Pressure and Temperature Compensation on SIL Rated Flow Trip

[shaunjones]

Has anyone had any experience in performing P&T compensation for a flow
trip in a SIL application? Our process currently employs a 2oo2 voting scheme for tripping using 2 SIL rated DP transmitters on an orifice plate. We are contemplating adding P&T compensation on these trips and are trying to determine the best method for performing this.
1) Should each flow transmitter employ it's own pressure and temperature transmitter for
compensation or
2)is it acceptable to employ only 1 PT and one TT for the
set of flow transmitters.

What have others seen or implemented?

Shaun Jones

 

[dcasto]

If you only have one PT and TT and the compensation is significant, which it must be because you are performing it, then you still have a single point failure. So I must asume gas flow or some really sensitive need on liquids. Why not install a individual flow transmitter like a fisher floboss for gas.

http://www.emersonprocess.com/flow/Emerson/products/fb103.html

For liquids, I'd use a MicroMotion direct read mass meter, no compensation needed.

 

[Ashereng]

You should check, but if the PT and TT are SIL 2 rated, then they should be good?

Personally, I haven't seen a SIL 2 trip based on flow. It is usually pressure.

"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]

Consider multivariable transmitters to perform the pressure and temperature conversion instead of send all signals to the SIS.

 

[shaunjones]

I would say that typically, a multivariable transmitter would be a good option, but for this application we are looking at SIL rated transmitters. So far, I haven't come across any multivariable which are SIL rated.

Shaun

 

[dcasto]

Why wouldn't the mutile variable transmitter have the same exact SIL as its individual counterpart?

 

[Ashereng]

As long as it has the certification, it should.

Having said that, I also have not come across one that is SIL 2 rated.

Then again, I haven't gone looking for one recently either so ....

"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?

 

[HEC]

Basic question, why does the SIL trip need to be based on compensated flow? Especially considering the current trip is based on actual flow (velocity). For recording purposes I can understand why a compensated flow is required, but why does this need to be normalised for the SIL trip?

Mark Hutton