Instrument calibration range question

[Indy]

Good evening,
I have a question regarding instrument range calibration calculation as it’s causing a little confusion.

If we have a line were the min pressure expected is 3 bar and the max pressure expected is 6 bar and the design pressure of the line is 16 bar then if we have a PT on this line would the calibration range include for the design pressure of the line eg PT calibration range would be 0-16 bar or would it be smaller to include the min/max pressure only?

Thank you

 

[danw2]

I'd range a PT 0-10bar because 10 is a nice round number and gets nice even major scale divisions (0, 1, 2, 4, etc) on a HMI chart/screen.

The 3-6bar working range is near the middle of 0-10 and there's plenty of room to catch any over pressure.

The spec sheet for a 'smart' PT that I have on my desk has 0-50 bar range with a 100:1 turndown, so it can be scaled all the way down to 0-0.5 if need be, but that says that it can spanned 0-10 for a trial and then 0-6 if for some reason the working range needs to be 'expanded'. Smart PT's all HART configurable in the field nowadays; when re-ranging the bigger issue is getting the HMI set to the right range,if a change is ever made.

 

[rotw]

As far as I know and as far as rotating machinery is concerned, calibration range are typically set based on min/max of all operating conditions (more generally operating envelope).

I also agree with the comment from danw2 that re-configuring the ranges is generally not big issue, it is more HMI side that can cause issues. For example, some flows for HMI display may be calculated based on scaling (proportional) coefficients which are set to match specific calibration ranges.

If you plan an escape, you must succeed as if you fail, you will be punished for trying. Never say or write down your plan. Heart is the only place where secrecy is granted.

 

[Indy]

Thank you for the replies.

 

[georgeverghese]

Depends on what you mean by "max expected" pressure. Is 6barg the max pressure reached when process controls have failed, or does it go higher. The PT calibration range should cover the pressure range seen when controls have failed also, if this PT is for pressure indication purposes only. If it is in controls service, ie PT feeding a PIC, then agree 0-10barg would be appropriate to improve on sensitivity.