Performance Evaluation of Water Flow Calibration Rig for Calibration and Measurement Capability (CMC) Claims

The National Metrology Laboratory of the Philippines (NMLPhil) has recently established a water flow calibration rig that operates on the static weighing flying-start-and-stop mode. It serves as the national primary standard of liquid flow rate and intends to calibrate liquid flow meters of flow rate between 2 L/min and 2000 L/min. However, its performance must be evaluated and validated before it can provide high accuracy calibration service and benefit the different industry sectors and secondary calibration laboratories. This paper presents techniques to evaluate the performance of the NMLPhil water flow calibration rig. First, the flow rate measurement process’s critical variables were investigated. Next, the sources of measurement uncertainties were analyzed and calculated using the Law of Propagation of Uncertainty (LPU) to realize the calibration rig’s achievable accuracy. The calibration uncertainty’s validity was investigated experimentally. Two flowmeters were calibrated simultaneously using the rig’s balances to determine the agreement between the obtained K-factors. Finally, the Calibration and Measurement Capability (CMC) was estimated based on the best measurement condition. The result of the experiment shows that it is practical and simpler to fix the collection time to 50 s, giving expanded uncertainty ranging from (0.054 to 0.090)% (k = 2). Therefore, the CMC of the water flow calibration rig was declared as 0.1 % with at least 50 s of collection time. Furthermore, the result shows that the deviation in K-factors was within the calculated uncertainty. Therefore, it confirms consistency in the calibration.