Comms Heartbeat Method Question

[MikeVT]

Good Morning!


I need to monitor ethernet comms, between 2 Compact Logix PLC's. I have done this before with a simple pair of timers, toggling a bit (on the sending side) and a timer monitoring a bit on the receiving side.



However, This is the 'spec' I'm dealing with, from an equipment vendor, regarding a DINT being monitored as a comms watchdog.



"[FONT=&quot]This value must continuously increment by 1 at every CPU cycle. When reach the Data Type max value, restart from 0. If the increment stops means that there is a PLC or a communication error."
[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]I have not used, or seen an example of the logic needed to monitor comms this way. I am asking for some examples of ladder logic, to accomplish this, please.[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]Thank you!
[/FONT]

 

[Rob...]

Quite simple really.

I use this standard often.

 

[Jlandwerlen]

If you are using produced/consumed this is very easy with connection status. However, to do it like they spec, create a buffer tag, call it something like LastValue. Each scan compare the current value and the last value, if they are equal for a period of time you have lost comms. You will need to move the current value into the last value after the timer.

Hopefully my explanation makes sense. I don't have software right now to play with.

 

[Scottryan03]

I would do something like this

 

[Jlandwerlen]

I would do something like this

What you wrote will not work, the move needs to be done after the timer, otherwise they will always be equal.

 

[Scottryan03]

What you wrote will not work, the move needs to be done after the timer, otherwise they will always be equal.

Yes you are correct. Timer prior to mov

 

[Engineerj22]

I would do something like this

That is the most unique color scheme I've seen!

 

[Scottryan03]

That is the most unique color scheme I've seen!

LOL, thanks! Easier on the eyes for me. I enjoy the rung color change when highlighted.