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.
1-3
27
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
FunctionRangeResolutionAccuracy
3.200 V
32.00 V
320.0 V
1000 V
320.0 mV0.1 mV±(0.1%+1)
320.00 0.1 ±(0.3%+3)*
3.200 k0.001 k±(0.2%+1)
32.00 k0.01 k±(0.2%+1)
(nS)
* When using the REL ∆ function to compensate for offsets.
FunctionRangeResolutionAccuracyTypical 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
27
Service Manual
Table 1-1. Specifications (cont)
FunctionOverload
Protection**
1000 V rms10 M in // with <100pF >120 dB at dc, 50 Hz, or 60 Hz >60 dB at 50 Hz or 60 Hz
1000 V rms10 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 rmsOpen 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 M32 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 Display3200 counts, updates 2/sec
Analog Display31 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 Coefficient0.1 x (specified accuracy)/°C (18°C or >28°C)
Relative Humidity0% to 95% (0°C to 35°C)
Altitude2000 meters
Battery Type9 V, NEDA 1604 or 6F22 or 006P
Battery Life1000 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)
Weight1.6 pounds (0.75 kg)
SafetyComplies 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.
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
2-3
27
Service Manual
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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