Loss of PROFIBUS Communication

Is one of the small wires touching another on the connector of the profibus or is one of the wires held to the connector with one strand.

Solid strand of cable.

Hi there,

I have had a similar problem to this before.

You should check that your screens on the PB cable are continuous and that they are all on the same earthing point. It could be that your older hub earthing point is different to that of the FC. This would cause huge interferences with the communications.

If you are lucky enough to have a decent oscilloscope then download the Profibus installation guides from www.profibus.com/downloads They have a fault finding section that will explain to you what the trace that you will see on the scope means. They will also give you a good few guidelines about the installation that might reveal your problem.

All in all - good luck and please keep us posted?

Regards,

Craig

Have looked at the earthing. This appears to be ok. The FC is mounted next to 5 others but they are on a different loop. I dont think there will be a quick fix to this problem.

Have you been able to look at the signal levels? FC are 'noisy' devices so there may be a possibility that this is coupled to the PB lines at this point swamping the signal. The fact it works with no other connections and less cable may reinforce this idea. Does this happen when FC is not running too (just SMPSnoise then) and can you power the control and no main power to test. If so, use a lower control voltage which would also reduce noise levels. What has the FC supplier suggested? If nothing else, I would try connecting a small filter capacitor (0.1μF) from the FC Ov connections (there may be two, analogue and digital) to ground which may help.