Introduction; Functional Description; Block Diagram Description - Fluke 27 Service Manual

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.
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).

2-3. Block Diagram Description

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;
Figure 2-1. Overall Functional Block Diagram
Theory of Operation

Introduction

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