Abstract: The apparatus consists of a mechanical acoustical driver producing sound vibrations in a fluid, such as a liquid or gas, within an enclosed space. A pickup transducer positioned within the tank measures the sound vibrations of the gas within the tank and transmits the same to an amplifier and a low pass filter. Either the same or another transducer positioned in the tank measures static pressure P output of which is amplified. A divider circuit receives the dynamic pressure signal and static pressure signal and provides electrical signal E proportional to (.DELTA.P/P). A differential amplifier receives the reference signal Erf and the signal E and supplies the error signal (Erf-E) to a gain controlled amplifier. The gain controlled amplifier amplifies the AC signal proportional to (Erf-E). The driver generates .DELTA.P in the tank proportional to the output of the gain controlled amplifier.

Abstract: The apparatus consists of a mechanical acoustical driver producing sound vibrations in a fluid, such as a liquid or gas, within an enclosed space. A pickup transducer positioned within the tank measures the sound vibrations of the gas within the tank and transmits the same to a lock-in amplifier and a low pass filter. The outputs of the lock-in amplifier and low pass filters are fed to differential amplifiers which amplify the difference between the dynamic fluid pressure changes caused by the sound vibrations and the static pressure. An acoustical resistor is positioned between the pickup transducer and the wall of the enclosed space for providing a fluid passage way therethrough. The acoustic resistor in conjunction with a nonlinear circuit element mounted at the output of the differential amplifiers linearizes the output of the apparatus providing accurate measurements of the material at both extremes of either very small volume or very large volume in the enclosed space.