Real Time Automatic Calibration of Flow Meters for Real-Time Hydraulic Modelling

Performance of flow meters is often a function of flow rate as well as properties (density and viscosity) of the fluid measured by the meters. Since comparison of flow meter readings is a key parameter in leak detection techniques, it is desirable that the readings from the flow meters are accurate and comparable. The idea behind real-time calibration of flow meters is to calibrate a flow meter (called the dependent flow meter) against another flow meter (called the independent flow meter) that is assumed to read correctly. The real-time calibration method is useful under two main conditions: i) when the reference flow meter has been calibrated to a high degree of accuracy and the flow readings from the meter are accurate; ii) when the pipeline operating conditions support the fact that the meter-in flow at one station equals the meter-out flow at the other station. By determining the deviation of the dependent flow meter reading from the independent flow meter reading, a time-averaged flow ratio is calculated. However, the flow ratio calculation and time averaging is only updated at prescribed conditions. The proper correction factor is ascertained and then applied to the dependent flow meter reading. The main advantage of using this technique is that the flow meter repeatability is reduced over time below the nominal accuracy of the dependent meter. Note that the term “calibration” in this context does not refer to the standard method of calibrating flow meter with a ‘prover’ but a technique to calculate correction multiplier for flow meter in other to improve the performance of hydraulic models.