Reliability in Fieldbus system

[Egui]

Is there any real case or study or paper where I can find a comparison between the reliability in classic hardwired I/O system(Junction box-marshalling-Controller) and field bus system.

Many customer do not like to take risk in change their way to do the thing....it´s obvious, it´s better safe than sorry.....

I am not talking about safety loops.(ESD)

In addition is there any cost study (installation safe money, etc)....

thanks in advance

 

[Ashereng]

Yes. Emerson has done extensive studies, paid for by them. Their sales reps will have these literature. And, they are more than happy to help you convice your client to go Foundation Fieldbus.

By the way, Fieldbus is one word, not two. Otherwise, it sounds like Greyhound bus, which is a different kind of bus.

Who is your current control system vendor? Almost all vendors I deal with have such literature too. Emerson is just the most organised and aggressive of them.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[JLSeagull]

Were you addressing safety shutdown systems the response would be that Foundation Fieldbus is not a player where real reliability and third party certification such as TUV, ABS, DNV etc. are required.

 

[controlnovice]

Which fieldbus are you referring? Foundation Fieldbus, Profibus, others?

Emerson has many cases on cost savings for Foundation Fieldbus. Just be careful....they don't tell you everything.

For example, we found that while there were savings in installation, the engineering was more expensive (more time to design), the instrumentation is more expensive, commissioning time was greater (despite what the sales rep indicates) and maintenance of the system is done by engineers instead of the technicians (much more costly). Again, this was our experience on two installations. Other outcomes may vary.....

The comparisons in manufacturer's literature are against standard 4-20mA instrumentation. If you compare it against HART, then the difference between the systems is much less.

I have not seen any papers on reliability. We have had no issues in the 5 years of service using Foundation Fieldbus.

______________________________________________________________________________
This is normally the space where people post something insightful.

 

[Ashereng]

"Fieldbus" is typically meant to mean "Foundation Fieldbus". Of course, this is only common to my industry and locatin.

Profibus we use Profibu.
Modbus we use Modbus (in all its incarnations).
DeviceNet we use DeviceNet.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[djs]

One way to look at the reliability of an instrument system is how many instruments will be affected by the failure of any one component. For example, in an analog system, the analog input card usually has between eight and sixteen inputs. Therefore the failure of one component will knock out between eight and sixteen instruments.

A networked system can be designed to any level of redundancy: eight, sixteen or even one. Of course as the level goes down so does the cost go up.

 

[Rheinhardt]

From my past experiences using remote IO on fieldbus systems is that it saves you time and money even at the installation as a contractor....

When it comes to plant maintenance and faultfinding this is were you really see a significant advantage.... It is really simple to troubleshoot no more cabinets tangled with tonnes of cables... The cost gets justified almost instantaniuosly...

We are at a point where we will never try to use Junction boxes as they are known, we have used various protocols but specialize in Siemens and thus use the Profibus mostly, but deviceNET, Interbus ect...They are all good..

Here are some links

http://kernow.curtin.edu.au/

http://www/Fieldbus/ads.htm

http://www.industrialnetworking.co.uk/mag/v7-5/f_safety.html

http://www.pepperl-fuchs.com/pa/interbtob/profibus/05113/index3_e.html

I like the last one

Regards
Rheinhardt

--Off all the things i've lost , i miss my mind the most--

 

[BigInch]

They are extremely reliable and for all practical purposes might even be ignored completely when analyzing reliability issues in any plant. Unless the electronics are exposed to ambient conditions outside their design specs, the actuators, valves and virtually all other types of equipment will have failure rates many orders of magnitude greater than the control electronics. It is actually safe (within all reason) to ignore their contribution to unreliability issues when taken in conjunction with almost any additional components.

 

[JLSeagull]

Solenoid valves, pressure switches and most discrete devices may fail in a manner that is not necessarily detected without testing. I believe that the data suggests that the field instruments are the weakest link in the chain. The data is available (I don't have it) from OREDA, etc.

The reliability of control room electronics differs. The typical DCS or PLC I/O and processor electronics may be comparable. However, triple the electronics in a voting scheme and reliability can be improved. I don't think that Fieldbus is a player in the safety shutdown field where triple and quad I/O, processors etc. are voted.

 

[techwizard]

hi JL
not only voting of TMR, the safety requirement is to hardwire the field instruments to the PLC subsystem. Triple redundant fiber for remote I/Os and DCs connectivity. That means the field instruments and FE are hardwired.

 

[Fieldbus]

Relaibility is such a little word to cover so many meanings.
If you mean; does the equipment (instruments & devices) fail more because they are 'fieldbus' over 4/20mA or HART, then the fact that Yokogawa and the rest are now offering life-time warranties suggests that they don't. Analog/Hart/fieldbus instruments are all pretty much the same as far as reliability goes.
Where fieldbus does have a problem is in connecting a ton of devices to one twisted-pair cable. It's not that the cable is itself likely to fail, but one helpful person puling one plug can take out a lot of stuff.
By the way, IEC61158-2 describes all 8 (or is it 9) industrial fieldbusses, and only a few of them offer redundancy to various degrees. For example, Profibus PA doesn't even offer a redundant systems interface card, and while FF has redundant interface cards (H1 pairs), there is only one mechanism to make the field cable redundant (check out

http://www.controlengeurope.com

and look at the current/June 2006 issue - click on the magazine front cover).

 

[JLSeagull]

Fieldbus
This thread question pertained to a reliability comparison between (Foundation) Fieldbus and individual I/O system (signals). For my purposes, reliability pertains to the probability to fail and the failure mode.

I must clearly acknowledge my limited knowledge of Foundation Fielbus due to very limited experience. My experience is so limited that ...

Still, hard-wired instruments are used in safety shutdown applications. As I understand TUV 5 certification for use in safety shutdown signals, the requirement is for the device to fail in a safe condition. TUV-5 is not so concerned about reliability in terms of up time, only how it fails. The Rosemount 3051S series instruments are "Safety Certified to IEC61508 by TUV for single input use in SIL 2 and dual input use in SIL 3 Safety Instrumented Systems.

As I interpret the Rosemount catalog, not all 3051S series models are certified. The model number selections for the output include A, B and F. Pick A is vanilla - 4-20 mA with HART. Pick B for 4-20 mA HART with the safety certification with a note that limits the range turndown. Pick C is Foundation Fieldbus.

I think that Rosemount applies their 12-year warranty across the 3051S series line. I don't know about all of their products. These Rosemount selections are not applicable to Yokogawa, Ohmart-Vega or other manufacturers. Surely other manufacturers have a limited set of model numbers that are TUV 5 certified.

I welcome any clarification if Foundation Fieldbus is used in IEC61508 or ISA 84 SIL levels 2 and 3 and the TUV 5 certification for such use.

I have long thought that Fieldbus has the potential to revolutionize the control systems business. I expected the revolution before the turn of the century - for initial cost savings and distribution of the PID function to the devices - not improved reliability. The FF revolution has been slow to arrive. Is it really reliable? I am not convinced. Convince me.

 

[Ashereng]

Is there any real case or study or paper where I can find a comparison between the reliability in classic hardwired I/O system(Junction box-marshalling-Controller) and field bus system.

Many customer do not like to take risk in change their way to do the thing....it´s obvious, it´s better safe than sorry.....

I am not talking about safety loops.(ESD)

In addition is there any cost study (installation safe money, etc)....

JL,

As I read the OP, the question is one of comparing reliability of fieldbus to traditional I/O system.

There is no mention of safety system. In fact, the poster strictly said "I am not talking about safety loops."

I am not sure how safety system usage got into the equation.

Having said that, I have learned from experience, I can not convince anyone of anything. Most people become convinced when they want to.

JL, you are an engineer. I don't expect to convince you of something you don't believe in. In fact, I don't expect you to do anything other than your conviction. That in essence, is what an engineer does. Don't you agree?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

Safety certification is about reliability. "Fieldbus" said "Relaibility is such a little word to cover so many meanings.". My rant is along the line of thought that individual transmitters hard wired to an I/O system are available for SIL 2. Are any bus structures such as Foundation Fieldbus, Profibus, Modbus 485 or Ethernet really that available? Perhaps the OREDA data reflects such reliability. I think that I lack access to the reliability reports that are marketed for instruments but they exist. I should search IHS for such data.

 

[Ashereng]

I am not sure I understand you.

Fieldbus is not for safety applications.

Yes, SIL rated safety certified equipment is reliable and safe - but that is not the point. Control system equipment do a different job.

Yes, you are correct. Most SIL rated equipment are more "reliable".

Then again, my Ford 150 can carry more than a Porche 911. Depends what you need.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

Do you really believe that Fieldbus is more reliable?

Reliability data exists for instrumentation device types. It is harder to obtain data based upon manufacturer and model. Instead of data for the Rosemount traditional and the Smar Fieldbus I only find data for a generic dp transmitter. Also, one must interpret the data for different system topologies. Fieldbus eliminates the DCS controller. However, the Fieldbus controller is in the weather and process area. This affects MTTR, etc. The bus cannot be more reliable than individual pairs. More field connections exist. Losing the bus has greater impact than losing a pair.

Everyone who publishes data has their own agenda. The operating company data should be superior to data from the manufacturers. OREDA collects reliability data among nine oil and gas operating companies. The OREDA software permits data analysis. OREDA publishes a Reliability Handbook that is updated annually. The cost is 545 Euros + shipping and handling. I do not know if the data distinguishes between Fieldbus and traditional instruments. Even if so it could be difficult to compare - apples and oranges. I lack access.

The manufacturers can give you some data. However, their disclaimer is that they only know about warranty repair - lacking long term installation data. I have seen MTBF data for a furnace flame detector over 600 years. This could because they shipped 600 units without a return within a year. One could question the data. Instead we use it for the SIL calculation and go on. We do not such calculation if it is not a safety system.

Profibus has comparisons too. How do you think that Profibus compares to Fieldbus in European publications where it is widely used?

If you can use traditional instruments for safety and cannot use Fieldbus for safety then are forced to use both engineering methods and store more spares. How can one believe that Foundation Fieldbus is more reliable?

http://www.dnv.com/publications/oilgas_news/articles/NewOffshoreReliabilityDataHandbookOREDA.asp

Many companies have done economic studies. The Fieldbus advantages in wiring are somewhat offset by the field power and increased engineering and design labor hours to implement the initial installation. Most manufacturers that sell Fieldbus also sell traditional instruments.

If FF were more economical and more reliable than traditional instruments, then more projects would use it. With Fieldbus instruments for regulatory control and traditional for safety you increase the spares requirements and reduce interchangeability. Fieldbus saves lots of wire for long runs. Not so much savings for short runs to the control room and widely spread measurement and control element interactions. Instead of gathering instrument from a real estate area one must engineer the multidrop runs. This delay increases project engineering labor and cycle time.
Search for “comparison Fieldbus mA” or consider adding Profibus to the search. You will find the following links among comparisons. Are any really independent?

http://www.br-automation.com/cps/rd...llowed.htm?caller=products_85693_ENG_HTML.htm

http://zone.ni.com/devzone/conceptd.nsf/webmain/DD9137E0DD677BA28625687C0000EC9B

http://www.fieldbus.org/endusersupp...apore05/presentations/fieldbus comparison.pdf

…

 

[Fieldbus]

Safety was not really the issue here, but since we've started.... TUV approval has been granted for ProfiSAFE and for the software protocol called FF-SIS. ProfiSAFE allows the conjunction of safety related and non-safety related instrumentation within the same system and on the same hi-way. FF-SIS will get there as well except that there aren't many FF-SIS devices yet and no logic solvers.
TRUNKSAFE (a specific product from one company, not a generic standard) seems to make FF more reliable than individual hard-wired instruments since everything is duplicated right down to the individual instrument (H1 card, power conditioner, trunk cable, spur interface) and all components are continuously active (there is no switching between primary & secondary, eliminating the possibility that the secondary may have failed prior to be called into action) and no software is used to monitor the redundant components).

 

[charlesflau]

To All,

We are in the middle of commissioning our fieldbus based control system and ran into many Valtek 3400IQ positioner failure problems. We are still working on resolving them.

Any suggestions are welcome and appreciated.

 

[Ashereng]

charlesflau,

On an earlier job about 2-3 years ago, we also ran into problems with Foundation Fieldbus control system and positioners. I can't quite recall all the details, but I think it was a HWL PlantScape system with Rosemount positioners.

I think in the end, they replaced the positioners.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

We have a client petrochemical complex with dirty wet instrument air. Although other valve manufacturers are acceptable, the client only permits the Fisher-Rosemount DVC style positioners. Most are HART not FF.