Nodes and HART mea culpa

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I just can’t leave this topic alone: node counts.  I wouldn’t bring it up again except Jim Montague said this in “Can Foundation fieldbus (FF) stay hungry?” – “To be fair, I know installed nodes are important milestones for fieldbuses because they measure how far and wide it’s being adopted, but these totals have little use beyond superficial marketing.”  I don’t think it is superficial to emphasize how far and wide fieldbuses are being adopted!

Hmmm, maybe HART is a fieldbus.  I knew that HART devices transmit their measured value digitally not just as a 4-20mA signal.  We pick those values up (in addition to the other digitally transmitted parameters) when we bring HART devices onto PROFIBUS and PROFINET.  But until I read something this week about the ability to place a maximum of three HART devices on a 4-20mA “bus” I never really thought of HART as a fieldbus.  And of course it’s still at 1200 baud (compared to FF and PROFIBUS PA at 31.25k baud).  I wonder if anyone is actually bussing HART.  My conclusion, for all practical purposes HART is not a fieldbus.  (mea culpa withdrawn)

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