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Programmable Logic Controllers, 5th Edition by William Bolton

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Chapter 14. Programs
This chapter extends the examples given in previous chapters to show programs developed to complete specific tasks. These include tasks that involve temperature control and a number involving pneumatic valves.

14.1. Temperature Control

Consider the task of using a PLC as an on/off controller for a heater in the control of temperature in some enclosure. The heater is to be switched on when the temperature falls below the required temperature and switched off when the temperature is at or above the required temperature. The basic algorithm might be considered to be:
IF temperature below set value
THEN
DO switch on heater
ELSE
DO switch off heater
ENDIF
What can be considered to be required to give the input to a PLC is a sensor-signal ...

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