Are FOUNDATION fieldbus and PROFIBUS PA the same thing?

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Are FOUNDATION fieldbus and PROFIBUS PA the same thing? is the title of an excellent blog post on the Pepperl+Fuchs USA Blog.  In fact, I liked the title so well I “borrowed” it to title this post.

The short answer to the question is “no.”  But there are some nuances.

PROFIBUS PA and Foundation Fieldbus use the exact same physical layer, Manchester-encoded, bus-powered.  This infrastructure moves telegrams of up to 244 bytes at 31.25 Kbits/sec.  But the application layers are different so they cannot talk to each other.

PROFIBUS PA is designed to complement PROFIBUS DP; in fact, they use the same protocol (on different physical layers).  This is an advantage when you have some process devices and some discrete devices because you can do both with one protocol, one set of tools, and one knowledge base.  If higher speeds are needed (especially if bus power is not needed), some process devices use PROFIBUS DP.

Foundation Fieldbus’ claim to fame is control in the field.  If you need to implement control loops outside of the controller, use FF; PROFIBUS doesn’t do this.  If you have some process and some discrete devices, use PROFIBUS; FF doesn’t do this.

The one point not to lose track of in all this is: “Use a fieldbus!”

Or as Jim Simmons from DuPont said at the PI North America General Assembly Meeting 2012: “Any new control system installation should have to justify NOT using fieldbus technologies.”

–Carl Henning

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