1. Introduction
1.3. Terminology
18 Analog Input Module 2MLF-AV8A, AC8A User's Guide R200
Honeywell September 2010
can be displayed as 0 and 1, respectively, in a digital system. This is called as the binary
numbering system. Decimals stored in binary numbering systems are called binary coded
decimals (BCD). Figure 3 displays the digital value of the physical parameter.
Figure 3 – Digital value
Figure 4 – Process in PLC
As the PLC processes only binary numbers, analog values cannot be directly input to the
PLC’s CPU for calculation. Conversion from analog to digital (as shown in Figure 4) is
required. This is done using Analog to Digital converter (A/D conversion module).
Similarly, to get an analog output from a digital value, a Digital to Analog converter
(D/A conversion module) is used.
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