Profibus questions

A

Thread Starter

arocon

I have novice questions about profibus on Siemens Simatic S7 PLC. Could anyone reply me explain me it will be great help.

1) Where termination resistance to be on - at the end or at the beginning or both end. How about if in between there is repeater?

2) On PLC if there is only one profibus connection then where the connection will be ? At the top or bottom?

3) Are incoming and outgoing connection in a node interchangeable or we need to follow like incoming on the left and outgoing on the right?
 
>1) Where termination resistance to be on - at the end or at the beginning or both end. How about if in between there is repeater?<

I always put the PLC at the start of the profibus segment, thus making the termination at the other end only.

The termination is needed on the end of EACH SEGMENT.

If you have PLC -> Nodes -> Repeater -> Nodes then it would be classed as two segments, I would have a termination point on the PLC segment and another on the Repeater Segment.

>2) On PLC if there is only one profibus connection then where the connection will be ? At the top or bottom?<

I don't quite follow your question. The S7 ranges will be MPI/Profibus ports on the top (first) port and Profibus on the second (bottom) if a second is fitted. The first port is switchable by configuration.

>3) Are incoming and outgoing connection in a node interchangeable or we need to follow like incoming on the left and outgoing on the right?<

No. The IN and OUT connections on a node, or plug, are not interchangable. If you do then your mileage may vary but certainly diagnosing problems will be more difficult.
Some nodes may be more tolerant of the error depending on the internals but if it's the last node and has an internal termination resistor, it will not work.

Be very careful about the physical configuration and installation of Profibus because this is where 90% of problems occur.

Good Luck
Patrick
 
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