Best Fieldbus for Discrete Instruments (On-off valves)? 2

[Loopee]

The more I study the possiblities the more uncertain I become about what to use. We are doing an estimate for a chemical process plant where Foundation Fieldbus(FF) has been decided for use with Analog - Transmitters and Positioners.

The question is what to do with the on-off valves and switches? My first impression was that FF would be overkill and unecessarily expensive. I then moved to the Profibus world. It seemed to be very similar on the hardware level which I liked. However when I began to look at the availability, the first two common topworks companies I checked (in the US)seemed to only be set up for the high speed version that requires separate power and not the PA version which does not.

This plant is very large with two areas with concentrated process and then many small areas spread way out- a tank half a mile away , wastewater, etc.

The Actuator and topworks people seem to more set up for AS-i bus than anything but I was shying away from it because of its length limitations -100 meters(300 meters with repeaters).

I've received some component prices and was surprised to learn that profibus topworks were not much less expensive than FF.

We are expanding an existing ABB DCS system and I really hate the idea of having FF for analog and back to the wire-everything-standard I/O for the discrete stuff.
If anyone has gone through this and can give me some conclusions you reached , I would much appreciate it.

 

[JLSeagull]

You could use the analog outputs to DVC valve position controllers thus use Foundation Fieldbus devices for on/off applications. This is practical for sequenced level applications in a manner similar to starting and stopping pumps. Others can advise whether anyone considers Foundation Fieldbus suitable for process safety shutdown valves.

In my experience, we use the SIS with digital outputs to control the solenoids. The valve position is still typically done with open and closed position switches. I too am a interested in feedback related to industry trends for the safety shutdown valves including partial stroke testing, position transmitters, Fieldbus, etc.

 

[Loopee]

Thank you Seagull for your response. There is a lot to consider when choosing a particular one - I'm learning. The actuator people I've talked to since I posted this thread seem to be generally pushing me to AS-i. Since that's what they have developed.
I'm going to a ABB Automation World Conference at the end of this month in Houston and hope to learn a lot in their workshops.
I'll share when I get back.

 

[controlnovice]

I've installed both AS-i and Profibus for digital applications.

Our plants are very small, and we don't have the lengths you are concerned with, although for a couple of the AS-i segments, we did need repeaters.

My preference is AS-i bus. But I think it is more for the interface between it and our DCS system (Emerson's DeltaV). I don't see one advantage over the other in hardware, network or ability.

For hardware, I really like StoneL's offering on valves and especially the disconnect switches for hazardous areas. You can disconnect individual instruments from the main trunk line without disruption to anything else.

Foundation Fieldbus is not a good solution for discrete instrumentation.

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[JimCasey]

ASi. Very fast,inexpensive, but not burdened with additional features.

 

[Loopee]

Thanks to JimCasey and controlnovice for your info. It all helps. I was also looking at the StoneL switches but it seemed that every spur with a switch would take a tremendous amount of room in the field cabinets.

 

[controlnovice]

On the StoneL devices, we actually installed a switch in the field, close to each device it was serving.

One thing I didn't like about StoneL's design was the lids, or covers, for the EXP rated enclosures. If the lid was dropped, it can go "out of round", and never get the lid/cover back on the device.

But still much easier than having to remove/undo the screws or bolts of the other manufacturers.

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[nkwe]

You could install Remote I/O stations with AS-i controllers. Use copper to link up the stations within the same process area. Use fiber optic to link up Remote I/O stations back to central control. The cost of equipment will be high, but you will also save on cabling (material & Labour)

 

[ozmosis]

I would second controlnovice's recommendation of ASi:

http://www.as-interface.net/System/

It is simple to use, simple to connect (devices just push through the rubberized cable to make contact with power and data). There seems to be plenty of devices that can connect so it is not a proprietry protocol.