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Programmable Logic Controllers, 6th Edition by William Bolton

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Chapter 7

Internal Relays

Abstract

This chapter continues from the previous chapters on programming and introduces the concept in programming of internal relays. Programs involving such operations are developed.

Keywords

internal relays

This chapter continues from the previous chapters on programming and introduces internal relays. A variety of other terms are often used to describe these elements, such as auxiliary relays, markers, flags, coils, and bit storage. These are one of the elements included among the special built-in functions with PLCs and are very widely used in programming. A small PLC might have a hundred or more internal relays, some of them battery backed so that they can be used in situations where it is necessary to ensure ...

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