Instrument Calibration

[Homayun]

Hi guys.
One of the things we run into often when doing a revamp is the need to recalibrate the instruments; Temperature, Pressure instruments as well as Level instruments.

My question is why do we need to calibrate an existing instrument?
For example, suppose we are changing the operating condition of an existing tower from 25 Barg to 20 barg..Would there be a need to recalibrate the pressure instrument? Why?

Thanks

 

[ash9144]

Regardless of changing operating pressure or service all instruments should be on some type of preventive program to periodically recalibrate as much as possible. And if a unit has been down for some time all instrumentation should be checked before restarting. This is just good engineering practice.

 

[JLSeagull]

Consider instrument validation instead of calibration. The calibration for the latest series of electronic transmitters stays very solid. Range changes can be done with a hand held communicator. It is always a good practice to validate (applying pressure etc.) to assure that the transmitter is working, and to verify that the transmitter range matches the display range.

 

[KiwiMace]

Older instruments with screws for zero and range will wander around a bit. You need to dial them back in on a test bench. Definitely loop test as part of Commissioning.

In your 25bar changing to 20bar example - You choke the resolution of the control loop down into 80% of the full range. Might mess with the loop gain too.