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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Students have asked these similar questions
I want you to draw a ladder logic diagram of a garage door to control it by PLC. In my case we have different inputs and outputs and all of them gotta be used in the diagram. I can perfectly interpret the diagram so no need to explain it, I will just require you to draw it.
INPUTS : open push button ( OPB ) - close push button ( CPB ) - open limit switch ( OLS ) - close limit switch ( CLS ) - obstacle detection sensor ( ODS ) - safety sensor ( SS ) - emergency stop push button ( ESPB ) - reset button ( RB )
OUTPUTS : motor starts ( MS ) - motor stops ( MSTP ) - motor forward ( MF ) - motor reverse ( MR ) - Error display ( ER )
OPERATİNG MODES : automatic mode ( AM ) - manual mode ( MM )
NECESSARY TIMERS : T1 ( delay door movement after obstacle detection ) - T2 ( delay door movement after reversing )
Here is my excercise for today. Please I am requiring a good logic diagram taking into consideration all what was mentioned before.
so to sum up, I want you to write a logic ladder diagram…
Traffic Light System
Construct a PLC program for a traffic light system with the following condition:
The green light will be ON for 10 second, followed by the yellow light for 3 second and red
light for 20. The system will run continuously until the START/STOP switch is deactivated.
Figure 12: The traffic light system
Two Directional Control of Traffic Light
Extend the PLC program for the traffic light system with the following condition:.
Red = north/south
Green = north/south
Amber = north/south
Green = east/west
Amber = east/west
Red = east/west
-25 s
·5 s
25 s
5 s
Draw the logic circuit diagram for the following function:
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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