HP-738AR-Manual-sn-001 电路图.pdf

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1、II: C 01 . HEWLETT-PACKARDCOMPANY.- -. 738AR VOLTMETER CALIBRATOR co CD :II RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 OPERAT.lNGANDSERVICING MANUAL MODEL738A/AR VOLTMETER CALIBRATOR SERIALSPREFIXED:001- voLntETER CAU8RArOR -,. .- .- O!JTlIf.LCCfOI .-;:. . ooatJI. ,.,.,.

2、 JAA.AAI- .llaIUS . -. CopyrightHEWLETT-PACKARD COMPANY1960 1501 PAGE MILLROAD,PALO ALTO, CALIFORNIA,U.S.A. 00202-2 Printed:10/61 Model 738A SPECIFICATIONS VOLTAGE RANGE: LEVELS: WORKING VOLTAGE ACCURACY: LONG-TERM STABILITY: OUTPUT VOLTAGE FUNCTION: HUMANDDISTORTION: ATTENUATOR ACCURACY: LOAD IMPED

3、ANCE: POWER SUPPLY: DIMENSIONS: WEIGHT: 300microvoltsto 300 volts Calibrationvoltage 300microvoltsto 300 volts instepsof .3,.5, 1, 2 and 3 volts withmultipliersof .001, .01, .1, 1, 10 and 100.Trackingvoltage.1to 1 volt in.1voltsteps; and 0 to 3voltsin .5 voltsteps. 300 volts working voltage intoatte

4、nuator,accuratewithin 0.1% dc and 0.25%acafterone-halfhourwarmup. Lessthan 0.1% dcdriftperweek;lessthan 0.25%acdrift perweek. DCpositiveto ground, dcnegativetoground,ac400cycle rmsvalueorac400cyclepeak-to-peakvalue. Lessthan 0.2%total Within0.1%,or5microvolts,whicheverislarger Designed toworkinto a

5、3 megohm input impedance. When working into 10megohmsimpedance, the voltagefrom20to 200 volts will beapproximately0.15% high. 115/230volts10%,50-60cycles,approximately350 watts Rack Mount:19incheswide, 7incheshigh, 15inchesdeep Rack Mount:Net 38lbs.Shippingapproximately75lbs Anyoutput frequencyfrom4

6、00 to 1000cpsavailableonspecialorder. iii SECTION I .CONTENTS GENERAL DESCRIPTION Model 738A PAGE 1 - 1 1 - 2 1 - 3 Introduction PowerCable Operation on 230 Volts 1-1 1-1 I - 1 SECTIONIIOPERATING INSTRUCTIONS 2 - 1 2 - 2 2 - 3 2 - 4 2 - 5 2 - 6 Installation ExternalLoad PreventingErrorsFromGroundCur

7、rents Stability and Warmup OperatingInstructions Calibratingthe 738A II-I II-I II- 1 11-3 II-4 11-4 SECTIONIIITHEORYOF OPERAnON 3 - 1 3 - 2 3 - 3 3 - 4 Introduction DCGeneratorSection ACGeneratorSection Output Attenuator III - 1 III - 1 III - 2 III - 2 SECTIONIVMAINTENANCE 4 - 1 4 - 2 4 - 3 4 - 4 4

8、- 5 4 - 6 Introduction TubeReplacement Cleaning theAirFilter Adjusting theFrequencyof theACOutput TestingandTroubleShooting theCalibrationGenerator. MethodsofCalibration. IV-1 IV-1 IV-1 IV1 IV-2 IV3 SECTION VTABLE OF REPLACEABLE PARTS TableofReplaceableParts iv V-I ., . Model 738A 1-1INTRODUCTION Th

9、eHewlett-PackardModel 738AVoltmeterCali- bratorisacompact,completelyself-contained, precisiongeneratorforcalibratinghigh-impedance electronicvoltmeters,oscilloscopes,etc.Special designassuresaccurateandreliablecalibrating voltagesfrom0.3millivoltup to 300 VOlts, in precisionsteps.Accuracyof outputat

10、tenuatoris within 0.1%or5Jlvolt,whicheverisgreater, when loadedbyameterwithaninputimpedance of3megohms.Nooperatingadjustmentsarere- quired,otherthan weeklystandardization. TheI/ifJVoltmeterCalibratorconsistsof twosepa- rateinter-connectedunitsmounted ononesmall rackpanel.Thevoltagegeneratorsectionin

11、cludesa regulatedpowersupply whichproducesthe300volts dc workingstandard,a conventional lowdistortion rcoscillatorwith AGC, and astabilizedamplifier whichgeneratesthe 400cycle300 voltrmsworking standard.The300 voltpeak-to-peakvoltageis derivedfromthe300 voltrmsvoltage through a resistivenetwork.Thet

12、ype of voltagerequiredis selectedby asimpleoutputselectorand fed to the attenuatorsection. Theattenuatorsectionconsistsofcontrolswitches andaseriesof voltagedividersconstructedwith 0.1% wirewound,non-inductive,ceramic-corere- sistors.Theattenuatoracceptsthedesired300 volt workingstandardand willdeli

13、vercalibrating voltagesortrackingvoltages. Calibratingvoltagesrunfrom300microvoltsto 300voltsin25precisestepsina .3, .5, 1, 2, 3sequence.Twotrackingrangesareavailable: either0.1 volt to 1 voltin1/10voltstepsor0 to 3voltsin1/2voltsteps. Nostandardizingvoltmeterisincluded withthe Model 738A.Theamplitu

14、deof the 738A output voltagecannotbeadjustedaccuratelyagainstacon- ventionalvoltmetersincethe 0.1%stabilityofthe 738Aishigherthantheaccuracyofmostmeters. Onlyspecialhigh-resolutionmetersthatcanbe readtoanaccuracyofatleast0.1%,orother standardslaboratorymethods,shouldbeusedfor Sect. 1Page1 SECTIONI G

15、ENERALDESCRIPTION standardizingthe 738A whenmaximumaccuracyis desired.Ifmaximumaccuracyisnotimportant alessaccuratevoltmetermaybe used, in which casetheaccuracyof the 738A will depend upon theaccuracyof themeterused. TheModel 738Aisdesignedformounting in a standard19-inchrelayrack.A fan inthecabinet

16、 assuresadequateventilation. Physically,theinstrumentisbuiltin twoseparately housedsectionsmounted on thefrontpanel, an attenuatorsectionand ageneratorsection.The attenuatorsectioniseasilyremovedforservice orreplacementbyremovinga fewscrews,knobs, and two BNCconnectors.Thecircuitryofthe generatorsec

17、tioniseasilyaccessiblefrombelow thechassis. 1-2POWERCABLE Thethree-conductorpowercableforthe 738Ais terminatedin apolarized,three-contactconnector recommendedby the NationalElectricalManu- facturersAssociationforprotectionofoperating personnel.Thethirdcontactisanoffsetround pin, added to astandardtw

18、o-bladeconnectorwhich groundstheinstrumentchassiswhenusedwith a suitablereceptacle.Tousethisconnectorin a standard,two-contactreceptacle,ortodisconnect thethird(ground)leadinthecable,anadapteris available.Referto Section IIbeforegroundcon- nectorsaremade. 1-3OPERATIONON230VOLTS Thisinstrumentisnorma

19、llysuppliedfor115 volt operation,unlessspecificallyorderedfor230 volt operation.Thepowertransformerhasa dual primarythatmaybeeasilyconnectedforeither USor230 voltoperation.Theschematicdiagram illustratesbothmethodsof connection. Alwaysre- placethepowerlinefusewith theratingspecified inSectionV,Table

20、ofReplaceableParts,forthe particularlinevoltageyouareusing. Sect.IIPage0 TABLE2-1.INTERNAL RESISTANCEANDMINIMUM LOAD FOR1%ACCURACY Model 738A ApproximateLoad InternalResistanceResistancewhich Output VoltageofGeneratorProduces1%Decrease inOhms in Output Voltage 3000*# 2004000400K 1004000400K 50260026

21、0K 301600160K 201150115K 1058058K 529529K 318018K 248048K I142042K .526026K .317017K .248048K .142042K .0526026K .0317017K .0212512.5K .01666.6K .005353.5K .00321.52.1K .002575.7K .001505.0K .0005313.0K .0003212.0K * Withinthelimitsoftheregulators. #Theminimumload shouldbegreaterthan 16,000ohmsto pr

22、eventoverloadofthepowersupplies.With a 16,000 ohmloadtherewill be nochangeinaccuracy. Model738ASec.IIPageI J SECTIONII OPERATINGINSTRUCTIONS 2-1INSTALLATION Nospecialinstructionsarerequiredforinstalling theModel 738AVoltmeterCalibrator.Itcanbe usedeitherin arackoron atestbench.A fan inthecabinetassu

23、resadequateventilationineither mounting,providingtheairfilteriskeptclean andtheventilatingholesintherightsidearenot blocked.Adequateairflow throughthefiltermust bemaintained.Inspecttheairfilterweekly. Damagetotheinstrumentcanoccurifthefilter becomescloggedandairflowisrestricted.See paragraph4-3,Clea

24、ningtheAirFilter. terminalsshould beshuntedwith 4.12megohms. Thelowervoltagerangeswillnotchangewith loadresistancesabove3megohms. Thefollowingequationmaybeusedtodetermine thevalueofshuntresistancenecessarytoobtain maximumaccuracywhencalibratinghighim- dedancedevices: 3Rm R- 3 m Allinstrumentsthatope

25、ratefromapowerline developspuriousvoltagesbetweentheirchassis 2-3PREVENTINGERRORSFROM GROUNDCURRENTS A.INTRODUCTION Withsomesacrificeinaccuracythe738Amaybe usedtocalibrateinstrumentshavinganinputre- sistancelessthan 3megohms.Undernocon- ditionsshouldtheloadontheOUTPUTterminals belessthan 1,000ohmspe

26、rvolt.Table2-1in- dicatesboth theinternalresistanceofthecali- bratorforeachoutputvoltageandtheminimum externalloadfora1%decreasein theindicated voltage. Inputresistanceofinstrument undertest(inmegohms). Shuntresistanceinmegohms Rm Rxwhere, Groundcurrentsbetweentheinstrumentbeing calibratedandtheMode

27、l 738Amustbeminimized torealizetheratedaccuracyoftheCalibrator. A 10microvoltsignal,developedbygroundcur- rentsbetweenthetwoinstruments,willintroduce a1%erroronthe1millivoltrangeand a 3.3% erroronthe0.3millivoltrange.Whenusingthe lowervoltagerangesyoumustminimizeground currentsinthesignalleads. CAUT

28、ION THEOUTPUT OF THIS INSTRUMENT MAY CON- TAINVOLTAGES WHICH ARE DANGEROUS. When connectingordisconnectingtheoutput ofthis instrument,switchtheOUTPUTSELECTORto OFFfirst. 2-2EXTERNALLOAD CAUTION THIS INSTRUMENTISDESIGNED TOOPERATE INTOA3MEGOHMLOAD.THEMINIMUM SAFELOADIS1,000OHMSPERVOLT.IF A SHORT ORLO

29、WRESISTANCEISCONNECTED TOTHEOUTPUTTERMINALSPERMANENT DAMAGE WILL RESULT.Notethatanycalibrating metermustalsohavethisresistance. TheModel 738Aisdesignedtoproducecalibrating voltagesthatareaccuratetowithin0.1%or5j.lv, whicheverisgreater,with anexternalloadof3 megohms.Ifthemeterbeingcheckedhasahigher i

30、nputresistance,suchas11megohms,theoutput voltagesbetween 20and200voltswillbeasmuch as0.15% high.Forhighestaccuracywhencali- bratingan11megohminstrument,theOUTPUT Sect. IIPage2Model 738A OPERATINGCONTROLS 42 illIII ,. o o ftO VOLTMETERCALIBRATOR MOO(,_ 11W.(TNCKARO -.D.-ooC-ulOIlfo/lA 65 o o 1.Select

31、theoutput voltagerequiredbythemeter tobecalibrated. 3. Setforfull-scalereading. 2.Selectforusedesired-Tocalibrate,orto checkmeterscaletracking.Fortracking, selectrangecorrespondingtometerscale undertest. 4. Switch throughtheentirerangetoobserve accuracyateachmetercalibrationpoint. S.Calibrate300 vdc

32、 output. 6.Calibrate300 vac output. Figure2-1 Model 738ASec. IlPage3 o0 o0 d - MOSTRELIABLE andground.The738Aisdesignedtominimizethe developmentofsuchsignalsonitsownchassis. Tominimizetheeffectsofthesecurrentsfurther, theinstrumentbeingcalibratedshould begrounded withitsownlow-resistanceground,orthe

33、738A maybeinsulatedfromgroundsothatitcannotpro- videtheground-returnpath.SeeFigure2-2and thenextparagraph. B.GROUNDING ARRANGEMENTS Groundingarrangementsmostoftenencoun- tered,togetherwithcommentontheirrelative merits,areshowninFigure2-2.Thegrounding arrangementfoundmostreliableprovidesa low- resist

34、anceconnectiontothepower-linegroundfor theinstrumentbeingcalibratedandinsulatesthe 738Achassisfromground.Sothatthe738Amay beeasilydisconnectedfromthepower-lineground, anadapterisavailablein whichthegroundcon- nectionontheNEMApowerplugisanexternalpig- tailleadandmaybeconnectedordisconnectedas desired

35、. UNDESIRABLE.GROUNDSEEKINGCURRENTSFROMMETER UNDERTESTARECONDUCTEDTHROUGHCONNECTINGLEADSTOGROUND. C.CHECKING FORPRESENCEOF UNWANTED CURRENT- -Tocheckforeffectsfromground currents: 1)Connectthe738Atothevoltmetertobecali- brated.Setthe738Afor1millivoltoutput. Note readingonvoltmeter. 2)Removeoraddgrou

36、ndconnectionsasthecase maybeandagainnotevoltmeterreading.The readingwithandwithoutgroundconnectionsshould remainconstant.Ifthereadingdoesnotremain constant,usethegroundingarrangementwhichre- sultsinthelowestreading.Findthesourceofthe groundcurrentandprovideitwitha low-resistance connectiontothepower

37、-lineground. UNDESIRABLEIF LARGERFFIELDSAREPRESENTANDINDUCED CURRENTSFEEDFROMONEINSTRUMENTTOTHEOTHER. ),-_O_Q;l SATISFACTORYIFVOLTMETERISWELLGROUNDED. 000 00 C:-:00 . 2-4STABILITYANDWARMUP Checkand,ifnecessary,calibratetheModel 738A Cqlibratoruponreceipt.Allowatleast30minute warmupbeforecheckingthec

38、alibration. SATISFACTORYIFCURRENTFROMOTHERINSTRUMENTSINRACK CANNOTFEEDBACKTHROUGHCONNECTINGLEADSTOGROUND. ., The738Ahasbeenaccuratelysetatthefactoryand shouldremainaccurateto within0.1%forovera weekwithoutreadjustment.Toobtainbestaccuracy afterthisperiodseeparagraph2-6,Calibrating the738A. Figure2-2

39、.Desirableandundesirablearrange- mentsforgroundinginstrument chassiswhenusingtheVoltmeter CalibrationGenerator Sect.IIPage4 Theaccuracyofthe738Aisdeterminedby: 1)Theprecisionwith whichitiscalibrated(the accuracyofthecalibratingmeter). 2)Theaccuracyoftheoutputattenuators(0.1%). 3)Theamplitudestabilit

40、yvstime. Model738A 2)SettheFUNCTIONswitchtoCALIBRATE, and MULTIPLIERtoO. 3)C.onnect thevoltmeterinputtothe738A output bytwoplainwiresorashieldedcablewith the shieldconnectedtothebottomOUTPUT binding post.Observeprecautionsdiscussedinparagraphs 2-3and2-5. 2-6CALIBRATINGTHE738A 4)SettheMULTIPLIERand R

41、ANGEselectorsfor thedesiredvoltage. Therearethreeoutput-voltagecalibratingadjust- ments:the300-voltdc outputadjustment,the300- voltrmsacoutputadjustment,both on thefront panel;andthe300-voltpeak-to-peakacadjustment ontheleftsideoftheelectronicschassisjustto therearoftheattenuatorsection.Thedcvoltage

42、 mustbesetcorrectlyfirst,thermsacvoltage second,and thepeak-to-peakacVOltagelast.Itis importantthatthe300-voltdcoutput besetaccu- ratelybeforeanyotheradjustmentsareattempted. Makeallthreecalibrationadjustmentsin onepro- cedure,asshown inthefollowingFigures: 4)Thevalueoftheexternalloadresistance. The

43、738Areachesitsmaximumstabilityof 0.1% perweekafterabout30minuteswarmuptime. Afterthiswarmup,thenormaldriftofthedcout- putvoltageisabout 0.1%perweek.Anydriftex- ceedingthisamountindicatessubnormaloperation. Ifthe738Ahasbeencalibratedwithin a week,ade- quateaccuracyformostaverageuses(1%)is reachedafte

44、ronly 2minuteswarmup.Repeated turningonandoffdoesnotnoticeablyaffectthe accuracyoftheoutputvoltage. 2-5OPERATINGINSTRUCTIONS Tousethe738Atocalibrateanoscilloscopeor voltmeter,proceedasfollows: 1)Turnonthe738Aandallow towarmupfor3 to30minutes,depending onaccuracyrequired. Figure2-3. Figure2-4. Figure

45、2-5. CalibrationI CalibrationII Calibration1II Model 738A o o CALIBRATIONI o Sect.IIPage5 RO 1.Connecta 3OO-voltmeterofcalibration standardquality, having anaccuracyof 0.1% orbetterandappropriateresolution,tothe OUTPUTtenninalsof the 738Aasshown. 2. Setthecontrolson the 738Aasshown. 3.Turnon 738A an

46、d allow towannupfor 30minutes. 4.Ifnecessary,adjustpotentiometerR63,ac- cessiblethrough the panel holemarkedOC, toobtain exactly 300 volts. Disconnectthe standardmeter. Figure2-3 Sect.IIPage6 CALIBRATIONII Model738A o o o o RO Thisprocedureassumesthattheprocedure shown intheprecedingillustration,CAL

47、IBRA- TIONI,hasbeenperfonned. 1.WithOUTPUTSELECTORon OFF,connect eitheranelectrostaticorthermocoupletype 300-voltac-dcmeterofcalibrationstandard accuracytotheOUTPUTterminalsofthe 738Aasshown. 2. SwitchtheOUTPUTSELECTORbetween DC-andDC+andnotethemidpointbetween thereadings. 3.SettheOUTPUTSELECTORto 4

48、00RMS. 4.Ifnecessary,adjustpotentiometerR40, accessiblethroughthefrontpanelholemark- edAC, toobtainthemidpointreadingnoted instep2. Figure2-4 J Model 738A - 0 W= .TOI . JJ 0 7 CALIBRATIONIII v o o 4 Sect,IIPage7 r!iJ400H o 00 Thisprocedureassumesthattheprocedure shownintheprecedingillustrations,CALI

49、- BRATION IandCALIBRATION II,hasbeen performed. 1.SwitchtfiI;Model 400Htothe100-voltrange. 2. Connectthe738Atothe400Hasshown, with the738A OUTPUT SELECTORsettoOFF. 3.Setcontrolsasfollows: RANGEswitchto1 MULTIPLIERswitchto100 OUTPUT SELECTORto400RMS FUNCTIONswitchtoCALIBRATE 4.Onthe400Hadjust.00lV-40OCPScontroluntil themeterreadsexactly100.Thiscontrolis mountedon abracketnearthefrompanel ontheleftsideofthechassis,asviewed fromthefrom. 5.While 100voltsremainacrossthe400H,turn themechanicalmeterzerountilthemeter