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Model 195Instruction ManualContains Operating and Servicing Information for theModel 195 Digital Multimeter

Publication Date: August 1983Document Number: 195-90%OIC

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WARRANTYKeithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period o f 1 year fromdate of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batter-ies, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective,

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio. Youwill be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility.Repairs will he made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balanceof the original warranty period, or at least 90 days.

LIMITATION OF WARRANTYThis warranty does not apply to defects resulting from product modification without Keithleys express written consent, or misuseof any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leak-age, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIEDWARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREINARE BUYERS SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT,INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRU-MENTS AND SOFTWARE EVEN IF KEITHLBY INSTRUMENTS. INC.. HAS BEEN ADVISED IN ADVANCE OF THE POS-SIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGESsHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTSOF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAM-AGE TO PROPERTY.

Road - Cleveland, OH 44139 - 440-248-0400 -Fax: 440-24X-6168 * http://www.keithley.com

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Instruction ManualModel 195Digital Multimater

01992 , Keithley Instruments, Inc.Cleveland, Ohio, U.S.A.

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SPECIFICATIONS

MAXIMLIM ALLOWABLE INPUT: IWDV peakBENCH READING RATE: 5 readbwlaecond.

2Mo 10 n -2LmnA -2v o.oJ + 7 o.ayI+ 1 0.015+1*oMn Irn -x0* -1v 0.06 + 5 o,1m+ 5 o.m+*+Afterpu&btto or bus rminx.*I wldktigitnwdr. counts- *2 bcept *t4 0 x-a rangeafterZerobIg,.CONFRXJRATlON: Automatic 2- or 44erminal.MAXMM ALLOWABLE INTDT: 36oV peak or 250, nns.BEN~NdEADWG RATE: 3 readb&sRand except 2OMO ange, 1 reading/TRMS AC VOLTS (Option 19.50)w/a Eigiw ACCURACY1YEAR),*~%rd*+cwnal

,I rv..di#t mode. divide cmlm error by 10. Above Irn.TEMPERAnJRE coEFFIclBNr loo-ISOC & 2ax5owz Leu tha rt(O.lXapplicable accuracy speeificatlonl/C.RESPONSE:True mot mea squarr, AC coupled.CREST FACTOR (ratio of peak to rmsl: Up to 3:l allowable.INPUT IMPEDANCE: 2Mn shunted by lea than 75pF.MAXIMUM ALLOWABLE fNf%T: IWOV peak. IOV.Hz.BENCH READING RATE: 3 rexlii/secod.CMRRz Greater than @dB at DC, 50 or 6OHz (with IkR in either lead).BANDWIDTH: -3dB at 2SOkHz ypical.DC AMPS (Option 1950)w/1 wa, -TURFACamAcY (1YEAR,,* coEFRm MAnMuMRESO *Pkd~+rounw *,%rd*+cemw/c VOLTAGERANGE LvnON 1828C wwc b 28Be5oQc BmEN20 A me. 0.14+40* 0.01+7. 0.03?m#t4 InA W-9+10 0.01+0.5 0.25v2m.4 lti 0.09+10 0.0110.5 0.25vx&A 0.09+10222, 0.01+0.5 02.5v0.09+10 0.01+0.5 0.28v2.4 lOP.4 O.C9+lO o.ol+o.5 1 t,n 4vdkit mode,coun*- *:2 kxapl 24 0 2Qx.4 nxe after zeroinn).t4fm pushbutton r buszeroins.OVERLOAD PROTECTION: 2A fuse LXOV), externally accessibleBENCH READING RATE: 5 r&igs/recond.

2.4 $4 Oh+353 0.04+10 1 v,I Ivldt@t mode,divide countevr by 10.Above 0.5% Range.RESPONSE:True mot mean square, AC coupled.CREST FACTOR (ratio of peak to rms): Up to 3:l allowable.OVERLOAD PROTECTION: 2A fure UOVI, externally acceaible.BENCH READING RATE: 3 read&/second.IEEE488 BUS IMPL!ZMENTATlONMuMIne Cad: DCL, LLO, SIX. GET, GTL. LINT. UNL, SPE. SPD.Unlllne Commands: IFC. REN. EOI. SRQ. ATN.Interface Fwuttow: SHI, AHl. T5, TEO. L4, LEO, SRl. R LI, PPO, DCI,DTI. co. El.PTble Paramemr: Range. Function, Zero. integration Period, Ave+EOI, T r. Terminator, Delay, loo-rdg. Storage, Calibration,i%i$,, Multl~O ff. Status, ServtceRequest. Self Test, Output Fannat.First reading is cotsct when step input is c~incldem with trigger.Ccwemhm Rates (DC Volta): UbnnmmA

tReadt&&nd. V.&m at .%Hz.Addrw Modes: TALK ONLY and ADDRESSABLE.FRONT PANEL PROGRAMS0 Clear - Camels program mode.1 Non-volattle RAM st.,,age - Store programs 3.4.5 and 8 data in NVRAM2 MuhI lex - Defeata nput amplifier multlplexlw3 IEEE 1w mode - ADDRESSABLE and TALK ONLY entry.4 Lhe frequency - Selects5si7. or tQH2 operation.5 Caltbntlo - Perfonnr digital calibration.6 Extended prognms - Enabler entry to aptiwal expanricn7 Data lq&Sf7 Allows 1co.readlq storage *t 9 pm*amma rogams.POe rate% alwstores highest, lowest and average reading.8 Dla~rtoatice TmublesbooHng aid and self-test.9 Trlggp: - Enables mnt panel or extemal tripgeflw.

GENERALDISPLAY: SIX 0.5 LED digiti with de&mdec?oint,Function and IEEEbus status also display exponent and polarity.- -.ISOLATION: Input LO to IEEELO orV*M; gnater tba lO*Il paralleled owe? t&round: 5ooV A, 5 x lo! y X@F.WARMup: 1 hour to rated accuracy.OzTpG ENVIRONMENT: O-5W C. 0% to 80% relative humidity up0.- -- -.STORAGE ENVIRONMENT: -25 to 65%.POWE R: 10542sv or 21&?50v (internal switch &ctEd), 5042 to 4wfiz.24V.A maximum. 9&llOV and lBo22OV version avatlable upon reauest.CONNECTORS: Amlog: Stitch selectable ront or rear, 5wa; Sold piatedbinding posts. Digttal: Tririgger input and %ltmeter Complete outputon rear panel, BNCs.DIMENSIONS, WEIGHT: 127mm &h X 216mm wide X 35%~ deep (5X 8S X 14%). Net wetit 3.2kp. (7 Ibs.).

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Safety PrecautionsThe following safety precautions should be observed before usingthis product and any associated instrumentation. Although some in-struments and accessories would normally be used with non-haz-ardous voltages, there am situations where hazardous conditionsmay be present.This product is intended for use by qualified personnel who recog-nize shock hazards and are familiar with the safety precautions re-quired to avoid possible injury. Read the operating informationcarefully before using the product.The types of product users am:Responsible body is the individual OI group responsible for the useand maintenance o f equipment, for ensuring that the equipment isoperated within its specifications and operating limits, and for en-suring that operators BT~adequately trained.Operators use the product for its intended function. They must betrained in electrical safety procedures and proper use of the instm-ment. They must be protected from electric shock and contact withhazardous live circuits.Maintenance personnel perform routine p rocedures on the productN keep it operating, for example, setting the line voltage or mplac-ing consumable materials. Maintenance procedures are described inthe manual. The procedures explicitly state if the operator may per-form them. Otherwise, they should be performed only by servicepersonnel.Service personnel are trained to work on live circuits, and performsafe installations and repairs of products. Only properly trained ser.vice personnel may perfmm installation and service procedures.Exercise extreme caution when a shock hazard is present. Lethalvoltage may be present on cable connector jacks or tat fixtures. TheAmerican National Standards Institute (ANSI) states that a shockhazard exists when voltage levels greater than 3OV RMS, 42.4Vpeak, or 60VDC are present. A good safety practice is to expectthat hazardous voltage is present in any unknown circuit beforemeasuring.

Users of this product must be protected from electric shock at atimes. The responsible body must ensure that users are preventedaccess and/or insulated from every connection point. In some caseconnections must be exposed to potential human contact. Pmducusers in these circumstances must be trained to protect themselvesfrom the risk o f electric shock. If the circuit is capable of operatingat or above 1000 volts, no conductive part o f the circuit may bexposed.As described in the International Electrotechnical Commiss ion@EC) Standard IEC 664, digital multimeter measuring circuits(e.g., Keithley Models l75A, 199,ZOOQ 2001, 2002, and 2010) arInstallation Category II. All othe r insmnnents signal terminals arInstallation Category I and must not he connected to mains.Do not cmmect switching cards directly to unlimited power circuitsThey am intended to be used with impedance limited sourcesNEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective devices to limit fault current and voltage to the card.Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect the connectingcables, test leads, and jumpers for possible wear, cracks, or breakbefore each use.For maximum safety, do not touch the product, test cables, or another instruments while power is applied to the circuit under tesALWAYS remove power fro m the entire test system and dischargany capacitors before: connecting or disconnecting cables or jumpers, installing or removing switching cards, or making internachanges, such as installing or removing jumpers.Da not touch any object that could provide a current path to thcommon side of the circuit under test or power line (earth) groundAlways make measurements with dry hands while standing on dry, insulated surface capable of withstanding the voltage beinmeasured.

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The instrument and accessories must be used in accordance with itsspecifications and operating instmctions or the safety of the equip-ment may be impaired.Do not exceed the maximum signal levels of the instruments and ac-cessories, as defined in the specifications and operating informa-tion, and as shown on the instrument or test fixture panels, orswitching card.When fuses are used in a product, replace with same type and ratingfor continued pmtection against fire hazard.Chassis connections must only be used as shield connections formeasuring circuits, NOT as safety earth ground connections.If you are using a test fixture, keep the lid closed while power is ap-plied to the device under test. Safe operation requires the use of alid interlock.lfa@ screw is present, connect it to safety earth gmund using thewire recommended in the user documentation.Then symbol on an btstmment indicates tha t the user should re-fer to the operating instructions located in the manual.TheA symbol on an instrument shows that it can source or mea-sure 1000 volts or more, including the combined effect o f normaland c~mrn~n mode voltages. Use standard safety precautions toavoid personal contact with these voltages.

The WARNING heading in a manual explains dangers that mightresult in personal injury or death. Always read the associated infor-mation very carefully before performing the indicated procedure.The CAUTION heading in a manual explains hazards that coulddamage the instrument. Such damage may invalidate the warranty.Instrumentation and accessories shall not be connected to humans.Before performing any maintenance, disconnect the line cord andall test cables.To maintain protection from electric shock and fire, replacementcomponents in mains circuits, including the power transformer, testleads, and input jacks, must be purchased from Kcithley Ins&wmats. Standard fuses, with applicable national safety approvals,may be used if the rating and type are the same. Other componentsthat are not safety related may be purchased from other suppliers aslong as they are equivalent to the original component. (Note that se-lected pats should be purchased only through Keithley Instrumentsto maintain accuracy and functionality of the product.) If you areunsure about the applicability of a replacement component, call aKeithley Instruments office for information.To clean an insuument, use a damp cloth or mild, water basedcleaner. Clean the exterior of the instrument only. Do not applycleaner directly to the instrument or allow liquids to enter or spillon the instrument. Products that consist of a circuit board with nocase or chassis (e.g., data acquisition board for installation into acomputer) should never require cleaning if handled according to it-stmctions. If the board becomes contaminated and operation is af-fccted, the board should be returned to the factory for propercleaning/servicing.

Rev. 7.199

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TABLE OF CONTENTSParagraph Title Page1.11.21.31.41.51.61.71.81.8.11.8.21.8.31.8.41.851.91.101.111.11.11.11.21.11.31.11.41.11.51.11.61.11.71.11.81.11.91.11.101.11.111.11.12

SECTION 1 GENERAL INFORMATIONIntroduction .................................................................................Model196Features ...........................................................................WarrantyInformation .........................................................................Manual Addenda .............................................................................Safety Symbolsand Terms .....................................................................Specifications. ...............................................................................Unpackingandlnspection ......................................................................PreparationForUse ...........................................................................LinePower ........................................................................ . .......LineVoltageSelection .......................................................................LineFrequency .............................................................................IEEEPrimaryAddress .......................................................................Model185OptionPreparation.. ..............................................................RepackingForShipment .......................................................................Using the Model 195 Instruction Manual ..........................................................Accessories ..................................................................................Model1301TemperaturaProbe ...............................................................ModellOlSRackMountingKit ................................................................Model1600AHighVoltageProbe.. ...........................................................Model1641KelvinTestLeadSet ..............................................................Model165150-AmpereShunt ................................................................Model1681Clip-OnTestLeadSet .............................................................Model1682ARFProbe ......................................................................Model1683UniversalTestLeadKit ............................................................Model 1685 Clamp-On AC Current Probe .......................................................Model 1691 General Purpose Test Lead Kit. .....................................................Model 1950 AC Voltage; AC and DC Current Option .............................................Model7008IEEE-488Cable.. ................................................................

SECTION 2 BASIC OMM OPERATIONIntroduction .................................................................................FrontPanelFamiliarization .....................................................................Controls ...................................................................................Terminals ..................................................................................Displayandlndicators .......................................................................TiltBail ....................................................................................RearPanelFamiliariration ......................................................................ConnectorsandTerminals ...................................................................INPUTSSwitch ............................................................................Fuses .....................................................................................Power-UpProcedure ..........................................................................DisplayMessage ..............................................................................OverflowIndication.. .......................................................................NoOptionMessage .........................................................................ControlSelection .............................................................................Function ..................................................................................Range ....................................................................................UsingZero .................................................................................Filtering ...................................................................................DisplayResolution.. ........................................................................InputTerminalSelection .....................................................................Triggering.. .................................................................................

l-ll-ll-ll-ll-1l-l1-21-2l-21-21-2l-2l-2l-21-3l-3l-31-31-31-3131-3131-3l-3l-31-3l-3

2.12.22.2.12.2.22.2.32.2.42.32.3.12.3.22.3.32.42.52.5.12.5.2Zl2:6:22.6.32.6.42.6.52.6.62.7

2-l2-12-12-22-22-22-22-32-32-32-324El2-62-52-62-52-62-72-72-7

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2.7.12.7.22.7.32.7.42.82.8.12.8.22.8.32.8.42.8.52.92.9.12.9.2

t:3:33.43.53.5.135.23.5.33.5.43.5.53.5.63.5.73.5.83.5.83.5.103.6

4.14.24.34.3.14.3.24.3.34.44.4.14.4.24.4.34.4.44.4.54.54.64.6.14.6.24.8.34.74.7.14.7.24.7.34.7.44.84.8.14.8.2

TABLE OF CONTENTS (CONT.)FrontPanelTriggering ....................................................................... 2-7ExternalTrigger ............................................................................ 2-7VoltmeterComplete.............................................................~ ........... 2-8TriggeringExample ......................................................................... 2-8

BasicMeasurements.. ........................................................................ 2-9OCVoltageMeasurements ................................................................... 2-9ResistanceMeasurements .................................................................. 2-10ACVoltageMeasurements .................................................................. 2-11OCCurrentMeasurements .................................................................. 2-11ACCurrentMeasurements .................................................................. 2-11TRMSConsiderations ........................................................................ 2-12TRMSMeasurementComparison ............................................................ 2-12CrestFactor .............................................................................. 2-13SECTION 3 FRONT PANEL PROGRAMSIntroduction ................................................................................. 3-lProgrammingControls ........................................................................ 3-1Front Panel Program Display Messages .......................................................... 3-1ProgrammingNotes ........................................................................... 3-1ProgramDescription .......................................................................... 3-3ProgramO.Clear ............................................................................ 3-3Program 1. Non-Volatile Storage .............................................................. 3-3Program2.Multiplex ........................................................................ 3-3Program 3 . IEEE Address and Talk-Only Mode ................................................... 33Program4.LineFrequency ................................................................... 3-4Program 5. Digital Calibration ................................................................. 3-4Program6.Expansion ........................................................................ 3-5Program7.OataLogger.. ................................................................... 3-5ProgramS.Oiagnostics ...................................................................... 3-7ProgramS.TriggerMode .................................................................... 3-8ProgremmingScalingFactors .................................................................. 3-8SECTION 4 IEEE-488 OPERATIONIntroduction ................................................................................. 4-lBusDescription .............................................................................. 4-lIEEE488BusLines ........................................................................... 4-2SusManagementLines ...................................................................... 4-2HandshakeLines ........................................................................... 4-2DataLines ................................................................................. 4-3BusCommends.. ............................................................................ 4-3UnilineCommands .......................................................................... 4-3UnivenalCommands ........................................................................ 4-3AddressedCommands ...................................................................... 4-4UnaddressCommands ...................................................................... 4-4Device-DependentCommands ................................................................ 4-4Command Codes ............................................................................. 44CommandSequence .............................................................. . ........... 4-4

Addressed Command Sequence ............................................................... 46UniversalCommandSequence ............................................................... 4-6Device-Dependent Command Sequence ....................................................... 4-6Hardwareconsiderations ...................................................................... 4-6Typical Controlled Systems .................................................................. 4-6BusConnections.. ......................................................................... 4-6PrimaryAddressProgramming ................................................................ 4-8Talk-Only Mode ............................................................................ 49Softwareconsiderations ....................................................................... 4-9Controller Interface Routines ................................................................. 4-9HP-85BASlCStatements .................................................................... 4-9

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4.034.8.44.94.9.14.9.24.9.34.8.44.9.54.9.64.9.74.9.84.104.10.14.10.24.10.34.10.44.10.54.10.84.10.74.10.84.10.94.10.104.10.114.10.124.10.134.10.144.10.154.10.164.10.174.10.184.10.194.10.204.114.11.14.11.24.11.34.12

5.15.25.35.45.555.15.5.25.5.35.545.5.56.126:3.16.3.26.3.36.3.4

TABLE OF CONTENTS (CONT.1InterfacaFunctionCodas ................................................................... 410Model 195 Interface Commands ........................... ............... ............... ..... 4-10General Bus Command Programming ........................................................... 411REN (Remote Enable) ............. ............... ............... ............... ............ 4-11IFClInterfaceClear) ........................................................................ 4-11LLOlLocalLockout) ....................................................................... 4-12GTL(GoToLocall ......................................................................... 4-12DCL(DeviceClear) ......................................................................... 4-12SDC (Selective Device Clear) ........................... ............... ............... ....... 412GETlGroupExecuteTriggsrJ ................................................................ 4-13Serial Polling (SPE, SPD) ................................................................... 413Device-Dependent Command Programming ..................................................... 4-13Execute(X) ............................................................................... 4-14FunctionfF) ............... ............... ............... ............... .......... . ....... 4.14Range(R) ................................................................................ 4-14Rate(S) .................................................................................... 4-16ZeroCommandIZ) ......................................................................... 4-17Filter. .................................................................................... 4-17Triggering (Tl ............................................................................. 4-17EOIIK) ................................................................................... 4-18Multiplex(A) .............................................................................. 4-18Delay(W) ................................................................................ 4-18StatusWord ........................................................................... 4-19SRQ Mode (M) and Status Bvte Format. ............... ............... ............... ......... 4-20BufferCommand (Qand El ............... ............... ............... ............... ..... 4-21DateFormat ........................................................................... 4-22DigitalCalibration ......... ..i .......................................................... 4-23Non-VolatileMemorvStoragefL) ............................................................ 4-24SelfTest .............................................................................. 4-24ProgrammingTerminator(Y). ............................................................ 4-24HitBunonlH) ............................................................................. 4-26Display(D) ............................................................................... 4-25

FrontPanelErrorMessages ................................................................... 426IDDCError ............................................................................... 4-26IDDCOError .............................................................................. 4-26NoRemoteError .......................................................................... 4-26ReadingRates .............................................................................. 4-27SECTION 6 PERFORMANCE VERIFICATIONIntroduction ................................................................................. 5-lEnvironmentalConditions ...................................................................... 51RecommendedTestEquipment ................................................................. 6-lInitialConditions .............................................................................. 5-lVerificationprocedure ......................................................................... 5-lDCVoltageAccuracyCheck .................................................................. 5-2ResistanceAccuracyCheck .................................................................. 52AC Voltage Accuracy Check (with Model 1950 Option) .............. ............... ............... 6-3DC Current Accuracy Check (with Model 1950 Option) ............... ............... ............. 6-4AC Current Accuracy Check (with Model 1950 Option) .............. ............... .............. 6-6SECTION 6 THEORY OF OPERATIONIntroduction ............. ..... . .............................................................. 6-lOverall Functional Description ................................................................. 8-1AnalogCircuitF/ .............................................................................. 6-lInputSwitchingandMultiplexer .............................................................. 6-lInputBufferAmpiifier ....................................................................... 8-3-2VReferenceSource ....................................................................... 6-3AIDConverter ............................................................................. 6-3

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6.46.4.16.4.26.4.36.4.46.4.56.4.66.4.76.4.8:i6:78.7.16.7.26.7.36.7.4

7.17.27.37.3.17.3.27.47.57.5.17.5.27.5.37.5.47.5.57.5.67.5.775.87.5.97.87.77.87.8.17.8.27.837.8.47.8.57.8.87.8.77.8.87.8.97.8.108.18.28.38.48.5

TABLE OF CONTENTS (CONT.1DigitalCircuitry ............................................................................... 8-5Microcomputer Block Diagram ................................................................ 8-5MemoryMapping ........................................................................... 65

AddressDecoding.. ........................................................................ 6-5MicrocomputerReset ....................................................................... 6-76522VIA .................................................................................. 6-7IEEElnterface ............................................................................... 6-7Display Board .............................................................................. 6-7Serial-Parallel Conversion .................................................................... 6-7PowerSupply ................................................................................ 6-8Modell950AClCurrentOption ................................................................. 6-8Circuit Operation During Measurements. ......................................................... 6-8DCVoltageMeasurement .................................................................... 8-8Circuit Operation During Resistance Measurements .............................................. 6-92- and 4-Terminal Resistance Considerations ................................................... 6-l 1Circuit Operation During Model 1950 Option Measurements ....................................... .8-11SECTION 7 MAINTENANCEIntroduction.. ............................................................................... 7-lLineVoltageSelection ......................................................................... 7-1FuseReplacement ............................................................................ 7-lLineFuse...............................................................................~ .. 7-1AmpsFuse ................................................................................ 7-2Model 1950 AC/Amps Option Installation ........................................................ 7-2CaObration ................................................................................... 7-3Recommended Calibration Equipment ......................................................... 7-3Environmental Conditions .................................................................... 7-3WarmUpPeriod ........................................................................... 7-3DCVoltageCalibration ...................................................................... 7-4ResistanceCalibration ....................................................................... 74ACVoltegeCalibration ...................................................................... 7-5AC and DC Current Calibration ................................................................ 7-8

Non-Volatile Storage of Calibration Constants. .................................................. 7-6CalibrationJumpers ......................................................................... 7-8Special Handling o f Static Sensitive Devices ...................................................... 7-7Disassembly Instructions ....................................................................... 7-7Troubleshooting ............................................................................ 7-0RecommendedTestEquipment ............................................................... 7-8Power-Up Self Diagnostics ................................................................... 7-8SelfDiagnosticProgram ..................................................................... 7-9PowerSupplyChecks ....................................................................... 7-9A/DConverrerandDisplay ................................................................... 7-9Input Attenuator and Ohms Source Checks ..................................................... 7-9Input Multiplexer and Buffer Amplifier ......................................................... 7-9Digital Circuitry. ............................................................................ 7-9Modell950AC/AmpsOption.. .............................................................. 7-9BufferAmplifierGainChecks ................................................................ 7-15

SECTION 8 REPLACEABLE PARTSIntroduction ................................................................................. ElPartsList .................................................................................... 8-IOrderinglnformation .......................................................................... 9-lFacton/Service ............................................................................... 8-lSchematic Diaarams and Component Location Drawinas ........................................... 8-l

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LIST OF TABLESTable Title Page2-l2-22-32-42-52-62-73-l3-23-33-43-54-l4-24-34-44-54-64-74-84-94-104-114-124-134-144-154-164-174-185-l5-25-35-45-55-86-l6-27-l7-27-37-47-57-67-77-87-97-107-117-127-137-14

Power Up Test Error MessagesRangeDetermination .................................................................. 2-FilterModes.. .......................................................................... 2-...................................Maximum Input Values ............................................ 2-........................................................................Resistance Range Output Values 2-............................................................... 2-1Four-wire Maximum Allowable Test Lead Resistance ..............................................Comparison of Average and TRMS Meter Reading. 2-1............................................... 2-1Front Panel Program Summary ................................................................. 3-General Front Panel Program Messages .......................................................... 3-lProgram 3. IEEE Parameters .................................................................... 3-4Program 7. Logging Rates. ..................................................................... 3-7ProgremE.Tests ............................................................................. 3-7IEEE-488 Bus Command Summary .............................................................. 4-3Hexadecimal and Decimal Commend Codes ...................................................... 4-4Typical Addressed Command Sequence .......................................................... 4-6Typical Device-Dependent Command Sequence ..................................................... 4-6IEEEContactDesignations.. ................................................................... 4-8HP-85 IEEE-488 BASIC Statements ............................................................ 4-10Model 195 Interface Function Codes ............................................................ 4-10IEEECommandGroups ....................................................................... 4-11GeneralEusCommands.. .................................................................... 4-11Default Conditions (Status Upon Power Up or After SDC or DCLI ................................... 4-12Device-Dependent Command Summary ......................................................... 4-15RangeCommands.. ......................................................................... 4-16Rats Commands ............................................................................. 4-17FilterCommends ............................................................................ 4-17StatusWordFormats ........................................................................ 4-19SRQMaskCommands ....................................................................... 4-20Status Byte Interpretation ..................................................................... 4-21Buffer Rate Commend Parameters ............................................................. 4-22Recommended Test Equipment for Performance Verification ........................................ 5-lLimitsforDCVoltsgeVeyiiication ............................................................... 5-2Limits for Resistance Venfrcation ................................................................ 5-3Limits for AC Voltage Verification ............................................................... 5-4Limits for DC Current Verification ................................................................ 5-4Limits for AC Current VerificationIntegration Delay Periods ............................................................... 5-5... ................................................................... 6-4Model 195 Memory Mapping ................................................................... 6-5LineVoltageSelection ......................................................................... 7-lLineFuseSelection ........................................................................... 7-lRecommended Test Equipment for Calibration .................................................... 7-3DC Voltage Calibration Parameters .............................................................. 7-4Psramstersfor Resistance Calibration. ........................................................... 7-4AC Voltage Calibration Parameters .............................................................. 7-5Model 1950 Frequency Compensation Parameters ................................................. 7-5Current Calibration Parameters ................................................................. 7-6StaticSensitiveDevices ....................................................................... 7-7Recommended Troubleshooting Equipment ...................................................... 7-8FETand Relay Switching Sequence for Various N Modes .......................................... 7-10ProgramE.Tests ............................................................................ 7-12PowerSupplyChecks ........................................................................ 7-13AIDConvsrterChecks ....................................................................... 7-13

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-15LIST OF TABLES (CONT.1

DisplayBoardChecks ................................................DCAnenuatorChecks ................................................Dhmsand -2V Reference Source Checks ................................Digital Circuitry Checks ...............................................Model 1950 Option Checks. ...........................................Buffer Amplifier Gain Checks ..........................................Index of Model 195 Schematics and Component Layouts ..................Mother Board 196-103, Parts List .......................................Display Board 195-113, Parts List .......................................Model 1950 AC Option 1950-153, Parts List ..............................

...... 7-16....... 8-l....... 8-3....... 8-7....... 8-8LIST OF ILLUSTRATIONS

Title PageInstrumentPackaging.. ....................................................................... 1-2Modell95FrontPanel ......................................................................... 2-1Model195RearPanel ......................................................................... 2-2External Trigger Input Pulse Specifications ........................................................ 2-8Voltmeter Complete Output Pulse Specifications .................................................. 2-8External Trigger Connections ................................................................... 2-8DCVoltageMeasurements ..................................................................... 2-9Two-Terminal Resistance Measurement, ........................................................ 2-10Four-Terminal Resistance Measurement ......................................................... 2-10ACVoltageMeasurement ..................................................................... 2-11DC and AC Current Measurement ............................................................... 2-12Front Panel Program Controls .................................................................. 3-2IEEEBusConfiguration ........................................................................ 4-lIEEEHandshakeSequence ..................................................................... 4-ZCommandCode .............................................................................. 45SvstemTvpes ................................................................................ 4-7IEEE-488Connector ........................................................................... 4-7IEEE-488Connections ......................................................................... 4-7Rear Panel of Model 195 Showing IEEE Connector ................................................. 4-7ContactAssignments ......................................................................... 4-8Tvpical IEEE-488 Bus Driver (One of 16) .......................................................... 4-8SRQ Mask and Status Byte Formats ............................................................ 4-21DataFormat ................................................................................ 4-23Hit Button Command Numbers ................................................................ 4-25IEEEDisplayErrorMessages ................................................................... 4-26Connections for Voltage Verification ............................................................. 5-2Connections for Verification of ZOSI,2003, and 2kB Ranges ......................................... 6-3Connections for Verification of 2OkD Through 20MD Ranges. ........................................ 5-3Verification Connections for Current ............................................................. 5-4BasicBlockDiagram .......................................................................... 6-2Simplified Schematic of the Multiplexer .......................................................... 8-3Simplified Schematic of the Input Buffer Amplifier ................................................. 6-3Simplified Schematic o f the -2V Reference Source. ............................................... 6-4Simplified A/D Converter Schematic ............................................................ 6-4A/D Converter Integrator Output Waveform ...................................................... 6-4Simplified Microcomputer Block Diagram ........................................................ 6-6Ciruit Operation During DC Voltage Measurements ................................................ 6-9FET Switching Sequence During DC Voltage Measurements ........................................ 6-9Resistance Measurement Simplified Circuit For 20-200kD Ranges ................................... 6-10FET Switching Sequence for 2OD. 2000 and 2kD Ranges. .......................................... 6-10FET Switching Sequence for 20kD and 200kD Ranges ............................................. 6-11FET Switching Sequence for 2MD and 20MD Ranges. ............................................. 6-11

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6-146-156-166-177-l7-27-37-47-57-67-7i-i8-28-38-48-58-68-7

LIST OF ILLUSTRATIONS (CONT.)Input Configuration During Two-Terminal Measurements ..........................................Input Configuration During Four-Terminal Measurements ..........................................instrument Configuration During Model 1950 Measurements .......................................FET Switching Sequence for Model 1950 Option Measurements ....................................Model1950lnstallation .......................................................................Voltage Calibration Connections ...............................................................Connections for Calibration of 20Qand 2OOD Ranges ..............................................Connections for Calibration of 2kD Through 20MD Ranges .........................................Location of Frequency Compensating Capacitors on Model 1950 ....................................Current Calibration Connections ...............................................................Calibration Jumper Locations. .................................................................Model195ExplodedView .....................................................................Model 1950AC Option, Component Location Drawing, Dwg. No. 1950-150 ............................Mother Board, Component Location Drawing, Dwg. No. 195100Display Board, Component Location Drawing, Dwg. No. 195110 ....................................Mother Board, Schematic Diagram, Dwg. No. 195-106 ................................................................................Display Board, Schematic Diagram, Dwg. No. 195116 ............................................Model 1950 AC Option, Schematic Diagram, Dwg. No. 1950-156 ...................................

6-16-18-16-17-7-747-7-7-7-8-8-1511El6al78-2827

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SECTION 1GENERAL INFORMATION1.1 INTRODUCTIONThe Model 195 System DMM is a fully programmable instru-ment with 5% digit resolution. In standard configuration, theModel 195 is capable of DC voltage measurements between1OOnVand 1OOOV n six ranges, and 2-teninal and 4-terminalresistance measurements between lOO& and 20MD on sevenranges. With the optional Model 1950 ACV and AC and DCcurrent option installed, the Model 195 can make TRMS ACvoltage measurements between 1pV and 700V on five ranges,TRMS AC current measurements between InA and 2A on fiveranges. and DC current measurements between lOOpA and 2Aon six ranges. The versatilitv of the Model 195 DMM is furtherenhanced bv the inclusion of a standard IEEE488 interface. Ahighlight of Model 195 operation is its digital calibration fea turewhich allows the user to easily perform calibration from thefront panel.1.2 MODEL 195 FEATURESSome important Model 195 features include:

1. Standard IEEE-488 Interface. A standard IEEE-488 inter-face allows the Model 195 to be programmed from asystem controller; readings may also ba transmitted overthe bus to other instrumentation in the talk-only mode.2. Front Panel Programs. Numerous internal programs tocontrol various operating modes such as digital calibrationand IEEE488 parameters are easily entered from the frontpanel.3. Non-volatile (NV) RAM Storage. A non-volatile RAMstores calibration constants, certain IEEE operating para-meters, and line frequency values even when the power isturned off.4. Digital Calibration. The Model 195 may ba easily calibratedby applying an appropriate calibration signal and runningthe front panel calibration program or bv commanding itover the bus. The calibration level may be at full range, or;:ssprne value entered from the front panel or over the IEEE5. Data Storage. A data storage buffer is included to allow up

to 100 readings to be internally stored a t a user-selectedrate. The buffer may be read and controllad from the frontpanel or over the IEEE-488 bus. In the talk-onlv mode, theoutput rate can also be programmed.6. Front and Rear Panel Input Terminals. Input teninals areduplicated on the front and rear panels to allow easy con-nections in both bench and rack-mounted situations. Theselected set of inputs is controlled by a rear panel switch.7. Trigger Input and Output. The Model 195 may be triggeredto take readings by applying an external trigger pulse or bvpushing a front panel bunon. A separate output pulse.which is active when the instrument comp letes a reading,is also available on the rear panel.

8. Auto Ranging. The Model 195 includes a fast auto ranfeature for easier measurements.9. Front Panel Zero. A single front panel zaro control allthe user to store a separate zero offset for each measufunction.

10. Filtering. D igital filtering is selectable from the front por bus.1.3 WARRANTY INFORMATIONWarranty information may be found inside the front covethis manual. Should it become necessary to exercise the wranty, contac t your nearest Keithlev representative or the tofv to determine the correct course of action. Keithley Insmanta maintains service facilities in the United Statea, WGermany, Great Britain, France, the Netherlands, Switzerlaand Austria. Information concerning the application, option, or service of your instrument may be directed to theplications engineer at any of thase locations. Check the infront cover of this manual for addresses.1.4 MANUAL ADDENDAlnfonation concerning improvements or changes to thestrument which occur after the printing of this manual wilfound on an addendum sheet included with this manual.sure to review these changes before attempting to operatservice the instrument.1.5 BAFH-Y SYMBOLS AND TERMSThe following safetv symbols and terms are usad in manual or found on the Model 195:The symbol A on the instrument indicates that the should refer to the operating instructions in this manual:Thesymbol & on the rnstmment indicates that a potenof 1OOOV r more may be present on the terminal(s). Standsafetv practices should be observed when such dangervoltages are encountered.The WARNING heading in this manual explains dangers could result in personal injury or death.The CAUTION heading in this manual explains hazards could damage the instrument.1.6 SPECIFICATIONSDetailed Model 195 specifications may be found immediapreceding this section of the manual.

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1.7 UNPACKING AND INSPECTION 1.9 REPACKING FOR SHIPMENTThe Model 195 System DMM was carefully inspected, bothmechanically and electrically, before shipment. Upon receivingthe Model 195, carefully unpack all items from the shippingcarton and check for any obvious signs of physical damagethat might have occurred during shipment. Report any dam-age to the shipping agent immediately. Retain the originalpacking materials in case reshipment becomes necessary. Thefollowing items are included with every Model 195 order:*Model 195 System DMM*Model 195 Instruction Manual*Additional accessories as ordered.1.8 PREPARATION FOR USEOnce the instrument is unpacked, it must be connected to anappropriate power source as described below.1.8.1 Line PowerThe Model 195 is designed to operate from 105125V or210-250V 50/60HZ AC power sources. A special power transformer may be installed for SO-1 OVand 195235V. The factoryset value is marked on the instrument immediately above theline cord receptacle on the rear panel. The line cord receptacleis designed to mats with the supplied 3wire power cord.

CAUTIONDo not attempt to operate the instrument ona supply voltage outside the indicated range,or damage to the instrument might occur.1.8.2 Line Voltame SelectionThe operating voltage of the instrument is internally selec table.Refer to Section 7. Maintenance for information on setting theline voltage.1.8.3 Line FrequencyThe instrument will display the programm ed line frequencyupon power up. The line frequency may be set by using a frontpanel Program as described in paragraph 3.5.5.1.8.4 IEEE Primary Address

Before shipping the Model 195, the instrument should be carefully packed in its original carton as shown in Figure l-l, First,wrap the instrument in plastic; once the instrument is in thebox, surround it with Styrofoam packing materia l.If the Model 195 must be returned to Keithlsy Instruments forrepair or calibration, include the following:*Write ATTENTION REPAIR DEPARTMENT on the shippinglabel.*Include the warranty status of the instrument.*Complete the service form at the back of this manual andreturn lt with the instrument.

CARDBOARDSTRIPINSTRUCTION

PROTECTIVECARDBOARD

Lx] MODEL95

If the Model 195 is to be connected to the IEEE-488 bus, itmust be programmed for the proper primary address. The fac-tory programmed value is 16, but the address may be changedas de&bed in Section 4.1.8.5 Model 1950 Option PreparationThe Model 1950 option extends the capabiliies of the Model195. allowing it to acouratelv measure AC voltaae and AC andDC current.The Model 1950 will be factory in&d if it waspurchased with the Model 195; however, the Model 1950 iseasily installed in the field, as described in Section 7.

Figure 1-l. Instrument Packaging

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1.10 USING THE MODEL 195 INSTRUCTION MANUALThis manual contains information necessary for operating, pro-gramming, and servicing the Model 195 System DMM and isdivided into the following sections:1. Section 2 contains basic DMM operating information, in-cluding front and rear panel layout and voltage. current andresistance measurement procedures.2. Front panel programming information may be found in Sec-tion 3.3. Information pertaining to the IEEE488 bus, includingprimary address selection. programming, and bus connec-tions, is contained in Section 4.4. For the more technically oriented, information on psrfor-msnce veriiication, theory of operation, and maintenanceand servicing information is contained in Sections5 through8.1.11 ACCESSORIESAccessories which can be used with the Model 195 aredescribed in the following paragraphs.1.11.1 Model 1301 Temperature ProbeThe Model 1301 Temperature Probe converts the Model 195into a digital thermometer capable of measuring temperaturesbetween -55C and + 155eC. The output of the Model 1301 islmV/OC and it can be used with any DMM with a minimumIOMC input impedance.1.11.2 Models lOISA and 1019s Rack Mounting KitsThe Model 1019A is a universal fixed rack mounting kit for theModel 195. The Model 1019s is a slide type universal rackmounting kit.1.11.3 Model IEOOA High Voltage ProbeThe Model 18OOA extends the Model 195 measuring capabili-ties to 40kV. The Model 18OOA has a 1OOO:l division ratio: aone-volt indication on the Model 195 corresponds to a 1kV in-put voltage.1.11.4 Model 1841 Kelvin Test Lead SetThe Model 1841 test leads are used when making 4-terminalresistinca measurements. The leads are made up of two twin-lead cables 1.2m (48 inches) in length. Each cable is terminatedby a twin banana plug on one end and a Kelvin spring-clip con-tact on the other end.1.11.5 Model 1851 SO-Ampere ShuntThe Model 1851 allows the Model 195 to make DC currentmeasurements up to 50A. With the Model 1950 option install-ed, the shunt can be used with the Model 195 to make AC cur-rent measurements up to 50A as well. The Model 1851 con-

sists of a 0.0019 f 1% 4teninal resistance and operates wthe Model 195 by developing a small measurable voltage;50A current will provide a reading of 50mV on the meter.1.11.8 Model 1681 Clip-On Test Lead SetThe Model 1881 set contains two leads 1.2m (48 inches) length. Each lead is terminated with a banana plug on one eand a spring-action clip-on probe on the other end.1.11.7 Model 1682A RF ProbeThe Model 1882A is an RF probe that extends the AC measing capabilities of the Model 195 to include the 1OOkHz250MHz frequency range. Note that the probe provides a Doutput, so the Model 1950 option is not necessary when maing RF measurements. The Model 1882A provides a one-voutput for a one-volt RMS input when used with instrumenhaving an input impedance of at least IOMD.1.11.8 Model 1683 Univereel Test Lead KitThe Model 1883 kit consists of two tsst leads lm (4lnJ length with 14 screw-in tips; four banana plugs, two spalugs, four alligator clips, two probes and two phone tips.1.11.9 Model 1685 Clamp-On AC Current ProbeThe Model 1885 measures 50Hz and 80Hz AC currents up 200A by clamping on to a single conductor, eliminating tneed to open the circuit. The Model 1885 detects the currethrough a conductor by measuring the magnetic field arouit. The output of the Model 1885 is W/A RMS.1.11.10 Model 1891 General Purpose Test Lead KitThe Model 1891 kit contains two 0 .9m (38in.) test leads; ealead is terminated with a probe tip on one end and a banaplug on the other end.1.11.11 Model 1950 AC Voltage; AC and DC CurrentOptionThe Model 1950 option expands the capabilities of the Mod195, allowing it to measure TRMS AC voltage between l+and 7OOV, TRMS AC current between 1nA and 2A, and Dcurrent between IOOpA and 2-A. The Model 1950 plugs inths Model 195 for easy installation.1.11.12 Model 7008 IEEE488 CablesThe Model 7008 cables are useful for connecting the Mod195 to the IEEE-498 bus. The Model 7009-3 is 0.9m Wt.1 length and has a standard IEEE488 connector on each enThe Model 70086 is 1.8m (8ft.l in length.

l-3/1-

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SECTION 2BASIC DMM OPERATION2.1 INTRODUCTIONModel 195 operation is divided into three general categories:basic bench operation, front panel program operation, andIEEE-489 operation. Basic bench operation, which is coveredin this section, consists of using the Model 195 to performbasic voltage, current, and resistance measurements. Frontpanel and IEEE programming csn also be used to greatly en-hance the capabilities of the instrument. These aspects arecovered in detail in Sections 3 and 4.2.2 FRONT PANEL FAMILIARIZATIONThe front panel layout of the Model 195 is shown in Figure 2-l.The front panel is generally divided into three sections: con-trols, terminals, and display and indicators. The followingparagraphs describe the purpose of each of these items indetail.2.2.1 ControlsAll the front panel controls except POWER are momentarycontact switches. Many controls include an annunciator lightto indicate the selected mode. Most buttons have a secondan,function for front panel progam operation as described in Sec-tion 3. The controls are color coded into functional groups foreasier operation.

1. POWER-The POWER switch controls the AC power the instrument. Depressing and releasing the switch onturns the power on. Depressing and releasing the switchsecond time turns the power off.2. FUNCTION-The four FUNCTION pushbuttons contthe type of measurement such as voltage, current, or restance as follows:

NOTEThe Model 195 cannot measure AC voltage or ACor DC current without the Model 1950 option in-stalled. Depressing the AMPS or AC buttonswithout this option installed will result in aNoCP message as described in paragraph2.5.2.

VOLTS-The VOLTS button places the instrument in tDC volts or AC volts (with the Model 1950 option) operatinmodes. When the VOLTS button is depressed, the indicatabove the button turns on. indicating the instrument is sfor that mode.OHMS-The OHMS button sets the Model 196 up measure resistance. When this button is depressed, the dicator above the bunon turns on.AMPS-With the Model 1950 option installed, the AMPbutton is used to place the instrument in the DC or AC cu

DISPLAY DISPLAY IEEEMANTISSA EXPONENT STATUS LIGHTSOHMSOLTS

CONTROL-IZERO R~SCU&~N PROGRAM RANGECONTROLS CONTROLSFILTER TRIGGERCONTROL CONTROLRgure 2-l. Model 195 Front Panel

2

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rent mode. When the AMPS button is depress@ , the indi:cator above it tums on.AC-When the Model 1959 is installed, the AC buttonplaces the instrument in ths AC voltage or currant mode,depending on the selection performed with the VOLTS orAMPS buttons. Depraasing the AC bunon once turns theAC indicator on; the instrument will measure en AC voltageor current in this mode. Depressing the AC button a secondtime turns the AC indicator of f; the instrument measures aDC voltage or current in this mode. Pressing AC whan inthe OHMS mode, places the instrument in the ACV mode.

3. RANGE-The RANGE buttons select the operating rangesof the instrument. The range in uss can ba determined fromthe dbplav dscknal Point and exponent value as describedin paragraph 2.6.2.AUTO-The AUTO button places the instrument in theautoranging mode. The instrument is operating in this modewhen the AUTO indicator is on. When in the autorangingmode, the instrumant automatically selects the best rangeto msasure the applied input signal.DOWN-Each time the DOWN button is operatad, the in-strument moves downrange one increment.UP-Each time the UP button is operated . the instrumentmoves uprange one increment.

4. MODIFIERS-The MODIFIER buttons control the zero,filter and raaolutk~ modes of the instrument as describedb&w.ZERO-The ZERO button controls a zero offset for baselinesuppression. Depressing the ZERO button once enableszero as indicated by the ZERO light. Pressing ZERO asecond time disables the zero mode.FILTER-The FILTER button controls the internal filter.Pressing this buttononce enables the filter: the indkatorlight will turn on to show that the filter is enabled. Depress-ing the FILTER button a second time disables the filter.RESOLN-The RESOLN button controls the displayresolution. Each time this button is operated, the resolutionchanges to the eltamate mode.

5. TRIG-The TRIG button is used to trigger readings whenthe instrument is in the front panel trigger mode. The TRIGbutton will be operational only if the TRIG indicator light ison. Tha instrumant may be placad in the correct triggermode through front panel Program 9 or through IEEE com-mands. One reading will be processed each time the TRIGbutton is operated.

6. PROGRAM-The PROGRAM buttons are used with thefront panel programs as described in Section 3.PROM-The PROM button is used as the first step inentering front panel programs 0 through 9.RECALL/ENT-The RECALL/ENT button is used to enterand recall dare associated w ith the front panel programs.

2.2.2 TerminalsThe terminals are used to connect the Model 195 to thevoltage, current, or resistance to be measured. Note that theteninals are duplicated on the rear panel and that the rearpanel INPUTS swftch must be in the proper position for thefront panel terminals to be active.1. VOLTS OHMS-The VOLT OHMS terminals are usedwhen making DC and AC (with the Model 1950) voltagemmSummnt8 and resistance measurements. The HI ter-minal is considered to be positive with raspact to the LO tar-minal when measuring DC voltage; the LO terminal isisolated from chassis gmund.2. OHMS SENSE-The OHMS sense terminals are usadwhen making &terminal resistance measurements.3. AMPS-The AMPS terminal is used in conjunction withthe Model 1950 option to make DC and AC current meas-urements.2.2.3 Ciapley and IndicatorsThe function of the display and indicators is described be low.1. Display-The display consists of a 5% digit mantissa and asingle digit exponent. Both the mantissa and exponent usaa leading minus sign to indicate negative valuaa. The signon the exponent changes to + for xero or positive values.The range in use may ba determined from the position ofthe decimal point and the exponent value as described inparagraph 2.52. The flashing rate of the decimal point in-

dicates the conversion rate.NOTEThe display will bs in the 5y2 digit mode uponpower-up.

2. IEEE Status Indicators-The REMOTE, TALK andUSTEN indicators are used when programming the instru-ment over the IEEE-488 bus. Refer to Section 4 for oom-plets IEEE programming information. These status lightsam not operational during front panel instrument operation.2.24 Tilt BailThe tilt bail, which is located on the bottom cover of the in&u-mant, is useful for elevating the front of the instrument to aconvenient viewing height. To extend the bail, first rotate it90 away from the bottom cover and push down on the legs tolock it into place. To retract the bail, pull the legs away fromthe bottom cover and.then rotate the bail until it is flush withthe bottom cover.2.3 REAR PANEL FAMILIARI2ATIONFigure 2-2 shows the rear panel layout of the Model 195.

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2.3.1 Connectors and Terminals 2.33 Fuses1. AC Receptacle-Power is applied through the suppliedpower cord to the 3-terminal AC receptacle. Note that theselected supply voltage is marked on the rear panel abovethe AC receptacla.

The Model 195 has two fuse holders on the rear panel. For formation on replacing these fuses, refer to Section 7 . The pupose of the two rear panel fuses is described below.

2. IEEE-498 Connector-This connector is used to connectthe instrument to the IEEE-489 bus. IEEE interface func-tions are marked above the connector.

1. LINE FUSE-This fuse provides protection for the Apower line input.2. AMPS FUSE-This fuse protects the Model 1950 optiofrom excassivs current.

3. VOLTS OHMS Terminals-These terminals perform thesame functions as the front panel VOLTS OHMS terminals.4. OHMS SENSE Terminals-These terminals are wad tomake f&terminal resistance measurements.5. AMPS-The rear panel AMPS terminal performs the samefunction as the similar AMPS terminal on the front panel.

CAUTIONThe AMPS FUSE only protects the instru-ment from excessive currents applied to theAMPS terminal: it does not protect the unitfrom excessive voltage applied to the otherinput terminals.2.4 POWER-UP PROCEDURE

6. EXTERNAL TRIGGER-This BNC connector is usad toapply pulses to trigger the Model 195 to take one or morereadings, depending on the selected trigger mode.7. VOLTMETER COMPLETE-This BNC output connectorprovides a pulse when the Model 195 has completed areading; it is useful for triggering other instrumentation.

The basic procedure for powering up the Model 195 is descried below.1. Connect the female end of the power cord to the AC recetacle on the rear panel. Connect the other end of the powcord to a grounded AC outlet.

2.3.2 INPUTS SwitchThe INPUTS switch selects either the front panel or rear panelterminals. When the switch button is at its inner most position,the front panel input terminals are selected. When the switch isout, the rear panel terminals are operational.

CAUTIONBe sure the power line voltage agrees withthe indicated value on the rear panel of theinstrument. Failure to heed this warningmay result in instrument damage. If neces-sary, the power line voltage may be changedas described in Section 7.EXTERNALTRIGGER INPUT VOLTMETERCOMPLETE OUTPUT

INPUT

SWITCHI

AMPS AC POWER LINE FUSE IEEE-458FUSE RECEPTACLE CONNECTORFigure 2-2. Model 195 Rear Panel

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WARNINGThe Model 195 is equipped with a 3wirepower cord designed to be used withgrounded outlets. When the proper conneo-dons ara made, instrument chassis is con-nected to power line ground. Failure to use aproperly grounded outlet may result in per-sonal injury or death because of electricshock.Turn on the power by depressing and releasing fhe POWERswitch on the front panel.The instrument will then begin operation by performing adisplay and indicatortest for about two seconds, All modeand IEEE indicators will turn on and the display will appearas follows:

To verify that all display segments are operating, comparethe instruments display during the rest with the abovefigure.Once the display test is completed, the instrument will per-form NVRAM, ROM, and RAM tests. If all these tests arepassed, the display will show the program med line frequen-cy and software revision level for about one second similarto the example below:

F60E 4F60 represent the line frequency, and E4 show the soft-ware revision level.

NOTEThe programmed line frequency should be thesame as the operating frequency. For informationon programming the line frequency, refer toparagraph 3.55.Following the line frequency and software revision level, theinstrument will display the programmed IEEE primary ad-dress. For example, with the factory programmed value of16. the display will show:

I If I6 I6. Following these display messages, the instrument will go

Program Mode: Disabled

into the normal operating mode and begin displaying read-ings. The instrument will be in the following modes:

IEEE Status: Local

Function and Range: 1OOOVDCResolution: 5% digitsFilter: OffZero: Off

7. Ifanyofthetestslistedinstep4fai1, theinstrumentwilldisplayoneoftheerrormessageslisted inTable2-1. ltis recommand-ed that the power-up procedure be repeated several times foverii that a consistent error occurs; if so, a problem whichmust be rectified before operation, exists in the instrument.See Section 7 for troubleshooting information.NOTEIf a NVRAM (Non-Volatile RAM) error occurs, in-strument operation may be restored by depress-ing any front panel momentary contact button.However, instrument functions associated withNVRAM storage cannot be guaranteed. These in-clude IEEE primary address, calibration accuracy,power line frequency, and Model 1950 optionstatus.

2.5 DISPLAY MESSAGESThe Model 195 has two display messages associated withbasic front panel operation. These masaagss indicate if anoverrange input occurs and whether or not the Model 1950 op-tion is installed. Note that the instrument has a number of addi-tional display messages associated with front panel program-ming (paragraph 3.4) and IEEE-488 programming (paragraph4.11).2.5.1 Overflow IndicationIf an overrange input is applied to the Model 195, the messagebelow will appear on the display as long as the overflow condi-tion persists:

Table 2-1. Power-Up Test Error MessagesDisplay Message CommentsNVRAM Failure Model 195 locks up, but operation may berestored by hining any button. Instrument cpera-tion associated with NVRAM not guaranteed.

71 ROM Error Model 195 locks up.

/ -1 IRAM Error / Model 195 locks up. j

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If the applied signal has a negative value. the leading minussign will be present on the display as well.2.5.2 No Option MeseegeThe Model 1950 option muat ba present within the instrumentbefore it can rneaaure AC voltage or AC and DC current. If thefront panel AC or AMPS button is depressed without theModel 1950 option installed. the following rneaaage will bediaplaved: I -- I( noUP (

NOTEOTEWhen the Model 1950 option is fir-at installed,hen the Model 1950 option is fir-at installed,option status muat be enabled with NVRAMption status muat be enabled with NVRAMstorage end the unit muat be momentarilytorage end the unit muat be momentarilypowered down, es described in paragraph 7.4.owered down, es described in paragraph 7.4.2.6 CONTROL SELECTIONSelecting the various front panel operating modes is simply amatter of depressing the appropriate button as described in thefollowing paragraphs.2.6.1 FunctionThe Model 195 muat be set up for the proper measudng func-tion with one of the four FUNCTION buttons.1. To meeaure a DC voltage, depress the VOLTS button. If theAC indicator is on, depress the AC button to remwe the in-strument from the AC mode.2. To rneaaura resistance, depress the OHMS button.3.To maaaure AC voltage (with the Model 1950 option),depress the VOLTS button. If the AC indicator ia off, depress the AC button to place the instrument in the ACmode.4. To measure DC current N&h the Model 19501. depress theAMPS button. If the AC indicator ia on, depress the AC indi-cator to remwe the instrument from the AC mode.

Requires Model 1950 rl *20pA range not applicNOTE: Full range values4/2 digit mode.

IDFat:sh

5. To measure AC current, (with the Model 1950 optiondepress the AMPS button. If the AC indicator ia off, depresthe AC button as well.NOTES1. The function light flashes for input voltages greater than3ov.2. The selected function affects the integration period and thaamplea averaged per reading. In DCV, DCA, and OHMSmodes, the nominal integration period is 16.66ma (60Hz) 2Oms 150Hz). corresponding to the S2 rate mode. lSeTable 4-13.) In ACV and ACA modes, the integration periois lOOma. corresponding to the S6 rate mode.2.6.2 RangeThe Model 195 may be operated in either the AUTO range omanual range modes. When selecting a range manually, thinstrument will move up or down range one increment eactime the UP or DOWN button is operated. The range in usmay be determined from the display by noting the position othe decimal rxint and the exrxment value. aa summarized iTable 2 -2. The valuea in the table assume maximum displacounts for the 5% digit raaok~tlon mode .The Model 195 ranges may be selected as follows:1. To p lace the instrument in the autorange mode, depreaa thAUTO button. The AUTO light will turn on and the inatrument will aaautne a range coraiatent with the applied signal2. To cancal the autorange mode, depress the AUTO buttonagain; the AUTO light will go out and the instrument will remain on the present range.3. Use the UP button to increment the range; the instrumentwill mova uprange one increment each tinie the UP button praeaed. Pressing UP will also cencel the autorange mode4. Use the DOWN bunon to decrement the range; the Mode196 will move down range once each time the DOWN button is operated. Pressing DOWN will also cancel the aut*range mode.2.6.3 Using ZeroThe zero mode serves as a meana cf baseline suppressionallowing a stored o ffset value to be subtracted from subae

Table 2-2. Range Determination

OHMS Full Range ACV Full RangeRange Display Range* Display200 19.9999 +o 200mV 199.999 -32000 199.99s +o2kD 1.99999 +3 2; 1.99999 -319.9999 +o20kD 19.9999 +3 2oov 199.999 +o200kD 199.999 +3 7oov 700.00 +o2Ml-l 1.99999 +620MR 19.9999 +6

>tion.rle to AC current measurementsI2donA 199.999 -62mA 1.99999 - 320mA 19.9999 -3200mA 199.999 -32A 1.99999 +o

rown for 5h digit display mode: least significant digit of mantiaaa eliminated in

2

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quent readings. When the ZERO button is pressed, the instru-ment will store the baseline reading with the next triggeredconversion; the ZERO LED will illuminate. All subsequentreadings will represent the difference between the appliedsignal level and the stored baseline. For example, if 1OOmV sstored. a value of 1OOmV will be subtracted from the inputvoltage value.A separate baseline can be stored for each of the five measur-ing functions: DCV; ACV; DCA; ACA; OHMS. The storedbaseline can be as small as the resolution of the instrument willallow or as large as full range. Some examplea are shown inthe following.Stored Baseline Applied Signal+ 10.5000 + 16.6000+ 2.5560 + 1.6000

Displayed Value+6.1000-0.75600-12.6000 +4.6000 f 17.1000NOTES:1, Using zero reduces the dynamic range of the measurement.For example, if the stored baseline is c 1 OOOOOVDC iththe instrument on the 2V range, an input voltage of-1 .OOOOOV r more will still overrange the instrument eventhough input voltages up to + 1.99999 would normally bewithin the capabilities of the 2V range. If the instrument is inthe autorange mode, it will move uprange if necessary.2. Setting the range lower than the stored baseline will over-range the display: the instrument will display the OFLOmessage under these conditions.3. tine control over when the zero baseline is stored may beachieved by placing the instrument in the one-shot triggermode (paragraph 2.7). Once the desired baseline is shownon the display, the instrument may be triggered to store the

baseline with the appropriate trigger stimulus.4. To store a new baseline value, the zero mode must disabledand then enabled once again. The new value will be storedwith the first triggered conversion.5. The zero mode should not be used to null the small offset inthe AC mode.To use the zero mode , perform the following steps:1. Disable the zero mode, if necessary, with the ZERO control.2. Select a function and range consistent with the anticipatedmeasurement.3. Connect the instrument to the signal to be used as a

baseline (See paragraph 2.6).WARNINGThe voltage present on the input terminalmay be larger than the displayed value whenusing the zaro mode. For exampla, if a16OVDC baseline is stored. an appliedvoltage of +17!W will result in a displayedvalue of only +25V.

4. If desired, place the instrument in the front panel one-shottrigger mode by pressing PRGM and TRIG in sequence. Thedecimal point will stop flashing, indicating the instrument iswaiting for a trigger to process the next reading.5. Press the ZERO button. If the instrument is in the con-tinuous mode , it will store the baseline with the first internal-ly triggered conversion. If the instrument was placed in theoneshot mode, the baseline will have been stored whenZERO wes pressad.6. Repeat the above procedure for each desired measuringfunction. All readings made with the zero mode enabled willhave the baseline subtracted from the applied signal value.The stored baseline will be retained until the zero mode isdisabled or until instrument power is turned off.7. To return the instrument to the normal display mode,disable the zero mode with the ZERO control.2.6.4 FilteringBasically, there are three different filter mutineS used in theModel 195. These filters may be directly controlled throughcommands given over the IEEE-488 bus as described in Sec-tion 4. In addition, the filter in use is selected from the frontpanel as follows:1. Enabling the filter with the FILTER bunon adds additionalfiltering. When the filter is enabled, the FILTER LED will beon. The FILTER light flashes until the final filtered reading isavailable.2. The range in use effects which filter is selected; d ifferentfiltering is used on the lowest lmost sensitive) ranges.3. The display resolution affects the amount of filtering; addi-tional filtering is added in the 5% digit mode.Table 2-3 Iis- the filter in use for the various operating com-binations. When the FILTER light is on, Filter 1 is selected.NOTES:1. Filtering cannot be totally disabled with the front panelFILTER button. It csn, however, be disabled with a corn-mand given over the IEEE bus as described in Section 4.2. Adding more filtering, slows down the response time of theinstrumant to sudden changes in input signal. For example,instrument response is slower with the front panel filterenabled than when is it disabled.

Table 2-3. Filter Modes

I )2000,.20MO all DkA ]

2-6

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26.6 Display Resolution SelectionThe display reeolution of the Model 195 may be set to either4/1 or 51% digits with the front panel RESOLN button. TOplace the instrument in the4% digit mode, prase RESOLN. Toreturn to 51% digits, press RESOLN again.2.6.6 Input Terminal SelectionThe Model 195 has two comple te sets of input terminals. Thefront panel set of terminals is convenient for making connec-tions when the instrument is operated on a bench. The rear setof terminals is useful for making connections when the Model195 is mounted in a rack. To select the appropriate set of ter-minals, use the rear panel INPUTS switch as follows:1. To use the rear panel terminals, depress end release theswitch so that the switch button is at its outer mos t posi-tion.2. To change to the front panel terminals, depreae and relsassthe INPUTS switch a second time so that the button is at itsinner most position.2.7 TRIGGERINGThe Model 195 may be triggered to take readings in threeways:1. With the front panel TRIG button when in the appropriatetrigger mode.2. Through a trigger pulse applied to the rear panel EXTER-NAL TRIGGER input connector when in an appropriate trlg-ger mode.3. With commands given over the IEEE bus as described in

Section 4.This section covers front panel end external triggering in detail.Also, included is a description of the Model 195 trigger outputpulse which can be used to trigger other instruments.2.7.1 Front Panel TriggeringFront panel triggering is done with the TRIG control. To usefront panel triggering perform the following steps:1. Enter the one-shot mode by depressing PRGM and TRIG(9) in sequence. The TRIG light will turn on and the decimalpoint on the display will cease flashing, indicating the instru-ment is in the oneshot trigger mode. While in this mode,no new readings are processed until a trigger stimulus isapplied.2. To trigger a single reading, depress end release the TRIGbutton once. The display decimal point will flash once andthe display will be updated with the most recent reading.The TRIG light goes out until the final, filtered reading isdisplayed.3. To continue processing readings, depress the TRIG button.One reading will be processed each time the TRIG button isoperated.4. To remove the instrument from the one-shot trigger mode,depress the PRGM and TRIG 19) buttons in sequence. The

TRIG light will go out end the display decimal point will fleat the conversion rate.NOTES:1. The PRGM, TRIG button sequence actually enters frpanel Program 9. The control sequence for this and otfront panel programs is described in more detail in Sect3.2. Each time the PRGM. TRIG button sequence is performthe instrument toggles between the continuous and oshot modes. This control sequence also affects IEEE triggering which is described in Section 4 .3. The front panel TRIG button can be used to control the reading data buffer. Each time the button is operated, reading is stored. These aspects are covered in Sectionend 4.4. The Model 195 must be in the correct tdgger mode,described in Section 4. before it will respond to a front pa

trigger stimulus. (The instrument is placed in the front pamods upon power-up.15. The display will continua to be updated during the filter pcessing pedod following the trigger stimulus; however, final filtered reading is not displayed until the TRIG liturns back on.6. Pressing any other front panel button will also triggerAID conversion.

2.7.2 External TriggerExternal trigger operates much like front panel triggering cept for the trigger stimulus its& In this caas. the triggerapplied to the rear panel BNC EXTERNAL TRIGGER connetor fsss Figure 2-Z). The input trigger pulse must conform TTL logic levels. Figure 2-3 shows the specifications for the put trigger pulse. To use external triggering, proceed follows:1. Connect the external trigger source to the rear panel BNEXTERNAL TRIGGER connector. The shield (outer) partthe connector is connected to digital common.

CAUTIONDo not exceed 30V between digital commonand chassis ground or damage to the lnstru-ment may occur.2. Place the instrument in the one-shot trigger mode depressing the PRGM end TRIG buttons in sequence. T

TRIG light will turn oh and the decimal point in the dispwill stop fleshing. The Model 195 will cease to procereadings while it is waiting for a trigger.3. To trigger the instrumant, apply a pulse to the EXTERNTRIGGER input. The instrument will process end dispone reading for sach input trigger pulse. The TRIG ligoes out until the fetal, filtered reading is displayed.4. To return the instrument to the continuous trigger mopress PRGM end TRIG in sequence. The TRIG light will out and the display decimal point will flesh at the conversirate.

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NOTES:1. External triggering can be used to control the fill rate of the100 readino buffer. One reading will be stored each time anexternal tribger pulse is received. See Sections 3 and 4.2. The Model 195 must be in appropriate trigger mode to re-spond to external triggering es described in Section 4.

TRlGGERSON NEGATIVEGOINGEDGE

CATION: DO not exceed normal l-m levslr.Figure 2-3. External Trigger Input Pulse Specifications

2.7.3 Voltmeter CompleteThe Model 195 has an available trigger pulse that can be usedto trigger other instrumentation. A single pulse, conforming tothe specifications in Figure 2-4, will appear at the VOLTMETERCOMPLETE output on the rear panel each time the Model 195completes a conversion. To use the VOLTMETER COMPLETEoutput, proceed as follows:1. Connect the Modal 195 to the instrument to be triggeredwith a suitable shieldsd cable. Use a standard BNC connec-tor to make the connect&f to the Model 195.

I.?111 r---nLHGnBEGIN NEXTREADING DONE INTEGRATION

LJ c l-n. OWFigure 2-4. Voltmeter Complete Output Pulse Specifi-cetlons

CAUTIONDo not exceed 30V between the VOLT-METER COMPLETE common (outer ring)and chassis ground or instrument damagemay occur.2. Select the desired function, range, trigger mode, and otheroperating parameters, es desired.3. In the continuous trigger modes, the instrument will outputpulses et the conversion rate: each pulse will occur after theModel 195 completes a conversion.4. In one of the one-shot trigger modes, the Model 195 willoutput a pulse once each time it is triggered after it com-pletes its reading.2.7.4 Triggering ExampleAs en example of using external input end output triggering,assume the Model 195 is to be used in conjunction with eKeith& Modal 230 Programmable Voltage Source. The Model230 can be programmed to output up to 100 voltage levels forgiven time periods. As each output voltage is applied, theModel 230 triggers the Model 195 to take a reading: When theModel 195 completes its reading, it triggers the Model 230 tooutput the next programmed voltage value, end the sequencerepeats automatically until all the readings have been taken.The readings can be stored in the Model 195 data buffer forrecall after the test is completed.To ss the Model 230 with the Model 195, perform the follow-ing steps:1. Connect the Model 195 to the Model 230 as shown in Figure2-5. Use suitable shielded cables with BNC connectors. TheModel 195 VOLTMETER COMPLETE OUTPUT should beconnected to the Model 230 EXTERNAL TRIGGER INPUT.The Model 195 EXTERNAL TRIGGER INPUT should beconnected to the Model 230 EXTERNAL TRIGGER OUT-PUT.2. Place both ins truments in the external tdgger mode.3. Connect both the Model 196 and the Model 230 to the cir-cuit under test. (See paragraph 2.8).4. Program the Model 230 with the desired output vo ltagesend dwell times. Set the Model 195 to the appropriate func-tion and range. If desired, enable the data buffer for readingstorage (See Section 31.5. Trigger the Model 195 with the front panel TRIG button.After the Model 195 has taken the reading, it will trigger the

Model 230 to advance to the next programmed value. Eachinstrument will trigger the other until all readings have beentaken.

pii&qTi$,

MODILlm MODrl,sFigure 2-5. External Trigger Connections

2-S

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2.8 BASIC MEASUREMENTSBasic measurement techniques for using the Model 195 tomeasure DC volts, resistance, and AC and DC current a re cov-ered in the following paragraphs .

NOTEAC voltage, and AC and DC current measure-ments can be made only if the Model 1950 optionis installed.Voltage measurements are made by connecting the sourcebetween the HI and LO VOLTS OHMS measurements. Twoterminal resistance measurements are made by connecting theresistance between the two VOLTS OHMS teminals. Four-terminal resistance measuremems require the use of both theVOLTS OHMS terminals and the OHMS SENSE terminals.Both AC and DC current measurements are made by connect-ing the source to the AMPS and VOLTS OHMS LO terminals.

WARNINGHazardous voltages may be present on theLO terminals. Any voltage applied to theVOLTS OHMS LO terminal will also be pre-sent on the OHMS SENSE LO terminal.The LO terminals on the Model 195 are designed to float fromchassis ground to