Transcription of Chapter 7 TIMERS, COUNTERS and T/C APPLICATIONS
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Chapter 7 TIMERS, COUNTERS and T/C APPLICATIONS
Ch 7 Timers, COUNTERS , T/C APPLICATIONS 1 Chapter 7 TIMERS, COUNTERS and T/C APPLICATIONS Introduction Timers and COUNTERS are discussed in the same Chapter since most rules apply to both. Timers and COUNTERS have been in existence for as long as relays and provide an important component in the development of logic. Timers were constructed in the past as an add-on device to relays slowing down the transition of the plunger from immediately opening or closing. The time delay was accomplished with a pneumatic bladder that allowed the air to escape either quickly or slowly depending on the setting of the timer . Quick was usually less than a second and slow was usually between 30 and 60 seconds.
Fig. 7-2 Pneumatic Delay Timer from Allen-Bradley Fig. 7-3 Pneumatic Off Delay Timer Symbols and Timing Diagram While these timers are only a sampling of the types of different timers, their function describes the main function of all timers, a time delay. While PLC vendors do not need to use the terms of
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