LG G4F-AD3A - Manual (Page 8)

Chapter 1 Introduction
1-2
1.2 Terminology
1.2.1 Analog value : A
A n a log value is a continuously changing value such as voltage, current, tem p e r a ture,
speed pressure, flux, etc. Tem perature, for exam ple, is continuously changing according
to the tim e . Because this tem p e ra ture itself is not available for input of the PLC, the
tem perature should be converted an analog electrical signal by transducer. Moreover, the
converted analog signal (voltage or current) has to be converted into a digital value with
the A/D m odule because the PLC can handle only digital values.
Figure 1.1 Analog value
1.2.2 Digital value : D
D igital value is a discrete data that are described in num bers such as 0, 1, 2, … In
general, a binary code system that are consist of 0(off) and 1(on) is used for expressing
digital value. Also, BCD or hexadecimal values are used.
B e c a u s e t h e C P U m o d u le 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 le.
In the other hand, the digital output of CPU m o d u le should be converted into analog
signal to be used for external devices. The D/A module (d igital-analog converter) is used
for converting digital values into analog output (voltage or current).
Figure 1.2 Digital value
tim e
value
tim e
value