Range Extension down to 1 mL/h of Micro Liquid Flow Calibration Facility at CSIR-NPL, India

The present paper outlines the efforts for the range extension of the existing CSIR-NPL micro liquid flow calibration facility (having flow range of (10–1500) mL/h) from 10 mL/h  down to 1 mL/h and its metrological assessment. The major challenges in this study are evaporation, flow rate stability and repeatability. To reduce the evaporation, a small quantity of mineral oil was mixed with distilled water in the collection beaker, forming a thin layer of oil over the beaker water surface, leading to reduced evaporation. For improving the flow stability and repeatability, a high-accuracy syringe pump with a 10 mL syringe and a precision balance of 82 g capacity have been used. The static weighing with standing start and standing finish method has been used for flow measurement. The expanded uncertainty (at k = 2 for approx. 95% confidence level) of the facility is found to be (1.0–0.30) % in the flow range (1–1500) mL/h for both totalized volume and volume flow rate measurements. Thus, CSIR-NPL is now able to maintain NMI status in micro liquid flow measurement.