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HART vs Fieldbus
At the risk of opening a can of worms, I'm asking everyone "Which field network would you recommend for ANALOG devices?"
By Michel A. Levesque, eng. on 3 June, 2002 - 2:28 pm

Hi all,

I'm talking about pressure, flow, temperature transmitters or control valves.
I see a lot of our customers on HART, very few on Fieldbus. Which one will win in the long run? Which is the better technological choice? I'm familiar with both networks, I just want to find out which way the industry as a whole is leaning.
Bonus question: "Which network is being used in your area?" (US, Canada, Europe, Asia)

By Bob Peterson on 3 June, 2002 - 3:55 pm

I don't consider HART to be a real network. It does not really reduce your field wiring. What it does do is dramatically simplify your life in the field. The ability to have a HART equiped transmitter that you can hook up a hand held communicator with is an immense time saver. I would never go back to straight analog transmitters. And anymore, digital, HART equipped transmitters are often priced lower then analog transmitters.

I have yet to see a single instrument bus be specified in the thousands of projects I have done or seen. The cost is just too high for the little you get. But, a majority of transmitters are probably supplied as smart transmitters, and usually specified that way cause its a no brainer anymore.

The problem for OEMs is that the HART equipped analog cards that AB has(for instance) are outrageously priced (compared to a regular analog input card). So your typical OEM is going to use a regular analog card. I think this is sort of sad as there is probably much that could be gained, but the cost is just so crazy its not worth it to the OEM. Plus there is not a HART card available for the SLC.

bob peterson

By ATECNA, Gonzalo Barros on 3 June, 2002 - 4:03 pm

Hi to all participants, Im new in this group and i'm glad to be here.

We are working with LonWorks Networks as fieldbus.
- Its open & interoperable technology.
- Smart devices.
- Peer to peer communication.
- Multiple media communication: Twisted Pair, Power Line, Radio transceivers, Intrinsically save transceivers. more information in "www.lonmark.org":http://www.lonmark.org or "www.echelon.com":http://www.echelon.com

We think that is very good choice for all kind of projects.

regards,
Gonzalo Barros
<http://www.atechna.com>

By Chris George on 4 June, 2002 - 12:13 pm

These days the term "fieldbus" tends to be a label for too many very different bus systems. To me, "fieldbus" refers to FOUNDATION fieldbus. Profibus is profibus, modbus is modbus, AS-I bus is AS-I bus, etc.

The main difference between HART and FOUNDATION fieldbus, for example, is that the measurement signal for HART is still analog. With FF, everything after the physical sensor is digital. With digital signals, if the data successfully moved from point A to point B, it is exactly and precisely the same data that was sent. Can the same be said for 4-20mA?

HART is not really a true network and rarely is installed as one. The benefit of HART lies in the diagnostic and programming features available. These features are available with digital "fieldbus" systems as well, but the use of all-digital signalling opens a lot of doors for signal accuracies and plant networking.

In my opinion, just as HART was slow to be accepted/adopted so will all-digital "fieldbus" systems. Personally, though, I have been involved with many end-users installing "fieldbus" systems (worldwide).

Chris George
SAIT
Calgary, AB
CANADA

By Reza Hasseli on 4 June, 2002 - 3:04 pm

Fieldbus is a network of sensors which are smart and due to its highly flexible characteristics, it will be dominated in the industrial automation. The time of old conventional 4-20mA devices is over. And thanks to the rapid improvements in the electronic technology we see day by day, smart sensors will be a common things in the industries.

HART is an intermediate solution between analog communication (i.e. 4-20mA) and digital network communication (i.e. Fieldbus) and will be put aside soon! because what fieldbus will offer is more than only the diagnostic feature that HART tends to offer.

Signal transfer in HART is still analog which is a good food for noises! where in fieldbus we don't have any noise alterring the measuring signal.

Bye
Reza Hasseli