Profibus bad signal analyse, help.

hello,
i have captured a bad signal from profibus DP.
Does anyone know what for problem i can have that causes this problem.

I am not experienced enough to be able to say wha can cause these wild disturbances.

Try to capture measurements between A-gnd, and B-gnd, in addition to A-B.

Also, if you can, try to disconnect sections of the bus, to see if the problem improves or disappears.

A dedicated Profibus tester can tell you at which node the problem occurs.

That signal look normal only for the first 18 micro seconds. After that there is a lot of noise induced on the line. The noise from 18 micro seconds to 42 micro seconds is very severe as if you have run the Profibus cable next to a drive or some other PWM source.

The gap between noise events at 40uS and 70uS might point to a 30kHz noise source...unless I am off by a few powers of 10.

-John

This looks like a handyscope screenshot. Could u post the waveform files from the scope here so I can have a closer look to the signals?
Can you also give us a short description of your network is built?
- Number of devices
- Cable distances
- Repeaters used

RE: files for handyscope

we have 7 devices total lengt of 60-meter
and none Repeaters.

i think we have a short in the A-B line.

Sorry that I did not respond earlier but somehow I didn’t see this thread being updated.
The scope images don’t show me a typical signal you get with a short between the A and B line but everything is possible (I can't see one good thing on that image ). You could measure this with an ohm-meter if the network can be disconnected.
I can’t see the second channel on the data you posted. How did you connect the scope? The best way is to connect the first channel to the A line and the second channel to the B line. Connect both grounds to the shielding. Then you show A-B (or was it B-A?) on your scope. The separate signals of the A and B line could be handy to see grounding and capacitive problems. Also connect your scope at an end of the network.
Are all your 7 devices connected in a straight line without spur lines? Also check the termination resistors which should be on at both ends of your network. The idle voltage on your image is an indication that this is not the case, but it could also be caused by the way you connected the scope.