Method and apparatus for measuring concentration of a chemical component in a gas mixture

• US 20040178803A1
• Filed: 04/02/2003
• Published: 09/16/2004
• Est. Priority Date: 03/14/2003
• Status: Active Grant

• Current Assignee: Steris Corporation
• Original Assignee: Steris Corporation
• Inventors: Centanni, Michael A.
• Granted Patent: US 6,946,852 B2
• Time in Patent Office: Days
• US Class Current: 324/662
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 27/228 Circuits therefor measuring capacitance per se G01R27/26
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath

Abstract

A chemical concentration detecting system for determining the relative concentration of a chemical component in a gas mixture. The gas mixture may include chemical components that are antimicrobial chemicals, as well as chemical components that are base chemicals, acting as a diluent for the antimicrobial chemical, or as a vehicle or carrier for the antimicrobial chemical. A capacitor is exposed to the gas mixture, wherein the gas mixture acts as a dielectric between the plates of the capacitor. Permittivity of the dielectric is affected by the relative concentrations of the chemical components, and thus a measurement of the capacitance is used to determine the relative concentration levels of the chemical components in the gas mixture.

Claims

1. A chemical concentration detecting system for determining a concentration of a first chemical component in a gas mixture, comprising:

a capacitor having first and second plates exposed to the gas mixture, said gas mixture being a dielectric therebetween; and

processing means for determining a change in an electrical property of the capacitor, said change in the electrical property varying according to the concentration of the first chemical component in the gas mixture.

2. A chemical concentration detecting system according to claim 1, wherein said first capacitor is selected from the group consisting of:

a parallel plate capacitor, a cylindrical capacitor, and a spherical capacitor.

3. A chemical concentration detecting system according to claim 1, wherein said processing means includes a memory for storing a set of data including capacitance values and corresponding concentration values indicative of the relative concentration of the first chemical component in the gas mixture.

4. A chemical concentration detecting system according to claim 3, wherein said processing means obtains a relative concentration from said set of data, in accordance with said first capacitance.

5. A chemical concentration detecting system according to claim 3, wherein said processing means uses said set of data to interpolate or extrapolate a relative concentration corresponding to the first capacitance.

6. A chemical concentration detecting system according to claim 3, wherein said processing means normalizes said relative concentration to provide an absolute concentration of said first chemical component in the gas mixture.

7. A chemical concentration detecting system according to claim 1, wherein said first chemical component is an antimicrobial chemical.

8. A chemical concentration detecting system according to claim 7, wherein said antimicrobial chemical is a gaseous oxidant.

9. A chemical concentration detecting system according to claim 7, wherein said antimicrobial chemical is selected from a group consisting of:

vaporized hydrogen peroxide, vaporized peracid, vaporized peracetic acid, vaporized bleach, ozone, ethylene oxide, ammonia gas, a halogen containing compound, and mixtures thereof.

10. A chemical concentration detecting system according to claim 9, wherein said halogen of said halogen containing compound is selected from the group consisting of:

chlorine and fluorine.

11. A chemical concentration detecting system according to claim 7, wherein said gas mixture includes a second chemical component that is a base chemical.

12. A chemical concentration detecting system according to claim 11, wherein said base chemical is at least one of:

(a) a diluent for said antimicrobial chemical, and (b) a vehicle for said antimicrobial chemical.

13. A chemical concentration detecting system according to claim 11, wherein said base fluid is selected from a group consisting of:

de-ionized water vapor, distilled water vapor, a vaporized alcohol, and mixtures thereof.

14. A chemical concentration detecting system according to claim 13, wherein said vaporized alcohol is a tertiary alcohol.

15. A chemical concentration detecting system according to claim 1, wherein said system further comprises:

a bridge circuit, wherein said capacitor forms a part of the bridge circuit.

16. A chemical concentration detecting system according to claim 1, wherein said system further comprises:

a charge transfer sensor circuit, wherein said capacitor forms a part of the charge transfer sensor circuit.

17. A method for determining a concentration of a first chemical component in a gas mixture, comprising:

exposing a capacitor, having first and second plates, to the gas mixture, said gas mixture comprising a dielectric therebetween; and

determining a change in an electrical property of the capacitor, said change in the electrical property varying according to the concentration of the first chemical component in the gas mixture.

18. A method according to claim 17, wherein said step of determining the change in an electrical property of the capacitor includes:

accessing pre-stored data including capacitance values and corresponding concentration values indicative of the concentration of the first chemical component in said gas mixture.

19. A method according to claim 18, wherein said step of determining the change in the electrical property of the capacitor includes:

interpolating or extrapolating from the pre-stored data the concentration of the first chemical component in said gas mixture.

20. A method according to claim 17, wherein said processing means normalizes said concentration to provide an absolute concentration of the first chemical component in said gas mixture.

21. A method according to claim 17, wherein said first chemical component is an antimicrobial chemical.

22. A method according to claim 21, wherein said antimicrobial chemical is a gaseous oxidant.

23. A method according to claim 22, wherein said antimicrobial chemical is selected from a group consisting of:

vaporized hydrogen peroxide, vaporized peracid, vaporized peracetic acid, vaporized bleach, ozone, ethylene oxide, ammonia gas, a halogen containing compound, and mixtures thereof.

24. A method according to claim 23, wherein said halogen of said halogen containing compound is selected from the group consisting of:

chlorine and fluorine.

25. A method according to claim 17, wherein said gas mixture includes a second chemical component that is a base chemical.

26. A method according to claim 25, wherein said base chemical is at least one of:

(a) a diluent for said antimicrobial chemical, and (b) a vehicle for said antimicrobial chemical.

27. A method according to claim 25, wherein said base fluid is selected from a group consisting of:

de-ionized water vapor, distilled water vapor, a vaporized alcohol, and mixtures thereof.

28. A method according to claim 27, wherein said alcohol is a tertiary alcohol.

29. A method for determining a concentration of a first chemical component in a gas mixture including at least two antimicrobial chemicals, comprising:

exposing a capacitor, having first and second plates, to the gas mixture, said gas mixture comprising a dielectric therebetween; and

determining a change in an electrical property of the capacitor, said change in the electrical property varying according to the concentration of the first chemical component in the gas mixture.

30. A method according to claim 29, wherein said gas mixture further includes a base chemical.

31. A method according to claim 30, wherein said at least two antimicrobial chemicals include vaporized hydrogen peroxide and ozone, and said base chemical is water vapor.

32. A method according to claim 30, wherein said at least two antimicrobial chemicals include ozone and ethylene oxide, and said base chemical is water vapor.