Programmable Logic Controllers
Programmable Logic Controllers
5th Edition
ISBN: 9780073373843
Author: Frank D. Petruzella
Publisher: McGraw-Hill Education
Question
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Chapter 7, Problem 1RQ
Program Plan Intro

Mechanical timing relays:

  • The main purpose of mechanical timing relays is to delay the opening and closing of contacts for circuit control.
  • Its operation is almost similar to that of a control relay.
  • The only difference is that the contacts of a mechanical timing relay are used to operate at a preset time interval, that is, after the coil is energized or de-energized.
  • One example for mechanical timing relay is Pneumatic timing relay.

Expert Solution & Answer
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Explanation of Solution

Difference between timed and instantaneous contacts of a mechanical timing relay:

Timed contactsInstantaneous contacts
Timed contacts change its state only when the time is lapsed.Instantaneous contacts change its state as long as the power is supplied to the timer coil.
Timed contacts are designed to delay the process control.Instantaneous contacts are designed to hold or seal the contacts in a control circuit.
When a coil is energized, these contacts delay from opening or closing.When a coil is energized, this contact closes off open immediately.

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