Keithley_181_Service_Manual 电路图.pdf

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1、Service Manual Model 181 Digital Nanovoltmeter 01981, Keithley Instruments, Inc. October 1981, Cleveland, Ohio, U.S.A. Document Number 30816 RadioFans.CN 收音机爱 好者资料库 Model 181 Service Manual Addendum INTRODUCTION This addendum to the Model 181 Service Manual is being provided in order to supply you w

2、ith the latest information in the least possible time. Please incorporate these changes into the manual before servicing the Model 181. Model 262 Low Thermal Voltage Divider This addendum concerns availability of the Keithley Model 262 Low Thermal Voltage Divider, which is recommended for verifying

3、accuracy and calibrating the Model 181 mV ranges. The Model 262 is a precision low thermal divider with divider ratios of 101:1, lO?l, lO”:l, and lO?l. A low thermal male-to-male output cable is included with the Model 262. Note that Model 181 veri- fication and calibration procedures that use the M

4、odel 262 are included in the Model 262 Instruc- tion Manual. Section 2, page 2-2: Include the Model 262 Low Thermal Voltage Divider in the list of available accessories. Table 3-1, page 3-1: Replace Item B in the table with the Model 262 Table 5-1, page 5-l: Replace Items B and F with the Model 262

5、I RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 TABLE OF CONTENTS SECTION 1 l-l l-2 1-3 1-4 2 2-l 2-2 2-3 2-4 2-5 2-6 2-7 2-6 2-9 z-10 2-11 3 3-l 3-2 3-3 3-4 3-5 3-6 3-7 3-6 3-9 3-10 3.11 4 4-l 4-2 4-6 4-7 4-8 4-9 4-10 4-11 4-12 4-13 4-14 4-15 4.16 4-17 4-16 4-19 4-20 4-21 4-22 4-23 4-24 4-25 4-26

6、 4-27 4-28 4-29 4-30 4-31 4-32 TITLE Generallnformation . Introduction . Warranty Information . ManualAddenda . Safety Symbols and Terms. . Accessories . General . Model 1463 Low-Thermal Connection Kit . Model 1484 Refill Kit . Model 1485 Female Connector . Model1486MaleConnector . Model 1488Shortin

7、g Plug . Model 1503 Low-Thermal Solder and Flux . Model1506lnputCable . Model1507lnputCable . Model 1615Maintenance Kit . Model1019 Universal Rack Mounting Kit . Performance Verification . General . . Recommended Test Equipment . Environmental Conditions . Performance Verification Procedure . Initia

8、l Conditions . DC Voltage Accuracy Check 12V to lOS/) . DC Voltage Accuracy Check (2mV to 2OOmV) . HiResolutionCheck . Damping Function Check . Filter Function Check . NoiseCheck . Theory of Operation . . General . . Power Supply . IEEE Standard Interface . Digital Section . Microcomputer Memory . A

9、ID Converter Control . AID Operation . Single Slope Phase . Serial/Parallel Conversion, Isolator Control . Clock Circuit . . . Display . D/A Converter . Nanovolt Preamp . Low Noise Design . Linearity and Gain . Feedback Elements . Offs at DC and line fre quency 60 or 60Hrl. ,lkR unbalance) IEEE-488

10、BUS IMPLEMENTATION: Multiline Commands: LXX. LLO. SDC. GET. Unlline Commands: IFC, REN, EOI, SRD. ATN. PROGRAMMASLE PARAMETERS: Front Panel Controls: Range. Filter. Zero, Dampin% Hi Resolution. Internal Parsmeters: SRCI Resoonse. Triswsr Modes. oats - Tetminators. ADDRESS MODES: Talk-Only and Addres

11、sable. TRIGGER MODES: one Shot: Updates OUtpUt buffer once at first valid c”“ersi” after tdocler on TALK and/or GET. GENERAL NOISE: Less than 30nV pip on lowest range with Filter on. INPVT CAPACITANCE: 5OOOpF on mV ranges. SETTLING TIME: 0.5s to within 25 digits 01 final reading with Filter on, Damp

12、ing off FILTER: 3pole diSital: RC = 0.5, 1 or 2 seconds depending 0” range. CONVERSION SPEED: 4 readings/second. DISPLAY: Seven 13mm (0.6 in.1 LEO digitswith appropriatedecimal point and polarity. OVERLOAD INDICATION: Display indicates polarity and OFLO. ANALOG OUTPUT: Accuracy: f 10.15% of displaye

13、d reading + lm”i The Constent: 400ms. Level: t 2V full scale on all ranges: x1 or x,000 gain ISOLATION: Input LO 10 Outpur LO or power line ground ,400” peak. 5 x lOW.Hz. greater than ,090 paralleled by ,soJ”F WARMUP: 1 hour IO rated SCCUE.CY when propedy zeroed, ENWRONMENTAL LIMITS: OperatinS: WC 1

14、0 35C. 0% la 80% re,atiw hwnidirf .storags: 2vc to 65C POWER: 105125V or 210-250” lintelm SWlWh selected,. 5060HZ. 30V.A maxim”m. INPUT CONNECTORS: Special low thermal to, 20OmV and lower ,ilnges Binding posts f”,2V to tooov rangss. DIMENSIONS. WEIGHT: 127mm high x 216mm wde I 359mm deep 15” x BK” x

15、 14W,. Net weight 3.85kg ,8K lb*., ACCESSORY SVPPLIED: Model ,606 Low Thermal Input Cable ACCESSORIES AVAILABLE: Model 1019 Rack Mounting Kit Model ,483 LOW Thermal Connectlo” Kl, Model 1484 Refill Kit for 1483 Kit Model 1485 Female LOW Thermal Input Conneclor Model ,486 Male LOW Thermal Input Conne

16、ctor MO:r :. 3. 7 Figure 2.8. Model 1815 2-2 Figure 2-9. Model 1019 MODEL 181 PERFORMANCE VERIFICATION Section 3. Performance Verification 3-6. DC Voltage Accuracy Check i2V to 1wOV Range1 3-4. Performance Verification Procedure Use the following procedure 10 verify fhe basic accuraw of the Model 18

17、1 ior DC voltage. /I the instrumwIl IS out of speciflcallon ar any point. perform a complete caIib,atiori iis 1 . : : (I .,181 Figure 3-l. DCV Performance Check CAUTION The performance verification and all service inform mation is intended for quaIlfled personnel using accurate and reliable test eqw

18、ment. WARNING Some procedures require the use of high voltage. Take care to prevent contact with live circuits which could cause electrical shock resulting in injury or death. 3.5. Initial Conditions Before beginning thu ver,f,ca,ion procedure. the ,i,slrument must meer the followng conditiorls: l,

19、the instrument has beer, subjected 1” extremes ol temperature, allow sufficient fime for interrlal kmperatures 10 reach wwronmental conditions TABLE 3-2 DC VOLTAGE PERFORMANCE CHECK 12v to 1OOOVl 1.89985 to 1.90015 ,6.9978 to 19.0021 ,E!xs,s 10 190.021 999.84 to999.16 I I 3-7. DC Voltage Accuracy Ch

20、eck l2mV to 200mVl CAUTION I PERFORMANCE VERIFICATION MODEL 181 A. Dbtnin a low thermal cable and divider box as described in Section 5. B. connect the low thermal cable between the 181 and the divider box. c. Connect the DC calibrator as shown ill Figure 32A. For the ZmV md 20mV rangm Allow n few n

21、linUk?S for fhc!rrnal FMFS to settle OUL Use Figure 338 for the 200mV range. Do Set the DC calibrator for OOWOOO output E. Sclnct the appropriate range as given in Table 3-3 Select the range manually by pressing the appropriate Front Panel button 01 select the range automatcaily by issuing the apt p

22、ropriate command over the bus. F, Zero the 181 by pressir,g the ZERO button on the Front Panel or by issuing the appropriate command over the bus. G Apply lhe riiquired voltage as specified in Table 33. Verity that the displayed reading IS wllllin speclficalions Note the X!X,lM Hi Repeat steps D thr

23、ough G on ,he remaining mV ranges, I, Reverse the polarity of the source and set i, t” 0000000 a, p”l Rerero the 181 by pressing the ZERO button twice. K. Apply the input as in step G. Verify rhr displayed rcadfng iwIth opposite polarityi is the same as in step G +3 digits no ,Y n Made, 181 Figure 3

24、.2A 2mV and 20mV Performance Check I I I I / Figure 3-28. 203 Millivolt Petiormance Check TABLE 3-3 DC VOLTAGE PERFORMANCE CHECK 3.8. HI RESOLUTION Check LJpon power up, ftlc 181 WIII ba in the 5% dlgiI mode ol leso lllfion iROl To cheek fho HI RES funclon prncood as follows, A Short thevolts IL0 2n

25、d HI togrthcr Press the ZERO butlor, on the Front Panel. lhis will obtain a stored bascline I3 Apply the signal and the displayed reading will cqual thn dilfr.rence between the stored baseline and the ,npu, SIgnal. 3-9. DAMPING Function Check Upor power up, the DAMPING fur,i:t,r,n IS r,f iDO, To che

26、ck 10 see Ihat thi! DAMPING function IS operaln! properly, use me l”llnwlilg procrd”,e: A. Select 2v ranq3 8. From a zero reading ;rprily a Fuil Scale signal and obserw the serrling time, 3-10. FILTER Function Check Upon Power up the Filter functfon is dfsabled IPlI To chock to see Li?at the FILTER

27、IS operatfrq properly ust? Ihe following procedure A. Select 2V range. H. Press the DAMPING burtor, and ti,w from a 7810 roedln apply R Full Scale signnl Dbscrve fhc settling time, C With DAMPING on press Ihc FILTER button Frorr a irro rradli,rg apply a Full Scalii signsl Obswvc tl,e sctllmg l,mr. D

28、o The settling Lyme will be lorrger with thr FILTER enablcti 1 IliS dlffercnce ic”Cals ,ili,l the FILTER is operating properly. Ths proccdur will wily work whcr DAMPING is “11 3.1,. NOISE Check Noise is detined Ion lowest range, as peak-wpeak excursion over a period of two minutes, tested after warm

29、up while the inpul is shorted with the Model 1488 3-2 I MODEL 181 Procedure for checking notse: A. Short the mv ,npu, w,h a Model ,488 Low Thermiil Short B. Select the 2mV range, C. Turn on HI RES so that 6% digits arc displayed. PERFORMANCE VERIFICATION MODEL 181 THEORY OF OPERATION Section 4. Theo

30、ry of Operation 4-l. GENERAL This section contains lndepth discussions of the maj”r circuit blocks, which are listed below: A. Power Supply (included on MotherboardI PC531. page B IEEE Standard lnrerface iinr:ludcd on MotherboardI PC 531, page 627 C DigItal Section (included on Mofhcrboradi PC531. p

31、age D Dispiay Display Board1 PC530, page 6,25. E D/A Converter iMotherboard PC531. page 627, F Nanovolt Preamp lNanovol Preamp Board1 PC526. page G A/D Corrvcrter (Analog Board) PC529, page 623, There are several figures and tables provided wilt1 each major circuit block that will aid in their oxpla

32、nation 4-z. Power supply While studying the theory of operation for the Power Supply. it will be helpful 1” refer t” the Schematic Diagram 30583D. Sheet 1 of 2. 4-3. The AC power is brought int” the 161 by a recessed line plug JlOll. Fuse FlOl and line plug J,O,l are located on the rear panels Switc

33、h SlOl is the main power swtch and ii is located on the Front Panel. Switch S102 is the 115V 1” 230V configuration switch and is located internally. 44 The regulated portion of the 181 power supply is sect tioned into six different supplies. There are three supplies (+15V, -15V, +5V) ior the analog

34、section of the 181. The other three supplies (+ 1%. -15V. -+ 5VI are for the digital sec- tion of the 181. The key to the Analog/Digital isolation is the split bobbin transformer TlOl. The digital supply winding, along with tbe primary windings, are at the bottom haIf of th bobbin, and the analog su

35、pply windings am located al the lw of the bobbin. 45. The six supplies “perate from four separate windings 01 transformer TlOl. The four windings are fed info four full wave bridae rectifiers: Two recfifiers for the analog section CR105 ani CR106 and two rectifiers for the digital sect“n CR104 and C

36、R107. Capacitors C128, C123. and Cl27 bypass regulators U12B l5VI, U129 (+ 15Vl and U130 I-15Vl respec- tively. These are the analog supplies. Capacitors Cl34 and Cl35 filter the input voltage to U136 and U137 respectively. Capacitors Cl32 and Cl33 bypass regulators U136 and Ul37 respectively. Capac

37、itor Cl30 filters the “utput of CRlC4 Regulator U135 receives its input from the regulated “utput of Ul36. Q103 and Q105 are configured as a high current gain voltage regulator. 0104 completes the unify gain loop by compensating the VeE drop of Q103. CR101 provides short circuit limiting t” the circ

38、uit. 4-6. IEEE Standard Interface While studying the theory of operation oi the IEEE Standard Interface, it will be helpful 1” refer to the Schematic Diagram 30583, sheet 1 of 2. I THEORY OF OPERATION MODEL 181 TABLE 4-l MICROCOMPUTER MEMORY MAP X5B30, Sheet 2 of 2 and 305 all bits ON yields IOV out

39、put at Ul18. 0 TO countet VR102 is configured as a rcfcrence for Ihe D/A circuil. RIO/, R108, RI09 arrd U119B scale the reference to ! 1OV. R107 provides an adjustment range on the + 1OV reference which calibrates positive Full Scale An offset for U119A is provided by Rlll, R112, R106 and VR102. Thi

40、s offset plus R113 and R114 provide the scaling which translates the OV to 1OV swing loutput of U1181 to Ihe desired 2 to + 2V swing. R106 calibrates negative full scale by altering the offset voltage on UllSA, Capacitor Cl37 filters the output and prevents it from appear ing like a staircase wavefo

41、rm. VRlO3, VRIO4 and RI30 arc configured as protection in case the analog output terminals should be momentarily shorted together or tied to groater lhan +3ov. 4-16. Nanovolt Presmp During the theory of operation of the Nanovolt preamp, it will be helpful to refer to the Schematic Diagram 30856D 4.1

42、7. Low Noise Design One of the major reasons for utilizing a differential input stage is the Supply Noise Reiecion Without proper matching, power supply noise would have to be or a submicrovolt level which would be impossible at low frequencies, Both bias cur rent nom and voltage noise arc the major

43、 components of Supply Noise. In order to minimize voltage noise, a pair of low noise bipolar supplies are generated on the Nanovolt Preamp board using U405 and IIS associated componen5 I I I N”li I I I I I 10 -va I I b s I I - _- - - - - I I THEORY OF OPERATION MODEL 181 rnuglyiblo, The bootstrap su

44、pply is decoupled from the input via C414. C415, R425and R426. Rejection from the + 15V sups plies is critic;iil as well. Therefore. current regulators CR406 and CR407 are a necessity iRp 1M ohm) since Rs of VR403 and VR404 is approximately 100 ohms, The key to maintaimng low current noise in the dr

45、ain circuit of Cl413 IS the selection of a low noise, high gain device for Q414 and maintaining low emitter and base impedances over the bandwidth, R431, R432 and R433 provide bias for Q414 and are referer:ed 10 _t VR for low noise contribution Noise contribution from the second stage depends upon drain loads of Q413, gain of the lir