we have on our place a S7-400 rack and in this rack one FM450-1 counter that a encoder connect to it via a barrier.lately we saw a external fault on the counter and we check all the things according to the FM450 manual include encoder,barrier,wiring between those, and even change the counter but still we have external fault.are there something special that we have not seen that?

if somebody knows please HELP us.

tanx