What is the different between foundation fieldbus and Profibus?

  • Both Profibus(PA) and FF H1 started off in the same working group and have much in common: the physical medium on which both operates is in accordance to IEC 1152-2 intrinsically saftey. Profibus DP which is used in 90% of profibus applications use either RS-485 or an Optical fibre link.

 

  • When comparing their implementation on the data layer in Profibus the input and output blocks are located in the controller itself. The controller(master) fetches the data from the field instruments. However no control blocks are moved into instruments. In FF, the input blocks along with the control block are moved into instruments consequently implementing ‘control in the field’.

 

  • The number of devices per segment/loop also varies in Profibus VS FF H1, with the later having a max of 127 and being limited to 32 due to bottleneck of RS-485 and FF to 31 itself. But practically FF system recommends no more than 12 devices per loop with a cycle time of 0.5s while profibus supports 24 with a delay of 400ms.

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