Question

Write a ladder logic program to monitor part of a process by using a watchdog timer.

The equipment consists of a tank equipped with a single mixer. The mixer has a sensor that detects rotation of the shaft. The rotation sensor becomes momentarily FALSE once each rotation (every 6 seconds).

When the start button is pushed, the process and the mixer start. The watch-dog timer pulses with each rotation of the mixer shaft to indicate that the mixer is running. Turn on a green light to show that the process is running and an amber light to show that the mixer is turning. If the watchdog fails, turn off the green and amber lights and turn on a red light.

The process runs for 20 seconds and then turns everything off. After a normal shut off, it should be possible to start another cycle by pressing the start button.

If the watchdog fails to pulse FALSE within the expected time, the entire process should be shut down, a red light should be turned on, and it should not be possible to start a new cycle until the error is cleared.

Answer 1