Design, Development, and Analysis of Ultrasonic Fall Rate Measuring System for Primary Pressure Standard

Pressure balances (PBs) are used as primary, secondary/transfer, and working pressure measuring instruments in National Metrology Institutes and several other calibration and pressure measurement laboratories across the globe. The fall rate measurement of the piston is one of the critical and important parameters and features in the characterization and performance evaluation of the PBs. In this paper, the design and developmental aspects of ultrasonic technique of piston fall rate measurement are reported. The developed system is based on the ultrasonic sensor which measures the piston position with a resolution of 0.01 mm. A software was developed in C# (Visual Studio.NET Framework) which controls and operates the hardware system as well as for recording the piston position as a function of time. The performance evaluation of the developed system has successfully been carried out by measuring the piston fall rate of a national primary hydraulic pressure standard established at National Physical Laboratory (NPL), India. The measurements have been taken as per OIML R-110 guidelines. The fall rate thus obtained is not only found well within the acceptable limits as 1.5 mm/min in the pressure range of (6–500) MPa for PBs having accuracy class of 0.005 but also far better than the requirements as 0.1 mm/min for the pressure range of (40–200) MPa.