Profibus network drops

Hi Guys,

Please remind me of something rather trivial, we have a profibus network that behaves itself well, except when we cycle power on one device, the entire network drop out.

I read some posts, and someone mentioned that if the devices are powered from different sources, and one slave drops, the entire network will fault due to a missing slave.

This confuses me a bit, my thinking is that the same would apply if you just pulled the profibus plug out, but that does not drop the network. also, this dropping of the network when we cycle power, only occurs on certain devices, not all devices. and all devices are powered from different sources.

sometimes we loose the network when we power on the devices after it has been off. and at times we loose the network when we power off the device.

can anyone share any ideas?

Is the station(s) that cause the problems, in the extreme ends of the physical daisy-chain ? If that is the case, you may need to make the ends socalled active terminators.

Is the profibus network properly configured, with ALL stations included in the network taken into account for the calculation of the token rotation time ? A faulty configuration may only reveal itself in the abnormal situations, such as removal or attaching stations.

I am not a profibus guru, bit manually increasing "retries" from 1 to 2 or 3 can make it less sensitive overall.

Different power sources should not be so important, but a common good ground is VERY important.
If the cablings is very long, then also consider to tie the screens on a ground busbar, rather than only in the connectors.

Profibus drop out

Check to see if the base that causes the problem is the last base in the network. If it is this is your problem. The profibus network ends need to be powered all the time. If you switch the power off to the last base on the network, you will drop out the rest of the bases.

Siemens do a small low cost device that is basically a powered end that would allow the power to be removed from the last base. Other than that I don't see why removing power or disconnecting a base would cause any problems.

Bryce

the devices that cause the trips are closer to the end. but we do have active terminators. i am not keen on changing the power supplies to a single power supply, as this would involve some serious cabling changes in the MCC. will attempt changing the retries though.