Patent ID: 9581297
Date: 2017-02-28
CPC Classifications: F17C,G01F,G01N

Claim:
1. A sensor assembly for measuring physical properties of a gas under pressure within a gas cylinder comprising: a gas cylinder body and a valve arrangement defining a fixed internal volume of the gas cylinder, the sensor assembly comprising a housing, a piezoelectric oscillator for immersion in the gas within the gas cylinder and a drive circuit operable to drive the piezoelectric oscillator such that the piezoelectric oscillator resonates at a resonant frequency, the sensor assembly being arranged to determine the density of the gas within the gas cylinder from the resonant frequency of the piezoelectric oscillator when immersed in said gas, wherein, in use, the housing is located within the fixed internal volume of the gas cylinder and comprises a first chamber and a second chamber, the first chamber being in fluid communication with the second chamber and substantially enclosing said piezoelectric oscillator, and the second chamber being in fluid communication with the interior of the gas cylinder; wherein the sensor assembly further comprises a processor arranged to determine, from the density measurement and from the internal volume of said gas cylinder, the mass of the gas within the gas cylinder.