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: 02/363 00 64 CHINA: Keithley Instruments China Yuan Chen Xin Building, Room 705 • 12 Yumin Road, Dewai, Madian • Beijing 100029 • 8610-62022886 • Fax: 8610-62022892 FRANCE: Keithley Instruments Sarl 3, allée des Garays • 91127 Palaiseau Cedex • 01-64 53 20 20 • Fax: 01-60 11 77 26 GERMANY: Keithley Instruments GmbH Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: 089/84 93 07-34 GREAT BRITAIN: Keithley Instruments Ltd The Minster • 58 Portman Road • Reading, Berkshire RG30 1EA • 0118-9 57 56 66 • Fax: 0118-9 59 64 69 INDIA: Keithley Instruments GmbH Flat 2B, WILOCRISSA • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: 91-80-509-1322 ITALY: Keithley Instruments s.r.l. Viale S. Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: 02-48 30 22 74 NETHERLANDS: Keithley Instruments B.V. Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: 0183-630821 SWITZERLAND: Keithley Instruments SA Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: 01-820 30 81 TAIWAN: Keithley Instruments Taiwan 1 Fl. 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3572-9077 • Fax: 886-3572-903

• 28775 Aurora Road • Cleveland, OH 44139 • 440-248-0400 • Fax: 440-248-6168 • http://www.keithley.com

9/00

Model 2750 Multimeter/Switch System

Service Manual

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

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

350V

PEAK

INPUT

FRONT/REAR

AMPS

CAT I

Input

Output

1000V

PEAK

500V PEAK

Input

3A, 250V

Output

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

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

350V

PEAK

INPUT

FRONT/REAR

AMPS

CAT I

Input

Output

1000V

PEAK

500V PEAK

3A, 250V

Shielded

Cable

Output

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

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

Output

350V PEAK

SENSE

Ω 4 WIRE

INPUT

FRONT/REAR

CAT I

INPUT

1000V

PEAK

500V PEAK

AMPS

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

Output

350V PEAK

SENSE

Ω 4 WIRE

INPUT

FRONT/REAR

CAT I

INPUT

1000V

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

Input

Output

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

500V PEAK

INPUT

FRONT/REAR

CAT I

AMPS

Input

3A, 250V

Output

Resistance Calibrator

Sense

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

Input

Output

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

500V PEAK

INPUT

FRONT/REAR

CAT I

AMPS

Input

Output

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.

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-17

Figure 1-7

Connections for Model 2750 dry circuit resistance veriﬁcation

2750 Veriﬁcation

Model 2750

Front Panel

Sense

Input

Output

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

500V

PEAK

INPUT

FRONT/REAR

CAT I

AMPS

Input

3A, 250V

Resistance Calibrator

Sense

Note: Use low-thermal cables to minimize noise.

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

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. Select the Model 2750 dry circuit resistance function by pressing SHIFT then DRYCKT.

5. 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, 100Ω, and 1kΩ range veriﬁcation.) Enable line sync ON by pressing SHIFT then LSYNC.

NOTE Maximum reading rate for the 1kΩ range is two readings per second.

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

7. Source the nominal full-scale resistance values for the 1Ω-1kΩ ranges summarized in Table 1-7, and verify that the readings are within calculated limits.

1-18 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Table 1-7

Limits for Model 2750 dry resistance veriﬁcation

Nominal

Ω Range

1Ω∗

10Ω∗

100Ω∗

1kΩ

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

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

accuracy specifications. See “Veriﬁcation limits.”

Resistance

1Ω

10Ω

100Ω

1kΩ

Verifying temperature

Thermocouple, thermistor, and RTD temperature readings are derived from DC volts and resistance measurements respectively. For that reason, it is not necessary to independently verify the accuracy of temperature measurements. As long as the DC volts and resistance functions meet or exceed speciﬁcations, temperature function accuracy is automatically veriﬁed. However, temperature veriﬁcation procedures are provided below for those who wish to separately verify temperature accuracy.

Thermocouple temperature

1. Connect the DC voltage calibrator output terminals to the Model 2750 INPUT jacks using low-thermal shielded connections. (Use 2-wire connections similar to those shown in Figure 1-1.) Be sure the INPUTS switch is in the FRONT position.

2. Conﬁgure the Model 2750 for °C units, type J temperature sensor, and 0°C simulated reference junction as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units:

UNITS: C. (If necessary, use the cursor and range keys to select °C units.) b. Press ENTER. The unit displays the sensor type: SENS: TCOUPLE. c. Make sure that TCOUPLE is displayed, then press ENTER. The unit then dis-

plays the thermocouple type: TYPE: K. d. Select a type J temperature sensor, then press ENTER. The unit then displays

the reference junction type: JUNC: SIM. e. Make certain that the simulated reference junction type is selected, then press

ENTER. The unit then displays the current simulated reference junction tem-

perature: SIM: 023.

f. Using the cursor and range keys, set the reference junction temperature to 0°C,

then press ENTER twice to complete the temperature conﬁguration process.

3. Select the temperature function by pressing the TEMP key.

4. Source each of the voltages summarized in Table 1-8, and verify that the temperature readings are within limits. Be sure to select the appropriate thermocouple type for each group of readings. (See step 2 above.)

Nominal Reading Limits

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

0.999860 to 1.000140Ω

9.99860 to 10.00140Ω

99.9820 to 100.0180Ω

0.999510 to 1.000490kΩ

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

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-19

Table 1-8

Thermocouple temperature veriﬁcation reading limits

Applied DC

Thermocouple Type

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

-7.659mV 0mV

42.280mV

-190.2 to -189.9°C

-0.2 to +0.2°C

749.8 to 750.2°C

2750 Veriﬁcation

* Voltages shown are based on ITS-90 standard using 0°C reference junction temperature. See text for proce-

dure to set reference junction temperature.

-5.730mV 0mV

54.138mV

-190.2 to -189.8°C

-0.2 to +0.2°C

1349.8 to 1350.2°C

RTD temperature

1. Connect the precision decade resistance box (listed in Table 1-1) to the Model 2750 INPUT and SENSE jacks using four-wire connections. (See Figure 1-5 for similar connecting scheme.) Be sure the INPUTS switch is in the FRONT position.

2. Conﬁgure the Model 2750 temperature function for ˚C units and RTD temperature sensor (α=0.00385) as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units:

UNITS: C. b. Press ENTER, and note the unit displays the sensor type: SENS: TCOUPLE. c. Using the cursor and range keys, set the display as follows: SENS: 4W-RTD. d. Press ENTER, and note the unit displays: TYPE: PT100. e. Using the cursor and range keys, set the unit for the following display: TYPE:

PT385.

f. Press ENTER to complete the temperature conﬁguration process.

3. Select the temperature function by pressing the TEMP key.

4. Set the decade resistance box to each of the values shown in Table 1-9, and verify that the temperature readings are within the required limits.

Table 1-9

Four-wire RTD temperature veriﬁcation reading limits

Applied Resistance* Reading Limits (1 year, 18°C to 28°C)

22.80Ω

100.00Ω

313.59Ω

*Based on α = 0.00385. See text.

-190.06 to -189.94°C

-0.06 to +0.06°C

599.94 to 600.06°C

1-20 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Verifying frequency

Follow the steps below to verify the Model 2750 frequency function:

1. Connect the function generator to the Model 2750 INPUT jacks. (See Figure 1-8.) Be sure the INPUTS switch is in the FRONT position.

2. Set the function generator to output a 1kHz, 1V RMS sine wave.

3. Select the Model 2750 frequency function by pressing the FREQ key.

4. Verify that the Model 2750 frequency reading is between 999.9Hz and 1.0001kHz.

Figure 1-8

Connections for Model 2750 frequency veriﬁcation

Function Generator

Model 2750

Front Panel

SENSE

Ω 4 WIRE

350V

PEAK

INPUT

FRONT/REAR

CAT I

INPUT

1000V PEAK

500V PEAK

AMPS

Banana Plug

Adapter

3A, 250V

50Ω

Coax

Cable

Function

Output

Model 7700 veriﬁcation

Use these procedures to verify measurement accuracy through the Model 7700 20Channel Multiplexer Card.

NOTE Although the following tests are based on the Model 7700 20-Channel Multi-

plexer, the same general procedures can be used for other plug-in modules that have similar capabilities. Refer to module documentation for speciﬁc information on terminals and connections for other plug-in modules.

BNC-to-Dual

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-21

Verifying DC voltage

Check DC voltage accuracy by applying accurate voltages from the DC voltage calibrator to the Model 7700 input terminals and verifying that the displayed readings fall within speciﬁed limits.

CAUTION Do not exceed 300V DC between the 7700 plug-in module INPUT H

and L terminals or between any adjacent channels.

Follow these steps to verify DC voltage accuracy:

1. Connect the Model 7700 CH1 H and L INPUT terminals to the DC voltage calibrator as shown in Figure 1-9.

NOTE 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.

Figure 1-9

Connections for Model 7700 DC volts veriﬁcation

7700 Veriﬁcation

CH1

INPUT SENSE

HLHL

HLHL CH21 CH22 CH11 CH12CH13 CH14 CH15 CH16

HLHL

AMPS

HLHL

CH3

CH1 CH2

Model 7700

Calibrator (Output DC Voltage)

CH5

CH6

CH4

HLHL

CH7 CH8 CH9 CH10

HLHLHLHLHLHL

HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Output HI

Output

Note: Use shielded, low-thermal cables

for 100mV and 1V ranges.

2. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

3. Select the DC volts function by pressing the DCV key, and set the Model 2750 to the 100mV range. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and then keying in 101.

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

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

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

Table 1-10. For each voltage setting, be sure that the reading is within stated limits.

7. Press the OPEN key to open Channel 1.

1-22 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Table 1-10

Plug-in module DCV reading limits

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

100mV

10V

100V

1000V

*Source positive and negative values for each range.

100.0000mV

1.000000V

10.00000V

100.0000V

300.000V

99.9935 to 100.0065mV

0.999963 to 1.000037V

9.99965 to 10.00035V

99.9946 to 100.0054V

299.976 to 300.024V

Verifying AC voltage

Check AC voltage accuracy by applying accurate AC voltages at speciﬁc frequencies from the AC voltage calibrator to the Model 7700 inputs and verifying that the displayed readings fall within speciﬁed ranges.

CAUTION Do not exceed 300V RMS between the 7700 plug-in module INPUT H

and L terminals or between adjacent channels, or 8 × 107VHz input, because instrument damage may occur.

Follow these steps to verify AC voltage accuracy:

1. Connect the Model 7700 CH1 H and L INPUT terminals to the AC voltage calibrator as shown in Figure 1-10.

Figure 1-10

Connections for Model 7700 AC volts veriﬁcation

CH1

CH5

CH6

CH4

CH3

CH1 CH2

INPUT SENSE

HLHL

HLHL CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

AMPS

HLHL

HLHLHLHLHLHL

CH7 CH8 CH9 CH10

HLHLHLHL

CH17 CH18 CH19 CH20

Model 7700

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Output

Shielded

Cable

Amplifier (Connect to calibrator)

Output

Calibrator (Output AC Voltage)

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-23

2. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

3. Select the AC volts function by pressing the ACV key. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and then keying in 101.

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

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

Table 1-11, and make sure that the respective Model 2750 readings fall within

stated limits.

6. Press the OPEN key to open Channel 1.

Table 1-11

Plug-in module ACV reading limits

7700 Veriﬁcation

ACV

Range

100mV

10V 100V 750V

*If the 5725A ampliﬁer is not available, change the 300V @ 50kHz step to 220V @ 50kHz. Reading limits

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

Applied AC

Voltage

100.0000mV

1.000000V

10.00000V

100.0000V

300.000V*

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

299.60 to 300.40V

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

299.27 to 300.73V

1-24 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Verifying DC current

Check DC current accuracy by applying accurate DC currents from the DC current calibrator to the input terminals of the Model 7700 and verify that the displayed readings fall within speciﬁed limits.

Follow these steps to verify DC current accuracy:

1. Connect the Model 7700 CH21 H and L terminals to the calibrator as shown in

Figure 1-11.

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

4. Set the Model 2750 for the 20mA range. Close Channel 21 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 121.

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

Table 1-12, and verify that the readings for each range are within stated limits.

6. Press the OPEN key to open Channel 21.

Figure 1-11

Connections for Model 7700 DC current veriﬁcation

INPUT SENSE

HLHL

CH21 CH22 CH11 CH12CH13 CH14 CH15 CH16

CH21

HLHL

Model 7700

CH3

CH1 CH2

HLHL

AMPS

CH4

CH5

CH6

HLHL

HLHLHLHLHLHL

CH7 CH8 CH9 CH10 HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Output HI

Output

Calibrator (Output DC Current)

Note: Be sure calibrator is set for

normal current output.

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-25

Table 1-12

Plug-in module 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

Verifying AC current

Check AC current accuracy by applying accurate AC voltage current at speciﬁc frequencies from the AC current calibrator to the Model 7700 input terminals and verify that the displayed readings fall within speciﬁed limits. Follow these steps to verify AC current:

1. Connect the Model 7700 CH21 H and L terminals to the calibrator as shown in

Figure 1-12.

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

4. Set the Model 2750 for the 1A range. Close Channel 21 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 121.

7700 Veriﬁcation

Figure 1-12

Connections for Model 7700 AC current veriﬁcation

Model 7700

CH5

CH6

CH4

CH3

CH1 CH2

INPUT SENSE

HLHL

CH21 CH22 CH11 CH12CH13 CH14 CH15 CH16

CH21

HLHL

AMPS

HLHL

HLHLHLHLHLHL

CH7 CH8 CH9 CH10 HLHLHLHL

HLHLHLHL

CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Output HI

Output

Calibrator (Output AC Current)

1-26 Performance Verification Model 2750 Multimeter/Switch System Service Manual

5. Source 1A and 3A, 1kHz full-scale AC currents as summarized in Table 1-13, and verify that the readings are within stated limits.

6. Press the OPEN key to open Channel 21.

Table 1-13

Plug-in module 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

Verifying normal resistance

Check normal resistance by connecting accurate resistance values to the Model 7700 and verify that its resistance readings are within the speciﬁed limits.

CAUTION Do not apply more than 300V between the 7700 plug-in module

INPUT or SENSE H and L terminal, or between any adjacent channels, or instrument damage could occur.

Follow these steps to verify normal resistance accuracy:

1. Using shielded Teﬂon or equivalent cables in a 4-wire conﬁguration, connect the Model 7700 CH1 H and L INPUT terminals, and CH11 H and L SENSE terminals to the calibrator as shown in Figure 1-13.

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

4. Select the Model 2750 4-wire resistance function by pressing the Ω4 key. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 101.

5. 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.)

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

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-27

Figure 1-13

Connections for Model 7700 resistance veriﬁcation (1Ω to 10MΩ ranges)

CH1

Model 7700

CH5

CH4

CH3

CH1 CH2

INPUT SENSE

HLHL

CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

AMPS

HLHL

HLHLHLHLHLHL

CH6

CH7 CH8 CH9 CH10 HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Sense HI

Output

Resistance Calibrator

7700 Veriﬁcation

CH11

Sense LO

Note: Use shielded, low-thermal cables

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

rized in Table 1-14, and verify that the readings are within calculated limits.

8. Connect the Model 7700 CH1 and CH11 terminals to the calibrator as shown in

Figure 1-14.

9. Disable external sense on the calibrator.

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

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

12. Press the OPEN key to open Channel 1.

Figure 1-14

Connections for Model 7700 resistance veriﬁcation (100MΩ range)

CH1

INPUT SENSE HLHL

Model 7700

CH4

CH3

CH1 CH2

HLHL

CH5

CH6

HLHL

CH7 CH8 CH9 CH10

HLHLHLHL

INPUT

(V, 2 WIRE)

Output

Calibrator (Output 2-wire Resistance)

to minimize noise. Enable or disable calibrator external sense as indicated in procedure.

HLHL CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

AMPS

CH11

HLHLHLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

SENSE

(OHMS, 4 WIRE)

Output

Note: Use shielded cables to minimize

noise. Disable calibrator external sense mode.

1-28 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Table 1-14

Limits for plug-in module normal resistance veriﬁcation

Nominal

Ω Range

1Ω∗

10Ω∗

100Ω∗

1kΩ

10kΩ

100kΩ

1MΩ

10MΩ

100MΩ

* Enable OCOMP for 1Ω, 10Ω, and 100Ω ranges.

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

speciﬁcations. See “Veriﬁcation limits.”

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

99.5770 to 100.4230MΩ

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 300V between the 7700 plug-in module

INPUT or SENSE H and L terminal, or between any adjacent channels, or instrument damage could occur.

Follow these steps to verify dry circuit resistance accuracy:

NOTE The 1kΩ range can tolerate 80% of range (0.8Ω) lead resistance. Ensure that

relay and cable connections have ≤0.8Ω of resistance before verifying the 1Ω range.

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-29

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

4. Select the Model 2750 4-wire resistance function by pressing the Ω4 key. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 101.

5. Set the Model 2750 for the dry circuit resistance function by pressing SHIFT then DRYCKT.

Figure 1-15

Connections for Model 7700 dry circuit resistance veriﬁcation

CH1

Model 7700

CH5

CH4

CH3

CH1 CH2

INPUT SENSE

HLHL

HLHL CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

AMPS

HLHL

HLHLHLHLHLHL

CH6

CH7 CH8 CH9 CH10

HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Sense HI

Output

Resistance Calibrator

7700 Veriﬁcation

CH11

Sense LO

Note: Use shielded, low-thermal cables

to minimize noise.

1-30 Performance Verification Model 2750 Multimeter/Switch System Service Manual

6. Set the Model 2750 for the 1Ω range, and make sure the FILTER is on. If previ-

ously disabled, enable OCOMP (offset-compensated ohms) by pressing SHIFT then OCOMP. (Use OCOMP for 1Ω, 10Ω, 100Ω, and 1kΩ range veriﬁcation.) Enable line sync (press SHIFT then LSYNC).

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

NOTE Maximum reading rate for 1kΩ dry circuit is two readings per second.

8. Source the nominal full-scale resistance values for the 1Ω-1kΩ ranges summarized

in Table 1-15, and verify that the readings are within calculated limits.

Table 1-15

Limits for plug-in module dry circuit resistance veriﬁcation

Nominal

Ω Range

1Ω∗

10Ω∗

100Ω∗

1kΩ

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

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

speciﬁcations. See “Veriﬁcation limits.”

Resistance

1Ω

10Ω

100Ω

1kΩ

Nominal Reading Limits

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

0.999860 to 1.000140Ω

9.99860 to 10.00140Ω

99.9820 to 100.0180Ω

0.999510 to 1.000490kΩ

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

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-31

Verifying temperature

Thermocouple temperature

1. Connect the DC voltage calibrator output terminals and ice point reference to the Model 7700 CH1 H and L INPUT terminals using low-thermal shielded connections, as shown in Figure 1-16.

Figure 1-16

Connections for Model 7700 thermocouple temperature veriﬁcation

7700 Veriﬁcation

CH1

INPUT SENSE HLHL

HLHL

CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

HLHL

AMPS

HLHL

CH4

CH3

CH1 CH2

Model 7700

CH5

CH6

HLHL

CH7 CH8 CH9 CH10 HLHLHLHL

HLHLHLHL

CH17 CH18 CH19 CH20

HLHLHLHLHLHL

Make HI and LO

Connections

in Ice Bath

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Twisted

Thermocouple Wire

Output

Ice Bath

Calibrator (Output DC Voltage)

Low Thermal

Copper Connection

Notes: This setup and reading limits

table does not include errors from ice point, thermocouple wire, and connections.

HI and LO connections from the calibrator and Model 7700 must be electrically isolated from each other.

1-32 Performance Verification Model 2750 Multimeter/Switch System Service Manual

3. Select the temperature function by pressing the TEMP key. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 101.

4. Conﬁgure the Model 2750 for °C units, type K temperature sensor, and internal reference junction as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units:

the thermocouple type: TYPE: J. d. Select a type K temperature sensor, then press ENTER. The unit displays the

reference junction type: JUNC: SIM. e. Select INT reference junction, then press ENTER.

NOTE Defaults for 7700, 7706, and 7708 modules are:

• K type.

• “C” units.

• Internal temperature sensor.

• Open Tdetect off.

• Sensor type: Tcouple.

5. Source each of the voltages summarized in Table 1-16 and verify that the temperature readings are within limits. Be sure to select the appropriate thermocouple type for each group of readings. (See step 3 above.) Open Channel 1 after the test is complete.

Table 1-16

Model 7700 thermocouple temperature veriﬁcation reading limits

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

*Voltages shown are based on ITS-90 standard.

-7.659mV 0mV

42.280mV

-5.730mV 0mV

54.138mV

-191.8 to -188.2°C

-1.0 to +1.0°C

749.0 to 751.0°C

-191.8 to -188.2°C

-1.0 to +1.0°C

1349.0 to 1351.0°C

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-33

RTD temperature

1. Connect the precision decade resistance box (listed in Table 1-1) to the Model 7700 CH1 and CH11 H and L terminals using four-wire connections. (See

Figure 1-14 for similar connecting scheme.)

3. Select the temperature function by pressing the TEMP key. Close Channel 1 by pressing the CLOSE key and keying in 101.

4. Conﬁgure the Model 2750 temperature function for °C units and RTD temperature sensor (α=0.00385) as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units:

PT385.

f. Press ENTER to complete the temperature conﬁguration process.

5. Set the decade resistance box to each of the values shown in Table 1-17, and verify that the temperature readings are within the required limits. Open Channel 1 when ﬁnished.

7700 Veriﬁcation

Table 1-17

Plug-in module four-wire RTD temperature veriﬁcation reading limits

Applied Resistance* Reading Limits (1 year, 18°C to 28°C)

22.80Ω

100.00Ω

313.59Ω

*Based on α = 0.00385. See text.

-190.06 to -189.94°C

-0.06 to +0.06°C

599.94 to 600.06°C

1-34 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Verifying frequency

Follow the steps below to verify the Model 2750 frequency function:

1. Connect the function generator to the Model 7700 CH1 H and L INPUT terminals (Figure 1-17).

2. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for one hour before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

3. Set the function generator to output a 1kHz, 1V RMS sine wave.

4. Select the Model 2750 frequency function by pressing the FREQ key. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 101.

5. Verify that the Model 2750 frequency reading is between 0.9999kHz and

1.0001kHz.

Figure 1-17

Connections for Model 7700 frequency veriﬁcation

CH1

CH1 CH2

INPUT SENSE HLHL

HLHL

CH21 CH22 CH11 CH12CH13 CH14 CH15 CH16

HLHL

AMPS

HLHL

CH5

CH6

CH4

CH3

HLHL

CH7 CH8 CH9 CH10 HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

HLHLHLHLHLHL

Model 7700

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Function Generator

50Ω

Coax

Cable

Function

Output

Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-35

Verifying ratio and average

Follow the procedure below to verify ratio and average.

CAUTION Exceeding 300V between the 7700 plug-in module INPUT or SENSE

H and L terminals may cause instrument damage.

1. Connect the Model 7700 CH1 and CH11 H and L terminals to the DC calibrator, as shown in Figure 1-18.

3. Select the Model 2750 DCV function and the 1V range. Close Channel 1 by pressing the CLOSE key, then ENTER for “SINGLE” channel, and keying in 101.

4. Select the Model 2750 RATIO function (press SHIFT then RATIO).

5. Set the calibrator output to 1.00000V DC, and allow the reading to settle.

6. Verify that the ratio reading is between 0.9999926 and 1.000074.

7. Press OPEN to open Channel 1.

Figure 1-18

Connections for Model 7700 ratio and average veriﬁcation

7700 Veriﬁcation

CH1

Model 7700

INPUT SENSE HLHL

HLHL CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

HLHL

AMPS

HLHL

CH4

CH3

CH1 CH2

CH11

CH5

CH6

HLHL

HLHLHLHLHLHL

CH7 CH8 CH9 CH10

HLHLHLHL

HLHLHLHL CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

DC Voltage Calibrator

Output

Note: Use shielded cables to

minimize noise.

1-36 Performance Verification Model 2750 Multimeter/Switch System Service Manual

Calibration

2-2 Calibration Model 2750 Multimeter/Switch System Service Manual

Introduction

Use the procedures in this section to calibrate the Model 2750. Calibration procedures include:

• Comprehensive calibration: Usually the only calibration required in the ﬁeld.

• Manufacturing calibration: Usually only performed at the factory (unless the unit has been repaired).

• Model 7700 calibration: Covers calibration procedures speciﬁc to Model 7700 cards.

WARNING The information in this section is intended only for qualiﬁed service

personnel. Do not attempt these procedures unless you are qualiﬁed to do so.

All the procedures require accurate calibration equipment to supply precise DC and AC voltages, DC and AC currents, and resistance values. Comprehensive calibration can be performed any time by an operator either from the front panel, or by using the SCPI commands sent either over the IEEE-488 bus or the RS-232 port. DC-only and AC-only calibration may be performed individually, if desired.

Environmental conditions

Conduct the calibration procedures in a location 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 Multimeter/Switch System to warm up for at least two hours before performing calibration.

If the instrument has been subjected to temperature extremes (those outside the ranges stated above) allow extra 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.

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 power-up, but the line voltage must be manually set to either 100V/120V or 220V/240V as described in Section 3.

Model 2750 Multimeter/Switch System Service Manual Calibration 2-3

Calibration considerations

When performing the calibration procedures:

• Make sure that the equipment is properly warmed up and connected to the appropriate input jacks. Make sure that the correct front or rear terminals are selected with the INPUTS switch.

• Make sure the calibrator is in OPERATE before you complete each calibration step.

• Always let the source signal settle before calibrating each point.

• If an error occurs during calibration, the Model 2750 will generate an appropriate error message. See Appendix B for more information.

WARNING Observe the following safety precautions when performing these tests:

• Some of the procedures in this section may expose you to danger-

ous 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.

Model 2750 Calibration

• 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.

2-4 Calibration Model 2750 Multimeter/Switch System Service Manual

Calibration code

Before performing comprehensive calibration, you must ﬁrst unlock calibration by entering the appropriate calibration code.

Front panel calibration code

For front panel calibration, follow these steps:

1. Access the calibration menu by pressing SHIFT then TEST, then use the up or down range key to display TEST: CALIB. Press ENTER, and note that the instrument displays the following:

CAL: DATES

2. Use the up or down range key to scroll through the available calibration items until the unit displays RUN, then press ENTER.

3. The Model 2750 then prompts you to enter a code: CODE? 000000 (The factory default code is 002750.) Use the left and right arrow keys to move

among the digits; use the up range key to increment numbers and press the down range key to specify alphabetic letters. Conﬁrm the code by pressing ENTER.

4. The Model 2750 allows you to deﬁne a new calibration code. Use the up and down range keys to toggle between yes and no. Choose N if you do not want to change the code. Choose Y if you want to change the code. The unit then prompts you to enter a new code. Enter the code, and press ENTER.

Remote calibration code

If you are performing calibration over the IEEE-488 bus or the RS-232 port, send this command to unlock calibration:

:CAL:PROT:CODE '<8-character string>'.

The default code command is:

:CAL:PROT:CODE 'KI002750'.

To change the code via remote, simply send the :CAL:PROT:CODE command twice, ﬁrst with the present code, then with the new code.

Model 2750 Multimeter/Switch System Service Manual Calibration 2-5

Comprehensive calibration

The comprehensive calibration procedure calibrates the DCV, DCI, ACV, ACI, and ohms functions. You can also choose to calibrate only the DCV/DCI and resistance or ACV/ACI functions.

These procedures are usually the only calibration required in the ﬁeld. Manufacturing calibration is normally done only at the factory, but it should also be done in the ﬁeld if the unit has been repaired. See “Manufacturing calibration” at the end of this section for more information.

Calibration cycle

Perform comprehensive calibration at least once a year, or every 90 days to ensure the unit meets the corresponding speciﬁcations.

Recommended equipment

Table 2-1 lists the recommended equipment you need for comprehensive, DC-only, and

AC-only calibration procedures. You can use alternate equipment, such as a DC transfer standard and characterized resistors, as long as the equipment has speciﬁcations at least as good as those listed in the table. In general, equipment uncertainty should be at least four times better than corresponding Model 2750 speciﬁcations.

Model 2750 Calibration

Table 2-1

Recommended equipment for comprehensive calibration

Fluke 5700A Calibrator:

AC Voltage

DC Voltage

10V: ±5ppm

100V: ±7ppm

Miscellaneous Equipment:

Keithley 8610 low-thermal shorting plug. Double banana plug to double banana plug shielded cable. BNC to double banana plug shielded cable.

*1kHz speciﬁcations. 10mV and 700V points require 1kHz only. All calibrator speciﬁcations are 90-day, 23°C ±5°C speciﬁcations

and indicate total absolute uncertainty at speciﬁed output.

(1kHz, 50kHz)* DC Current

10mV: ±710ppm

100mV: ±200ppm

1V: ±82ppm

10V: ±82ppm 100V: ±90ppm 700V: ±85ppm

10mA: ±60ppm

100mA: ±70ppm

1A: ±110ppm

AC Current

(1kHz) Resistance

100mA: ±190ppm

1A: ±690ppm 2A: ±670ppm

100kΩ: ±13ppm

100Ω: ±17ppm 10kΩ: ±11ppm

1MΩ: ±18ppm

2-6 Calibration Model 2750 Multimeter/Switch System Service Manual

Aborting calibration

You can abort the front panel calibration process at any time by pressing EXIT. The instrument will then ask you to conﬁrm your decision to abort with the following message:

ABORT CAL?

Press EXIT to abort calibration at this point, or press any other key to return to the calibration process.

NOTE The Model 2750 will not respond to any remote programming commands while

the ABORT CAL? message is displayed.

Front panel calibration

Follow the steps in the following paragraphs in the order shown for comprehensive, DC only, and AC only calibration procedures.

The procedures for front panel calibration include:

• Preparing the Model 2750 for calibration

• Front panel short and open calibration

• DC voltage calibration

• Resistance calibration

• DC current calibration

• AC voltage calibration

• AC current calibration

• Setting calibration dates

Preparing the Model 2750 for calibration

1. Turn on the Model 2750, and allow it to warm up for at least two hours before performing a calibration procedure.

2. Start the calibration process as follows: a. Access the calibration menu by pressing SHIFT then TEST, then display

TEST: CALIB using the up or down range key. Press ENTER.

b. Use the up or down range key to scroll through the available calibration menu

items until the unit displays RUN, then press ENTER.

c. At the prompt, enter the calibration code. (The default code is 002750.) Use

the left and right arrow keys to move among the digits; use the up range key to increment numbers, and press the down range key to specify alphabetic letters. Conﬁrm the code by pressing ENTER.

d. Choose N at the prompt to proceed without changing the code, then press

ENTER.

Model 2750 Multimeter/Switch System Service Manual Calibration 2-7

3. Choose which of the calibration tests summarized in Table 2-2 you want to run at the CAL: RUN prompt. Use the up and down range keys to scroll through the options; select your choice by pressing ENTER.

Table 2-2

Comprehensive calibration procedures

Procedure Menu Choice Procedures

Full calibration

DCV, DCI, and ohms

ACV and ACI

Front panel short and open calibration

At the Model 2750 prompt for a front panel short, do the following:

1. Connect the Model 8610 low-thermal short to the instrument front panel INPUT and SENSE terminals as shown in Figure 2-1. Make sure the INPUTS button is not pressed in so that the front inputs are selected. Wait at least three minutes before proceeding to allow for thermal equilibrium.

Figure 2-1

Low-thermal short connections

CONT

OCOMP

RATIO

CH AVG

SHIFT

LOCAL

POWER

MATH

DCV

EX TRIG

SAVE SETUP

OPEN

OUTPUT

DRYCKT

TRIG

DCIACV

LIMITS ON/OFFDELAY

STORE

RECALL

CONFIG HALT

STEP SCAN

PERIOD SENSOR

Ω

ACI

TEMP

FREQ

Ω

MONITOR

TYPE

CH-OFF CARD

RELFILTER

LSYNC

RS-232

TEST

GPIB

EXIT ENTER

DIGITS RATE

RANGE

AUTO

RANGE

Model 2750

SLOT 1

SLOT 2

SLOT 3

SLOT 4

SLOT 5

ALL

All comprehensive calibration steps

(DC and AC).

DC voltage, DC current, and resistance

calibration.

MODEL 2750 MULTIMETER/SWITCH SYSTEM

AC voltage and AC current calibration.

INTEGRA SERIES

S+

350V PEAK

SENSE

Ω 4 WIRE

INPUT

FRONT/REAR

CAT I

Model 2750 Calibration

INPUT

AMPS

1000V PEAK

500V PEAK

3A, 250V

Model 8610

Low-thermal

short

S- LO

NOTE Be sure to connect the low-thermal short properly to the HI, LO, and SENSE ter-

minals. Keep drafts away from low-thermal connections to avoid thermal drift, which could affect calibration accuracy.

2. Press ENTER to start short-circuit calibration. While the unit is calibrating, it will display:

CALIBRATING

2-8 Calibration Model 2750 Multimeter/Switch System Service Manual

3. When the unit is ﬁnished with short-circuit calibration, it will display the following prompt:

OPEN CIRCUIT

4. Remove the calibration short, and press ENTER. During this phase, the CALIBRATING message will be displayed.

NOTE Be sure to minimize movement near front input terminals. Excessive movements

can cause capacitive coupling errors, which could affect calibration accuracy.

DC volts calibration

After the front panel short and open procedure, the unit will prompt you for the ﬁrst DC voltage: +10V. Do the following:

1. Connect the calibrator to the Model 2750 as shown in Figure 2-2. Wait three minutes to allow for thermal equilibrium before proceeding.

Figure 2-2

Connections for DC volts and ohms calibration

Model 2750

Front Panel

Sense

Input

Output

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

500V PEAK

INPUT

FRONT/REAR

AMPS

CAT I

3A, 250V

DC Voltage and Resistance Calibrator

Sense

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 Calibration 2-9

NOTE Although 4-wire connections are shown, the sense leads are connected and dis-

connected at various points in this procedure by turning calibrator external sense on or off as appropriate. If your calibrator does not have provisions for turning external sense on and off, disconnect the sense leads when e xternal sensing is to be turned off, and connect the sense leads when external sensing is to be turned on.

2. Set the calibrator to output DC volts, and turn external sense off.

3. Perform the steps listed in Table 2-3 to complete DC volts calibration. For each calibration step:

• Set the calibrator to the indicated value, and make sure it is in OPERATE.

• Press the ENTER key to calibrate that step.

• Wait until the Model 2750 ﬁnishes each step. (The unit will display the CALIBRATING message while calibrating.)

NOTE If your calibrator cannot output the values recommended in Table 2-3, use the

left and right arrow keys, and the up and down range ke ys to set the Model 2750 display value to match the calibrator output voltage.

Table 2-3

DC volts calibration summary

Model 2750 Calibration

Calibration Step Calibrator Voltage Allowable Range

+10V

-10V

100V

+10.00000V

-10.00000V

+100.0000V

+9V to +11V

-9V to -11V

+90V to +110V

2-10 Calibration Model 2750 Multimeter/Switch System Service Manual

Resistance calibration

Completing the 100V DC calibration step ends the DC voltage calibration procedure. The Model 2750 will then prompt you to connect 100Ω. Follow these steps for resistance calibration:

1. Set the calibrator output for resistance, and turn on external sense.

NOTE Use external sense (4-wire Ω) when calibrating all resistance ranges. Be sure

that the calibrator external sense mode is turned on.

2. Perform the calibration steps summarized in Table 2-4. For each step:

• Set the calibrator to the indicated value, and place the unit in operate. (If the calibrator cannot output the exact resistance value, use the Model 2750 left and right arrow keys and the range keys to adjust the Model 2750 display to agree with the actual calibrator resistance.)

• Press the ENTER key to calibrate each point.

• Wait for the Model 2750 to complete each step before continuing.

Table 2-4

Ohms calibration summary

Calibration Step Calibrator Resistance* Allowable Range

100Ω

10kΩ

100kΩ

1MΩ

*Nominal resistance. Adjust Model 2750 calibration parameter to agree with actual value.

100Ω

10kΩ

100kΩ

1MΩ

90Ω to 110Ω 9kΩ to 11kΩ

90kΩ to 110kΩ

0.9MΩ to 1.1MΩ

Model 2750 Multimeter/Switch System Service Manual Calibration 2-11

DC current calibration

After the 1MΩ resistance point has been calibrated, the unit will prompt you to apply 10mA. Follow these steps for DC current calibration:

1. Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.

Figure 2-3

Connections for DC and AC amps calibration

Model 2750

Front Panel

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

INPUT

FRONT/REAR

AMPS

CAT I

DC and AC Current Calibrator

Output

Input

PEAK

500V PEAK

3A, 250V

Output

Amps

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

2. Calibrate each current step summarized in Table 2-5. For each step:

• Set the calibrator to the indicated DC current, and make sure the unit is in OPERATE.

• Make sure the Model 2750 display indicates the correct calibration current.

• Press ENTER to complete each step.

• Allow the Model 2750 to ﬁnish each step.

Model 2750 Calibration

NOTE If you are performing DC-only calibration, proceed to “Setting calibration

dates and saving calibration.”

Table 2-5

DC current calibration summary

Calibration Step Calibrator Current Allowable Range

10mA

100mA

10.00000mA

100.0000mA

1.000000A

9mA to 11mA

90mA to 110mA

0.9A to 1.1A

2-12 Calibration Model 2750 Multimeter/Switch System Service Manual

AC voltage calibration

Follow these steps for AC voltage calibration:

1. Connect the calibrator to the Model 2750 INPUT HI and LO terminals as shown in

Figure 2-4.

Figure 2-4

Connections for AC volts calibration

AC Voltage Calibrator

Model 2750

Front Panel

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

500V PEAK

INPUT

FRONT/REAR

AMPS

CAT I

3A, 250V

Input

Output

Input

2. Perform the calibration steps summarized in Table 2-6. For each step:

• Set the calibrator to the indicated value, and make sure the calibrator is in OPERATE.

• Press ENTER to complete each step.

• Wait until the Model 2750 completes each step.

Table 2-6

AC voltage calibration summary

Calibration Step Calibrator Voltage, Frequency

10mV AC at 1kHz 100mV AC at 1kHz 100mV AC at 50kHz

1V AC at 1kHz

1V AC at 50kHz 10V AC at 1kHz 10V AC at 50kHz

100V AC at 1kHz 100V AC at 50kHz 700V AC at 1kHz

10.00000mV, 1kHz

100.0000mV, 1kHz

100.0000mV, 50kHz

1.000000V, 1kHz

1.000000V, 50kHz

10.00000V, 1kHz

10.00000V, 50kHz

100.0000V, 1kHz

100.0000V, 50kHz

700.000V, 1kHz

Model 2750 Multimeter/Switch System Service Manual Calibration 2-13

AC current calibration

After the 700VAC at 1kHz point has been calibrated, the unit will prompt you for 100mA at 1kHz. Follow these steps for AC current calibration:

1. Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.

2. Perform the calibration steps summarized in Table 2-7. For each step:

• Set the calibrator to the indicated current and frequency, and make sure the unit is in OPERATE.

• Press ENTER to complete each calibration step.

• Allow the unit to complete each step before continuing.

Table 2-7

AC current calibration summary

Calibration Step Calibrator Current, Frequency

100mA at 1kHz

1A at 1kHz 2A at 1kHz

100.0000mA, 1kHz

1.000000A, 1kHz

2.000000A, 1kHz

Model 2750 Calibration

Setting calibration dates and saving calibration

At the end of the calibration procedure, the instrument will display the CALIBRATION COMPLETE message. Press ENTER to continue, and the Model 2750 will prompt you to enter the calibration date and the calibration due date. Set these dates as follows:

1. At the CAL DATE: prompt, use the left and right arrow keys and the range keys to set the calibration date, then press ENTER.

2. The unit will then prompt you to enter the next calibration due date with this prompt: CAL NDUE:. Use the left and right arrow keys and the range keys to set the calibration due date, then press ENTER.

3. The unit will prompt you to save new calibration constants with this message: SAVE CAL? YES. To save the new constants press ENTER. If you do not want to save the new constants press the down range key to toggle to NO, then press ENTER.

NOTE Calibration constants calculated during the present calibration procedure will

not be saved unless you choose the YES option. Previous calibration constants will be retained if you select NO.

2-14 Calibration Model 2750 Multimeter/Switch System Service Manual

Remote calibration

Follow the steps in this section to perform comprehensive procedures via remote. See Appendix B for a detailed list and description of remote calibration commands.

When sending calibration commands, be sure that the Model 2750 completes each step before sending the next command. You can do so either by observing the front panel CALIBRATING message, or by detecting the completion of each step over the bus. (See

Appendix B, “Detecting calibration step completion.”)

The procedures for calibrating the Model 2750 via remote include:

• Preparing the Model 2750 for calibration

• Front panel short and open calibration

• DC volts calibration

• Resistance calibration

• DC current calibration

• AC volts calibration

• AC current calibration

• Programming calibration dates

• Saving calibration constants

• Locking out calibration

NOTE As with front panel calibration, you can choose to perform comprehensive, DC-

only, or AC-only calibration. Be sure to include a space c har acter between eac h command and parameter.

Preparing the Model 2750 for calibration

1. Connect the Model 2750 to the IEEE-488 bus of the computer using a shielded IEEE-488 cable, such as the Keithley Model 7007, or connect the unit to a computer through the RS-232 port using a straight-through 9-pin to 9-pin cable (use a 9-25-pin adapter if necessary).

2. Turn on the Model 2750, and allow it to warm up for at least two hours before performing calibration.

3. Make sure the primary address of the Model 2750 is the same as the address speciﬁed in the program that you will be using to send commands. (Use the GPIB key.)

4. Unlock the calibration function by sending this command: :CAL:PROT:CODE 'KI002750' (The above command shows the default code, KI002750. Substitute the correct

code if changed.)

5. Send the following command to initiate calibration: :CAL:PROT:INIT

Model 2750 Multimeter/Switch System Service Manual Calibration 2-15

NOTE DC calibration can be partially performed if desired. For example, to calibrate

only the 100Ω range, perform the DCU and 100Ω range steps, then save calibration using :CAL:PROT:SAVE. Uncalibrated ranges will retain previous calibration constants and can be veriﬁed as discussed in Section 1.

Short and open calibration

1. Connect the Model 8610 low-thermal short to the instrument INPUT and SENSE terminals as shown in Figure 2-1. Make sure the INPUTS button is not pressed in so that the front inputs are active. Wait at least three minutes before proceeding to allow for thermal equilibrium.

NOTE Be sure to connect the low-thermal short properly to the HI, LO, and SENSE ter-

minals. Keep drafts away from low-thermal connections to avoid thermal drift, which could affect calibration accuracy.

2. Send the following command: :CAL:PROT:DC:STEP1

3. After the Model 2750 completes this step, remove the low-thermal short, and then send this command:

:CAL:PROT:DC:STEP2

Model 2750 Calibration

NOTE Be sure to minimize movement near front input terminals. Excessive movements

can cause capacitive coupling errors, which could affect calibration accuracy.

DC volts calibration

After the front panel short and open steps, do the following:

1. Connect the calibrator to the Model 2750 as shown in Figure 2-2. Allow three minutes for thermal equilibrium.

NOTE Although 4-wire connections are shown, the sense leads are connected and dis-

2. Perform the calibration steps summarized in Table 2-8. For each step:

• Set the calibrator to the indicated voltage, and make sure the unit is in operate. (Use the recommended voltage if possible.)

• Send the indicated programming command. (Change the voltage parameter if you are using a different calibration voltage.)

• Wait until the Model 2750 completes each step before continuing.

2-16 Calibration Model 2750 Multimeter/Switch System Service Manual

NOTE Ensure the calibrator has settled to the ﬁnal value. You can do so by verifying

that the “Settled” indicator is off, or by using the *OPC? (operation complete) query.

Table 2-8

DC voltage calibration programming steps

Calibration

Step Calibrator Voltage Calibration Command*

+10V

-10V

100V

*Use recommended value where possible. Change parameter accordingly if using a different calibrator voltage.

+10.00000V

-10.00000V

100.0000V

:CAL:PROT:DC:STEP3 10 :CAL:PROT:DC:STEP4 -10 :CAL:PROT:DC:STEP5 100

Parameter

Range

9 to 11

-9 to -11

90 to 110

Resistance calibration

Follow these steps for resistance calibration:

1. Set the calibrator to the resistance mode, and turn on external sensing.

NOTE Use external sense (4-wire Ω) when calibrating all resistance ranges. Be sure

that the calibrator external sense mode is turned on.

2. Perform the calibration steps summarized in Table 2-9. For each step:

• Set the calibrator to the indicated resistance, and make sure the unit is in operate. (Use the recommended resistance or the closest available value.)

• Send the indicated programming command. (Change the command parameter if you are using a different calibration resistance than that shown.)

• Wait until the Model 2750 completes each step before continuing.

Table 2-9

Resistance calibration programming steps

Calibration

Step

100Ω

10kΩ

100kΩ

1MΩ

*Use exact calibrator resistance value for parameter.

Calibrator Resistance Calibration Command* Parameter Range

100Ω

10kΩ

100kΩ

1MΩ

:CAL:PROT:DC:STEP6 100 :CAL:PROT:DC:STEP7 10E3 :CAL:PROT:DC:STEP8 100E3 :CAL:PROT:DC:STEP9 1E6

90 to 110

9E3 to 11E3

90E3 to 110E3

900E3 to 1.1E6

Model 2750 Multimeter/Switch System Service Manual Calibration 2-17

DC current calibration

After the 1MΩ resistance point has been calibrated, follow these steps for DC current calibration:

1. Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.

2. Perform the calibration steps listed in Table 2-10. For each step:

• Set the calibrator to the indicated current, and make sure the unit is in operate. (Use the recommended current if possible.)

• Send the indicated programming command. (Change the current parameter if you are using a different calibration current.)

• Wait until the Model 2750 completes each step before continuing.

NOTE If you are performing DC-only calibration, proceed to “Programming calibra-

tion dates.”

Table 2-10

DC current calibration programming steps

Model 2750 Calibration

Calibration

Step

10mA

100mA

*Change parameter if using different current.

Calibrator

Current Calibration Command* Parameter Range

10.00000mA

100.00000mA

1.000000A

:CAL:PROT:DC:STEP10 10E-3 :CAL:PROT:DC:STEP11 100E-3 :CAL:PROT:DC:STEP12 1

9E-3 to 11E-3

90E-3 to 110E-3

0.9 to 1.1

2-18 Calibration Model 2750 Multimeter/Switch System Service Manual

AC voltage calibration

Follow these steps for AC voltage calibration:

1. Connect the calibrator to the Model 2750 INPUT HI and LO terminals as shown in

Figure 2-4.

2. Perform the calibration steps summarized in Table 2-11. For each step:

• Set the calibrator to the indicated voltage and frequency, and make sure the unit is in operate. (You must use the stated voltage and frequency.)

• Send the indicated programming command.

• Wait until the Model 2750 completes each step before continuing.

Table 2-11

AC voltage calibration programming steps

Calibration Step Calibrator Voltage, Frequency Calibration Command

10mV AC at 1kHz 100mV AC at 1kHz 100mV AC at 50kHz

1VAC at 1kHz

1VAC at 50kHz 10VAC at 1kHz 10VAC at 50kHz

100VAC at 1kHz 100VAC at 50kHz 700VAC at 1kHz

10.00000mV, 1kHz

100.0000mV, 1kHZ

100.0000mV, 50kHz

1.000000V, 1kHz

1.000000V, 50kHz

10.00000V, 1kHz

10.00000V, 50kHz

100.0000V, 1kHz

100.0000V, 50kHz

700.000V, 1kHz

:CAL:PROT:AC:STEP1 :CAL:PROT:AC:STEP2 :CAL:PROT:AC:STEP3 :CAL:PROT:AC:STEP4 :CAL:PROT:AC:STEP5 :CAL:PROT:AC:STEP6 :CAL:PROT:AC:STEP7 :CAL:PROT:AC:STEP8 :CAL:PROT:AC:STEP9 :CAL:PROT:AC:STEP10

Model 2750 Multimeter/Switch System Service Manual Calibration 2-19

AC current calibration

Follow these steps for AC current calibration:

1. Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.

2. Perform the calibration steps summarized in Table 2-12. For each step:

• Set the calibrator to the indicated current and frequency, and make sure the unit is in operate. (You must use the stated current and frequency.)

• Send the indicated programming command.

• Wait until the Model 2750 completes each step before continuing.

Table 2-12

AC current calibration programming steps

Calibration Step Calibrator Current, Frequency Calibration Command

100mA at 1kHz

1A at 1kHz 2A at 1kHz

100.0000mA, 1kHz

1.000000A, 1kHz

2.000000A, 1kHz

:CAL:PROT:AC:STEP11 :CAL:PROT:AC:STEP12 :CAL:PROT:AC:STEP13

Programming calibration dates

Model 2750 Calibration

Program the present calibration date and calibration due date by sending the following commands:

:CAL:PROT:DATE <year>, <month>, <day> :CAL:PROT:NDUE <year>, <month>, <day>

For example, the following commands assume calibration dates of 3/5/2001 and 3/5/2002 respectively:

:CAL:PROT:DATE 2001, 3, 5 :CAL:PROT:NDUE 2002, 3, 5

Saving calibration constants

After completing the calibration procedure, send the following command to save the new calibration constants:

:CAL:PROT:SAVE

NOTE Calibration constants will not be saved unless the :CAL:PROT:SAVE command

is sent.

Locking out calibration

After saving calibration, send the following command to lock out calibration:

:CAL:PROT:LOCK

2-20 Calibration Model 2750 Multimeter/Switch System Service Manual

Manufacturing calibration

The manufacturing calibration procedure is normally performed only at the factory, but the necessary steps are included here in case the unit is repaired, and the unit requires these calibration procedures.

NOTE If the unit has been repaired, the entire comprehensive calibration procedure

should also be performed in addition to the manufacturing calibration procedure.

Recommended test equipment

Table 2-13 summarizes the test equipment required for the manufacturing calibration

steps. In addition, you will need the calibrator (Table 2-1) and signal generator to com- plete the comprehensive calibration steps.

Table 2-13

Recommended equipment for manufacturing calibration

Stanford Research Systems DS345 Function Generator:

1V RMS, 3Hz, ±5ppm 1V RMS, 1kHz, ±5ppm

Keithley Model 2001 or 2002 Digital Multimeter:

1V, 3Hz AC, ±0.13%

Keithley 7797 Calibration/Extender Board

Extender board preparation

Before performing manufacturing calibration, short the output HI, LO, SHI, and SLO terminals of the 7797 Calibration/Extender together using clean, solid copper wires. These connections will form a low-thermal short necessary for the manufacturing calibration procedure. The Calibration Extender Board should then be installed in scanner Slot #1.

Model 2750 Multimeter/Switch System Service Manual Calibration 2-21

Unlocking manufacturing calibration

To unlock manufacturing calibration, press and hold in the OPEN key while turning on the power.

Measuring function generator signal amplitude

The 3Hz function generator signal amplitude must be accurately measured using the digital multimeter listed in Table 2-13. Proceed as follows:

1. Connect the function generator output to the digital multimeter INPUT jacks. (See

Figure 2-5 for typical connections.)

2. Turn on the function generator and multimeter, and allow a two-hour warm-up period before measuring.

3. Set the function generator to output a 1V RMS sine wave at 3Hz; measure and record the signal amplitude.

Front panel manufacturing calibration

1. Install the shorted calibration extender board (see “Extender board preparation” earlier in this section) in scanner card Slot 1, and select the rear inputs with the INPUTS switch. Allow three minutes for thermal equilibrium.

2. Press in and hold the OPEN key while turning on the power.

3. Press SHIFT then TEST then display CALIB: TEST with the up or down range key. Press ENTER, select RUN, then enter the appropriate calibration code (default: 002750).

4. Select ALL at the CAL:RUN prompt.

5. Press ENTER to perform the ﬁrst manufacturing calibration step.

6. Perform the entire front panel comprehensive calibration procedure discussed earlier in this section. (See “Comprehensive calibration” earlier in this section.)

7. Connect the function generator to the Model 2750 front panel INPUT jacks as shown in Figure 2-5. Select the front input jacks with the INPUTS switch.

Model 2750 Calibration

2-22 Calibration Model 2750 Multimeter/Switch System Service Manual

Figure 2-5

Function generator connections for manufacturing calibration

Function Generator

Model 2750

Front Panel

SENSE

INPUT

Ω 4 WIRE

350V

PEAK

INPUT

FRONT/REAR

AMPS

CAT I

BNC-to-Dual

Banana Plug

Adapter

1000V PEAK

500V PEAK

50Ω

Coax

Cable

3A, 250V

Function

Output

Note: Output voltage must be accurately

measured. (See text.)

8. After the last AC current calibration step, the instrument will prompt you to enter 3Hz at 1V RMS and 1kHz with the following prompts:

• Low-frequency cal: Set the function generator to output a 1V RMS, 3Hz sine wave. Use the left and right arrow keys, and the range keys to adjust the display to agree with the generator amplitude you measured previously, then press ENTER.

• Frequency cal: Set the function generator to output a 1V RMS, 1kHz sine wave. Enter 1.000000kHz at the prompt, then press ENTER.

9. Set the calibration dates, then save calibration to complete the process.

Remote manufacturing calibration

2. Press in and hold the OPEN key while turning on the power.

3. Enable calibration by sending the :CODE command. For example, the default command is:

:CAL:PROT:CODE 'KI002750'

4. Initiate calibration by sending the following command: :CAL:PROT:INIT

5. Calibrate step 0 with the following command: :CAL:PROT:DC:STEP0

Model 2750 Multimeter/Switch System Service Manual Calibration 2-23

6. Perform the entire remote comprehensive calibration procedure discussed earlier in this section. (See “Comprehensive calibration” earlier in this section.)

7. Connect the function generator to the Model 2750 INPUT jacks as shown in

Figure 2-5. Select the front input jacks with the INPUTS switch.

8. Set the generator to output a 1V RMS, 3Hz sine wave, then send the following command:

:CAL:PROT:AC:STEP14 <Cal_voltage> Here <Cal_voltage> is the actual 3Hz generator signal amplitude you measured

previously.

9. Set the generator to output a 1V RMS, 1kHz sine wave, then send the following command:

:CAL:PROT:AC:STEP15 1E3

10. Send the following commands to set calibration dates, save calibration, and lock out calibration:

:CAL:PROT:DATE <year>, <month>, <day> :CAL:PROT:NDUE <year>, <month>, <day> :CAL:PROT:SAVE :CAL:PROT:LOCK

Model 7700 Calibration

Model 7700 calibration

The following procedures calibrate the temperature sensors on the Model 7700 plug-in modules.

NOTE For additional information about the Keithley modules, refer to the module

documentation.

Recommended test equipment

In order to calibrate the Model 7700, you will need equipment summarized in Table 2-14.

Table 2-14

Recommended equipment for Model 7700 calibration

Digital Thermometer:

18 to 28˚C, ±0.1˚C

Keithley 7797 Calibration/Extender Board

2-24 Calibration Model 2750 Multimeter/Switch System Service Manual

Extender board connections

The Model 7700 being calibrated should be connected to the 7797 Calibration/Extender Board, and the extender board should then be installed in scanner Slot #1. Note that the module being calibrated will be external to the Model 2750 to avoid card heating during calibration.

Model 7700 calibration

NOTE Before calibrating the Model 7700, make sure that power has been removed

from the card for at least two hours to allow card circuitry to cool down. After turning on the power during the calibration procedure, complete the procedure as quickly as possible to minimize card heating that could affect calibration accuracy. Allow the Model 2750 to warm up for at least two hours.

Front panel Model 7700 calibration

1. Connect the Model 7700 to the Model 7797 Calibration/Extender Board (see “Extender board connections”).

2. With the power off, install the Model 7700/7797 combination in Slot 1, and select the rear inputs with the INPUTS switch. Allow three minutes for thermal equilibrium.

3. Accurately measure and record the cold temperature of the Model 7700 card surface at the center of the card with an RTD sensor.

4. Press in and hold the Model 2750 OPEN key while turning on the power.

5. Press SHIFT then TEST, then display TEST:CALIB with the up or down range key. Press ENTER, select RUN, then enter the appropriate calibration code (default: 002750).

6. Using the up or down range key, select CARD at the CAL:RUN prompt, then press ENTER.

7. Set the display value to the cold calibration temperature (˚C) you measured in Step 3, then press ENTER to complete Model 7700 calibration.

Model 2750 Multimeter/Switch System Service Manual Calibration 2-25

Remote Model 7700 calibration

1. Connect the Model 7700 to the 7797 Calibration/Extender Board (see “Extender

board connections” above).

2. With the power off, install the Model 7700/7797 combination in Slot 1, and select the rear inputs with the INPUTS switch. Allow three minutes for thermal equilibrium.

3. Accurately measure and record the cold temperature of the Model 7700 card surface at the center of the card.

4. Press in and hold the Model 2750 OPEN key while turning on the power.

5. Enable calibration by sending the :CODE command. For example, the default command is:

:CAL:PROT:CODE 'KI002750'

6. Initiate calibration by sending the following command: :CAL:PROT:CARD1:INIT

7. Calibrate the Model 7700 with the following command: :CAL:PROT:CARD1:STEP0 <temp> Here <temp> is the cold calibration temperature (˚C) measured in Step 3.

8. Send the following commands to save calibration and lock out calibration: :CAL:PROT:CARD1:SAVE

:CAL:PROT:CARD1:LOCK

Model 7700 Calibration

2-26 Calibration Model 2750 Multimeter/Switch System Service Manual

Routine Maintenance

3-2 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

Introduction

The information in this section deals with routine type maintenance and includes procedures for setting the line voltage, replacing the Model 2750 line and front terminal AMPS fuses, and replacing the amps fuses for the Models 7700 plug-in module. Replacement of the Model 2750 non-volatile RAM battery and reading module relay card closure count is also covered.

Setting the line voltage and replacing the line fuse

WARNING Disconnect the line cord at the rear panel, and remove all test leads

connected to the instrument (front and rear) before replacing the line fuse.

The power line fuse is located in the power module next to the AC power receptacle (Figure 3-1). If the line voltage must be changed, or if the line fuse requires replacement, perform the following steps:

1. Place the tip of a ﬂat-blade screwdriver into the power module by the fuse holder assembly (Figure 3-1). Gently push in and to the left. Release pressure on the assembly, and its internal spring will push it out of the power module.

CAUTION For continued protection against ﬁre or instrument damage, replace

the fuse only with the type and rating listed. If the instrument repeatedly blows fuses, locate and correct the cause of the trouble before replacing the fuse.

2. Remove the fuse, and replace it with the type listed in Table 3-1.

Model 2750 Multimeter/Switch System Service Manual Routine Maintenance 3-3

Figure 3-1

Power module

Model 2750

DIGITAL I/O TRIG. LINK

RS-232

IEEE-488

SLT

MADE IN

U.S.A.

SLT

CAT I

Fuse

Line Voltage

Selector

220

240

0 0

120

Spring

Window

Fuse Holder Assembly

SLT

Routine Maintenance

CAUTION Operating the Model 2750 on the wrong line voltage may result in

instrument damage.

3. If conﬁguring the instrument for a different line voltage, remove the line voltage selector from the assembly, and rotate it to the proper position. When the selector is installed into the fuse holder assembly, the correct line voltage appears inverted in the window.

4. Install the fuse holder assembly into the power module by pushing it in until it locks in place.

Table 3-1

Power line fuse

Line Voltage Rating Keithley Part No.

100/120V 200/240V

0.630A, 250V, 5 × 20 mm, slow-blow

0.315A, 250V, 5 × 20 mm, slow-blow

FU-106-.630 FU-106-.315

3-4 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

Replacing the AMPS fuse

The front panel AMPS fuse protects the Model 2750 AMPS current input from an overcurrent condition. Follow the steps below to replace the AMPS fuse.

WARNING Make sure the instrument is disconnected from the power line and

other equipment before replacing the AMPS fuse.

1. Turn off the power, and disconnect the power line and test leads.

2. Using a screwdriver, rotate the fuse carrier one-quarter turn counterclockwise (Figure 3-2). Release pressure on the jack, and its internal spring will push the fuse carrier out of the socket.

CAUTION Do not use a fuse with a higher current rating than speciﬁed or instru-

ment damage may occur. If the instrument repeatedly blows fuses, locate and correct the cause of the trouble before replacing the fuse.

3. Remove the fuse, and replace it with the same type: 3A, 250V, fast-blow, Keithley part number FU-99-1.

4. Install the new fuse by reversing the above procedure.

Figure 3-2

AMPS fuse

SHIFT

LOCAL

POWER

MATH

DCV

EX TRIG

SAVE SETUP

OPEN

OUTPUT

DRYCKT

TRIG

RATIO

DCIACV

LIMITS ON/OFFDELAY

STORE

CONFIG HALT

STEP SCAN

CONT

CH AVG

ACIΩ2Ω4

RECALL

DIGITS RATE

Model 2750

SLOT 1

SLOT 2

SLOT 3

SLOT 4

RANGE

AUTO

RANGE

SLOT 5

MODEL 2750 MULTIMETER/SWITCH SYSTEM

INTEGRA SERIES

OCOMP

PERIOD SENSOR

TEMP

FREQ

MONITOR

TYPE

CH-OFF

CARD

RELFILTER

RS-232

LSYNC

GPIB

TEST

EXIT ENTER

SENSE

INPUT

Ω 4 WIRE

350V

1000V

PEAK

FRONT/REAR

CAT I

PEAK

500V PEAK

INPUT

AMPS

3A, 250V

Rotate

Counterclockwise

Model 2750 Multimeter/Switch System Service Manual Routine Maintenance 3-5

Replacing Model 7700 plug-in module amps fuses

WARNING The information in this section is intended only for qualiﬁed service

personnel. Do not perform these procedures unless you are qualiﬁed to do so.

WARNING Make sure that all plug-in module connections are de-energized and

disconnected before replacing module amps fuses.

1. Turn off the power, and disconnect the power line and external connections from the Model 7700.

2. Open the Model 7700 top cover.

3. Locate the amps fuses for CH21 and CH22 (Figure 3-3).

4. Remove the circuit board from the bottom plastic housing by removing the two bottom screws.

Figure 3-3

Model 7700 amps fuses

CH22 Fuse

Model 7700

SENSE CH1

INPUT

HLHL

CH21 CH22 CH11 CH12 CH13 CH14 CH15 CH16

CH2

HLHL

AMPS

HLHL

HLHLHLHLHLHL

CH6

CH5

CH4

CH3

CH21 Fuse

CH7 CH8 CH9 CH10

HLHLHLHL

CH17 CH18 CH19 CH20

INPUT

(V, 2 WIRE)

SENSE

(OHMS, 4 WIRE)

Routine Maintenance

3-6 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

5. De-solder the blown CH21 or CH22 fuse as required, taking care not to damage the circuit board or spread solder ﬂux around the board.

CAUTION Do not use a fuse with a higher current rating than speciﬁed or module

damage may occur.

6. Install a new 3A, 250V fast-blow fuse, Keithley part number FU-107-1.

7. Solder the new fuse in place using organic (OA based) ﬂux solder, again taking care not to damage the circuit board or spread solder ﬂux around the board.

8. Carefully clean the repaired area of the circuit board with a foam tipped swab or brush dipped in pure water, then blow dry the board with dry nitrogen gas. Allow the board to dry for several hours in a 50˚C low-humidity environment before use.

9. Reinstall the circuit board into the plastic housing, then close the top cover.

Replacing non-volatile RAM battery

The Model 2750 has a three-year lithium battery for non-volatile RAM. Use the procedure below to replace the battery, if required. Refer to the disassembly procedures in Section 5 and the parts list and component layout drawings at the end of Section 6 for more information.

WARNING There is a danger of explosion if the battery is incorrectly replaced.

Replace only with the same or equivalent type recommended by the manufacturer. Dispose of used batteries according to federal, state, and local laws.

The following procedure is intended only for qualiﬁed service personnel. Do not perform this procedure unless you are qualiﬁed to do so.

Disconnect the line cord and all connecting wires from the Model 2750 before removing the top cover.

Model 2750 Multimeter/Switch System Service Manual Routine Maintenance 3-7

WARNING The precautions below must be followed to avoid personal injury.

• Wear safety glasses or goggles when working with lithium

batteries.

• Do not short the battery terminals together.

• Keep lithium batteries away from all liquids.

• Do not attempt to recharge lithium batteries.

• Observe proper polarity when installing the battery.

• Do not incinerate or otherwise expose the battery to excessive heat

(>60°C).

• Bulk quantities of lithium batteries should be disposed of as hazardous waste.

• Dispose of used batteries according to all federal, state, and local laws.

Replace the battery as follows:

1. Before replacing the battery, refer to the troubleshooting procedures in Table 4-4 in

Section 4 to determine if the battery requires replacement

2. Remove the Model 2750 top cover using the disassembly procedures in Section 5.

3. Locate battery BT100 using the motherboard component layout drawing at the end of Section 6.

4. De-solder the battery from the top side of the circuit board.

5. Install a new battery, Keithley part number BA-51, taking care to observe proper polarity.

6. Solder the battery connection to the circuit board using organic (OA-based) ﬂux solder.

7. After soldering, remove all ﬂux using a foam-tipped swab or brush dipped in pure water. Blow dry the board with dry nitrogen gas, then allow the board to dry for several hours in a 50˚C, low-humidity environment before use.

8. Reinstall the top cover by following the disassembly procedures in Section 5 in reverse order.

Routine Maintenance

3-8 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

Plug-in module relay closure count

The Model 2750 keeps an internal count of the number of times each module relay has been closed. This count will help you determine if and when any relays require replacement (see module contact life speciﬁcations). The count can be read or reset only via remote as outlined below.

Closure count commands

Table 3-2 summarizes closure count commands.

Table 3-2

Closure count commands

Command Description

:ROUTe

:CLOSe

:COUNt? (@clist)

:INTerval < NRf> :INTerval?

:RCOunt (@clist)

* Unit must be in manufacturing calibration mode. See text below.

Route subsystem.

Path to CLOSe commands.

Query count for channels in clist (channel list).

Set count update interval in minutes (10 to 1440). Query count update interval.

Reset count for channels in clist.*

Reading relay closure count

To determine the closure count of speciﬁc channels, send this query via remote:

:ROUTe:CLOSe:COUNt? (@clist)

Here, clist is the summary of channels. For example, to determine the closure count of channels 1 and 4 of a module in slot 1, the following query would be sent:

:ROUT:CLOS:COUN? (@101,104)

The following query would determine the closure count of slot 1 module channels 1 through 10:

:ROUT:CLOS:COUN? (@101:110)

Model 2750 Multimeter/Switch System Service Manual Routine Maintenance 3-9

Resetting relay closure count

NOTE The Model 2750 must be in the manufacturing calibration mode to reset the clo-

sure count. To do so, press and hold the OPEN key while turning on the power, then send the :CAL:PROT:CODE “code” to unlock calibration (default code: KI002750). After resetting relay counts, send :CAL:PROT:LOCK to lock out calibration.

To reset the relay closure count of speciﬁc channels to 0, send this command via remote:

:ROUTe:CLOSe:RCOunt (@clist)

Again clist is the summary of channels to be reset. For example, the following command resets channels 2 and 7 of a module in slot 1 to 0:

:ROUT:CLOS:RCO (@102,107)

The following command resets the count of slot 1 module channels 1 through 10:

:ROUT:CLOS:RCO (@101:110)

Setting count update interval

Relay closure counts are updated in temporary RAM every time a channel is closed regardless of how it was closed: by an SCPI command, front panel control, or during a scan. These counts are permanently written to the EEPROM on the card only at a user-settable time interval (which has a factory default of 15 minutes), or whenever the counts are queried. Valid intervals (set in integer number of minutes) are between 10 and 1440 minutes (24 hrs). Relay closures are counted only when a relay cycles from open to closed state. If you send multiple close commands to the same channel without sending an open command, only the ﬁrst closure will be counted.

The lower the interval, the less chance there is of losing relay counts due to power failures. However, writing to the EEPROM more often may reduce scanning throughput. The higher the interval, the less scanning throughput is reduced, but more relay counts may be lost in the event of a power failure.

To set the count update interval, send this command:

:ROUTe:CLOSe:COUNt:INTerval <interval>

For example, to set the interval to 30 minutes, send this command:

:ROUT:CLOS:COUN:INT 30

Routine Maintenance

3-10 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

Rack mounting

Rack mount kit

Model 4288-7 rack mount kit — Mounts a Model 2750 in a standard 19-inch rack. Includes rear brackets to provide additional support for a mainframe that has two or more switching modules installed.

NOTE The Model 2750 includes hardware that allows it to be mounted to the front r ails

of a standard 19-inch rack. With two or more switching modules installed, rear support brackets may be required. The Model 4288-7 rack mount kit includes rear support brackets.

Rack mount procedure

The Model 2750 can be mounted in a standard 19-inch rack. For a mainframe that has one or no switching modules installed, the Model 2750 can be secured to the front rails of the rack.

The hardware necessary to secure the mainframe to the front rails of the rack is supplied with the Model 2750. The supplied hardware kit includes four dress screws and four retaining clips. Each retaining clip has a captive nut.

Perform the following steps to mount the Model 2750 to the front rails of the rack:

WARNING Make sure the Model 2750 is turned off, the line cord is disconnected,

and it is not connected to any external circuitry.

1. Select a location in the rack. The mainframe takes up 3.5 inches of vertical space.

Model 2750 Multimeter/Switch System Service Manual Routine Maintenance 3-11

2. Using Figure 3-4 as a guide, install two retaining clips on the left front rail. Slide each retaining clip over a mounting hole such that the captive nut is positioned on the inside of the rack cabinet. In a similar manner, install two retaining clips on the right front rail.

Figure 3-4

Rack preparation

Left Front Rack Rail

1.75”

Retaining Clips with Nuts

3. Remove the four foot assemblies from the bottom of the Model 2750. The retaining screw for an assembly is located under the rubber foot. Simply pull off the rubber feet to gain access to the screws. Retain these foot assemblies for future use.

4. Position the Model 2750 in the rack and loosely attach the front panel to the rack rails using the four supplied dress screws.

5. Tighten the four dress screws.

CAUTION For a Model 2750 that has two or more installed switching modules,

rear brackets may be required to support the additional weight. The Model 4288-7 is a rack mount kit for the Model 2750 that uses rear support brackets.

Routine Maintenance

3-12 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual

Troubleshooting

4-2 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

Introduction

This section of the manual will assist you in troubleshooting and repairing the Model

2750. Included are self-tests, test procedures, troubleshooting tables, and circuit descriptions. It is left to the discretion of the repair technician to select the appropriate tests and documentation needed to troubleshoot the instrument. Refer to the disassembly procedures in Section 5 and the parts lists in Section 6 for further information.

WARNING The information in this section is intended only for qualiﬁed service

personnel. Do not perform these procedures unless you are qualiﬁed to do so. Some of these procedures may expose you to hazardous voltages that could cause personal injury or death. Use caution when working with hazardous voltages.

The metal shield located on the motherboard is at analog LO potential and may have hazardous voltages. To avoid a possible shock hazard, connect the metal shield to chassis ground before servicing.

Repair considerations

Before making any repairs to the Model 2750, be sure to read the following considerations.

CAUTION The PC boards are built using surface mount techniques and require

specialized equipment and skills for repair. If you are not equipped and/or qualiﬁed, it is strongly recommended that you send the unit back to the factory for repairs or limit repairs to the PC board replacement level. Without proper equipment and training, you could damage a PC board beyond repair.

• Repairs will require various degrees of disassembly. However, it is recommended that the Front Panel Tests be performed prior to any disassembly. The disassembly instructions for the Model 2750 are contained in Section 5 of this manual.

• Do not make repairs to surface mount PC boards unless equipped and qualiﬁed to do so (see previous CAUTION).

• When working inside the unit and replacing parts, be sure to adhere to the handling precautions and cleaning procedures explained in Section 5.

• Many CMOS devices are installed in the Model 2750. These static-sensitive devices require special handling as explained in Section 5.

• Whenever a circuit board is removed or a component is replaced, the Model 2750 must be recalibrated. See Section 2 for details on calibrating the unit.

Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-3

Power-on self-test

During the power-on sequence, the Model 2750 will perform a checksum test on its EPROM (U156 and U157) and test its RAM (U151, U152, U164 and U193). If one of these tests fails, the instrument will lock up.

Front panel tests

There are two front panel tests: one to test the functionality of the front panel keys and one to test the display. In the event of a test failure, refer to “Display board checks” for details on troubleshooting the display board.

KEY test

The KEY test allows you to check the functionality of each front panel key. Perform the following steps to run the KEY test:

1. Press SHIFT and then TEST to access the self-test options.

2. Use the up or down RANGE key to display “TEST: KEY.”

3. Press ENTER to start the test. When a key is pressed, the label name for that key is displayed to indicate that it is functioning properly. When the key is released, the message “NO KEY PRESS” is displayed.

4. Pressing EXIT tests the EXIT key. However, the second consecutive press of EXIT aborts the test and returns the instrument to normal operation.

DISP test

The display test allows you to verify that each segment and annunciator in the vacuum ﬂuorescent display is working properly. Perform the following steps to run the display test:

1. Press SHIFT and then TEST to access the self-test options.

2. Use the up or down RANGE key to display “TEST: DISP.”

3. Press ENTER to start the test. There are ﬁve parts to the display test. Each time ENTER is pressed, the next part of the test sequence is selected. The ﬁve parts of the test sequence are as follows:

a. All annunciators are displayed. b. The segments of each digit are sequentially displayed. c. The 12 digits (and annunciators) are sequentially displayed. d. The annunciators located at either end of the display are sequentially

displayed.

e. The LEDs are displayed.

4. When ﬁnished, abort the display test by pressing EXIT. The instrument returns to normal operation.

Troubleshooting

4-4 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

Principles of operation

The following information is provided to support the troubleshooting tests and procedures covered in this section of the manual. Refer to the following block diagrams:

Figure 4-1 — Power supply block diagram.

Figure 4-2 — Digital circuitry block diagram.

Figure 4-3 — Analog circuitry block diagram.

Power supply

The following information provides some basic circuit theory that can be used as an aid to troubleshoot the power supply. A block diagram of the power supply is shown in

Figure 4-1.

Figure 4-1

Power supply block diagram

Fuse

Power

Switch

Line

Voltage

Select

Switch

Power

Transformer

CR104 C156, C175 C281, U144 C273, C274

CR116, CR117

C104, U101

CR102, CR115

C131, C148

U119, U125

CR103

C146 U124

+5VD

D Common

+37V

D Common

+18V +15.7V

A Common

-15.7V

-18V

+5V

A Common

Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-5

AC power is applied to the AC power module receptacle. Power is routed through the line fuse and line voltage selection switch of the power module to the power transformer. The power transformer has a total of four secondary windings for the various supplies.

AC voltage for the display ﬁlaments is taken from a power transformer secondary at F1 and F2, and then routed to the display board.

Each DC supply uses a rectiﬁer and a capacitive ﬁlter, and many supplies use an IC regulator. Table 4-1 summarizes rectiﬁer, ﬁlter, and regulator circuits for the various DC supplies.

Table 4-1

Power supply components

Supply Rectiﬁer Filter Regulator

+5VD +37V +15.7V

-15.7V +5V, +5VRL, +5V2 +18V

-18V

CR104 CR116, CR117 CR102, CR115 CR102, CR115 CR103 CR102 CR102

C281, C156, C175, C273, C274 C104 C148 C131 C146 C148 C131

U144 U101 U125 U119 U124

Troubleshooting

4-6 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

Display board

Display board components are shown in the digital circuitry block diagram in Figure 4-2.

Figure 4-2

Digital circuitry block diagram

Analog

Circuitry

(See Figure 4-3)

U122 U127 U170 U173 U174 U195 U196

XADTX

XADCLK

XADTS

XADRX

Slot

Control

P T

U175 U150 U155

Trigger

U146

Trigger

Link

NVRAM

Line Sync

Control

U179 U180 U181 U182 U183 U184 U186

U136

ADTX

ADCLK

ADTS

ADRXB

TRIG IN

TRIG OUT

ROM

U156, U157

68332

µP

U135

Data OUT

Digital OUT

BAT

BT100

U151, U152 U164, U193

OUT

Data IN

RAM

Battery

Back

Control/

Realtime Clock

U171

Display Board

Controller

U401

XTAL Y101

RS-232

U159

GPIB

U158, U160,

U161

Digital Output

U188, U189

Digital Input

Y103

Keypad

Display

DS401

RS-232

Port

IEEE-488

Bus

Digital

I/O

U146, U191

U192

Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-7

Microcontroller

U401 is the display board microcontroller that controls the display and interprets key data. The microcontroller uses three internal peripheral I/O ports for the various control and read functions.

Display data is serially transmitted to the microcontroller from the digital section via the TXB line to the microcontroller RDI terminal. In a similar manner, key data is serially sent back to the digital section through the RXB line via TDO. The 4MHz clock for the microcontroller is generated by crystal Y401.

Display

DS401 is the display module, which can display up to 12 alphanumeric characters and includes the various annunciators and ﬁve LED annunciators.

The display uses a common multiplexing scheme with each character refreshed in sequence. U402 and U403 are the drivers for the display characters and annunciators. Note that data for the drivers are serially transmitted from the microcontroller (MOSI and PC1).

Filament voltage for the display is derived from the power supply transformer (F1 and F2). The display drivers require +37VDC and +5VDC, which are supplied by U144 (+5VD) and U101 (+37V).

Key matrix

The front panel keys (S401-S430) are organized into a row-column matrix to minimize the number of microcontroller peripheral lines required to read the keyboard. A key is read by strobing the columns and reading all rows for each strobed column. Key-down data is interpreted by the display microcontroller and sent back to the main microprocessor using proprietary encoding schemes.

Digital circuitry

Refer to Figure 4-2 for the following discussion on digital circuitry.

Microprocessor

U135 is a 68332 microprocessor that oversees all operating aspects of the instrument. The MPU has a 16-bit data bus and provides a 21-bit address bus. It also has parallel and serial ports for controlling various circuits. For example, the RXD and TXD lines are used for the RS-232 interface.

The MPU clock frequency of 19.92MHz is controlled by crystal Y101. MPU RESET is performed momentarily on power-up.

Memory circuits

ROMs U156 and U157 store the ﬁrmware code for instrument operation. U157 stores the D0-D7 bits of each data word, and U156 stores the D8-D15 bits. RAMs U151, U152, U164, and U193 provide battery backed operating storage.

Troubleshooting

4-8 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

Semi-permanent storage facilities include NVRAM U136. This IC stores such information as instrument setup and calibration constants. Data transmission from this device is done in a serial fashion.

U194, U171, Y103, and BT100 make up the battery watchdog control, along with the realtime clock. U171 automatically senses when the +5VD supply is being powered down and then switches to BT100 for power.

RS-232 interface

Serial data transmission and reception is performed by the TXD and RXD lines of the MPU. U159 provides the necessary voltage level conversion for the RS-232 interface port.

IEEE-488 interface

U158, U160, and U161 make up the IEEE-488 interface. U158, a 9914A GPIA, takes care of routine bus overhead such as handshaking, while U160 and U161 provide the necessary buffering and drive capabilities.

Trigger circuits

Buffering for Trigger Link input and output is performed by U146. Trigger input and output is controlled by the TP5 and PC2 lines of the MPU.

Digital I/O

U146, U191, and U192 make up the digital input circuitry. External triggering can occur on J1006 or J1007. U192 allows hardware handshaking to external controllers by gating off triggers.

U188 and U189 provide digital output. The two driver ICs, U188 and U189, provide current sink capability of 250mA each.

Module slot control

U122, U127, U170, U173, U174, U195, and U196 make up the control circuitry that allows communication of relay data to Slot 1, Slot 2, Slot 3, Slot 4, or Slot 5.

Line sync

U179, U180, U181, U182, U183, U184, and U186 are used to control A/D triggers synchronized at the zero cross point of the power line voltage. U186 controls zero crossing detection, while U182 and U183 preserve the trigger states until the zero crossing threshold is detected.

Analog circuitry

Refer to Figure 4-3 for the following discussion on analog circuitry.

Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-9

Figure 4-3

Analog circuitry block diagram

A/D MUX

Front Terminals

S101

Overload

Protection

Q103, 107, 117,

CR101, 113,

U128,140, 143

VR110, 111

ADC

U165

Digital

Circuitry

(See Figure 4-2)

Front Terminals

S101

Scanner Outputs

Front Terminals

S101

Scanner Outputs

Front Terminals

S101

Scanner Outputs

Dry Circuit

Stability

Clamp

C152, C164,

K104

INPUT

SENSE

AMPS

DCV

Divider R117, Q109, Q114, Q136

Current

Shunts

K103, R158,

R205, R338

½K102, U102, U103, U105,

U112, U118, U111, U110, U117

K101

SSP*

Q101, Q102

SSP* CR105, Q159

DCV/100

Q124, Q125, Q126, ½K102, U123, U133

SSP*

Q150, Q151

SSP*

Q122, Q135

DCA

ACA

AC Switching

Gain

ACV,

FREQ

Ohms I-Source

Q119, Q123,

DCV

OHMS

DCV & Ohms

Switching K101, Q104, Q108, Q113

BUFCOM

Buffer U113

Dry Circuit

Voltage Clamps

U162, U206

Low Ohms

Sensing

Q106

A/D

MUX &

Gain U129, U132 U163, U166

Temp.

Sensor

(CJC)

Protection

DS101,

102

Troubleshooting

Scanner Outputs

Scanner

Inputs

Scanner

Inputs

Slot 1

Slot 5

* Solid State Protection

Slot

Control

Temp. Sensors

4-10 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

INPUT HI

INPUT HI protection is provided by the SSP (Solid State Protection) circuit. The SSP is primarily made up of Q101 and Q102. An overload condition opens Q101 and Q102, which disconnects the analog input signal from the rest of the analog circuit.

Note that for the 100VDC and 1000VDC ranges, Q101 and Q102 of the SSP are open. The DC voltage signal is routed through the DCV Divider (Q114 and Q136 on) to the DCV switching circuit.

AMPS input

The ACA or DCA input signal is applied to the Current Shunt circuit, which is made up of K103, R158, R205, and R338. For the 20mA DC range, 5.1Ω (R205 R338 + R158) is shunted across the input. Relay K103 is energized (set state) to select the shunts. For all other DCA ranges, and all ACA ranges, 0.1Ω (R158) is shunted across the input (K103 reset).

The ACA signal is then sent to the AC Switching & Gain circuit, while the DCA signal is routed directly to the A/D MUX & Gain circuit.

Signal switching

Signal switching for DCV and OHMS is done by the DCV & Ohms Switching circuit. FETs Q113, Q104, and Q108 connect the DCV or ohms signal to the X1 buffer (U113). For offset-compensated ohms and all dry-circuit ohms measurements, the signal is routed directly to the A/D mux by Q106, bypassing U113.

Note that the reference current for OHMS is generated by the Ohms I-Source circuit. For 4-wire ohms measurements, SENSE LO is connected to U163.

Signal switching and gain for ACV, FREQ and ACA is done by the AC Switching & Gain circuit, which is primarily made up of K102, U102, U103, U105, U112, U118, U111, U110, and U117. Note that U111 is used for frequency adjustment. The states of these analog switches vary from unit to unit.

Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-11

Multiplexer and A/D converter

All input signals, except FREQ, are routed to the A/D MUX & Gain circuit. The multiplexer (U163) switches the various signals for measurement. In addition to the input signal, the multiplexer also switches among reference and zero signals at various phases of the measurement cycle.

When the input signal is selected by the MUX, it is ampliﬁed by U132 and U166. Gain is controlled by switches in U129 and associated resistors.

The multiplexed signals of the measurement cycle are routed to the A/D Converter (U165) where it converts the analog signals to digital form. The digital signals are then routed through an opto-isolator to the MPU to calculate a reading.

The multiplexer ampliﬁer has an overload protection circuit. The circuit reduces the multiplexer gain to unity during overload conditions. This circuit is made up of primarily CR101, CR113, Q103, Q107, Q117, U128, U140, U143, VR110, and VR111.

Scanner card signals

Scanner card input signals are connected directly to installed scanner cards. Scanner card output signals are routed internally to the INPUTS switch, which selects between the front panel terminals and the scanner card outputs.

The Model 7700, 7706, and 7708 modules contain CJC (voltage) temperature sensors. These sensors are multiplexed into U163 at various phases of the measurement cycle.

Dry circuit ohms

Figure 4-4 shows a simpliﬁed schematic of the dry circuit ohms circuitry. Dry circuit ohms

measurements are made similar to those for conventional ohms in that a 10µA to 10mA current source (depending on ohms range) forces a current through the DUT resistance, and the voltage across the device is measured. In the case of dry circuit ohms, however, there are two clamps that act to limit the voltage across the DUT to 20mV. Normally the voltage is sensed across the SENSE HI and LO terminals, and the main clamp restricts the DUT voltage to 20mV. A secondary clamp monitors the voltage across INPUT HI and LO and acts to restrict the voltage to 50mV if the SENSE terminals are not connected to the DUT. When either clamp acts to limit the voltage across the DUT, the current source goes into compliance, effectively turning the current source into a voltage source thus limiting the DUT voltage to 20mV or 50mV as the case may be. Note that a 0.8µF capacitor and 100kΩ resistor are connected across the DUT during dry circuit ohms measurements for stabilization.

Troubleshooting

4-12 Troubleshooting Model 2750 Multimeter/Switch System Service Manual

Figure 4-4

Simpliﬁed schematic of dry circuit ohms

20mV Reference

(Main Clamp,

Monitors SENSE HI)

50mV Reference

(Secondary Clamp,

Monitors INPUT HI)

10µA

100µA

1mA

10mA

I Source

↔

SSP*

0.8µF

INPUT

DUT

INPUT

100kΩ

1MΩ

SSP*

SENSE

SSP*

SENSE

*SSP: Solid State Protection Circuit

Mux

A/D

Converter

Gain Amp

Keithley 2750 Service Manual

Specifications and Main Features

Frequently Asked Questions

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