Theory of Operation
Introduction 2
2-3
Introduction 2-1.
This section describes the theory of operation for the Fluke 76 multimeter.
Functional block descriptions present an overview of circuit operation followed by circuit
descriptions, which detail the major circuit functions. Schematic diagrams are provided in
Section 5.
Functional Block Description 2-2.
The instrument is partitioned into analog and digital sections. (See Figure 2-1 Block
Diagram.) The integrated multimeter chip (U4) performs both analog and digital
functions, which are explained in more detail below.
The analog section of U4 contains the a/d converter, active filter, frequency comparator,
analog signal routing, range switching, and power supply functions.
The digital section of U4 executes software functions, formats data for the display, drives
the display, and controls most analog and digital logic functions. The push button
initiates various operating modes for the meter. Output from the digital section can be
viewed on the liquid crystal display (LCD) and is audible through the beeper.
LCD
ANALOG
SECTION
INPUT SIGNAL
CONDITIONING
INPUT PROTECTION
INPUTS
U1 INTEGRATED MULTIMETER IC
MICROPROCESSOR
FUNCTION
SWITCH
POWER
SUPPLY
V
REF
BEEPER
l1f.eps
Figure 2-1. Block Diagram
Circuit Descriptions 2-3.
The following paragraphs discuss the functional blocks in Figure 2-1. Consult the
schematic diagrams, located in Section 5, for additional circuit details not provided in this
section.
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