S7 300 series PLC losinf program on conection of MPI connector.

Has anyone else experienced a problem of an S7 300 series PLC both stopping and losing its entire config. when an MPI cable is connected.
It happened to me twice recently, fortunately no serious damage was incurred as a result of the PLC crashes.
While on the first occurrence, I concluded a static discharge was probably the cause, the second occurrence with intense precautions suggests this was NOT the cause.
At this point, the only thing I can come up with is that the initial current draw of the adapter caused the PLC to crash.
Has anyone else experienced a similar event?
TIA, Tom
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stopping
incurred
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Unfortunately, yes. The MPI port on the older S7-300 CPU range seems to be particularly sensitive to static discharge, surge, or even a difference in earth potential between the PLC and the other end of the cable - and the end result is (usually) a dead adapter.
On one installation of ours, after a power surge the PLC was fine, but as soon as an adapter was plugged in, the PLC fried it - irreparably. We had to replace the CPU and two adapters (one of them on loan from Siemens ;-) to get back to normal.
My advice: *Never* leave anything permanently connected to the PLC MPI port. By all means, plug in and do what you need to, but always unplug at the end of the day.
Cameron:-)
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On Tue, 01 Mar 2005 17:08:34 GMT

Our 315 and 318 cpu's will sometimes crash when connecting to the mpi ports. However, we have never lost the configuration.
To avoid problems, we leave the adapters plugged into the ports and plug the cable in and out when necessary. Although I can't promise that it won't, I have not seen it fail that way.
It's a good way to sell adapters, but it doesn't do much for selling plc's.
Chris
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Thanks for the responses guys,
Much appreciated, Tom

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It's not that bad.. AIUI, Siemen's newer CPUs (ie. the ones you can buy now) are a bit more robust than the older ones from a couple of years back.
There are a few PLC brands out there that have a reputation for crashing on error - mostly European ones (Siemens, Telemechanique) and older US ones (Square-D).
If you know about it, you work around it - and not use them on Crusher plants or pharmaceuticals - it's when you *don't* know that you have a problem ;-)
Cameron:-)
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This has been my experience as well. I've never had an AB controller crash (watch the math overflows on Micros and deal with it in the ladder).
Interesting experience, though. AB SLC 5/05 that lost its config after a very minor power interruption... less that 700 ms. The bat was good in it so I called AB and asked about this.
They told me I'd better use a better power supply on that puppy or it might happen again. Seems AB firmware will see a 'flicker' that short as processor problem and clear the config as a safety measure to insure that all real-world outputs drop off. We've designed around that ever since, as well as making sure to use better 480 x 120 power supplies.
I'm still trying to decide if AB's approach is the right idea or not in the event of a major processor hardware fault.
Jake

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