Fieldbus Speeds

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Last week one response on the Atlanta Course Evaluation thought my comparison of fieldbus speeds was “sales-weasely.”  Must have been written by a muggle.  <smile>  To be fair, he also said that I did not say anything untrue.  Anyway, the writer objected to my comparing the speeds of PROFIBUS DP and DeviceNet but not PROFIBUS PA and DeviceNet.  Comparing PROFIBUS DP and DeviceNet is a reasonable comparison – they cover the same application space.  (Those speeds by the way, PROFIBUS DP moves 244 bytes at up to 12Mbaud while DeviceNet moves 8 bytes at up to 0.5Mbaud.)

But comparing PROFIBUS PA and DeviceNet is the age-old apples to oranges comparison.  PROFIBUS PA covers the process instrument application space while DeviceNet does not.  PROFIBUS PA should be compared to Foundation Fieldbus; both run at 31.25kbaud.

There will be more on PROFIBUS and a little on PROFINET at the PROFIBUS one-day training class tomorrow in Albuquerque.  Still seats available and walk-ins are welcome.

–Carl Henning

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