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HART Compatible Analog IO cards
HART Compatible Analog Input Output Cards

Hello everyone,

I have a query regarding selection of Analog IO cards for our plant DCS system. We are in the process of ordering our DCS system and considering it as a one time investment. It is the best time to decide whether to go for HART compatible Analog IO cards or not.

To be honest, I haven't yet worked on HART compatible Analog IOs yet in my 9 years of experience. Rather I have worked on conventional 4-20mA signal. I have gone through the internet, and there are a lot of advantages mentioned of HART compatible cards, for example detailed device diagnostic information etc.

Is it preferred to go for HART compatible Analog IO cards (rather than normal Analog IO cards) at the expense of extra cost? Does the benefits outweigh the additional costs? And shall we go only for Analog Inputs like transmitters or shall we go for Analog outputs as well like Control valves positioners and VFDs?

Any help in this regard would be highly appreciated.

One vendor recently announced HART compatible AI cards. I read their spec and their manual and did not understand whether I could tag multiple variables from a multivariable device, like a Coriolis flow meter.

I pressed them for an answer and after a lot of hemming a hawing the vendor admitted that the HART compatibility does not mean the use of primary, secondary, tertiary and quatenary variables by the AI card (or its controller box), rather HART compatibility only extends to HART pass-through, where asset management software can fetch HART diagnostic data from the field instruments through the AI cards. I wouldn't have known that, had I not pressed for the information.

I don't know if other vendors take that same approach or not. I see lots of TriLoop and Moore Industries break-out boxes, so I wonder if HART enabled AI ever really does fetch those vaunted HART variables.

Frankly, I rarely, if every, find a clear statement of HART functionality anywhere, except on whatever the name of the HART Foundation is nowadays, Fieldbus something or other, but those descriptions are not vendor/device specific, it's HART in general. The field instrument suppliers assumes that mentioning the version of HART covers all they need to say about HART.

I'd have to say that you, as the user, have to spell out what you want HART to do, and ask the vendor to prove that they can do it, because I, for one, find it a glossed-over topic.

There's a couple threads out in forum land that ask 'how can I read this particular HART diagnostic value?' that have never had an answer. There's a least one that asks whether a specific vendor's HART AI card can read secondary and tertiary HART variables. No answer for that one, either.

It would be informative to the rest of us, if you'd post whatever your findings are on HART enabled AI's.appreciated.

By Dave Ferguson on 13 October, 2018 - 10:24 pm

Just did a project with Rockwell Hart IO, they can do Asset management from an asset management system.

They also support primary, secondary, tertiary and quaternary values.....they also support diagnostic values ......

I also was capable of pulling tons of other Hart diagnostic and administrative info with excel from the processor......

Dave Ferguson
Control Systems Engineer