Pipe or compact provers are often used in Metering Systems for frequent calibration on actual process conditions. The base volume of these provers needs to be regularly determined to the lowest possible measurement uncertainty. Prover calibration is recommended to:
Verify its accuracy;
Check its mechanical conditions;
Fulfill contractual custody transfer requirements;
Comply with API’s minimum recommended calibration of every 3 years.
Prover calibrations usually are done by a waterdraw or by master meters in accordance with API MPMS Chapter 4.9. A waterdraw calibration unit is generally portable and consists of a water reservoir, a low-pressure centrifugal pump, associated pipe work, hoses and a four-way valve. The centrifugal pump circulates water from the reservoir through the prover. The water is then returned either into the field standard test measures and/or back into the reservoir. To reduce the uncertainty caused by test measure scale reading errors, the number of test measures filled during a calibration pass shall be kept to the minimum possible, based upon the volume of the prover and the number and sizes of the test measures available. ODS Metering Systems performs a prover calibration with our own waterdraw apparatus, master meter and/or gravimetrical calibration equipment in association with a Notified Body (NOBO) and traceable to international acceptable standards. The calibration equipment is fabricated to meet API MPMS Chapter 4.7 criteria and calibrated by the National Institutes of Technology (NIST) or other national metrology institute.