FLUKE 45 Dual Display Multimeter. Service Manual (For IEC 1010 Meters Only)

LIMITED WARRANTY & LIMITATION OF LIABILITY

Each Fluke product is warranted to be free from defects in material and workmanship under

normal use and service. The warranty period is one year and begins on the date of shipment.

Parts, product repairs and services are warranted for 90 days. This warranty extends only to the

original buyer or end-user customer of a Fluke authorized reseller, and does not apply to fuses,

disposable batteries or to any product which, in Fluke’s opinion, has been misused, altered,

neglected or damaged by accident or abnormal conditions of operation or handling. Fluke

warrants that software will operate substantially in accordance with its functional specifications for

90 days and that it has been properly recorded on non-defective media. Fluke does not warrant

that software will be error free or operate without interruption.

Fluke authorized resellers shall extend this warranty on new and unused products to end-user

customers only but have no authority to extend a greater or different warranty on behalf of Fluke.

Warranty support is available if product is purchased through a Fluke authorized sales outlet or

Buyer has paid the applicable international price. Fluke reserves the right to invoice Buyer for

importation costs of repair/replacement parts when product purchased in one country is submitted

for repair in another country.

Fluke’s warranty obligation is limited, at Fluke’s option, to refund of the purchase price, free of

charge repair, or replacement of a defective product which is returned to a Fluke authorized

service center within the warranty period.

To obtain warranty service, contact your nearest Fluke authorized service center or send the

product, with a description of the difficulty, postage and insurance prepaid (FOB Destination), to

the nearest Fluke authorized service center. Fluke assumes no risk for damage in transit.

Following warranty repair, the product will be returned to Buyer, transportation prepaid (FOB

Destination). If Fluke determines that the failure was caused by misuse, alteration, accident or

abnormal condition of operation or handling, Fluke will provide an estimate of repair costs and

obtain authorization before commencing the work. Following repair, the product will be returned to

the Buyer transportation prepaid and the Buyer will be billed for the repair and return

transportation charges (FOB Shipping Point).

THIS WARRANTY IS BUYER’S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER

WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY

OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. FLUKE SHALL NOT BE LIABLE

FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSSES,

INCLUDING LOSS OF DATA, WHETHER ARISING FROM BREACH OF WARRANTY OR BASED ON

CONTRACT, TORT, RELIANCE OR ANY OTHER THEORY.

Since some countries or states do not allow limitation of the term of an implied warranty, or

exclusion or limitation of incidental or consequential damages, the limitations and exclusions of

this warranty may not apply to every buyer. If any provision of this Warranty is held invalid or

unenforceable by a court of competent jurisdiction, such holding will not affect the validity or

enforceability of any other provision.

To locate an authorized service center, visit us on the World Wide Web: www.fluke.com

or call Fluke using the phone numbers listed below:

USA and Canada: 1-888-99-FLUKE (1-888-993-5853)

Europe: +31 402-675-200

Japan: +81-3-3434-0181

Singapore: +65-738-5655

Anywhere in the world: +1-425-446-5500

Fluke Corporation

Fluke Europe B.V.

P.O. Box 9090

P.O. Box 1186

Everett, WA 98206-9090

5602 BD Eindhoven

U.S.A.

The Netherlands

5/94

Table of Contents

Chapter

Title

Page

Introduction and Specifications

1-1

1-1.

Introduction

1-3

1-2.

Operating Instructions

1-3

1-3.

Options and Accessories

1-3

1-4.

Organization of the Service Manual

1-4

1-5.

Conventions

1-5

1-6.

Specifications

1-6

Theory of Operation

2-1

2-1.

Introduction

2-3

2-2.

Functional Block Description

2-3

2-3.

Power Supply

2-3

2-4.

Analog Measurement Processor

2-3

2-5.

Input Protection Circuit

2-3

2-6.

Input Signal Conditioning

2-3

2-7.

Analog-to-Digital (A/D) Converter

2-3

2-8.

Serial Communication (Guard Crossing)

2-3

2-9.

Digital Kernel

2-5

2-10.

Display Assembly

2-5

2-11.

IEEE-488 Interface Option (-05)

2-5

2-12.

Battery Pack Option (-01)

2-5

2-13.

Detailed Circuit Description

2-5

2-14.

Power Supply Circuit Description

2-5

2-15.

Raw DC Supply

2-6

2-16.

5-Volt Switching Supply

2-6

2-17.

Inverter

2-7

2-18.

Analog Measurement Processor

2-7

2-19.

Input Protection

2-10

2-20.

Input Signal Conditioning

2-10

2-21.

Relays

2-11

2-22.

DC Volts

2-12

2-23.

Ohms

2-12

2-24.

100 MΩ and 300 MΩ Ranges

2-14

2-25.

AC Volts

2-14

Service Manual

2-26.

DCmA

2-15

2-27.

ACmA

2-15

2-28.

Amps

2-15

2-29.

Diode/Continuity Test

2-15

2-30.

Frequency

2-15

2-31.

Active Filter

2-16

2-32.

A/D Converter

2-17

2-33.

Serial Communication (Guard Crossing)

2-18

2-34.

Digital Kernel

2-18

2-35.

RS-232 Interface

2-19

2-36.

Microprocessor

2-19

2-37.

EEROM

2-19

2-38.

RAM

2-20

2-39.

ROM

2-20

2-40.

IEEE-488 Option Connections

2-20

2-41.

Display Assembly

2-20

2-42.

Main Assembly Connector

2-20

2-43.

Front Panel Switches

2-20

2-44.

Display

2-21

2-45.

Beeper Drive Circuit

2-21

2-46.

Watchdog Timer and Reset Circuit

2-21

2-47.

Display Controller with FIP

2-22

General Maintenance

3-1

3-1.

Introduction

3-3

3-2.

Warranty Repairs and Shipping Information

3-3

3-3.

General Maintenance Information

3-3

3-4.

Required Equipment

3-3

3-5.

Power Requirements

3-3

3-6.

Static Safe Handling

3-3

3-7.

Cleaning

3-4

3-8.

Fuse Test and Replacement

3-4

3-9.

Line Fuse

3-4

3-10.

Current Input Fuses

3-4

3-11.

Testing Current Input Fuses

3-4

3-12.

Replacing the 500 mA and 440 mA Input Fuses (F1 and F5)

3-5

3-13.

Replacing the 10 A Input Jack Fuse (F2)

3-6

3-14.

Disassembly Procedures

3-7

3-15.

Remove the Meter Case

3-7

3-16.

Remove Handle and Mounting Brackets

3-7

3-17.

Remove the Front Panel Assembly

3-8

3-18.

Remove the Display PCA

3-8

3-19.

Remove the IEEE-488 Option

3-9

3-20.

Remove the Main PCA

3-9

3-21.

Remove the Analog Measurement Processor Shields

3-9

3-22.

Remove the Rms PCA

3-10

3-23.

Remove the Battery Option

3-10

3-24.

Disconnect Miscellaneous Chassis Components

3-10

3-25.

Assembly Procedures

3-10

3-26.

Install Miscellaneous Chassis Components

3-10

3-27.

Install the Battery Option

3-11

3-28.

Install the Rms PCA

3-11

3-29.

Install the Analog Measurement Processor Shields

3-11

3-30.

Install the Main PCA

3-11

Contents (continued)

3-31.

Install the IEEE-488 Option

3-12

3-32.

Assemble the Front Panel Assembly

3-12

3-33.

Install the Front Panel Assembly

3-15

3-34.

Install the Handle and Mounting Brackets

3-15

3-35.

Install the Meter Case

3-15

Performance Testing and Calibration

4-1

4-1.

Introduction

4-3

4-2.

Required Equipment

4-3

4-3.

Performance Tests

4-4

4-4.

Front Panel Calibration

4-7

4-5.

Introduction

4-7

4-6.

Entering Calibration Mode

4-8

4-7.

Exiting Calibration Mode

4-9

4-8.

DC Volts Calibration (Front Panel)

4-9

4-9.

AC Volts Calibration (Front Panel)

4-9

4-10.

DC and AC Milliamp Calibration (Front Panel)

4-9

4-11.

DC and AC Amps Calibration (Front Panel)

4-11

4-12.

Ohms Calibration (Front Panel)

4-11

4-13.

Alternate Ohms Calibration (Front Panel)

4-13

4-14.

Continuity/Hysteresis Threshold Calibration (Front Panel)

4-13

4-15.

Frequency Calibration (Front Panel)

4-13

4-16.

C2 Adjustment Procedure

4-13

4-17.

Editing the Prompt for Different Calibration Points

4-14

4-18.

Calibration Using the Computer Interface

4-15

4-19.

Setup

4-15

4-20.

RS-232 Interface

4-15

4-21.

IEEE-488 Interface

4-16

4-22.

The Calibration Procedure

4-18

4-23.

DC Volts Calibration (Computer Interface)

4-19

4-24.

AC Volts Calibration (Computer Interface)

4-19

4-25.

DC and AC Milliamps Calibration (Computer Interface)

4-19

4-26.

DC and AC Amps Calibration (Computer Interface)

4-19

4-27.

Ohms Calibration (Computer Interface)

4-19

4-28.

Continuity/Hysteresis Threshold Calibration (Computer Interface)

4-20

4-29.

Frequency Calibration (Computer Interface)

4-20

4-30.

Concluding Calibration Using the Computer Interface

4-20

4-31.

Alternate Ohms Calibration (Computer Interface)

4-20

Diagnostic Testing and Troubleshooting

5-1

5-1.

Introduction

5-3

5-2.

Servicing Surface-Mount Assemblies

5-3

5-3.

Error Codes

5-4

5-4.

General Troubleshooting Procedures

5-10

5-5.

Power Supply Troubleshooting

5-10

5-6.

Raw DC Supply

5-10

5-7.

5-Volt Switching Supply

5-11

5-8.

Inverter

5-12

5-9.

Analog Troubleshooting

5-13

5-10.

Uart Test

5-13

5-11.

DC Volts Troubleshooting

5-14

5-12.

AC Volts Troubleshooting

5-14

5-13.

Ohms Troubleshooting

5-14

5-14. Digital Troubleshooting

5-15

iii

Service Manual

5-15. Display Assembly Troubleshooting

5-17

5-16. Calibration Failures

5-19

5-17.

Introduction

5-19

5-18.

Calibration-Related Components

5-20

5-19.

Calibration Interrelationships

5-21

5-20.

Retrieving Calibration Constants

5-21

5-21.

Replacing the EEROM A1U5

5-21

List of Replaceable Parts

6-1

6-1.

Introduction

6-3

6-2.

How to Obtain Parts

6-3

6-3.

How to Contact Fluke

6-4

6-4.

Manual Status Information

6-4

6-5.

Newer Instruments

6-4

6-6.

Parts

6-4

Option -01 Battery Pack

7-1

7-1.

Introduction

7-3

7-2.

Specifications

7-3

7-3.

Theory of Operation

7-3

7-4.

Functional Block Description

7-3

7-5.

Switching Power Supply

7-5

7-6.

Cycle/Float Charge Rate Switch

7-5

7-7.

Low Battery Indicator Detector

7-5

7-8.

Low Battery Disconnect

7-5

7-9.

Constant Voltage Trickle Charger

7-6

7-10.

Other Circuits

7-6

7-11. General Maintenance

7-6

7-12.

Removal

7-6

7-13.

Installation

7-7

7-14. Performance Testing

7-9

7-15.

General Operability

7-9

7-16.

Low Battery Indicator Detector and Low Battery Disconnect Test.

7-10

7-17.

Cycle/Float Charge Rate Switch Test

7-10

7-18. Calibration

7-12

7-19. Troubleshooting

7-13

7-20. Additional Tests

7-14

7-21. Schematic Diagram

7-14

7-22. List of Replaceable Parts

7-14

Option -05 IEEE-488 Interface

8-1

8-1.

Introduction

8-3

8-2.

Theory of Operation

8-3

8-3.

Functional Block Description

8-3

8-4.

Detailed Circuit Description

8-3

8-5.

Main Assembly Connectors

8-3

8-6.

Address Decoding Circuit

8-3

8-7.

Isolation Circuits

8-4

8-8.

IEEE-488 Controller

8-4

8-9.

IEEE-488 Transceivers/Connector

8-5

8-10. General Maintenance

8-8

8-11.

Removing the IEEE-488 Interface Option

8-8

8-12.

Installing the IEEE-488 Interface Option

8-9

List of Tables

Table

Title

Page

1-1.

Accessories

1-4

2-1.

Analog Measurement Processor Pin Name Description

2-9

2-2.

Relay Operation

2-11

2-3.

Reference Resistance

2-13

2-4.

AC Volts Input Signal Dividers

2-14

2-5.

Front Panel Switch Scanning

2-21

2-6.

Display Initialization Modes

2-23

3-1.

Fuses

3-6

4-1.

Recommended Test Equipment

4-3

4-2.

Performance Tests for Volts, Diode Test, Ohms, and Frequency Functions

4-5

4-3.

Performance Tests for mA Current Functions

4-7

4-4.

Performance Tests for Current Functions

4-7

4-5.

Front Panel Calibration

4-10

4-6.

Specifications Increase with Different Calibration Points

4-15

4-7.

Calibration Using the Computer Interface

4-17

4-8.

Calibration Mode Computer Interface Commands

4-21

4-9.

EEROM Calibration Constants

4-22

5-1.

Error Codes

5-5

5-2.

Power Supplies

5-11

5-3.

DC Volts Troubleshooting

5-14

5-4.

AC Volts Troubleshooting

5-15

5-5.

Display Initialization

5-18

5-6.

Calibration Steps and Related Components

5-22

5-7.

Components Unique to Calibration Steps

5-23

5-8.

Calibration Hierarchy

5-24

5-9.

Calibration Constants

5-24

6-1.

Manual Status Information

6-4

6-2.

Final Assembly

6-5

6-3.

A1 Main PCA

6-8

6-4.

A1A1 True Rms PCA

6-12

6-5.

A2 Display PCA

6-13

7-1.

Option -01 Battery Pack Final Assembly

7-15

7-2.

A4 Battery Pack PCA

7-16

8-1.

IEEE-488 Transceiver Control

8-6

8-2.

Option -05 IEEE - 488 Interface Final Assembly

8-13

vii

List of Figures

Figure

Title

Page

2-1.

Overall Functional Block Diagram

2-4

2-2.

Analog Simplified Schematic Diagram

2-8

2-3.

DC Volts 300 V Range Simplified Schematic

2-12

2-4.

Ohms Simplified Schematic

2-13

2-5.

AC Buffer Simplified Schematic

2-14

2-6.

DC mA and Amps Simplified Schematic

2-16

2-7.

Active Filter Simplified Schematic

2-17

2-8.

A/D Converter Simplified Schematic

2-18

2-9.

Command Byte Transfer Waveforms

2-23

2-10.

Grid Control Signal Timing

2-24

2-11.

Grid-Anode Timing Relationships

2-24

3-1.

Replacing the Line Fuse (F3)

3-5

3-2.

Replacing the External 100 mA Input Fuse (F1)

3-6

3-3.

Removing the Case

3-7

3-4.

Removing the Handle and Handle Mounting Brackets

3-8

3-5.

Assembly Details

3-13

4-1.

Four Wire Configuration

4-12

4-2.

C2 Location

4-14

5-1.

Test Point Locator

5-6

5-2.

Volt Switching Supply

5-12

5-3.

Main Processor Timing

5-16

5-4.

Display Controller to Microprocessor Signals

5-17

5-5.

Primary Display

5-18

5-6.

Secondary Display

5-18

6-1.

Final Assembly

6-6

6-2.

A1 Main PCA

6-11

6-3.

A1A1 True Rms PCA

6-12

6-4.

A2 Display PCA

6-14

7-1.

Battery Pack Option Functional Block Diagram

7-4

7-2.

Removing the Case

7-7

7-3.

Installing the Battery Kit

7-8

7-4.

Battery Pack Option Connecting Cable

7-9

7-5.

Cycle/Float Charge Rate Switch Test

7-11

7-6.

Unplugging the Battery Pack Connectors

7-13

7-7.

Test Points and Adjustments

7-14

Introduction and Specifications

Introduction

1-1.

Introduction

The Fluke 45 Dual Display Multimeter (also referred to as "the meter") is a 4-1/2-digit

(30,000-count) meter with a 5-digit (100,000-count) high resolution mode designed for

bench-top, field service, and system applications. The meter uses a dual vacuum-

fluorescent display, allowing for two types of readings from a single input. Primary and

secondary displays show the user-defined readings side by side. Even though the

readings are made sequentially, the displays show both readings at all times for ease of

comparison.

Some features provided by the meter are:

• Computer interface operation via the RS-232 interface (included) or the IEEE-488

interface (optional). The meter is fully programmable for use on the IEEE Standard

488.1 (1987). The meter is also designed in compliance with supplemental standard

IEEE-488.2 (1987).

• True rms ac

•

(AC + DC) rms, calculated

• Frequency measurements to greater than 1 MHz.

•

1 µV sensitivity in volts dc

• Decibels with variable reference impedance and audio power measurement

capability.

• A compare mode to determine if a measurement is within, above, or below a

designated range.

•

100,000, 30,000, and 3,000 selectable count resolution, with reading speeds of 2.5, 5,

and 20 readings per second (rps), respectively.

• Built-in self-tests with closed-case calibration (no internal adjustments).

1-2.

Operating Instructions

Full operating instructions are provided in the Fluke 45 Users Manual. Reference to

these instructions may be necessary during some of the maintenance and repair

procedures presented in this Service Manual. For quick references, an operating

instruction summary is presented on the inside of the front cover of the Service Manual.

For more detailed information, refer to the Users Manual.

1-3.

Options and Accessories

Three options are available. These options can be installed either at the factory or in the

field. The following discussions pertain to the field-installable option kits:

• The Battery Kit (Option -01K) consists of a rechargeable, 8 V, lead-acid battery,

with battery bracket and charger assembly. The battery has a typical operating time

of eight hours and is fully operable at ambient temperatures between 0 and 50ºC.

• The IEEE-488 Interface Kit (Option -05K) consists of a printed circuit assembly,

connecting cables, and mounting hardware. This option provides full

programmability, external trigger input, and automated calibration. The IEEE-488

computer interface command set is identical to the RS-232 interface commands

wherever possible.

• Option -15K combines Options -01K and -05K as a single kit.

1-3

Service Manual

The Fluke 45 Dual Display Multimeter can be mounted in a standard 19-inch rack panel

on either the right-hand or left-hand side using the Fluke M00-200-634 Rack Mount Kit.

Accessories for the Fluke 45 are listed in Table 1-1.

Table 1-1. Accessories

Model

Description

C40

Soft carrying case. Provides padded protection for the meter. Includes a pocket for the

manual and pouch for the test leads and line cord.

M00-200-

Rackmount Kit. Allows meter to be mounted on either the right or left side of a standard

634

19-inch rack.

RS40

RS-232 terminal interface cable. Connects other Fluke 45 to any terminal or printer with

properly configured DTE connector (DB-25, female pins), including an IBM PC®, IBM

PC/XT® or IBM PS/2 (models 25, 30, 50, P60, 70, and 80).

RS41

RS-232 modem cable. Connects the Fluke 45 to a modem.

S45

QuickStart™, a PC software package, simplifies operation of the Fluke 45 when using

the RS-232 computer interface. Readings are recorded in files that can be accessed by

Lotus 1-2-3®, dBase III® and other graphics packages.

Y8021

Shielded IEEE-488 one-meter (39.4 inches) cable, with plug and jack at each end.

Y8022

Shielded IEEE-488 two-meter (78.8 inches) cable, with plug and jack at each end.

Y8023

Shielded IEEE-488 four-meter (13 feet) cable, with plug and jack at each end.

QuickStart 45 is a trademark of Fluke Corporation.

Lotus is a registered trademark of Lotus Development Co.

dBase III is a registered trademark of Ashton-Tate.

IBM PC and IBM PC/XT are registered trademarks of International Business Machines.

1-4. Organization of the Service Manual

This manual focuses on component-level repair of the Fluke 45 Dual Display

Multimeter. To that end, manual chapters are often interdependent; effective

troubleshooting may require not only reference to the troubleshooting procedures in

Chapter 5, but also some understanding of the detailed Theory of Operation in Chapter 2

and some tracing of circuit operation in the Schematic Diagrams presented in Chapter 9.

Often, scanning the table of contents will yield an appropriate place to start using the

manual. A comprehensive table of contents is presented at the front of the manual; local

tables of contents are also presented at the beginning of each chapter for ease of

reference. If you know the topic name, the index at the end of the manual is probably a

good place to start.

The following chapter descriptions serve to introduce the manual:

Chapter 1. Introduction and Specifications

Introduces the Fluke 45 Dual Display Multimeter, describing its features, options, and

accessories. This chapter also discusses use of the Service Manual and the various

conventions used in describing the meter’s circuitry. Finally, a complete set of

specifications is presented.

1-4

Introduction and Specifications

Conventions

Chapter 2. Theory of Operation

This chapter first categorizes meter circuitry into functional blocks, with a description of

each block’s role in overall operation. A detailed circuit description is then given for

each block. These descriptions explore operation to the component level and fully

support troubleshooting procedures defined in Chapter 5.

Chapter 3. General Maintenance

Provides maintenance information covering handling, cleaning, and fuse replacement.

Access and reassembly procedures are also explained in this chapter.

Chapter 4. Performance Testing and Calibration

This chapter provides performance verification procedures that are tied to the

specifications presented in Chapter 1. To maintain these specifications, a full calibration

procedure is also presented.

Chapter 5. Diagnostic Testing and Troubleshooting

The troubleshooting procedures presented in this chapter rely closely on both the Theory

of Operation presented in Chapter 2 and the Schematic Diagrams shown in Chapter 9.

Chapter 3 provides access information.

Chapter 6. List of Replaceable Parts

Includes parts lists for all standard assemblies. Information on how and where to order

parts is also provided.

Chapter 7. Option -01 Battery Pack

Each option is allocated a separate chapter: 7 for the Battery Pack Option -01 and 8 for

the IEEE-488 Interface Option -05. Option -15 incorporates both Options -01 and -05.

Chapter 7 includes the full range of Service Manual topics (specifications, theory of

operation, maintenance, list of replaceable parts, etc.) for the Battery Pack option.

Schematic diagrams for the options are found in Chapter 9.

Chapter 8. Option -05 IEEE-488 Interface

Includes the full range of Service Manual topics (specifications, theory of operation,

maintenance, list of replaceable parts, etc.) for the IEEE-488 Interface option. Schematic

diagrams for the options are found in Chapter 9.

Chapter 9. Schematic Diagrams

Includes schematic diagrams for all standard and optional assemblies. A list of

mnemonic definitions is also included to aid in identifying signal name abbreviations.

1-5. Conventions

Throughout the manual set, certain notational conventions are used. A summary of these

conventions follows:

• Instrument Reference

The Fluke 45 Dual Display Multimeter is usually called the "meter."

• Printed Circuit Assembly

1-5

Service Manual

The term "pca" is used to represent a printed circuit assembly and its

attached parts.

•

Signal Logic Polarity

On schematic diagrams, a signal name followed by a "*" is active (or

asserted) low. Signals not so marked are active high.

•

Circuit Nodes

Individual pins or connections on a component are specified with a dash (-)

following the component reference designator. For example, pin 19 of U30

would be U30-19.

•

User Notation

For front panel operation,

XXX An uppercase word or symbol without parentheses indicates a button

to be pressed by the user. Buttons can be pressed in four

ways:

1. Press a single button to select a function or operation.

2. Press a combination of buttons, one after the other.

3. Press and hold down a button, then press another button.

4. Press multiple buttons simultaneously.

For computer interface operation,

XXX

An uppercase word without parentheses identifies a command

by name.

<XXX> Angle brackets around all uppercase letters mean press

the<XXX> key.

(xxx)

When associated with a keyword, a lowercase word in

parentheses indicates an input required by the user.

1-6.

Specifications

The following contains the specifications for the Fluke 45 Dual Display Multimeter.

These specifications assume:

• A 1-year calibration cycle

• An operating temperature of 18 to 28ºC

• Relative humidity not exceeding 90% (non-condensing)

Accuracy is expressed as ±(percentage of reading + counts).

Reading Rates and Display Counts

Rate

Readings per Second

Full Range Display Counts

Slow

2.5

99,999*

Medium

30,000

Fast

3,000

* Ohms full range will typically be 98,000 counts

1-6

Introduction and Specifications

Specifications

Response Times

Refer to Chapter 4 of the Users Manual for detailed information.

DC Voltage

Resolution

Accuracy

Range

Slow

Medium

Fast

(6 months)

(1 year)

300 mV

10 µV

100 µV

0.02% + 2

0.025%+2

3 V

100 µV

1 mV

0.02% + 2

0.025% +2

30 V

1 mV

10 mV

0.02% + 2

0.025%+2

300 V

10 mV

100 mV

0.02% + 2

0.025% +2

1000 V

100 mV

1 V

0.02% + 2

0.025%+2

100 mV

1 µV

0.02% + 6

0.025%+6

1000 mV

10 µV

0.02% + 6

0.025% +6

10 V

100 µV

0.02% + 6

0.025%+6

100 V

1 mV

0.02% + 6

0.025% +6

1000 V

10 mV

0.02% + 6

0.025%+6

Input Impedance

10 MΩ in parallel with <100 pF

Note

In the dual display mode, when the volts ac and volts dc functions are

selected, the 10 MΩ dc input divider is in parallel with the 1 MΩ ac

divider.

Normal Mode Rejection Ratio

>80 dB at 50 or 60 Hz, slow and medium rates

>54 dB for frequencies between 50-440 Hz, slow and medium rates

>60 dB at 50 Hz, fast rate (Note: Fast rate has no filtering)

Maximum Allowable AC Voltage While Measuring DC Voltage

Peak Normal Mode Signal

Range

Max Allowable Peak AC Voltage

NMRR* >80dB**

NMRR >60 dB**

300 mV

100 mV

20 V

15 V

3 V

1000 mV

20 V

15 V

30 V

10 V

1000 V

50 V

300 V

100 V

1000 V

50 V

300 V

1000 V

200 V

1000 V

* NMRR is the Normal Mode Rejection Ratio

** Normal Mode Rejection Ratio at 50 or 60 Hz ± 0.1%

Common Mode Rejection Ratio

>90 dB at dc, 50 or 60 Hz, (1 kΩ unbalanced, medium and slow rates)

1-7

Service Manual

Maximum Functional Input

1000 V dc or peak ac on any range

True Rms AC Voltage, AC-Coupled

Resolution

Range

Slow

Medium

Fast

300 mV

10 µV

100 µV

3 V

100 µV

1 mV

30 V

1 mV

10 mV

300 V

10 mV

100 mV

750 V

100 mV

1 V

100 mV

1 µV

1000 mV

10 µV

10 V

100 µV

100 V

1 mV

750 V

10 mV

Accuracy

Max Input

Frequency

Linear Accuracy

dB Accuracy

Power*

at Upper

Freq

Slow

Medium

Fast

Slow/Med

Fast

20-50 Hz

1% + 100

1% + 10

7% + 2

0.15

0.72

2% + 10

750 V

50 Hz -10 kHz

0.2% + 100

0.2% + 10

0.5% +

0.08

0.17

0.4% + 10

750 V

10 - 20 kHz

0.5% + 100

0.5% + 10

0.5% +

0.11

0.17

1% + 10

750 V

20 - 50 kHz

2% + 200

2% + 20

2% + 3

0.29

0.34

4% + 20

400 V

50 - 100 kHz

5% + 500

5% + 50

5% + 6

0.70

0.78

10% + 50

200 V

* Error in power mode will not exceed twice the linear accuracy specification

Accuracy specifications apply within the following limits, based on reading rate:

Slow Reading Rate:

Between 15,000 and 99,999 counts (full range)

Medium Reading Rate:

Between 1,500 and 30,000 counts (full range)

Fast Reading Rate:

Between 150 and 3,000 counts (full range)

Decibel Resolution

Resolution

Slow & Medium

Fast

0.01 dB

0.1 dB

1-8

Introduction and Specifications

Specifications

Input Impedance

1 MΩ in parallel with <100 pF

Maximum Crest Factor

3.0

Common Mode Rejection Ratio

>60 dB at 50 or 60 Hz (1 kΩ unbalanced medium rate)

Maximum Input

750 V rms, 1000 V peak

2 x 10⁷ Volt-Hertz product on any range, normal mode input

1 x 10⁶ Volt-Hertz product on any range, common mode input

(AC + DC) Voltage Accuracy

Total Measurement Error will not exceed the sum of the separate ac and dc accuracy

specifications, plus 1 display count. Refer to the table under "Maximum Allowable AC

Voltage While Measuring DC Voltage or (AC + DC) Voltage" located on page 1-6.

Note

When measuring AC + DC, (or any dual display combination of AC and

DC) in the fast reading rate, the Fluke 45 may show significant reading

errors. This results from a lack of filtering on the DC portion of the

measurement for the fast reading rate. To avoid this problem, use only the

"slow" and "medium" reading rates for AC + DC or AC and DC

combinations.

Maximum Frequency of AC Voltage Input While Measuring AC Current

When the meter makes ac current and ac voltage measurements using the dual display,

the maximum frequency of the voltage input is limited to the maximum frequency of the

current function. For example, if you are making an ac current measurement on the 10 A

range, the maximum frequency of the voltage input must be less than 2 kHz.

DC Current

Range

Resolution

Burden

Slow

Medium

Fast

Accuracy

Voltage*

30 mA

1 µA

10 µA

0.05% + 3

0.45 V

100 mA

10 µA

100 µA

0.05% + 2

1.4 V

10 A

1 mA

10 mA

0.2% + 5

0.25 V

10 mA

100 nA

.05% + 15

0.14 V

100 mA

1 µA

0.05% + 5

1.4 V

10 A

100 µA

0.2% + 7

0.25 V

*Typical at full range

1-9

Service Manual

Maximum Input

300 mA dc or ac rms. Protected with a 500 mA, 250 V, IEC 127-sheet I,

fastblow fuse and a 440 mA, 1000 V, fast blow fuse.

10 A dc ac rms continuous, or 20 A dc or ac rms for 30 seconds maximum.

protected with a 11 A, 1000 V, 17,000 A interrupt rating, fast blow fuse.

Note

Resistance between the COM binding post and the meter’s internal

measuring circuits is approximately .003 Ω

AC Current

Resolution

Range

Burden Voltage*

Slow

Medium

Fast

10 mA

100 µA

0.14 V

30 mA

1 µA

10 µA

0.45 V

100 mA

1 µA

10 µA

100 µA

1.4 V

10 A

100 µA

1 mA

10 mA

0.25 V

* Typical at full range

Accuracy

Range

Frequency

Slow

Medium

Fast

mA (To 100 mA)

20-50 Hz

2% + 100

2% + 10

7% + 2

mA (To 100 mA)

50 Hz - 10 kHz

0.5% + 100

0.5% + 10

0.8% + 2

mA (To 100 mA)

10 - 20 kHz

2% + 200

2% + 20

2% + 3

A (1-10 A)

20 - 50 Hz

2% + 100

2% + 10

7% + 2

A (1 - 10 A)

50 Hz - 2 kHz

1% + 100

1% + 10

1.3% + 2

A (0.5 to 1 A)

20 - 50 Hz

2% + 300

2% + 30

7% + 4

A (0.5 to 1 A)

50 Hz - 2 kHz

1% + 300

1% + 30

1.3% + 4

mA accuracy specifications apply within the following limits, based on reading rate:

Slow Reading Rate:

Between 15,000 and 99,999 counts (full range)

Medium Reading Rate: Between 1,500 and 30,000 counts (full range)

Fast Reading Rate:

Between 150 and 3,000 counts (full range)

1-10

Introduction and Specifications

Specifications

Maximum Crest Factor

3.0

Maximum Input

300 mA dc or ac rms. Protected with a 500 mA, 250 V, IEC 127-sheet I, fast

blow fuse and a 440 mA, 1000 V, fast blow fuse.

10 A dc or ac rms continuous, or 20 A dc or ac rms for 30 seconds maximum.

Protected with a 11 A, 1000 V, 17,000 A interrupt rating, fast blow fuse.

Note

Resistance between the COM binding post and the meter’s internal

measuring circuits is approximately .003 Ω.

Ohms

Typical

Max Current

Range

Resolution

Accuracy

Full Scale

Through the

Voltage

Unknown

Slow

Medium

Fast

300 Ω

10 mΩ

100

0.05% + 2 + 0.02Ω

0.25

1 mA

mΩ

3 kΩ

100 mΩ

1Ω

0.05% + 2

0.24

120 µA

30 kΩ

1 Ω

10 Ω

0.05% + 2

0.29

14 µA

300 kΩ

10 Ω

100 Ω

0.05% + 2

0.29

1.5 µA

3 MΩ

100 Ω

1 kΩ

0.06% + 2

0.3

150 µA

30 MΩ

1 kΩ

0.25% + 3

2.25

320 µA

300

100 kΩ

1 MΩ

2.0

320 µA

MΩ*

100 Ω

1 mΩ

0.05% + 8 + 0.02Ω

0.09

1 mA

1000 Ω

10 mΩ

0.05% + 8 + 0.02Ω

0.10

12 µA

10 kΩ

100 mΩ

0.05% + 8

0.11

14 µA

100 kΩ

1 Ω

0.05% + 8

0.11

1.5 µA

1000 kΩ

10 Ω

0.06% + 8

0.12

150 µA

10 MΩ

100 Ω

0.25% + 6

1.5

150 µA

100 MΩ

100 kΩ

2% + 2

2.75

320 µA

* Because of the method used to measure resistance, the 100 MΩ (slow) and 300 MΩ(medium and fast)

ranges cannot measure below 3.2 MΩ and 20 MΩ, respectively. "UL" (underload) is shown on the display

for resistances below these nominal points, and the computer interface outputs "+1E-9".

1-11

Introduction and Specifications

Specifications

Frequency

5 Hz to > 1 MHz

Applicable Functions

Volts AC and Current AC

Resolution

Range

Accuracy

Slow & Medium

Fast

1000 Hz

.01 Hz

.1 Hz

.05% + 2

10 kHz

.1 Hz

1 Hz

.05% +1

100 kHz

1 Hz

10 Hz

.05% +1

1000 kHz

10 Hz

100 Hz

.05% +1

1 MHz

100 Hz

1 kHz

* For measurement of 1 MHz and lower, accuracy is .05% + 1.

For measurement above 1 MHz, accuracy is not specified.

Sensitivity of AC Voltage

Frequency

Level (Sine Wave)

5 Hz - 100 kHz

30 mV rms

100 kHz - 300 kHz

100 mV rms

300 kHz - 1 MHz

1 V rms

Above 1 MHz

Not Specified

Sensitivity Level of AC Current

Frequency

Input

Level

5 Hz - 20 kHz

100 mA

>3 mA rms

45 Hz - 2 kHz

10 A

>3 A rms

Note

When the meter is set to measure frequency and there is no input signal

(i.e., the input terminals are open), the meter may read approximately 25

kHz (rather than zero). This is due to internal capacitive pickup of the

inverter power supply into the high-impedance, input circuitry. With

source impedance of < 2 kΩ, this pickup will not affect the accuracy or

stability of the frequency reading.

1-13

Service Manual

Environmental

Warmup Time

1 hour to rated specifications

Temperature Coefficient

<0.1 times the applicable accuracy specification per degree C for 0°C to 18°C and 28°C

to 50°C

Electromagnetic Compatibility

In an RF field of 1 V/m on all ranges and functions:

Total Accuracy = Specified Accuracy + .4% of range. Performance above 1 V/m is

not specified.

Operating Temperature

0°C to 50°C

Storage Temperature

40°C to + 70°C

Elevated temperature storage of battery will accelerate battery self-discharge. Maximum

storage time before battery must be recharged:

20 - 25°C

1000 days

50°C

180 days

70°C

40 days

Relative Humidity

To 90% at 0°C to 28°C , (non condensing)

To 80% at 28°C to 35°C,

To 70% at 35°C to 50°C except to 70%

at 0°C to 50°C for the 1000 kΩ, 3 MΩ, 10 MΩ, 30 MΩ, 100

MΩ, and 300 MΩ

ranges.

Altitude

Operating

0 to 10,000 feet

Non-operating

0 to 40,000 feet

Vibration

3 G @ 55 Hz

Shock

Half sine 40G. Per Mil-T- 28800D, Class 3, Style E.

Bench Handling. Per Mil-T-28800D, Class 3.

1-14

Introduction and Specifications

Specifications

General

Common Mode Voltage

1000 V dc or rms ac maximum from any input to earth

Size

9.3 cm high, 21.6 cm wide, 28.6 cm deep

Weight

Net, 2.4 kg without battery; 3.2 kg with battery; Shipping, 4.0 kg without battery, 4.8

with battery.

Power

90 to 264 V ac (no switching required), 50 and 60 Hz. 15 VA maximum

Safety

Compliant with the following standards:

ANSI/ISA S82.01-1994

CAN/CSA-C22.2 No. 1010. 1-92

EN61010.1:1993 to 1000 V Overvoltage Cat I, 600 V Overvoltage Cat II

UL3111-1. See the following for an explanation of CATI and CATII categories.

CAT I:

OVERVOLTAGE (Installation) CATAGORY I, Pollution Degree 2 per IEC1010-1

refers to the level of Impulse Withstand Voltage protection provided. Equipment of

OVERVOLTAGE CATEGORY I is equipment for connection to circuits in which

measures are taken to limit the transient over voltages to an appropriate low level.

Examples include protect electronic circuits.

CAT II:

OVERVOLTAGE (Installation) CATAGORY II, Pollution Degree 2 per IEC1010-1

refers to the level of Impulse Withstand Voltage protection provided. Equipment of

OVERVOLTAGE CATEGORY II is energy-consuming equipment to be supplied

from the fixed installation. Examples include household, office, and laboratory

appliances.

Electromagnetic Compatibility

Meets FCC Part 15 Subpart J.

EN61326-1 (1998)

RS-232-C

Baud rates:

300, 600, 1200, 2400, 4800 and 9600

Odd, even or no parity One stop bit

1-15

Chapter 2

Theory of Operation

Title

Page

2-1.

Introduction

2-3

2-2.

Functional Block Description

2-3

2-3.

Power Supply

2-3

2-4.

Analog Measurement Processor

2-3

2-5.

Input Protection Circuit

2-3

2-6.

Input Signal Conditioning

2-3

2-7.

Analog-to-Digital (A/D) Converter

2-3

2-8.

Serial Communication (Guard Crossing)

2-3

2-9.

Digital Kernel

2-5

2-10.

Display Assembly

2-5

2-11.

IEEE-488 Interface Option (-05)

2-5

2-12.

Battery Pack Option (-01)

2-5

2-13.

Detailed Circuit Description

2-5

2-14.

Power Supply Circuit Description

2-5

2-15.

Raw DC Supply

2-6

2-16.

5-Volt Switching Supply

2-6

2-17.

Inverter

2-7

2-18.

Analog Measurement Processor

2-7

2-19.

Input Protection

2-10

2-20.

Input Signal Conditioning

2-10

2-21.

Relays

2-11

2-22.

DC Volts

2-12

2-23.

Ohms

2-12

2-24.

100 MΩ and 300 MΩ Ranges

2-14

2-25.

AC Volts

2-14

2-26.

DCmA

2-15

2-27.

ACmA

2-15

2-28.

Amps

2-15

2-29.

Diode/Continuity Test

2-15

2-30.

Frequency

2-15

2-31.

Active Filter

2-16

2-32.

A/D Converter

2-17

2-33.

Serial Communication (Guard Crossing)

2-18

2-34.

Digital Kernel

2-18

2-35.

RS-232 Interface

2-19

2-1

Theory of Operation

Introduction

2-1.

Introduction

This chapter presents a layered description of Fluke 45 circuitry. First, the multimeter is

described in general terms with a Functional Block Description. Then, each block is

detailed further (often to the component level) with Detailed Circuit Descriptions. Refer

to Chapter 9 of this manual for full schematic diagrams.

Signal names followed by a ’*’ are active (asserted) low. Signal names not so marked are

active high.

2-2.

Functional Block Description

Refer to Figure 2-1, Overall Functional Block Diagram, during the following functional

block descriptions.

2-3.

Power Supply

The Power Supply functional block provides voltages required by both the vacuum-

fluorescent display (-30 V dc, -5.2 V dc, and 5 V ac) and the in-guard circuitry (-5.25 V

dc and 5.25 V dc). Within the Power Supply, the Raw DC Supply converts ac line

voltage to dc levels and the 5 V Switching Supply converts this raw dc to 5 V ±0.25 V

dc, which is used by the Inverter in generating the above-mentioned outputs.

2-4.

Analog Measurement Processor

The Analog Measurement Processor (A1U1) provides input signal conditioning, ranging,

a/d conversion, and frequency measurement. This custom chip is controlled by the Main

Processor (A1U6), with communication carried out over a special serial interface.

2-5.

Input Protection Circuit

Input protection safeguards the meter against a number of over-voltage and over-current

conditions. Depending on the type of input, protection circuits or fuses are used.

2-6.

Input Signal Conditioning

The input signal (voltage, current, or resistance) must be scaled or conditioned to a dc

voltage that can be measured by the a/d converter. High dc voltage levels must be

attenuated. Resistances, currents, and ac voltages must be converted to a representative

dc voltage. DC-type measurements (dc volts, dc current, ohms, and diode test) are then

filtered by an active filter. AC measurements (ac volts and ac current) are passively

filtered after being converted to a dc voltage.

2-7.

Analog-to-Digital (A/D) Converter

The voltage level from the signal conditioning circuits charges (or integrates) a capacitor

for an exact amount of time. The capacitor discharge time, which is proportional to the

level of the unknown input signal, is measured by the digital circuits in the Analog

Measurement Processor and sent to the microprocessor.

2-8.

Serial Communication (Guard Crossing)

This functional block provides a high isolation voltage communication path between the

Digital Kernel and the Analog Measurement Processor. This bi-directional

communication circuit also requires power supply voltages from the Power Supply

block.

2-3

Theory of Operation

Detailed Circuit Description

2-9.

Digital Kernel

The Digital Kernel functional block is responsible for the coordination of all activities

within the meter. This block requires power supply voltages from the Power Supply and

reset signals from the Display Assembly.

Specifically, the Digital Kernel Microprocessor performs the following functions:

• Executes the instructions in ROM

• Stores temporary data in RAM

• Store meter configuration and calibration data in EEROM

• Communicates with the Analog Measurement Processor via the Serial

Communication (Guard Crossing) block

• Communicates with the Display Controller to display readings and user interface

information

• Scans the user interface keyboard found on the Display Assembly

• Communicates via the RS-232 interface and optional IEEE-488 interface.

2-10.

Display Assembly

The Display Assembly controller communicates with the main Microprocessor over a

three-wire communication channel. Commands from the Microprocessor inform the

Display Controller how to modify its internal display memory. The Display Controller

then drives the grid and anode signals to illuminate the required segments on the

Display. The A2 Display Assembly requires power supply voltages from the Power

Supply and a clock signal from the A1U6 Microprocessor.

2-11.

IEEE-488 Interface Option (-05)

Theory of operation for the IEEE-488 Interface Option (-05) is presented in Chapter 8 of

this manual. The related schematic diagram is found in Chapter 9.

2-12.

Battery Pack Option (-01)

Chapter 7 of this manual contains the theory of operation for the Battery Pack Option

(-01). Refer to Chapter 9 for the related schematic diagram.

2-13. Detailed Circuit Description

2-14. Power Supply Circuit Description

The Power Supply consists of the following three functional sections:

• Raw DC Supply

The Raw DC Supply converts line voltage (90 V to 264 V ac) to a dc output of 7.5 V

to 5 V.

•

5 V Switching Supply

The 5 V Switching Supply converts the Raw DC Supply output to 5.1 V ± 0.25 V dc.

• Inverter

Using the 5 V Switching Supply output, the Inverter generates the -30 V dc, -5 V dc,

and 5 V ac supply levels needed for the vacuum-fluorescent display. Also, the

2-5

Service Manual

Inverter provides isolated positive and negative 5.25 V outputs for the in-guard

circuitry.

2-15.

Raw DC Supply

The Raw DC Supply uses a power transformer (A1T3) that operates on input line

voltages ranging from 90 V to 264 V ac. Since there is no power switch in the

transformer input circuit, the Raw DC Supply is energized whenever the meter is

connected to line power. The transformer uses an internal 275 V ac MOV (metal-oxide

varistor) to clamp line transients. This MOV normally acts as an open circuit; when the

peak voltage exceeds approximately 400 V, the MOV turns on and, working with the

line impedance in series with the line fuse, limits the transient peak voltage to 400 to 500

V. All line voltages use a T 0.125 A, 250 V (slow blow) fuse.

On the secondary side of the transformer, the output is rectified by diodes A1CR2 and

A1CR3 and filtered by capacitor A1C27. In addition, A1C26 reduces rectifier diode

switching emi emissions from the meter. The meter power switch (A1S1) is also

connected in the output of the Raw DC Supply; it connects the Raw DC Supply either to

the 5-V Switching Supply (when the meter is ON) or to the Battery Charger Switching

Supply through A1J1-7 (when the meter is OFF.)

2-16.

5-Volt Switching Supply

The 5-Volt Switching Supply incorporates the A1U11 controller device and several

external components. Operating on an input of 7.5 V dc to 35 V dc, the 5-volt Switching

Supply uses a pulse-width modulation technique to regulate its output at 5.1 V dc. The

nominal switching frequency is 40 kHz.

With the controller, the output voltage is controlled by varying the duty cycle (ON time)

of the switch transistor in A1U11. (Controller device A1U11 contains the supply

reference, oscillator, switch transistor, pulse-width modulator comparator, switch drive

circuit, current-limit comparator, and current-limit reference.) Resistors A1R41 and

A1R42, in conjunction with the reference circuit, set the input levels to the pulse-width

modulating comparator. Resistors A1R35 (in parallel with A1R41) and A1R36 (in

parallel with A1R42) are used in production to adjust the 5.1 V supply output. Removing

A1R35 decreases the output by approximately 5%. Removing A1R36 increases the

output by approximately 7%.

Within the controller, the output of the comparator is combined with the oscillator signal

to form the drive signal for the switch transistor. Diode A1CR6 operates as a

complementary switch with the switch transistor. Dual inductor A1T1 is a magnetic

device that regulates current pulses as the switch transistor is turned on and off. A

current shunt (A1R47, A1R48, and A1R49) senses the overall current flowing through

diode A1CR5 and the switch transistor of A1U11. If this current rises too high, the duty

cycle (ON time) of the switch transistor is reduced to current-limit the supply. Capacitor

A1C33 serves as a filter capacitor and energy storage device, and A1C34 and A1C35 are

the output filter capacitors.

The boost circuit (A1CR4 and A1C32) supplies the controller A1U11 with sufficient

supply voltage when the switching supply input is low. For example, this condition may

occur when the meter is operating on low line voltage.

Resistor A1R40 and capacitors A1C28 and A1C29 are needed for proper dynamic

performance of the switching supply. Capacitor A1C30 sets the operating frequency of

the supply.

2-6

Theory of Operation

Detailed Circuit Description

2-17.

Inverter

The inverter uses transistors A1Q10, A1Q11, A1Q12, and A1Q13 connected to form an

astable 30-kHz multivibrator. The operating frequency and drive to the transistors are

determined by the values of the interconnecting resistors and capacitors. The inverter

transformer (A1T2) primary is connected across the collectors of the multivibrator

transistors; the primary winding is thereby driven by a symmetrical square wave.

Resistor A1R46 and capacitor A1C41 form a filter network to reduce the amplitude of

current pulses generated by the switching of the inverter transistors.

The secondary windings of A1T2 are used for three sets of supply voltages. The first

winding of the A1T2 secondary provides out-guard outputs using the following rectifier

diodes and filter capacitors to provide the required voltages for the display and the

battery trickle charger circuit.

• A1CR11 and A1C45: -30 V supply

• A1CR12 and A1C47: -5 V supply

• A1CR10 and A1C46: +30 V source for the battery trickle charger.

Next, an isolated secondary winding provides the various in-guard supplies. Dual diodes

A1CR8 and A1CR9 and capacitors A1C43 and A1C44 are the rectifiers and filters for

the in-guard +5.25 V and -5.25 V supplies. Dual diode A1CR7 and capacitor A1C42 are

the rectifier and capacitor for the relay (5.25 V dc) supply.

A third transformer winding provides the heater power (FIL1, FIL2) for the vacuum-

fluorescent display. Zener diode A1VR3 and resistor A1R55 bias this winding at

approximately 5 volts more positive than the -30 V supply.

2-18.

Analog Measurement Processor

Refer to Figure 2-2 for an overall picture of the Analog Measurement Processor chip and

its peripheral circuits. Table 2-1 describes Analog Measurement Processor chip signal

names.

The Analog Measurement Processor (A1U1) is a 68-pin CMOS device that, under

control of the Main Processor (A1U6), performs the following functions:

• Input signal routing

• Input signal conditioning

• Range switching

• Active filtering of dc-type measurements. The active filter is disabled for fast

reading rate measurements.

• A/D conversion

• Support for direct volts, direct current, true rms alternating volts, true rms alternating

current, ohms, frequency, and continuity/diode test functions.

Two separate signal paths are used, one for dc/ohms and one for ac. For dc, the 3 V

range and below are coupled directly to the a/d converter; higher voltages are attenuated.

For ohms, the dc circuitry is augmented with an internal ohms source voltage regulator

controlled through an extra set of switches. For ac, inputs are routed through the ac

buffer, with attenuation being controlled by the a/d converter.

The a/d converter uses a modified dual-slope minor cycle method. The basic

measurement unit, a minor cycle, consists of a fixed time integrate period for the

unknown input, a variable reference integrate period, a variable hold period, and various

short transition periods. A minor cycle period equals 25 ms.

2-7

Theory of Operation

Detailed Circuit Description

Table 2-1. Analog Measurement Processor Pin Name Description

Name

Description

VDD

+5 V supply

ACBO

AC buffer output

AIN

Amps input

AGND2

Analog ground #2

ACR4

AC buffer range 4

ACR3

AC buffer range 3

ACR2

AC buffer range 2

ACR1

AC buffer range 1

VSSACR

-5 V supply for AC ranging

(not used)

A/D converter low input

GRD

Guard

RRS

Reference resistor sense for ohms

Tap #4 on the DCV input divider/ohms reference network

Tap #3 on the DCV input divider/ohms reference network

Tap #1 on the DCV input divider/ohms reference network

GRD

Guard

V2F

Tap #2 active filter input on the DCV input divider/ohms reference network

Tap #2 on the DCV input divider/ohms reference network

GRD

Guard

Tap #0 on the DCV input divider/ohms reference network

GRD

Guard

OVS

Ohms and volts sense input

GRD

Guard

AGND1

Analog ground #1

(not used)

DGND

Digital ground

FC0

Function control #0

FC1

Function control #1

FC2

Function control #2

FC3

Function control #3

FC4

Function control #4

FC5

Function control #5

FC6

(not used)

FC7

(not used)

OSCIN

Crystal oscillator input

OSCO

Crystal oscillator output

MRST

Master reset

Analog send

Analog receive

Serial clock

Chip select

BRS

Baud rate select

VSS

-5 V

INT

Integrator output

SUM

Integrator summing node

B.1

Buffer output, 100 mV range

B.3

Buffer output, 300 mV range

Buffer output, 1000 mV range

Buffer output, 3 V range

2-9

Service Manual

Table 2-1. Analog Measurement Processor Pin Name Description (cont)

Name

Description

VREF+

A/D reference plus

VREF-

A/D reference minus

RAO

A/D reference amplifier output

RA+

A/D reference amplifier noninverting input

RA-

A/D reference amplifier inverting input

AFO

Active filter output

MOF

Megohms filter

AFI

Active filter input

FAI

Filter amplifier inverting input

FAO

Filter amplifier output

RMSF

RMS output, filtered

ARTN

Analog return

(not used)

RMSO

RMS converter output

BIAS2

Bias input

VSSF

-5 V dc, filtered

BIAS1

Bias input

RMSI

RMS converter input

2-19.

Input Protection

Input protection safeguards the meter against a number of over-voltage and over-current

conditions. The various input protection schemes are as follows:

• In the Voltage mode of operation, MOVs A1RV1, A1RV2 and A1RV3 clamp input

voltage transients to about 1800 volts, and A1R5, A1RT1 and A1R6 limit the

current. In this mode, A1R7 and the 10-MΩ resistor in A1Z1 protect A1U1.

• In the Ohms and Diode Test modes, A1Q1 clamps voltage inputs of both polarities,

and A1R5 and thermistor A1RT1 limit the overload current. With large overloads,

A1RT1 heats up and increases in resistance. Components A1R9 and A1Z1 protect

A1U1.

• The [100 mA] input is protected by fuses F1 and F5. With this input, A1R4 protects

A1U1.

• The [10 A] input is protected by fuse A1F2, with A1R8 protecting A1U1.

2-20.

Input Signal Conditioning

The input signal (voltage, current, or resistance) must be scaled or conditioned to a form

that can be measured by the a/d converter. High dc voltage levels must be attenuated.

Resistances, currents, and ac voltages must be converted to a representative dc voltage.

DC-type measurements (dc volts, dc current, ohms, and diode test) are then filtered by

the active filter. AC measurements (ac volts and ac current) are passively filtered after

being converted to a dc voltage. In the medium and fast measurement rates, the a/d

converter uses one of two ranges: ±300 mV and ±3 V full scale. In the slow rate, the a/d

converter uses one of two additional ranges (±100 mV and ±1000 mV full scale), for a

total of four ranges.

2-10

Theory of Operation

Detailed Circuit Description

2-21. Relays

Latching relays A1K1, A1K2, and A1K3 route and connect the input signal to the

functional blocks required by the selected function. The Analog Measurement Processor

(A1U1) function control outputs, which are 8-ms positive pulses (0 V to VDD) at FC0 to

FC5 (pins 28 to 33), control the relay driver, A1U2. The A1U2 drivers are NPN

Darlington pairs. Relay functions are defined in Table 2-2.

Table 2-2. Relay Operation

Relays

Function

A1K

A1K2

A1K3

DC mV, 3 V

Reset

Set

DC 10 V, 30 V, 100 V, 300 V, 1000 V

Set

ACV

Set

Reset

Ohms & k ohms

Reset

Set

M ohms

Reset

Set

Diode Test

Reset

Set

mA DC and ADC

Set

Reset

mA AC and AAC

Set

Frequency

Set

Reset

2-11

Service Manual

A1R6 &

A1R7

A1K1

VΩ

A1R5 &

A1RT1

A1Z1

10M

S10

ACTIVE

HIGH

FILTER

A1Z1

A/D

10.01k

A1R9

LOW

A1K2

COM

qb03f.eps

Figure 2-3. DC Volts 300 V Range Simplified Schematic

2-22. DC Volts

For the mV and 3 V ranges, the input signal is applied to A1U1 through A1R6, A1R7,

and A1K1. The signal is routed directly through A1U1 to the active filter and the a/d

converter without attenuation. Higher voltages are attenuated by the dc input divider

A1Z1.

For the 300 V range, switches S3 and S9 in A1U1 connect the A1Z1 10-MΩ resistor to

the A1Z1 10.01-kΩ resistor, forming a 1000:1 divider. See Figure 2-3. The S10 switch in

A1U1 routes the signal to the active filter. Pin 3 of A1Z1 serves as divider common,

which is also the a/d converter low signal sensed through A1R9.

2-23. Ohms

Resistance measurements are made using the ratio ohms technique. See Figure 2-4. A

voltage source is connected in series with the reference resistor (A1Z1) and the unknown

resistor. Since the same current then flows through both resistors, the unknown

resistance is determined from the ratio of the voltage drops across the reference and

unknown resistors.

2-12

Theory of Operation

Detailed Circuit Description

Depending on the range, S3, S6, S9, S13, or S15 connects the Analog Measurement

Processor ohms voltage source to a reference resistor. The resulting current passes

through the reference resistor, A1K2, the protection resistors A1RT1 and A1R5, and the

unknown resistance. The a/d converter integrates with the voltage across the unknown

through the OVS input (pin 23). For DE- integrate reference, the a/d converter uses the

voltage across the reference resistor through RRS (pin 13) and Ohms Reference High

through S5 (pin 21), S14 (pin 19), S17 (pin 16), S11 (pin 15) or S8 (pin 14). Reference

resistances are identified in Table 2-3.

OHMS

VOLTAGE

SOURCE

LOW

A/D

A1Z1

RREF

INTEGRATE

VR REF

REFERENCE

RESISTOR

A1R9

HIGH

A1K2

A1RT1&A1R5

A1R6 & A1R7

ACTIVE

HIGH

A1K1

FILTER

V Ω

A/D

VR^X UNKNOWN

INTEGRATE

RESISTOR

UNKNOWN R

COM

LOW

VR X

IXRX

VR REF =

IX RREF RREF

qb04f.eps

Figure 2-4. Ohms Simplified Schematic

Table 2-3. Reference Resistance

Range

Voltage Source

A1Z1 Reference Resistor

100 Ω /300 Ω

3 V

1 kΩ

1000 Ω/3 kΩ

1.3 V

10.01 kΩ

10 kΩ/30 kΩ

1.3 V

100.5 kΩ

100 kΩ/300 kΩ

1.3 V

1 MΩ

1000 kΩ/3 MΩ/10 MΩ

1.3 V

10 MΩ

30 MΩ

3 V

10 MΩ

100 MΩ/300 MΩ

3 V

10 MΩ

Diode Test

3 V

1 kΩ

2-13

Service Manual

A1R5 &

A1RT1

A1C1

A1Z2

A1K3

1.111M

A1AR1

A1C7

RMS

COVERTER

A1Z2

2.776k

A1R2

A1Z2 FEEDBACK

A1Z2

RESISTOR

115.7

qb05f.eps

Figure 2-5. AC Buffer Simplified Schematic

Table 2-4. AC Volts Input Signal Dividers

Range (Drive Signal)

A1Z2 Feedback Resistor

Overall Gain

100/300 mV (ACR1)

111.1 kΩ

2.5

1000 mV/3 V (ACR2)

12.25 kΩ || 111.1 kΩ

.25

10/30 V (ACR3)

1.013 kΩ || 111.1 kΩ

.025

100/300/750 V (ACR4)

2.776 kΩ

.0025

2-24.

100 MΩ and 300 MΩ Ranges

The 100 MΩ and 300 MΩ ranges perform a conductance reading; the mathematical

reciprocal of this reading is used as a display in ohms. The reference resistor (A1Z1, 10

MΩ) is integrated first, then the unknown resistance is used for DE- integrate reference.

2-25.

AC Volts

AC voltage and ac current inputs are scaled by the ac buffer, then converted to a

representative dc voltage by the true rms ac-to-dc converter.

Refer to Figure 2-5. JFETs A1Q2 to A1Q8 switch the ranges of the buffer amplifier

A1AR1. The JFET drive signals, ACR1 to ACR4 (pins 5 to 8) turn the JFETs either on at

0 V or off at -VAC. The ratio of the feedback resistor to the 1.111-MΩ input resistor

divides the input signal by 10, 100, or 1000. These arrangements are summarized in

Table 2-4. This signal is then amplified by 25 using the 2.776-kΩ and 115.7Ωbuffer

output divider resistors. The A1Z2 111.1-kΩ feedback resistor is left in parallel with the

higher range feedback resistors. For the 300/750 V range, the 2.776-kΩresistor becomes

the feedback element. A1R15 and A1C2 compensate the 300-mV range of the ac buffer.

The ac signal is then routed to the rms converter by Analog Measurement Processor

switch S38. Capacitors A1C1, A1C7, A1A1C2, and A1A1C3 function as dc blocking

capacitors. A1A1R1 provides input bias current for the rms converter buffer, and

A1A1C1 is the converter’s averaging capacitor.

The rms converter output is divided down by 2.5 by A1Z4; A1R19 and A1C10 form the

passive filter for ac volts. Analog Measurement Processor switch S80 shorts A1R19 both

during ranging and in the fast measurement rate. Components A1R16, A1R17, A1C3,

2-14

Theory of Operation

Detailed Circuit Description

A1C4, A1C5, and A1C6 provide a filtered power supply for the ac buffer, the ac buffer

switching JFETs, and the rms converter.

2-26.

DCmA

Current through A1R2 develops a voltage that is proportional to the input. This dc

voltage is routed through A1R4 to the active filter, then to the a/d converter. The 100

mA current range uses the 3 V range of the a/d converter. See Figure 2-6.

2-27.

ACmA

In ACmA, relay A1K3 connects the ac voltage developed across A1R2 to the ac buffer.

The signal is then conditioned as described for ac volts.

2-28.

Amps

The dc voltage output of the 10 amp shunt (A1R3) is routed directly to the a/d converter

through the Analog Measurement Processor OVS input (pin 23). For ac amps, the ac

voltage output of the shunt is routed to the rms converter through Analog Measurement

Processor switches S35 and S37.

2-29.

Diode/Continuity Test

In Diode Test, the meter front end is in the 300 ohm range configuration. The a/d

converter measures the dc voltage at the binding posts through the OVS input (pin 23).

For the continuity function, the frequency/continuity comparator senses the signal

through Analog Measurement Processor switches S35 and S41. The comparator toggles

when the input goes below about 20 mV.

2-30.

Frequency

The frequency/continuity comparator uses the ac volts/ac mA output of the ac buffer as

its input at the Analog Measurement Processor ACBO input (pin 2). In the 10 A ac

range, the signal is routed to the comparator through Analog Measurement Processor

switches S35 and S41.

2-15

Service Manual

A1K3

RMS

BUFFER

CONVERTER

RESET

A1R4

ACTIVE

A/D

FILTER

A1R2

S36

RMS

ACA

CONVERTER

A1K1

10A

A1F2

A/D

A1R8

A1R3

DCA

ACTIVE

COM

.01

FILTER

qb06f.eps

Figure 2-6. DC mA and Amps Simplified Schematic

2-31. Active Filter

Refer to Figure 2-7. The two-pole active filter consisting of A1R21, A1R22, A1C12, and

A1C13 filters noise on the a-d converter input signal for the DCV, DCmA, DCA,

OHMS, kOHMS, and Diode Test functions. Resistor A1R22 provides a 200-kΩ input

impedance for the filter, except as follows:

• Resistors A1R6 and A1R7 provide the 200-kΩ input impedance for the 100 mV dc,

300 mV dc, 1000 mV dc, 3 V dc, ohms, and kilohms ranges.

• Resistor A1R10 and the 100.5 kΩ resistor in A1Z1 provide the 200 kΩ impedance

for the 10 V and 30 V dc ranges.

• Resistor A1R4 provides the impedance for the two DCmA ranges.

Analog Measurement Processor switch S82 shorts out A1R21 during ranging. Switch

S87 shorts out A1R22 both during ranging and in the measurements listed above. For the

1000 kΩ, 3 MΩ, 10 MΩ, 30 MΩ, 100 MΩ, and 300 MΩ ranges, the active filter is

bypassed, and switch S83 selects C14 as the filter.

2-16

Theory of Operation

Detailed Circuit Description

A1R22

ACTIVE

FILTER

A/D

INPUT

A1C12

A1C13

S87

A1R21

S82

A1C14

FILTER

qb07f.eps

Figure 2-7. Active Filter Simplified Schematic

2-32.

A/D Converter

Figure 2-8 shows the dual slope a/d converter used in the Fluke 45. A voltage level

proportional to the unknown input signal charges (integrates) a capacitor for an exact

amount of time. This capacitor is then discharged by a reference voltage of opposite

polarity. The capacitor discharge time, which is proportional to the level of the unknown

input signal, is measured by the digital circuits in the Analog Measurement Processor

and sent to the microprocessor.

In the medium and fast measurement rates, the a/d converter uses the ±300 mV or ±3 V

range. These ranges typically uprange at a display of 32,000 in the medium rate. In the

slow rate, the a/d converter uses one of two additional ranges: ±100 mV and ±1000 mV.

The uprange point for these additional ranges is a display of 99,999. In the ohms

function only, a typical uprange point is a display of about 98,000.

During the integrate phase, the a/d buffer in Analog Measurement Processor A1U1

applies the signal to be measured to one of the four integrate resistors in resistor network

A1Z3. The choice of resistor depends on the measurement range. Switch S69 connects

output B.1 (pin 47) for the 100-mV range; S71 uses output B.3 (pin 48) for the 300-mV

range; S73 uses output B1 (pin 49) for the 1000 mV range; and S75 uses output B3 (pin

50) for the 3 V range. Refer to Figure 8-1.

The current through the selected integrator resistor charges integrator capacitor A1C16.

After the integrate phase, the buffer applies the opposite polarity reference voltage, and

the integrator integrates back down until the comparator toggles. A counter measures the

integrate reference time. If the a/d converter is overloaded and the integrator does not

return to its starting point by the end of the integrate reference phase, S77 discharges

integrator capacitor A1C16.

The reference voltage for volts, current, and diode test modes is provided by a 6.3 V

zener diode, A1VR1. The reference amplifier in the Analog Measurement Processor

2-17

Service Manual

provides 2 mA of current through A1VR1. Resistor network A1Z3 divides the 6.3 V

down to 1.1 V.

+ REFERENCE

(- INPUT)

REFERENCE

COUNTER

A1C16

A/D

COMPARATOR

S77

INTREGRATE

REFERENCE

-REFERENCE

(+ INPUT)

A1Z3

INPUT

BUFFER

INTEGRATOR

INTEGRATE

INPUT

qb08f.eps

Figure 2-8. A/D Converter Simplified Schematic

2-33.

Serial Communication (Guard Crossing)

The Microprocessor communicates with the Analog Measurement Processor using this

isolated two-wire, full-duplex asynchronous interface circuit.

When the Microprocessor is transmitting to the Analog Measurement Processor, the

transmit data bits appear at A1U6-11, which drives the combination of AQ19, A1R33

and A1U3-1. The optocoupler A1U3 then optically transfers this information to its

output circuit, comprised of A1U3-7, A1R30, A1R28 and A1R27. The transmitted data

is then presented to A1TP4 and A1U1-40.

When the Analog Measurement Processor is transmitting data back to the

Microprocessor, the data bits appear at A1U1-39, which drives the input of a Darlington

driver A1U2-1. The Darlington driver output then drives A1R29 and A1U4-1 to transfer

the information to the output of the optocoupler at A1U4-7. Resistors A1R32 and A1R34

complete the optocoupler output circuit. Data is then routed to A1TP7 and A1U6-10 on

the Microprocessor.

2-34.

Digital Kernel

The Digital Kernel is composed of six functional circuit blocks: the RS-232 interface,

the Microprocessor, the EEROM (Electrically Erasable Read Only Memory), the RAM

(Random Access Memory), the ROM (Read Only Memory), and the IEEE-488 Option

Connections. These blocks are described in the following paragraphs.

2-18

Theory of Operation

Detailed Circuit Description

2-35.

RS-232 Interface

The RS-232 interface is composed of connector A1J5, RS-232 level shifter A1U7 and

the hardware serial communication interface (SCI) in Microprocessor A1U6.

The transmit signal from the SCI (A1U6-14) goes to the RS-232 driver (A1U7-12),

where it is inverted and shifted to transition between approximately +5.0 and -5.0 V dc.

When nothing is being transmitted by the meter, the driver output A1U7-5 is -5.0 V dc.

The receive signal from A1J5 goes to the RS-232 receiver A1U7-4, where it is inverted

and shifted to transition between +5.0 and 0 V dc. When nothing is being transmitted to

the meter, the receiver output A1U7-13 is +5.0 V dc.

Data Terminal Ready (DTR) is a modem control signal controlled by the

Microprocessor. This signal is an RS-232 output generated by driver A1U7-7; it is at

+5.0 V dc when the meter is powered up.

2-36.

Microprocessor

The Microprocessor utilizes an eight-bit data bus and a sixteen-bit address bus to access

memory locations in ROM (A1U8), RAM (A1U10), and the IEEE-488 option. The upper

three bits of the address bus are decoded by A1U9 to generate chip select signals for the

ROM (A1U9-6) and RAM (A1U9-8). The Microprocessor enables the reading of

memory by driving RD* (A1U6-67) low, and writing of memory by driving WR*

(A1U6-66) low. The IEEE-488 option also makes use of the signal R/W* (read when

high, write when low) that is generated by A1U6-65.

The Microprocessor operates with a memory cycle time of 1.085 us as determined by the

3.6864 MHz crystal A1Y2. The system clock signal (A1U6-68) is a square wave with a

frequency of 921.6 kHz. It is used by the Display Assembly and the IEEE-488 option

assembly after being damped by series resistor A1R57.

The Microprocessor uses synchronous communication to store and retrieve meter

configuration and calibration information in the EEROM (A1U5). See the EEROM

description for more detailed information.

The Microprocessor communicates to the Display Controller using a synchronous, three-

wire communication interface described in detail in the Display Controller Theory of

Operation.

The Microprocessor communicates to the Analog Measurement Processor (via the Serial

Communication circuit) using an asynchronous communication protocol.

Communication to the Analog Measurement Processor originates at A1U6-11 (which is

normally low when no communication is being done). Communication from the Analog

Measurement Processor to the Microprocessor appears at A1U6-10 and is normally low

(unless communication is in progress.)

2-37.

EEROM

The EEROM contains 64 registers, each of which is 16 bits long. These registers are

used to provide non-volatile storage of meter configuration and calibration information.

When the Microprocessor is communicating to the EEROM, Chip Select (A1U5-2) goes

high to enable the EEROM interface.

When the Microprocessor is reading data from the EEROM, the data bits are serially

shifted out on the Data Out signal (A1U5-6) with each one-to-zero transition of the

Serial Clock (A1U5-3).

When the Microprocessor is writing commands and data to the EEROM, the bits are

serially shifted into the EEROM on the Data In signal (A1U5-5) with each zero-to-one

transition of the Serial Clock (A1U5-3). The EEROM drives the Data Out signal (A1U5-

2-19

Service Manual

6) low to indicate that it is busy writing the register, thereby controlling the timing of the

write cycle. The microprocessor waits for this signal to go high before performing other

EEROM operations. If the EEROM fails to drive this signal high, the microprocessor

waits indefinitely.

New data is written to a register only after old data in that register is erased. After each

such erase or write cycle, the microprocessor polls the status of EEROM by setting Chip

Select (A1U5-2) high and checking the state of the Data Out signal (A1U5-6). If Data

Out is low, the erase/write cycle is still in progress. If Data Out is high, the EEROM is

ready for another command.

2-38.

RAM

The RAM is a 8192 x 8 bit device that provides the temporary data storage used by the

operating software of the meter. The chip select for this device (A1U10-20) goes low for

any memory cycle between hexadecimal addresses 2000 and 3FFF. The RD* signal from

the Microprocessor enables the reading of data when it is low, and the WR* signal writes

data into the RAM when it is low.

2-39.

ROM

The ROM provides the instruction storage for the Microprocessor. The chip select for

this device (A1U8-20) goes low for any memory cycle between hexadecimal addresses

4000 and FFFF (accessing 48 kbytes.) Whenever this device is chip selected, the

instruction in the addressed location is output to the data bus and read by the

Microprocessor.

2-40.

IEEE-488 Option Connections

The interconnection to the IEEE-488 option is implemented by two ribbon cables that

mount to the 14-position and 20-position connectors on the Main PCA. The 14-position

connector (A1J3) routes the 8-bit data bus, RD*, R/W*, E, RESET and OPTSW* signals

to the option. The 20-position connector (A1J2) routes the 16-bit address bus and the

WR* memory control signal to the option. This connector also routes the IEEE-488

interrupt and option sense signals from the option. See Chapter 8 for further information.

2-41.

Display Assembly

Display Assembly operation classified into six functional circuit blocks: the Main

Assembly Connector, the Front Panel Switches, the Display, the Beeper Drive Circuit,

the Watchdog Timer/Reset Circuit, and the Display Controller. These blocks are

described in the following paragraphs.

2-42.

Main Assembly Connector

The Main Assembly Connector is a 20-pin connector (A2J1) that provides the interface

between the Main Assembly and the other functional blocks on the Display Assembly.

Seven of the connector pins provide the necessary connections to the four power supply

voltages (-30 V dc, -5 V dc, +5 V dc, and 5 V ac). Six pins are used to provide the

interface to the Front Panel Switches (A2SWR1 through A2SWR6). The other seven

signals interface the Microprocessor to the Display Controller and pass the reset signals

between the assemblies.

2-43.

Front Panel Switches

The microprocessor scans the 19 Front Panel Switches (A2S1 through A2S18, and

A2S21) using only six interface signals (plus the ground connection already available

2-20

Theory of Operation

Detailed Circuit Description

from the power supply). These six signals (SWR1 through SWR6) are connected to a bi-

directional I/O port on the microprocessor. Each successive column has one less switch.

This arrangement allows the unused interface signals to function as strobe signals when

their respective column is driven by the microprocessor. The microprocessor cycles

through six steps to scan the complete Front Panel Switch matrix. Table 2-5 shows the

interface signal state and, if the signal state is an output, the switches that may be

detected as closed.

In step 1, six port bits are set to input, and the interface signal values are read. In steps 2

through 6, the bit listed as output is set to output zero, the other bits are read, and bits

indicated by a Z are ignored.

Each of the interface signals is pulled up to the +5 V dc supply by a 10 kΩ resistor in

network A2Z1. Normally, the resistance between any two of the interface signals is

approximately 20 kΩ. Checking resistances between any two signals (SWR1 through

SWR6) verifies proper termination by resistor network A2Z1.

2-44.

Display

The custom vacuum-fluorescent display (A2DS1) comprises a filament, 11 grids

(numbered 0 through 10 from right to left on the display), and up to 14 anodes under

each grid. The anodes make up the digits and annunciators for their respective area of the

display. The grids are positioned between the filament and the anodes.

The filament is driven by a 5 V ac signal that is centered on a -25 V dc level. When a

grid is driven to +5 V dc, the electrons from the filament are accelerated toward the

anodes that are under that grid. Anodes under that grid that are also driven to +5 V dc are

illuminated, but the anodes that are driven to -30 V dc are not. Grids are sequentially

driven to +5 V dc, one at a time. The sequence is from GRID(0) to GRID(10), which is

right to left as the display is viewed.

2-45.

Beeper Drive Circuit

The Beeper Drive circuit is controlled by U1. A 3.6-kHz square wave appears at the PPO

output of U1 and across the parallel combination of A2LS1 and A2R10, causing the

beeper to resonate.

Table 2-5. Front Panel Switch Scanning

Interface Signal States or Key Sensed

Step

SWR6

SWR5

SWR4

SWR3

SWR2

SWR1

A2S8

A2S17

A2S10

A2S12

A2S18

A2S13

A2S1

A2S2

A2S3

A2S4

A2S11

A2S7

A2S9

A2S5

A2S6

A2S14

A2S15

A2S16

n/a

A2S21

A2Sn indicates switch closure sensed.

0 indicates strobe driven to logic 0.

Z indicates high impedance input; state ignored.

2-46. Watchdog Timer and Reset Circuit

This circuit provides active high and active low reset signals to the rest of the system at

power-up or a system reset if the Microprocessor does not communicate with the

Display Processor for a 5-second period. The Watchdog Timer and Reset Circuit is

2-21

Service Manual

comprised of dual retriggerable monostable multivibrator A2U5, NAND gates from

A2U6, diode A2CR3, and various resistive and capacitive timing components.

At power-up, capacitor A2C3 begins to charge up through resistor A2R3. The voltage

level on A2C3 is detected by an input of Schmitt-Trigger NAND gate A2U6-12. The

output of this gate (A2U6-11) then drives the active high reset signal (RESET) to the rest

of the system. When the voltage on A2C3 is below the input threshold of A2U6-12,

A2U6-11 is high. As soon as A2C3 charges up to the threshold of A2U6-12, A2U6-11

goes low. The RESET signal drives NAND gate inputs A2U6-1 and A2U6-2, to generate

the active low reset signal (RESET*) at A2U6-3.

When the RESET signal transitions from high to low (A2U5-1), the Watchdog Timer is

triggered initially, causing A2U5-13 to go high. This half of the dual retriggerable

monostable multivibrator uses timing components A2R2 and A2C2 to define a nominal

4.75-second watchdog timeout period. Each time a low-to-high transition of DISTX is

detected on A2U5-2, capacitor A2C2 is discharged to restart the timeout period. If there

are no low-to-high transitions on DISTX during the 4.75-second period, A2U5-13

transitions from high to low, triggers the other half of A2U5, and causes output A2U5-12

to go low. A2U5-12 is then inverted by A2U6 to drive the RESET signal high, causing a

system reset. The low duration of A2U5-12 is determined by timing components A2Z1

and A2C4 and is nominally 460 µs. When A2U5-12 goes high again, RESET goes low to

retrigger the Watchdog Timer.

2-47.

Display Controller with FIP

The Display Controller is a 4-bit, single-chip microcomputer with high-voltage outputs

that drive a vacuum-fluorescent display directly. The controller receives commands over

a three-wire communication channel from the Microprocessor on the Main Assembly.

Each command is transferred serially to the Display Controller on the display transmit

(DISTX) signal, with bits being clocked into the Display Controller on the rising edges

of the display clock signal (DSCLK). Responses from the Display Controller are sent to

the Microprocessor on the display receive signal (DISRX) and are clocked out of the

Display Controller on the falling edge of DSCLK.

Figure 2-9 shows the waveforms during a single command byte transfer. Note that a high

DISRX signal is used to hold off further transfers until the Display Controller has

processed the previously received byte of the command.

Once reset, the Display Controller performs a series of self-tests, initializing display

memory and holding the DISRX signal high. After DISRX goes low, the Display

Controller is ready for communication; on the first command byte from the

Microprocessor, the Display Controller responds with a self-test results response. If all

self-tests pass, a response of 00000001 (binary) is returned. If any self-test fails, a

response of 01010101 (binary) is returned. The Display Controller initializes its display

memory to one of four display patterns depending on the states of the DTEST* (A2U1-

41) and LTE* (A2U1-13) inputs. The DTEST* input is pulled up by A2Z1, but may be

pulled down by jumpering A2TP4 to A2TP3 (GND). The LTE* input is pulled down by

A2R12, but may be pulled up by jumpering A2TP5 to A2TP6 (VCC). The default

conditions of DTEST* and LTE* cause the Display Controller to turn all segments on

bright at power-up.

Table 2-6 defines the logic and the selection process for the four display initialization

modes.

The two display test patterns are a mixture of on and off segments forming a

recognizable pattern that allows for simple testing of display operation. The Display

Controller provides 10 grid control outputs and 14 anode control outputs. Each of these

24 high-voltage outputs provides an active driver to the +5 V dc supply and a passive 70

2-22

Theory of Operation

Detailed Circuit Description

kΩ (nominal) pull-down to the -30 V dc supply. These pull-downs are internal to the

Display Controller.

The output port, P63, of the Display Controller, is used as a grid control output for

GRID(10), of the vacuum-fluorescent display. A high voltage output, from P63, is

provided with a 10 kΩ resistor (A2R1), and PNP transistor (A2Q1) provide an active

driver to the +5 V dc supply and a passive 47 kΩ pull-down (A2R4) to -30 V dc.

The Display Controller drives the vacuum-fluorescent display in a multiplexed manner

by strobing each grid individually while the segment data for that display area is

presented on the anode outputs. Each grid is strobed for approximately 427

microseconds every 5.368 milliseconds, resulting in each grid on the display being

strobed about 170 times per second. The grid strobing sequence is from GRID(0) to

GRID(10), which results in right-to-left strobing of grid areas on the display. Figure 2-10

shows grid control signal timing.

The single grid strobing process involves turning off the previously enabled grid,

outputting the anode data for the next grid, and then enabling the next grid. This

procedure ensures that there is some time between grid strobes so that no shadowing

occurs on the display. Figure 2-11 describes the timing relationship between an

individual grid control signal and the anode control signals.

DSCLK

DISTX

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

DISRX

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

Clear to receive

qb09.eps

Figure 2-9. Command Byte Transfer Waveforms

Table 2-6. Display Initialization Modes

A2TP4 Dtest*

A2TP5 LTE*

Power-Up Display

Initialization

All Segments OFF

All Segments ON (default)

Display Test Pattern #1

Display Test Pattern #2

2-23

Chapter 3

General Maintenance

Title

Page

3-1.

Introduction

3-3

3-2.

Warranty Repairs and Shipping Information

3-3

3-3.

General Maintenance Information

3-3

3-4.

Required Equipment

3-3

3-5.

Power Requirements

3-3

3-6.

Static Safe Handling

3-3

3-7.

Cleaning

3-4

3-8.

Fuse Test and Replacement

3-4

3-9.

Line Fuse

3-4

3-10.

Current Input Fuses

3-4

3-11.

Testing Current Input Fuses

3-4

3-12.

Replacing the 500 mA and 440 mA Input Fuses (F1 and F5)

3-5

3-13.

Replacing the 10 A Input Jack Fuse (F2)

3-6

3-14.

Disassembly Procedures

3-7

3-15.

Remove the Meter Case

3-7

3-16.

Remove Handle and Mounting Brackets

3-7

3-17.

Remove the Front Panel Assembly

3-8

3-18.

Remove the Display PCA

3-8

3-19.

Remove the IEEE-488 Option

3-9

3-20.

Remove the Main PCA

3-9

3-21.

Remove the Analog Measurement Processor Shields

3-9

3-22.

Remove the Rms PCA

3-10

3-23.

Remove the Battery Option

3-10

3-24.

Disconnect Miscellaneous Chassis Components

3-10

3-25.

Assembly Procedures

3-10

3-26.

Install Miscellaneous Chassis Components

3-10

3-27.

Install the Battery Option

3-11

3-28.

Install the Rms PCA

3-11

3-29.

Install the Analog Measurement Processor Shields

3-11

3-30.

Install the Main PCA

3-11

3-31.

Install the IEEE-488 Option

3-12

3-32.

Assemble the Front Panel Assembly

3-12

3-33.

Install the Front Panel Assembly

3-15

3-34.

Install the Handle and Mounting Brackets

3-15

3-35.

Install the Meter Case

3-15

3-1

General Maintenance

Introduction

3-1.

Introduction

This provides handling, cleaning, fuse replacement, disassembly, and assembly

instructions.

3-2.

Warranty Repairs and Shipping Information

If your meter is still under warranty, see the warranty information at the front of this

manual for instructions on returning the unit. A list of Fluke telephone numbers and our

website address can be found at the end of the warranty information and in Chapter 6.

3-3.

General Maintenance Information

3-4.

Required Equipment

Equipment required for calibration, troubleshooting, and repair of the Fluke 45 is listed

in Table 4-4.

3-5.

Power Requirements

Warning

To avoid shock hazard, connect the meter power cord to a

power receptacle with earth ground.

If you have not already done so, plug the line cord into the connector on the rear of the

meter. The meter operates on any line voltage between 90 V ac and 264 V ac without

adjustment, and at any frequency between 45 and 440 Hz. However, the meter is only

warranted to meet published specifications at 50/60 Hz. The meter draws a maximum of

15 VA.

3-6.

Static Safe Handling

All integrated circuits, including surface mounted ICs, are susceptible to damage from

electrostatic discharge (ESD). Modern integrated circuit assemblies are more susceptible

to damage from ESD than ever before. Integrated circuits today can be built with circuit

lines less than one micron thick, allowing more than a million transistors on a 1/4-inch

square chip. These submicron structures are sensitive to static voltages under 100 volts.

This much voltage can be generated on a dry day by simply moving your arm. A person

can develop a charge of 2,000 volts by walking across a vinyl tile floor, and polyester

clothing can easily generate 5,000 to 15,000 volts during movement against the wearer.

These low voltage static problems are often undetected because a static charge must be

in the 30,000 to 40,000 volt range before a person will feel a shock.

Most electronic components manufactured today can be degraded or destroyed by ESD.

While protection networks are used in CMOS devices, they can only reduce, not

eliminate, component susceptibility to ESD.

ESD may not cause an immediate failure in a component; a delayed failure or

"wounding" effect is caused when the semiconductor’s insulation layers or junctions are

punctured. The static problem is thus complicated in that failure may occur anywhere

from two hours to six months after the initial damage.

3-3

Service Manual

Two failure modes are associated with ESD. First, a person who has acquired a static

charge can touch a component or assembly and cause a transient discharge to pass

through the device. The resulting current ruptures the junctions of a semiconductor. The

second failure mode does not require contact with another object. Simply exposing a

device to the electric field surrounding a charged object can destroy or degrade a

component. MOS devices can fail when exposed to static fields as low as 30 volts.

Observe the following rules for handling static-sensitive devices:

1. Handle all static-sensitive components at a static-safe work area.

Use grounded static control table mats on all repair benches, and always wear a

grounded wrist strap. Handle boards by their nonconductive edges only. Store

plastic, vinyl, and Styrofoam objects outside the work area.

2. Store and transport all static-sensitive components and assemblies in static shielding

bags or containers.

Static shielding bags and containers protect components and assemblies from direct

static discharge and external static fields. Store components in their original packages

until they are ready for use.

3-7.

Cleaning

Warning

To avoid electrical shock or damage to the meter, never allow

water inside the case. To avoid damaging the meter’s housing,

never apply solvents to the meter.

If the meter requires cleaning, wipe it down with a cloth that is lightly dampened with

water or a mild detergent. Do not use aromatic hydrocarbons, chlorinated solvents, or

methanol-based fluids when wiping the meter.

3-8.

Fuse Test and Replacement

3-9.

Line Fuse

The line fuse (a T 125 mA, 250 V, slow blow) is located on the rear panel. The fuse is in

series with the power supply. For replacement, unplug the line cord and remove the fuse

holder with fuse as shown in Figure 3-1. The meter is shipped with a replacement fuse.

3-10.

Current Input Fuses

The 100 mA and 10 A inputs are protected by replaceable fuses.

• The 100 mA input is protected by 2 fuses, F1 and F5. F1 is rated at F 500 mA, 250 V

(fast blow), 1500 A minimum breaking capacity, IEC-127 Sheet I and F5 is rated at

440 mA, 1000 V, 10,000 A minimum interrupt rating, (fast blow) fuse.

• The 10 A input is also protected by a fuse, F2, rated at F 11 A, 1000 V (fast blow),

17,000 A breaking capacity.

3-11.

Testing Current Input Fuses

Perform the following procedure to test these fuses:

1. Plug a test lead into the

input terminal, and power up the meter.

2. Press

to select the ohms function.

3-4

FLUKE 45 Dual Display Multimeter. Service Manual (For IEC 1010 Meters Only) - page 1