Why calibrate?

Key elements in determining compliance to national and international standards are the validity and accuracy of inspection, measurement and test results. As flow meter performances degrade over time, these instruments must be calibrated to provide the necessary level of confidence in the results of the tests being conducted.

There are several reasons why a flow meter falls out of calibration: physical modifications may occur from corrosion or dirt within the process; internal parts degrade slowly and will eventually have an impact on meter performance or flow meter may receive mechanical or pneumatic impacts resulting from process variations, improper installation or initialization or procedure. The most common reasons for calibrating flow meters are:

Reasons for calibrating flow meters

 

CoriolisCoating and wear of the flow tube
ThermalContamination of sensor or/and restrictor; sensor wear; modification of the orientation of the sensor
TurbineBearings affected by chemicals or dirt; bearing service affects calibration; rotors wear
Variable AreaMaterial build-up; plugging; tube abrasion
MagneticLiner damage; electrode coating
Positive DisplacementDirty liquids, corrosion and abrasion change the volume; bearing wear degrades accuracy; gear service affects calibration; solids can cause plugging
Differential pressureOrifice plates, nozzles and venturis are subject to wear: orifices plate get knocked out of position. Pitot tubes become clogged
UltrasonicChanges in the sonic properties of the fluids; lack of contact between transducer and pipe wall
VortexFlow meter mounted improperly in pipe; vibration; shedder wear