OB86 and checking if fault is solved

Hi,

lets say that wehave one S7-1500 and one ET200S connected through profibus. I remove profibus connection from ET and detect a problem using OB86. At this point I would display some alarm to HMI. Normally, we should be able to reset any fault after the problem has been solved.

If a request is sent to reset all alarms, do I use some function like DeviceStates to check if everything is OK at that point, or there is some better way?

I now that there is an incoming / outgoing event is OB86, which could be considered as problem occurred / problem solved pair. This becomes more complicated when there are multiple problems and multiple incoming . outgoing messages, so you need to match one with another.

How do you handle such scenarios?

You can use the OB86 to set a bit with the fault that is happening, but you should never rely on OB86 to reset the bit. I had a machine programmed in this way and the bit that was set was non-volatile too.

So we had an error on a profibus node (a joystick), we though it would be broken as considering as it was a small system we would power down the machine replace the joystick and power it back up.

Guess what? problem solved while the machine was down, so OB86 never ran to reset the fault bit. We had to pull the profibus cable and put if back again to clear the fault.

On other systems we had a function made that would actually map out the profibus network and write a bit if the node was found. This was done with SFC51. We could then take the bit address as an alarm.
If you want, you can check for the presence of only the nodes that actually exist and take it from there.