Resonant cavity gas density sensor

A sensor for use in determining the density of a gas, the sensor comprising:

• a cavity arranged to receive the gas whose density is to be determined;
• and
• a diaphragm dividing the cavity into two distinct chambers;
• the sensor being characterised by:
• excitation means for exciting the gas in the cavity into resonant vibration in a first mode in which the diaphragm vibrates with the gas, and in a second mode in which the diaphragm does not significantly take part in the vibration of the gas;
• and
• pick-up means for sensing the respective frequencies of the first and second modes of vibration;
• whereby the density of the gas may be determined from said frequencies.

A sensor for use in determining the density of a gas, the sensor comprising:

• a first cavity arranged to receive a gas whose density is to be determined;
• and
• a diaphragm dividing the first cavity into two distinct chambers;
• the sensor being characterised by:
• first excitation means for exciting the gas in the first cavity into resonant vibration in a mode in which the diaphragm vibrates with the gas;
• first pick-up means for sensing the frequency of the vibration of the gas in the first cavity;
• a second cavity arranged to receive the gas whose density is to be determined;
• second excitation means for exciting the gas in the second cavity into resonant vibration;
• and
• second pick-up means for sensing the frequency of the vibration of the gas in the second cavity;
• whereby the density of the gas may be determined from said frequencies.