Introduction; Functional Block Description - Fluke 78 Service Manual

2-1. Introduction

Chapter 2 provides theory of operation for the Fluke 78 Automotive Meter.
An overview of circuit operation is presented in the form of functional block
descriptions. Circuit descriptions cover the major circuit functions in more detail.
Schematic diagrams are in Chapter 5.

2-2. Functional Block Description

The instrument is partitioned into analog and digital sections. See Figure 2-1. The
integrated multimeter IC (U1) performs both analog and digital functions, which are
explained in more detail below.
The analog section of U1 contains the a/d converter, active filter, ac converter, frequency
comparator, analog signal routing, range switching, and power supply functions.
The digital section of U1 executes software functions, formats data for the display,
drives the display, and controls most analog and digital logic functions. The pushbutton
selects 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.
V
REF
BEEPER
INPUTS
INPUT PROTECTION
INPUT SIGNAL
CONDITIONING
U1 INTEGRATED MULTIMETER IC
ANALOG
SECTION
MICROPROCESSOR
LCD
Figure 2-1. Block Diagram
Theory of Operation

Introduction

POWER
SUPPLY
FUNCTION
SWITCH
zr01f.eps
2
2-3