s7-300 dp problem

Hi, I have a problem with a system with a 315-2DP from siemens and several ET200 modules spread al over the machine. With an interval of some days we get a system faillure at the CPU. When I look at the diagnostic buffer there are three ET200 modules that went into faillure. We can reset immediately so the problem occurs not very long. The three modules are in the same cabinet and are the last three in de Profibus chain. First I thougt of a faillure of the profibuscable or connectors but sometimes we get a normal stop of the machine while running: there is also a stopbutton connected on one of these three modules, so al the problems seem to arise in the same place. The connections/contact al seem alright. Is it possible that this could happen through a voltage drop/spike on the 24VDC ? Another thing to mension: there are a lot of vibrations in the area...
Any hints would be apreciated.

You can do two things:

1: Add the appropriate error-OB that will avoid the CPU from faulting.
Dont remember exactly which one (OB83, OB86 ?), I am writing this from an airport lounge and dont have STEP7 right now.

2: Tweak the Profibus setup to allow more "retries" when there is a problem on the bus. This may be a bit complicated, but it requires you to use a "user-specified" bus profile in stead of "DP" or "Standard". The bus profile is set in the HW config under the properties of the Profibus network.
Default is 1 retry. Try with 3 for example.

Of course, the problem may be hardware related with the vibrations. You may have to change the hardware to counter the vibrations.

try decreasing bus speed if it's possible just to see if fault pops up again , how long is your profibus segment?

Catalin,In case you mean distance: I say aprox. 50 meters of profibus cables. There are 28 ET200 modules and two 315 cpu's (the communication between the two CPU's is almost nothing, the 28 modules are used with one cpu)Jesper, maybe switching two modules to see if the problem occurs elsewhere would be a good idea? I will try this tomorrow. Thanks.