Gas Flowrate Calibration Using a Piston Prover and A Laser Doppler Displacement Meter

摘要

A Laser Doppler Displacement Meter (LDDM) is used to improve the performance of a mercury sealed piston device for the calibration of gas flow at low flow rates. With a 0.5 inch retroreflector at the center of the piston and a LDDM laser head at the top of the tube, the piston displacement and its corresponding velocity can be measured with a resolution down to 10 nm and a data rate of up to 800,000 data/sec. The advantage of using the LDDM is fast and accurate readings not affected by piston rocking or sticking. Preliminary test data have shown an accuracy of 0.2% of reading. Based on an error budget calculation, an accuracy of 0.1% of reading can be readily achieved with better pressure and temperature sensors.