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METER CALIBRATION
The method of proving should be selected, and necessary provisions made, during the design
stage of the installation. Of the most common used systems, portable provers have the advantage
of more closely reproducing the condition under which the product is normally delivered.
Use this information for all flow meters, except on Liquefied Propane Gas (LPG) flow meters.
Use Accurate Prover
Scientifically designed provers are commercially available for proving meters, and no other kind
should be used. Even scientifically designed provers should be checked periodically for accuracy.
Weights and Measures officials have been very cooperative in giving assistance to checking
privately owned volumetric provers.
Recommended size of test measure:
The prover capacity should be equal to at least one minute’s flow through the meter at its
maximum rate.
These provers are not merely truck compartments or drums, but are scientifically designed test
measures, having proper drainage means built into them, a calibration gauge glass neck, and
protection against deformation (which causes volume changes).
A “homemade” prover, whether a drum or a tank is not likely to be satisfactory, and may cause
expensive errors due to inaccurate meter calibration.
Setting a Prover
The prover should be set level, using the levels provided on the prover, or separate ones. This
insures consistent results when moving the prover from meter to meter.
Where to Test a Meter
The best place to test is in its normal operating position, instead of a test stand. In this way, the
correctness of the installation and of the operation conditions will be verified by the test. Always
test a meter with the same liquid it is to measure, because a difference in viscosity, temperature
and system plumbing slightly affects meter accuracy.
Discharge Line from Meter
Where a portable prover is used, the liquid is generally discharged in to the prover in the same
manner, as a normal delivery would be made. Where a special test connection is used, the
discharge line must be arranged to drain to the same point on each test. The meter flow rate and
off/on is controlled at the end of the discharge line.
Wetting the Prover
Reset the meter register to zero, and fill the prover to the zero or 100% marking of the scale.
Disregard the meter reading. Drain the prover, and reset the register. The reason for disregarding
the first meter reading is that the prover must be wetted, as its calibrated capacity is determined
on its wet measure capacity by its manufacturer, and because the prover will be wet for the
subsequent tests to be run.
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