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Programmable Logic Controllers, 5th Edition by William Bolton

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Chapter 4. I/O Processing
This chapter continues the discussion of inputs and outputs from Chapter 2 and is a brief consideration of the processing of the signals from input and output devices. The input/output (I/O) unit provides the interface between the PLC controller and the outside world and must therefore provide the necessary signal conditioning to get the signal to the required level and also to isolate it from possible electrical hazards such as high voltages. This chapter includes the forms of typical input/output modules and, in an installation where sensors are some distance from the PLC processing, their communication links to the PLC.

4.1. Input/Output Units

Input signals from sensors and outputs required for actuating devices can ...

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