How to use input in different ways

[JDowell]

Hi all. New here and wondering if you can help. I have a flasher unit I want to test via PLC. The issue I am having is the input signal is 12v+ constant until a pulse signal is detected on the flasher unit, at which point the same input signal swaps to a 2hz pulse.
What I want to do is have the PLC pick up the 12v constant signal for say 3 seconds, send a pulsed output (which I can do) but then read this from the input to confirm it is copying the pulses.
Hope this makes sense and thanks in advance for any help with this

 

[drbitboy]

So the PLC program will be running in one of two states:

1. Waiting for an input memory bit to be 1 for 3s (indicating that the physical input signal has been 12V for 3s)
2. Send a (2Hz, 50% duty cycle?) pulsed output, and confirm whether or not the input memory bit is following that output pulse.

Is that correct? Assuming yes, are there any other inputs, outputs, or other behavior? E.g.

• When to start, or restart state 1 above perhaps with reset button?
• How, in state 2 above, to indicate whether or not the input is following the pulsed output?
• If the input is not, or stops, follow the pulsed output for a time, but then does start following again, should the failure indication be reset?

Are you looking for suggestions or actual code? Is this a homework assignment for school?

 

[JDowell]

HI, That method makes total sense, I dont know why I didnt think about putting a 3s delay on the input to see if it is a solid signal or not....
In terms of determining which output is occurring I was intending to simply use a status message on the PLC .
And suggestions are all I needed, was just drawing a blank as I am very new to PLC programming.