Keithley 195A User manual

Model 195A
Digital Multimeter
Instruction Manual
105A DIGriAt MULTIMETER
OHMS VOLTS
SENSE OHMS
laiiil
AUTO
msmsm DOWN
PROG
PRGM
Contains Operating and Servicing Information
KEITH LEY

WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for aperiod of 1year from date of
shipment.
Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries,
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 be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance of the origi-
nal warranty period, or at least 90 days.
LIMITATION OF WARRANTV
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 leakage, 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 APARTICULAR 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, INDI-
RECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND
SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY 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 DAMAGE TO PROPERTY.
KEITHLEY
Keithley Instruments, Inc. •28775 Aurora Road •Cleveland, OH 44139 •216-248-0400 •Fax: [phone] •http://www.keithley.com
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Model 195A Digital Multimeter
Instruction Manual
©1984, Keithley Instruments, Inc.
Test Instrumentation Group
All rights reserved.
Cleveland, Ohio, U.S.A.
April 1991, Sixth Printing
Document Number: 195A-901-01 Rev. F

SPECIFICATIONS
DC VOLTS
{SVz Digits) ACCURACYtt TEMPERATURE
±(%rdg +counts) COEFFICIENT
RANGE RESO- LUTION INPUT
RESISTANCE 24Hr.,
23°±1°C 1Yr.,
18°-28°C ±(%rdg +counts)/°C 0°-18°C &28°-50°C
20mV 100 nV >1G12 0.01+40 0.025 +40 0.003 +2
200mV 1fxV >1G12 0.01+ 60.025+ 60.003 +0.5
2VWfN >1G12 0.01+ 80.020+ 80.003 +0.5
20 V100 ^V 10M12 0.01+ 60.030+ 60.003 +0.5
200 VImV 10M12 0.01+ 80.025+ 80.003 +0.5
1000 VlOmV 10M12 0.01+ 60.025+ 60.003 +0.5
tAfter pushbutton or bus zeroing.
$ln digit mode, counts =±2 (except ±4 on 20mV range after zeroing).
NMRR: Greater than 60dB at 50 or 60Hz.
CMRR: Greater than 120dB at DC and 50 or 60Hz (with Ikfi in either lead).
MAXIMUM ALLOWABLE INPUT: 1000V peak.
BENCH READING RATE: 5readings/second.
OHMS
{SVz Digits) ACCURACYtt TEMPERATURE
±{%rdg +counts) COEFFICIENT
RANGE RESO- LUTION OUTPUT
1short Vopen 24Hr.,
123°±1°C 1Yr.,
18°-28°C ±(%rdg +counts)/°C
0°-18°C &28°-50°C
20 12 100/412 -2mA -2V 0.015 +25 0.025 +25 0.003 +2
200 12 1ml2 -2mA -2V 0.015 +70.025 +70.003 +0.5
2kl2 10ml2 -2mA -2V 0.015 +50.022 +50.003 +0.5
20 kl2 100ml2 -20 iiA -2V 0.015 +70.025 +70.003 +0.5
200 kl2 112 -20 /4A -2V 0.015 +50.022 +50.003 +0.5
2M12 10 12 -200 nA -2V 0.03 +70.050 +70.015+1
20M12 100 12 -200 nA -2V 0.06 +50.100 +50.025+1
tAfter pushbutton or bus zeroing.
tin 4y2-digit mode, counts= ±2 (except ±4 on 2012 range after zeroing).
CONFIGURATION: Automatic 2- or 4-terminal.
MAXIMUM ALLOWABLE INPUT: 360V peak or 250V rms.
BENCH READNG RATE: 3readings/second except 20M12 range, 1reading/second.
TEMPERATURE
(Sy2Digits)
TRMS AC VOLTS (Option 1950)
(5!^ Digits) ACCURACY (1 Year)t
±(%rdg +counts)
RESO- 18°-28°C
RANGE LUTION 20Hz-45Hz 45Hz-10kHz 10kHz-20kHz 20kHz-50kHz
200mV* 1/4V 0.8 +200 0.3 +200 0.7 +200 2.0 +300
2V10 /4V 0.8 +200 0.3 +200 0.7 +200 2.0 +250
20 V100 /iV 0.8 +200 0.3 +200 0.7 +200 1.5 +250
200 VImV 0.8 +200 0.3 +200 0.7 +200 1.5 +250
700 VlOmV 0.8 +200 0.3 +200 0.7 +200 1.5 +250
tiln 414 digit mode, divide count error by 10.
*Above ImV.
TEMPERATURE COEFFICIENT (0°-18°C &28°-50°C): Less than ±(0.1 xappli-
cable accuracy specification )/°C.
RESPONSE: True root mean square, AC coupled.
CREST FACTOR (ratio of peak to rms): Up to 3:1 allowable.
INPUT IMPEDANCE: 2M12 shunted by less than 75pF.
MAXIMUM ALLOWABLE INPUT: 1000V peak, IOVHz.
BENCH READING RATE: 3readings/second.
CMRR: Greater than 60dB at DC, 50 or 60Hz (with Ikfi in either lead).
BANDWIDTH: -3dB at 250kHz typical.
DC AMPS (Option 1950)
(514 Digits)
TEMPERATURE
RANGE RESO- LUTION
ACCURACY (1 YEAR)n
+(%rdg +counts)
18°-28°C
COEFFICIENT
±(%rdg +counts)/°C
0°-18°C &28°-50°C
MAXIMUM
VOLTAGE
BURDEN
20 ptA lOOpA 0.14+40t 0.01+2 0.03V
200 /4A InA 0.09+10 0.01+0.5 0.25V
2mA lOnA 0.09+10 0.01+0.5 0.25V
20mA lOOnA 0.09+10 0.01+0.5 0.25V
200mA I/4A0.09+10 0.01+0.5 0.28V
2AIO/4A0.09+10 0.01+0.5 1V
tin 4)4 digit mode, counts =±2 (except ±4 on 20/tA range after zeroing).
tAfter pushbutton or bus zeroing.
OVERLOAD PROTECTION: 2A fuse (250V), externally accessible.
BENCH READING RATE: 5readings/second.
4-WIRE TEMPERATURE
ACCURACY^ COEFFICIENT
RESO- ±(%rdg +counts) ±(%rdg-i-counts)/°C
SPAN LUTION 1YR„ 18”-28^C QQ-18°C &28°-50°C
°C
-200.00° to 230.00° 0.01° 0.03 +10 0.003 +0.4
230.00° to 630.00° 0.01° 0.03 +40 0.003 +4
-220.00° to -200.00° 0.01° 0.03 +40 0.003 +4
-328.00° to 446.00° 0.01° 0.03 -h 18 0.003 +0.7
446.00° to 1100.00° 0.01° 0.03 +72 0.003 +7
-360.00° to -328.00° 0.01° 0.03 +72 0.003 +7
^Autorange mode, excluding probe errors.
RTD TYPE: 10012 platinum; DIN 43 760 or IPTS-68, Programmable alpha and delta
3- or 4-wire.
MAXIMUM LEAD RESISTANCE (each lead): 4-wire: 2512.
3-wire: 1512.
SENSOR CURRENT: 1.0mA maximum, RMS.
BENCH READING RATE: 1.2 reading per second.
MAXIMUM COMMON MODE VOLTAGE: 500V (42V with Model 1951 connected).
COMMON MODE REJECTION: Less than 0.005°C/volt at DC, 50Hz and 60Hz
(10012 unbalance, LO driven).
MAXIMUM ALLOWABLE INPUT: 360V peak, 250V rms.
TRMS AC AMPS (Option 1950)
(5V2 Digits)
RANGE RESO-
LUTION
ACCURACY (1 YEAR)t*
45Hz-10kHz
±(%rdg +counts)
18°-28°C
TEMPERATURE
COEFFICIENT
±(%rdg +counts)/°C
0°-18°C &28°-50°C
MAXIMUM
VOLTAGE
BURDEN
200 fxA InA 0.6 +250 0.04+10 0.25V
2mA lOnA 0.6 +250 0.04+10 0.25V
20mA lOOnA 0.6 +250 0.04+10 0.25V
200mA 1/4A 0.6 +250 0.04+10 0.28V
2A10 /4A 0.6 +250 0.04+10 1V
tin 414 digit mode, divide count error by 10.
*Above 0.5% of range.
RESPONSE: True root mean square, AC coupled.
CREST FACTOR (ratio of peak to rms): Up to 3:1 allowable.
OVERLOAD PROTECTION: 2A fuse (250V), externally accessible.
BENCH READING RATE: 3readings/second.

IEEE-488 BUS IMPLEMENTATION
Multiline Commands: DCL, LLO, SDC, GET, GTL, UNT, UNL, SPE, SPD.
Uniline Commands: IFC, REN, EOl, SRQ, ATN.
Interface Functions: SHI, AH1, T5, TEO, L4, LEO, SRI, RL1, PPO, DC1,
DTI, CO, El.
Programmable Parameters: Range, Function, Zero, Integration Period, Averaging,
EOl, Trigger, Terminator, Delay*, 100-rdg. Storage, Calibration, Display, Multiplex
Off, Status, Service Request, Self Test, Output Format.
*First reading is correct when step input is coincident with trigger.
Conversion Rates (DC Volts):
MAXIMUM
USEABLE INTEGRATION TRIGGER TO READING
RESOLUTION PERIOD FIRST BYTE OUT RATEt
3V2 Digit 3.3 ms 17ms 76
472 Digit 16.66mst 30ms 36
572 Digit 100 ms 114ms 9
tReadings/second.
tZOms at 50Hz.
Address Modes: TALK ONLY and ADDRESSABLE.
FRONT PANEL PROGRAMS
0Clear— Cancels program mode.
1Non-Volatile RAM Storage—Store programs 3, 4, 5, 6and 8data in NVRAM
2Multiplex— Defeats input amplifier multiplexing.
3IEEE bus mode-ADDRESSABLE and TALK ONLY entry.
4Line Frequency— Selects 50Hz or 60Hz operation.
5Calibration —Performs digital calibration.
6Temperature-Allows °C and °F temperature measurements.
7Data Logger—Allows 100-reading storage at 9programmable rates; also stores
highest, lowest and average reading.
8Diagnostics—Troubleshooting aid and self-test.
9Trigger— Enables front panel or external triggering.
GENERAL
DISPLAY: Six 0.5" LED digits with decimal point, exponent and polarity. Function
and IEEE bus status also displayed.
RANGING: Manual or fast autoranging (150ms per range change on DCV).
ISOLATION: Input LO to IEEE LO or power line ground: 500V max, 5x10^
V«Hz; greater than lO^fi paralleled by 300pF.
WARMUP: 1hour to rated accuracy.
OPERATING ENVIRONMENT: 0°-50°C, 0% to 80% relative humidity up to 35°C.
STORAGE ENVIRONMENT: -25° to 65°C.
POWER: 105-125V or 210-250V (internal switch selected), 50Hz to 400Hz, 24V*A
maximum. 90-1 10V and 180-220V version available upon request.
CONNECTORS: Analog: Switch selectable front or rear, 5-way gold plated binding
posts. Digital: Trigger input and Voltmeter Complete output on rear panel, BNCs.
DIMENSIONS, WEIGHT: 127mm high x216mm wide x359mm deep (5" x872"
X141/8 "). Net weight 3.2kg (7 lbs.).
Specifications subject to change without notice.

TABLE OF CONTENTS
Paragraph Title
SECTION 1-GENERAL INFORMATION
1.1 Introduction
1.2 Model 195A Features
1.3 Warranty Information
1.4 Manual Addenda
1.5 Safety Symbols and Terms
1.6 Specifications
1.7 Unpacking and Inspection
1.8 Preparation For Use
1.8.1 Line Power
1.8.2 Line Voltage Selection
1.8.3 Line Frequency
1.8.4 IEEE Primary Address
1.8.5 Model 195A Option Preparation
1.9 Repacking For Shipment
1.10 Using the Model 195A Instruction Manual
1.11 Accessories
1.11.1 Model 1019 Rack Mounting Kit
1.1 1.2 Model 1600A High Voltage Probe
1.11.3 Model 1641 Kelvin Test Lead Set
1.11.4 Model 1651 50-Ampere Shunt
1.11.5 Model 1681 Clip-On Test Lead Set
1.11.6 Model 1682A RF Probe
1.1 1.7 Model 1683 Universal Test Lead Kit
1.11.8 Model 1685 Clamp-On AC Current Probe
1.11.9 Model 1691 General Purpose Test Lead Kit
1.11.10 Model 1950 AC Voltage; AC and DC Current Option ..
1.11.11 Model 1951 Input Adapter Box
1.11.12 Model 7008 IEEE-488 Cable
1.11.13 Model 8691 Connector Kit
1.11.14 Model 8693 General Purpose Emmersion Probe
1.11.15 Model 8695 Surface Probe
1.11.16 Model 8696 Air/Gas Probe
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SECTION 2-BASIC DMM OPERATION
2.1Introduction
2.2 Front Panel Familiarization
2.2.1 Controls
2.2.2 Terminals
2.2.3 Display and Indicators
2.2.4 Tilt Bail
2.3 Rear Panel Familiarization
2.3.1 Connectors and Terminals
2.3.2 INPUTS Switch
2.3.3 Fuses
2.4 Power-Up Procedure
2.5 Display Message
2.5.1 Overflow Indication
2.5.2 No Option Message
2.6 Control Selection
2.6.1 Function
2.6.2 Range
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TABLE OF CONTENTS (CONT.)
2.6.3 Using Zero
2.6.4 Filtering
2.6.5 Display Resolution
2.6.6 Input Terminal Selection
2.7 Triggering
2.7.1 Front Panel Triggering
2.7.2 External Trigger
2.7.3 Voltmeter Complete
2.7.4 Triggering Example
2.8 Basic Measurements
2.8. 1DC Voltage Measurements
2.8.2 Resistance Measurements
2.8.3 Temperature Measurements
2.8.4 AC Voltage Measurements
2.8.5 DC Current Measurements
2.8.6 AC Current Measurements
2.9 TRMS Considerations
2.9.1 TRMS Measurement Comparison
2.9.2 Crest Factor
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SECTION 3FRONT PANEL PROGRAMS
3.1 Introduction
3.2 Programming Controls
3.3 Front Panel Program Display Messages
3.4 Programming Notes
3.5 Program Description
3.5. 1Program 0. Clear
3.5.2 Program 1.Non-Volatile Storage
3.5.3 Program 2. Multiplex
3.5.4 Program 3. IEEE Address and Talk-Only Mode
3.5.5 Program 4. Line Frequency
3.5.6 Program 5. Digital Calibration
3.5.7 Program 6. Temperature Measurement
3.5.8 Program 7. Data Logger
3.5.9 Program 8. Diagnostics
3.5.10 Program 9. Trigger Mode
3.6 Programming Scaling Factors
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SECTION 4IEEE-488 OPERATION
4.1 Introduction
4.2 Bus Description
4.3 IEEE-488 Bus Lines
4.3.1 Bus Management Lines
4.3.2 Handshake Lines
4.3.3 Data Lines
4.4 Bus Commands
4.4.1 Uniline Commands
4.4.2 Universal Commands
4.4.3 Addressed Commands
4.4.4 Unaddress Commands
4.4.5 Device-Dependent Commands
4.5 Command Codes
4.6 Command Sequence
4.6.1 Addressed Command Sequence .
.
4.6.2 Universal Command Sequence ..
.
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TABLE OF CONTENTS (CONT.)
4.6.3
Device-Dependent Command Sequence
4.7 Hardware Considerations
4.7.1 Typical Controlled Systems
4.7.2 Bus Connections
4.7.3 Primary Address Programming
4.7.4 Talk-Only Mode
4.8 Software Considerations
4.8.1 Controller Interface Routines
4.8.2 HP-85 BASICStatements
4.8.3 Interface Function Codes
4.8.4 Model 195 Interface Commands
4.9 General Bus Command Programming
4.9.1 REN (Remote Enable)
4.9.2 IFC (Interface Clear)
4.9.3 LLO (Local Lockout)
4.9.4 GTL (Go To Local)
4.9.5 DCL (Device Clear)
4.9.6 SDC (Selective Device Clear)
4.9.7 GET (Group Execute Trigger)
4.9.8 Serial Polling (SPE, SPD)
4.10 Device-Dependent Command Programming
4.10.1 Execute (X)
4.10.2 Function (F)
4.10.3 Range (R)
4.10.4 Rate(S)
4.10.5 Zero Command (Z)
4.10.6 Filter
4.10.7 Triggering (T)
4.10.8 EDI (K)
4.10.9 Multiplex (A)
4.10.10 Delay (W)
4.10.11 Status Word (U)
4.10.12 SRQ Mode (M) and Status Byte Format
4.10.13 Buffer Command (Q and B)
4.10.14 Data Format (G)
4.10.15 Digital Calibration (D)
4.10.16 Non-Volatile Memory Storage (L)
4.10.17 Self Test (J)
4.10.18 Programming Terminator (Y)
4.10.19 Hit Button (H)
4.10.20 Display (D)
4. 1 1 Front Panel Error Messages
4.11.1 IDDC Error
4.11.2 IDDCO Error
4. 11.3 No Remote Error
4.12 Reading Rates
SECTION 5PERFORMANCE VERIFICATION
5.1 Introduction
5.2 Environmental Conditions
5.3 Recommended Test Equipment
5.4 Initial Conditions
5.5 Verification Procedure
5.5.1 DC Voltage Accuracy Check
5.5.2 Resistance Accuracy Check
5.5.3 AC Voltage Accuracy Check (with Model 1950 Option)
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iii

TABLE OF CONTENTS (CONT.)
5.5.4 DC Current Accuracy Check (with Model 1950 Option)
5.5.5 AC Current Accuracy Check (with Model 1950 Option)
5.5.6 Temperature Accuracy Check
SECTION 6THEORY OF OPERATION
6.1 Introduction
6.2 Overall Functional Description
6.3 Analog Circuitry
6.3.1 Input Switching and Multiplexer
6.3.2 Input Buffer Amplifier
6.3.3 -2V Reference Source
6.3.4 A/D Converter
6.4 Digital Circuitry
6.4. 1Microcomputer Block Diagram
6.4.2 Memory Mapping
6.4.3 Address Decoding
6.4.4 Microcomputer Reset
6.4.5 6522 VIA
6.4.6 IEEE Interface
6.4.7 Display Board
6.4.8 Serial-Parallel Conversion
6.5 Power Supply
6.6 Model 1950 AC/Current Option
6.7 Circuit Operation During Measurements
6.7.1 DC Voltage Measurement
6.7.2 Circuit Operation During Resistance Measurements
6.7.3 2- and 4-Terminal Resistance Considerations
6.7.4 Circuit Operation During Model 1950 Option Measurements
6.8 Temperature Measurement
6.8.1 RTD Resistance Measurement
6.8.2 FET Switching Sequence
6.8.3 Reading Calculations
SECTION 7MAINTENANCE
7.1 Introduction
7.2 Line Voltage Selection
7.3 Fuse Replacement
7.3.1 Line Fuse
7.3.2 Amps Fuse
7.4 Model 1950 AC/Amps Option Installation
7.5 Calibration
7.5.1 Recommended Calibration Equipment
7.5.2 Environmental Conditions
7.5.3 Warm-Up Period
7.5.4 DC Voltage Calibration
7.5.5 Resistance Calibration
7.5.6 AC Voltage Calibration
7.5.7 AC and DC Current Calibration
7.5.8 Temperature Calibration
7.5.9 Non-Volatile Storage of Calibration Constants
7.5.10 Calibration Jumpers
7.6 Special Handling of Static Sensitive Devices
7.7 Disassembly Instructions
7.8 Troubleshooting
7.8.1 Recommended Test Equipment
7.8.2 Power-Up Self Diagnostics
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IV

TABLE OF CONTENTS (CONT.)
7.8.3 Self Diagnostic Program
7.8.4 Power Supply Checks
7.8.5 A/D Converter and Display
7.8.6 Input Attenuator and Ohms Source Checks
7.8.7 Input Multiplexer and Buffer Amplifier
7.8.8 Digital Circuitry
7.8.9 Model 1950 AC/Amps Option
7.8.10 Buffer Amplifier Gain Checks
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SECTION 8REPLACEABLE PARTS
8.1 Introduction
8.2 Parts List
8.3 Ordering Information
8.4 Factory Service
8.5 Schematic Diagrams and Component Location Drawings
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V

LIST OF ILLUSTRATIONS
Figure Title Page
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Model 195A Front Panel
Model 195A Rear Panel
.
2-1
2-3
External Trigger Input Pulse Specifications
Voltmeter Complete Output Pulse Specifications
External Trigger Connections
DC Voltage Measurements
Two-Terminal Resistance Measurement
Four-Terminal Resistance Measurement
Model 195A Probe Wiring
Sensor Connections
AC Voltage Measurement
DC and AC Current Measurement
Front Panel Program Controls
IEEE Bus Configuration
IEEE Handshake Sequence
Command Code
System Types
IEEE-488 Connector
IEEE-488 Connections
Rear Panel of Model 195 Showing IEEE Connector
Contact Assignments
Typical IEEE-488 Bus Driver (One of 16)
SRQ Mask and Status Byte Formats
Data Format
Hit Button Command Numbers
IEEE Display Error Messages
Connections for Voltage Verification
Connections for Verification of 20fi, 2000, and 2k0 Ranges
Connections for Verification of 20k0 Through 20MO Ranges
Verification Connections for Current
2-8
2-8
2-10
2-11
2-11
2-12
2-12
2-13
2-14
~3-1
4-1
4-2
4-5
4-7
4-7
4-7
4-7
4-8
4-
8
4-21
4-23
4-25
4-26
'5-2
5-
3
5-3
5-4
Connections for Temperature Verification
Basic Block Diagram
Simplified Schematic of the Multiplexer
Simplified Schematic of the Input Buffer Amplifier
Simplified Schematic of the —2V Reference Source
Simplified A/D Converter Schematic
A/D Converter Integrator Output Waveform
Simplified Microcomputer Block Diagram
Ciruit Operation During DC Voltage Measurements
FET Switching Sequence During DC Voltage Measurements .. .
,
Resistance Measurement Simplified Circuit For20-200kf2 Ranges
FET Switching Sequence for20Q, 2000 and 2kfi Ranges
FET Switching Sequence for 20k0 and 200k0 Ranges
FET Switching Sequence for 2M0 and 20M0 Ranges
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 .
Simplifier Circuit of RTD Resistance Measurement
FET Switching Sequence
5-
6
6
-
2
6-3
6-4
6-5
6-5
6-6
6-8
6-11
6-12
6-13
6-13
6-13
6-14
6-14
6-14
6-15
6-15
6-16
6-17
6-18
vi

LIST OF ILLUSTRATIONS (CONT.)
7-1
7-2
7-3
7-4
7-5
7-6
7-
7
8
-
1
8-2
8-3
8-4
8-5
8-6
8-7
8-8
8-9
Model 1950 Installation
Voltage Calibration Connections
Connections for Calibration of 20Q and 2000 Ranges
Connections for Calibration of 2k0 Through 20MO Ranges
Location of Frequency Compensating Capacitors on Model 1950
Current Calibration Connections
Calibration Jumper Locations
Model 195 Exploded View
NVRAM Board, Component Location Drawing, Dwg. No. 195-160
Model 1950 AC Option, Component Location Drawing, Dwg. No. 1950-150
Mother Board, Component Location Drawing, Dwg. No. 195-100
Display Board, Component Location Drawing, Dwg. No. 195-110
NVRAM Board, Schematic Diagram
Mother Board, Schematic Diagram, Dwg. No. 195-106
Display Board, Schematic Diagram, Dwg. No. 195-116
Model 1950 AC Option, Schematic Diagram, Dwg. No. 1950-156
7-3
7-4
7-5
7-5
7-6
7-7
7-8
_8-2
8-11
8-13
8-15
8-19
8-21
8-23
8-31
8-33

LIST OF TABLES
Table Title Page
2-1 Power Up Test Error Messages
2-2 Range Determination
2-3 Filter Modes
2-4 Maximum Input Values
2-5 Resistance Range Output Values
2-6 Comparison of Average and TRMS Meter Reading
2-
7Comparison of Average and TRMS Meter Reading
3-
1Front Panel Program Summary
3-2 General Front Panel Program Messages
3-3 Program 3. IEEE Parameters
3-4 Program 7. Logging Rates
3-
5Programs. Tests
4-
1IEEE-488 Bus Command Summary
4-2 Hexadecimal and Decimal Command Codes
4-3 Typical Addressed Command Sequence
4-4 Typical Device-Dependent Command Sequence
4-5 IEEE Contact Designations
4-6 HP-85 IEEE-488 BASIC Statements
4-7 Model 195 Interface Function Codes
4-8 IEEE Command Groups
4-9 General Bus Commands
4-10 Default Conditions (Status Upon Power Up or After SDC or DCL)
4-1 1Device-Dependent Command Summary
4-12 Range Commands
4-13 Rate Commands
4-14 Filter Commands
4-15 Status Word Formats
4-16 SRQ Mask Commands
4-17 Status Byte Interpretation
4-
18 Buffer Rate Command Parameters
5-
1Recommended Test Equipment for Performance Verification
5-2 Limits for DC Voltage Verification
5-3 Limits for Resistance Verification
5-4 Limits for AC Voltage Verification
5-5 Limits for DC Current Verification
5-6 Limitsfor AC Current Verification
5-
7Limits for Temperature Verification
6-
1Integration Delay Periods
6-
2Model 195 Memory Mapping
7-
1Line Voltage Selection
7-2 Line Fuse Selection
7-3 Recommended Test Equipment for Calibration
7-4 DC Voltage Calibration Parameters
7-5 Parameters for Resistance Calibration
7-6 AC Voltage Calibration Parameters
7-7 Model 1950 Frequency Compensation Parameters
7-8 Current Calibration Parameters
7-9 Static Sensitive Devices
7-10 Static-Sensitive Devces
7-11 Recommended Troubleshooting Equipment
7-12 FET and Relay Switching Sequence for Various NModes
2-4
2-5
2-7
2-9
2-11
2-12
2-15
3-2
3-2
3-4
3-8
3-
9
4-
3
4-4
4-6
4-6
4-8
4-10
4-10
4-11
4-11
4-12
4-15
4-16
4-17
4-17
4-19
4-20
4-21
4-22
5-1
5-2
5-3
5-4
5-5
5-5
5-
6
6-
6
6-
7
7-
1
7-1
7-3
7-4
7-4
7-6
7-6
7-7
7-7
7-9
7-10
7-12
viii

LIST OF TABLES (CONT.)
7-13 Program 8. Tests
7-14 Power Supply Checks
7-15 A/D Converter Checks
7-16 Display Board Checks
7-17 DC Attenuator Checks
7-18 Ohms and -2V Reference Source Checks
7-19 Digital Circuitry Checks
7-20 Model 1950 Option Checks
7-
21 Buffer Amplifier Gain Checks
8-
1Index of Model 195 Schematics and Component Layouts
8-2 Mother Board, Parts List
8-3 NVRAM Board, Parts List
8-4 Display Board, Parts List
8-5 Model 1950 AC Optional Parts List
8-6 Mechanical Parts List
7-15
7-15
7-16
7-16
7-17
7-17
7-18
7-18
7-
19
'8-1
8-3
8-7
8-8
8-9
8
-
10
IX

SAFETY PRECAUTIONS
This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety
precautions required to avoid possible injury. Read over the manual carefully before operating this instrument.
Exercise extreme caution when ashock hazard is present at the instrument’s input. The American National Standards Institute
(ANSI) stetes that ashock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. Agood safety
practice is to expect that hazardous voltage is present in any unknown circuit before measuring.
Inspect the test leads for possible wear, cracks or breaks before each use. If any defects are found, replace with test leads that
have the same measure of safety as those supplied with the instrument.
For optimum safety do not touch the test leads or the instrument while power is applied to the circuit under test. Turn the
power off and discharge all capacitors, before connecting or disconnecting the instrument.
Do not touch any object which could provide acurrent path to the common side of the circuit under test or power line (earth)
ground. Always make measurements with dry hands while standing on adry, insulated surface, which is capable of with-
standing the voltage being measured.
Exercise extreme safety precaution when testing high energy power circuits (AC line or mains, etc.).
Do not exceed the instrument's maximum allowable input as defined in the specifications and operation section.
SAFETY PRECAUTIONS FOR HIGH ENERGY CIRCUITS
To optimize safety when measuring voltage in high energy distribution circuits, read and observe the directions in the follow-
ing warning.
WARNING
Dangerous arcs of an explosive nature in ahigh energy circuit can cause
severe personal injury or death. If the meter is connected to ahigh energy cir-
cuit when set to acurrent range, low resistance range or any other low im-
pedance range, the circuit is virtually shorted. Dangerous arcing can result
even when the meter is set to avoltage range if the minimum safety spacing
is reduced.
When making measurements in high energy circuits use test leads that meet the following requirements:
1. Test leads should be fully insulated.
2. Only use test leads that can be connected to the circuit (e.g. alligator or spade lugs) for ahands-off measurement.
3. Use test leads that do not reduce the arc protection by decreasing the voltage spacing betw^een conductors or terminals.
Use the following sequence when testing power circuit:
1.De-energize the circuit using the regular installed connect-disconnect device such as the circuit breaker, main switch, etc.
2. Attach the test leads to the circuit under test. Use appropriate safety rated leads for this application.
3. Set the DMM to the proper function and range.
4. Energize the circuit using the installed connect-disconnect device and make measurements without disconnecting the
DMM.
5. De-energize the circuit using the installed connect-disconnect device and make measurements without disconnecting the
DMM.
6. Disconnect the test leads from the circuit under test.
X

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 195A Digital Multimeter is afully programmable in-
strument with 5V2 digit resolution. In standard configuration,
the Model 195A is capable of DC voltage measurements be-
tween lOOnV and lOOOV on six ranges, 2-terminal and
4-terminal resistance measurements between 100/>tQ and
20Mfi on seven ranges and temperature measurements in the
range of -220°C and +630°C and betw^een -360°F and
-I- 1100°F. The instrument is designed to work with platinum
RTD probes, afactor which contributes to high accuracy.
With the optional Model 1950 ACV and AC and DC current
option installed, the Model 195A can make TRMS AC voltage
measurements between 1/iV and 700V on five ranges, TRMS
AC current measurements between 1nA and 2A on five
ranges and DC current measurements between 100pA and
2A on six ranges. The versatility of the Model 195A DMM is
further enhanced by the inclusion of astandard IEEE-488 in-
terface. Ahighlight of Model 195A operation is its digital
calibration feature which allows the user to easily perform
calibration from the front panel.
1.2 MODEL 19SA FEATURES
Some important Model 195A features include:
1. Standard IEEE-488 Interface. Astandard IEEE-488 inter-
face allows the Model 195A to be programmed from a
system controller; readings may also be 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 calibra-
tion and IEEE-488 parameters are easily entered from the
front panel.
3. Non-Volatile (NV) RAM Storage. Anon-volatile RAM
stores calibration constants, certain IEEE operating
parameters, and line frequency values even w'hen the
power is turned off.
4. Digital Calibration. The Model 195A may be easily
calibrated by applying an appropriate calibration signal
and running the front panel calibration program or by
commanding it over the bus. The calibration level may be
at full range, or at some value entered from the front
panel or over the IEEE bus.
5. Data Storage. Adata storage buffer is included to allow
up to 100 readings to be internally stored at auser-
selected rate. The buffer may be read and controlled from
the front panel or over the IEEE-488 bus. In the talk-only
mode, the output rate can also be programmed.
6. Front and Rear Panel Input Terminals. Input terminals 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 the rear panel
sw'itch.
7. Trigger Input and Output. The Model 195A may be trig-
gered to take readings by applying an external trigger
pulse or by pushing afront panel button. Aseparate out-
put pulse, which is active when the Instrument completes
areading, is also available on the rear panel.
8. Auto Ranging. The Model 195A includes afast auto
ranging feature for easier measurements.
9. Front Panel Zero. Asingle front panel zero control allows
the user to store aseparate zero offset for each measur-
ing function.
10.
Filtering. Digital filtering is selectable from the front panel
or bus.
Temperature measurement features include:
1. High Accuracy. Because platinum RTD probes have
predictable resistance change with temperature and are
highly linear, temperature measurements are made with a
greater degree of accuracy than is possible with ther-
mistor or thermocouple type probes.
2. Ease of Use. The temperature measuring mode is easily
entered from the front panel or over the IEEE bus.
Sophisticated software automatically measures the probe
resistance and calculates the reading.
3. Dual Scale Temperature Measurements. Temperature
readout may be obtained in either °C or °F. Readings are
available on the display and over the IEEE bus.
4. Front Panel Calibration. Temperature calibration may be
performed from the front panel. Probe errors can be
minimized with the calibration procedure.
5. Four Wire Resistance Measurements. Resistance
measurements using the 4-wire method minimize the ef-
fects of lead resistance.
6. Selectable 3-wire or 4-wire Operation. The instrument
may be used with either 3-wire or 4-wlre probes; the mode
of operation is easily changed from the front panel.
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 the nearest Keithley representative or the fac-
tory to determine the correct course of action. Keithley In-
struments maintains service facilities in the United States,
West Germany, Great Britain, France, the Netherlands,
Switzerland, and Austria. Information concerning the ap-
plication, operation, or service of your instrument may be
directed to the applications engineer at any of these loca-
tions. Check the inside front cover of this manual for ad-
dresses.
1-1

1.4 MANUAL ADDENDA
Information 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 SAFTEY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual or found on the Model 195A:
The symbol on the instrument indicates that the user
should refer to the operating instructions in this manual.
The symbol the Instrument Indicates that apotential
of 1000V or more may be present on the terminal(s). Stan-
dard safety 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 195A specifications may be found immediate-
ly preceding this section of the manual.
1.7 UNPACKING AND INSPECTION
The Model 195A DMM w^as carefully inspected, both
mechanically and electrically, before shipment. Upon receiv-
ing the Model 195A, carefully unpack all items from the ship-
ping carton and check for any obvious signs of physical
damage that might have occurred during shipment. Report
any damage to the shipping agent immediately. Retain the
original packing materials in case reshipment becomes
necessary. The following items are included with every Model
195A order:
•Model 195A DMM
•Model 195A Instruction Manual
•Additional accessories as ordered.
If an additional instruction manual is required, order the
manual package (Keithley Part Number 195A-901-00). The
manual package Includes an instruction manual and all perti-
nent addenda.
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 195A is designed to operate from 105-1 25V or
210-250V 50/60HZ AC power sources. Aspecial powder
transformer may be installed for 90-1 10V and 195-235V. 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 mate with the supplied 3-wire power
cord.
CAUTION
Do not attempt to operate the instrument
on asupply voltage outside the indicated
range, or damage to the instrument might
occur.
NOTE
The NMRR specification is at 50 or 60Hz,
±.1 %. For line frequencies out of this tolerance
the filter mode can be used to improve measure-
ment ability.
1.8.2 Line Voltage Selection
The operating voltage of the instrument is internally select-
able. Refer to Section 7Maintenance for information on set-
ting 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
If the Model 195A is to be connected to the IEEE-488 bus, it
must be programmed for the proper primary address. The
factory programmed value is 16, but the address may be
changed as described in Section 4.
1.8.5 Model 1950 Option Preparation
The Model 1950 option extends the capabilities of the Model
195A, allowing it to accurately measure AC voltage and AC
and DC current. The Model 1950 will be factory installed if it
was purchased with the Model 195A; however, the Model
1950 Is easily installed In the field, as described in Section 7.
1.9
REPACKING FOR SHIPMENT
Before shipping the Model 195A, the Instrument should be
wrapped in plastic and carefully packed in its original carton.
If the Model 195A must be returned to Keithley 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 it with the instrument.
1-2

1.10 USING THE MODEL 195A INSTRUCTION
MANUAL
This manual contains information necessary for operating,
programming, and servicing the Model 195A DMM and is
divided into the following sections:
1. Section 2contains 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
Section 3.
3. Information pertaining to the IEEE-488 bus, including
primary address selection, programming, and bus connec-
tions, is contained in Section 4.
4. For the more technically oriented, information on perfor-
mance verification, theory of operation, and maintenance
and servicing information is contained in Sections 5
through 8.
1.11 ACCESSORIES
Accessories which can be used with the Model 195A are
described in the following paragraphs.
1.11.1 Models 1019A and 1019S Rack Mounting Kits
The Model 1019A is auniversal fixed rack mounting kit for the
Model 195A. The Model 1019S Is aslide type universal rack
mounting kit.
1.11.2 Model 1600A High Voltage Probe
The Model 1600A extends the Model 195A measuring
capabilities to 40kV. The Model 1600A has a1000:1 division
ratio; aone-volt indication on the Model 195A corresponds to
aIkV input voltage.
1.11.3 Model 1641 Kelvin Test Lead Set
The Model 1641 test leads are used when making 4-terminal
resistance measurements. The leads are made up of two
twin-lead cables 1.2m (48 inches) in length. Each cable is ter-
minated by atwin banana plug on one end and aKelvin
spring-clip contact on the other end.
1.11.4 Model 1651 50-Ampere Shunt
The Model 1651 allows the Model 195A to make DC current
measurements up to 50A. With the Model 1950 option in-
stalled, the shunt can be used with the Model 195A to make
AC current measurements up to 50A as well. The Model 1651
consists of a0.0010 ±1%4-terminal resistance and operates
with the Model 195A by developing asmall measurable
voltage; a50A current wmII provide areading of 50mV on the
meter.
1.11.5 Model 1681 Clip-On Test Lead Set
The Model 1681 set contains tw^o leads 1.2m (48 inches) in
length. Each lead is terminated with abanana plug on one
end and aspring-action clip-on probe on the other end.
1.11.6 Model 1682A RF Probe
The Model 1682A is an RF probe that extends the AC
measuring capabilities of the Model 195A to include the
100kHz to 250MHz frequency range. Note that the probe
provides aDC output, so the Model 1950 option is not
necessary when making RF measurements. The Model
1682A provides aone-volt output for aone-volt RMS Input
when used wMth Instruments having an input impedance of at
least 10MQ.
1.11.7 Model 1683 Universal Test Lead Kit
The Model 1683 kit consists of tw^o test leads Im (4in.) in
length with 14 screw-in tips; four banana plugs, two spade
lugs, four alligator clips, two probes and tw'O phone tips.
1.11.8 Model 1685 Clamp-On AC Current Probe
The Model 1685 measures 50Hz and 60Hz AC currents up to
200A by clamping on to asingle conductor, eliminating the
need to open the circuit. The Model 1685 detects the current
through aconductor by measuring the magnetic field around
It. The output of the Model 1685 is 1V/A RMS.
1.11.9 Model 1691 General Purpose Test Lead Kit
The Model 1691 kit contains tw'O 0.9m (36in.) test leads; each
lead is terminated with aprobe tip on one end and abanana
plug on the other end.
1.11.10 Model 1950 AC Voltage; AC and DC Current
Option
The Model 1950 option expands the capabilities of the Model
195A, allowing it to measure TRMS AC voltage between I/4V
and 700V, TRMS AC current between InA and 2A, and DC
current betw^een lOOpA and 2A. The Model 1950 plugs into
the Model 195A for easy installation.
1.11.11 Model 1951 Input Adapter Box
The Model 1951 provides ameans of interfacing probes ter-
minated w'ith a4-wMre instrumentation connector to the
banana jacks on the instrument.
1.11.12 Model 7008 IEEE-488 Cable
The Model 7008 cables are useful for connecting the Model
195A to the IEEE-488 bus. The Model 7008-3 is 0.9m (3ft.) in
length and has astandard IEEE-488 connector on each end.
The Model 7008-6 is 1.8m(6ft.) in length.
1-3

1.11.13 Model 8691 Connector Kit
The Model 8691 Connector Kit contains amale 4-wire con-
nector, afemale 4-wire connector with attached coiled cable
(mates with connector on Model 1951), and male and female
3-wire adapters.
1.11.14 Model 8693 General Purpose Immersion Probe
The Model 8693 is ageneral purpose probe designed for im-
mersion in liquids as well as other general purpose applica-
tions. The Model 8693 measures between -220°C and
+630°C and has abasic tolerance of +0.3°C at 0°C.
1.11.15 Model 8695 Surface Probe
The Model 8695 probe is designed to measure the flat sur-
faces of solids in the range of -50°C to -i-260°C. The Model
8695 has abasic tolerance of ±0.3°C at 0°C.
1.11.16 Model 8696 Air/Gas Probe
The Model 8696 probe has an exposed junction within apro-
tective shroud. The measurement range of the Model 8696 is
between -50°C and -l-260°C; the probe has abasic tolerance
of ±0.3°C at 0°C.