Keithley 2750 Service Manual

Model 2750 Multimeter/Switch System

Service Manual

A GREATER MEASURE OF CONFIDENCE

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a
period of 3 years 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 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 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 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 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 Instruments, Inc.

BELGIUM: Keithley Instruments B.V. Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02/363 00 40 • Fax: [phone]
CHINA: Keithley Instruments China Yuan Chen Xin Building, Room 705 • 12 Yumin Road, Dewai, Madian • Beijing 100029 • 8610-62022886 • Fax: [phone]
FRANCE: Keithley Instruments Sarl 3, allée des Garays • 91127 Palaiseau Cedex • 01-64 53 20 20 • Fax: [phone]
GERMANY: Keithley Instruments GmbH Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: [phone]
GREAT BRITAIN: Keithley Instruments Ltd The Minster • 58 Portman Road • Reading, Berkshire RG30 1EA • 0118-9 57 56 66 • Fax: [phone]
INDIA: Keithley Instruments GmbH Flat 2B, WILOCRISSA • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: [phone]
ITALY: Keithley Instruments s.r.l. Viale S. Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: [phone]
NETHERLANDS: Keithley Instruments B.V. Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: [phone]
SWITZERLAND: Keithley Instruments SA Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: [phone]
TAIWAN: Keithley Instruments Taiwan 1 Fl. 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3572-9077 • Fax: [phone]

• 28775 Aurora Road • Cleveland, OH 44139 • 440-248-0400 • Fax: [phone] • http://www.keithley.com

9/00

Model 2750 Multimeter/Switch System

Service Manual

©2001, Keithley Instruments, Inc.

All rights reserved.

Cleveland, Ohio, U.S.A.

First Printing, March 2001

Document Number: 2750-902-01 Rev. A

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created
for this manual. The Revision Level letter increases alphabetically as the manual undergoes sub­sequent updates. Addenda, which are released between Revisions, contain important change in­formation that the user should incorporate immediately into the manual. Addenda are numbered
sequentially. When a new Revision is created, all Addenda associated with the previous Revision
of the manual are incorporated into the new Revision of the manual. Each new Revision includes
a revised copy of this print history page.

Revision A (Document Number 2750-902-01).............................................................. March 2001

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.
Other brand names are trademarks or registered trademarks of their respective holders.

Safety Precautions

The following safety precautions should be observed before using this product and any associated in­strumentation. Although some instruments and accessories would normally be used with non-hazardous
voltages, there are situations where hazardous conditions may be present.

This product is intended for use by qualified personnel who recognize shock hazards and are familiar
with the safety precautions required to avoid possible injury. Read the operating information carefully
before using the product.

The types of product users are:

Responsible body

ensuring that the equipment is operated within its specifications and operating limits, and for ensuring
that operators are adequately trained.

Operators

and proper use of the instrument. They must be protected from electric shock and contact with hazardous
live circuits.

Maintenance personnel

setting the line voltage or replacing consumable materials. Maintenance procedures are described in the
manual. The procedures explicitly state if the operator may perform them. Otherwise, they should be
performed only by service personnel.

Service personnel

ucts. Only properly trained service personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that are rated Installation Category I and
Installation Category II, as described in the International Electrotechnical Commission (IEC) Standard
IEC 60664. Most measurement, control, and data I/O signals are Installation Category I and must not
be directly connected to mains voltage or to voltage sources with high transient over-voltages. Installa­tion Category II connections require protection for high transient over-voltages often associated with lo­cal AC mains connections. The user should assume all measurement, control, and data I/O connections
are for connection to Category I sources unless otherwise marked or described in the Manual.

Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable con­nector jacks or test fixtures. The American National Standards Institute (ANSI) states that a shock haz­ard exists when voltage levels greater than 30V RMS, 42.4V peak, or 60VDC are present.

practice is to expect that hazardous voltage is present 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 access and/or insulated from every connection point. In some cases, con­nections must be exposed to potential human contact. Product users in these circumstances must be
trained to protect themselves from the risk of electric shock. If the circuit is capable of operating at or
above 1000 volts,

Do not connect switching cards directly to unlimited power circuits. They are intended to be used with
impedance limited sources. NEVER connect switching cards directly to AC mains. When connecting
sources to switching cards, install protective devices to limit fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connected to a properly grounded power re­ceptacle. Inspect the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks be­fore each use.

When installing equipment where access to the main power cord is restricted, such as rack mounting, a
separate main input power disconnect device must be provided, in close proximity to the equipment and
within easy reach of the operator.

is the individual or group responsible for the use and maintenance of equipment, for

use the product for its intended function. They must be trained in electrical safety procedures

are trained to work on live circuits, and perform safe installations and repairs of prod-

no conductive part of the circuit may be exposed.

perform routine procedures on the product to keep it operating, for example,

A good safety

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 jumpers, installing or removing switching cards, or making internal
changes, such as installing or removing jumpers.

Do 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 instructions
or the safety of the equipment may be impaired.

Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications
and operating information, and as shown on the instrument or test fixture panels, or switching card.

When fuses are used in a product, replace with same type and rating for continued protection 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 applied to the device under test. Safe operation
requires the use of a lid interlock.

If a screw is present, connect it to safety earth ground using the wire recommended in the user documentation.

!

The symbol on an instrument indicates that the user should refer to the operating instructions located in
the manual.

The symbol on an instrument shows that it can source or measure 1000 volts or more, including the com­bined effect of normal and common mode voltages. Use standard safety precautions to avoid personal contact
with these voltages.

The

WARNING

read the associated information very carefully before performing the indicated procedure.

The

CAUTION

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 Keithley Instruments. 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 as they are equivalent to the original
component. (Note that selected parts 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 instrument, 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 instructions. If the board becomes contami­nated and operation is affected, the board should be returned to the factory for proper cleaning/servicing.

heading in a manual explains dangers that might result in personal injury or death. Always

heading in a manual explains hazards that could damage the instrument. Such damage may

Rev. 2/01

Table of Contents

1 Performance Verification

Introduction ................................................................................ 1-2

Verification test requirements ..................................................... 1-3

Environmental conditions ................................................... 1-3

Warmup period .................................................................... 1-3

Line power .......................................................................... 1-3

Recommended test equipment ................................................... 1-4

Verification limits ....................................................................... 1-5

Example reading limit calculation ...................................... 1-5

Calculating resistance reading limits .................................. 1-5

Restoring factory defaults .......................................................... 1-6

Performing the verification test procedures ............................... 1-6

Verification test summary ................................................... 1-6

Test considerations .............................................................. 1-7

Model 2750 verification ............................................................. 1-8

Verifying DC voltage .......................................................... 1-8

Verifying AC voltage ......................................................... 1-10

Verifying DC current ......................................................... 1-11

Verifying AC current ......................................................... 1-13

Verifying normal resistance .............................................. 1-14

Verifying dry circuit resistance ......................................... 1-16

Verifying temperature ....................................................... 1-18

Verifying frequency .......................................................... 1-20

Model 7700 verification ........................................................... 1-20

Verifying DC voltage ........................................................ 1-21

Verifying AC voltage ......................................................... 1-22

Verifying DC current ......................................................... 1-24

Verifying AC current ......................................................... 1-25

Verifying normal resistance .............................................. 1-26

Verifying dry circuit resistance ......................................... 1-28

Verifying temperature ....................................................... 1-31

Verifying frequency .......................................................... 1-34

Verifying ratio and average ............................................... 1-35

2 Calibration

Introduction ................................................................................ 2-2

Environmental conditions ........................................................... 2-2

Warmup period .................................................................... 2-2

Line power ........................................................................... 2-2

Calibration considerations .......................................................... 2-3

Calibration code .......................................................................... 2-4

Front panel calibration code ................................................ 2-4

Remote calibration code ...................................................... 2-4

Comprehensive calibration ......................................................... 2-5

Calibration cycle .................................................................. 2-5

Recommended equipment ................................................... 2-5

Aborting calibration ............................................................ 2-6

Front panel calibration ........................................................ 2-6

Remote calibration ............................................................ 2-14

Manufacturing calibration ........................................................ 2-20

Recommended test equipment .......................................... 2-20

Extender board preparation ............................................... 2-20

Unlocking manufacturing calibration ................................ 2-21

Measuring function generator signal amplitude ................ 2-21

Front panel manufacturing calibration .............................. 2-21

Remote manufacturing calibration .................................... 2-22

Model 7700 calibration ............................................................. 2-23

Recommended test equipment .......................................... 2-23

Extender board connections .............................................. 2-24

Model 7700 calibration ..................................................... 2-24

3 Routine Maintenance

Introduction ................................................................................ 3-2

Setting the line voltage and replacing the line fuse .................... 3-2

Replacing the AMPS fuse ........................................................... 3-4

Replacing Model 7700 plug-in module amps fuses ................... 3-5

Replacing non-volatile RAM battery ......................................... 3-6

Replace the battery as follows: ............................................ 3-7

Plug-in module relay closure count ............................................ 3-8

Closure count commands .................................................... 3-8

Reading relay closure count ................................................ 3-8

Resetting relay closure count .............................................. 3-9

Setting count update interval ............................................... 3-9

Rack mounting .......................................................................... 3-10

Rack mount kit .................................................................. 3-10

Rack mount procedure ...................................................... 3-10

4 Troubleshooting

Introduction ................................................................................ 4-2

Repair considerations ................................................................. 4-2

Power-on self-test ....................................................................... 4-3

Front panel tests ......................................................................... 4-3

KEY test .............................................................................. 4-3

DISP test ............................................................................. 4-3

Principles of operation ............................................................... 4-4

Power supply ....................................................................... 4-4

Display board ...................................................................... 4-6

Digital circuitry ................................................................... 4-7

Analog circuitry .................................................................. 4-8

Troubleshooting ....................................................................... 4-13

Display board checks ........................................................ 4-13

Power supply checks ......................................................... 4-13

Digital circuitry checks ..................................................... 4-14

Analog signal switching states .......................................... 4-15

No comm link error .................................................................. 4-23

5 Disassembly

Introduction ................................................................................ 5-2

Handling and cleaning ............................................................... 5-2

Handling PC boards ............................................................ 5-2

Solder repairs ...................................................................... 5-2

Static sensitive devices ........................................................ 5-3

Assembly drawings .................................................................... 5-3

Disassembly procedures ............................................................. 5-4

Case cover removal ............................................................. 5-4

Motherboard removal .......................................................... 5-4

Card cage removal .............................................................. 5-5

Front panel disassembly ...................................................... 5-5

Removing power components ............................................. 5-5

Instrument reassembly ............................................................... 5-6

Input terminal wire connections .......................................... 5-6

Power module wire connections ......................................... 5-7

6 Replaceable Parts

Introduction ................................................................................ 6-2

Parts lists .................................................................................... 6-2

Ordering information ................................................................. 6-2

Factory service ........................................................................... 6-2

Component layouts .................................................................... 6-3

A Specifications

B Calibration Reference

Introduction ............................................................................... B-2

Command summary ................................................................... B-2

Miscellaneous calibration commands ........................................ B-4

DC calibration commands ......................................................... B-8

AC calibration commands ....................................................... B-13

Manufacturing calibration commands ..................................... B-15

Model 7700 calibration commands ......................................... B-16

Remote error reporting ............................................................ B-21

Error summary .................................................................. B-21

Error queue ....................................................................... B-24

Status byte EAV (Error Available) bit .............................. B-25

Generating an SRQ on error ............................................. B-25

Detecting calibration step completion ..................................... B-25

Using the *OPC? query .................................................... B-25

Using the *OPC command ............................................... B-26

Generating an SRQ on calibration complete .................... B-26

C Calibration Program

Introduction ............................................................................... C-2

Computer hardware requirements ............................................. C-2

Software requirements ............................................................... C-2

Calibration equipment ............................................................... C-2

General program instructions .................................................... C-3

List of Illustrations

1 Performance Verification

Figure 1-1 Connections for Model 2750 DC volts verification ............... 1-9

Figure 1-2 Connections for Model 2750 AC volts verification ............. 1-10

Figure 1-3 Connections for Model 2750 DC current verification ......... 1-12

Figure 1-4 Connections for Model 2750 AC current verification .......... 1-13

Figure 1-5 Connections for Model 2750 resistance verification

(1Ω to 10MΩ ranges) .......................................................... 1-14

Figure 1-6 Connections for Model 2750 resistance verification

(100MΩ range) .................................................................... 1-15

Figure 1-7 Connections for Model 2750 dry circuit

resistance verification .......................................................... 1-17

Figure 1-8 Connections for Model 2750 frequency verification ........... 1-20

Figure 1-9 Connections for Model 7700 DC volts verification ............. 1-21

Figure 1-10 Connections for Model 7700 AC volts verification ............. 1-22

Figure 1-11 Connections for Model 7700 DC current verification ......... 1-24

Figure 1-12 Connections for Model 7700 AC current verification .......... 1-25

Figure 1-13 Connections for Model 7700 resistance verification

(1Ω to 10MΩ ranges) .......................................................... 1-27

Figure 1-14 Connections for Model 7700 resistance verification

(100MΩ range) .................................................................... 1-27

Figure 1-15 Connections for Model 7700 dry circuit

resistance verification .......................................................... 1-29

Figure 1-16 Connections for Model 7700 thermocouple

temperature verification ....................................................... 1-31

Figure 1-17 Connections for Model 7700 frequency verification ........... 1-34

Figure 1-18 Connections for Model 7700 ratio and

average verification .............................................................. 1-35

2 Calibration

Figure 2-1 Low-thermal short connections .............................................. 2-7

Figure 2-2 Connections for DC volts and ohms calibration .................... 2-8

Figure 2-3 Connections for DC and AC amps calibration ..................... 2-11

Figure 2-4 Connections for AC volts calibration ................................... 2-12

Figure 2-5 Function generator connections

for manufacturing calibration .............................................. 2-22

3 Routine Maintenance

Figure 3-1 Power module ........................................................................ 3-3

Figure 3-2 AMPS fuse ............................................................................. 3-4

Figure 3-3 Model 7700 amps fuses ......................................................... 3-5

Figure 3-4 Rack preparation .................................................................. 3-11

4 Troubleshooting

Figure 4-1 Power supply block diagram .................................................. 4-4

Figure 4-2 Digital circuitry block diagram .............................................. 4-6

Figure 4-3 Analog circuitry block diagram ............................................. 4-9

Figure 4-4 Simplified schematic of dry circuit ohms ............................. 4-12

C Calibration Program

Figure C-1 Model 2750 calibration program ........................................... C-3

List of Tables

1 Performance Verification

Table 1-1 Recommended verification equipment .................................. 1-4

Table 1-2 DCV reading limits ................................................................ 1-9

Table 1-3 ACV reading limits .............................................................. 1-11

Table 1-4 DCI limits ............................................................................ 1-12

Table 1-5 ACI limits ............................................................................. 1-13

Table 1-6 Limits for normal resistance verification ............................. 1-16

Table 1-7 Limits for Model 2750 dry resistance verification ............... 1-18

Table 1-8 Thermocouple temperature verification reading limits ........ 1-19

Table 1-9 Four-wire RTD temperature verification reading limits ...... 1-19

Table 1-10 Plug-in module DCV reading limits .................................... 1-22

Table 1-11 Plug-in module ACV reading limits .................................... 1-23

Table 1-12 Plug-in module DCI limits ................................................... 1-25

Table 1-13 Plug-in module ACI limits ................................................... 1-26

Table 1-14 Limits for plug-in module normal resistance verification ... 1-28
Table 1-15 Limits for plug-in module dry circuit

Table 1-16 Model 7700 thermocouple temperature

Table 1-17 Plug-in module four-wire RTD temperature

resistance verification .......................................................... 1-30

verification reading limits .................................................... 1-32

verification reading limits .................................................... 1-33

2 Calibration

Table 2-1 Recommended equipment for comprehensive calibration ..... 2-5

Table 2-2 Comprehensive calibration procedures .................................. 2-7

Table 2-3 DC volts calibration summary ............................................... 2-9

Table 2-4 Ohms calibration summary .................................................. 2-10

Table 2-5 DC current calibration summary .......................................... 2-11

Table 2-6 AC voltage calibration summary ......................................... 2-12

Table 2-7 AC current calibration summary .......................................... 2-13

Table 2-8 DC voltage calibration programming steps ......................... 2-16

Table 2-9 Resistance calibration programming steps .......................... 2-16

Table 2-10 DC current calibration programming steps .......................... 2-17

Table 2-11 AC voltage calibration programming steps ......................... 2-18

Table 2-12 AC current calibration programming steps .......................... 2-19

Table 2-13 Recommended equipment for manufacturing calibration ... 2-20

Table 2-14 Recommended equipment for Model 7700 calibration ....... 2-23

3 Routine Maintenance

Table 3-1 Power line fuse ....................................................................... 3-3

Table 3-2 Closure count commands ....................................................... 3-8

4 Troubleshooting

Table 4-1 Power supply components ...................................................... 4-5

Table 4-2 Display board checks ........................................................... 4-13

Table 4-3 Power supply checks ............................................................ 4-13

Table 4-4 Digital circuitry checks ........................................................ 4-14

Table 4-5 DCV signal switching .......................................................... 4-15

Table 4-6 ACV and FREQ signal switching ........................................ 4-16

Table 4-7
Table 4-8
Table 4-9
Table 4-10
Table 4-11

Table 4-12 DCA signal switching .......................................................... 4-20

Table 4-13 ACA signal switching .......................................................... 4-20

Table 4-14 DCV signal multiplexing and gain ....................................... 4-21

Table 4-15 ACV and ACA signal multiplexing and gain ....................... 4-21

Table 4-16 DCA signal multiplexing and gain ....................................... 4-21

Table 4-17
Table 4-18
Table 4-19

Table 4-20 Switching device locations ................................................... 4-23

Ω

2 signal switching .............................................................. 4-17

Ω

4 signal switching .............................................................. 4-18

Ω

4 dry circuit signal switching ............................................ 4-19

Ω2/Ω

4 reference signal switching ........................................ 4-19

Ω

4 dry circuit reference signal switching ............................ 4-20

Ω

2 signal multiplexing and gain .......................................... 4-22

Ω

4 signal multiplexing and gain .......................................... 4-22

Ω

4 dry circuit signal multiplexing and gain ......................... 4-22

5 Disassembly

Table 5-1 Input terminal wire colors ...................................................... 5-6

Table 5-2 Power module wire colors ...................................................... 5-7

6 Replaceable Parts

Table 6-1 Model 2750 motherboard parts list ........................................ 6-3

Table 6-2 Model 2750 display board parts list ..................................... 6-12

Table 6-3 Model 2750 backplane board parts list ................................ 6-13

Table 6-4 Model 2750 miscellaneous parts list .................................... 6-14

Table 6-5 Model 7700 module parts list ............................................... 6-15

B Calibration Reference

Table B-1 Remote calibration command summary ................................ B-2

Table B-2 DC calibration commands ..................................................... B-8

Table B-3 AC calibration commands ................................................... B-13

Table B-4 Model 7700 calibration commands ..................................... B-16

Table B-5 Calibration errors ................................................................ B-21

1

Performance Verification

1-2 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Introduction

Use the procedures in this section to verify that Model 2750 Multimeter/Switch System
accuracy is within the limits stated in the instrument’s one-year accuracy specifications.
You can perform these verification procedures:

• Make sure that the instrument was not damaged during shipment, and that the unit
meets factory specifications.

• If the instrument’s accuracy is questionable.

• Following calibration.

WARNING

NOTE

There are two general verification procedures in this section:

•

Model 2750 verification

the Model 2750 using the front panel terminals.

•

Model 7700 verification —

ment made through the Model 7700 20-Channel Multiplexer. Note that the same
general procedures can be used to verify measurement accuracy of other Model
2750 plug-in modules that have similar functions. For specific information about
the individual modules, refer to the corresponding module documentation.

The information in this section is intended only for qualified service
personnel. Do not attempt these procedures unless you are qualified to
do so.

If the instrument is still under warranty and its performance is outside specified
limits, contact your Keithley representative or the factory to determine the cor­rect course of action. If the unit is not under warranty, and it fails to meet speci­fied limits, refer to the calibration procedures in Section 2.

— Covers procedures to verify measurement accuracy of

Discusses procedures to verify accuracy of measure-

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-3

Verification test requirements

Be sure that you perform the verification tests:

• Under the proper environmental conditions.

• After the specified warmup period.

• Using the correct line voltage.

• Using the proper calibration equipment.

• Using the specified reading limits.

Environmental conditions

Conduct your performance verification procedures in a test environment that has:

• An ambient temperature of 18° to 28°C (65° to 82°F).

• A relative humidity of less than 80% unless otherwise noted.

Warmup period

Allow the Model 2750 to warm up for at least two hours before conducting the verification
procedures.

If the instrument has been subjected to temperature extremes (those outside the ranges
stated above), allow additional time for the instrument’s internal temperature to stabilize.
Typically, allow one extra hour to stabilize a unit that is 10°C (18°F) outside the specified
temperature range.

Also, allow the test equipment to warm up for the minimum time specified by the manu­facturer.

Line power

The Model 2750 requires a line voltage of 100V/120V/220V/240V, ±10% and a line fre­quency of 45Hz to 66Hz or 360Hz to 440Hz. Note that the line frequency is automatically
sensed at powerup, but the line voltage must be manually set to either 100V/120V or
220V/240V as described in Section 3.

1-4 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Recommended test equipment

Table 1-1 summarizes recommended verification equipment. You can use alternate equip-

ment as long as that equipment has specifications at least as good as those listed in

Table 1-1. In general, equipment uncertainty should be at least four times better than cor-

responding Model 2750 specifications. Keep in mind, however, that calibrator uncertainty
will add to the uncertainty of each measurement.

Table 1-1

Recommended verification equipment

Fluke 5700A Calibrator:

AC Voltage

DC Voltage

100mV:±14ppm

1.0V:±7ppm
10V:±5ppm

100V:±7ppm

1000V:±9ppm

Fluke 5725A Amplifier:

AC Voltage, 50kHz: 700V, ±375ppm
DC Current, 3A, ±500ppm
AC Current, 1kHz, 3A, ±457ppm

Stanford Research Systems DS345 Function Generator:

1V RMS 1kHz, ±5ppm

General Radio 1433-T Precision Decade Resistance Box:

10Ω to 400Ω, ±0.02%

Miscellaneous Equipment:

Double banana plug to double banana plug shielded cables (2)
BNC to double banana plug shielded cable

Note: The Fluke 5725A amplifier is necessary only if you wish to verify the 750V AC range at 50kHz and 3A AC and DC current

ranges at 3A. Verification at 220V, 50kHz, and 2.2A on the current ranges using only the 5700A calibrator is adequate for most
applications. Calibrator 1Ω uncertainty is not four times better than Model 2750 1Ω range accuracy.

(1kHz, 50kHz) DC Current

100mV:±200ppm

1.0V:±82ppm
10V:±82ppm

100V:±90ppm
700V:±85ppm

20mA:±60ppm

100mA:±70ppm

1A:±110ppm

2.2A:±94ppm

AC Current

(1kHZ) Resistance

1A:±690ppm

2.2A:±682ppm

1Ω:±95ppm

10Ω:±17ppm

100Ω:±17ppm

1kΩ:±12ppm

10kΩ:±11ppm

100kΩ:±13ppm

1MΩ:±18ppm

10MΩ:±37ppm

100MΩ:±120ppm

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-5

Verification limits

The verification limits stated in this section have been calculated using only the Model
2750 one-year accuracy specifications, and they do not include test equipment uncertainty.
If a particular measurement falls slightly outside the allowable range, recalculate new lim­its based on both Model 2750 specifications and pertinent calibration equipment
specifications.

Example reading limit calculation

The following is an example of how reading limits have been calculated. Assume you are
testing the 10V DC range using a 10V input value. Using the Model 2750 one-year accu­racy specification for 10V DC of ± (30ppm of reading + 5ppm of range), the calculated
limits are:

Reading limits = 10V ± [(10V × 30ppm) + (10V × 5ppm)]
Reading limits = 10V ± (0.0003 + 0.00005)
Reading limits = 10V ± 0.00035V
Reading limits = 9.99965V to 10.00035V

Calculating resistance reading limits

Resistance reading limits must be recalculated based on the actual calibration resistance
values supplied by the equipment manufacturer. Calculations are performed in the same
manner as shown in the preceding example, except, of course, that you should use the
actual calibration resistance values instead of the nominal values when performing your
calculations.

For example, assume that you are testing the 10kΩ range using an actual 10.03kΩ calibra­tion resistance value. Using Model 2750 one-year 10kΩ range accuracy of ± (100ppm of
reading + 6ppm of range), the calculated reading limits are:

Reading limits = 10.03kΩ ± [(10.03kΩ × 100ppm) + (10kΩ × 6ppm)]
Reading limits = 10.02894kΩ to 10.03106k

Ω

1-6 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Restoring factory defaults

Before performing the verification procedures, restore the instrument to its factory
defaults as follows:

1. Press SHIFT and then SETUP. The instrument will display the following prompt:
RESTORE: FACT.

2. Using either range key, select FACT, then restore the factory default conditions by
pressing ENTER.

Performing the verification test procedures

Verification test summary

Verification tests can be performed either through the Model 2750 front panel terminals or
through plug-in modules. This section contains the following procedures:

•

Model 2750 verification

through the front panel terminals.

•

Model 7700 verification

available plug-in modules with the same functions as the Model 7700 20-Channel
Multiplexer Card.

— Use this procedure to test Model 2750 accuracy

— Use this procedure to test accuracy through any of the

Model 2750 tests

Model 2750 verification test procedures include:

• DC volts

• AC volts

• DC current

• AC current

• Resistance

• Temperature

• Frequency

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-7

Model 7700 tests

Model 7700 verification test procedures include:

• DC volts

• AC volts

• DC current

• AC current

• Resistance

• Temperature

• Frequency

• Ratio and average

Test considerations

When performing the verification procedures:

• Be sure to restore factory defaults as outlined above.

• Make sure the equipment is properly warmed up and connected to the correct input
terminals. Also make sure that the INPUTS switch is in the correct position.

• Do not use autoranging for any verification tests because autorange hysteresis may
cause the Model 2750 to be on an incorrect range. For each test signal, you must
manually set the correct range for the Model 2750 using the range keys.

• Make sure the calibrator is in operate before you verify each measurement.

• Always let the source signal settle before taking a reading.

1-8 Performance Verification Model 2750 Multimeter/Switch System Service Manual

WARNING

Observe the following safety precautions when performing these tests:

•

Some of the procedures in this section may expose you to danger­ous voltages. Use standard safety precautions when such danger­ous voltages are encountered to avoid personal injury or death
caused by electric shock.

•

For the front panel terminals only, the maximum common-mode
voltage (voltage between INPUT LO and chassis ground) is 500V
peak. Exceeding this value may cause a breakdown in insulation,
creating a shock hazard.

•

For the plug-in modules, the maximum common-mode voltage
(voltage between any plug-in module terminal and chassis ground)
is listed in the module’s specifications. Exceeding this value may
cause a breakdown in insulation, creating a shock hazard.

•

When using the front panel terminals simultaneously with plug-in
modules, all cable insulation voltage ratings must equal or exceed
the maximum voltage applied to either the front panel terminals or
the plug-in module terminals.

Model 2750 verification

Perform these tests to verify accuracy using the Model 2750 front panel terminals.

Verifying DC voltage

Check DC voltage accuracy by applying accurate voltages from the DC voltage calibrator
to the Model 2750 INPUT jacks and verify that the displayed readings fall within specified
limits.

CAUTION

Follow these steps to verify DC voltage accuracy:

1. Connect the Model 2750 HI and LO INPUT jacks to the DC voltage calibrator as
shown in Figure 1-1. Make sure the INPUTS switch is set to the FRONT position.

NOTE

Do not exceed 1000V peak between front terminals INPUT HI and
INPUT LO because instrument damage may occur.

Use shielded, low-thermal connections when testing the 100mV and 1V ranges
to avoid errors caused by noise or thermal effects. Connect the shield to the cal­ibrator’s output LO terminal.

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-9

Figure 1-1

Connections for Model 2750 DC volts verification

Calibrator (Output DC Voltage)

2750 Verification

Model 2750

Front Panel

SENSE

INPUT

Ω 4 WIRE

HI

350V

!

PEAK

LO

INPUT

F

R

FRONT/REAR

AMPS

CAT I

Input

HI

Output

HI

1000V

PEAK

500V
PEAK

Input

3A, 250V

LO

Output

LO

Note: Use shielded, low-thermal cables

for 100mV and 1V ranges.

2. Select the DC volts function by pressing the

DCV

key, and set the Model 2750 to

the 100mV range.

3. Set the calibrator output to 0.00000mV DC, and allow the reading to settle.

4. Enable the Model 2750 REL mode. Leave REL enabled for the remainder of the
DC volts verification test.

5. Source positive and negative and full-scale voltages for each of the ranges listed in

Table 1-2. For each voltage setting, be sure that the reading is within stated limits.

Table 1-2

DCV reading limits

Range Applied DC Voltage* Reading Limits (1 year, 18°C to 28°C)

100mV

1V

10V

100V

1000V**

*Source positive and negative values for each range.

**Refer to specifications DC note 5 for signal >500V.

100.0000mV

1.000000V

10.00000V

100.0000V

1000.000V

99.9935 to 100.0065mV

0.999963 to 1.000037V

9.99965 to 10.00035V

99.9946 to 100.0054V

999.931 to 1000.069V

1-10 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Verifying AC voltage

Check AC voltage accuracy by applying accurate AC voltages at specific frequencies from
the AC voltage calibrator to the Model 2750 inputs and verifying that the displayed read­ings fall within specified ranges.

CAUTION

Do not exceed 1000V peak between front terminals INPUT HI and
INPUT LO, or 8 × 107VHz input, because instrument damage may
occur.

Follow these steps to verify AC voltage accuracy:

1. Connect the Model 2750 HI and LO INPUT jacks to the AC voltage calibrator as
shown in Figure 1-2. Be sure the INPUTS switch is in the FRONT position.

Figure 1-2

Connections for Model 2750 AC volts verification

Note: Amplifier required only for

700V, 50kHz output.

Model 2750

Front Panel

SENSE

INPUT

Ω 4 WIRE

HI

350V

!

PEAK

LO

INPUT

F

R

FRONT/REAR

AMPS

CAT I

Input

LO

Input

HI

Output

HI

1000V

PEAK

500V
PEAK

3A, 250V

Shielded

Cable

Output

LO

Amplifier (Connect to Calibrator)

Calibrator (Output AC Voltage)

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-11

2. Select the AC volts function by pressing the ACV key.

3. Set the Model 2750 for the 100mV range; make sure that REL is disabled.

4. Source 1kHz and 50kHz AC voltages for each of the ranges summarized in

Table 1-3, and make sure the respective Model 2750 readings fall within stated

limits.

Table 1-3

ACV reading limits

2750 Verification

ACV

Range

100mV

1V

10V
100V
750V

* If the 5725A amplifier is not available, change the 700V @ 50kHz step to 220V @ 50kHz. Reading

limits for 220V @ 50kHz = 219.36 to 220.64V.

Applied AC

100.0000mV

1.000000V

10.00000V

100.0000V

700.000V*

Verifying DC current

Check DC current accuracy by applying accurate DC currents from the DC current cali­brator to the AMPS input of the Model 2750 and verify that the displayed readings fall
within specified limits.

Follow these steps to verify DC current accuracy:

1. Connect the Model 2750 AMPS and INPUT LO jacks to the calibrator as shown in

Figure 1-3. Be sure the INPUTS switch is in the FRONT position.

2. Select the DC current measurement function by pressing the DCI key.

Voltage

1kHz Reading Limits

(1 year, 18°C to 28°C)

99.910 to 100.090mV

0.99910 to 1.00090V

9.9910 to 10.0090V

99.910 to 100.090V

699.36 to 700.64V

50kHz Reading Limits

(1 year, 18°C to 28°C)

99.830 to 100.170mV

0.99830 to 1.00170V

9.98300 to 10.0170V

99.830 to 100.170V

698.79 to 701.21V

1-12 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Figure 1-3

Connections for Model 2750 DC current verification

Calibrator (Output DC Current)

Model 2750

Front Panel

Output

Input

LO

HI

Output

350V
PEAK

SENSE

Ω 4 WIRE

INPUT

F

FRONT/REAR

CAT I

INPUT

HI

1000V

!

PEAK

LO

500V
PEAK

R

AMPS

LO

Amps

Note: Be sure calibrator is set for normal current output.

3. Set the Model 2750 for the 20mA range.

4. Source positive and negative full-scale currents for each of the ranges listed in

Table 1-4, and verify that the readings for each range are within stated limits.

Table 1-4

DCI limits

DCI Range Applied DC Current* Reading Limits (1 year, 18°C to 28°C)

20mA

100mA

1A
3A

* Source positive and negative currents with values shown.

** If the Fluke 5725 amplifier is not available, apply 2.2A from calibrator. Reading limits for 2.2A input

are: 2.197240 to 2.202760A.

20.0000mA

100.0000mA

1.000000A

3.000000A**

19.89960 to 20.01040mA

99.9100 to 100.0900mA

0.999160 to 1.000840A

2.99628 to 3.00372A

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-13

Verifying AC current

Check AC current accuracy by applying accurate AC voltage current at specific frequen­cies from the AC current calibrator to the Model 2750 input, and verify that the displayed
readings fall within specified limits. Follow these steps to verify AC current:

1. Connect the Model 2750 AMPS and INPUT LO jacks to the calibrator as shown in

Figure 1-4. Be sure the INPUTS switch is in the FRONT position.

2. Select the AC current function by pressing the ACI key.

Figure 1-4

Connections for Model 2750 AC current verification

Calibrator (Output AC Current)

Model 2750

Front Panel

Output

Input

PEAK

500V
PEAK

3A, 250V

LO

HI

Output

LO

350V
PEAK

SENSE

Ω 4 WIRE

INPUT

F

FRONT/REAR

CAT I

INPUT

HI

1000V

!

LO

R

AMPS

2750 Verification

Amps

3. Set the Model 2750 for the 1A range.

4. Source 1A and 3A, 1kHz full-scale AC currents as summarized in Table 1-5, and
verify that the readings are within stated limits.

Table 1-5

ACI limits

ACV Range Applied AC Voltage Reading Limits @ 1kHz (1 year, 18°C to 28°C)

1A
3A

* If the Fluke 5725A amplifier is not available, apply 2.2A from the calibrator. Reading limits for 2.2A are

2.1949 to 2.2051A.

1.000000A

3.00000A*

0.99860 to 1.00140A

2.9817 to 3.0183A

1-14 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Verifying normal resistance

Check the normal resistance function by connecting accurate resistance values to the
Model 2750 and verifying that its resistance readings are within the specified limits.

CAUTION Do not apply more than 1000V peak between front terminals INPUT

HI and LO or more than 350V peak between SENSE HI and LO, or
instrument damage could occur.

Follow these steps to verify resistance accuracy:

1. Using shielded, Teflon-insulated or equivalent cables in a 4-wire configuration,
connect the Model 2750 INPUT and SENSE jacks to the calibrator as shown in

Figure 1-5. Be sure the INPUTS switch is in the FRONT position.

2. Set the calibrator for 4-wire resistance with external sense on.

Figure 1-5

Connections for Model 2750 resistance verification (1Ω to 10MΩ ranges)

Model 2750

Front Panel

Sense

LO

Sense

HI

Sense

Input

HI

HI

Output

SENSE

INPUT

Ω 4 WIRE

HI

350V

1000V

!

PEAK

PEAK

LO

500V
PEAK

INPUT

F

R

FRONT/REAR

CAT I

AMPS

Input

3A, 250V

LO

HI

Output

LO

Resistance Calibrator

Sense

LO

Note: Use shielded, low-thermal cables to minimize noise.

Enable or disable calibrator external sense as indicated
in procedure.

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-15

3. Select the Model 2750 4-wire resistance function by pressing the Ω4 key, then

choose the SLOW integration rate with the RATE key.

4. Set the Model 2750 for the 1Ω range, and make sure the FILTER is on. Enable

OCOMP (offset-compensated ohms) by pressing SHIFT then OCOMP. (Use
OCOMP for 1Ω, 10Ω, and 100Ω range verification.)

5. Recalculate reading limits based on actual calibrator resistance values.

6. Source the nominal full-scale resistance values for the 1Ω-10MΩ ranges summa-

rized in Table 1-6, and verify that the readings are within calculated limits.

7. Connect the Model 2750 INPUT and SENSE jacks to the calibrator as shown in

Figure 1-6.

8. Disable external sense on the calibrator.

9. Set the Model 2750 for the 100MΩ range.

10. Source a nominal 100MΩ resistance value and verify that the reading is within cal­culated limits for the 100MΩ range.

Figure 1-6

Connections for Model 2750 resistance verification (100MΩ range)

Calibrator (Output 2-wire Resistance)

2750 Verification

Model 2750

Front Panel

Sense

LO

Sense

Input

HI

HI

Output

SENSE

INPUT

Ω 4 WIRE

HI

350V

1000V

!

PEAK

PEAK

LO

500V
PEAK

INPUT

F

R

FRONT/REAR

CAT I

AMPS

Input

LO

HI

Output

LO

Note: Use shielded cables to minimize noise.

Disable calibrator external sense mode.

1-16 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Table 1-6

Limits for normal resistance verification

Nominal

Ω Range

10Ω∗

100Ω∗

10kΩ

100kΩ

10MΩ

100MΩ

* Enable OCOMP (offset-compensated ohms) when testing 1Ω, 10Ω, and 100Ω ranges.

** Calculate limits based on actual calibration resistance values and Model 2750 one-year resistance accuracy

specifications. See “Verification limits.”

1Ω∗

1kΩ

1MΩ

Resistance

1Ω

10Ω

100Ω

1kΩ

10kΩ

100kΩ

1MΩ

10MΩ

100MΩ

Nominal Reading Limits

(1 year, 18°C to 28°C) Recalculated Limits**

0.999820 to 1.000180Ω

9.99880 to 10.00120Ω

99.9880 to 100.0120Ω

0.999894 to 1.000106kΩ

9.99894 to 10.00106kΩ

99.9890 to 100.0110kΩ

0.999890 to 1.000110MΩ

9.99590 to 10.00410MΩ

99.7970 to 100.2030MΩ

Verifying dry circuit resistance

Check the dry circuit resistance function by connecting accurate resistance values to the
Model 2750 and verifying that its resistance readings are within the specified limits.

CAUTION Do not apply more than 1000V peak between front terminals INPUT

HI and LO or more than 350V peak between SENSE HI and LO, or
instrument damage could occur.

__________ to __________ Ω
__________ to __________ Ω
__________ to __________ Ω
__________ to __________ kΩ
__________ to __________ kΩ
__________ to __________ kΩ
__________ to __________ MΩ
__________ to __________ MΩ
__________ to __________ MΩ

Follow these steps to verify dry circuit resistance accuracy:

1. Using shielded, Teflon-insulated or equivalent cables in a 4-wire configuration,
connect the Model 2750 INPUT and SENSE jacks to the calibrator as shown in

Figure 1-7. Be sure the INPUTS switch is in the FRONT position.