Fluke II Series Service Manual

Theory of Operation
INTRODUCTION
INTRODUCTION
2-1.
This
section contains
a brief overview of the
70, 73, 75,
77, 21,
and 23 Series
II
Multimeters,
followed
by
a
more detailed explanation
of operation.
FUNCTIONAL
BLOCK
DESCRIPTION
2-2.
The
heart of the
instrument consists of
a two-chip CMOS
system:
Ul,
a primarily
analog IC,
and
U2,
a
calculator-style microcomputer
(see Figure 2-1).
The
analog chip,
Ul, contains the
a/d
converter,
active filter, ac converter,
analog signal
routing,
range
switching, and
power supply functions.
Peripherals
to
Ul
include
function switching,
voltage
reference, and the crystal.
The
microcomputer,
U2,
controls the
a/d converter function and
range switching, reads
and formats
the
a/d samples, and drives the liquid crystal
display (LCD).
DETAILED
DESCRIPTION 2-3.
The
following
paragraphs
describe the
70, 73, 75,
77,
21 and
23 Series II multimeters
in
more detail.
While reading
this description, refer
to the schematic diagram
in Section
5.
Voltage
Signal Conditioning 2-4.
Input divider
Z1 and
dc blocking capacitor
Cl make up an input
voltage signal
conditioning circuit.
Figure
2-1.
Overview
2-3

Fluke II Series Specifications

General

True RMS	Yes
Temperature	-40 °C to 400 °C
Continuity	Yes
Diode Test	Yes
Safety Rating	CAT III 600V
Voltage DC	600V
Voltage AC	600V
Current DC	10A
Current AC	10A
Resistance	40MΩ
Battery Life	400 hours
Warranty	3 years