Siemens ET200

From what you are asking (and describing) it sounds like your earthing system is correct (PLC logic being brought back to a central earthing point preventing ground loops, voltage potential rise issues, etc).

Hi there,

Firstly - is it the ET200S or ET200M range? S - is used in substations, while M is used mainly in the plant area.

You have to be very carefull with your earthing of the profibus and the earthing of the actual IM module.

If you RTFM (Read The F#cking Manual) for the ET200 range of cards - you will see that there are two methods for earthing.

What you need to make sure of in either case is that all the ET200 stations share the same earth point i.e. Each M connector must go to the same earth point. You should also make sure that you use the correct Profibus connector as well as the correct Profibus cable (it is usually a purple colour). You also need to make sure that the screen of the bus cable is continous, i.e. the screen must run through all the stations.

You are losing the whole bus - because of you have a floating earth and your screens are not continous. You will have to go and make sure each IM is on the same earth point as well as the screen continous.

Please feel free to download the Profibus standards (for free) from the Profibus web site (there is also a very good user guide that will explain with pictures all of the above) as well as the ET200 manual from the Siemens website (again for free).

If you follow the guidelines - you will have no more problems. The same will aplly to the majority of bus systems.

Regards,

Craig