Section 4-Theory Of Operation; Introduction; Overall Functional Description - Keithley 175 Instruction Manual

SECTION 4
THEORY OF OPERATION
4.1 INTRODUCTION
This section contains an overall functional description of the
Model 175. Information pertaining to the Model 1758 Batten/
Pack option is also included. Detailed schematics and com-
ponent layout drawings are located at the end of this instruc-
tion manual.
4.2 OVERALL FUNCTIONAL DESCRIPTION
The Model 175 is a 4 % digit _+20,000 count DMM with five
AC and DC voltage ranges. 7 resistance ranges and 5 AC and
DC current ranges. A simplified block diagram of the Model
175 is shown in Figure 4-l. The heart of the Model 175 is the
AID converter that translates the conditioned analog input
signals into a form usable by the microcomputer.
4.3 ANALOG CIRCUITRY
The following paragraphs conlair a description of the input
multiplexer, buffer amplifier, -2V reference and AID cons
wrier circuits. These circuits may be found on schematic
diagram number 175-106 located at the end of this manual.
RESISTORS
10 AMPS
RANGE CONTROL
FUNCTION
n OFlIVE
MlCRO COMPUTER
LCD DISPLAY
Figure 4-1. Similplifisd Block Diagram
4-1