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Each prove is subject to several tests:
Approve extrapolates the meter factor based on the position of the flow rate on the performance curve. It then compares that calculated meter factor with the proved meter factor to get a percentage difference.
This test passes if the percentage difference is within 0.1% limits of the performance curve.
This test passes if the meter factor is within the tolerance limits of the control charts. The tolerance limits are based on a 99.5% confidence level of the student distribution table. Test 2 cannot be performed until there have been three successful proves.
The confidence level includes all previous passed proves and the current untested meter factor when calculating the tolerance limits.
The meter factors are normalised to the base flow rate.
This test passes if the meter factor is within 0.1% of the previous prove (passed or failed).
Test 3 cannot be performed on the first prove.
Prove Pass Conditions
If there are three or more passed proves for the base curve then the following tests will be applied:
(test 1 passes or test 3 passes) and test 2 passes
If there are less than three passed proves for the base curve then the tests becomes simpler:
test 1 passes or test 3 passes