problem with Siemens interrupt card


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The CPU is Siemens s7- 416 2DP Siemens code 6es7 416-2xk01-0ab0), the card is DI16xDC 24V alarm (siemens code 6es7 421-7bh00-0ab0). The input card reads 2 syncro signal from one electrocam and one proxy signal.
The problem occurs very rarely (2 times in 3 months): the input card stop the reading without any error message.
I verify that in this condition the input card don't read also one 24V fixed.
The big problem is that I don't receive any error message.
The problem never occurs with the same card and the new cpu 416-2xk02...
My conclusion is that the problem is linked to CPU version and in the old plant I added one watchdog function monitoring a 24v signal. I'm waiting considerations and experience about the same card.

ing. Ivan Messori
BMA Engineering