Programmable Logic Controllers
5th Edition
ISBN: 9780073373843
Author: Frank D. Petruzella
Publisher: McGraw-Hill Education
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Question
Chapter 7, Problem 1RQ
Program Plan Intro
- 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
Explanation of Solution
Difference between timed and instantaneous contacts of a mechanical timing relay:
Timed contacts | Instantaneous 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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Chapter 7 Solutions
Programmable Logic Controllers
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