Measuring and testing – Gas analysis – By vibration
Patent
1993-06-22
1995-02-07
Williams, Hezron E.
Measuring and testing
Gas analysis
By vibration
73 3004, 73 32A, G01N 2902, G01N 400, G01L 908
Patent
active
053867149
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB91/02156 filed on Dec. 5, 1991.
This invention relates to sensors, and is more particularly but not exclusively concerned with gas density sensors suitable for use in domestic gas metering.
There have been several proposals recently for domestic gas meters incorporating solid state or other electrically operated devices which sense volumetric flow rate. However, it is now increasingly being thought desirable that domestic gas metering should be based upon a mass flow rate measurement rather than a volumetric flow rate measurement. This can be achieved by measuring the density of the gas as well as its volumetric flow rate, and then combining the two measurements.
There exists a need, therefore, for a sensor which can be used to measure gas density in a domestic gas metering context. However, use in this context requires that the sensor should be capable of being inexpensively mass produced, and should use as little or less power for its operation as the associated solid state or other volumetric flow rate sensing device. It is an object of the present invention to provide such a sensor.
According to one aspect of the present invention, there is provided a sensor for use in determining the density of a gas, the sensor comprising: means being at least partly movable within the cavity; in a mode in which the dividing means vibrates with the gas; gas; said signal representative of the velocity of sound in the gas.
The excitation means may be additionally arranged to excite the gas in the cavity into resonant vibration in a second mode in which the dividing means does not significantly take part in the vibration of the gas, and the pick-up means may be arranged to sense the frequency of said second mode of resonant vibration, the frequency of said second mode of resonant vibration serving as said signal representative of the velocity of sound in the gas.
Alternatively, the signal producing means may comprise 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 resonant vibration of the gas in the second cavity, the frequency of resonant vibration of the gas in the second cavity serving as said signal representative of the velocity of sound in the gas.
According to a second aspect of the present invention, there is provided a sensor for use in determining the density of a gas, the sensor comprising: 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 second modes of vibration;
In a preferred embodiment of this second aspect of the invention, the position of the diaphragm within the cavity and the modes of vibration of the gas are selected such that the first mode has an antinode (or region of maximum gas displacement) at the diaphragm, and the second mode has a node (or region of minimum gas displacement) at the diaphragm. Thus the diaphragm is preferably positioned substantially midway between the opposite ends of the cavity, whereby the two chambers are of substantially equal length, and the first and second modes are preferably modes 1 and 2 respectively.
According to a third aspect of the invention, there is provided a sensor for use in determining the density of a gas, the sensor comprising: to be determined; resonant vibration in a mode in which the diaphragm vibrates with the gas; in the first cavity; resonant vibration; and in the second cavity;
In a preferred embodiment of this third aspect of the invention, the dimensions of the second cavity and/or the mode of vibration of the gas therein are selected such that the respective frequencies of vibration of the gas in the two cavities are similar. Additionally, the position of the diaphragm within the first cavity and the mode of vibration of the gas in the first cavity are again selected such that the mode has an antinode at the diaph
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patent: 3295360 (1967-01-01), Dimeff
patent: 4262523 (1981-04-01), Stansfeld
patent: 4872335 (1989-10-01), Tsuruoka et al.
patent: 4961345 (1990-10-01), Tsuruoka et al.
patent: 5159843 (1992-11-01), Shakkottai et al.
Asman Sanford J.
Roskos Joseph W.
Schlumberger Industries Limited
Williams Hezron E.
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