Liquid Level Measurement by the Detection of Abrupt Pressure Changes in a Tube in Contact with a Liquid Surface

Abstract

A dynamic tube pressure method was proposed for a liquid level measurement. The reliability of our in-house manufactured prototype level measurement system was investigated for water samples in a vial as a preliminary study. The prototype instrument, equipped with a stepper motor and a differential pressure sensor, was used to measure the travel distance of the tube from an initial zero position to the liquid surface. Unlike a conventional bubbler method, our dynamic tube pressure method is based on the abrupt changes in the tube pressure to directly detect the liquid surface. Optimum conditions were determined from the measurements of the travel distance with different-sized tubes at various ambient base pressures and various descending tube speeds. In addition, we proposed a gravimetric calibration method. In the gravimetric calibration method, the travel distances are used instead of the liquid level, which can be obtained from the measurement data of the travel distance. The travel distance versus the weight calibration curve showed a good linear relationship (R2 = 0.9999), and standard deviations of the travel distance over the whole range of experimental conditions were less than 0.1 mm. In a further study, our present system will also be used in the measurement of density and surface tension by minimizing the contact time with high-temperature and highly-corrosive molten salts.