Fieldbus Failure in S7 300 PLC

hi everybody im facing a unusual problem in s7 300 plc . when im using 1.5 mbps as baud rate in profibus network all the drives connected in the network shows healthy till i have not given the start command . But as soon i give it a start command the drive shows the fault of Fieldbus failure. and it happens everytime. But thats not the case with 187.5 kbps,its working fine with this baud rate.

i have checked the earthing of all drives & cpu network.

So please give any reason for this problem or any solutions??????

Problems I have faced in the past relate to either poor earthing or distance. You could try remaking off the ends of the cable. There is obviously some attenuation in the cable somewhere that you are getting away with at 187.5 but is causing problems at 1.5Mb...

Obviously, it is related to the noise that the drives generate.
You provide very little detail about your network.
Also, how long are the cables from the drives to the motors, are you using screened cables, etc. etc.

@deepak

You should download this document and read it carefully.

Kalle