Hello everyone,

I'm currently facing a profibus dp problem for some time already and I can't find a solution.

My profibus network has about 50 nodes spread across about 400m of cable, it has 7 repeaters, 2 dp/dp couplers, 2 olm, 100m of fiber optic cable, parker drives, along with other non-siemens components. My CPU is a S7-400

The problem is that my machine stop usually 1-2 times a day due to communication errors, all failures come from nodes in a segment after one repeater, but the failing node is random. Even when the machine does not stop, I monitor it with profitrace and I get illegals and repeats on random nodes (all in the same segment)

What I already did:

- Check all the terminations switches

- Replaced the repeater right before the segment

- Replaced some segments of cable

My questions:

- How can I track the signal to find faulty cables with the osciloscope in a network with repeaters

- What tests can I do to possibly find the failure

- How can I test if any device is messing with the network, for example drives

Help me please!

Hello,
The symptoms you are listing (illegal frames, repeats, random nature) seems to indicate EMC problems (perturbations) on that specific segment.
I would check how well the mounting rules of the cabling are complied with, especially the way the shielding is appropriately grounded at the entrance of each cabinet, the grounding of the cabinets and interconnection of cabinets with equipotentials, etc ...
Drives themselves can be source of perturbations if their housing of filters are badly grounded, or if the bus cables run near the power cables.

Good grounding is always a question of large contact surfaces (low impedance contact).

Regarding diagnostics, OB86 is called each time a slave is missing and when it comes back.
You can use the header information of OB86 by program to find out what slave was missing.
You have also the diagnostic buffer as help, giving the same type of information.

Eventually you can use SFC51 to read a status list like described in this FAQ

Hope it helps