjustments eins NT Iv 5 4 31 Final Adjustments AS hp ds Vu Moke asus ata ek V 6 4 3 Phase Meter Option Alignment 2 2 2 aoa a s s s Ns Iv 6 4 4 116 117 or 119 Preamplifier Alignment IV 7 44A Preliminary Steps ss Vw REUS EU e e 7 448 1 2 e ogre ny Sree 9 7 45 Model 118 Preamplifier Alignment teat Poet 4 W8 45 Preliminary Steps ah ots Moe cde IV 8 ASB ProCcedUFe oor RIT A E PIC crt IV B TROUBLESHOOTING E e re N 5 1 Introd etion 22 He ee cS vods Ses N Xa MM 5 2 Equipment 2 2 mt ane NS PESOS 1 5 3 initial os uk oe 9 a Geog Gers ane Ae oy RO V 1 5 4 Power 5 5 Reference Checks cle X ikea Weiser a 5 6 Signal Channel Vert i vec qx PAA had BGA Preamplifier d sc osx oy p EX ES Scene ped ue d e AD ae ERE tes 3 5 68 Signal Amplifier
4. amp dB Oct Amplitude Transfer 12 Amplitude Transtar WP LU ELT BALES LEAD DEGREES t Toa 6 Phasa fransfer 12 dB Oct Phase Transfer too es OR 8 5 T t V TO I7 anion 3 1 i E at zor ee te 5 E 40 15 20 25 38 8 40 48 50 gt 19 50 4 35 40 A amp ao bs CLAFSUD fief Tie TE 09 TIME CONSTANTS N TC GBIANTS IN TL 6 dB Oct Step Function Response 12 d8 Oet Step Function Response Figure 11 22 OUTPUT FILTER TRANSFER FUNCTIONS 11 20 Jan 30 02 O5 36P NOTE When operating the Signal Channel in the Bandpass mode particularly with high the frequency dia s must also be fine adjusted for peak meter reading Otherwise the filter rolloff will attenuare the signal and also cause a phase error circumstances attenuation and phase shift in the Signal Channel must be minimized or accounted for 34 OUTPUT CHANNEL OPERATION 34A FILTER TIME CONSTANT The amplified and filtered signal is synchronously detected with respect to the phase shifted Reference Channel signal and the detected signal is applied to the RC low pass filter
5. Table 111 68 DIGITAL OUTPUT TRUTH TABLES 111 26 Feb O7 O2 02 21P 3 9 PHASE MEASUREMENTS To measure phase with a Model 174A the Phase controls are adjusted to obtain a positive peak indication the same s for an amplitude measurement When positive peak is achieved the Phase controls will indicate the number of degrees by which the input signal eads the applied reference If the angle is greater than 180 it may be more convenient to subtract the indicated angle from 360 and state the difference as the angle by which the input signal lags the reference NOTE Any internal phase shifts such as might be intraduced by the signal amplifiers must be taken into account for accurate measurements Sometimes after the lock in amplifier has been peaked up a change in an experimental parameter will cause a phase shift and resultant loss in peak indication this happens it may be of interest to know whether the shift was a lead or a lag To determine the direction of a phase shift simply re adjust the M124A Phase controls as required to restore the peak indication and while so doing note whether the new phase setting is higher or lower than the ald one If the new phase setting is higher the phase shift of the signal relative to the reference was in the teading direction If the new phase sett ng is lower then the shift was in the lagging direction As mentioned previously when the phase controls are adjust
6. It is important to realize that even though the VCO will phase lock over a two decade frequency range the boundaries of the two decades are determined by the setting of the Oscillator Range switch The tracking range corresponding to each position of the switch is as follows Xl 0 2 Hz to 21 He X10 5223 cT SEP 2 Hz to 210 He x100 CURVE wei iR OE 20 Hz to 2 1 kHz cuore Ree 200 Hz ta 21 kHz 1 xix cxx Z META to 210 kHz In the Internal mode a sinewave output from the Oscillator is provided for synchronizing the experiment The Qscil lator can free run accurately at any selected frequency from 200 mHz to 210 kHz Also the Oscillator s frequency may be contratled by a voltage applied to a rear panel jack Phase Controls The Phase Controls combine quadrature outputs from the VCO such that the resultant sinewave presented to the Synchronous Detector has the desired phase relation to the reference sync input and or output 3 16 SYNCHRONOUS DETECTOR The Synchronous Octector inverts the polarity of the part of the input signal corresponding to the negative excursion of the phase shifted sinewave from the VCO and passes the remaining waveform uninverted Therefore the dc Ponent of the resultant waveform is praportianal to the value of signal at the same frequency and phase as the Phase shifted VCO sinewave Because the detected signal
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8. open for conversions to continue Sensitivity Switch Position A see Truth Table Sensitivity Switch Position C see Truth Table Sensitivity Switch Position see Truth Digital Ground DVM Overload Output Logic 1 Overload OVM Overload Output Logic 1 Overload Digital Ground Digital Ground DVM 2nd Most Significant Digit B DVM 2nd Mast Significant Digit D DVM 3rd Mast Significant Digit B DVM 3rd Most Significant Digit DVM Lease Significant Digit NOTE Logic 3 5 V 1 V Logic O 0 2 02 V and output levels are proportionally less with Jess than full scale inputs For example if the programmed saasitiv ity is 200 mV and a 100 mV signal is applied the digital display will indicate 0 500 half scale the BCD output will be 0 500 and the recorder output will be 5 V Function When Applied to Madel 131 System Modet 262 1 Polarity Not used Digit 1 A Digit 1 C Digit 2 A Ground Digit 3 A Digit 3 C Digit 4 A Digit 4 C Digit 5 A Digit 5 C Digit 5 D EXECUTE Not used Not used BUSY frem Model 262 Digit 6 A Digit 6 Digit 6 B Digit 6 D Digit 1 B Digit 1 D Digit 2 8 Digit 2 D Digit 3 Digit 3 D Digit 4 B Digit 4 D Digit 5 B The DYM used in the Model 124A has 3 4 digits Nixie tube display Each digit is represented at the rear panel connector in 3 Coded Decimal BCD formar The Mast Significant Digit is the lef
9. Table 1 2 MODEL 124A DY NAMIC RANGE SPECIFICATIONS Over ride considerations apply as explained in Subsection 3 21 Output impedance is 600 2 Interna line frequency pickup is less than 20 nV rms referred to the Direct inputs of a Type 116 Preamplifier in any Signa Channel mode except Bandpass and Notch where the level may rise ta 500 nV at highest settings Reference Channel A sinewave output at the reference oscillator frequency Amplitude is continuously adjustable by means of the front panel Level control over a range of OV to 10V rms with less than 2 distortion Output impedance is 600 ohms 1 2 DYNAMIC RANGE SPECIFICATIONS Vary as a function of the operating Dynamic Range Tradeoff as indicated in the table above 2F OTHER CHARACTERISTICS Overload Front panel light indicates overload at critical circuits Reference Unlock Front panel light indicates that the reference oscillator has not completed frequency lock Internal Calibrator Square wave calibrator signal supplied Rms amplitude of fundamental frequency component adjustable from 20 nV to 100 mV in 1 2 5 sequence Typical accuracy indicated in Figure 1 3 Ambient Temperature Range Unit can operated at ambient temperatures ranging from 15 to 45 C Auxiliary Power Output Regulated 24 V at up to 100 mA is available at rear panel connector Power Requirements 105 215 210 250 50 60 2 unit can also be powered fram batterics by
10. 3 12 Phase Modification rs Page 1 1 1 3 1 3 1 3 13 1 4 r5 1 1 QUI M1 11 1 11 3 11 3 Wha 111 4 111 5 rs 1 6 13 WTS 111 18 HEY M17 1 18 1 18 1 19 IH 21 1 21 11 21 Ht 21 11 22 11 23 11 24 Ht 27 Ht 28 1 78 1 29 1 29 M 29 Jan 29 02 11 44A P 04 VI 3 13 Mixer Monitor Modification s he EUIS Mii iui Hr29 3 14 Remote Programming Option Modification ah oan VR ee AEE RRS ees E ur30 3 15 Selective External Reference Modification alc UR e an uM 11 37 ALIGNMENT PROCEDURE 1 1 4 1 Introduction s s s ooo o o n M IE D EE IV 1 42 Equipment Needed QS Reg this di oe dr dst OO A IV 1 4 3 Proced rg x oso ee RR vU ups i SUR ae Ta wae hy A IV t oc 43A Preliminary Steps V Weg AIDE ab SUVs hea oh AE Vat 1 1 4 3B 24 V Adjustments R6028 R6010 Power Supply Board 2 1V 1 4 3C Initial Reference Oscillator Board Adjustments Iv 3 430 Auxiliary Reference Board Adjustments 3 4 56 Mixer Board Adjustments eo y ns AGS A IV 4 4 5 Intermediate Amplifier Board Adjustments
11. Either a one section or a two section filter may be selected with the center knob of the Time Constant switch The one section filter has a 6 dB octave rolloff character istic and an equivalent noise bandwidth of 1 4TC The 3 dB down point on the frequency axis is 1 271 In the time domain it has step function response of 1 e t TC The rise time from 1095 of full amplitude to 80 of full amplitude is 2 2TC seconds from 0 to 95 is 3TC seconds With the TC switch set to 300 s the equivalent noise bandwidth is 800 The twa section filter has 12 dB octave rolloff character istic and equivalent noise bandwidth of 1 8TC The 6 dB down point on the frequency axis is 1 27TC In the time domain it has a step function response of 1 01 UTC The rise time from 10 of full amplitude to 90 of full amplitude is 3 3TC seconds and from 0 to 95 is 4 8TC seconds the operator requires a time constant greater than 300 seconds he can place the Time Constant switch in the Ext position and connect a pair of capacitors of equal value between pins 8 9 and 10 11 of the rear panel octal socket determine the time constant for this external mode multiply the single capacitor value in Farads by 30 megohms The external capacitors should be low leakage film types mylar polycarbonate polystyrene teflon rated at 25 V or higher The Time Constant should ser so that the output noise either
12. 1 1 0 10 10 102 104 CENTER FREQUENCY Eour Ein TURNS RATIO 1 100 Figure TYPICAL NOISE FIGURE CONTOURS FOR Figure t 88 TYPICAL AMPLITUDE TRANSFER CURVES MODEL 116 OPERATING IN THE TRANSFORMER MODE FOR MODEL 116 OPERATING IN THE TRANSFORMER MODE 1 8 Jan 30 02 28 check frequency response curves below before op erating in shaded region SOURCE RESISTANCE OHMS ot 290K 103 3x10 104 3 104 105 FREQUENCY Hz Figure 11 94 TYPICAL NOISE FIGURE CONTOURS FOR MODEL 119 OPERATING IN THE TRANSFORMER MODE 10 SOURC 20 SOURCE 5n SOURCE S 00 SOURCE 4000 SOURCE a a gt gt gt 105 2 5 104 2 5 105 2 5 105 FREQUENCY Figure 111 98 TYPICAL AMPLITUDE TRANSFER CURVES FOR MODEL 119 OPERATING IN THE TRANSFORMER MODE Jan 30 02 28 SOURCE RESISTANCE OHMS 5 10 io 193 104 10 2 02 CENTER FREQUENCY Hz Figure 111 10 TYPICAL NOISE FIGURE CONTOURS FOR MODEL 118 18 10 09 Jan 30 02 28 NOTCH OUTP
13. 3 10 1 X100 net freq 401 Hz Remove the shorting plug from the input of the Preamplifier Then connect the External Signal Generator to the A Input Be sure the Input Selector of the Preamplifier is set to A The frequency of the signal generator output should be 800 Hz Adjust the amplitude of the signal generator output for an scale indication on the Model 124A panel meter Then carefully vary the frequency of the signal generator output for maximum deftection of the panel meter Readjust the amplitude of the signal generator output for exactly fuil scale deflection of the Model 124A panel meter Set the function switch to HI DYNAMIC RANGE and the Time Constant switch to 1 SEC Set the Sensitivity switch to 100 uV Adjust the Reference Frequency controls for a panel meter beat of about 1 Hz Adjust R3018 SYMMETRY ADJ for minimum pk pk amplitude in the observed beat Set the Phase switch to 90 Then and record the pk pk amplitude of the beat Adjust R3018 SYMMETRY ADJ as required to reduce the amplitude of the beat by exactly one half Reset the Phase switch to Q and check to ste Feb 07 O2 26P that the beat is the same amplitude 0 as it k 90 Reset the Time Constant to 300 ms Remove the signal from the input and reconnect the shorting plug removed in step b INTERMEDIATE AMPLIFIER BOARD ADJUSTMENTS 1
14. Direct and Model 119 Direct ee 111 7 Typical Noise Figure Contours for Model 116 Operating in the Transfarmer Mode 1 8 ILBB Typical Amplitude Transfer Curves for Model 116 Operating in the Transformer Mode 1 8 Typical Noise Figure Contours for Model 119 Operating the Transformer Mode 11 9 111 98 Typical Amplitude Transfer Curves for Model 119 Operating in the Transformer Mode dr 411 10 Noise Figure Contours for Model 118 CPUS I 10 11 Typical Noise Figure Contours for Model 190 Transformer Plus Preamplifier Deck 8 111 778 Modet 190 Wiring Diagram Hr TI 11 11 Typical Amplitude Transfer Curves for Model 190 FEM Witt III 11D Photo of Model 190 Transformer 1 11 11 12 B H Curves and Waveforms 11 11 111 13 Degaussing Waveforms Ger AE dd By ak aoa geht epe s Qo ET 11 14 Model 124A Bandpass Characteristics Gy NO er ge 20 UR yet Fg HI 12 MI 15 Model 124A Notch Characteristics 0 Ce gre c peut e ar EL 11 16 Model 124A Low Pass Characteristics Mr12 11 17 Model 124A High Pass Characteristics 2 ME12 1 18 Dynamic Range Characteristics af the Model 124A 2 EA IA 11 14 1 19 Output Offset as
15. FREQUENCY NOT T RIOOI SIGNAL OUT zo Z0 qe4 T 2 1090 SIGNAL ce eee IN n A CX eo EN SIGNAL lt j BOARD R2303 ZERO SUPP CAL M T P200 INT RESO METER AMP QUT INTERMEDIATE AMP BOARD R3218 OCA I ZERO A3306 2 ZERO R3018 SYM R3IOI BAL MIXER BOARD C4002 200 Y SINT ESE R4030 ZERO 1 FREQ ADU R4044 ZERO 2 3 4002 09 T E 2 1 4003 180 4000 902 2 REFERENCE 4001 270 2 OSCILLATOR BOARD R4017 AC BAL 2 4004 OUT RAOOS AP BAL R4305 E ZERO 3 R4040 1 ZERO 1 R4033 E ZERO 2 2008 Hz 7 4 4 2 AMPLITUDE ts fe T _ R5020 R5015 CAL ADJ gt EXT ZERO TP 5001 1600 7 72 SYMMETRY 5038 INT ZERO 7 SYMMETRY AUXILIARY REFERENCE BOARD TP60Q0 24 v 5000 EXT 96010 24 V ADJA 5002 6002 24 SENSE POWER SUPPLY COMMON BOARD 26028 24 V ADJ e Figure 19 1 MODEL 1244 ADJUSTMENTS AND TESTPOINTS Feb 07 O2 O2 25P 4 Adjust R6010 24 V ADJ for a DVM indication of 324 0 V 4 30 INITIAL REFERENCE OSCILLATOR BOARD ADJUSTMENTS 1 Turn off the power Then remove the Reference Oscillator board and plug the Extender board into the unit in place of the Reference Oscillator board 2 Plug th
16. V pk pk at the oscilloscope 8 Connect the oscilloscope to J3 9 Mixer board Then set the Sensitivity switch to 5 mV and adjust the Reference vernier for 1 V pk pk amplitude in the observed signal 9 Set the Sensitivity switch to 50 mV 10 Adjust the GAIN trim potentiometer located on the Phase board for 1 V pk pk amplitude in the observed signal 11 Set the NORM PHASE switch back to PHASE Then set the Model 124A Function switch to LOW DRIFT 12 Observing the oscilloscope adjust the front panel Reference Level vernier until the amplitude of the Monitored sin wave is just high enough to cause bath negative and positive clipping 13 Adjust the CLIPPING SYMMETRY trim poten tiometer located on the Phase board far symmetrical clipping of the observed signal Then remove the ascillascope 14 Connect the DVM digital voltmeter to the front panel Function OUT connector Then adjust the A2 AMPLITUDE trim potentiometer located the Phase board for a DVM indication of 9 00 V 15 Carefully set the front panel Phase dial for peak DVM indication Then readjust the A2 AMPLITUDE trim patentiometer for the desired 9 00 V reading This completes the Phase board alignment 4 4 MODEL 116 117 OR 119 PREAMPLIFIER ALIGNMENT To align the preamplifier it will be necessary to use a Model 183 Remote Preamplificr Adapter with extender cable 4 44 PRELIMINARY STEPS 1 Plug the Model 183 Remote Preamp
17. X10 The factor of ten gain reduction achieved when K1009 is anergized and K1008 is de energized is accomplished by reducing the amplitude of the signal applied to the amplifier input with a relay controlled attenuator 1 Transfer the oscilloscope to TP1001 violet testpoint The observed signal should be a 1 11 V pk pk square wave indicating that the Siqnal Amplifier has a gain of ten If the signal is normal chances are the amplifier Circuit is functioning normally If the signal is absent the problem could lie with the amplifier circuit or with K 1008 the energized input relay 2 Set the Sensitivity switch to 10 mV The signal amplituda should decrease to 11 mV pk pk indicating that the gain of both the Preamplifier and Signal Amplifier went down by a factor of ten If the signal is as indicated chances are that the Signal Amplifier P 04 7 Apr 15 02 1 31 JO 0124 39 TM NIYO 581 TIWON NO 11 Y300M 123310 03194340 13000 SNIHOIIMS ONY MIYO LA 453 SRY OL 8350440 SY SNIQNOJS3H ISVUIAW S H3XIM JHA 1943 3H1 2195 N3dWD2 DI SY LNDO22W DINI NIAYA IG 150 SHANI 350 51 HO 91 7300 HO4 ONY XlddY 5381814 NIG BS LITE 031115
18. ZERO SUPPRESS CAL R2303 b di Set the Function switch to LO DRIFT Set the Zero Suppress Polarity switch to Set the Zero Suppress dial to 1 00 one turn from the fully counterclockwise position Connect the DVM to the front panel FUNCTION OUT connector Then adjust R2303 ZERO SUPPRESS CAL for a DVM indication of 10 00 V 2 METER CAL R2305 a Note the panel meter indication It should be near full scale to the right Adjust R2305 METER CAL for exactly full seale panel meter deflection Set the Zero Suppress Polarity switch to the center OFF position 4 3G FINAL REFERENCE OSCILLATOR BOARD ADJUSTMENTS 11 AC BAL 1 and BAL 2 ADJUSTMENTS R4003 and R4017 bi f 9 Connect the voltmeter TP4000 white testpaint Set the Model 124A Reference Frequency con trols to NORM 4 00 100 400 Hz Set the Reference Level switch to 1 and the Reference Vernier fully clockwise Connect the Frequency Counter to the REF OUT connector Carefully note the signal level at TP4000 Then transfer the ac voltmeter to TPA002 blue test point and note the signal level there Adjust R4003 AC BAL 1 so that the amplitude at 4002 is the same as it is at 4000 the difference between the frequency indi cated by the counter about 400 Hz and the frequency set by the Reference Frequency con trols e
19. additional background information for setting the controls to their optimum positions To set up the Signal Channel controls the operator must know the frequency or frequency range of the signal It also helps if he knows the expected amplitude the amount and type of noise obscuring the signal the signal source impedance The stimulus to the experiment s often chopped Detecting at this chopping frequency eliminates all but the signal related to the stimulus Princeton Applied Research Corpo ration manufactures several models of light chopper which are ideally suited to photo detection applications Chopping the souree light finds its analog for other kinds of experiments in chopping the stimulus de rf ac sound D np 6119 DIRECT MODE i TRANSFORMER PLUS FREQUENCY He Figure Hig OPTIMUM PERFORMANCE REGIONS OF THE PREAMPLIFIERS 3 heat etc The chopping frequency range must be fairly well known and sync signals must be available Of course the frequency of interest may not be a result of chopping at all The chopping technique discussed here merely serves as an example 3 28 PREAMPLIFIER CHOICE Four models of plug in preamplifiers are available each one Providing optimum low noise performance over a given input resistance v frequency range as shown graphicatly in Figure 111 2 Two of these preamplifiers can be operated beth in direct and transformer
20. avoid using transformer input because internal phase and ampli tude variations as a function of frequency could not be accounted for 4 Set the Zero Offset toggle to neutral Then adjust the Phase controls for a positive peak Also if the Bandpass mode is used fine adjust the frequency controls for a positive peak 5 Adjust the fine sensitivity screwdriver control for an exact full scale meter indication This throws the gain calibration off so after the phase measurement is complete the instrument should be recalibrated The Sensitivity switch setting at which this full scale adjustment is made is referred to below as the reference full scale range Because of the limited range of the fine sensitivity control for a fixed reference amplitude it is not always possible to adjust for exact full scale meter indication such a situation a different tevel of reference signal should be used If this is not possible an intermediate level on the scale can be referred to as full scale However the following procedure and readings must be madified accordingly Set the Zero Offset control to and turn the Offset vernier exactly ten turns clockwise frorn zero The overload lamp will light and the meter will peg downscale 6 Increase the sensitivity by a factor of 10 sensitivity control 3 positions ccw so that the meter again reads on scale 7 Adjust the Phase dial far up scale peak If oper
21. few tenths of a percent If the Reference Jan 30 Oz2 05 38 Channel s sinewave is used an accuracy of better than a tenth of a percent be achieved The following proce uses the Calibrator nutput because it is more aent to continue on into the sensitivity adjustment The operator ought to be able to adapt this procedure to using the reference sinewave if he requires more accuracy Make the following preliminary control settings 1 Reference Channel The Frequency switches should be set to or near the frequency which is to be used or expected when operating with the experiment and the mode switch should he set to Internal The Phase quadrant selector should he set to 270 and the fine phase control set to 90 Note that this adds up to 0 getting this way allows the fine control s overlap to adjust the phase through Q when adjusting for maximum meter indication in the steps that follow 2 Preamplifier Operate single ended direct Connect the Calibrator output to the Preamp input Use a short cable RG 58 U RG 59 U having BNC connectors at both ends 3 Output Channel The Time Constant switch should be set such that the signal driving the meter is well filtered However too long a time constant will make the adjustment time too long Typically if the operating frequency were 400 Hz a good time constant setting is 100 ms The Zero Offset toggle should be set to the neutral off posi
22. is the selected tuned frequency and is that selected by the switch For all modes bear in mind that if the signal bandwidth is limited ahead of the lock in amplifier the limited bandwidth applies In considering equivalent noise bandwidth remember that the output meter is average responding meter calibrated indicate the rms amplitude of a sinewave Gaussian noise which has or has not been band limited by filtering in the Signal and Output Channels makes the meter indicate 7 2 times the actual rms value When the Q switch is set to 10 ENBW bandpass mode the Q of the tuned amplifier is not 15 7 as indicated above but is instead 12 34 This lower Q is necessary to campensate the noise response of the ac voltmeter cir cuitry the voltmeter were true rms responding voltmeter then Q of 15 7 would indeed be proper With an average responding voltmeter circuit such as is employed in the Model 124A exactly the same overall response is obtained with a Q of 12 34 In any case 10 ENBW operation should prove suitable in most applications 3 21 DYNAMIC RANGE TOTAL DYNAMIC RANGE of a lock in amplifier is efined as the quotient af the maximum input that can be applied to the input without overload divided by the minimum discernible signal MDS Dynamic Range in turn is divided into two parts each referenced to the input signal required to give full scale output The quotient of the amount of signal
23. of the Zero Suppress feature to expand signal amplitude variations Suppose one had a 70 signal Assuming this signal were measured on the 100 sensitivity range the resulting meter indication would be 70 of full scale To examine small variations in this signal one would first set the polarity switch to assume initial meter indication was to the right followed by adjusting the dial for null The dial setting required would be 0 70 and the meter sensitivity would be 100 uV with respect to the 70 uV ambient level A recorder connected ta the output would allow the amplitude variations as a function of some experimental parameter to be recorded Because the range of the Offset dial extends to ten times full saale the measurement can be modified slightly so that the amplitude variatians are greatly expanded In the example at hand the Sensitivity switch could be set to 10 Because the signal amplitude 70 is less than ten times the selected sensitivity 10 x 10 uV 100 pV it is within range of the offset dial f the dial were adjusted for null setting of 7 00 the meter range would then be 10 full scale with respect to the 70 ambient signal level 3 5 HARMONIC RESPONSE The Synchronous Detector responds to signals which are harmanically related to and synchronized with the fun damental The harmonic response is less than the funda mental response but still may be large enough to cause signif
24. period and it is this rectangular wave that would be observed at the Mixer Monitar connector The amplitude of the Mixer Monitor output is 555 mV peak with a full scale input signal at 0 and operating in the LO DRIFT mode Operated in NORMAL the Mixer Monitor signal decreases to 55 5 mV for a ful scale input and in HI it decreases to 5 55 mV The output resistance is 1000 ohms It might be mentioned that the waveforms illustrated in Figure 11 24 apply only at frequencies below 50 kHz and with a naise free input signal At higher frequencies switching spikes become visible and some Mixer filtering effects become evident Even relatively small amounts of input noise can completely obscure the signal at the Mixer Monitor output especially in FLAT mode operation 3 14 REMOTE PROGRAMMING OPTION MODIFICATION 1241 83 In units equipped with this option the Sensitivity and Dynamic Range Tradeoff can be remotely controlled by applying logic ground to the appropriate pins of the rear panel Remote Interface connector 8001 Associated with the connector is a pushbutton switch that transfers the instrument fram local to remote operation and vice versa In Local operation the Sensitivity and Dynamic Range Tradeoff are controlled the front panel controls in the usual manner In Remote operation these parameters are independent of the front panel control settings and are determined instead by the inputs to the Remote Interface conn
25. required for full scale output divided by the minimum discernible signal is called the OUTPUT DYNAMIC RANGE The quotient of the maxi mum input without overload OVL divided by the amount of signal required for full scale output is called the DYNAMIC RESERVE of the lock in amplifier Thus TOTAL DYNAMIC RANGE is simply the sum logarith mic of the OUTPUT DYNAMIC RANGE and the DYNAMIC RESERVE All three are important in specify ing the dynamic range characteristics of a lock in amplifier because depending on where the division is made the suitability of the lock in amplifier to making a particular 11 33 type of measurement can vary greatly A lock in amplifier with a Total Dynamic Range of 10 could have that Total Dynamic Range divided in several different ways For example it could have a Dynamic Reserve of 103 and an Output Dynamic Range of 10 in which case it would be well suited to processing very noisy signals but ill suited to processing small amplitude noise free signals It could have a Dynamic Reserve of 10 and an Output Dynamic Range of 10 in which case it could still process moderately noisy signals and also be suitable for processing reasonably small noise free signals Finally it could have a Dynamic Reserve of 10 and an Output Dynamic Range of 10 in which case its capability of processing a noisy signal would be severely restricted while its ability to process a small noise free signal would be very good Th
26. still has noise an it RC low pass filters that follow the synchronous detector are used to eliminate all but the de component representing the wanted signal A de amplifier IwPUTS 116 118 torris REFERE NCE CHANNEL SIGNAL CHANNEL SYNC ScH URL MY Tuss SYNCHRONOUS DETECTOR Mi tar lor Prose Senait 4 FUNCTION SYNG DRIVER ATTENUATOR ee SINE WAVE OUTPUT VOLTAGE COMTROLLED PA 5E LOCKED OSCILLATOR CALIBRATOR DRIwER AND ATTENUATOR FREQUENCY CALIBRATOR SQUARE WAVE SOM WEF UMLOCK INDICATOR Figure 11 1 FUNCTIONAL BLOCK DIAGRAM MODEL 124A dtz Jan 30 O02 05 24 following the Detector provides the final gain This ampli fier drives the output connector and panel meter To determine the amplitude of a signal the operator simply adjusts the phase controls for maximum meter indication The meter directly indicates the signal amplitude In addition after making this adjustment the phase of the input signa relative to the reference may accurately read from the Phase dial 3 2 SIGNAL CHANNEL OPERATION 3 2A INTRODUCTION The function of each control is indicated in Figure 1 1 Instead of repeating the information given there this subsection provides
27. switch to ACVM The mater indication should remain unchanged Note that ac voltmeter operation is achieved simply by taking the drive to the Mixer Sehmitt Trigger from the Signal Channel instead of fram the Reference Channel No new circuits activated If the instrument has passed all tests to this point bur the unit s still malfunctioning in some way not revealed by these tests then the problem is beyond the scope of this V6 troubleshooting procedure and the operator should contact the factory or one of its authorized representatives for advice on how to proceed 5 7 NOISE CHECKS These checks allow th operator to determine whether the internally generated noise in his instrument is normal Note that these checks vary according to the type of preamplifier used 1 Set the front pansl controls as follows NOTE If preamplifier is a Model 184 go directly to step 10 Input Selector Models 116 117 118 amp 119 Transformer Direct switch Models 116 amp 119 DI RECT Ground Isolation Model 185 IN Sensitivity Modals 116 117 amp 119 1mV Models 1188 185 10 mV Signal Mode BANDPASS Signal Frequency dials 4 05 Signal Range X100 Signal Q 100 Reference Frequency dials 4 05 Reference Frequency Range X100 Phase switch 270 Phase dial 90 Zero Offset toggle switch OFF center position Function switch ACVM Calibrate switch 1mV 2 Connect a cable from the front panel CALIBRATE connector
28. to the Reference Chan nel s n jack The pk pk voltage can be anywhere between 100 mV and 3 V Set the signal generator s frequency to approximately 1 kHz 28 Monitor the Reference Channel s Out jack with the oscilloscope The waveform should be a 28 V 2 V pk pk sinewave 27 Set the Frequency Mode switch ta EXT The Ref Unlock light should come on Observe the frequency af the oscilloscope waveform It should have begun increasing as soon as the Mode switch was set to EXT After several seconds it should stop increasing When it stops the Ref Unlock tight should go out The meter will go to Zero also 28 Note the frequency of the oscilloscope waveform Then place the Reference Mode switch to 1 2 the frequeney should double This completes the Reference Channel checks The Sensi tivity Range checks follow 29 Set the Reference Mode switch back to INT 30 Set both the Signal Channel Sensitivity and the 2 Calibrator output to 100 mV The meter should remain at full scale 1 NOTE Catibratar to 10 mV with Model 178 Preamplifier Progressively rotate the Sensitivity and Calibrator switches one position at a time in a counterclockwise direction The meter should remain at full scale 2 if the two switches are in corresponding positions If the meter wavers too much in the low nV settings increase the Time Constant to 10 seconds If using the Model 118 Preamplifier remember that the instrument is 10 X
29. units previously purchased THERE ARE NO WARRANTIES WHICH EXTEND BEYOND THE DESCRIPTION HEREIN THIS WARRANTY IS IN LIEU OF AND EXCLUDES ANY AND ALL OTHER WARRANTIES OR REPRE SENTATIONS EXPRESSED IMPLIED OR STATUTORY IN CLUDING MERCHANTABILITY AND FITNESS AS WELL AS ANY AND ALL OTHER OBLIGATIONS OR LIABILITIES OF EG amp G PRINCETON APPLIED RESEARCH INCLUDING BUT NOT LIMITED TO SPECIAL OR CONSEQUENTIAL DAMAGES NO PERSON FIRM OR CORPORATION I AUTHORIZED TO ASSUME FOR EG amp G PRINCETON APPLIED RESEARCH ANY ADDITIONAL OBLIGATION OR LIABILITY NOT EXPRESSLY PROVIDED FOR HEREIN EXCEPT IN WRITING DULY EXE BY AN OFFICER OF EG amp G PRINCETON APPLIED RESEARCH p 2 rd Jan z9 O2 11 44A TABLE QF CONTENTS aection CHARACTERISTICS o o e dom Rum 1 1 IntFrOdUCtIOn oxphm wo up noQ UA SAGO SOE Dae 1 2 Specifications rants ge Bek 12A Signal Channel Specifications DERE 1 2B Reference Channel Specifications 1 2 Demodulator Characteristics 12D 22 5 2 1 2 Dynamic Range Specifications 1 2F Other Characteristics tt INITIAL CHECKS Ded E che eH UR 2 1 Introduction 2 2 Equipment Needed TP o us 2 3 ees US RE eee uet OPERATING INSTRUCTIONS 3 1 Block Diagram Discussion 31A Intr
30. 0 5 good working value for the response to even harmonics Actual symmetry error varies with the phase setting so that the response to even harmonics can be less than 0 5 The harmonic sensitivity of the Synchronous Detector is one reason for minimizing the passband of the Signal Channel The portion of overall output due to harmonics will be reduced by the attenuation factor the Signal Channel provides at those frequencies Transfer curves in Figures 11 14 through 111 17 should be referred to Table 11 4 lists typical measured synchronous detector responses to harmonics Table 11 5 fists overall responses to these same harmonics if operating in the Bandpass mode with a of 10 Harmonic 0 30 180 270 219 015 05 0 2 0 5 3rd 35 35 35 35 4th 0 13 0 55 025 07 5th 1596 1596 1596 15 Table 111 4 TYPICAL HARMONIC RESPONSE OPERATING IN THE FLAT MODE Harmonic o 90 180 270 2nd 0 017 0 017 0 008 0 04 3rd 1 2 1 2 1 2 1 2 4th 0 0035 0 01476 0 00676 0 01796 5th 0 35 0 35 0 35 0 35 Table 111 5 TYPICAL HARMONIC RESPONSE OPERATING iN BANDPASS MODE WITH 10 These considerations and examples assume the worst Possible phase relationship between the harmonic and the reference signal Practically encountered phase relationships are not usually the worst case and the true will be than the computed error 11 22 A related problem i that of errors resulting fr
31. 0 nA range Jan z9 O2 11 46A SECTION II INITIAL CHECKS 2 1 INTRODUCTION The following procedure is provided to facilitate initial performance checking of the Model 124A In general the procedure should be performed after inspecting the in strument for shipping damage any noted to be reported to the carrier and to Princeton Applied Research Corpora tion but before using it experimentally IN THE CASE UNITS HAVING A DIGITAL PANEL METER IT IS IMPORTANT THAT THE PHRASE meter full scale BE PROPERLY INTERPRETED READ THE PARAGRAPH BEGINNING WITH tn reading the display PAGE 11 24 BEFORE PROCEEDING WITH THE INITIAL CHECKS Should any difficulty be encountered in carrying out these checks contact the factory or one of its authorized representatives 2 2 EQUIPMENT NEEDED 1 General purpose oscilloscope 2 Oscillator having any 1 kHz repetitive waveshape that crosses its mean exactly twice each cycle and having a pk pk voltage anywhere between 100 mV and 3 V 3 Assorted BNC cables 2 3 PROCEDURE for digital units see page 111 24 before proceeding NOTE This procedure must be performed in sequence 1 Install a preamplifier if not already installed 2 Check the rear panel 115 230 switch Make sure the number showing in the window corresponds to the line voltage to be used 3 Turn the front panel Power switch OFF 4 Plug the line cord into the rear panel and wall receptacles 5
32. 1 ZERO 2 ADJUST R4044 b Connect two jumpers one from 4007 B2 and ground and the other from TP4008 E2 and ground These are both gold pin testpoints down on the board Connect the voltmeter to TP4003 violet test point Adjust R4044 1 ZERO 2 such that the moni tored voltage drifts equally plus and minus about zero Remove the jumper which extends fram TP4008 2 and ground but feave the jumper which extends from 4007 B2 and ground 7 ZERO 2 ADJUST b Adjust R4033 ZERO 2 ADJ for equal drift about as measured at TP4003 violet test point Remove the jumper which extends from TP4007 B2 and ground 8 Turn off the power Then remove the Reference Oscillator board from the extender remove the extender and return the Reference Oscillator board to its Proper place in the instrument Turn the power back on 4 3D AUXILIARY REFERENCE BOARD ADJUSTMENTS 1 INTERNAL ZERO SYMMETRY ADJUST R5038 a b Connect the oscilloscope to the frant panel CALIBRATE OUT connector The sweep time should be 0 2 ms cm and the oscilloscope should be adjusted to trigger on the positive slope of a 222 mV pk pk square wave Carefully note the duration of the positive half Cycle of the square wave Then trigger on the negative slope of the square wave and carefully note the duration of the negative half cycle The two half cycles should hav
33. 111 2 Be sure the Sensitivity sett ng considered is that appropriate to the expected signal level For a noisy signal the Sensitivity setting will be very much different from that used in the preceding step where one was measuring the signal plus noise c Set the controls as determined in b and attempt the measurement Some experimentation may be required to achieve the optimum control settings Pre Mixer Overload Circuits ahead of the Mixer only overload when the input level exceeds the Tuned Amplifier Limits indi cated in Table 111 2 In any case there is relatively little one do at the Model 124A in the case of pre mixer overload The only action that might help is to reduce the sensitivity For example suppose one wished to measure a 500 uV signal accompanied by 400 mV of noise From Table 11 2 it is clear that the Tuned Amplifier would overload if the measurement were attempted on the 500 LV sensitivity range However by setting the Sensitivity switch to 1 mV the overload talerance is increased to 720 mV and the Measurement can be made This technique is most useful when one is near an overload tolerance cross over point as in the example just given Shouid one be far from such a point the likelihood of improving the situation in this matter becomes remote For example suppose one had 1 HV signal accompanied by 40 mV of noise The nearest sensitivity position that could be used without overloading the
34. 124AL 0 2 Hz 210 kHz Sensitivity 21 full scale ranges in 1 2 5 sequence Full scale voltages are determined by the choice of preamplifier Sensitivity and all other preamplifier determined specifi cations are given in Table 1 1 Signal Channel Modes of Operation 1 FLAT Flat response within 176 from 10 Hz to 110 kHz 2 from 110 kH2 to 210 kHz and 10 below 10 Hz 2 BANDPASS Provides a tunable bandpass response with the center frequency set by front panel digital dials over a range of 2 Hz to 110 kHz Setting accuracy is within 296 0 05 Hz whichever is greater Bandwidth is adjustable over a range of 1 to 100 at 3 dB points corresponding to a range of Q between 100 and 1 by means of the front panel Q control 3 NOTCH Essentially the same as the Flat mode but with the addition of a tunable notch that provides up to B dB of attenuation at any specific frequency The notch is tunad with the same controls as set the bandpass frequency 4 LOW PASS Essentially the same as the Flat mode but with the addition of a low pass filter that provides a 12 dB per octave rolloff above the set frequency HIGH PASS Essentially the same as the Low Pass mode but with the substitution of ahigh pass filter in place of the low pass filter 5 1 28 REFERENCE CHANNEL SPECIFICATIONS Modes 1 INTERNAL Frequency of the internal reference oscillator is set by means of front panel digital dials and or rear
35. 14 mV pk pk may be necessary to slightly adjust the third Signal Frequency dial to obtain the indicated amplitude The amplitude drops off sharply if the dial is set high or low If the indicated affects sre observed the selactive amplifier circuits of the Signal Amplifier are functioning nor mall y 5 6C INTERMEDIATE AMPLIFIER There are two amplifiers on the Intermediate Amplifier board each with a nominal gain of ten The relay switching on the board controlled by the Sensitivity switch actuates various attenuators 5o that the overall board gain varies from X100 to 2 according to the Sensitivity switch position Not all possible gains are checked Instead each decade is checked and also the X1 X0 5 X0 2 sequence within one decade This is sufficient to check all of the relays as well as the amplifiers Note from the schematic on page VI 13 that the front panel Sensitivity Adjustment affects the gain of the second amplifier and hence the overall gain of the intermediate Amplifier Hence it may be necessary to change the setting of this adjustment to obtain signals of the indicated level However once set the control setting should not have to be changed again at least not for the remainder of the Intermediate Amplifier checks 1 Set the Sensitivity switch to 100 nV and the Function switch to NORMAL Then set the Calibrator output to 2 uV 200 nV with a Model 118 185 2 Monitor the signal at TP2000 green te
36. 200 and in HI DYNAMIC RANGE it is X2000 For a given sensitivity changing the function does not change the output dc level because the ac gain vari s as wall as to keep the overall instrument gain constant Thus the dc amplifiers are checked simply by monitoring the dc output and observing that it does not change as the Function switch is rotated through its three PSD positions 1 Adjust the Phase dial and third Signal Frequency dial 2 3 for maximum panel meter deflection Then set the screwdriver adjustable Sensitivity Adj control for exactly full scale panel meter deflection If this cannot be done there is probably a malfunction one of the dc amplifiers or in the meter The meter can be eliminated by checking the dc level at the front panel Function Out connector Ten volts corresponds to full scale pane meter deflection At this point the Function switch should still be set to LO DRIFT Succassively sat it to NORMAL and then to DYNAMIC RANGE The panel mater should continue to indicate full scale 1396 If it does one can reasonably assume that the dc amplifiers are functioning normally If necessary one could check the output of the first dc amplifier separately This is most easily done at R3228 the emitter resistor of Q3203 schematic on page VI 22 The voltage there should be 1 5 V 0 5 V The output of the second amplifier should of course be 10 V Check the ACVM function by setting the Function
37. ATE Function Output Stability Output Noise LOW DRIFT 150 uV C lt 100 HV rms NORMAL 1mV C lt 1 mV rms HIGH DYN RANGE lt 10mv C 10 mV rms Demodulator Overload Limits Dependent on Function switch setting as follows see Subsection 3 21 for over ride considerations 10 x full scale 100 x full scale 1000 x full scale LOW DRIFT NORMAL HIGH DYN RANGE This limit is defined as the ratio at the input of the maximum pk pk voltage of a non coherent signal before overload to the pk pk voltage of a full scale coherent sinewave Note that in terms of pk pk noise to rms signal the instrument will accept without overload interfering signals having an amplitude up to 3000 times the sensitivity setting Sce discussion in Subsection 3 21 Filter Time Constants 1 ms to 300 s in 1 3 10 sequence and a minimum time constant position having a time constant of less than 1 ms determined by internal stray capacitance The External position allows capacitance to be added via a rear panel connector to obtain special values of time constant Either 6 or 12 dB octave rolloff as selected by means of front panel switch is provided Measured with tima constant of 1 and 12 dB 14 Equivalent Noise Bandwidth 416 minimum 300 s time constant with 12 dB octave rolloff Zero Suppress Calibrated control permits off setting zero 1000 of full scale on Normal and High Dynamic
38. ESS OF LIGHTS IF REF OSC 15 NOT SELECTS OPERATING SELECTIVE AMPLIFIER FREQ LOCKED REF INPUT MODE OF SIGNAL Qs tsap DOES NOT INDICATE PHASE UNLOCK CHANNEL OVERLOAD INDICATOR SELECTS OVERALL FULL SCALE SENSITIVITY AVERAGE READING METER CALIBRATED IN RMS FOR SINE WAVE INPUT USED WHEN CALIBRATING SENSITIVITY LECTS CAL VOLTAGE CAL IN BAND PASS B WITH HIGH 9 PLUG IN PREAMP MODEL 16 17 16 OR 119 SELECT ACCORDING TO FREQ RANGE AND SOURCE IMPEDANCE SEE SPECS MODEL INCREASES OVERALL SENS BY K IG pA OSC RANGE occi Ny OUTPUT fiDV ELECTS INSTRUMENT SELECTS OPERATING IN EXTERNAL POINT CORRESP TO METER F 5 POSITION MODE OF OSCILLATOR MODE SET ACTS AS WIDEBAND RMS 2 POSITION EXPECTED RANGE SELECTS LEVEL OUTPUT OF SIGNAL VOLTMETER IN PSD OSCILLATOR LOCKS OSC PHASE LOCKS OF REFERENCE CHANNEL POSITIONS ACTS AS TO SECOND HARMONIC AUTOMATICALLY SINE WAVE c AMPLIFIER MULTIPLIER IN INT OUTPUT SELECT PHASE OF SYNCHRONOUS 1 AMPLIFI DETECTION WITH RESPECT TO REF REFERENCE INPUT TO SELECT EXACT FREQUENCY OF WHICH OSCILLATOR OSCILLATOR IF OPERATING IN LOCKS OSC LOCKS INTERNAL MODE NOT FUNCTIONAL POSITIVE GOING ZERO WHEN OPERATING IN EXTERNAL MODE CROSSING Figure MODEL 124A LOCK IN AMPLIFIER 2 5 e Jan 29 02 11 45A 1 2 SPECIFICATIONS 12A SIGNAL CHANNEL SPECIFICATIONS Frequency Range Model 124A 2 Hz 210 kHz Model
39. Jan 29 027 11 43A MODEL 124A LOCK IN AMPLIFIER OPERATING AND SERVICE MANUAL Jy EG 6 PRINCETON APPLIED RESEARCH e eani Gasp MOL 1244 Copyright 2 1979 PRINCETON APPLIED RESEARCH Printed 0 5 Jan 29 02 11 43A SHOULD YOUR EQUIPMENT REQUIRE SERVICE Contact the factory 609 452 2111 your local factory representative to discuss the problem In many cases it will be possible to expedite servicing by localizing the problem to a particular plug in circuit board B if it is necessary to send any equipment back to the fac tary we need the following information 1 Model number and serial number 2 Your name instrument user 3 Your address 4 Address to which instrument should be returned 5 Your telephone number and extension 6 Symptoms in detail including control settings 7 Your purchase arder number for repair charges does not apply to repairs in warranty 8 Shipping instructions if you wish ta authorize ship ment by any method other than normal surface transportation US CUSTOMERS Ship the equipment being returned to EG amp G PRINCETON APPLIED RESEARCH 7 Raszel Road Off Alexander Road East of Route 1 Princeton New Jersey D CUSTOMERS OUTSIDE OF U S A To avoid delay in customs clearance of equipment being returned please contact the lactory or the nearest factory distributor for complete shipping information Address co
40. MODE REJECTION for a null in the ac voltmeter indication 4 HIGH FREQUENCY COMMON MODE REJECTION C109 Change the setting of the Reference Frequency controls ta 10 00 NORMAL xi0k The fre quency of the applied signal will now be 100 kHz Set the M124A Reference output level to 0 5 V While continuing to monitor the signal at R132 with the voltmeter or oscilloscope adjust C109 for a null in the ac signal level a 6 DC ZERO CHECK a Disconnect the calibrator output from the pre amplifier inputs Also remove the ac voltmeter from R132 and connect the DVM to this point instead b The indicated voltage should be 0 V 50 mV If 8 it is not touch up the setting of R119 as required to obtain an indicated voltage of 0 00 V This completes the preamptitier alignment The preampli fier cover can now be returned to its normal position 4 5 MODEL 118 PREAMPLIFIER ALIGNMENT To align the preamplifier it will be nec ssary to use a Model 183 Remote Preamplifier Adapter with extender cable 45 PRELIMINARY STEPS Perform steps 1 through 4 inclusive of the procedure outlined in Subsection 4 44 4 5H PROCEDURE 1 DC ZERO R105 and R133 Connect the DVM to R125 b Adjust R105 DC ZERO for an indicated voltage of 0 0 V Alternate the voltmeter between resistors R125 and R144 and adjust R133 DC ZERO until the voltage at both points is the same Readjust R105 DC
41. N AND DEGAUSSING page 111 11 3 2H SELECTIVE AMPLIFIER Noise other than source thermal noise is usually not wideband and is often difficult to compute Some kinds of noise can be dealt with very effectively using the Selective Amplifier Examples include flicker or noise nom synchronous signals arising from the experiment non synchronous signals from external pickup such as from the ac power line fast transients and harmonics of the reference frequency Reducing the noise level ahead of the mixer reduces the dynamic range demands on the mixer thereby allowing signals to be measured which could not be measured otherwise The Selective Amplifier can be operated in five different modes Flat Bandpass Notch Low Pass and High Pass Figures 11 74 through 111 17 illustrate typical transfer characteristics of the Selective Amplifier for the last four of these modes Ultimate attenuation of the four frequency dependent curves exceed 80 dB In selecting filtering parameters the operator must be careful to keep the signal frequency well within the passband selected or to make the passband such as to accommodate the signal over the range that it will occupy If phase is important actual measurements of phase error over the frequency range of questionable phase accuracy would be best These regions of questionable accuracy can be determined from the individual transfer characteristics of the preamplifier transformer and Select
42. NOTE if the preamplifier to be used is a Mndel 118 or 186 set the Calibrator Output javel to 100 and the Sensitivity to 1 mV In the case of a type 117 Preamplifier or Model 116 or 119 operated direct both the Sensitivity and the Calibrator Output level should be set to 1 mV For all preamplifiers the Function switch should be set to NORMAL 1 Connect a cable from the Calibrate Qutput to the Preamplifier Input 2 Monitor the signal at TP 1000 green testpoint on the Signal board The observed signal should be an 11 mV pk pk square wave at 399 Hz indicating that the preamplifier gain is five fifty for a Model 118 NOTE A square wave with an rms value fundamental frequency companent only of 1 mV has a pk pk amplitude of 2 22 mV Therefore the total signal amplitude at the output of the Preamplifier is 2 22 x 5 11 mV This 2 22 factor must be taken into account throughout the entire procedure The opera tor 5 again cautioned not to spend an undue amount of effort convincing himsalf that the observed signals comply with the text descriptions down to the last decimal place most instances of malfunction the signal discrepancy will be so large as to leave no doubt if the signal is as indicated the operator can conclude that the Preamplifier is functioning properly in its gain af five mode gain of fifty for Model 118 or Model 188 If the signal is incorrect or missing the t
43. Range only System Gain Stability 100 ppm C 100 24 Hr in the Flat mode and with Function switch set to NORMAL 1 20 OUTPUTS Meter Reading Choice of either center zero lefthand 2 panel meter of taut band construction providing 0 5 linearity Optional Digital Readout The Model 124A may be ordered with an optional digital readout in place of the standard panel meter The readout is a 3 digit display with a linearity of 0 05 of the reading 1 count In addition a BCD output is provided at the rear panei The output levels OTL TTL compatible Logic 0 0 2 V 0 2 V 5 maximum sinking current Logic 1 3 5 V 1 0V 100 maximum sourcing current Function Out A dc signal corresponding to the panel meter reading An output of 10 corresponds to full scale deflection The output impedance is 1 Signal Monitor Enables continuous monitoring of the signal channel output ahead of the demodulator In LO DRIFT operation a full scale rms input sinewave gives a 100 mV rms sinewave at the Signal Monitor jack NORMAL operation the signal monitor output with a full scale input is 10 mV and in HI it is 1 mV Dynamic 29 02 11 46A Output Dynamic Range Operating Dynamic Range Tradeoff LO DRIFT 6 6 x 10 NORMAL 10 DYN RNG 10 Reserve Dynamic Reserve PSD PSD Total Dynamic Range Dynamic Range 10 6 6 x 10 6 6 x 10 10 10 10 10 108
44. Set the front panel controls as follows Meter Check mechanical zero Adjust if necessary Preamplifier Input DIRECT if applicable Sensitivity switch 1 mV if using a Model 118 Preamplifier set the Sensitivity switch to 10 mV Signal Channel Mode FLAT Signal Frequency dials 4 05 Signal Frequency range X100 switch 100 Time Constant 300 ms ero Offset potentiometer fully counterclockwise 10 X Full Scale switch OFF center position Preamplifier Mode A Reference Frequency dials Red NORMAL Diaits 4 05 41 1 Reference Frequency range X100 Reference Mode INTERNAL Reference Level 10 Phase potentiometer 90 9 full turns Phase switch 180 Function switch ACVM Calibrator switch 1 mV 6 Connect cable between the Calibrator BNC jack and the preamplifier s A input 7 Turn the Power on and wait five minutes for warmup NOTE In an actual measurement application allow one hour warmup for optimum performance 8 The Meter should read to the right 9 Set the Signal Mode switch to BANDPASS 10 Adjust the right most Signal Channel frequency dial for a peak on the meter approximately full scale 11 Switch the switch back and forth between 100 and 10 ENBW positions and adjust the Notch front panel screwdriver adjustment for minimum change between the two positions less than 1 of F S change After adjusting leave the at 100 12 Set the Sensitivity ADJ pote
45. Tuned Amplifier is 100 uN where the signal would be only 1 of full scale Given the high noise level it would be very difficult to detect a 1 of full scale signal even if a very long time constant were used At no time can the input exceed 720 mV rms without overloading the instrument With large input signals this limit prevents one from processing very noisy signals However by inserting an attenuator ahead of the lock in amplifier large amplitude signals having poor signal to noise ratios can be measured 3 2L OFFSET DUE TO NOISE Because of imperfections in the Phase Sensitive Detector large input noise levels can cause offsets to appear at the output As shown in Figure 111 19 these offsets are generally so small as to be negligible Even with the extremely high 1000 times ful scale noise levels which can be processed in high dynamic reserve operation the offset is typically only 196 d x o v 4 E gt u 5 a OFFSET RMS NONCOHERENT INPUT SIGNAL RELATIVE TO FULL SCALE Figure 111 19 TYPICAL OUTPUT OFFSET AS A FUNCTION OF INPUT NOISE 3 2M OVERLOAD RECOVERY The frequency range of the Signal Channel excluding the Preamplifier range is 2 Hz to 210 kHe on the standard models 200 mHz to 210 kHz if requested upon ordering Unless very low frequency response is really needed we advise that units not be ardered with 200 mHz response because larger coupling capacitors ma
46. UT RESONANCE OUTPUT aui T UDE AMPLITUDE v FREQVENCY FREQUENCY 7 Relate Retgtive Voltage Voltage Go Free 4 L oot or oz 4 ON Qu 0 Ol 602 05 10 2 5 0 30 0 100 e SP CON umo E e 280 490 90 60 609 309 309 e Phose O 0 0 399 0 60 f 909 90 02 95 OF 9 2 05 10 2 5 10 20 100 o 05 4 02 10 2 10 20 30 p0 Figure 111 14 MODEL 124A BANDPASS CHARACTERISTICS Figure 111 15 MODEL 124A NOTCH CHARACTERISTICS 444 05140 924100 Relotive Voltage Gain Horati ei itor NORMALIZE FREDU 00 05 0 1 02 9 519 2 5 10 20 50 199 O o 05 os ta 5 10 44608 180 150 1209 1209 Phase boe PHASE 909 60 tren Normalized Frequency NORMALIZED FREQUENCY P 1 e 1 LLL zx 92 os os o 2 5 9 00 OF 04 t 02 05 10 2 S 0 20 50 Figura 111 16 MODEL 124A LOW PASS CHARACTERISTICS 11 12 Figure 111 17 MODEL 124A HIGH PASS cHanactenistics Jan 30 O2 O5 29P signal bandwidths are specified as the number of Hz between two points of given attenuation on the response characteristic Suppose one had a filter with a given signat bandwidth and some amount af wideband noise measured in volts Hz were applied to it At the output of the filter would measure some amo
47. W d Disconnect the cable which extends from CAL OUT to the A INPUT 431 FINAL ADJUSTMENTS The following adjustments can be made only after the instrument has been thoroughly warmed up with the cover in place At the factory a special top cover is used one having holes drilled in it to give access to R3101 R3218 and C1007 The first two of these adjustments are located on the Mixer board The third is located on the Signal board It is not expected that the person doing the alignment will drill holes in his cover By substituting a piece of cardboard for the cover the alignment can be successfully completed Be sure the holes are accurately located and no larger than they have to be With the cover in place allow a one hour warmup before proceeding 1 AC BAL ADJ R3101 MIXER BOARD Set the front panel controls as follows Reference Frequency controls NORM 4 00 x10 Sensitivity switch 5mV Time Constant MIN Functian switch HIGH DYNAMIC RANGE ib Connect a shorting plug to the A Input c Connect the oscilloscope to the FUNCTION OUT connector d Adjust R3101 AC BAL ADJ so that the square wave ripple observed is minimum It should be possible to get it below 400 mV pk pk 2 HIGH FREQUENCY NULL ADJUSTMENT C1007 SIGNAL ROARD Set the controls as follows Signal Frequency 10 95 X 10K 109 5 kHz Reference Frequency 10 95 X10K 109 5 kHz Function ACVM Calibrate and Sensitivi
48. Y Figure 111 3 DISTORTION v FREQUENCY MODEL 118 2 GROUNDING In any system processing low level signals proper grounding to minimize the effects of ground loop currents usually at the power frequency is an important consideration With the exception of the Models 184 and 185 all of the 124A preamplifiers allow both differential and single ended operation Two properties of these preamplifiers allow them to achieve a high degree of immunity to ground loap currents In differential operation their extremely high common mode rejection assures an almost total rejection of Jan 30 O2 O5 25P unwanted signals which appear at both inputs at the same phase and amplitude the usual case for ground loop interference In single ended aperation their unique input grounding system in which signal ground floats off chassis ground by ten ohms assures a high degree of rejection As a result of this ten ohm ground ground loop signals are effectively attenuated by the ratio of ten ohms to the braid resistance typically 20 of the cable carrying the signal from the source to the input 4 Ground around Figure 141 4 GROUND LOOP VOLTAGE REJECTION USING DIFFERENTIAL INPUTS Despite the immunity granted by the ten ohm ground far better rejection can achieved in processing a signal from a single ended source if one operates differentially as shown in Figure 11 4 In single ende
49. ZERO for 0 0 R125 2 COMMON MODE REJECTION R130 AND RC BAL R103 Set the Sensitivity to 1 mV Then connect the M124A Reference output to both the A and B preamplifier inputs Reduce the frequency to 40 H2 a Monitor the signal at R125 with the ac voitmeter Then alternately adjust R130 CMR ADJ and R103 RC BAL for a null in the measured signal level Continue until no further improvement in the null can be obtained b This completes the preamplifier alignment Apr 15 02 O3 06P SECTION V TROUBLESHOOTING 5 1 INTRODUCTION This section consists of a series of procedures to be fallowed in troubleshooting the Model 124A The purpose of the procedure is to narrow tha trouble down to a specific circuit board by making voltage and waveform chacks at critical points Once the faulty board has been identified the operator can contact the factory or one of its authorized representatives for advice on how to get the instrument back into operation the shortest possible time t may prove expedient to simply exchange tha board for a new one In the case of units still in Warranty it is particularly important that the factory or one of its authorized representatives be contacted before doing any repair work on the board itself because any damage that occurs as result of unauthorized work could invalidate the Warranty Although past experience indicates that most instrument failures turn out to be the fault
50. a Function of Input Noise 2 11 20 Reference Oscillator Slewing Rate 2 eo 111 18 111 21 Net Phase Difference Between Signal and Reference Channels as Function of Frequency 11 19 22 Output Filter Transfer Functions o 11 20 11 23 Typical Calibration Accuracy aed qu 1824 11 24 Mixer Output for In Phase and Quadrature Signals E TE E E 11 29 Iv t Mode 124A Adjustments and Testpoints 2 2 TABLES Number Page 1 1 Preamplifier Specifications rta ha Sah sep te BEG ie on BA gil aed Sav 1 1 1 2 Model 124A Dynamic Range Specifications 1 5 Stability and Output Noise as a Function of Operating Dynamic Tradenff iL 15 1 2 Maximum RMS Input Levels for Mixer and Tuned Amplifier Overload as a Function of Sensitivity and Operating Dynamic Range EE radio sin gen es og LPs b eas ee est AG or 1 16 r3 Maximum Frequency Acquisition Times of Oscillator HI 19 11 4 Typical Harmonic Response Operating in the Flat Mode 1 22 111 5 Typical Harmonic Response Operating in Bandpass Mode with A 10 rd 11 22 NEGA Digital Output Pin Assignments lt u HE25 1 68 Digital Output Truth Tables 1 26 1 7 Interface Connector Signals and Pins In 28 ura External Time Constant Connector Signals and Pins p rino mb te 22 1139 ILB Remote P
51. al Monitor jack sets the signal to a more convenient level The Signal Monitor output impedance is 600 ohms The output signal amplitude corresponding to a full scale input depends on the dynamic range In LO DRIFT a full scale input yields 100 mV rms out sinewave in sinewave out In NORMAL a full scale input yields 10 mV out and in HI DYNAMIC RANGE a full scale input yields 1 mV rms out These figures depend on the true operating dynamic range which as explained earlier according to the selected sensitivity can differ from the dynamic range selected with the Function switch 3 3 REFERENCE CHANNEL OPERATION SYNC INPUT OUTPUT In the External Syne mode the Reference Channel VCO automatically phase locks to any kind of reference wave farm at a frequency within the two decades listed in Table 111 18 11 3 the only requirements being that the waveform cross its mean exactly twice each cycle that it have a peak to peak amplitude of at least 100 mV and that it be synchronized with the signal of interest The positive going zero crossing of the zero reference phase of the VCO sinewave is coincident with the positive going zero crossing of the sync input waveform The VCO can be made to lock to the second harmonic of the reference signal by placing the Mode switch in the Ext 1 2 position Maximum sync input frequency in f 2 is 105 kHz Sync input R megohm A Reference Unlock pane indicator lights when the VCO is
52. and control over the digital display sensitivity is lost To salve this problem an additional toggle switch has been added to the rear panel of instruments equipped with bath options This switch has two positions NORM and D P M 1 000 For operation with the remote programming option inactive this option is controlled by a rear panel push button the switch should be set to NORM in which position the display functions exactly as described in Subsection 3 8 In remote programming operation the switch should be set to 1 000 in which position the digital panel meter indicates the input signal level as a fraction of full scale independent of the selected sensitiv ity A full scale input gives a display indication of 1 000 independent of whether the programmed sensitivity is T mV 2 mV 5 mV or some other value Similarly with a full scale input applied the BCD output will be 1 000 and Feb 07 02 02 23P the recorder output will be 10 V The display indication and output levels are proportionally fess with less than full scale inputs For example if the programmed sensitiv ity is 200 mV and a 100 mV signal is applied the digital display will indicate 0 500 half scale the BCD output will be 0 500 and the recorder output will be 5 V 3 15 SELECTIVE EXTERNAL REFERENCE MODIFICATION 1241 77 In some applications it may happen that the reference signal produced by the experimental apparatus is of very poor quality th
53. annel the operator only need use a Af as determined by the Selective Amplifier setting with preamplifier limitations considered Althaugh the discussion of noise considerations is not complete simple example at this point illustrates the use of the foregoing equations and illustrates how a transformer can on occasion improve the signal to noise ratio Suppose that one intended to operate the Model 124A in an experiment having a source impedance of 10 ohms Further suppose the signal frequency to be 5 kHz A Model 116 Preamplifier is chosen In order to see how a transformer can improve low noise performance the noise for the Direct mode is first calculated Then the noise for transformer operation is calculated and the results com pared Since the source thermal noise contributing to the total noise is dependent on bandwidth the Signa Channel bandwidth is minimized by setting the Mode switch in the Bandpass position and the switch to the 10 ENBW equivalent noise bandwidth position The Frequency controls are set to 5 kHz In addition other control settings are made according to instructions in other parts of this section The source thermal noise in this case is V4KTBR where k is Boltzmann s constant 1 38 x 10723 joules K Jan 30 02 O5 25P T is the absolute temperature of the source presumed ta be 290 K for the example B is the noise bandwidth 500 Hz with switch set to 10 ENBW and F
54. ard and give each a brief visual damage inspection If charred or otherwise damaged components noticed there is little point in going further 3 Be sure to check the fuses There are two on the Power Supply hoard and one at the rear panel They are discussed in Subsection 5 4 which follows 5 4 POWER SUPPLY 1 On the Power Supply board check the voltage at TP6000 red testpaint for 24 V and at TP6002 yellow testpoint for 24 V If the voltages are correct go on to Subsection 5 5 lf the voltages are incorrect or missing proper power supply operation must be established before any further checks can he made Note from the schematic on page VI 23 that the 24 V regulator supplies the reference voltage for the 24 V regulator Thus any trouble with the 24 V supply would cause loss of regulation in the 24 circuit as well 2 Note that the unregulated input to both regulators is fused If a check shows one of these fuses to be blown try replacing it once If it blows again it will be necessary to locate and repair the short One way to narrow the short down is to pull afl boards but the Power Supply board power off when boards are removed or replaced and then to turn the power back on If the fuse still blows the trouble is most likely on the Power Supply board If it does not blow the board having the short can be easily determined by returning them one at a time until the fuse blows 3
55. as read on the panel meter or on the external monitor is reduced to an acreptable level If the signal amplitude is steady independent of noise a fairly long time constant can be used because the lag time in setting the phase controls can usually be tolerated However if the signa varies over a period of time and the operator wants to observe the variations a shorter time constant must be used at the expense of greater noise Sometimes for the latter case the Signal Channel filter can be readjusted for less noise after operating parameters are better established When operating the instrument as a wideband ac voltmeter placing the function switch in the ACVM position the Time Constant switch should be set ta dampen the meter 1 21 3 4B OFFSET CONTROLS The ten turn dial and its associated polarity switch allow calibrated offsets of up to ten times full scale to be applied Two applications for this feature are that it allows small amplitude variations a signal to be expanded and examined in detail and that it allows a signal amplitude to be read with greater resolution than is possible with the panel meter alone For example suppose one had a meter indication to the right To read the amplitude with the greatest possible resolution the polarity switch would be set to 93 and the dial adjusted for null at which time the signal amplitude could be read directly from the dial The following example illustrates use
56. at is it is accompanied by much noise and interference As explained earlier in the manual use of a simple low pass filter in series with the reference signal will usually clean up such a signal sufficiently to make it acceptable to the Model 124A reference circuits Never theless there could arise situations where this relatively simple technique would prove inadequate If this is the case the best one can do is to pass the reference signal through a tuned bandpass filter of moderate perhaps 10 Even the poorest reference waveform once it has been passed through such a filter will be of sufficiently good quality to allow normal reference channel operation The sacrifice one makes using such a filter is that for all practical purposes the tracking capabllity of the Reference Channel is given up Any change in the frequency of the reference signal results in amplitude loss and phase shift as the frequency moves out af the center of the passband Such a filter can of course be connected externally However in the case of Model 124A s equipped with the Selective External Reference Modification a Q of 10 filter is Provided internally These units are equipped with a rear panel switch that allows the Selective External tuned Reference mode to be selected With the switch in the NORMAL position the instrument works exactly as de scribed previously With the switch in the SEL EXT position the instrument operates in the Selectiv
57. ating in the Bandpass mode alternately adjust the Vernier and Signal Channel Frequency fine controls for an up seale peak Alternate between the two adjustments until no further increase in the meter indication can be obtained 8 8 Adjust the fine sensitivity screwdriver control for an exact meter null which incidentally corresponds to a more exact full scale setting for the 10 x less sensitive range 10 Change the Phase quadrant 90 and return the Zero Offset toggle to neutral center position The meter should read near zero but the small phase error will probably cause a reading slightly off null Adjust the Phase dial control for exact meter null Turn the Sensitivity switch counterclockwise as far as possible without overlaad while making th s adjustment 11 Return the Sensitivity switch to the reference full scale range setting 12 Apply the signal whose phase is to be measured to the Preamplifier input The meter indication with respect to the unity meter scale is accurately equal to the cosine of the phase angle if the reference signal and measured signal are exactly equal in amplitude Be cause the full scala output is 10 V the output voltage is 10 x the cosine of the phase angle If the reference signal and the signal whose phase is being measured are unequal in amplitude the cosine function must also be multiplied by the ratio of the amplitudes of the two signals Vret Vx The amplitudes were measu
58. bandwidth about dc by ynchranous detector which is locked to the synchronizing gnal A low pass filter eliminates frequency components above dc so that the detector output is a dc voltage proportional to the in phase component of the fundamental signal Proper selection of signal channel and output channel filtering parameters can render the final noise bandwidth extremely narrow The rms value of the funda mental signal is indicated on the panel meter when the synchronous detection phase is adjusted for max mum detector output A switch is provided that allows drift to be traded for dynamic reserve n addition an output dc offset feature is provided to allow higher sensitivity settings for relatively steady signals These features permit selection of the optimum aperating mode for each experimental situation Other design features include selection of output filter time constants to 300 seconds optional digital panel meter with BCD output a built in calibrator and independent use of the phase lockable oscillator and tuned amplifier for general purpose laboratory work The Model 124A may also be used as a conventional wideband laboratory voltmeter Accessories include an ac zero offset several light choppers a computer interface system and a wide assortment of low noise preamplifiers Specification 116 Input 2 Selected by front panel switch Direct 100 meg SE DE Transformer Low Z SE DE Bandwidth Dire
59. be necessary to take into account the factor of ten higher gain of this nreampli fier This is dane by always selecting a sensitivity that ig a factor of ten lower than that called for in the Procedure 2 Connect the BNC shorting plugs to both inputs of the Preamplifier 3 Remove the top and bottom covers The top cover slides off to the rear after removing the two screws underneath the upper cover overhang at the rear of the instrument The bottom cover slides off to the rear after removing the two screws which secure the two rear bumper feet i 4 Set the Model 124A controls as follows Sensitivity 500 uV Mode FLAT Signal Frequency Digits 4 00 Signal Frequency Multiplier X100 Signal 1 Reference Frequency Controls NORM 4 00 100 Reference Mode INT VCO Reference Level 10 Reference Level Vernier CAL fully clockwise Phase dial 0 00 Phase switch 0 Time Constant MIN 6 dB 12 dB switch Zero Suppress Toggle switch OFF center position Zero Suppress dial 0 00 Function HI DYNAMIC RANGE Calibrate 100 mV Power ON 5 Allow a fifteen minute warmup 4 3B 24 V ADJUSTMENTS R6028 and R6010 POWER SUPPLY BOARD 1 Monitor the voltage at 6002 yellow testpoint with the digital voltmeter referred to hereafter as DVM 2 Adjust R6028 24 V ADJ for a DVM indication of 24 0 V 3 Transfer the DVM to 000 red testpoint ZAI RIOI5 FREQ ADJ HIGH
60. coupled modes and al four of them can be operated single ended or differentially A Mode 190 transformer can be used with any the plug ins to improve low frequency performance when working from low source impedances Use of the Noise Figure contours is discussed in Subsection 3 2G Another consideration in selecting a preamplifier is its ability amplify without distortion an experiment requires measurement of low level harmonics the presence of a high level fundamental it is important that the preamplifier not add significant harmonic signals by non linearly amplifying the fundamental Except in the case of the Model 118 Preamplifier the distortion generated by preamplifiers operating in the direct mode is so small as to be unmeasurable using conventional methods The 118 however distort more under certain conditions as indicated in Figure 111 3 the transformer mode both phase shift and distortion must be measured for each individual operating condition CURVES 1und 2 APPLY FOR ALL MODEL 124 ENSITIVITY PSD SETTING COMBINATIONS EXCEPT 5 LO DR SEN 10 thru 500 mV PSD NORMAL SEN 31 thru 00 RNG SEN 100 pV thru 500 FOR THESE COMBINATIONS CURVES 3ond APPLY 2 2v lt aa 5a zomv 2 Fr 10 107 FREQUENC
61. ct 0 2 Hz 210 kHz Transformerb 1 5 Hz 10 kHz Direct 120 dB at 60 Hz Transformer 140 dB at 60 Hz Common Mode Rejection Ratio Full Scale Direct 100 nV 100 nv Sensitivity Transtarmer 1 Maximum Input Direct 200 V dc 200 V dc Transformer 10 mV rms sine wave Voltage ay be wired for 1 50 to 1 350 turns ratio Standard is 1 100 Varies with source impedance Model 117 100 megohms SE DE 0 2 Hz 210 kHz 120 dB at 60 Hz Model 118 Model 119 10 kilahms SE DE Selected by front panel switch Direct 100 meg SE DE Transformer Low Z SE DE Direct 0 2 Hz 210 kHz Transformer 1 kHz 210 kHz 0 2 Hz 210 kHz Direct 120 dB at 60 Hz Transformer 120 dB at 60 Hz 110 dB at 60 Hz 10 nV Direct 100 nV Transformer 1 nV 5 Direct 200 V de Transformer 10 mV rms sine wave NOTE A current sensitive preamplifier Model 184 is also available See ACCESSORIES list at end of specs Table t 1 PREAMPLIFIER SPECIFICATIONS 2 1 SELECT EXACT CENTER SELECTS TIME CONSTANT OF OUTPUT FREQUENCY OF SELECTIVE LP FILTER 6 OR 12 dB OCTAvE ROLLOFF AMPLIFIER CRANKS IN dt OFFSET IN FRONT DF OUTPUT AMPLIFIER TURN 1 FULL SCALE I FOR A TOTAL OF tO FULL SCALES FREQUENCY RANGE ADJUST FOR ZERO TOGGLE SELECT POLARITY gt TRANSFER OF CENTER FREQUENCY iN NOTCH DECIMAL POINT MODE SELECTS SHARPN
62. ction that determines the dynamic tradeoff independent of the setting of the Function switch and it is the true or operating dynamic tradeoff that determines the overload and stability characteristics of the instrument Thus in using the tables that define the Overload and Output Stability character istics of the Model 124A the operator must always take care to read the data from the column corresponding to the true dynamic tradeoff which may differ from that selected with the Function switch Tha dynamic tradeoff abtained as a function of the setting af the Function and Sensitivity switches is as follows 1f the FUNCTION switch is set to Then LO DRIFT AND ACVM The unit operates in LO DRIFT exeept when the Sensitivity switch is set to 100 nV 200 nV or 500 nV For those positions the unit operates in the NORMAL mode and the NORMAL mode drift and noise tolerance specifications apply NORMAL The unit operates in NORMAL with Sensitivity switch settings af 100 nV through 50 mV With settings of 100 mV through 500 mV it transfers to LO DRIFT The unit operates in with Sensitivity switch settings of 100 nV through 5 mV With settings of 10 mV through 50 mV it transfers to NORMAL and with settings of 100 mV through 500 mV it transfers to LO DRIFT Generally speaking one should operate with the switch set LO DRIFT to take advantage of the excellent output stability obtained with this setting see Table Ho
63. d operation the preamplifier sees the potential difference between the center con ductor of the cable and the braid and any ground loop signal on the braid can be attenuated but not rejected altogether differential operation the preamplifier sees the potential difference between the Input and the B Input Ground loop signal current flowing in the braid is of no consequence However when operating differentially it is important to assure that common mode interference arising in ground Ipops is just that ie without a significant differential component This should not prove a problem as iong as both signal cables are the same length and follow the same path 3 20 REMOTE PREAMPLIFIER ADAPTER In situations where very low signal levels are encountered it may be desirable to operate the preamplifier very close to the signal source to reduce noise and stray pickup while leaving the main Lock In unit at a convenient operating location This may be accomplished with the accessory Remote Preamp Adapter Model 183 see Figure 111 5 3 2 SINGLE ENDED DIFFERENTIAL AND THANSFORMER INPUTS All of the preamplifiers have switch selectable single ended differential inputs The differential inputs be used to combine signals B as well as to provide common mode rejection 11 4 impedance matching of the source and loading considera tions often require that the input impedance of the preamplifier h
64. e being too large for the selected sensitivity When this is the case the panel meter indication exceeds full scale and the Overload light turns on The solution is simply to select a sensitivity setting which yields an on scale indication DC Amplifier overload can also be produced by high amplitude quadrature signal component or by high amplitude spikes and other noise which may be reaching the Output Amplifier the latter is particu larly true when operating in the Flat mode The test and solution is simply to increase the Time Constant setting Except when operating with extremely noisy signals a time constant of one second should suffice to eliminate quadrature and transient overload of the dc amplifiers 2 Demodulator Overload Overload at the demodulator is also easily detected one has only to monitor the signal at the Signal Monitor connector with an oscilloscope If the signal exceeds 1 5 V pk the demodulator is overloading If the signal is less than 1 5 V pk it is not There are several possible courses of action when faced with Mixer demodulator overload First one always has the option of operating the instrument with less sensitivity Second operating with a narrower band width ahead of the Mixer may prove helpful the instrument is being operated in the Flat mode and operation in the LOW PASS HIGH PASS or better vet the BANDPASS mode is possible a considerable reduction in noise at the input to th
65. e External Reference mode providing the front panel Reference Made switch is set to INT VCO If the front panel Reference Mode switch is in any other position when the rear panel switch is set to SEL EXT improper Reference Channel operation results 1 31 The only other consideration in using the Selective External Reference mode is to tune the Reference Channel to the frequency of the input reference signal This is easily done by applying the reference signal and then monitoring the amplitude of the signal at the Reference OUT connector with the Signal Channel A suitable procedure follows 1 Set the controls as follows Power ON Selective External Selector switch rear panel SEL EXT Reference Mode switch INT VCO Reference Level switch 10 if preamp is Model 118 set to 1 Reference Level Vernier CAL Function switch ACVM Sensitivity 500 mV Signal Mode FLAT Signal Input switch 2 Set the Reference Frequency controls to the approxi mate frequency of the Reference signal 3 Connect the Reference signal to the REF IN connec tor NOTE The amplitude of the Reference signal should be in the range of 100 mV pk nk to 3 V pk pk 4 Connect a cable from the REF OUT connector to the A Input connector of the preamplifier The panel meter should show some deflection If it does not adjust the Reference Frequency controls as required to obtain some deflection and then further adjust them for maximu
66. e Mixer may be achieved hy making the transfer If the instrument is operating in bandpass to begin with increasing the Q will further decrease the bandwidth If the inter ference is at a single frequency removed from the signal frequency operating in the Notch mode with the signal channe tuned to the interference frequency may prove to be the best solution Jan 30 O2 05 32 This third choice is to make a different tradeoff of dynamic reserve for output dynamic range If the instrument is already operating with the Function switch set to HI no improvement by this means is possible If however it is operating with the switch set to NORMAL a factor of ten reduction in the Mixer input signal amplitude can be abtained simply by setting the Function switch to the Function switch is set to L DRIFT a factor of 100 reduction in Mixer input signal amplitude is possible the first factor of ten by setting the switch to NORMAL the second by setting it to Hl In other words in choosing the position for this switch be sure to take the Mixer overload considerations into account as well as output drift requirements Also one should be aware of the dynamic override transfers that take place for certain positions of the Sensitivity switch as explained earlier Note that the Function switch gives a simple test Mixer overload as well which though not as definitive as monitoring the signal at the Signal Monitor jack may still p
67. e Reference Channel Mode switch to EXT The REF UNLOCK light should glow for a few 2 seconds and then extinguish Monitor the signal at the Reference Qut nector with the oscilloscope One should observe a 1 V rms 2 8 V V pk pk sinewave at 1 kHz d Set the toggle switch to EXT f 2 Again the REF UNLOCK light should glow this time for about seven seconds and then extinguish le Verify that the signal at the Reference Out connector is unchanged in amplitude but that its frequency has doubled 2 kHz f Reset the Reference Mode switch to INT VCO but leave the signal generator connected to the Reference Input cannector NOTE If normal indications were obtained in steps a through one can reasonably assume that the Auxiliary Reference board is functioning normally and go to Subsection 5 6 If abnormal indications were noted there is a good possibility of a malfunctian this board The remaining steps in this sequence may Prove helpful in narrowing the prablam down to the specific malfunctioning circuit 9 5 Regulator Check the voltage at the positive end of capacitor C5004 This voltage which is indicative of the current flow through Q5001 and hence the 5 V load should be 11 V 3 V C5004 is the 35 uF capacitor located near the upper edge of the board Next check the 5 V regulator output which should be 5 V 0 5 V This is most easily checked at the positive end of capacito
68. e Reference Oscillator board into the Extender board turn on the power and allow a five minute warmup 3 E ZERO 3 ADJUST R4305 a b c 9 Connect the dc voltmeter not the DVM TP4004 gray testpoint Connect a jumper between CR4007 and R4050 as indicated on the Parts Location Diagram on page 1 16 Under no circumstances use chassis ground as the circuit may oscillate Adjust 4305 ZERO 3 ADJ for V 1 V at the testpoint Note that this i an open loop high gain adjustment and so will be difficult to set and once set will drift quickly from the ideal 0 reading Remove the jumper The dc voltage at the gray testpoint should stabilize at 3 8 V 20 5 V 4 ZERO 1 ADJUST R4040 al 5 fd Cannect two jumpers one from TP4005 B1 ta ground and the other fram TP4006 E1 to ground TP4005 and TP4006 are both gold pin testpoints down on the board Connect the voltmeter to TP4001 green test Point Adjust R4040 ZERO 1 so that the monitored voltage is drifting equally about zero Remove the jumper which extends from TP4006 E1 and ground but leave the jumper which extends from TP4005 B1 and ground 5 E ZERO 1 ADJUST R4030 a b Adjust R4030 E ZERO 1 ADJ for equal drift about zero in the monitored voltage voltmeter still connected ta TP4001 Remove the jumper which extends from TP4005 B1 and ground Ivi 6
69. e exactly the same duration If they da not adjust R5038 INT ZERO ADJ as required to obtain the desired symmetry 3 DC CALIBRATE ADJUST R5015 a ft Set the front panel Calibrate switch to 222 mV dc Remove the oscilloscope from the Calibrate jack and connect the DVM there instead Adjust R5015 DC CAL ADJ for a DVM indication of 2220 V Remove the DVM Feb O7 O2 02 25P 4 EXT ZERO SYMMETRY ADJUST R5020 a 15 d e ti Set the front panel Reference Level switch to Connect the oscilloscope to 5000 green test point Connect a cable from the REF OUT jack to the R F IN jack While observing the square wave at gradually rotate the front panel Reference Ver nier counterclockwise As the control is adjusted a point will be reached where the symmetry of the square wave will begin to degrade When this occurs adjust R5020 EXT ZERO SYMMETRY ADJ as required to maintain as near perfect symmetry as Dossible Continue until the wave form locks to either or ground indicating that the vernier is too far counterclockwise Set the Reference Level switch to 10 and rotate the vernier to the fully clockwise CAL position Remove the cable interconnecting the REF IN and REF OUT connectors 4 3E MIXER BOARD ADJUSTMENTS 1 Turn off the power Then remove the Mixer board and plug in the Extender board in its place 2 Plug the M
70. e known However do nat confuse imped ance matching with optimum input impedance for low noise operation The fatter is discussed in detail in Subsection 3 2G The input impedance of each preamplifier direct mode is Model 116 100 megohms 20 pF Model 117 100 megohms 20 pF Model 118 10 kilohms 170 pF Model 119 100 megohms 20 pF These impedances are for each input to ground In the differential mode for all models except the 118 the impedance from input to input is twice that stated double C half For the Model 118 the input impedance for the differential mode is about the same as the impedance for single ended operation In addition the diff input impedance of the Model 118 varies with sensitivity and the setting of the PSD switch common mode input impedance is 25 for combinations In the Lo Drift mode on the 10 mV through 500 mV sensitivity ranges the input impedance is about three times that specified In the Normal mode the higher impedance applies to the 1 mV through 500 mV ranges and in the Hi Dynamic Range mode it applies to the 100 pV through 500 mV ranges For th preamplifiers having internal transformers the Input switch operates the same for the transformer as it does for direct The input impedance is very low in the transformer mode Figure 5 MODEL 183 REMOTE PREAMPLIFIER ADAPTER Jan 30 02 O5 25P an external transformer such as the 190 is used it i
71. e output of the Mixer and before any filtering Figure 11 24 illustrates the Mixer output corresponding to in phase and quadrature signals respectively If the signal and reference inputs to the Mixer are either in phase or 90 out of phase the signal at the output of the Mixer will be as shown For signals 180 out of phase the Mixer output will be the inverse of the 90 output Taking the maximum possible area that can be enclosed by ane cycle one polarity as a unit output the Output averaged over a cycle for any Mixer input phase relationship is simply the unit output times the cosine of the angle between the input and reference signals APPLICABLE ONLY BELOW 50 FOR NOISELESS INPUT SIGNALI t 5 AND REF BO Qut OF PHASE Figure 111 24 MIXER OUTPUT FOR IN PHASE AND QUADRATURE SIGNALS 111 29 Feb O7 O2 02 22P The cosine response depends on th sinusoidal nature of the input signal If the signal were a square wave and the tuned amplifier were not used the Mixer output would vary linearly with the angle between the signal and reference inputs Nevertheless maximum output would still be at 0 and 180 and zero output would be obtained at 90 and 270 Note that when the Model 124A is being operated in the Phase Meter mode assuming the instrument in question is equipped with that option internal limiting circuitry converts any input to a rectangular wave of the same
72. ected the FSD DYNAMIC RESERVE varies from 10 to 103 and the OUTPUT DYNAMIC RANGE varies from 10 to 105 The TOTAL DYNAMIC RANGE is 10 for LO ORIFT and NORMAL operation and 108 for HIGH DYNAMIC Jan 30 02 05 50 104 50 OVL PSO OVL TOTAL DYN RNG NORMAL PRE PSD OVL TOTAL RNGPESERVE o z x a 4 a LO ORIFT NOTE Tha in ac icated vpliven ievabia Ter at of axianded TOTAL OYNAMIC RESERVE are masimums positions af the nsilivify switch Figure 111 18 DYNAMIC RANGE CHARACTERISTICS OF THE MODEL 124A RANGE Reserve operation In applications where the PSO OVL level is exceeded the appropriate pre PSD passband lirniting is used to reduce the noise below the PSD OVL level that the measurement can be made Use of the Bandpass Notch Lo Pass and Hi Pass characteristics in this manner does not improve the overall achievable improve ment in signal to noise ratio but it does achieve a real improvement in Dynamic Reserve and hence in Total Dynamic Range In FLAT mode operation the PSD OYNAMIC RANGE and the TOTAL DYNAMIC RANGE are the same It should be noted that the Dynamic Range characteristics shown in Figure 18 are maximums not applicable for all positions of the Sensitivity switch In LO DRIFT operation maximum Total Dynamic Range is attained with the Sensitivity switch set to 1 4 V Below J uV the Model 124A au
73. ector Table 111 9 indicates the pin assignments of this connector Note that there are three groups of control input lines To obtain any given combination of Sensitivity and Dynamic Tradeoff one input in each group is grounded Usually all of the other pins can be left floating However in a noisy environment particularly where the cable leading to 38001 is relatively long it may be advisable to apply logic 1 3 5 V 1 V to the other active input pins to assure stable operation Otherwise transient pickup cauld cause undesired switching of the Sensitivity and Dynamic Range Tradeoff A connector AMPHENOL 57 30360 that mates with 18001 is supplied with the modification In addition to the three groups of input lines two outputs OVERLOAD and REF UNLOCK are provided Each of these outputs is up when the corresponding lamp is illuminated and down when the corresponding lamp is dark There are two operating restrictions that the operator should bear in mind when operating unit equipped with this modification First of all the Dynamic Tradeatt Over rides that occur as a function of selected program med Sensitivity apply in Remote Programmed operatian exactly the same as in Local operation For details see page 111 15 Second there is a reduction in the amount of 24 V power available for external use From Table 1 8 100 mA are available In the case of units equipped with the Remote Programming Option the
74. ed for peak meter reading they indicate the phase of the signal with respect to the reference signal However more accurate determination can be made hy taking advantage of the greater quadrature adjustment sensitivity Also the phase shift differences between the Reference Channel and the Signal Channel must be accounted for if accurate phase determination is required When adjusting for the peak the meter reading varies around the peak as the sine of the phase angle for small errors If the phase is adjusted for quadrature null instead the meter reading varies around null the cosine of the phase angle for small errors Therefore for any small number of degrees change of the Phase vernier while adjusting for a quadrature null the meter reading changes much more than for the same vernier change while adjusting for an in phase peak Two high sensitivity procedures follow Procedure 1 This procedure is relatively simple and can be used with signals that vary in amplitude independent of noise 1 Measure the amplitude of the signal in the normal manner so that the controls are initially optimized for time constant dynamic range Signal Channel filter settings etc Use the Bandpass mode and high if possible frequency constant to eliminate the effects of harmonics on making the null settings below If the frequency is changing it would be best to use a wide bandwidth and avoid using a transformer input because
75. his check Signal BANDPASS Function ACVM Signal Q 100 Calibrate 2 mV Sensitivity 2mV Preamp Input Selector A Remove the shorting plug from the A Input of the preamplifier and connect a cable from the A Input to the Calibrate Output Adjust the third dial of Signal Frequency control for peak panel meter indication Feb O7 O2 02 26P d Change the setting of the Signal Q switch from 100 to 10 ENBW The signal amplitude should not change If it does change the setting of the front panel NOTCH ADJUST screwdriver ad justment as required so that no amplitude change takes place when the is switched from 100 to 10 ENBW Leave the set to 100 e Now set the gird Signal Frequency dial 787 Note Both Signal and Reference Frequency controls should be set the same f Adjust R1015 SIG FREQ ADJ for maximum panel meter indication 2 HIGH FREQUENCY NULL ADJUSTMENT C1007 Set the controls as follows Signal Frequency controls 10 95 X10K 109 5 kHz Reference Frequency controls NORM 10 95 X10K 109 5 kHz b Adjust the third dial of the Reference Frequency controls for peak panel meter indication Care fully note the panel meter indication ic Set the Q Selector to 10 ENBW If the meter indication changes adjust C1007 HIGH FREQ NULL so that there is no meter indication change as the is switched back and forth between 100 and 10 ENBW Leave the set to 10 ENB
76. ibrate Output to 2 mV The amplitude of the observed signal should decrease to 0 14 V pk pk indicating the gain reduction which occurs as K2007 is de anergized and 2008 is energized 6 Set the Sensitivity switch to 5 mV The amplitude of the observed signal should decrease to 57 mV pk pk reflecting the gain reduction which occurs as K2008 drops out and K2009 is energized of the Intermediate Amplifier board relays have now been checked f proper operation to this point was obtained the Intermediate Amplifier board can be sumed to be functioning normally 5 60 MIXER BOARD AC GAIN is either X11 X1 1 as determined by attenuator controlling ralays K3101 and K3102 The gains are made 10 high to compensate for the fact that although the instrumant reads out in rms the Mixer is average responding 1 Set the Sensitivity switch 50 uV and the Calibrate Output to 500 uV 50 with a Model 118 or 185 Then monitor the signal at the front panel SIGNAL MONITOR connector The observed signal should have a pk pk amplitude of 28 3 mV This signa will be noisy 2 Set the Sensitivity switch to 100 and increase the Calibrator Output to 1 mV 100 with a Model 118 or 185 The observed signal should remain the same in amplitude gain decrease compensated by increased calibrator output but the noise should decrease If the indicated signal levels were observad one can assume that the ac amplifier p
77. icant errors in the fundamental measurement Remembering that synchronous detection has features similar to full wave rectification one would see imme diately from symmetry considerations that the response to even harmonics is different from the response to odd harmonics For odd harmonics the detector response relative to the fundamental response is simply 1 n where is the number of the harmonic For example the third harmanic response is 1 3 the fundamental response the fifth harmonic response is 1 5 the fundamental response etc Theoretically the Synchronous Detector should have no response a1 all to even harmonics However the reference waveform is not perfectly symmetrical causing a small Jan 30 O2 O5 37P response The even harmonic response due ta dissymmetry can be expressed as sin nz 1 2 Response Relative to Fundamental where is the number of the fundamental and e is the fractional departure of the half period from the actual halt period of the reference waveform If n is even and ne is very much smaller than unity the expression simplifies to approximately 78 2 In other words the response to all even harmonics is about the same and is determined by the symmetry of the reference signal at the Phase Sensitive Detector general a given half cycle of the reference signal will be within 0 3 af half the period giving 0 003 as the value of e Inserting this into the formula ane obtains
78. ignal driving the synchronous detector is a clean Sinewave the rms voltage indication will be very accurate The filter in the Signal Channel can be used to clean up a waveform if necessary If the waveform is not clean however the meter reading will still be within 10 or 12 Percent of the wideband rms amplitude of the input signal Plus noise This wideband capability is very useful for wideband noise and complex waveform measurements As in lock in operation the Time Constant is used ta smooth the meter indication However bear in mind that 07 02 02 20P MAXIMUM ERROR h FREQUENCY Figure 111 23 TYPICAL CALIBRATION ACCURACY both the signal and the noise contribute to the output of the detector ACVM operation The signal to noise ratio is the signal p us noise is measured with the time constant serving solely to smooth the output not improved Instead indication It should be noted that in ACVM operation the Model 124A is effectively in the LO DRIFT made except for the 100 nV 200 nV or 500 nV sensitivity settings where the unit operates in the NORMAL mode Consequently for all the drift but the three NORMAL mode ranges overload characteristics of the LO DRIFT mode apply 3 8 DIGITAL PANEL METER MODIFICATION 1241 98 requested upon purchasing digit Nixie display may be installed instead of the panel meter This display provides direct n
79. included at the back of this manual The Synchronous Detector is the heart of the instrument around which are situated the Signal Channel the Refer ence Channel and the Output Amplifier The Signal Channel amplifies and filters the signal cleaning it up as much as possible before passing it along the Synchronous Detector The Reference Channel controls synchronization 3 1B SIGNAL CHANNEL Preamplifier Four models of plug in preamplifier are available the Model 116 the Model 117 the 118 and the 118 Together they cover the whole frequency spectrum fram near dc to 210 kHz each model having the best kind of input circuit for optimum low noise performance in its frequency range The Model 116 may be considered the general purpose choice performing well in most situations Specific data for the four preamplifier models is given in the specifications in Section and in the discussions in Subsection 3 2 Selective Amplifier The Selective Amplifier functions as a variable filter which may be operated in the high pass low pass notch bandpass or flat mode Because rms noise amplitude is a direct function af bandwidth much of the noise can be rejected in this stage by filtering out all but the band containing the wanted signal In addition odd harmonics to which the Synchronous Detector is sensitive can be eliminated Intermediate Amplifier The Intermediate Amplifier provides additianal gain so
80. internal phase variations as function of frequency could not be accounted for 2 Disconnect the signal from the Preamplifier and connect the sinewave from the Reference Channel Qut Jack to the Preamplifier s A input If this output is already being used for synchronizing the experiment use a T connector The amplitude must be low enough so that the Signal Channel is not overloaded The phase of this sinewave is going to he used for zero reference f a clean sinewave having a phase more suitable for zero reference is available use it If a transformer input is used it is important that the Reference output impedance be made to took the game as that of the signal source appropriately designed attenuator can generally be used to achieve this goal Otherwise phase measurement errors will be introduced 3 Set the Preamplifier Mode switch to A The Transformer Direct switch should be set as priate for the intended input coupling 4 Set the Zero Offset switch to OFF center position 5 Adjust the Phase controls far an exact meter null Increase the Signal Channel sensitivity as much as possible without overload while making this adjust ment 6 Record the Phase dial setting phase zero 7 Disconnect the Reference Channel sinewave from the Preamplifier and reconnect the Reference Channel sinewave from the Preamplifier and reconnect the signal to be measured 8 Adjust the Phase contr
81. ive Amplifier settings The best thing to do is to keep the bandwidth wide enough so that phase and amplitude errors not a problem Phase control errors are discussed in Subsection 3 3B Special procedures for making accurate phase mea surements given in Subsection 3 9 In particular before operating in LOW PASS or HIGH PASS the operator is advised to check Figures 111 16 and 111 17 ta determine the amplitude responses in these modes as a function of Equivalent noise bandwidth is a concept applied to wideband noise Although most bothersome noise is not wideband but rather coherent non synehronous signal equivalent noise bandwidth considerations useful helping to choose operating parameters The concept of equivalent noise bandwidth arises from the fact that Noise Bandwidth 15 unattenuated rectangular bandwidth while continued on page HI 13 OCCA T HOT i A 5 55 2 1 Jan 30 02 O5 27P SOURCE RESISTANCE OHMS 107 Check response curves before operating in shaded region w ten Pd o 1 gt z 1 1 V 4 5 l li o o o 222 60300 Aa agaa 092 58 193 ARA
82. ixer board inta the Extender board turn the power back on and allow a five minute warmup Set the Function switch to LO DRIFT 3 AMP 2 ZERO ADJUST R3306 5 Connect jumpers from TP3301 TP3302 and to TP3303 Note that these are not board edge testpoints but rather gold pin testpoints down on the board Adjust R3306 AMP 2 ZERO for 0 on the front panel meter This is a drifty open loop adjustment Remove the jumpers Turn off the power separate the Mixer board and the Extender and remove the Extender Then return the Mixer board the instrument and turn the power back on 4 DC AMP 1 ZERO R3218 a bi Set the Function switch to HI DYN RANGE Connect the DVM to the FUNCTION OUT jack Adjust R3218 DC AMP 1 ZERO tor 0 00 V at the DVM Remove the v4 12 5 AC BAL ADJ 93101 fa Connect the oscilloscope to the front panel FUNCTION OUT connector b Ser the Time Constant switch to MIN c Adjust R3101 AC BAL ADJ for minimum ripple as observed at the oscilloseope d Increase the time constant to 300 ms and remove 6 The oscilloscope SYMMETRY ADJUST R3018 b n 8 h Gl k Change the insuument control settings as fol lows Signal Frequency Digits 8 00 Signal Mode BANDPASS Signal 20 Function ACVM Sensitivity 10 mV Reference Frequency controls NORM
83. ke recovery time from overload much longer than for units with 2 Hz response Typical maximum overload recovery time for units having 2 Hz LF response is 30 seconds for 200 mHz units 80 seconds 11 17 Jan 30 O2 O5 34P DEGREES LEAD LAG OF YCO 1 1 0 004 0 003 0 002 0 001 o 0 00 0 002 0003 0004 s 0 4 0 3 02 01 94 0 2 0 z w 25 40 20 io 10 20 49 ve 85 xi 4k 2k u o 1 ze 4k xion iren _ 152 _ sak 448 44k 1328 176k FI SYNC SIGNAL SLEWING RATE Hx SECOND Figure 111 20 TYPICAL REFERENCE OSCILLATOR SLEWING RATE 3 2N SIGNAL MONITOR The output of the Signal Channel goes to the Synchronous Detector and to the Signal Monitor jack The Signal Monitor output is useful for monitoring the signal after Signal Channel filtering the operator can thereby improve his idea of how much noise is present ahead of the Mixer In addition this output makes the 124A usable as a straightforward Low Noise Tuned Amplifier which can find many applications Notice from the Functional Block Diagram Figure 111 1 that the signal from the Signal Channel is attenuated before being applied to the Signal Monitor jack This is because the amplification in the Signal Channel is such as to make the average responding meter at the Detector output indicate the rms value af the detected signal The attenuator at the Sign
84. lifier Adapter into the Model 124A Then interconnect the Model 183 and the Preamplifier with the Extender Cable 2 Remove the two screws at the rear of the preamplifier that secure the cover Then slide the cover back onto the cable to get it out of the way 3 Set the Preamplifier Input Selector to A B In the case of a Model 116 or Model 119 set the Mode selector to DIRECT 4 Set the Model 124A controls as fotlows Sensitivity 500 uV Made FLAT Signal Channet Frequency dials setting immaterial multiplier switch setting immaterial Q Selector setting immaterial Reference Channel Frequency dials 4 00 NORMAL multiplier switch X100 Mode INT VCO Phase switch 0 Phase dial 90 07 Reference Level 1 0 V rms Function NORMAL Calibrator Output Level setting immaterial Power ON 4 48 PROCEDURE 1 BIAS ADJUST R101 07 02 O2 27P Connect the DVM to that end of R130 which is in common with R127 and R133 a Adjust R101 BIAS ADJUST for voltage indication of 5 1 V b 2 DC ZERO R119 Transfer the DVM to either end of R132 b Adjust R119 DC ZERO for a voltage indication of 0 00 V 3 COMMON MODE REJECTION R136 a Connect the M124A Reference Channel output to both the A and B inputs of the preamplifier NOTE 1f an overload indication occurs ignore it b Monitor the signal at R132 with ac voltmeter or sensitive oscilloscope Then adjust R136 COMMON
85. m meter indication If the meter indication exceeds full scale use the Reference Level vernier to reduce the indication to about 50 of full scale Then readjust the Reference Frequency controls for the desired maximum indication This completes the tuning procedure The internal bandpass f ter is now tuned to the reference frequency The cable interconnecting the REF OUT connector and the A input of the Preamplifier can now be removed and the instrument operated in the usual manner bearing in mind that if the reference frequency is changed retuning will be required Feb 07 O2 O2 24P SECTION IV ALIGNMENT PROCEDURE 4 1 INTRODUCTION The Model 124A Amplifier is a reliable conserva tively designed instrument High quality stable components have been used throughout in its construction and one can reasonably expect a long period of troublefree operation without any need for realignment However to be assured of continued high confidence in the experimental data obtained with the Model 1244 it may be advisable to run through the follawing alignment at one year intervals and after doing a repair on the instrument Due to possible interaction between some of the adjustments it is necessary that they be carried out in the indicated sequence Any decision to make a partial alignment should be reserved to someone having sufficient knowledge of the Model 124A to fully understand all possible interactions Figure 1 ide
86. may be if the Model 124A is to be successfully incorporated into a larger digital system Three different signals are provided for this purpose The first is the END OF CONVERSION level at pin 14 of the Digital Output connector This output is up nominally 43 5 V while conversion is in progress and down for the full duration of the display plus reset time The second signal provided at pin 19 of the Digital Output connector is a 75 us logic one pulse CON VERSION COMPLETE generated at the end of the conversion period The third signal provided at pin 18 is the inverse CONVERSION COMPLETE also 75 but at logic 0 In the case of an instrument equipped with both the Remote Programming Option and Digital Panel Meter option there are same special considerations that must be observed for proper operation In units equipped with the Digital Panel Meter option alone switching controlled by the front panel Sensitivity switch sets the digital display sensitivity In the case of units equipped with the Remote Programming option the Sensitivity switch is rendered ineffective when the sensitivity is being cantrolled re motely and control over the digital display sensitivity is lost To salve this problem an additional toggle switch has been added to the rear panel of instruments equipped with both options This switch has two positions NORM and D P M 1 000 For operation with the remote programming option inactive this option i
87. more sensitive than is marked on the Sensitivity switch and set the switches accord ingly Just be sure to check all sensitivities for which Calibrator voltages are available 31 This completes the Sensitivity Range checks The Output Offset and Overload checks follow 32 Remove the Input signal to the Preamplifier 33 Set the Time Constant switch to 300 ms 34 Set the Sensitivity switch to 1 mV 35 Place the 10 X Full Scale switch to 36 Adjust the Offset potentiameter for exactly one turn clockwise The meter should indicate positive full scale 12 37 Place the 10 X Full Scale switch The meter should now indicate negative full scale 2 38 Increase the Offset potentiometer setting to 1 6 turns The Overload fight should come on 139 Return the 10 X Full Scale switch to its neutral off position The Overload light will go out This completes the Initial Checks the instrument performed as indicated one can be reasonably sure that it is operating properly Jan 29 02 11 47A SECTION OPERATING INSTRUCTIONS 3 1 BLOCK DIAGRAM DISCUSSION 3 1A INTRODUCTION Before discussing the actual operation of the Model 124A let us examine a functional block diagram to better understand what each adjustment does and how the various adjustments relate to or influence one another The functional block diagram is located on the following page Schernatics and a chassis wiring diagram
88. n ru Ld 111 24 lower logic level and sourcing 0 1 mA at the upper logic Tevel During normal operation the digital meter is triggered internally at a rate of approximately 10 times per second Other internal trigger rates can be obtained by changing the value of the resistor nominally 300 KO connected between pins 1 and 15 of DJ 2 upper connector on Digital Panel meter With this resistor removed the rate is reduced to twice a second There may be occasions where it is advantageous to trigger externally such as to facilitate operation of the Model 124A in conjunction with other signal processing equipment which may be monitoring the digital output Considerations that govern external trig gering are that the internal trigger must be inhibited and that the proper external trigger must be applied Internal triggering is inhibited by grounding pin 23 BUSY of the digital output connector The external trigger is applied to pin 20 it must be a logic one that goes to logic zero for at least one and a half microseconds but for less than two milliseconds This unit resets on the negative going transi tion conversion commences on the positive going transi tion fhe maximum allowable external trigger rate is 60 Hz When the Model 124A is being operated internally triggered the usual case it is important that signals be provided to indicate when a conversion is in progress or nat in progress as the case
89. nds 200 21021 2 2 seconds X10K 2 1 kHz to 210 kHz 2 seconds Once the frequency has locked the phase will track at the rate shown in the diagram on the following page Phase Adjustment Calibrated 10 turn potentiometer pro vides 0 100 phase shift Linearity of phase setting is within 2 from 2 Hz to 21 kHz and within 5 from 21 kHz to 210 kHz Resolution is 0 1 A four position quadrant switch provides 90 phase shift increments 1 22 DEMODULATOR CHARACTERISTICS ACVM An ACVM position on the function switch permits the Model 124A to be used as a conventional or frequency selective ac voltmeter Accuracy is within 1 from 2 Hz to 20 kHz increasing to 1096 at 210 kHz Dc Output Stability and Noise Dependent on the operating mode selected by the front pane Function switch s shown in the Stability amp Noise Table next page can be shortened appreciably by momentarily switching to internal Made and manually setting the oscillator to the praper frequency Jan 29 02 11 46A DEGAEES LEAD LAG OF VCO 0 004 0001 0 002 000 0 4 0 3 0 2 04 40 30 20 18 4k T3578 ik EIE sB k 44 SYNC SIGNAL SLEWING RATE CHANNEL FREQUENCY RANGE SECOND 0 001 9 5 44k Figure 1 2 SYNC SIGNAL SLEWING R
90. ntifies the adjustments and board edge testpoints To identify the gold pin type testpaints by their number these testpoints are not located at the board edge it will be necessary to refer to the appropriate individual board parts location diagram in Section VI Some of these testpoints are also identified by an E or number printed on the board This number also appears in the text references allowing the testpoints to be easily identified Note that this alignment procedure is not intended to be used in troubleshooting If the unit is suspected to be malfunctioning go directly to Section V which deals with troubleshooting The instrument must be working normally before it can he aligned 4 2 EQUIPMENT NEEDED DC Voltmeter with center zero A coupled scope may be used instead 2 Digital Voltmeter 3 General purpose oscilloscope 4 General purpose sinewave generator 5 Frequency counter 8 AC Voltmeter such as the Model 4N0EL 7 Two BNC shorting plugs CW 159 U Amphenol or equivalent Research 8 Extender Board Princeton 1710 00 14035 Applied 9 Nonmetallic alignment tool to be used for high frequency screwdriver adjustments 4 3 PROCEDURE 4 3A PRELIMINARY STEPS 1 Plug in any of the tollowing preamplifiers Model 116 operated direct Model 117 Model 118 or Model 119 operated direct NOTE Model 118 or Model 185 Preamplifier is used it will
91. ntiometer front panet screwdriver adjustment for exactly full scale meter indication 13 Set the Signal Mode switch to NOTCH The meter should now indicate 40 15 of positive full scale 14 Set the Signal Mode switch to LOW PASS The meter should now indicate 90 10 of positive full scale 15 Set the Signal Mode switch to HIGH PASS The meter should continue to indicate 90 10 of positive full scale 16 Set the Signal Mode switch to BANDPASS This completes the Signal Channel checks The Phase and Function checks follow 17 Set the Function switch ta LO DRIFT 18 Set the Q Selector to 10 ENBW Then adjust the Phase potentiometer for zero on the meter Lock the potentiometer 19 Set the Phase switch to 270 Adjust if needed the Sensitivity screwdriver control for plus full scale meter indication 20 Set the Phase switch to 90 The meter should indicate minus full scale 12 Jan 29 02 11 47A 21 Set the Phase switch to 07 The meter should indicate zero 2 of full scale 22 Set the Phase switch back to 2707 The meter should indicate positive full scale 1 23 Set the Function switch to NORMAL The meter should remain at positive full scale t 196 24 Set the Function switch to HI DYN RANGE The meter should continue ta indicate positive full scale 51 This completes the Phase and Function checks The Reference Channel checks follow 25 Cannect the Signal Generatar
92. oduction 318 Signal Channel 2 2 2 s dE en 2316 Reference Channel 3 10 Synchronous Detector 3 2 Signal Channel Operation Ss oy are as 32A Introduction 3 28 Preamplifier Choice JC Grounding oe 3 20 Remote Preamplifier Adapter ac 3 32b Single Ended Differential and Transformer Inputs 32F Common Mode Rejection a a 2 1 ae 3 26 Noise and Source Resistance 32H Selective 2 2 3 2 Dynamic Range Po cas 3 2 Dynamic Override 32K JOverlosd uos ea 321 OffsetDueto Noise 3 2M Overload Recovery s 3 2N X Signal Monitor Mw deter An res G s 3 3 Reference Channel 2 Synetnput Output 3 38 PhaseControls 5 rn 34 Output Channel Operation ww ee ee 444A Filter Tim Constant 3 48 Offset Controls 2 3 5 Harmonic Response TET AL de 3 6 Sensitivity and Notch Calibration hea ene ee 3 7 AC Voltmeter Operation 3 8 Digital Panel Meter Modification 30 Z Phase Measurements 5 l l s 3 10 Rear Panel Connectors cat ate 3 10A Interface Connector 9 3 10B Ext Time Constant TI at 3 11 Battery ess
93. odulator bandwidth LO DRIFT operation on and setting the Function switch ta NORMAL or HI causes the Overload light to go out the problem is obviously one of Mixer overload Similarly if the switch is set ta NORMAL Overload Indicator on and setting it to causes it to go out the same 15 true does not necessarily follow that failure of the MAXIMUM RMS SIGNAL INPUT TUNED AMP LIMITS MIXER LIMITS SENS H D R N L D H D R N L D 100 110 11 19 6 19 6 200 nV 254 WV 25 uV D d 500 nv 635 uV 8 1 10 mV 110 uV 11 E d 19 6 mV 2uM 2 54 mV 254 uV 25 uV d 6 35 mV 635 63 10 uV 11 0 1 10 110 20 19 3 2 54 mV 254 i d i 50 6 35 mV 635 uV 100 110 mV 71 0 1 10 mV 196 mV 4 i 200 193 mV 19 3 mV 2 54 mV B id t 500 6 35 5 zi 720 mV 110 mV 11 0 mV 720 mV 196 mV 2mV re 193 19 3 mV E n m is 10 mV kn 720 mV 110 720 mV 196 mV 29 5k i 193 mV e 196 mV 50 mY 2 gt 196 mV 100 mV PE i 720 720 200 mV zh 5 720 mV 500 mV ih w 720 mV Table 111 2 MAXIMUM RMS INPUT LEVELS FOR MIXER AND TUNED AMPLIFIFR OVERLOAD ASA FUNCTION OF SENSITIVITY AND OPERATING DYNAMIC RANGE 11 76 Jan 30 02 05 may still be possible even with the higher input noise level If the n
94. of a specific component failure on one of the boards it is of course perfectly possible that some component other than the one located on a circuit board could go bad Where this 15 the case the person troubleshooting will have to appropriately adapt the procedure to isolate the faulty component In general it is suggested that the person who carries out the troubleshooting procedure be well grounded in basic transistor electranics The procedure is more to be thought of as a general guide for an experienced repairman than as a minutely detailed treatise to educate the newcomer 5 2 EQUIPMENT REQUIRED 1 General purpose oscillascope 2 DC Voltmeter 3 Signal Generator able to supply a 1 V rms sinewave at 1 kHz 4 Extender Board Princeton Applied Research 1710 00 1403S This item is not really required for any of tha checks called for in the following pages However it will prove indispensible for the trouble shooter who wants to go a little beyond the checks provided to isolate the trouble more specifically than is possible with the procedure In using the board be sure to install and remove circuit boards with the power off 5 3 INITIAL STEPS 1 Remove the top cover it slides off to the rear after th two screws which secure it are removed These two serews are located on the underside of the upper cover overhang at the rear of the instrument 1 2 After removing the hold down strap lift each circuit bo
95. oise exceeds 110 pV but is less than 1 10 mV FLAT mode operation is only possible with the Functian switch set to although NORMAL ar conceivably even LO DRIFT aperation may still be possible by sufficiently narrowing the bandwidth ahead of the Mixer If the Noise level exceeds 1 10 mV then FLAT mode operation becomes impossible and the operator must narraw the bandwidth ahead of the Mixer Finally if the input noise exceeds 19 6 mV rms the Selective Amplifier overloads and the signal cannot be measured with the Model 124A The only possibilities in that case to narrow the bandwidth ahead of the lock in amplifier or to attenuate ahead of the lock in amplifier whichever technique most conveniently reduces the input noise below the 19 6 mV limit As a general rule it is most desirable to operate in LO DRIFT and with the bandwidth ahead of the Mixer at maximum FLAT If the noise levels are such as to force tradeoffs the operator must decide which is better to give up first output drift or a flat pre mixer response according to his individual requirements Where the noise level is extremely high there is no choice but to give up both One way to approach the problem is to a Set the Function switch to ACVM to get an idea of the signal plus noise rms amplitude 6 Based on an estimate of the signal amplitude determine the best combination of operating dynamic range and pre detector bandwidth con troi from Table
96. oise ratio is equal to the maximum possible value x antilog NF 20 esig E the noise contributed by the amplifier being negligible under the near zero nnise figure conditions In this example the transformer increases the signal to noise ratio by factor of 10 Signal to Noise Improvement Ratio 1Q NF unmatched NF matched 20 10 20 1 20 10 10 However because of the noise contributed by the trans former and because a transformer influences bandwidth the results obtained using a real transformer are never as good as the ideal theoretical results predicted in the example Also it is seldom convenient ta obtain a transformer having exactly the ideal turns ratio It is best therefore to use noise figure contours and amplitude transfer curves obtained empirically for the individual transformer Figure is set of NF contours for the Model 116 built in transformer and Figure MI BB is its amplitude transfer curves The 10 ohm amplitude transfer curve indicates that in this example the transformer does not change the 10 equivalent noise bandwidth as set with the Q switch so that remains 8 9 x 10 V rms The noise figure for a 10 ohm source at a center frequency of 5 kHz is about 1 5 dB a vast improvement over the 20 dB NF obtained without the transformer NOTE for optimum noise performance with a trans former it is important that the transformer not be magnetized See TRANSFORMER MAGNETIZATIO
97. ols for exact meter null Increase the Signal Channel sensitivity as much as possible without overload while making this adjust ment 9 The difference between the zero reference phase recorded in step 6 and the phase set in step 8 is the accurate phase of the signal with respect to the reference signal Procedure 2 This Procedure is more complicated but it has the advantage of providing a voltage output amp digital output if the optional digital meter is installed proportional to the cosine of the phase angle which can be sent to a computer or used for other purposes It is important that the amplitude independent of noise of the zero reference signal and the signal whose phase is to be measured be 111 27 Feob 07 O2 O2 21P constant This proc dure is often used to monitor the relative phase change as an ongoing function of time of a signal that does not vary in amplitude 1 Measure the amplitude of the zero phase reference signal and the signal whose phase is to be measured in the normal manner and record the amplitudes mea sured If the relative phase variations of a signal are to be measured however the amplitude need not be known but it must be constant 2 Apply the zero phase reference signal to the input 3 Set up the Signal Channel filter parameters If the frequency is constant use a of 100 and the Bandpass mode 1f the frequency is changing it would be best to use a wide bandwidth and ta
98. om suh harmonic components of the input signal Sub harmonic signals do not directly contrihute to the output indication that is the Detector does not respond to them However if a sub harmonic is distorted in the Signal Channel output errors can be introduced This is because distortion results in higher harmonics being generated to which the Detector is sensitive especially the harmonic at the primary fre quency of detection Sub harmanics are not generally a significant component of the input signal except perhaps when the Reference Channel is operated in the Ext f 2 made In this situation and ones similar to it the second harmonic is regarded as the fundamental for the Signal Channel and the original sync input fundamental is regarded a large amplitude sub harmonic Care must be exercised to not distort the fundamental although it be attenuated by filtering in the Signal Channel Distortion in the Signal Channel other than due to OVLD clipping occurs mostly in the Preampli fier 3 6 SENSITIVITY AND NOTCH CALIBRATION The accuracy of the sensitivity calibration in the Bandpass mode requires that the notch be properly adjusted There fore each time the sensitivity is calibrated it is wise to first make the fine notch adjustment In HIGH PASS and LOW PASS the notch adjustment has very little effect because a of is narmally used in these modes In FLAT the adjustment has no effect at all The procedu
99. ortion of the Mixer circuitry is functioning normally 5 6E MIXER SCHMITT TRIGGERS Connect the oscillascope to TP3002 One should observe a 400 Hz square wave with the lower level at 12 V and the upper one at 0 V If this waveform is as indicated the Mixer Schmitt Triggers are probably working normally the waveform is absent check for a 2 8 V pk pk sinewave at C3005 before concluding there is a problem in the Schmitt Trigger circuit Note from the schematic on page VI 19 that the blue testpoint gives access to only one half of ihe complementary Schmitt Trigger output The comple ment collector of Q3003 could be checked at R3112 or at R3110 Apr 15 02 03 08P 5 6F MIXER CIRCUIT 1 Set both the Sensitivity and Calibrate switches to 5 2 mV Calibrate Output to 500 uV with Model 118 and the Function switch to LO DRIFT Monitor the signal at the junction of R3202 and R3204 Then set the Phase switch to 270 The observed signal should be a full wave rectified sine wave although a slight adjustmant of the Phase dial may be required to obtain this waveform The amplitude of the half waves should be about 80 mV relative to a V baseline If the signal is as indicated the Mixer circuit is probably functioning normally 5 6G DC AMPLIFIERS With Sensitivity switch settings from 1 through 5 mV the dc gain is determined solaly by the position of the Function switch In LO DRIFT it is X20 in NORMAL it is X
100. otal output noise may be converted to an equivalent input noise by dividing by the amplifier gain The noise figure expressed in these terms becomes 2 Noise Figure total rms noise voltage referred to amp input dB 20 logio source thermal noise voltage rms Each amplifier has its own characteristic noise figure which varies as a function of frequency and source resistance These figures are obtained experimentally and plotted graphically Figures 111 7 through 111 11 include typical sets of noise figure contours for the Madels 116 117 118 and 119 operating in direct and transformer modes Using the applicable set of contours the total equivalent rms input noise can be determined 3 Total equivalent rms input noise voltage source thermal noise x antilog NF 20 volts rms Notice from these equations that the bandwidth must be specified usually determined by the external circuitry and or the amplifier bandwidth Figures 111 7 through 111 17 include response curves of the preamplifiers from which the bandwidth may be obtained in the direct modes the bandwidth is wider than the widest Tuned Amplifier Bandwidth However a more interesting place to deter mine noise l vel is at th output of the Tuned Amplifier Because there is gain ahead of the Tuned Amplifier its noise contribution referred to the input is negligible compared to that of the preamplifier In computing the total equivalent input noise of the signal ch
101. out of sync with the reference signal Often the frequency of the signal being detected is Changing As long as the reference maintains a fixed frequency and phase relationship to the signal detection is no different than for fixed frequency signals However it is necessary that the frequency does not change so fast that the oscillator cannot stay locked in Figure 111 20 provides slewing rate information for the oscillator Because of the rapidity of the External Reference circuitry response time care must be taken to assure that there are no extra mean crossings in the applied reference signal If extra crossings should occur the Model 174A will see them as bursts of some higher reference frequency which the Reference Channel will attempt to follow causing phase lock 1055 and improper drive to the demodu lator There are three common ways in which problems of this nature occur First any noise accompanying the signal cause multiple mean crossings to occur in the region of the rise and fall of the reference signal Thus the reference signal applied must be relatively clean Frequently moder ately noisy signals can be cleaned up sufficiently for satisfactory operation by using a simple single section Jan 30 02 O5 35P P 17
102. panel VCO cantrol voltage Setting accu racy is within 2 or 0 05 Hz whichever is greater control voltage of to 10 V corresponds to the full frequency range all bands input imped ance is 10 kilohms The amplitude stability is typically Model 124AL has significantly longer sever overload recovary time BO 8 vs 30 s with 5000 times full scale overload for minute Two additional preamplifiers the Madel 184 and the 185 availabia For information contact the factory the factory r pr sentativ in yaur area 0 01 The frequency stability is typically 0 05 of the set frequency 2 EXTERNAL The internal reference oscillator will lock in both frequency and phase to virtually any externally generated signal cross ng its mean only twice each cycle Maximum input voltage is 20 V dc Minimum time required on either side of the mean is 100 ns Amplitude excursion must be at least 50 mV above and below the mean Input impedance is 1 megohrn When locked on the reference oscillator wilt track the external signal over a frequency range of 100 1 within the range of the set band of frequencies Maximum frequency acquisition lack on times for each fre quency band are given in the following table BAND FREQUENCY RANGE MAXIMUM TIME X eese 0 2 Hzto21Hz 15 minutes 10 2 210 2 2 minutes X100 20 2 10 seco
103. r A Sensitivity 50 mV Signal Made FLAT Reference Frequency controls NORM 4 00 X 100 Reference Mode INT Re ference Level switch 1 V Reference Level vernier fully clockwise Phase dial 9 00 907 Phase switch 270 Time Constant 300 ms 6 dB Zero Offset dial 0 00 fully counterclackwise Zero Offset switch OFF center pasition Function switch ACVM NORM PHASE switch rear panel PHASE 3 Connect a cable from the Reference Channel OUT connector to the Preamplifier A Input 4 Connect the oscilloscope dc coupled to pin 9 of the Phase board NOTE This board is mounted against the Signal Amplifier board shield 5 The signal observed at the oscilloscope should be a 400 Hz square wave After verifying that the signal is as indicated rotate the front panel Reference Level vernier counterclockwise as required ta make the square wave noisy 6 Adjust the 2 DC control located on the Phase board for best symmetry in the observed square wave When best symmetry is obtained try further reducing the Reference Output amplitude and repeat the symmetry adjustment Repeat these two steps until no further improvement in the setting of the symmetry adjustment be made 7 Before proceeding check at nin 5 of the Phase board for a sinewave output with an amplitude of approxi mately 20 to 60 mV pk pk Then set the rear panel NORM PHASE switch to NORM and adjust the Reference Level Vernier for 1
104. r C5005 the 15 uF 6 V located near the upper edge at about the center of the board h Schmitt Triggers Check for a 399 Hz square wave at TP5001 blue testpoint The upper and lower fevels of the square wave should be 4 5 V 1 V and 0 3 V 10 3 V respectively f the signal is as described the Schmitt Trigger driven from the 180 output of the Reference Oscillator is functioning normally Next transfer the ascillascope to TP5000 green testpoint A 1 KHz square wave with the same level limits as described in the preceding para graph should be observed If the signal is normal one can conclude that the Schmitt Trigger driven from the External Reference signal is functioning normally li Frequency Comparator A thorough checkout Procedure for this circuit is beyond the scope of this manual Nevertheless failure to pass the following two tests is a clear indication of malfunction these tests are passed clear conclusions concerning the normality of these circuits can be made Apr 15 02 O3 07P Test 1 Check for 44 V 1 at pin 11 of integrated circuit UBOD6 NOTE packages 45001 through U5006 are labeled as 1 through 6 with labels consisting of small etched foil digits on the side of the board Opposite the components Pin T of each 14 digit package is similarly marked The pins are counted clockwise viewed from the label side 2 Check for a 399 Hz square wave at 5002 gray
105. red step 1 For small angles much higher resolution can be obtained by increasing the sensitivity Remember however to always refer voltoges and meter readings obtained with increased sensitivity back to the full scale reference range by a multiplier equal to the ratio of the ranges 13 Use a cosine table or a computer to convert the readings and voltages obtained to the phase angle 3 10 REAR PANEL CONNECTORS 3 10A INTERFACE CONNECTOR 49 J9 is a 14 pin connector having outputs as given in Table This connector mates with Amphenol 2457 30140 and is wired for compatibility with the Model 127 which is a two phase accessory If it is desired to operate a Madel Pin Signal sree eaten Oe dae ea o pe 2aaa ess Ground 24 V de date UR 24 V dc No connection dard 244 22 Q Reference D uo OC ERO AR DURS ROS do 90 Reference gi eundo Se 180 Reference estie cha edt axe wre ae ae ds Signal Out LEM s Signal Ground dM sinite s d eet d eye ze naga No connection dep YE AR ve e E EI Hel VCO Input AES Reference Input No connection vigens iesus 270 Reference 11 28 Table 111 7 INTERFACE CONNECTOR SIGNALS AND PINS Feb Oz O2 02 22P 123 AC Zero Offset Accessory with
106. requency Controls set to 5 kHz R is the source resistance in ohrns given as 10 ohms Thus See ete Ax 1 38 1077 x 29 x 10 x 10x5x 107 8 9 x 10 V rms From Figure 111 7 the noise figure for the Model 116 at a center frequency of 5 kHz and a source impedance of 10 ohms is 20 dB Substituting E and this NF into equation 3 we get total equivalent rms input noise 8 9 1079 x 1020720 B9 nV rms With a transformer inserted between the signal source and the amplifier input we can increase the effective source impedance to a value that reduces the noise figure to 1655 than 0 1 dB From Figure 111 7 the source resistance should be about 200 kilohms The transformer turns ratio required for this impedance increase 15 R2 R 141 The thermal source noise at the amplifier input is equal to the noise generated by the 10 ohm source multiplied by the turns ratio With noise figure near zero the total equivalent rms input noise is also equal to the noise generated by the 10 ohm source multiplied by the turns ratio 1 25 uV rms Although the numerical value of equivalent input noise is much larger than before the signal to noise ratio is sub stantially increased This can be seen by considering all of the transformed source signal voltage as appearing at the amplifier input terminals possible because the Model 116 input resistance is much larger than 200 kilohms presented by the transformer the signal to n
107. res given here are combined procedures first for adjusting the notch and then for calibrating the sensitivity The fine Notch adjustment should be made for exactly zero center frequency signal transfer through the Signal Channel when in the Notch mode However because the Calibrator Output is square wave containing harmonies it would be difficult to use this signal for making the fine notch adjustment in the Notch mode the harmonics would disallow an output zero and adjusting for a definite value would be difficult The Reference Channel s sinewave output would be better but it is not pure enough to allow for an accurate setting One good way to adjust the notch in the Notch mode is by using a separate high purity sinewave source An alternative way to make the fine notch adjustment is to adjust the Notch Adj control for proper center frequency signal transfer through the Signal Channel when in the Bandpass mode If the adjustment is off changing the Q will change the gain at the center frequency Making the fine natch adjustment is easy if this last fact is made use of i e the fine notch adjustment should be made such that a change of Q does not change the gain at the center frequency The latter method has the merit of allowing a less pure waveform to be used because the harmonics are eliminated in the Bandpass mode If Q s of 100 and 50 are used the Calibrator waveform can be used for an adjustment within a
108. rogramming Connector Pin Assignments 11 30 1 Gain and Relay Switching for the Model 124A 2 2 2 QM Jan 29 02 11 45A SECTION 1 CHARACTERISTICS 11 INTRODUCTION The Model 124A Lock In Amplifier accurately measures the rms amplitude and phase of weak signals huried in noise Signals in the range of picovolts up to 500 millivolts at frequencies from 0 2 Hz to 210 kHz can be measured quickly and precisely Meter and voltage outputs are provided for the amplitude and the phase of the signal may be read from a dial These measurements are with reference ta a synchronizing signal supplied to or supplied by the 1244 In either the External or External f 2 mode of operation the instrument will accept any reference wave form that crosses its mean twice each cycle and will lock to and track that signal over a 100 1 frequency range In the Internal mode the frequency is determined by front panel dials or by an externally derived voltage A selection of plug in preamplifiers is available for pro viding optimum low noise performance over a wide range of input frequencies and source resistances After preampli fication noise and harmonies accompanying the signal are attenuated in the Signal Channel by filtering out ail frequencies except the band in which the signal lies Flat band pass band reject high pass and low pass filtering modes may be selected The remaining band of frequencies i converted to an equivalent
109. rouble probably is in the Preamplifier and the operator can nroceed to the schematic for his particu lar Preamplifier if he wishes to troubleshoot further As can be seen from the Signal hoard schematic on page V1 9 the signal is actually being monitored after relay K1008 on the Signal board Hence if the signal is missing it might be worth checking for the signal on coupling capacitor C1004 to isolate the relay Also take a moment to be sure that the Calibrator Output signal is normal that is a square wave with a pk pk amplitude of 2 22 times the selected Calibrator Out put level 3 Change the Sensitivity setting to 500 uV thereby energizing Preamplifier relay K100 and increasing the Preamplifier gain to X50 X500 for a Model 118 ora Model 185 The amplitude of the signal at 1000 should increase to 111 mV pk pk reflecting the increased gain If this check is normal one can reasonably assume that the preamplifier is functioning normally at least with respect to providing the proper gain Noise and common mode rejection checks are beyond the scope of this procedure Hf this check does not give a normal indication but step 2 does give a normal indication relay K100 should be suspected 5 68 SIGNAL AMPLIFIER The Signal Amplifier gain measured from the output of the Preamplifier to the output of the Signal Amplifier is either X10 K1008 energized or X1 K1009 energized Note that the gain of the amplifier circuit is always
110. rove useful If the Function switch is set to LO DRIFT and the Overload light is light to extinguish when making this test means the Mixer is not overloading It may prove useful to know the maximum rms input sinewave signal that can be apptied to the input of the instrument without overloading the Mixer as a func tion of the Sensitivity and Operating Dynamic Trade off The input overload limits for both the mixer and the tuned amplifier are shown in Table 111 2 referring to this table the operator can quickly determine the best way to process a given signal with the Model 124A for example suppose one had a signal of nominally 1 V amplitude Consider the possibilities for measuring this signal given different noise levels From Table 111 2 the mixer limit with a Sensitivity setting of one microvolt is 1 10 mV 110 or 11 according to the dynamic iradeoff What this means practically is that for noise levels below 11 V the signal could be measured in the FLAT mode with the Function switch set to LO DRIFT Narmal and Hi operation is of course also possible If the noise level is greater than 11 but less than 110 LO DRIFT operation in the FLAT mode is not possible and the operator will have to either operate in NORMAL or Hi or narrow the noise bandwidth ahead of the Mixer by means of the tuned amplifier This is usually best accomplished by operating in BANDPASS sufficient narrowing of the pre dem
111. rrespondence to EG amp G PRINCETON APPLIED RESEARCH 2565 Princeton NJ 08540 3 Phone 609 452 2111 TELEX B4 3409 4 at Ue WARRANTY amp PRINCETON APPLIED RESEARCH warrants each in strumant of its manufacture to ba free from delects in material and workmanship Obligations under this Warranty shall be limited to replacing repairing or giving credit for the purchase price at our option of any instrument returned freight prepaid to our factory within ONE year of delivery to the original purchaser provided prior authorization for such return has been given by our authorized representative This Warranty shall not apply to any instrument which aur in spaction shall disclose to our satisfaction has become defec tive or unworkable due to abuse mishandling misuse acci dent alteration negligence improper installation or other causes beyond our control Instruments manufactured by others and included in or supplied with our equipment are not covered by this Warranty but carry the original manufacturers warranty which is extended to our customers and may be mora restrictive Certain subassemblies accessories or com ponents may be specifically excluded from this Warranty in which case such exclusions are listed in the instruction Manual supplied with each instrument We reserve the right to make changes in design at any time without incurring any obligation to install same on
112. s connected to the preamptifier single ended The ansforme r alone provides sufficient common mode rejec Figure 111 6 5 d Wu 8 1 z 8 3 3 2 8 v3 RECT 9 3 FREQUENCY Figure 11 6 TYPICAL COMMON MODE REJECTION 3 2F COMMON MODE REJECTION Figure 111 6 illustrates the common mode rejection charac teristics of the preamplifiers in both differential direct and transformer mode operation Note that the CMR is much higher for the transformer mode than for the direct mode 3 2G NOISE AND SOURCE RESISTANCE Best preamplifier performance is realized under those conditions where the overall signal to noise ratio is least degraded In many instances the thermal noise generated by the signal source res stance is the dominant factor in determining the input signal to noise ratio In this respect amplifier naise performance can be specified by the amount of noise the amplifier adds to the amplified source thermal noise expressed in decibels this is called the Noise Figure 1 Noise Figure total ems noise voliage at the amplifier output 20 10910 Imi 2 2 gain x source thermal noise voltage rms where the Source Thermal Noise 4K TRAf volts rms gt and Boltzmann s constant 1 38 x 1022 joules K T absolute temperature in kelvins Af equivalent noise bandwidth in Hz R 7 source resistance in ohms The t
113. s controlled by a rear panel push button the switch should be set to NORM in which position the display functions exactly as described in Subsection 3 8 In remote programmed operation the switch should be set to O P M 1 000 in which position the digital panel meter indicates the input signal level as a fraction of full scale independent of the selected sensitiv 07 02 O2 20P A full scale input gives a display indication of 1 000 indenendent of whether the programmed sensitivity is 1 mV 2 mV 6 mV or some other value Similarly with a full scale input applied the BCD output will be 1 000 and the recorder output will be 10 V The display indication Model 124A J7 Pin 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Function Polarity Logic 1 4 volts Overload Output Logic 1 Overload Overload Output Logic 1 Overload DVM Mast Significant Digit A Digital Ground DVM 2nd Mast Significant Digit A DVM 2nd Most Significant Digit C DVM 3rd Most Significant Digit A DVM 3rd Most Significant Digit C DVM Least Significant Digit A DVM Least Significant Digit Spare END OF CONVERSION Spare Spare DVM Least Significant Digit CONVERSION COMPLETE CONVERSION COMPLETE Ext Trigger Input Spare Spare NOT BUSY input Output data will remain fixed when this line is at logic 0 Must 1
114. se levels are reduced ta 80 mA Pin Use OVERLOAD logic 0 lamp off Dee AEE ed oat REF UNLOCK logic 1 lamp 3 1 leise me No connection 100 nV Sensitivity a Yeas Sensitivity r a ae ot Oe wan en E A 10 uV Sensitivity 22 100 Sensitivity 1 mV Sensitivity DN XR Re Ps 10 mV Sensitivity m MDC RE 100 mV Sensitivity E led tue d LO DRIFT Tradeoff Milas ovas sth NORMAL Tradeoff 78 DYNAMIC RANGE Reserve Tradeoff 29 32 oes eC E oos eia connection ea 1 0 Sensitivity Multiplier 34 Sensitivity Multiplier 1 30 36 2 0 Sensitivity Multiplier Ground sete sitae WE MUEVE NU ET HORS Table 1119 REMOTE PROGRAMMING CONNECTOR PIN ASSIGNMENTS the case of an instrument equipped with both the Remote Programming Option and the Digital Pane Meter option there are some special considerations that must be observed for proper operation In units equipped with the Digital Panel Meter option alone switching controlled by the front panel Sensitivity switch sets the digital display sensitivity In the case of units equipped with the Remote Programming optian the Sensitivity switch is rendered ineffective when the sensitivity is being controlled remote ly
115. stpoint The observed signal should be a 399 Hz sinewave with a pk pk amplitude of 0 28 V It is perfectly normal for this signal to be obscured by noise If this signal is as indicated one can assume that both amplifiers on the Intermediate Amplifier board are functioning nor mally If the signal is not normal the problem could be with one of the two amplifier circuits or with one of the relays With this combination of Sensitivity and Function the energized relays K2003 2005 and K2007 3 Set the Sensitivity to 1 uV and the Calibrate Output to 20 aV 2 with a Model 118 or 185 The Observed signal should still have the same amplitude tha gain reduction is exactly compensated by the increased calibrator output but the noise should have gone down by a factor of ten The only relay change between this step and the preceding one is that K2004 is now energized and K2003 de energized 14 Set the Sensitivity switch to 10 uV and the Calibrate Output to 200 20 with a 118 185 V 5 The Mixer board ac gain As in the preceding step the decrease in gain is compensated by the increase in calibrator output and the amplitude of the observed signal should remain constant 0 28 V pk pk A further factor of ten reduction in the observed noise will take place The relay state changes are that K2006 is now energized and K2005 is de energized 5 Set the Sensitivity switch to 2 mV and the Cal
116. supplying 31 V to rear pane connector Batteries must be able to supply at least 400 mA at 31 V and 360 mA at 31 V NOTE Thasa maximum values and do not apply tor positions of the Sensitivity switch For a general discussion of tha meaning af these terms and thaw significance see Appendix at the raar of thia manual Also see Subsection 3 21 5 z 5 1 i i 1 o FMEQUENCY Figure 1 3 TYPICAL CALIBRATOR ACCURACY Size 17 1 8 W x 7 H x 18 1 4 D 43 6 cm W x 17 8 H x 45 5 cm 0 Weight 34 65 15 5 Accessories Model 173 AC Zero Offset provides square wave at the reference frequency which can be used to suppress signals at the input of the Model 124A Other accessories include a computer interface system fixed and variable speed light choppers and a broad selection of special purpose preamplitiers The AM 1 AM 2 and 190 input transformers allow better noise performance to be achieved when using a high input impedance preamplifier to Process a signal arising in a low source impedance The Model 184 Current Sensitive Preamplifier is alsa available This preamplifier which plugs in like the Models 116 117 118 and 119 Preamplifiers provides 1 V out for input currents ranging from 1 nA to 10 as selected a front panel Range switch Frequency range varies with sensitivity being 2 Hz to kHz on the 1 nA range and 2 Hz to 200 kHz on the 1
117. testpoint The lower level of the square wave should be 0 V There should be two upper levels both between 3 and 4 The signal generator should be disconnected from the Reference Input at this time NOTE If steps g through i fail to identify the faulty circuit but the board continues to malfunction there is a strong possibility that the trouble is with the associated wiring or switches 5 6 SIGNAL CHANNEL All of the gain switching in the Model 124A is done by means of relays In the following checks the various amplifiers are isolated by appropriately selecting the sitivity and Function By applying a suitable signal and checking at critical points a malfunctioning amplifier can be quickly identifiad Table V 1 which lists the gain and energized relays for all possible combinations af Sensitivity and PSD Function is provided as a convenient reference Note that overload level signals applied at various points throughout the following procedure to assure that the signal level at the output of the early amplifiers will be above the noise floor Anytime the applied signal is greater than the selected sensitivity overload is a possibility and the operator should not be concerned if the Overload light glows during such a measurement However if the Overload fight should glaw with normal signal levels applied a malfunction is indicated and it should ba corrected before proceeding 5 64 PREAMPLIFIER
118. that the signal plus noise applied to the Synchronous Detector is as large as possible without overload Presenting a large signal to the Synchronous Detector minimizes for a given overall sensitivity the noise and dc drift contributed by the Output Channel Also avadabla tha Model 184 Photometric Preamplifier and the 185 Single Ended Low Noise Preamplifier These two wera d veloped later than the preamolifiers discussed trig manual For informatian and sp cifications contact the factory Separate instruction manuals provided for the Modals 184 and 185 The Intermediate Amplifier is coupled thereby eliminat ing de drift problems in the Signal Channel 3 16 REFERENCE CHANNEL Voltage Controlled Oscillator The VCO either locks onto a synchronizing signal from the experiment or provides a synchronizing signal to the experiment The VCO drives the Synchronous Detector so that the experiment and the Model 124A are properly synchronized The VCO automatically phase locks any kind of refer ence waveform having a frequency within approximately two decades of the Reference Channel band setting the only requirements being that the waveform cross the mean twice only each cycle that it have pk pk amplitude of at least 100 mV and that it be synchronized with the signal of interest The VCO can lock to the second harmonic of the reference signal if desired
119. the 124A a special cable is available which interconnects between the Model 123 and 19 of the Modei 124A Nate that the VCO Input pin 11 is also accessible by means of a rear panel BNC jack 3 108 EXT TIME CONSTANT 18 is the External Time Constant socket By connecting external capacitors to the proper pins of this socket time constants excess of 300 s can be obtained Two capacitors are required one to be connected between pins B and 9 and the other between pins 10 and 11 The resulting time constant is 3C x 107 seconds where C is the capacitance single capacitor in farads A table of the signals provided at this connector follows Pin Function Ve beads oot senda SOR E RA Ra m Ground rM 24 V maximum of 100 mA 24 V maximum of 100 mA Bid tence sis iaa ee inani ey No connection 31 V in for battery operation a UD ate sean etes No connection tess acc iy n gc 31 V in for battery operation 8 lead of first time constant capacitor 9 Other lead of first time constant capacitor 10 One lead of second time constant capacitor 11 Other lead of second time constant capacitor Table 111 8 EXTERNAL TIME CONSTANT CONNECTOR SIGNALS AND PINS 3 11 BATTERY OPERATION Battery operation of the Model 124A Amplifier may be necessary where no ac po
120. the control settings The Calibrator output is a square wave having its fundamental component as indicated for each switch position Therefore when calibrating the sensi tivity the Mode switch should be set to the Bandpass Position and the C switch set at 10 or higher if the be used when operating is higher than 10 calibrate with that Q setting All other controls should be left as set for the notch adjustment An attenuator packaged in a small box having male and female BNC connectors is provided with each Mode 116 and 119 This attenuator attenuates 100 1 so that the Model 124A can be calibrated in the transf rmer made The attenuator output Z is 1 ohm If the transformer mode is ta be used connect the male BNC connector of the attenuator directly to the input BNC and connect the calibrator output to the attenuator s female jack with a short cable t is important that if another source is used for calibra tion the source presents an impedance of exactly 50 ohms to the attenuator After these settings are made the actual procedure is simpte Adjust the fine Phase control for maximum meter indication Then adjust the Sensitivity screwdriver control for an accurate full scale meter indication 3 7 AC VOLTMETER OPERATION With the Function switch in the ACVM position the Signal Channel output is used to operate the Synchronous Detector This makes the Model 124 operate as rms voltmeter the s
121. the requlator input fuses are not blown but the 24 V levels are missing or incorrect check the unregu lated supply levels naminally 31 V to isolate the Problem the Power Supply board or to the Unregulated Supply components line fuse trans former rectifiers or filter capacitors Note that the high power transistors are not located on the Power Supplv board but are instead mounted on the same plate as the transformer and filter capacitors 55 REFERENCE CHECKS 1 Control Settings Meter Check the mechanical zero and adjust it if necessary Preamplifier Plug in a Model 117 Preamplifier or a Model 116 or 119 operated the DIRECT mode A Model 118 or Model 185 can also be used but certain Signal Channel cheeks will have to be modified as indicated in the text Apr 15 02 03 07P 2 Sensitivity Signal Channel Mode FLAT Reference Channel Mode INT VCO Reference Frequency 3 99 X100 399 Hz Reference Level 1 V rms inner knob fully clockwise Phase switch 0 Phase dial 90 Time Constant 300 ms 6 dB octave Zero Offset dial 0 00 fully counterclockwise toggle switch center OFF position Function switch NORMAL Calibrator 1 mV 100 gV if preamplifier is Model 118 Power switch ON Reference Oscillator Board a Check for 3 8 V 05 V at TP4004 gray testpoint on Reference Oscillator board As indicated by the schematic on page VI 15 4004 monitors the o
122. through an amplifier limiter that has a canstant amplitude clipped rectangular output This signal when synchronously de madulated yields a dc output that is a linear function of the phase difference between the reference and input signals The phase sensitivity is 100 mV out per degree with the Function switch set to LOW DRIFT Only LOW DRIFT operation be used and the Sensitivity switch is constrained to settings in the range of 1 to 500 mV In the case of units equipped with the Digital Panel Meter option Phase measurements can only be made with the Sensitivity switch set to 1 10 uV 100 pV 1 mV 10 mV or 100 mV In other words the 27 and 5 positions should not be used for making phase measurements if the unit is equipped with a digital panel meter phase meter operation the input signal should be limited to less than ten times full scale but not more than 200 mV for Sensitivity switch settings from uV to 100 mV For the 200 mV and 500 mV sensitivity positions the maximum input signal is 500 mV The phase indication will not be in error by mare than 5 maximum providing the signa amplitude is at least 100 aV ar 20 of full scale as indicated by the setting of the Sensitivity switch whichever is greater 3 13 MIXER MONITOR MODIFICATION 1241 92 Units equipped with the Mixer Monitor Option have an additional rear panel BNC connector The signal available at this output is taken directly from th
123. tion and the function switch set to the PSD position to be used in the experiment The gain error introduced when switching from one PSD position to another is very small about 0 5 maximum 4 Signal Channel The Sensitivity switch should be set to the intended operating position However if one of the nV ranges is used internal noise can cause the meter reading to waver too much for making an accurate adjustment It better therefore to use one of the uV or mV Positions The gain error when switching back down to the nV range for operation will be less than the adjustment error if adjusted in a nV range The Calibrator switch should be set to the same level as the Sensitivity switch The Frequency switches should be set to exacily the same settings as the Reference Channel frequency switches The Mode switch should be ser to the Bandpass pasitian 11 23 The switch should be set ta 50 Proceed to make the Notch adjustment as follows 1 Adjust the Signal Channel frequency control and fine Phase control for maximum meter indication 2 Change the switch setting to 100 if the merer indication changes adjust the Notch Adj screwdriver control to Minimize the change Continue switching the back and forth between 50 and 100 and adjusting the Notch Adj potentiometer for no change in the meter reading Now that the Notch is adjusted before adjusting the fine sensitivity control make the following changes in
124. tmost of the four digits displayed The Teletype d 21 for overload is 1 digit to the left of the Most Significant Digit The notation A B C amp D after the digit notation abv efers to column headings of the truth table The value of each of these outputs when at a logic 1 is 1 2 4 amp 8 respective Figure 111 6 DIGITAL OUTPUT ASSIGNMENTS 11 25 For each digit the A B C amp D outputs taken together represent a number 0 to 9 in BCD format Feb O7 O2 02 21P Digital Output for Each Display Figure Display Shows Teletype Digit Always 0 except mark when meter overtoads 1 Teletype Format via 262 131 Front Panel Display Sigmticant Digit No Disptay Range Binary Coded Decimal Digital Output w gt uw Fixed in place PXTXIX X XEX las x x Truth Table for lid Sensitivity switch 1 Owl thru 9 each Printout is in microvalts Digital Gutput for Each Switch Setting Switch RCO Digital Output Setting 4 C NOTE Princeton Applied Research Corporation manu factures a cable suitable for interconnecting a Model 124A and a Model 282 Teleprinter System Interface Module part of the Model 131 Instrument Computer Interface System The part number of this cable is 6020 0023 06 sche matic drawing of this cable is included in Section VII on VIH 31
125. to the preamplifier input 3 Adjust the right most Signal Frequancy control for peak panel meter indication 4 Set the Function switch to NORMAL Then adjust the Phase dial for peak meter indication 5 Set the front panel Sensitivity Calibrate adjustment for exactly full scale meter indication 6 Set the Signal Q switch to 10 7 Remove the cable that interconnects the Calibrate Output and the Preamplifier Input Then short the Preamplifier input using a shorting plug such as the CW 159 U 8 Set the Sensitivity switch to 100 nV Then set the Time Constant switch to 100 ms Preamplifier is Model 116 117 or 119 or to 300 ms Preamplifier is Model 118 or 185 8 Note the pk pk meter fluctuates about zero over a ten second period If the preamplifier is a Model 116 117 118 the fluctuations should not exceed 25 of meter full scale If the preamplifier is Model 118 Apr 15 O2 03 09P Model 185 tha fluctuations should not exceed 80 THROUGH 9 WITH A MODEL 184 PREAMPLIFIER of mater full scale 11 Connect BNC cap shielded open to the Model 10 184 only Set the controls as indicated in step 1 184 input with the follawing exceptions The Sensitivity of the Model 124A should set to 1 uV the Q to 10 the 12 Note the pk pk fluctuations of the panel meter over a Time Constant to 1 SEC and the Preamplifier Range ten second period They should not exceed t50 of con
126. tomatically transfers to NORMAL operation as described on 11 15 In NORMAL and HIGH DYNAMIC 111 14 RANGE Reserve operation maximum Total Range 15 attained with the Sensitivity switch set to 100 nV For all three Dynamic Tradeoff possibilities as the Sensi tivity switch is set successively lower sensitivities the Total Dynamic Range available is proportionally reduced Situations could arise where the signal to be measured was of relatively high amplitude and accompanied by enough noise and interference to require that the lock in amplifier have a very wide Total Dynamic Range Where this is the attenuators can be used ahead of the lock in amplifier to reduce the signal plus interference sufficiently to take advantage of the inherently wide Total Dynamic Range of the Model 124A It is almost inconceivable that a real measurement problem could exist that would require alf of the Total Dynamic Range available with this instrument For a more detailed discussion of Dynamic Range the reader is referred to the Appendix at the rear of the manual Jan 30 O2 O5 31P 3 2 DYNAMIC OVER RIDE Although the frant panel FUNCTION switch allows the serator to select LO DRIFT NORMAL or HI DYNAMIC ANGE Reserve operatian it is important to understand that the instrument does not necessarily operate with the dynamie tradeoff selected Far certain positions of the Sensitivity switch there is override a
127. trol to 1077 DO NOT ATTEMPT STEPS 2 meter full scale
128. ty 7 mV b Remove the shorting plug from the Input of the Preamplifier and connect a cable from the A Input to the Calibrate Output c Adjust the third dial of the Reference Frequency controls for peak pane meter indication fully note the meter indication d Set the Selector to 10 ENBW If the meter indication changes adjust C1007 HIGH FREQ NULL so that there is no meter indication Change as the Q is switched back and forth between 100 and 10 ENBW e Remove the cable interconnecting the CAL out put and A Input Then return the shorting plug to the A Input 3 DC AMP 1 ZERO ADJ R3218 MIXER BOARD a Set the cantrols as follows Sensitivity 500 uV Signal Frequency Digits 4 00 Signal Frequency Multiplier 100 Reference Frequency controls NORM 4 00 X100 Function HIGH DYNAMIC RANGE b Connect the DVM te the FUNCTION OUT connector c Adjust R3218 DC 1 ZERO ADJ for 0 00 V at the DVM This completes the alignment All test equipment can be removed and the covers secured in place 4 3 PHASE METER OPTION ALIGNMENT The following alignment is carried our only on units equipped with the Phase Meter Option This procedure is to be performed after the regular alignment is completed 07 02 O2 27P 1 Remove the top cover Then tura on the power and allow a fifteen minute warmup 2 Set the Model 124A controls as follows Input Selector Preamplifie
129. umerical readout of the output and the corresponding digital logic is available at a rear panet connector This logic is well suited for sending Lock In output information to a computer via a Model Instrument Computer Interface System In reading the display the numerals correspond directly to the signal voltage However some care must be exercised in interpreting the decimal indication On any 1 range 1 100 1 mV 10 mV 100 mV etc at full scale output the meter will read 1 000 Above full scale the meter will follow until overload occurs On 2 ranges however at full scale the meter will try to read 2 000 the decimal and three right hand numerals will not illuminate at full scale On 5 ranges at full scale the meter will read 500 and above full scale the meter will follow until overload occurs 1 voltage output at full scale is 10 V all ranges polarity symbol is displayed for positive readings HV 10 pV but will instead read 1 BLANK 1 sign is displayed for a negative reading The information displayed on the digital meter is provided binary coded decimal form at connector 47 at the rear Table 111 6 identifies the pins at which this information is Positive logic is employed 71 is 3 5 V 1 V and a O is 0 2 V 0 2 V All digital output signals are capable of sinking 5 mA at the provided and gives the output levels Meme is a trademark of Burroughs Corporatio
130. unt of rms noise voltage The equivalent noise bandwidth of the filter is defined as the unattenuated bandwidth of an equivalent theoretical but physically impossible perfectly sharp filter that with the same wideband input noise yields the same rms output noise amplitude as the filter of interest On the Model 124A notice from Figures 111 16 and 111 17 that the frequency dial setting corresponds to the last point for which the response is unity However signal bandwidth is ordinarily taken between 3 dB half power points on the rolloff characteristic For the Bandpass mode 3 dB bandwidth is obtained from the standard formula for fg Af3ggl Calculating ENBW equivalent naise bandwidth from the 3 dB bandwidth is frequently complicated However an exact conversion is seldom required The 3 dB bandwidth and ENBW are of the same order of magnitude with the generally applicable and sufficiently accurate conversion factor being 7 2 The FLAT mode ENBW is simply the 3 dB upper lirnit multiplied by 7 2 The same applies to a close approximation for operation in the NOTCH mode In LOW PASS operation the ENBW is the product of the 3 dB down frequency as determined from Figure 111 16 times 1 2 In HI PASS operation the ENBW is 7 2 times the square of the upper limit divided by the sum of the upper limit frequency and the 3 dB down frequency as deter mined from Figure 111 17 In BANDPASS operation the ENBW is 7 2 times where f
131. us the manner in which Dynamic Reserve is traded for Output Dynamic Range in a lock in amplifier is one of the major factors involved in determining the suitability of the instrument for making a given measurement In the case of the 124A the operator has control of the dynamic tradeoff so that the dynamic range characteristics of the instrument can be optimized for the type ot measurement at hand The front panel Functian switch gives the operator the choice of LOW DRIFT NORMAL and HIGH DYNAMIC RANGE Reserve operation Each position of the switch corre sponds to a different division of the Total Dynamic Range into its Dynamic Reserve and Qutput Dynamic Range components The Dynamic Range characteristics of the Model 124A are illustrated in Figure 111 18 Referring to the figure note that two different OVL fevels are indicated The first of these the PSD OVL level defines where the Phase Sensitive Detector overloads relative to a full scale input signal It is this overload level that determines the maximum tolerable input signal when the instrument is operated in the FLAT mode When the instrument is not being operated in the Flat mode then the maximum tolerable input is extended ta the PRE PSD OVL for signals not in the passband of the characteristic selected BANDPASS NOTCH HI PASS LO PASS Note that the PSD DYNAMIC RANGE of the instrument is 10 regardless of the selected dynamic tradeoff Depending on the tradeoff sel
132. utput of the Butter between the front panel Reference Frequency dials and the Voltage Controlled oscillator If the voltage reading is correct one can reasonably assume that the dial controlied voltage dividers and Buffer A3 are functioning normally Monitor TP4002 blue testpaint with the ascil loscope and check for 2 8 V 3 3 V pk pk sinewave at 399 Hz NOTE A faulty circuit will usually give indication of gross error For this reason it is not generally advisable to spend much time trying to determine whether the frequency or amplitude are exactly as specified This applies to both this step and to tha remainder of the procedure c Similarly check for a 2 8 V 5 3 V pk pk at 399 Hz at TP4003 violet at TP4000 white and at 4001 green These testpoints together with 4002 give access to the four outputs of the Reference Oscillator If these signals are normal one be reasonably confident that the Refer ence Oscillator board is functioning normally d Transfer the oscilloscope to the Reference Out put connector front panel and check for a 2 8 V 3 V nk pk sinewave at 399 Hz If this signal is as indicated one can assume that the Hefer ence Output Power Amplifier located the Power Supply board is functioning normally 3 Auxiliary Reference Board a Connect 1 V pk pk sinewave at 1 kHz from the signal generator to the Reference Channel IN connector b Set th
133. wer is available or as last resort where power line interference is a problem Battery operation is particularly straightforward because the neces sary internal points are avaitable at the 11 socket Two batteries are required to supply 31 V 400 mA and the other to supply 31 V 360 mA The 31 V source should be connected to pin 7 The 31V sourre should be connected to pin Ground for both is at pin 1 It is generally good idea to fuse the battery lines external to the instrument and to provide ON OFF switch as well The front panel ON OFF switch is not functional when the instrument is operated from batteries The tine cord should be disconnected Other than the already mentioned ON OFF switch not functioning there is only one other point of difference between a battery operated instrument and one operated from the line and that is that the pilot lamps which illuminate the panel meter will not light Because of the ac power requirements of the digital panel meter UNITS INCORPORATING THE DIGITAL PANEL METER OPTION CANNOT BE ATED FROM BATTERIES 3 12 PHASE METER MODIFICATION 1241 85 124A equipped with this option can be operated either as a normal lock in amplifier or as a Phase Meter depending on the position of the rear panel NORMAL PHASE switch When the instrument is operated as a phase meter the input signal after some initial ac gain is routed
134. wever if the noise level of the signal is high enough to overload the demodulator as explained in the following paragraphs one can operate in either NORMAL or HI in which the noise tolerance is increased by a factor of 10 or 100 respectively the expense of degraded output stability DYNAMIC OUTPUT RMS OUTPUT TRADEOFF STABILITY NOISE VOLTAGE LOW DRIFT 15 pzm C 10 ppm Hz NORMAL 100 com G 100 ppm Hz HI 1000 1000 ppm Hz Table 111 1 STABILITY OUTPUT NOISE AS A FUNCTION OF OPERATING DYNAMIC TRADEOFF 15 32K OVERLOAD Depending on the nature of the ingut signal plus noise and on the control settings overload can occur at several different paints in the instrument All of the critical points are monitored so that an overload anywhere in the instrument will operate the OVERLOAD light From an operator s point of view the problem with regard to overload is not one of determining whether overload is taking place the Overload indicator light performs this function automatically but rather of determining the Proper action to take to eliminate the overload The appropriate remedial action in turn depends on where the instrument is overloading Each overload type is con sidered in the following paragraphs 1 DC Amplifier Overload Overload of the dc amplifiers is the easiest type of overload to identify and detect Such overload is usually the result of the signal amplitude independent of nois
135. xactly 400 Hz Then readjust R4003 AC BAL 1 as required to reduce the difference frequency by exactly a factor of two Adjust R4017 AC BAL 2 for a counter indica tion of exactly 400 2 HIGH FREQUENCY AMPLITUDE ADJUST 4010 and 200 kHz FREQ C4002 b 4 fn 9 Set the Reference Frequency controls ta NORM 2 00 and X10K Note and record the frequency indicated on the counter Set the Reference Frequency controls to ADD 10 10 00 and X10K Connect the ac voltmeter to 4002 blue testpoint Adjust C4010 HIGH FREQ ADJ for an ac voltmeter indication of exactly 1 V rms Be sure to use the non metallic alignment tool for this adjustment Adjust C4002 200 kHz FREQ ADJ for a counter indication exactly ten times that noted in step p Reset the Reference Frequency controls to NORM 2 00 and X10K The frequency should be the same as noted in b If it has changed record the new frequency and then set the Frequency controls back to ADD 10 10 00 and X10K Readjust C4002 200 kHz FREQ ADJ to obtain a counter reading exactly ten times the new frequency 4 3H SIGNAL BOARD ADJUSTMENTS 1 SIGNAL FREQUENCY ADJUST R1015 b Set the controls as follows Signal Frequency controls 4 05 X100 405 Hz Reference Frequency controls NORM 4 05 100 405 Hz Note Do not change Reference controls during t

Princeton Applied Research/EG&G Model 124A Lock

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Princeton Applied Research/EG&amp;G Model 124A Lock

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Princeton Applied Research/EG&G Model 124A Lock