Keithley 195 User manual

Model 195
Instruction Manual
Contains Operating and Servicing Information for the
Model 195 Digital Multimeter
Publication Date: August 1983
Document Number: 195-90%OIC

WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year from
date 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. You
will 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 balance
of the original warranty period, or at least 90 days.
LIMITATION OF WARRANTY
This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or misuse
of 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 IMPLIED
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN
ARE BUYER’S 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 DAMAGES’sHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS
OF 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

Instruction Manual
Model 195
Digital Multimater
01992, Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.

SPECIFICATIONS
MAXIMLIM ALLOWABLE INPUT: IWDV peak
BENCH 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&b”tto” orbusrrminx.
*I” wldktigitnwdr. counts-*2 bcept *t4 0” x-a rangeafterZerobIg,.
CONFRXJRATlON: Automatic 2- or 44erminal.
MAXM”M ALLOWABLE INT’DT: 36oVpeak or 250, nns.
BEN~NdEADWG RATE: 3 readb&sRand except2OMOrange, 1reading/
TRMS AC VOLTS (Option 19.50)
w/aEigiw ACCURACY(1YEAR),
*~%rd*+cwnal
,I” rv..di#t mode. divide cmlm error by 10. Above Irn”.
TEMPERAnJRE coEFFIclBNr loo-ISOC& 2ax5owz Leu tha” rt(O.lX
applicable accuracyspeeificatlonl/‘C.
RESPONSE:True mot mea” squarr, AC coupled.
CRESTFACTOR (ratio of peak to rmsl: Up to 3:l allowable.
INPUT IMPEDANCE: 2Mn shuntedby lea than 75pF.
MAXIMUM ALLOWABLE fNf%T: IWOV peak. IO’V.Hz.
BENCH READING RATE: 3 rexlii/seco”d.
CMRRzGreater than @dB at DC, 50 or 6OHz(with IkR in either lead).
BANDWIDTH: -3dB at 2SOkHztypical.
DC AMPS (Option 1950)
w/1wa, -TURF
ACamAcY(1YEAR,,* coEFRm MAnMuM
RESO *Pkd~+rounw
*,%rd*+cemw/‘c VOLTAGE
RANGE LvnON 18’28’C wwc b 28Be5oQc BmEN
20!A me. 0.14+40* 0.01+7. 0.03”
?m#t‘4 InA W-9+10 0.01+0.5 0.25v
2m.4 lti 0.09+10 0.0110.5 0.25v
x&A 0.09+10
222, 0.01+0.5 02.5v
0.09+10 0.01+0.5 0.28v
2.4 lOP.4 O.C9+lO o.ol+o.5 1 ”
t,n 4vdkit mode,coun*- *:2 kxapl 24 0” 2Qx.4nnxe afterzeroinn).
t4fm pushbuttonorbuszeroins.
OVERLOAD PROTECTION: 2A fuseLXOV), externally accessible
BENCH READING RATE: 5 r&i”gs/recond.
2.4 $4 Oh+353 0.04+10 1 v
,I” ‘Ivldt@tmode,dividecounte”vr by 10.Above0.5%Range.
RESPONSE:True mot meansquare, AC coupled.
CRESTFACTOR (ratio of peak to rms): Up to 3:l allowable.
OVERLOAD PROTECTION: 2A fure UOVI, externally acceaible.
BENCH READING RATE: 3 read&/second.
IEEE488 BUS IMPL!ZMENTATlON
MuMIne Cad: DCL, LLO, SIX. GET, GTL. LINT. UNL, SPE.SPD.
Unlllne Commands:IFC. REN. EOI. SRQ. ATN.
Interface Fwuttow: SHI, AHl. T5, TEO. L4, LEO,SRl. RLI, PPO,DCI,
DTI. co. El.
PTble Paramemr: Range.Function,Zero. integration Period, Ave+
EOI, T r. Terminator, Delay’, loo-rdg. Storage, Calibration,
i%i$,, Multl~Off. Status,ServtceRequest.SelfTest,Output Fannat.
‘First reading is cotsct when step input is c~incldemwith trigger.
Ccwemhm Rates(DC Volta): UbnnmmA
tReadt&&nd. V.&mat.%Hz.
Addrw Modes: TALK ONLY and ADDRESSABLE.
FRONT PANEL PROGRAMS
0 Clear - Camels program mode.
1 Non-volattle RAM st.,,age- Storeprograms3.4.5 and8datain NVRAM
2 MuhI lex - Defeatainput amplifier multlplexlw
3 IEEE1w mode- ADDRESSABLE and TALK ONLY entry.
4 Lhe frequency- Selects5si7. or tQH2 operation.
5 Caltbntlo” - Perfonnr digital calibration.
6 Extendedprognms - Enablerentry to aptiwal expanricn
7 Data lq&Sf7- Allows 1co.readlq storage*t 9 pm*amma rogams. POle rate%alw
storeshighest, lowest and average reading.
8 Dla~rtoatice- TmublesbooHngaid and self-test.
9 Trlggp: - Enablesfmnt panel or extemal tripgeflw.
GENERAL
DISPLAY: SIX0.5” LED digiti with de&md
ec?
oint,
Functionand IEEEbus statusalso display exponent and polarity.
- -.
ISOLATION: Input LO to IEEELO or
V*M; gnater tba” lO*Il paralleled owe?It&round: 5ooVA, 5 x lo’ ! y X’@F.
WARMup: 1 hour to rated accuracy.
OzTpG ENVIRONMENT: O”-5WC.0% to 80% relative humidity up
0
.- -- -.
STORAGE ENVIRONMENT: -25’ to 65%.
POWER: 10542sv or 21&?50v (internal switch &ctEd), 5042 to 4wfiz.
24V.A maximum. ‘9&llOV and lBo22OV version avatlable upon reauest.
CONNECTORS: Amlog: Stitch selectablefront or rear, 5wa; Sold piated
binding posts. Digttal: ‘Tririgger”input and %ltmeter Complete” output
on rear panel, BNCs.
DIMENSIONS, WEIGHT: 127mml&h X 216mmwide X 35%~” deep(5”
X 8’S” X 14%“).Net wetit 3.2kp.(7 Ibs.).

Safety Precautions
‘The following safety precautions should be observed before using
this 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 conditions
may 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 information
carefully before using the product.
The types of product users am:
Responsiblebody is the individual OIgroup responsible for the use
and maintenance of equipment, for ensuring that the equipment is
operated 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 be
trained in electrical safety procedures and proper use of the instm-
ment. They must be protected from electric shock and contact with
hazardous live circuits.
Maintenance personnel perform routine procedures on the product
N keep it operating, for example, setting the line voltage or mplac-
ing consumable materials. Maintenance procedures are described in
the manual. The procedures explicitly state if the operator may per-
form them. Otherwise, they should be performed only by service
personnel.
Servicepersonnel are trained to work on live circuits, and perform
safe installations and repairs of products. Only properly trained ser.
vice personnel may perfm’m installation and service procedures.
Exercise extreme caution when a shock hazard is present. Lethal
voltage may be present on cable connector jacks or tat fixtures. The
American National Standards Institute (ANSI) states that a shock
hazard exists when voltage levels greater than 3OV RMS, 42.4V
peak, or 60VDC are present. A good safety practice is to expect
that hazardous voltage ispresent in any unknown circuit before
measuring.
Users of this product must be protected from electric shock at all
times. The responsible body must ensure that users are prevented
accessand/or insulated from every connection point. In some cases,
connections must be exposed to potential human contact. Pmduct
users in these circumstances must be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating
ator above 1000 volts, no conductive part of the circuit may be
exposed.
As described in the International Electrotechnical Commission
@EC) Standard IEC 664, digital multimeter measuring circuits
(e.g., Keithley Models l75A, 199,ZOOQ2001, 2002, and 2010) are
Installation Category II. All other insmnnents’ signal terminals are
Installation Category I and must not he connected to mains.
Do not cmmect switching cards directly to unlimited power circuits.
They am intended to be used with impedance limited sources.
NEVER connect switching cards directly to AC mains. When con-
necting sourcesto switching cards, install protective devices to lim-
it fault current and voltage to the card.
Before operating an instrument, make sure the line cord is connect-
ed to a properly grounded power receptacle. Inspect the connecting
cables, test leads, and jumpers for possible wear, cracks, or breaks
before each use.
For maximum safety, do not touch the product, test cables, or any
other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
any capacitors before: connecting or disconnecting cables or jump-
ers, installing or removing switching cards, or making internal
changes, such as installing or removing jumpers.
Da not touch any object that could provide a current path to the
common side of the circuit under test or power line (earth) ground.
Always make measurements with dry hands while standing on a
dry, insulated surface capable of withstanding the voltage being
measured.

The instrument and accessories must be used in accordance with its
specifications 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, or
switching card.
When fuses are used in a product, replace with sametype and rating
for continued pmtection against fire hazard.
Chassis connections must only be used as shield connections for
measuring 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 a
lid interlock.
lfa@ screw is present, connect it to safety earth gmund using the
wire recommended in the user documentation.
Then symbol on an btstmment indicates that 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 of normal
and c~mrn~n mode voltages. Use standard safety precautions to
avoid personal contact with these voltages.
The WARNING heading in a manual explains dangers that might
result 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 could
damage 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 and
all test cables.
To maintain protection from electric shock and fire, replacement
components in mains circuits, including the power transformer, test
leads, and input jacks, must be purchased from Kcithley Ins&w
mats. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. Other components
that are not safety related may be purchased from other suppliers as
long asthey are equivalent to the original component. (Note that se-
lected pats should be purchased only through Keithley Instruments
to maintain accuracy and functionality of the product.) If you are
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.
To clean an insuument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill
on the instrument. Products that consist of a circuit board with no
case or chassis (e.g., data acquisition board for installation into a
computer) 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 proper
cleaning/servicing.
Rev. 7.199

TABLE OF CONTENTS
Paragraph Title Page
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.8.1
1.8.2
1.8.3
1.8.4
1.85
1.9
1.10
1.11
1.11.1
1.11.2
1.11.3
1.11.4
1.11.5
1.11.6
1.11.7
1.11.8
1.11.9
1.11.10
1.11.11
1.11.12
SECTION 1 GENERAL INFORMATION
Introduction .................................................................................
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 OPERATION
Introduction .................................................................................
FrontPanelFamiliarization .....................................................................
Controls ...................................................................................
Terminals ..................................................................................
Displayandlndicators .......................................................................
TiltBail ....................................................................................
RearPanelFamiliariration ......................................................................
ConnectorsandTerminals ...................................................................
INPUTSSwitch ............................................................................
Fuses .....................................................................................
Power-UpProcedure ..........................................................................
DisplayMessage ..............................................................................
OverflowIndication.. .......................................................................
NoOptionMessage .........................................................................
ControlSelection .............................................................................
Function ..................................................................................
Range ....................................................................................
UsingZero .................................................................................
Filtering ...................................................................................
DisplayResolution.. ........................................................................
InputTerminalSelection .....................................................................
Triggering.. .................................................................................
l-l
l-l
l-l
l-l
l-1
l-l
1-2
1-2
l-2
1-2
1-2
l-2
l-2
l-2
1-3
l-3
l-3
1-3
1-3
1-3
13
1-3
13
1-3
l-3
l-3
1-3
l-3
2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.3
2.3.1
2.3.2
2.3.3
2.4
2.5
2.5.1
2.5.2
Zl
2:6:2
2.6.3
2.6.4
2.6.5
2.6.6
2.7
2-l
2-1
2-1
2-2
2-2
2-2
2-2
2-3
2-3
2-3
2-3
24
El
2-6
2-5
2-6
2-5
2-6
2-7
2-7
2-7
i

2.7.1
2.7.2
2.7.3
2.7.4
2.8
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.9
2.9.1
2.9.2
t:
3:3
3.4
3.5
3.5.1
35.2
3.5.3
3.5.4
3.5.5
3.5.6
3.5.7
3.5.8
3.5.8
3.5.10
3.6
4.1
4.2
4.3
4.3.1
4.3.2
4.3.3
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5
4.5
4.6
4.6.1
4.6.2
4.8.3
4.7
4.7.1
4.7.2
4.7.3
4.7.4
4.8
4.8.1
4.8.2
TABLE OF CONTENTS (CONT.)
FrontPanelTriggering ....................................................................... 2-7
ExternalTrigger ............................................................................ 2-7
VoltmeterComplete.............................................................~ ........... 2-8
TriggeringExample ......................................................................... 2-8
BasicMeasurements.. ........................................................................ 2-9
OCVoltageMeasurements ................................................................... 2-9
ResistanceMeasurements .................................................................. 2-10
ACVoltageMeasurements .................................................................. 2-11
OCCurrentMeasurements .................................................................. 2-11
ACCurrentMeasurements .................................................................. 2-11
TRMSConsiderations ........................................................................ 2-12
TRMSMeasurementComparison ............................................................ 2-12
CrestFactor .............................................................................. 2-13
SECTION 3 FRONT PANEL PROGRAMS
Introduction ................................................................................. 3-l
ProgrammingControls ........................................................................ 3-1
Front Panel Program Display Messages .......................................................... 3-1
ProgrammingNotes ........................................................................... 3-1
ProgramDescription .......................................................................... 3-3
ProgramO.Clear ............................................................................ 3-3
Program 1. Non-Volatile Storage .............................................................. 3-3
Program2.Multiplex ........................................................................ 3-3
Program 3. IEEEAddress and Talk-Only Mode ................................................... 33
Program4.LineFrequency ................................................................... 3-4
Program 5. Digital Calibration ................................................................. 3-4
Program6.Expansion ........................................................................ 3-5
Program7.OataLogger.. ................................................................... 3-5
ProgramS.Oiagnostics ...................................................................... 3-7
ProgramS.TriggerMode .................................................................... 3-8
ProgremmingScalingFactors .................................................................. 3-8
SECTION 4 IEEE-488 OPERATION
Introduction ................................................................................. 4-l
BusDescription .............................................................................. 4-l
IEEE488BusLines ........................................................................... 4-2
SusManagementLines ...................................................................... 4-2
HandshakeLines ........................................................................... 4-2
DataLines ................................................................................. 4-3
BusCommends.. ............................................................................ 4-3
UnilineCommands .......................................................................... 4-3
UnivenalCommands ........................................................................ 4-3
AddressedCommands ...................................................................... 4-4
UnaddressCommands ...................................................................... 4-4
Device-DependentCommands ................................................................ 4-4
Command Codes ............................................................................. 44
CommandSequence .............................................................. . ........... 4-4
Addressed Command Sequence ............................................................... 46
UniversalCommandSequence ............................................................... 4-6
Device-Dependent Command Sequence ....................................................... 4-6
Hardwareconsiderations ...................................................................... 4-6
Typical Controlled Systems .................................................................. 4-6
BusConnections.. ......................................................................... 4-6
PrimaryAddressProgramming ................................................................ 4-8
Talk-Only Mode ............................................................................ 49
Softwareconsiderations ....................................................................... 4-9
Controller Interface Routines ................................................................. 4-9
HP-85BASlCStatements .................................................................... 4-9
ii

4.03
4.8.4
4.9
4.9.1
4.9.2
4.9.3
4.8.4
4.9.5
4.9.6
4.9.7
4.9.8
4.10
4.10.1
4.10.2
4.10.3
4.10.4
4.10.5
4.10.8
4.10.7
4.10.8
4.10.9
4.10.10
4.10.11
4.10.12
4.10.13
4.10.14
4.10.15
4.10.16
4.10.17
4.10.18
4.10.19
4.10.20
4.11
4.11.1
4.11.2
4.11.3
4.12
5.1
5.2
5.3
5.4
5.5
55.1
5.5.2
5.5.3
5.54
5.5.5
6.1
2
6:3.1
6.3.2
6.3.3
6.3.4
TABLE OF CONTENTS (CONT.1
InterfacaFunctionCodas ................................................................... 410
Model 195 Interface Commands .............................................................. 4-10
General Bus Command Programming ........................................................... 411
REN (Remote Enable) ...................................................................... 4-11
IFClInterfaceClear) ........................................................................ 4-11
LLOlLocalLockout) ....................................................................... 4-12
GTL(GoToLocall ......................................................................... 4-12
DCL(DeviceClear) ......................................................................... 4-12
SDC (Selective Device Clear) ................................................................ 412
GETlGroupExecuteTriggsrJ ................................................................ 4-13
Serial Polling (SPE, SPD) ................................................................... 413
Device-Dependent Command Programming ..................................................... 4-13
Execute(X) ............................................................................... 4-14
FunctionfF) ...................................................................... . ....... 4.14
Range(R) ................................................................................ 4-14
Rate(S) .................................................................................... 4-16
ZeroCommandIZ) ......................................................................... 4-17
Filter. .................................................................................... 4-17
Triggering (Tl ............................................................................. 4-17
EOIIK) ................................................................................... 4-18
Multiplex(A) .............................................................................. 4-18
Delay(W) ................................................................................ 4-18
StatusWord ........................................................................... 4-19
SRQ Mode (M) and Status Bvte Format. ...................................................... 4-20
BufferCommand (Qand El ................................................................. 4-21
DateFormat ........................................................................... 4-22
DigitalCalibration ......... ..i .......................................................... 4-23
Non-VolatileMemorvStoragefL) ............................................................ 4-24
SelfTest .............................................................................. 4-24
ProgrammingTerminator(Y). ............................................................ 4-24
HitBunonlH) ............................................................................. 4-26
Display(D) ............................................................................... 4-25
FrontPanelErrorMessages ................................................................... 426
IDDCError ............................................................................... 4-26
IDDCOError .............................................................................. 4-26
NoRemoteError .......................................................................... 4-26
ReadingRates .............................................................................. 4-27
SECTION 6 PERFORMANCE VERIFICATION
Introduction ................................................................................. 5-l
EnvironmentalConditions ...................................................................... 51
RecommendedTestEquipment ................................................................. 6-l
InitialConditions .............................................................................. 5-l
Verificationprocedure ......................................................................... 5-l
DCVoltageAccuracyCheck .................................................................. 5-2
ResistanceAccuracyCheck .................................................................. 52
AC Voltage Accuracy Check (with Model 1950 Option) ............................................ 6-3
DC Current Accuracy Check (with Model 1950 Option) ........................................... 6-4
AC Current Accuracy Check (with Model 1950 Option) ........................................... 6-6
SECTION 6 THEORY OF OPERATION
Introduction .................. . .............................................................. 6-l
Overall Functional Description ................................................................. 8-1
AnalogCircuitF/ .............................................................................. 6-l
InputSwitchingandMultiplexer .............................................................. 6-l
InputBufferAmpiifier ....................................................................... 8-3
-2VReferenceSource ....................................................................... 6-3
AIDConverter ............................................................................. 6-3
iii

6.4
6.4.1
6.4.2
6.4.3
6.4.4
6.4.5
6.4.6
6.4.7
6.4.8
:i
6:7
8.7.1
6.7.2
6.7.3
6.7.4
7.1
7.2
7.3
7.3.1
7.3.2
7.4
7.5
7.5.1
7.5.2
7.5.3
7.5.4
7.5.5
7.5.6
7.5.7
75.8
7.5.9
7.8
7.7
7.8
7.8.1
7.8.2
7.83
7.8.4
7.8.5
7.8.8
7.8.7
7.8.8
7.8.9
7.8.10
8.1
8.2
8.3
8.4
8.5
TABLE OF CONTENTS (CONT.1
DigitalCircuitry ............................................................................... 8-5
Microcomputer Block Diagram ................................................................ 8-5
MemoryMapping ........................................................................... 65
AddressDecoding.. ........................................................................ 6-5
MicrocomputerReset ....................................................................... 6-7
6522VIA .................................................................................. 6-7
IEEElnterface ............................................................................... 6-7
Display Board .............................................................................. 6-7
Serial-Parallel Conversion .................................................................... 6-7
PowerSupply ................................................................................ 6-8
Modell950AClCurrentOption ................................................................. 6-8
Circuit Operation During Measurements. ......................................................... 6-8
DCVoltageMeasurement .................................................................... 8-8
Circuit Operation During Resistance Measurements .............................................. 6-9
2- and 4-Terminal Resistance Considerations ................................................... 6-l 1
Circuit Operation During Model 1950 Option Measurements ....................................... .8-11
SECTION 7 MAINTENANCE
Introduction.. ............................................................................... 7-l
LineVoltageSelection ......................................................................... 7-1
FuseReplacement ............................................................................ 7-l
LineFuse...............................................................................~ .. 7-1
AmpsFuse ................................................................................ 7-2
Model 1950 AC/Amps Option Installation ........................................................ 7-2
CaObration ................................................................................... 7-3
Recommended Calibration Equipment ......................................................... 7-3
Environmental Conditions .................................................................... 7-3
WarmUpPeriod ........................................................................... 7-3
DCVoltageCalibration ...................................................................... 7-4
ResistanceCalibration ....................................................................... 74
ACVoltegeCalibration ...................................................................... 7-5
AC and DC Current Calibration ................................................................ 7-8
Non-Volatile Storage of Calibration Constants. .................................................. 7-6
CalibrationJumpers ......................................................................... 7-8
Special Handling of Static Sensitive Devices ...................................................... 7-7
Disassembly Instructions ....................................................................... 7-7
Troubleshooting ............................................................................ 7-0
RecommendedTestEquipment ............................................................... 7-8
Power-Up Self Diagnostics ................................................................... 7-8
SelfDiagnosticProgram ..................................................................... 7-9
PowerSupplyChecks ....................................................................... 7-9
A/DConverrerandDisplay ................................................................... 7-9
Input Attenuator and Ohms Source Checks ..................................................... 7-9
Input Multiplexer and Buffer Amplifier ......................................................... 7-9
Digital Circuitry. ............................................................................ 7-9
Modell950AC/AmpsOption.. .............................................................. 7-9
BufferAmplifierGainChecks ................................................................ 7-15
SECTION 8 REPLACEABLE PARTS
Introduction ................................................................................. El
PartsList .................................................................................... 8-I
Orderinglnformation .......................................................................... 9-l
Facton/Service ............................................................................... 8-l
Schematic Diaarams and Component Location Drawinas ........................................... 8-l
iv

LIST OF TABLES
Table Title Page
2-l
2-2
2-3
2-4
2-5
2-6
2-7
3-l
3-2
3-3
3-4
3-5
4-l
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
4-16
4-17
4-18
5-l
5-2
5-3
5-4
5-5
5-8
6-l
6-2
7-l
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
7-10
7-11
7-12
7-13
7-14
Power Up Test Error Messages
RangeDetermination .................................................................. 2-4
FilterModes.. .......................................................................... 2-5
...................................
Maximum Input Values ............................................ 2-6
........................................................................
Resistance Range Output Values 2-g
............................................................... 2-10
Four-wire Maximum Allowable Test Lead Resistance ..............................................
Comparison of Average and TRMS Meter Reading. 2-11
............................................... 2-12
Front Panel Program Summary ................................................................. 3-l
General Front Panel Program Messages .......................................................... 3-l
Program 3. IEEEParameters .................................................................... 3-4
Program 7. Logging Rates. ..................................................................... 3-7
ProgremE.Tests ............................................................................. 3-7
IEEE-488 Bus Command Summary .............................................................. 4-3
Hexadecimal and Decimal Commend Codes ...................................................... 4-4
Typical Addressed Command Sequence .......................................................... 4-6
Typical Device-Dependent Command Sequence ..................................................... 4-6
IEEEContactDesignations.. ................................................................... 4-8
HP-85 IEEE-488 BASIC Statements ............................................................ 4-10
Model 195 Interface Function Codes ............................................................ 4-10
IEEECommandGroups ....................................................................... 4-11
GeneralEusCommands.. .................................................................... 4-11
Default Conditions (Status Upon Power Up or After SDC or DCLI ................................... 4-12
Device-Dependent Command Summary ......................................................... 4-15
RangeCommands.. ......................................................................... 4-16
Rats Commands ............................................................................. 4-17
FilterCommends ............................................................................ 4-17
StatusWordFormats ........................................................................ 4-19
SRQMaskCommands ....................................................................... 4-20
Status Byte Interpretation ..................................................................... 4-21
Buffer Rate Commend Parameters ............................................................. 4-22
Recommended Test Equipment for Performance Verification ........................................ 5-l
LimitsforDCVoltsgeVeyiiication ............................................................... 5-2
Limits for Resistance Venfrcation ................................................................ 5-3
Limits for AC Voltage Verification ............................................................... 5-4
Limits for DC Current Verification ................................................................ 5-4
Limits for AC Current Verification
Integration Delay Periods ............................................................... 5-5
... ................................................................... 6-4
Model 195 Memory Mapping ................................................................... 6-5
LineVoltageSelection ......................................................................... 7-l
LineFuseSelection ........................................................................... 7-l
Recommended Test Equipment for Calibration .................................................... 7-3
DC Voltage Calibration Parameters .............................................................. 7-4
Psramstersfor Resistance Calibration. ........................................................... 7-4
AC Voltage Calibration Parameters .............................................................. 7-5
Model 1950 Frequency Compensation Parameters ................................................. 7-5
Current Calibration Parameters ................................................................. 7-6
StaticSensitiveDevices ....................................................................... 7-7
Recommended Troubleshooting Equipment ...................................................... 7-8
FETand Relay Switching Sequence for Various N Modes .......................................... 7-10
ProgramE.Tests ............................................................................ 7-12
PowerSupplyChecks ........................................................................ 7-13
AIDConvsrterChecks ....................................................................... 7-13

7-15
7-16
7-17
7-16
7-19
7-20
8-1
8-2
8-3
8-4
LIST 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
....... 8-8
LIST OF ILLUSTRATIONS
Figure Title Page
l-l
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
3-1
4-l
4-2
4-3
4-4
i-i
4-7
4-8
4-9
4-10
4-11
4-12
4-13
5-1
5-2
53
5-4
6-1
6-2
63
6-4
6-5
6-6
6-7
6-6
6-9
6-10
6-11
6-12
6-13
InstrumentPackaging.. ....................................................................... 1-2
Modell95FrontPanel ......................................................................... 2-1
Model195RearPanel ......................................................................... 2-2
External Trigger Input Pulse Specifications ........................................................ 2-8
Voltmeter Complete Output Pulse Specifications .................................................. 2-8
External Trigger Connections ................................................................... 2-8
DCVoltageMeasurements ..................................................................... 2-9
Two-Terminal Resistance Measurement, ........................................................ 2-10
Four-Terminal Resistance Measurement ......................................................... 2-10
ACVoltageMeasurement ..................................................................... 2-11
DC and AC Current Measurement ............................................................... 2-12
Front Panel Program Controls .................................................................. 3-2
IEEEBusConfiguration ........................................................................ 4-l
IEEEHandshakeSequence ..................................................................... 4-Z
CommandCode .............................................................................. 45
SvstemTvpes ................................................................................ 4-7
IEEE-488Connector ........................................................................... 4-7
IEEE-488Connections ......................................................................... 4-7
Rear Panel of Model 195 Showing IEEEConnector ................................................. 4-7
ContactAssignments ......................................................................... 4-8
Tvpical IEEE-488 Bus Driver (One of 16) .......................................................... 4-8
SRQ Mask and Status Byte Formats ............................................................ 4-21
DataFormat ................................................................................ 4-23
Hit Button Command Numbers ................................................................ 4-25
IEEEDisplayErrorMessages ................................................................... 4-26
Connections for Voltage Verification ............................................................. 5-2
Connections for Verification of ZOSI,2003, and 2kB Ranges ......................................... 6-3
Connections for Verification of 2OkDThrough 20MD Ranges. ........................................ 5-3
Verification Connections for Current ............................................................. 5-4
BasicBlockDiagram .......................................................................... 6-2
Simplified Schematic of the Multiplexer .......................................................... 8-3
Simplified Schematic of the Input Buffer Amplifier ................................................. 6-3
Simplified Schematic of the -2V Reference Source. ............................................... 6-4
Simplified A/D Converter Schematic ............................................................ 6-4
A/D Converter Integrator Output Waveform ...................................................... 6-4
Simplified Microcomputer Block Diagram ........................................................ 6-6
Ciruit Operation During DC Voltage Measurements ................................................ 6-9
FET Switching Sequence During DC Voltage Measurements ........................................ 6-9
Resistance Measurement Simplified Circuit For 20-200kD Ranges ................................... 6-10
FET Switching Sequence for 2OD.2000 and 2kD Ranges. .......................................... 6-10
FET Switching Sequence for 20kD and 200kD Ranges ............................................. 6-11
FET Switching Sequence for 2MD and 20MD Ranges. ............................................. 6-11
vi

6-14
6-15
6-16
6-17
7-l
7-2
7-3
7-4
7-5
7-6
7-7
i-i
8-2
8-3
8-4
8-5
8-6
8-7
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 2OODRanges ..............................................
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. 195100
Display 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 ...................................
6-11
6-12
8-12
6-12
7-3
7-4
74
7-5
7-6
7-6
7-7
8-2
8-10
511
El6
al7
8-25
827
vii/viii

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 195 System DMM is a fully programmable instru-
ment with 5’% digit resolution. In standard configuration, the
Model 195 is capable of DC voltage measurements between
1OOnVand 1OOOVon six ranges, and 2-teninal and 4-terminal
resistance measurements between lOO& and 20MD on seven
ranges. With the optional Model 1950 ACV and AC and DC
current option installed, the Model 195 can make TRMS AC
voltage measurements between 1pV and 700V on five ranges,
TRMS AC current measurements between InA and 2A on five
ranges. and DC current measurements between lOOpA and 2A
on six ranges. The versatilitv of the Model 195 DMM is further
enhanced bv the inclusion of a standard IEEE488 interface. A
highlight of Model 195 operation is its digital calibration feature
which allows the user to easily perform calibration from the
front panel.
1.2 MODEL 195 FEATURES
Some important Model 195 features include:
1. Standard IEEE-488 Interface. A standard IEEE-488 inter-
face allows the Model 195 to be programmed from a
system controller; readings may also ba transmitted over
the bus to other instrumentation in the talk-only mode.
2. Front Panel Programs. Numerous internal programs to
control various operating modes such as digital calibration
and IEEE488 parameters are easily entered from the front
panel.
3. Non-volatile (NV) RAM Storage. A non-volatile RAM
stores calibration constants, certain IEEE operating para-
meters, and line frequency values even when the power is
turned off.
4. Digital Calibration. The Model 195 may ba easily calibrated
by applying an appropriate calibration signal and running
the front panel calibration program or bv commanding it
over the bus. The calibration level may be at full range, or
;:ssprne value entered from the front panel or over the IEEE
5. Data Storage. A data storage buffer is included to allow up
to 100 readings to be internally stored at a user-selected
rate. The buffer may be read and controllad from the front
panel or over the IEEE-488 bus. In the talk-onlv mode, the
output rate can also be programmed.
6. Front and Rear Panel Input Terminals. Input teninals are
duplicated on the front and rear panels to allow easy con-
nections in both bench and rack-mounted situations. The
selected set of inputs is controlled by a rear panel switch.
7. Trigger Input and Output. The Model 195may be triggered
to take readings by applying an external trigger pulse or bv
pushing a front panel bunon. A separate output pulse.
which is active when the instrument completes a reading,
is also available on the rear panel.
8. Auto Ranging. The Model 195 includes a fast auto ranging
feature for easier measurements.
9. Front Panel Zero. A single front panel zaro control allows
the user to store a separate zero offset for each measuring
function.
10. Filtering. Digital filtering is selectable from the front panel
or bus.
1.3 WARRANTY INFORMATION
Warranty information may be found inside the front cover of
this manual. Should it become necessary to exercise the war-
ranty, contact your nearest Keithlev representative or the fac-
tofv to determine the correct course of action. Keithley Instm-
manta maintains service facilities in the United Statea, West
Germany, Great Britain, France, the Netherlands, Switzerland.
and Austria. Information concerning the application, opera-
tion, or service of your instrument may be directed to the ap
plications engineer at any of thase locations. Check the inside
front cover of this manual for addresses.
1.4 MANUAL ADDENDA
lnfonation concerning improvements or changes to the in-
strument which occur after the printing of this manual will be
found on an addendum sheet included with this manual. Be
sure to review these changes before attempting to operate or
service the instrument.
1.5 BAFH-Y SYMBOLS AND TERMS
The following safetv symbols and terms are usad in this
manual or found on the Model 195:
The symbol A on the instrument indicates that the user
should refer to the operating instructions in this manual:
Thesymbol & on the rnstmment indicates that a potential
of 1OOOVor more may be present on the terminal(s). Standard
safetv practices should be observed when such dangerous
voltages are encountered.
The WARNING heading in this manual explains dangers that
could result in personal injury or death.
The CAUTION heading in this manual explains hazards that
could damage the instrument.
1.6 SPECIFICATIONS
Detailed Model 195 specifications may be found immediately
preceding this section of the manual.
l-l

1.7 UNPACKING AND INSPECTION 1.9 REPACKING FOR SHIPMENT
The Model 195 System DMM was carefully inspected, both
mechanically and electrically, before shipment. Upon receiving
the Model 195, carefully unpack all items from the shipping
carton and check for any obvious signs of physical damage
that might have occurred during shipment. Report any dam-
age to the shipping agent immediately. Retain the original
packing materials in case reshipment becomes necessary. The
following items are included with every Model 195 order:
*Model 195 System DMM
*Model 195 Instruction Manual
*Additional accessories as ordered.
1.8 PREPARATION FOR USE
Once the instrument is unpacked, it must be connected to an
appropriate power source as described below.
1.8.1 Line Power
The Model 195 is designed to operate from 105125V or
210-250V 50/60HZ AC power sources. A special power trans
former may be installed for SO-11OVand 195235V. The factory
set value is marked on the instrument immediately above the
line cord receptacle on the rear panel. The line cord receptacle
is designed to mats with the supplied 3wire power cord.
CAUTION
Do not attempt to operate the instrument on
a supply voltage outside the indicated range,
or damage to the instrument might occur.
1.8.2 Line Voltame Selection
The operating voltage of the instrument is internally selectable.
Refer to Section 7. Maintenance for information on setting the
line voltage.
1.8.3 Line Frequency
The instrument will display the programmed line frequency
upon power up. The line frequency may be set by using a front
panel Program as described in paragraph 3.5.5.
1.8.4 IEEE Primary Address
Before shipping the Model 195, the instrument should be care
fully packed in its original carton as shown in Figure l-l, First,
wrap the instrument in plastic; once the instrument is in the
box, surround it with Styrofoam packing material.
If the Model 195 must be returned to Keithlsy Instruments for
repair or calibration, include the following:
*Write ATTENTION REPAIR DEPARTMENT on the shipping
label.
*Include the warranty status of the instrument.
*Complete the service form at the back of this manual and
return lt with the instrument.
CARDBOARD
STRIP
INSTRUCTION
PROTECTIVE
CARDBOARD
Lx] MODEL195
If the Model 195 is to be connected to the IEEE-488 bus, it
must be programmed for the proper primary address. The fac-
tory programmed value is 16, but the address may be changed
as de&bed in Section 4.
1.8.5 Model 1950 Option Preparation
The Model 1950 option extends the capabiliies of the Model
195. allowing it to acouratelv measure AC voltaae and AC and
DC current.The Model 1950 will be factory in&d if it was
purchased with the Model 195; however, the Model 1950 is
easily installed in the field, as described in Section 7. Figure 1-l. Instrument Packaging
l-2

1.10 USING THE MODEL 195 INSTRUCTION MANUAL
This manual contains information necessary for operating, pro-
gramming, and servicing the Model 195 System DMM and is
divided into the following sections:
1. Section 2 contains basic DMM operating information, in-
cluding front and rear panel layout and voltage. current and
resistance measurement procedures.
2. Front panel programming information may be found in Sec-
tion 3.
3. Information pertaining to the IEEE488 bus, including
primary 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 maintenance
and servicing information is contained in Sections5 through
8.
1.11 ACCESSORIES
Accessories which can be used with the Model 195 are
described in the following paragraphs.
1.11.1 Model 1301 Temperature Probe
The Model 1301 Temperature Probe converts the Model 195
into a digital thermometer capable of measuring temperatures
between -55°C and + 155eC. The output of the Model 1301 is
lmV/OC and it can be used with any DMM with a minimum
IOMC input impedance.
1.11.2 Models lOISA and 1019s Rack Mounting Kits
The Model 1019A is a universal fixed rack mounting kit for the
Model 195. The Model 1019s is a slide type universal rack
mounting kit.
1.11.3 Model IEOOA High Voltage Probe
The Model 18OOAextends the Model 195 measuring capabili-
ties to 40kV. The Model 18OOAhas a 1OOO:ldivision ratio: a
one-volt indication on the Model 195 corresponds to a 1kV in-
put voltage.
1.11.4 Model 1841 Kelvin Test Lead Set
The Model 1841 test leads are used when making 4-terminal
resistinca measurements. The leads are made up of two twin-
lead cables 1.2m (48 inches) in length. Each cable is terminated
by 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 Shunt
The Model 1851 allows the Model 195 to make DC current
measurements up to 50A. With the Model 1950 option install-
ed, the shunt can be used with the Model 195to 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 with
the Model 195 by developing a small measurable voltage; a
50A current will provide a reading of 50mV on the meter.
1.11.8 Model 1681 Clip-On Test Lead Set
The Model 1881 set contains two leads 1.2m (48 inches) in
length. Each lead is terminated with a banana plug on one end
and a spring-action clip-on probe on the other end.
1.11.7 Model 1682A RF Probe
The Model 1882A is an RF probe that extends the AC measur-
ing capabilities of the Model 195 to include the 1OOkHzto
250MHz frequency range. Note that the probe provides a DC
output, so the Model 1950 option is not necessary when mak-
ing RF measurements. The Model 1882A provides a one-volt
output for a one-volt RMS input when used with instruments
having an input impedance of at least IOMD.
1.11.8 Model 1683 Univereel Test Lead Kit
The Model 1883 kit consists of two tsst leads lm (4lnJ in
length with 14 screw-in tips; four banana plugs, two spade
lugs, four alligator clips, two probes and two phone tips.
1.11.9 Model 1685 Clamp-On AC Current Probe
The Model 1885 measures 50Hz and 80Hz AC currents up to
200A by clamping on to a single conductor, eliminating the
need to open the circuit. The Model 1885 detects the current
through a conductor by measuring the magnetic field around
it. The output of the Model 1885 is W/A RMS.
1.11.10 Model 1891 General Purpose Test Lead Kit
The Model 1891 kit contains two 0.9m (38in.) test leads; each
lead is terminated with a probe tip on one end and a banana
plug on the other end.
1.11.11 Model 1950 AC Voltage; AC and DC Current
Option
The Model 1950 option expands the capabilities of the Model
195, allowing it to measure TRMS AC voltage between l+’
and 7OOV,TRMS AC current between 1nA and 2A, and DC
current between IOOpA and 2-A. The Model 1950 plugs into
ths Model 195 for easy installation.
1.11.12 Model 7008 IEEE488 Cables
The Model 7008 cables are useful for connecting the Model
195 to the IEEE-498 bus. The Model 7009-3 is 0.9m Wt.1 in
length and has a standard IEEE488 connector on each end.
The Model 70086 is 1.8m (8ft.l in length.
l-3/1-4

SECTION 2
BASIC DMM OPERATION
2.1 INTRODUCTION
Model 195 operation is divided into three general categories:
basic bench operation, front panel program operation, and
IEEE-489 operation. Basic bench operation, which is covered
in this section, consists of using the Model 195 to perform
basic voltage, current, and resistance measurements. Front
panel and IEEE programming csn also be used to greatly en-
hance the capabilities of the instrument. These aspects are
covered in detail in Sections 3 and 4.
2.2 FRONT PANEL FAMILIARIZATION
The 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 following
paragraphs describe the purpose of each of these items in
detail.
2.2.1 Controls
All the front panel controls except POWER are momentary
contact switches. Many controls include an annunciator light
to 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 for
easier operation.
1. POWER-The POWER switch controls the AC power to
the instrument. Depressing and releasing the switch once
turns the power on. Depressing and releasing the switch a
second time turns the power off.
2. FUNCTION-The four FUNCTION pushbuttons control
the type of measurement such as voltage, current, or resis
tance as follows:
NOTE
The Model 195 cannot measure AC voltage or AC
or DC current without the Model 1950 option in-
stalled. Depressing the AMPS or AC buttons
without this option installed will result in a
“NoCP” message as described in paragraph
2.5.2.
VOLTS-The VOLTS button places the instrument in the
DC volts or AC volts (with the Model 1950 option) operating
modes. When the VOLTS button is depressed, the indicator
above the button turns on. indicating the instrument is set
for that mode.
OHMS-The OHMS button sets the Model 196 up to
measure resistance. When this button is depressed, the in-
dicator above the bunon turns on.
AMPS-With the Model 1950 option installed, the AMPS
button is used to place the instrument in the DC or AC cur-
DISPLAY DISPLAY IEEE
MANTISSA EXPONENT STATUS LIGHTS
OHMSVOLTS
CONTROL-I
ZERO R~SCU&~N PROGRAM RANGE
CONTROLS CONTROLS
FILTER TRIGGER
CONTROL CONTROL
Rgure 2-l. Model 195 Front Panel
2-l

rent mode. When the AMPS button is depress@, the indi:
cator above it tums on.
AC-When the Model 1959 is installed, the AC button
places the instrument in ths AC voltage or currant mode,
depending on the selection performed with the VOLTS or
AMPS buttons. Depraasing the AC bunon once turns the
AC indicator on; the instrument will measure en AC voltage
or current in this mode. Depressing the AC button a second
time turns the AC indicator off; the instrument measures a
DC voltage or current in this mode. Pressing AC whan in
the OHMS mode, places the instrument in the ACV mode.
3. RANGE-The RANGE buttons select the operating ranges
of the instrument. The range in uss can ba determined from
the dbplav dscknal Point and exponent value as described
in paragraph 2.6.2.
AUTO-The AUTO button places the instrument in the
autoranging mode. The instrument is operating in this mode
when the AUTO indicator is on. When in the autoranging
mode, the instrumant automatically selects the best range
to 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 instrument
moves uprange one increment.
4. MODIFIERS-The MODIFIER buttons control the zero,
filter and raaolutk~ modes of the instrument as described
b&w.
ZERO-The ZERO button controls a zero offset for baseline
suppression. Depressing the ZERO button once enables
zero as indicated by the ZERO light. Pressing ZERO a
second time disables the zero mode.
FILTER-The FILTER button controls the internal filter.
Pressing this button’once enables the filter: the indkator
light 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 display
resolution. Each time this button is operated, the resolution
changes to the eltamate mode.
5. TRIG-The TRIG button is used to trigger readings when
the instrument is in the front panel trigger mode. The TRIG
button will be operational only if the TRIG indicator light is
on. Tha instrumant may be placad in the correct trigger
mode through front panel Program 9 or through IEEEcom-
mands. One reading will be processed each time the TRIG
button is operated.
6. PROGRAM-The PROGRAM buttons are used with the
front panel programs as described in Section 3.
PROM-The PROM button is used as the first step in
entering front panel programs 0 through 9.
RECALL/ENT-The RECALL/ENT button is used to enter
and recall dare associated with the front panel programs.
2.2.2 Terminals
The terminals are used to connect the Model 195 to the
voltage, current, or resistance to be measured. Note that the
teninals are duplicated on the rear panel and that the rear
panel INPUTS swftch must be in the proper position for the
front panel terminals to be active.
1. VOLTS OHMS-The VOLT OHMS terminals are used
when making DC and AC (with the Model 1950) voltage
mmSummnt8 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 is
isolated from chassis gmund.
2. OHMS SENSE-The OHMS sense terminals are usad
when making &terminal resistance measurements.
3. AMPS-The AMPS terminal is used in conjunction with
the Model 1950 option to make DC and AC current meas-
urements.
2.2.3 Ciapley and Indicators
The function of the display and indicators is described below.
1. Display-The display consists of a 5% digit mantissa and a
single digit exponent. Both the mantissa and exponent usa
a leading minus sign to indicate negative’ valuaa. The sign
on the exponent changes to + for xero or positive values.
The range in use may ba determined from the position of
the decimal point and the exponent value as described in
paragraph 2.52. The flashing rate of the decimal point in-
dicates the conversion rate.
NOTE
The display will bs in the 5y2 digit mode upon
power-up.
2. IEEE Status Indicators-The REMOTE, TALK and
USTEN 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 lights
am not operational during front panel instrument operation.
2.24 Tilt Bail
The tilt bail, which is located on the bottom cover of the in&u-
mant, is useful for elevating the front of the instrument to a
convenient viewing height. To extend the bail, first rotate it
90“ away from the bottom cover and push down on the legs to
lock it into place. To retract the bail, pull the legs away from
the bottom cover and.then rotate the bail until it is flush with
the bottom cover.
2.3 REAR PANEL FAMILIARI2ATION
Figure 2-2 shows the rear panel layout of the Model 195.
2-2