Terminology; Analog Value : A; Digital Value : D - LG G3F-AD3A User Manual

Chapter 1 Introduction

1.2 Terminology

1.2.1 Analog value : A

A n a l og value is a continuously changing value such as voltage, current, tem pe r ature,
speed pressure, flux, etc. Tem perature, for exam ple, is continuously changing according
to the tim e . Because t his tem p e r a ture itself is not available for input of the PLC, the
tem perature shoul d be converted an analog electrical si gnal by transducer. Moreover, the
convert ed analog signal (vol tage or current) has to be converted into a digital value with
the A/D m odule because the PLC can handle only digital values.

1.2.2 Digital value : D

D igital value is a di screte data that are described in num bers such as 0, 1, 2, ...
general, a binary code system t hat are consi st of 0(off) and 1(on) is used for expressing
di gital value. Also, BCD or hexadecimal values are used.
Because the CPU module of PLC can handle dig ital value only, the analog signal from
external devices should be converted into analog signals with A/D m o d u l e.
In the other hand, the digital output of CPU m o d u le shoul d be converted int o analog
si gnal to be used for external devices. The D/A module (d igital - anal og converter) is used
for converting digital values into analog output (voltage or current).
value
Figure 1.1 Analog value
value
Figure 1.2 Digital value
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