Diagnosing Profibus with a scope.

[TurpoUrpo]

Nice 1st post bumb of 5,5 year old thread.

This is not what you should do as 1st post.

 

[JesperMP]

I think he forgot to attach a picture of the scope curve that he refers to.

 

[TurpoUrpo]

I think he forgot to attach a picture of the scope curve that he refers to.

No, those are in previous post. From 2007...

ps. fluke has premade set on its scope for many fieldbuses: http://www.youtube.com/watch?v=3vofpO027pY

 

[JesperMP]

The way he phrased the following:

What to you think from this signal then?

I think "this" refers to a picture that he forgot to attach.

 

[TurpoUrpo]

The way he phrased the following:
I think "this" refers to a picture that he forgot to attach.

For me it seems he refers to those signals. Maybe he comes for his second post.. to clarify.

 

[RheinhardtP]

JesperMP did you ever end up using a scope for your profibus signal analysis?

 

[JesperMP]

JesperMP did you ever end up using a scope for your profibus signal analysis?

No.
We once had serious problems on a project. And we couldnt resolve it by doing a passive check of things (connectors, cabling, shielding, grounding). To be dead sure we found the problem we rented a Profitrace tester. Using this we found out that it was the entire plant ground that was floating.
I think we could have determined this with a scope. It was the shape of the curves that indicated the earthing problems.
I still have the scope method in the back of my head if I shall ever encounter a profibus problem somewhere in the middle of nowhere.

 

[drbig]

Profibus Reflections

Recently we had issues on profibus communications failures. I highly suspect it is a reflections related. One thing about reflection on profibus is very hard to diagnose as it tell incorrect fault location. We changed many parts along the networks but it does not solve the issues. We finally change the end resistor and it solved everything!

 

[grnick50]

We mainly use two tools to troubleshoot Profibus networks:
1. Fluke 125s oscilloscope
2. Procentec's profitrace analyses.

With these tools we be never been defeated. Especially with the second tool.
You could use a simple scope but the issue would be the trigger of the scope.
All you would see would be square pulses moving around the screen.
What makes profitrace special is that it's DSO can trigger on the messages, so that you can see the quality of the pulses for each slave.
The scope is only one from a series of features it has.

The Fluke 125s is not a protocol analyzer but a bus health monitor. It knows the characteristics that a Profibus pulse should have and it will tell you if that is within the nominal ranges.
The greate thing about the 125s is that you can use it for Profibus, mod bus, Canopen, device net, RS485. You can even setup a custom protocol if you know it's properties. The 125s can also operate as a sumple 40Mhz scope, as a harmonics analyzer and as attend recorder.

I highly recommend both tools.

Regards Nik