This is mostly known to everyone that a square root extractor is required for Orifice Flow Transmitter as the relationship of flow verses pressure is not linear but has square-root relationship.
But the next question is ? where should you do this square-root extraction process ?
In Transmitter or DCS or both or none?
But the next question is ? where should you do this square-root extraction process ?
In Transmitter or DCS or both or none?
Interface issue between System and field instrument engineer
The first point of caution is proper interface between requisition engineer and system engineer.
Sometimes the engineer purchasing transmitter assumes it will be done in DCS
While the system engineer assumes it will be done in Transmitter
And NOBODY does it.
Similarly, the converse is also true.
The Square-root extraction is done at both place, which again is incorrect.
In short NOBODY doing it Or EVERYBODY (Field as well as DCS ) doing it should be avoided.
It should be done at one place ONLY.
Sometimes the engineer purchasing transmitter assumes it will be done in DCS
While the system engineer assumes it will be done in Transmitter
And NOBODY does it.
Similarly, the converse is also true.
The Square-root extraction is done at both place, which again is incorrect.
In short NOBODY doing it Or EVERYBODY (Field as well as DCS ) doing it should be avoided.
It should be done at one place ONLY.
Next Question where should you prefer doing the extraction ?
Well after having discussion with few dependable Vendors they suggest it should be done at the system side.
Reason:- Transmitter’s electronic computational capability is not superior as compared to System (DCS/SIS) side.
So it is advisable to give that task to the System side.
Please note this is just a recommendation as I have done projects where client preferred having it done in Transmitter while I have also worked on projects where it was done in System side.
But if it is not enforced by client you could do it at the system side.
Reason:- Transmitter’s electronic computational capability is not superior as compared to System (DCS/SIS) side.
So it is advisable to give that task to the System side.
Please note this is just a recommendation as I have done projects where client preferred having it done in Transmitter while I have also worked on projects where it was done in System side.
But if it is not enforced by client you could do it at the system side.
Display a Square-rooted output at field But Square-root extraction require in DCS ?
The situation:- Suppose you want square-root extraction to be done in System side, but the Transmitter in the field has display.
Hence in the field when someone looks at the transmitter, he would not have a calculator to read the pressure output and do the square root extraction manually.
So “We would need the transmitter to display the square-rooted output in the field as that is what is useful for someone looking at the display in field”
But we want the extraction to be done at system end.
The solution:- This feature is available with various vendors but it should be properly communicated.
Following information must be passed on :-
1.Tx will be blind or have a display
2.What range Tx should display example:- 0 to 100 lb/hr
3.Clearly indicate :The Extraction is to be done in Control system side.
In order to display the “Square rooted output” transmitter will do it locally just for display but wont send the Square-root extracted signal to DCS. That task will be done by DCS.
Thanks for reading !!
Hope its been of value to you.
PS: This is as per best of my current understanding.
Hence in the field when someone looks at the transmitter, he would not have a calculator to read the pressure output and do the square root extraction manually.
So “We would need the transmitter to display the square-rooted output in the field as that is what is useful for someone looking at the display in field”
But we want the extraction to be done at system end.
The solution:- This feature is available with various vendors but it should be properly communicated.
Following information must be passed on :-
1.Tx will be blind or have a display
2.What range Tx should display example:- 0 to 100 lb/hr
3.Clearly indicate :The Extraction is to be done in Control system side.
In order to display the “Square rooted output” transmitter will do it locally just for display but wont send the Square-root extracted signal to DCS. That task will be done by DCS.
Thanks for reading !!
Hope its been of value to you.
PS: This is as per best of my current understanding.
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