Quiz Corner: Calibration techniques

Which of the following techniques would be applicable when calibrating a flowmeter used to measure the flow of raw materials in a process plant?

1. Flow laboratory
2. Flow calibration facility
3. Signal simulation
4. Dimensional check

The value of the raw materials passing through a flowmeter in this service could be millions of dollars, so wasting even small amounts in a continuous operation could result in a large financial penalty. While this flowmeter may warrant the best possible calibration, most plants will not pay the costs and will avoid dealing with the logistics of sending such flowmeters to a flow laboratory. Answer A is usually not viable.

A wet calibration can be performed in a flow calibration facility where the flowmeter is calibrated to a master meter. Some plants maintain an inhouse flow calibration facility, such as a flow bench, that can calibrate flowmeters at commonly encountered technologies and flow rates. This service may also be available locally. Answer B may be applicable.

Most process plants have the capability of simulating signals to perform flowmeter calibration. Examples include inputting differential pressures to calibrate differential pressure transmitters, frequency signals to calibrate vortex shedding flowmeters and millivolt signals to calibrate magnetic flowmeters. Note that these are dry calibration techniques that do not calibrate flowmeter elements, such as their orifice plates, vortex shedder primaries and magnetic flowmeter primaries, respectively. Answer C is usually applicable.

Checking dimensions is a dry calibration technique that can be used for some flowmeters, such as checking the dimensions of an orifice plate. Answer D is sometimes applicable.

Additional complicating factors

Sometimes a combination of these techniques is performed, such as both simulating signals to calibrate a differential pressure transmitter and checking the dimensions of its orifice plate.