Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Textbook Question
Chapter 39, Problem 1RQ
Why are NEMA symbols such as push buttons, float switches, or limit switches not used in programmable logic controller schematics?
Expert Solution & Answer
To determine
Identify why the NEMA symbols for components such as push buttons, limit switches and float switches are not used in the schematic of a programmable controller.
Explanation of Solution
The programmable logic controller can only recognise whether a contact is open or closed. It doesn’t know if the contact is connected to components such as float switches, push buttons and so on.
Thus, there is no NEMA symbol used to identify components such as push buttons, limit switches and float switches in the schematic of a programmable controller.
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Chapter 39 Solutions
Understanding Motor Controls
Ch. 39 - Why are NEMA symbols such as push buttons, float...Ch. 39 - Prob. 2RQCh. 39 - Why are normally closed components such as STOP...Ch. 39 - Prob. 4RQCh. 39 - Prob. 5RQCh. 39 - List four basic rules for developing a program for...Ch. 39 - A PLC requires that times be programmed in...Ch. 39 - When programming in Boolean, what statement should...Ch. 39 - When programming in Boolean, what statement should...Ch. 39 - In a control circuit, it is imperative that a coil...
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