Profibus techenical problem

Our automation system is based on siemens PCS7 v 5.2, and in one station we have connected 27 variable frequency drivers (Ekels type) on the profibus to S7-400.
The problem is that every time we lost the last driver (27) that connected to the cooler, and we check the terminator resistor, then we connected a new external terminator resistor, and we changed different profibus speeds, and finally we replace the VFD but all were not sucessful.
Can any body provide some guide lines or any ideas to help for solving this problem

Thank you in advance for you help

My email address is [email protected]

Elkawafi

So by station you mean you have 1 Master (S7-400) with 27 VFD's as slaves? Are you sure there isnt an address conflict? The VFD is configured as slave? Profibus is token ring topology, you are connecting direct to the bus, not jumping from slave to slave? The terminators are just on the end devices in the segment? Could distance be an issue, its RS485 in most cases which limits to 4000 feet unless a repeater is used.

At 1.5 MB ,I think that the maximum segment length is 100M - he should run the bus from slave to slave , and not spur off (though you can get away with it sometimes)- I'm not sure I get the true meaning of token ring - profibus should be a straight line of segments , the master can be located anywhere - so long as the ends of the network are terminated as you correctly say - NOT the end at the processor UNLESS it is at the end .It is worth checking the cabling very carefully - the network might work perfectly well with swapped A and B's , but adding the last segment can cause the network to fall over - check all cables to make sure that you don't have any swapped pairs . If the network is running in a noisy location , you can earth each segment as it enters each panel ( according to spec this should be done anyway) . I have had the same problem - what was supposed to be 30M between devices because of greed ended up being over 200M . I set the group up with no EMR in the factory , and as more equipment was added , the network started to fall over - we had what should have been on paper as around 220M worth of cable , it turned out that there was getting on for 1000M . Only pinging the network through with a BT200 revealed the true length - at the end of the day the only thing to do was slow the network down .

Fred Floggle said:

I'm not sure I get the true meaning of token ring

Click to expand...

see http://www.dia.uniroma3.it/autom/Reti_e_Sistemi_Automazione/PDF/Profibus_lucidi.pdf

The higher the transmission rate the shorter the bus length. I believe for 1.5M it is 200 meters and 93.75kbits/s or below its 1200 meters, I wasnt thinking about the high speed but bus length can have a bearing.

Token means that comm is passed from master to master for a specific time period, may not have much bearing on this situation overall.

What you call a spur I think is what I was talking about Where I show Slave to Slave I dont think should be done with slaves but I think you can "spur" with a Master...not positive tho.