Hi all,

I have one S7-1500 PLC connected to a Profibus device through a couple of Siemens OLM G12 V4.0. PLC and one of the OLMs are in one cabinet and the ofther OLM and device in another. I have used this architecture in many installations and I have never had any problem, but in this one the PLC keeps loosing connection with the device (it is around 50-100 ms disconnections). 

I have tried reducing Profibus speed, but problem does not dissapear. 

Would like to know if anybody has any idea what could be the originin or these short disconnections (electrical noise? ...).

Thanks in advance

dchartier

Hello;

Problems can arise on optical networks from many sources: the fiber optic cable, the RS 485 Profibus connetor, the setup of the terminators, and other sources.

Whenever we had to work out the kinks in our optical networks, we always started with the basic network troubleshooting steps, especialy examining the contents of te Diagnostic Buffer of the CPU.  If the messages from the diagnostic buffer messages did not give a decent result, we would then follow the Torubleshooting guide from this manual:

https://support.industry.siemens.com/cs/ca/en/view/109476821

I have attached the troubleshooting section of the manual as a separate attachment. Tell us if  it provides adequate guidance.

Hope this helps,

Daniel Chartier

 Hi Daniel,

Thanks you so much for your answer. The thing is that device failure error is so short (around 50-100 ms) and sporadic, so it is hard to see the led behaviour when this happens. Yesterday we checked all connectors and we measured the signal quality (we got 4.3 V so the signal strength is so good). At this point the only thing we can test is reducing the power transmission using S5 dip switch, but I do not really think this is the problem as this architecture have been used many times without having this problem.

If somebody has any idea about where could be the error I would be so grateful.

Best regards

Duris_I

Hello,

you did measuring probably till OLMs on PB network. I think that Daniel already gave same idea as I have - problem on optical network. This is very important part of network and stability with absolutelly correct Optical ines preparation. You need unplug all parts of PB network and check only Optical lines with diagnostic system/HW for that Optical parts. I have experience especially with mouse and rats at some places with no good cover systems to have safe optics placed. If you have some spare OLMs, do systematically some replace of them with time tests.

 Hi Ivan,

Thanks for your feedback. I think if the problem were in the optical line I should get some low voltage measuring OLM quality signal,  shouldn´t I? Last option for me it is to replace OLMs and see if the problem is because any failure of them.

Best regards.

Duris_I

Hi,

maybe but my intention could be check typical different parts, unlugged to measure as own parts, for sure. From your log is strange the last minutes where cca 8min it was all ok, looks like, if I compare that with previous events that occured generally every minute. This could be also some situation that need some importent look at. If I could say also, it is also important how you did that measuring of Voltage, if it recognize also some short abnormalities in Voltage drop quickly, hope you understand this. I don't expect some multimeters here quite helpful.

Hi,

We measured the voltage using a multi meter, maybe it would be better to use a oscilloscope to check this. It is kind annoying as, for example, one day PLC can have just 1 disconnection and other a lot..

Thanks you all.

Best regards.

Hi all,

Any other suggestions? we still have same problem and we did not find the origin..

Thanks!

AutoGen_4612448

Hi all,

Any other suggestions? we still have same problem and we did not find the origin..

Thanks!

 Actually, I am thinking about changing OLM from G11 version to G11-1300 version which has more optical range (even I am getting maximun signal quality). Do you think this will solve the problem?

Best regards