which one is better dcs or fieldbus

as I read in some books fieldbus(foundation fieldbus)is growing in oil and gas industries and DCS would be out of order
but in Iran we still use DCS(mainly yokogawa) even in new plants I 'd like to know what happens in the world and your country .tell me about your experience where we use dcs and
F fieldbus?

I do not use Fieldbus or DCS quite frankly. PLCs are good!!!

Kind of like asking which is better, a computer or ethernet?

DCS

Fieldbus

Dear Alaric
I know alittle about both of them they are control system
so your sentecse dosn"t make sence to my question
i want to know about your country still use dcs in new plants
why don"t use dcs all over plant in most oil or gas industries use only
dcs or hybrid(dcs and ff)

Haha, no your question does not make sense, DCS and FieldBuses are like Servers and their ethernet..

Alone with FieldBus you cant control anything. It is not CONTROL SYSTEM, it is only for data transfer. The data transfer could be from plc to plc or plc to valve or from temperature sensor to plc.

Foundation Fieldbus is consortium promoting their solution for fieldbus. Profibus group would be another.

Hmmm, I've heard that Foundation Field Bus (FFB) devices can control other FFB devices directly, unlike other types of Field Bus (ie. Profibus) devices.

Haha, no your question does not make sense

Click to expand...

dear TurpoUrpo your post doesn't seem polite!!!
I think we should respect each other and share our knowledge here!!
I passed a smar foundation field bus course (syscon -process view).in FFB you can program smart devices like transmitter and
valve positioner so it isn't just for data transfering
so FFB is control system and has alot of benefit compare with
DCS but they still use DCS .WHY?

Hamid,

You can program and configure FFB devices with something like Syscon's product, however that is not the same as controlling them.

A DCS implements a communications network (usually proprietary) to communicate to the devices on it's network.

This is similar to a PLC using a Fieldbus network (like ControlNet) to communicate to other PLCs or devices.

The actual controlling is done by the control system itself through the Fieldbus network.

For example, a PLC may control a control valve on a Fieldbus network.

Or on a DCS, a DCS controller may communicate with a valve, motor, etc... over the DCS network.

Hamid, I don't think anyone was intending to insult you. I myself was thinking "it's like comparing apples to Ethernet". Hopefully the others have given you a good idea of the differences.

I also feel it is a shame that you feel it is necessary (and perhaps it is necessary) to defend your country in your signature. I am a big fan of Persian history and your wonderful people. Unfortunately politics tends to get in the way.

OG

unclehamid said:

so FFB is control system and has alot of benefit compare with DCS but they still use DCS .WHY?

Click to expand...

For standardization or perhaps to save on engineering costs? Maybe geo-political pressures make supplies of certain field-bus equipment an uncertain commodity?

The truth is, none of here can really answer that question. You'd really have to ask those who are commissioning the system as anything we tell you would be speculation.

I started writing a lengthy response to this thread, but I don't think that this forum is really the place to get into a lengthy discussion on this. I think that Alaric put it pretty well, it's "Kind of like asking which is better, a computer or ethernet?"

For what it's worth, here is my (hopefully brief) opinion though, it is in the context of Foundation Fieldbus (FF), from your post, I'll assume that you're thinking about FF which is where the Oil & Gas industry seems to be heading.

Given that you (unclehamid) are in Oil and Gas, and without getting into the whys, I think it's pretty much certain that you will be using a DCS to control your plant (although you will no doubt have many PLCs on packaged equipment). Some DCS vendors have more FF capability and experience than others, if you have not already done your DCS vendor selection, then this is something that you need to look at during the process. The right answer will also depend to a great extent on your choice of field equipment vendor and what you're actually going to do with the FF information (other than the basic I/O values, i.e., the diagnostics).

I think that the question you should have asked, though not necessarily in a PLC forum, is "will my DCS use traditional I/O or Foundation Fieldbus ?". Even that answer to that is not simple and will, depending on your timeframe for implementation, probably be no better than BOTH! Safety Rated Foundation Fieldbus is "coming soon", but not currently available, plants currently using FF use it for Process Control only - not Safety Systems.


I think that there are far too many factors influencing the decision on whether to use FF or not to go into here. Probably the best place to start reading up about FF is on the Fieldbus Foundation web site, www.fieldbus.org. Then talk to your DCS vendor (bearing in mind that he will have a vested interest in promoting his view).

A couple of bullets on the pros and cons of FF to get you started, they are my personal opinion - everyone will have their own!

Pros
Advanced diagnostic capability of field devices (a fact, but you need to make use of it)
Reduced field wiring costs (debatable)
Ease of configuration (debatable)
Control in the Field


Cons
Relatively new technology, for the end-user, the EPC and some DCS vendors
Choice of hazardous area protection technique is not straightforward
Control in the Field (yes it IS in pros and cons)

OK, I've rambled on longer than I meant to, but hope it helps

regards
Dave


oh, and rambling on again, just picking up on some earlier comments in the thread, in line with my bullets above, FF does allow "Control in the Field" - typically, a valve controller can contain the PID block and get it's input from another device on the FF bus. You do need to configure it though and usually communicate with the operator - normally through the DCS.

I think Unclehamid might have been asking.
Is it better to let the foundation Fieldbus devices do the controlling or should that be done in the DCS.
For example
A flowmeter can talk directly to a control valve and the PID function could be in either. Provided you supply 24 VDC they will happily control the flow.
The alternative is the flow meter talks to the DCS the DCS has the PID function and it commands the control valve.
Ask yourselves which is more direct and reliable?
In the Delta V system you can have either or a mix, it looks identical to the operator.
Either way you still need something to provide an interface for the operator, record data, alarms etc.
The FF projects we have done recently still do the control in the DCS but I think that's going to change in the future, almost all the FF instruments are capable of solving PID.

Roy

unclehamid

thanks all of you escpically stevendt it was really usefull
I feel lake of info about DCS and FF in this site
and this topic can extend
about my signeture about 2 years ago I had a post
http://www.plctalk.net/qanda/showthread.php?t=28604
and someone tried to associated it to inrichment of uranium
some people think all iranian people have a chain of centerfuges in their dinning room!!!