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HMRC internal manual

Oils Technical Manual

Computer systems: meter proving

Flow computers assist in meter proving by monitoring:

  • pressure & temperature up and downstream of the proving loop;
  • the proving loop 4 way valve position (also controls the valve);
  • switches actuated by the proving sphere; and
  • meter pulses from the meter under test.

The flow computer can be expected to perform the following calculations on the raw data to achieve accurate results:

  • correction for the effects of pressure and temperature on the liquid at the prover and at the meter under test;
  • correction for the effects of pressure and temperature on the prover and of the meter under test; and
  • the flow computer will repeat prover runs until consistent data is achieved or the number of runs exceeds a defined limit.

The flow computer calculates and reports the flowrate (m3/h) to ensure that the meter under test is calibrated to the correct flowrate. For each run the flow computer will report the calculated K factor and the percentage deviation of the factor from the average of the proving so far.

The calculation is:

 (  A v e r a g e  K  F a c t o r  -  R u n  K  F a c t o r  )  x 100
Average K Factor  

The K Factor is the relationship between the rotation of the turbine in the meter (measured in pulses generated by the meter rotor) and the known volume of product flowing through it.

For Example: To ensure correct results, the flow computer would continuously monitor the inlet and outlet pressures, temperatures and meter flow rate. An alarm would be generated if one or more of these values or the rate of change of a value is outside defined limits.

Each proving operation should produce a report detailing each prover run reporting the constants used, the recommended K factor, the product density, the stream pressure, temperature & flow rate, the calculated K factor and the K factor deviation percentage.