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Blog
Which Profibus for instrumentation?
January 2, 2008
This morning our Process & Advanced Control newsletter went out, and there's an article in that newsletter about the company that won the HART Plant of the Year Award. The full article is in the December issue of Control Engineering, but the newsletter article is based on a press release sent out by Emerson Process Management noting that much Emerson equipment is used in that plant, and they were also open-minded enough to point out that the HART data is being sent over Profibus DP networks.
That seemed odd to me. I thought for instrumentation it is more traditional to use Profibus PA, so I contacted Carl Henning at PTO to see if that is indeed correct. If you're also curious, here's how he responded:
"DP is used in many process instruments. When Intrinsically Safe is not required the speed can be an advantage. Recognize that PA and DP refer to the physical layer - the protocol is the same. DP is RS-485 serial and PA is Manchester-encoded bus-powered (identical physical layer as Foundation Fieldbus). Therefore it makes sense to bring HART directly into DP as it has higher speeds. PA is necessary for Intrinsically Safe situations. If there are any IS areas in this installation, HART is there, so no need to go through PA.
"It is very typical to bring HART data into DP networks. We now have specified a proxy to bring HART directly to PROFINET when Industrial Ethernet is desired as well."
Thank you Carl. Always informative.
Posted by Peter Welander on January 2, 2008 | Comments (0)