Introduction to Industrial Automation

A/D conversion (b).

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Basic Operating Principles of PLCs 

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the alteration of the signal adapting block. Specific analog input modules (instead of the alteration 

block) carry micro-switches (DIP switches) for selecting the type of analog input signals. In mod-

ules with a small number of inputs, there is no signal adapting block or DIP switches, and thus 

each module is manufactured for a specific type of analog signal. The analog signals supplied in 

an analog input module are standard and compatible with the corresponding output signals of the 

analog input devices (sensors or transducers). I
and the standard analog signals that we find in the analog input modules are shown.

Another significant operational difference between the analog input modules (except for 

the A/D converter) and the digital input modules is that the former are equipped with a local 

memory for storing the digital values of the analog inputs. I

diagram of an analog input module is depicted. In this case, a thermocouple (e.g., a couple of 

platinum-platinum of R type) detects the temperature of an object and, subsequently, applies