WO1996000374A1 - Procede de test fonctionnel de capteurs de gaz toxiques - Google Patents

Procede de test fonctionnel de capteurs de gaz toxiques Download PDF

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Publication number
WO1996000374A1
WO1996000374A1 PCT/US1994/007195 US9407195W WO9600374A1 WO 1996000374 A1 WO1996000374 A1 WO 1996000374A1 US 9407195 W US9407195 W US 9407195W WO 9600374 A1 WO9600374 A1 WO 9600374A1
Authority
WO
WIPO (PCT)
Prior art keywords
toxic gas
absorption
sensor
sample
toxic
Prior art date
Application number
PCT/US1994/007195
Other languages
English (en)
Inventor
Jacob Yauman Wong
Original Assignee
Telaire Systems, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US07/894,919 priority Critical patent/US5335534A/en
Priority claimed from US07/894,919 external-priority patent/US5335534A/en
Application filed by Telaire Systems, Inc. filed Critical Telaire Systems, Inc.
Priority to PCT/US1994/007195 priority patent/WO1996000374A1/fr
Priority to AU71784/94A priority patent/AU7178494A/en
Publication of WO1996000374A1 publication Critical patent/WO1996000374A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis

Definitions

  • the present invention relates to a method for determining whether a toxic gas sensor is functioning properly at any particular time. Surprisingly, no toxic gas is needed to perform the test.
  • Toxic gas sensors are widely used for sensing a build-up in the concentration of a toxic gas, for example, carbon monoxide, methane, hydrogen sulfide, and others, to protect the lives of persons who are exposed to the toxic gas. It is essential that the toxic gas sensor operate reliably, and to this end it is desirable to test the operation of the sensor from time to time.
  • a toxic gas for example, carbon monoxide, methane, hydrogen sulfide, and others
  • the senor is calibrated by exposing it to an accurately controlled concentration of the toxic gas and noting the output reading of the sensor.
  • the sensor is transported, handled, and put into daily use where it is exposed to a number of environmental stresses.
  • the sensors may be found to have changed due to aging, due to chemical reactions with environmental elements such as moisture, particulates, smoke, various gases, insects, soot, and oil vapors, and due to chemical instabilities. In most instances, these environmental stresses affect the functioning and sensitivity of the sensors.
  • the present invention is directed to a method for testing the operation of a toxic gas sensor without using any toxic gas.
  • Each toxic gas has absorption bands at characteristic wavelengths in which the toxic gas absorbs radiation. Normally those absorption bands lie in the infrared portion of the electromagnetic spectrum. Because the bands are related to the molecular structure of the gas, each gas is characterized by its own peculiar set of absorption bands.
  • a well known technique for detection of a gas is to monitor the absorption of radiation by one of its absorption bands. When the gas to be detected is present, some of the radiation is absorbed. The absorption is measured and is related to the concentration of the gas. This is called the NDIR (Non-Dispersive InfraRed) technique.
  • NDIR Non-Dispersive InfraRed
  • the set of absorption bands belonging to a particular gas is unique, it is not unusual for a few of the spectral bands for different gases to overlap. Ordinarily, such overlapping is considered undesirable because if the measurement is carried out in such an overlapping band, it is not clear which of several gases produced the observed absorption. This problem is referred to as interference or non
  • carbon monoxide has an absorption band centered at 4.67 microns in the infrared portion of the spectrum.
  • CO carbon monoxide
  • C0 2 carbon dioxide
  • N 2 0 nitrous oxide
  • Figure 1 depicts these three absorption bands.
  • an NDIR sensor devised for detecting carbon monoxide by using the 4.67 absorption band of carbon monoxide may yield erroneous results unless special precautions are taken. It is well known that carbon dioxide gas is present in the atmosphere, typically in concentrations as great as several thousand parts per million. Unless special precautions are taken to keep carbon dioxide out of the sample chamber, the attempted measurement of carbon monoxide may be inaccurate. On the other hand, nitrous oxide N 2 0 gas is present in the atmosphere only in trace quantities and for many purposes this would not be a problem.
  • the presence of an interfering gas requires the addition of a reference channel to the sensor so as to compensate the readings for the presence of the interfering gas.
  • the present inventor has turned this overlapping of spectral bands, normally considered disadvantageous, into a very helpful technique for checking the operation of an NDIR sensor to assure that it is operating properly.
  • Figure 1 is a graph showing the absorption spectra of carbon monoxide, carbon dioxide, and nitrous oxide versus wavelength.
  • the present invention is based on the fact that the detector of an NDIR instrument responds to the total radiation falling upon it.
  • the instrument registers the total amount of absorption that has occurred, but it cannot tell which of two interfering gases caused an observed absorption.
  • the present inventor has been able to turn this fact into an advantage when the operation of a toxic gas senor is to be checked. It is necessary first to find a non-toxic gas that interferes with the toxic gas to be measured by having an absorption band that overlaps the absorption band of the toxic gas.
  • the non-toxic gas carbon dioxide has an absorption band that overlaps the absorption band of the toxic gas carbon monoxide.
  • CO toxic gas carbon monoxide
  • carbon dioxide has an absorption band centered at 4.26 microns that partially overlaps the 4.67 micron absorption band of carbon monoxide.
  • nitrogen gas (N 2 ) has no absorption band that overlaps the 4.67 micron band of carbon monoxide. Therefore, one could mix carbon dioxide gas with nitrogen gas to produce a non- toxic testing sample.
  • the interference of carbon dioxide gas on the carbon monoxide absorption band being detected is such that for every 100 parts per million (ppm) of carbon dioxide the instrument registers four parts per million of carbon monoxide gas.
  • a safe gas carbon dioxide
  • a toxic gas carbon monoxide
  • the method of the present invention should find application wherever it is desired to test sensors of toxic gases to verify that the sensors are functioning accurately.
  • the method is simple to use and requires no toxic gas.

Landscapes

  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

On peut contrôler le fonctionnement correct d'un capteur de gaz toxiques à absorption non dispersive dans l'infrarouge (NDIR) à l'aide d'un gaz non toxique présentant une bande d'absorption chevauchant la bande d'absorption utilisée pour mesurer le gaz toxique. Le capteur NDIR ne peut distinguer lequel des deux gaz est responsable de l'absorption observée de rayonnement dans le capteur. Etant donné que des détecteurs de gaz toxiques fonctionnent habituellement à de faibles niveaux de concentration, le degré de chevauchement entre la bande d'absorption du gaz toxique et le gaz non toxique peut être relativement réduit, puisqu'une plus grande concentration du gaz non toxique peut être utilisée sans effet négatif. On peut appliquer le procédé à des capteurs de détection, par exemple, de monoxyde de carbone ou de méthane.
PCT/US1994/007195 1992-06-08 1994-06-27 Procede de test fonctionnel de capteurs de gaz toxiques WO1996000374A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US07/894,919 US5335534A (en) 1992-06-08 1992-06-08 Functional testing method for toxic gas sensors
PCT/US1994/007195 WO1996000374A1 (fr) 1992-06-08 1994-06-27 Procede de test fonctionnel de capteurs de gaz toxiques
AU71784/94A AU7178494A (en) 1992-06-08 1994-06-27 Functional testing method for toxic gas sensors

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/894,919 US5335534A (en) 1992-06-08 1992-06-08 Functional testing method for toxic gas sensors
PCT/US1994/007195 WO1996000374A1 (fr) 1992-06-08 1994-06-27 Procede de test fonctionnel de capteurs de gaz toxiques

Publications (1)

Publication Number Publication Date
WO1996000374A1 true WO1996000374A1 (fr) 1996-01-04

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1994/007195 WO1996000374A1 (fr) 1992-06-08 1994-06-27 Procede de test fonctionnel de capteurs de gaz toxiques

Country Status (1)

Country Link
WO (1) WO1996000374A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6263839A (ja) * 1985-08-16 1987-03-20 Yokogawa Electric Corp ガス分析計における自動校正方法及びその装置
US5077469A (en) * 1989-09-30 1991-12-31 Hartmann & Braun Ag Calibrating a nondispersive infrared gas analyzer
US5335534A (en) * 1992-06-08 1994-08-09 Gaztech International Corporation Functional testing method for toxic gas sensors

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6263839A (ja) * 1985-08-16 1987-03-20 Yokogawa Electric Corp ガス分析計における自動校正方法及びその装置
US5077469A (en) * 1989-09-30 1991-12-31 Hartmann & Braun Ag Calibrating a nondispersive infrared gas analyzer
US5335534A (en) * 1992-06-08 1994-08-09 Gaztech International Corporation Functional testing method for toxic gas sensors

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
APPLIED OPTICS, Volume 15, Number 12, issued December 1976, E.R. MURRAY et al., "Remote Measurement of HC1, CH4 and N20 Using a Single-Ended Chemical-Laser Lidar System", pages 3140-3148. *

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