S7 CPU315DP Profibus fault

LiamC · Nov 21, 2009

I have been using S7 and Profibus for last 10 years, and have only recently learnt that if the bus fault LED is off, the network can still have a lot of errors. Does anyone out there know what percentage of errors cause the bus LED to switch on ?

manmeetvirdi · Nov 21, 2009

Hi LiamC
Just for curiosity sake can you specifically tell what kind of network error can be there with bus fault LED off?

doyletuttle · Nov 21, 2009

I recently had a profibus cable issue. When one of my stations would make a horizontal move the machine would shut down. I watched the cpu and never did I see the LED fault light come on, but when I went online to the CPU diagnostic and looked at the buffer it would show up and that was the only way that I found it.

STL??? · Nov 21, 2009

What OB's are loaded in the plc?

LiamC · Nov 23, 2009

Ob35,40,61,81,82,85,86,100,101,102,121,122.

LiamC · Nov 23, 2009

manmeetvirdi said:
Hi LiamC
Just for curiosity sake can you specifically tell what kind of network error can be there with bus fault LED off?

As i understand it (i'm still reading up on this), we are dealing with intermittent errors, that profibus is built to handle. So failed transmissions due to say bad cabling may be one reason. Because profibus will retry the transmission it may then succeed, so we never see the bus fault LED come on. A good profibus analyzer will diagnose this sort of problem, (i am now going to aquire one).

TurpoUrpo · Nov 23, 2009

Ob82,86,100,122

These are:

OB82 : Profibus DPV1 diagnstic errors call this ob. Example, if ASi gateway connected trough Profibus to S7 detecs error, in its submodules or in itself, it send diagnostic data and ob82 is called. That data can be processed in that OB.

OB86 : called if Station fails. Example: Same ASi gateway looses connection trough profibus to cpu, then OB86 is called with data on error, eg address that belongs to dropped slave and if its incoming or outcoming error.

OB100 : Executed at startup.

OB122 : Programming error.

Longhorn · Nov 23, 2009

LiamC said:
Because profibus will retry the transmission it may then succeed, so we never see the bus fault LED come on. A good profibus analyzer will diagnose this sort of problem, (i am now going to aquire one).

We use Profitrace analyser to troubleshoot our Profibus loops, as for the errors, the number of retries and syncs can be configured via HW configuration in S7. I would highly recommend profitrace though:

http://www.procentec.com/profitrace2/index.php

JesperMP · Nov 23, 2009

I have been using S7 and Profibus for last 10 years, and have only recently learnt that if the bus fault LED is off, the network can still have a lot of errors.

Because profibus will retry the transmission it may then succeed, so we never see the bus fault LED come on.

Profibus may tolerate the occasional error, but not a lot of errors as you put it. The deafult number of retries before the Profibus faults is 1 (one).
I read your thread as that you do not have an actual problem, you are merely thinking about what if.
If you have a big installation, where the Profibus installation is regularly modified, then I think it is a very good idea to get an analyser. But for the smaller installation it is overkill.

S7 CPU315DP Profibus fault

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