PLC coding to monitor digital status changing

[unsaint32]

I have this water meter that sends pulse signals to a 1769-IQ card (high speed DI card). When I turn on an output to open the water valve, I need to make sure the meter pulse signal changes at least once every second. If the pulse signal status does not change within a second (due to control voltage loss or meter malfunction), I need to shut the water valve. The pulse signal could be either 1 or 0 when the meter stops pulsing. I know I need to use a timer DN bit to trigger an alarm that shuts off the valve. Any suggestions?

 

[unsaint32]

I think I got it. I will create two timers, one for when the meter pulse is 1, the other for when the meter pulse is 0. XIC DN bits in parallel means the pulse status not changing. Thanks.

 

[Mickey]

Use the pulse from the meter to reset the timer, if no pulse the timer times out and you get your alarm.

 

[unsaint32]

Use the pulse from the meter to reset the timer, if no pulse the timer times out and you get your alarm.

That was my initial approach but the problem with that is that the pulse state can be at 1 when it stops pulsing, in which case the status not changing but the timer never times.