Diagnosing Profibus with a scope.

Hi.

I have seen some instructions for diagnosing DH+ with a scope.
And I have heard that it should also be possible with Profibus.
Does anyone know instructions how to exactly accomplish this ?

Thanks.

PS. Tried google but it didnt lead me to anything useful.

Hello Jesper;
Great question. I have seen that there is a section in the Profibus Certified Engineer training that covers this technique, and have often wondered if anyone could volunteer the information...

Here is one document I have downloaded that shows examples of oscilloscope tracings for diagnostics, but on Profibus-PA networks:

Another document from Manchester Metropolitain University suggests this manual for training of Profibus maintenance engineers with oscilloscopes:
[16] PROFIBUS Commissioning and Maintenance Course leaflet; Manchester Metropolitan University



Another document,
Quality of Profibus Installations Max Felser
Berne University of Applied Sciences

shows the following trace with reflections on a Profibus-DP line:

and suggests the following manual:

[5] PROFIBUS Installation Recommendation for

Commissioning, Version 1.0.0, PROFIBUS
​

International, Nov 2005, Order No: 8.032


But this is as far as i got.

Of course there are alternatives, Siemens BT200, Siemens Amprolyser, the Procentec Profitrace...

Hope this helps,
Daniel Chartier

Hello,

What is it that you exactly want. You could put the signal on a scope and you should see some kind of blocwave. Normaly in ideaal circumstances this should be a perfect bloc. But in pratisch it's a bloc with small spikes in front of the Block and the edges are a litlle bit curved. The normal dc level is at 6V. 5V is acceptable but on the low side. I'll try to send some grafhs with this reply

Rudi

gonna throw my dumb arse thoughts in here.

How do you use a scope to check a protocol?

and mine!

How do you use a scope to check a protocol?

Click to expand...

While theoretically possible, that certainly wouldn't be very easy.

What you can do with a scope is check the physical/electrical state of the bus. The graphs that Fritz-Frederic provided show this very nicely.

I used to do something fairly similar checking the busses on the older ABB/Kent K90s ten or 20 years ago (there are still half a dozen of these still running, that I know of). They used a Tri-State switch to multiplex signals onto the buss (8T01, if my memory serves me well) and it turned out that they deteriorated over the years. After a while I could tell at a glance when trouble was looming and take action before the failure occurred.

As far as I'm concerned, Jesper, the answer is "yes", you can do it, but it takes a fair amount of time and experience to get used to knowing what you're looking for. Given the fact that manufacturing quality has improved significantly over te past years, the biggest problem may simply be getting enough exposure to deteriorating or faulty networks, to build up the necessary background of experience.

The new Fluke scopes have bus testing functionality built into them
http://www.fluke.fr/comx/pubs.aspx?locale=uken&mag=testit&issue=282&page=1&template=testit-t1

expensive though!

rsdoran said:

How do you use a scope to check a protocol?

Click to expand...

It is not the protocol itself that is checked. It is electrical qualities such as cable quality, connection quality, noise, refections. Other problems I can find with the diagnostics tools built into STEP7.

The background is that I dont have an analyser. It is not the cost it is more that my toolbox is more than full already.
Until now I have not encountered any problems that I couldnt figure out myself, but I fear that sometime I will run into a tricky problem in the middle of nowhere.
An oscilloscope can often be found locally, so that is why I think that I could use that for last-resort troubleshooting.

It could be nice if there are some samples with "good" waves, and various kinds of "bad" waves - with explanation of the cause.

edit:
Daniel, nice document, but can the recommendations be used for DP ? Maybe there is some guide for RS485 in general.

Hi all my 1st reply.

I sat the certified profibus installers course and would fully recommend it.

You need software like profitrace and & proficore device. A handy scope that is dual channel and has an external trigger. Connect them onto the profibus network and start fault finding.
You can then see:
Reflections, reflection measurement, noise pickup, measure cable problems, telegrams, class messages, extended diag etc etc.

Great course and great kit. Purchased it afterwards and we now do regular health checks on our profibus systems.

Rob

It sounds like you are talking about a dedicated analyser.
What I am after is more a "poor mans profibus testing method with an ordinary oscilloscope".

Hi,

The problem is then how do you detect what device is causing a problem with just a scope? You can see the wrong levels but thats not a reel help.

Thats why you need the external trigger to be set by *** "profitrace software for us" so you capture specific device data / errors / telegrams for and individual profibus device.

Rob

The info from a scope can help me even if it doesnt point to the exact location of the error.
I know it is possible to diagnose something if not everything with a scope. This because I have seen other posters claim that they can do it.

I have used a scope to read DeviceNet packets but only as an attempt to understand how the system works. It is of no value at all as a diagnostic tool as infinitely simpler methods are readily available. The NetAlert DeviceNet Meter from Woodhead is invaluable for working with this system. I am not sure whether they produce a Profibus variant.

Andybr

Examples

To make a good diagnose on a PROFIBUS network you will need two things.

A protocol analyser will give you the general state of the network. It will detect things like wrong GSD files, configuration errors, timing problems, illegal messages, retries and much more. When it shows that there many retries and/or illegal messages, this could indicate that there is an electrical or timing problem.

The oscilloscope will show you the condition of the electrical signal. It can be used to show problems with termination resistors, bad cables, EMC interference, too much cable, long stub lines, ….

JesperMP said:

It could be nice if there are some samples with "good" waves, and various kinds of "bad" waves - with explanation of the cause.

Click to expand...

Check the atached files for some examples

Re: Examples

What to you think from this signal then?
Compared to the previous examples it looks pretty bad, what could be the cause?

The end resisitors are fine.
Baud rate = 1,5M; string length = around 100m.

Jobbe said:

To make a good diagnose on a PROFIBUS network you will need two things.

A protocol analyser will give you the general state of the network. It will detect things like wrong GSD files, configuration errors, timing problems, illegal messages, retries and much more. When it shows that there many retries and/or illegal messages, this could indicate that there is an electrical or timing problem.

The oscilloscope will show you the condition of the electrical signal. It can be used to show problems with termination resistors, bad cables, EMC interference, too much cable, long stub lines, ….




Check the atached files for some examples

Click to expand...