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Programmable Logic Controllers, 6th Edition by William Bolton

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Chapter 9

Timers

Abstract

This chapter shows how timer blocks, on-delay and off-delay, can be used in programs, also pulse timers and retentive timers. Programs involving such operations are developed.

Keywords

timers

In many control tasks there is a need to control time. For example, a motor or a pump might need to be controlled to operate for a particular interval of time or perhaps be switched on after some time interval. PLCs thus have timers as built-in devices. Timers count seconds or fractions of seconds using the internal CPU clock. This chapter shows how such timer function blocks can be programmed to carry out control tasks.

9.1 Types of Timers

PLC manufacturers differ on how timers should be programmed and hence how they can ...

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