Ultra low power NDIR gas sensor fire detector

• US 7,335,885 B2
• Filed: 03/03/2006
• Issued: 02/26/2008
• Est. Priority Date: 11/21/2005
• Status: Expired due to Fees

• Current Assignee: Airware, Inc.
• Original Assignee: Airwave Technologies Incorporated
• Inventors: Wong, Jacob Y.
• Primary Examiner(s): Porta; David
• Assistant Examiner(s): Malevic; Djura
• Application Number:
  US11/367,440
• Publication Number:
  US 20070114412A1
• Time in Patent Office: 725 Days
• Field of Search: 250/339.15, 250/339.3, 250/339.06, 250/339.03, 250/339.01, 250/339.12, 340/627, 340/328, 340/629
• US Class Current: 250/339.15
• CPC Class Codes: G01J 3/108 for measurement in the infrared range
• CPC Class Codes: G01N 2021/3137 with selection of wavelengths after the sample
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01T 1/00 Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation G01T3/00, G01T5/00 take precedence

Abstract

A fire detector and method for generating an alarm signal in response to a fire uses an NDIR sensor to generate a detector signal based upon one or more absorption bands selected from the 15.1μ absorption band of CO2, the 6.27μ absorption band of H2O and the 4.67μ absorption band for CO and generates an alarm signal when a signal processor receives the detector signal and a preselected criterion is met that is indicative of the onset of a fire based upon an analysis of the detector signal using a detection algorithm that relies upon a trending pattern of the detector signal such as recognizing a substantial drop in the detector signal strength. The fire detector has a waveguide sample chamber (which can be of a re-entrant design) with at least one opening covered by a thin filtering membrane and a heat exchanger thermally connected to the sample chamber with at least one opening covered by another thin filtering membrane. If the NDIR sensor is to detect H2O molecules, the filtering membrane on the heat exchanger (which can be integrally formed out of aluminum with the sample chamber) allows H2O molecules to pass through it and inside surfaces of both the sample chamber and the heat exchanger are coated with a hydrophobic coating to prevent condensation of H2O molecules.

Claims

1. A fire detector, comprising:

an NDIR sensor that generates a detector signal based upon an active source and at least one absorption band selected from the group consisting of a 15.1μ

absorption band of CO₂, a 6.27μ

absorption band of H₂O and a 4.67μ

absorption band for CO; and

a signal processor which receives the detector signal and generates an alarm signal to warn of a fire when a preselected criterion is met;

wherein the NDIR sensor is comprised of;

a waveguide sample chamber with at least one opening covered by a thin filtering membrane that allows CO₂ and H₂O molecules to diffuse freely into and out of the sample chamber but rejects dust and smoke particles from entering the sample chamber;

a heat exchanger thermally connected to the sample chamber with at least one opening covered by at least one second thin filtering membrane that allows preselected molecules to diffuse freely into and out of the heat chamber but rejects dust and smoke particles from entering the heat exchanger; and

an infrared components assembly that houses the active source and a detector which is thermally coupled to an end of the sample chamber; and

wherein the at least one absorption band is the 6.27μ

absorption band of H₂O, the at least one second thin filtering membrane allows H₂O molecules to pass through it and inside surfaces of both the sample chamber and the heat exchanger are coated with a hydrophobic coating to prevent condensation of H₂O molecules.

2. The fire detector of claim 1, wherein the signal processor relies upon a detection algorithm that is based upon a sudden drop of the detector output signal indicative of the onset of a fire.

3. The fire detector of claim 2, wherein the detector signal drop is excess of 20% from the then prevailing signal level.

4. The fire detector of claim 1, the sample chamber and the heat exchanger are integrally formed out of aluminum and the sample chamber is of a reentrant design.

5. The fire detector of claim 1, wherein the detector signal is based upon two or more of the absorption bands selected from the group consisting of the 15.1μ

absorption band of CO₂, the 6.27μ

absorption band of H₂O and the 4.67μ

absorption band for CO.

6. The fire detector of claim 1, wherein the signal processor utilizes synchronized signal processing from the detector signal.

7. The fire detector of claim 6, wherein the signal processor relies upon a detection algorithm that is based upon a synchronized output signal representative of gas concentration of at least one of the gasses selected from the group consisting of CO, CO₂ and H₂O.

8. The fire detector of claim 1, wherein the CO₂ sensor is used as a standalone smoke detector.

9. The fire detector of claim 1, wherein the CO₂ sensor is combined with a smoke detector.

10. A method for generating an alarm signal in response to a fire, comprising the steps of:

using a NOIR sensor with an active source to generate a detector signal based upon at least one absorption band selected from the group consisting of a 15.1μ

absorption band of CO₂, a 6.27μ

absorption band of H₂O and a 4.67μ

absorption band for CO; and

generating the alarm signal when a preselected criterion indicative of the onset of a fire is met based upon an analysis of the detector signal;

wherein the detector signal is based upon two or more of the absorption bands selected from the group consisting of the 15.1μ

absorption band of CO₂, the 6.27μ

absorption band of H₂O and the 4.67μ

absorption band for CO.

11. The method of claim 10, wherein the analysis of the detector signal is performed by using a detection algorithm that relies upon a trending pattern of the detector signal.

12. The method of claim 10, wherein the trending pattern includes a substantial drop in the detector signal strength when a species that is the subject of the at least one absorption band subsequently arrives near the sensor as the fire persists.

13. The method of claim 12, wherein the analysis of the detector signal is performed by using a detection algorithm that analyzes the synchronized output signal.