Fluke 27 Service Manual

27
®
Multimeter
Service Manual
For IEC 61010 CAT III Meters Only
PN 690206 November 1998
© 1998 Fluke Corporation, All rights reserved. Printed in U.S.A. All product names are trademarks of their respective companies.

Table of Contents

Chapter Title Page
1 Introduction and Specifications........................................................... 1-1
1-1. Using the Meter Safely .......................................................................... 1-3
1-2. Operating Instructions ............................................................................ 1-4
1-3. Specifications ......................................................................................... 1-5
2 Theory of Operation .............................................................................. 2-1
2-1. Introduction ........................................................................................... 2-3
2-2. Functional Description ........................................................................... 2-3
2-3. Block Diagram Description ................................................................... 2-4
2-4. Input Overload Protection ................................................................. 2-4
2-5. Function Switching Circuits .............................................................. 2-4
2-6. Signal Conditioning Circuits ............................................................. 2-4
2-7. Custom Analog IC (U1) .................................................................... 2-4
2-8. Peripherals to U1 ............................................................................... 2-6
2-9. Microcomputer Control ..................................................................... 2-6
2-10. Display .............................................................................................. 2-7
3 Maintenance........................................................................................... 3-1
3-1. Introduction ........................................................................................... 3-3
3-2. Service Information ............................................................................... 3-4
3-3. Operator Maintenance ............................................................................ 3-4
3-4. Battery Replacement ......................................................................... 3-5
3-5. Fuse Test ........................................................................................... 3-6
3-6. Fuse Replacement .............................................................................. 3-6
3-7. General Maintenance Information ......................................................... 3-7
3-8. Handling Precautions for Static-Sensitive Devices ........................... 3-7
3-9. Disassembly ....................................................................................... 3-7
3-10. Reassembly ........................................................................................ 3-10
3-11. Cleaning ............................................................................................ 3-12
3-12. Performance Tests ................................................................................. 3-12
3-13. Display Test ....................................................................................... 3-12
3-14. Voltage Functions Performance Verification .................................... 3-13
3-15. AC and DC Current Performance Verification .................................. 3-13
3-16. Ohms Function Performance Verification ......................................... 3-14
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3-17. Diode Test Performance Verification ................................................ 3-15
3-18. Calibration Adjustment .......................................................................... 3-15
3-19. Calibration Preparation ...................................................................... 3-15
3-20. DC Voltage Connection .................................................................... 3-16
3-21. AC Voltage Calibration ..................................................................... 3-16
3-22. Troubleshooting ..................................................................................... 3-17
3-23. Power-Up Self Test ........................................................................... 3-17
3-24. Overall System Check ....................................................................... 3-17
3-25. DC Voltage Signal Tracing ............................................................... 3-18
3-26. Fault Diagnosis Guide ....................................................................... 3-19
4 List of Replaceable Parts...................................................................... 4-1
4-1. Introduction ........................................................................................... 4-3
4-2. How to Obtain Parts ............................................................................... 4-3
4-3. Manual Status Information .................................................................... 4-3
4-4. Newer Instruments ................................................................................. 4-4
4-5. Service Centers ...................................................................................... 4-4
4-6. Parts Lists .............................................................................................. 4-5
5 Schematic Diagrams ............................................................................. 5-1
ii

List of Tables

Table Title Page
1-1. Specifications.......................................................................................................... 1-5
3-1. Recommended Test Equipment .............................................................................. 3-3
3-2. Replacement Fuses.................................................................................................. 3-6
3-3. Ohm Function Performance Test ............................................................................ 3-15
3-4. Fault Diagnosis Guide............................................................................................. 3-19
4-1. Final Assembly ....................................................................................................... 4-6
4-2. A1 Main PCA ......................................................................................................... 4-8
4-3. A2 Digital PCA....................................................................................................... 4-11
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iv

List of Figures

Figure Title Page
3-1. Battery and Fuse Replacement................................................................................ 3-5
3-2. Disassembly............................................................................................................ 3-8
3-3. Calibration Adjustment Locations .......................................................................... 3-16
4-1. Final Assembly ....................................................................................................... 4-7
4-2. A1 Main PCA ......................................................................................................... 4-10
4-3. A2 Digital PCA....................................................................................................... 4-11
5-1. A1 Main PCA and A2 Digital PCA........................................................................ 5-3
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Chapter 1

Introduction and Specifications

Title Page
1-1. Using the Meter Safely........................................................................ 1-3
1-2. Operating Instructions.......................................................................... 1-4
1-3. Specifications....................................................................................... 1-5
1-1
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1-2
1-1. Using the Meter Safely
Use the meter as described in this manual. Otherwise the safety features provided by the meter might be impaired. A Warning identifies conditions and actions that pose hazards to the user; a Caution identifies conditions and actions that might damage the meter. Read First: Safety Information.
Read First: Safety Information
This meter complies with EN 61010-1:1993, ANSI/ISA S82.01­1994 and CAN/CSA C22.2 No. 1010.1-92 Overvoltage Category III. Use the meter only as specified in the Users Manual, otherwise the protection provided by the meter may be impaired.
Warning
To avoid possible electric shock or personal injury:
Do not use the meter if it is damaged. Before use, inspect the
case for cracks or missing plastic. Pay particular attention to the insulation surrounding the connectors.
Introduction and Specifications

Using the Meter Safely

1
Inspect the test leads for damaged insulation or exposed metal.
Check test lead continuity. Replace damaged leads.
Do not use the meter if it operates abnormally. Protection may be
impaired. When in doubt, have the meter serviced.
Do not operate the meter around explosive gas, vapor or dust.
Do not apply more than the rated voltage, as marked on the meter,
between terminals or between any terminal and earth ground.
Before each use, verify the meter’s operation by measuring a
known voltage.
When servicing the meter, use only specified replacement parts.
Use caution when working above 30 V ac rms, 42 V ac peak, or 60
V dc. Such voltages pose a shock hazard.
Keep your fingers behind the finger guards on the probe when
making measurements.
Connect the common test lead before connecting the live test
lead. Disconnect the live test lead first.
Remove test leads from the meter before opening the battery
door.
Make sure the battery door is closed and latched before operating
the meter.
Use only a single 9 V battery, properly installed in the meter case,
to power the meter.
Follow all equipment safety procedures.
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Service Manual
Before measuring current, check the meter’s fuses (see “How to
Test the Fuse”).
Never touch the probe to a voltage source when the test leads are
plugged into the 10 A or 40 mA input jacks.
To avoid false readings, which could lead to possible electric
shock or personal injury, replace the meter’s battery as soon as the low battery indicator (
Avoid working alone.
To avoid possible damage to the meter or to equipment under test:
Disconnect the power to the circuit under test and
discharge all high voltage capacitors before testing resistance, continuity or diodes.
Use the proper function and range for your measurement
applications.
) appears.
Caution
When measuring current, turn off circuit power before
connecting the meter in the circuit. Remember to place the meter in series with the current.
This manual presents service information for the Fluke 27 Multimeters. Included are a theory of operation, general maintenance procedures, performance tests, calibration procedures, troubleshooting information, a list of replaceable parts, and a schematic diagram.
1-2. Operating Instructions
For operating instructions, refer to the Users Manual provided with the instrument at time of purchase.
1-4
Introduction and Specifications
1-3. Specifications
Instrument specifications are presented in Table 1-1.
Table 1-1. Specifications
Function Range Resolution Accuracy
3.200 V
32.00 V
320.0 V 1000 V
320.0 mV 0.1 mV ±(0.1%+1)
320.00 0.1 ±(0.3%+3)*
3.200 k 0.001 k ±(0.2%+1)
32.00 k 0.01 k ±(0.2%+1)
(nS)
* When using the REL function to compensate for offsets.
320.0 k 0.1 k ±(0.2%+1)
3.200 M 0.001 M ±(0.2%+1)
32.00 M
32.00 nS
2.080 V 0.001 V ±(1%+1) typical
3.200 V 0.001 V ±(0.5%+3) ±(2%+3) ±(4%+ 10)
32.00 V 0.01 V ±(0.5%+3) ±(2%+3) ±(4%+ 10)
320.0 V 0.1 V ±(0.5%+3) ±(2%+3) ±(4%+ 10) 1000 V 1 V ±(1%+3) ±(3%+3) Not Specified
320.0 mV 0.1 mV ±(0.5% +3) ±(2%+3) ±(4%+10)
0.001 V
0.01 V
0.1 V 1 V
0.01 M
0.01 nS
40 Hz-2 kHz 2 kHz -10 kHz 10 kHz -30 kHz
±(0.1%+1) ±(0.1%+1) ±(0.1%+1) ±(0.1%+1)
±(1%+1) ±(0.2%+10)

Specifications

1
Function Range Resolution Accuracy Typical Burden Voltage
m /A
µA
mA/A
40-1000 Hz
µA
40-1000 Hz
32.00 mA
320.0 mA
10.00 A
320.0 µA 3200 µA
32.00 mA
320.0 mA
10.00 A
320.0 µA 3200 µA
0.01 mA
0.1 mA
0.01 A
0.1 µA 1 µA
0.01 mA
0.1 mA
0.01 A
0.1 µA 1 µA
±(0.75%+2) ±(0.75%+2) ±(0.75%+2)
±(0.75%+2) ±(0.75%+2)
±(1.5%+2) ±(1.5%+2) ±(1.5%+2)
±(1.5%+2) ±(1.5%+2)
5.6 mV/mA
5.6 mV/mA 50 mV/A
0.5 mV/µA
0.5 mV/µA
5.6 mV/mA
5.6 mV/mA 50 mV/A
0.5 mV/µA
0.5 mV/µA
1-5
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Service Manual
Table 1-1. Specifications (cont)
Function Overload
Protection**
1000 V rms 10 M in // with <100pF >120 dB at dc, 50 Hz, or 60 Hz >60 dB at 50 Hz or 60 Hz 1000 V rms 10 M in // with <100pF >120 dB at dc, 50 Hz, or 60 Hz >60 dB at 50 Hz or 60 Hz 1000 V rms
1000 V rms
1000 V rms Open Circuit Test
Input Impedance
(nominal)
10 M
in // with <100pF (ac coupled) 10 M
in // with <100pF (ac coupled)
Common Mode Rejection
Ratio
unbalance)
(1 k
>60 dB, dc to 60 Hz
>60 dB, dc to 60 Hz
Full Scale Voltage
Normal Mode
Rejection
Voltage
Up to 3.2 M 32 M or nS
<2.8 V dc <420 mV dc <1.3 V dc
** 107 V Hz Max
Basic electrical accuracy is specified from 18°C to 28°C with relative humidity up to 95%, for a period of one year after calibration. All ac conversions are ac coupled, average responding, and calibrated to read the true rms value of a sine wave input. Accuracy is specified as ±([% of reading] + [number of least significant digits]).
Ranging is either automatic or manual in all functions with more than one range. Test resistance below approximately 270 J in
function produces a continuous audible tone.
the
Maximum voltage between any terminal and earth ground
Fuse protection
mA or µA A
Digital Display 3200 counts, updates 2/sec Analog Display 31 segments, updates 25/sec Operating Temperature -150°C to 55°C, to -40°C for 20 minutes when taken from 20°C
Storage Temperature -55°C to 85°C without battery, to 60°C with battery Electromagnetic Compatibility
Temperature Coefficient 0.1 x (specified accuracy)/°C (18°C or >28°C) Relative Humidity 0% to 95% (0°C to 35°C)
Altitude 2000 meters Battery Type 9 V, NEDA 1604 or 6F22 or 006P Battery Life 1000 hrs typical Shock, Vibration and Water
Resistance Size (HxWxL) 2.2 in x 3.75 in x 8 in (5.6 cm x 9.5 cm x 20.3 cm) Weight 1.6 pounds (0.75 kg) Safety Complies with ANSI/ISA S82.01-1994, CAN/CSA 22.2 NO. 1010.1:1992 to
1000 V
44/100 A 1000 V Fast 11 A 1000 V Fast
In an RF field of 2 V/m on all ranges and functions (except mVac), total accuracy = specified accuracy + 1.0% or range. For mVac, total accuracy = specified accuracy + 1.5% or range. EN 61326-1:1997.
0% to 70% (35°C to 55°C)
Per MIL-T-28800 for a Style A, Class 2 Instrument
1000 V Overvoltage Category III. UL License pending to UL3111-1. TUV License pending to EN61010-1.
1-6
Chapter 2

Theory of Operation

Title Page
2-1. Introduction ......................................................................................... 2-3
2-2. Functional Description......................................................................... 2-3
2-3. Block Diagram Description ................................................................. 2-4
2-4. Input Overload Protection ............................................................... 2-4
2-5. Function Switching Circuits ............................................................ 2-4
2-6. Signal Conditioning Circuits ........................................................... 2-4
2-7. Custom Analog IC (U1) .................................................................. 2-4
2-8. Peripherals to U1............................................................................. 2-6
2-9. Microcomputer Control................................................................... 2-6
2-10. Display ............................................................................................ 2-7
2-1
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2-2
2-1. Introduction
This chapter describes how the Fluke 27 works. First, a functional description presents an overview of operation. This is followed by a block diagram description, which describes the major circuit functions in more detail. For reference, a detailed schematic diagram is included in Chapter 5.
2-2. Functional Description
A block diagram of the Fluke 27 circuitry is shown in Figure 2-1. As this figure shows, the instrument is composed of two major functional sections: the analog section and the digital section. Each section contains one major active component and one or more peripheral circuits. Most analog functions are performed by a custom analog IC (U 1) and analog peripherals to U1. Digital functions are performed by a CMOS, 4-bit microcomputer, U2.
The custom analog IC contains the A/D converter, signal conditioning circuits, and the digital control circuitry required for communication with the microcomputer. Although the custom IC is primarily analog, digital circuits provide state machine control for the A/D converter, a read counter for A/D samples, decoding ROMs for analog switch drive, and bus control for communication with the microcomputer.
Theory of Operation

Introduction

2
The microcomputer controls the A/D converter, initiates the range and function switching, formats data for display, and drives the display. The mode push buttons supply input to the microcomputer to initiate various modes. Output from the microcomputer is displayed on the liquid crystal display (LCD).
Figure 2-1. Overall Functional Block Diagram
aac01s.tif
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2-3. Block Diagram Description

2-4. Input Overload Protection

Each of the blocks in the Figure 2-1 is discussed in the following paragraphs. In many cases, circuit sections are described in greater detail than is shown in the Figure 2-1; therefore, it may be helpful to refer to the schematic located near the back of this manual.
Overload protection for the volts/ohms/diode-test input (J1) is provided by a network of five metal-oxide varistors (RV1 through RV5) a current-limiting resistor (R2) and a thermistor (RT1).
A 44/100A, 1000 V fuse provides protection for the mA/µA input (J2) current shunts. An
11 A, 1000 V fuse provides protection for the 10 A input (J3) current shunt. In addition, for the µA and mA ranges, a bridge rectifier (U7) and four diodes (CR1, CR2, CR3, CR4) ensure that the fuses (instead of the shunts) open in very high current overload conditions.
Transistors Q1, Q2, and Q1 provide additional overload protection for the millivolt and ohms functions. If sufficient overload voltage is present, the transistors turn on and connect that input to common through limiting resistors R2 and RT1, thereby protecting the circuitry in U1. A clamp circuit (CR6 and Q15) connected to the volt/ohms/diode-test input through Z1 and C3 provides similar protection for the volts/ohms/diode-test input.

2-5. Function Switching Circuits

Input signals are routed from the overload protection circuits to the function switch. The function switch is a rotary switch with two double-sided wafers which provide the
necessary switching to select each of the various functions. In addition, battery voltage is routed through the function switch from the battery voltage regulator to U1, and from U1 to U2.

2-6. Signal Conditioning Circuits

Each input signal is routed through signal conditioning circuitry before reaching U1. Input signals received through the volts/ohms/diode-test input (J1) are routed through Z1, a precision resistor network. The resistor network provides precise input scaling for the various voltage ranges, and it provides precision reference resistors for the ohms function. The capacitors in parallel with the various resistors in Z1 are used in the ac voltage functions; the variable capacitors provide calibration adjustment for the high frequency ac ranges.
Current inputs received through the mA/ µA input (J2) and the A input (J3) develop a voltage across shunt resistors R14, R20, and R23 (320 µA, 32 mA, and 10 A respectively). Resistors R9 and R10 comprise a 10:1 divider for the 3200-µA and 320­mA current ranges.

2-7. Custom Analog IC (U1)

The analog-to-digital converter, autorange switching, and most of the remaining active analog circuitry (including additional signal conditioning) are contained in U1, a custom LSI package. Peripherals to U1 include the system clock, the reference voltage regulator for the A/D converter, and some filtering and amplifier stabilization components. U1 also contains digital circuitry for state machine control over the A/D decoding ROMs for analog switch drive and read counter preset, and registers to store control outputs from the microcomputer.
2-4
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