Acoustic Bridge Volumeter

A new method is proposed for measuring the volume of a container using gas compressibility laws. A container whose volume is to be measured, a reference container of known volume and a bypass tube are so arranged that their electric equivalents form a bridge circuit. A loudspeaker is mounted so that one face thereof applies alternating compression to the volume undergoing measurement, while the opposite face applies compression of opposite phase to the reference volume. These compressions cause sound pressure within the two volumes and the bypass tube. And there exists within the bypass tube the balance point where the sound pressure vanishes: the bypass tube forms the ratio arms of the acoustic bridge circuit. The position of this balance point is a function of the ratio of the two volumes. Furthermore, it is affected by none of the static pressure, the gas composition, the temperature and the compression amplitude. The volume to be measured can be obtained by simple calculation from the position of the balance point. An experimental apparatus was built; that included a container whose volume could be varied from 2 to 10 [×10-3m3] by pouring water and an electret microphone for picking up the sound pressure along the bypass tube. The proposed method has been verified experimentally with this apparatus.