Method of and apparatus for measuring the molecular weight of a gas

Patent metadata

Field	Value
Publication number	US-9459191-B2
Application number	US-201113989232-A
Country	US
Kind code	B2
Filing date	Nov 28, 2011
Priority date	Nov 29, 2010
Publication date	Oct 4, 2016
Grant date	Oct 4, 2016

Abstract

There is provided a meter for measuring the molecular weight of a gas, the meter comprising a housing having an inlet and an interior for receiving said gas to be measured, a sensor assembly comprising a high-frequency planar piezoelectric crystal oscillator located within said housing so that, in use, the piezoelectric crystal oscillator is in contact with said gas, said sensor assembly being arranged: to drive the piezoelectric crystal oscillator such that the piezoelectric crystal oscillator resonates at a single resonant frequency; to measure said single resonant frequency of said piezoelectric crystal oscillator to determine the density of gas; and to determine from the density, determined or pre-determined pressure of the gas and determined or pre-determined temperature of the gas, the molecular weight of the gas.

First claim

The invention claimed is:

1. A method of measuring the molecular weight of a gas, the method comprising:
a) driving single high-frequency planar piezoelectric crystal oscillator in contact with the gas utilizing a drive circuit, such that the piezoelectric crystal oscillator resonates at a single resonant frequency despite changes in the Q factor of the piezoelectric oscillator; and
b) measuring said single resonant frequency of said piezoelectric crystal to determine the density of gas; and
c) determining the molecular weight of the gas from the density, a determined or pre-determined pressure of the gas, and a determined or pre-determined temperature of the gas based on a change in frequency being linearly proportional to a change in density.

2. A method according to claim 1 , further comprising measuring the pressure of the gas.

3. A method according to claim 2 , wherein the pressure of the gas is measured using an electronic pressure sensor.

4. A method according to claim 1 , wherein the pre-determined pressure of the gas is the fixed output pressure of a gas regulator located upstream of said oscillator.

5. A method according to claim 1 , wherein the pre-determined pressure of the gas is atmospheric pressure.

6. A method according to claim 1 , further comprising measuring the temperature of the gas with a temperature sensor.

7. A meter for measuring the molecular weight of a gas, the meter comprising a housing having an inlet and an interior for receiving said gas to be measured, a sensor assembly comprising a single high-frequency planar piezoelectric crystal oscillator located within said housing so that, in use, the single piezoelectric crystal oscillator is in contact with said gas, said sensor assembly being arranged:
to drive the piezoelectric crystal oscillator such that the piezoelectric crystal oscillator resonates at a single resonant frequency despite changes in the Q factor of the piezoelectric oscillator;
to measure said single resonant frequency of said piezoelectric crystal oscillator to determine the density of gas; and
to determine from the density, a determined or pre-determined pressure of the gas, and a determined or pre-determined temperature of the gas based on a change in frequency being linearly proportional to a change in density, the molecular weight of the gas.

8. A meter according to claim 7 , wherein the sensor assembly comprises a drive circuit comprising a Darlington pair arranged in a feedback configuration from a common emitter amplifier.

9. A meter according to claim 7 , further comprising a pressure sensor for measuring the pressure of the gas.

10. A meter according to claim 9 , wherein said pressure sensor is an electronic pressure sensor.

11. A meter according to claim 7 , wherein the meter is located downstream of a fixed pressure regulator, wherein the pressure of the gas has a predetermined value based on the output of said fixed pressure regulator.

12. A meter according to claim 7 , further comprising a restricted orifice upstream of said inlet and an outlet to atmosphere downstream of said inlet, wherein said pre-determined pressure of gas is atmospheric pressure.

13. A meter according to claim 7 , wherein the sensor assembly further comprises a temperature sensor.

14. A method or meter according to claim 7 , wherein said piezoelectric crystal oscillator comprises at least two planar tines.

15. A meter according to claim 7 , wherein said piezoelectric crystal oscillator has a resonant frequency of 32 kHz or greater.

16. A computer program product executable by a programmable processing apparatus, comprising one or more software portions for performing the steps of claim 1 .

17. A computer usable storage medium having a computer program product according to claim 16 stored thereon.

18. A method according to claim 1 , wherein said piezoelectric crystal oscillator comprises at least two planar tines.

19. A method according to claim 1 , wherein said piezoelectric crystal oscillator has a resonant frequency of 32 kHz or greater.

Assignees

• Downie Neil Alexander
• Air Prod & Chem

Inventors

• Downie Neil Alexander

Classifications

• G01N2291/021

  Gases · CPC title

• G01N2291/02818

  Density, viscosity · CPC title

• G01N29/036 Primary

  by measuring frequency or resonance of acoustic waves · CPC title

• G01N9/002 Primary

  using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis (G01N9/34 takes precedence) · CPC title

• G01N9/00

  Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity · CPC title