Programmable Logic Controller (PLC) Questions and Answers

This PLC is being used to start and stop an electric motor, and also to shut it down automatically if any of three “shutdown” conditions occur:

• Excessive vibration
• Overcurrent (overload heater contact)
• High winding temperature

The status of each shutdown contact is as follows:

• Vibration contact: closed when okay, opens when vibration becomes excessive
• Overload contact: closed when okay, opens when overloaded
• Temperature contact: open when okay, closes when hot

Draw a PLC ladder-logic program to start and stop this motor. Be sure to make the program latching so that the operator does not have to hold the Start button to keep the motor running.

Answer :

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Credits : by Tony R. Kuphaldt – under CC BY 1.0

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