Infrared optical gas-measuring system

• US 5,942,755 A
• Filed: 09/02/1997
• Issued: 08/24/1999
• Est. Priority Date: 02/19/1997
• Status: Expired due to Fees

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Dragerwerk AG
• Inventors: Dreyer, Peter
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): GAGLIARDI, ALBERT J
• Application Number:
  US08/920,127
• Time in Patent Office: 721 Days
• Field of Search: 250/339.13, 250/343, 250/339.12
• US Class Current: 250/339.13
• CPC Class Codes: G01J 3/108 for measurement in the infrared range
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

An infrared optical gas-measuring system with two infrared radiation sources (1, 2) and with at least one multispectral sensor (5). The system is suitable for determining the concentrations of different components of a gas flow. The two infrared radiation sources (1, 2) radiate in different spectral ranges with two different cycle frequencies f₁, f₂. The rays emitted are first passed through a radiation coupler (3), after which they pass through the gas flow to be measured, which is limited by windows (8), at right angles to the direction of flow. The rays finally enter a multispectral sensor (5), of which there is at least one, for measuring the intensity.

Claims

1. An infrared optical gas-measuring system, comprising:

two infrared radiation sources radiating in different spectral ranges with two different cycle frequencies f₁, f₂ ;

a radiation coupler, emitted rays from said radiation sources being first passed through said radiation coupler;

sample holding means for holding a gas flow to be measured, said holding means being limited by windows, said emitted rays passing through said gas flow, at right angles to a direction of said gas flow, subsequent to passing through said radiation coupler;

a multispectral sensor, including at least four infrared radiation detectors, for the measurement of the intensity of said emitted rays, after said emitted rays have passed through said gas flow.

2. The infrared optical gas-measuring system in accordance with claim 1, wherein a first of said infrared radiation sources radiates in the spectral range of 7.5 to 14 μ

m and a second of said infrared radiation sources radiates in the spectral range of 2.5 to 4.3 μ

m, and that a cycle frequency f₂ of said second infrared radiation source is higher than a cycle frequency f₁ of said first infrared radiation source.

3. The infrared optical gas-measuring system in accordance with claim 2, wherein said gas flow is a respiratory flow and said first infrared radiation source measures a concentration of gaseous anesthetics in the respiratory flow and said second infrared radiation source measures a concentrations of CO₂ and N₂ O in the respiratory flow, resolved for individual breaths.

4. The infrared optical gas-measuring system in accordance with claim 1 wherein said multispectral sensor has a radiation mixer and exactly four infrared radiation detectors with corresponding different upstream infrared filters adapted to the absorption bands of the gases to be measured.

5. The infrared optical gas-measuring system in accordance with claim 1 wherein said multispectral sensor is provided with at least one semiconductor detector.

6. The infrared optical gas-measuring system in accordance with claim 1 wherein another multispectral sensor is provided such that two multispectral sensors are used and the radiation from said two infrared radiation sources is split by a beam splitter between said two multispectral sensors corresponding to the wavelength ranges of said two infrared radiation sources.

7. The infrared optical gas-measuring system in accordance with claim 1 wherein said two multispectral sensors are arranged at right angles to one another.

8. An infrared optical gas-measuring system, comprising:

a first infrared radiation source radiating in a first spectral range with a first cycle frequency f₁ and having a first time constant, said first spectral range including a characteristic wavelength of a first gas;

a second infrared radiation source radiating in a second spectral range with a second cycle frequency f₂ and having a second time constant, said second spectral range including a characteristic wavelength of a second gas, said first cycle frequency and said first time constant being different from said second cycle frequency and said second time constant;

a radiation coupler combining radiation from said first and second radiation sources into a combined radiation beam;

sample holding means for holding a gas flow to be measured in said combined radiation beam;

a multispectral sensor, including a plurality of infrared radiation detectors, for the measurement of the intensity of said characteristic wavelengths of said first and second gases after said combined radiation beam has passed through said gas flow.

9. A system in accordance with claim 8, wherein:

said multispectral sensor using a measurement method for said second gas requiring a second gas measurement cycle frequency;

said time constant of said first radiation source producing a modulation amplitude at said second gas measurement cycle frequency below a require signal-to-noise ratio;

said second radiation source being incapable of producing said characteristic wavelength of said first gas.

10. A system in accordance with claim 8, wherein:

said first spectral range includes characteristic wavelengths for a first set of gases and a reference wavelength;

said second spectral range includes characteristic wavelengths for a second set of gases;

said multispectral sensor and said infrared radiation detectors measure intensity of said characteristic wavelengths of said first and second set of gases and a reference wavelength after said combined radiation beam has passed through said gas flow.

11. A system in accordance with claim 10, wherein:

said first set of gases include gaseous anesthetics;

said second set of gases include CO₂ and N₂ O.

12. A system in accordance with claim 8, wherein:

said second radiation source is a microincandescent lamp with a tungsten filament sealed in a quartz bulb, said microincandescent lamp operates with a filament temperature of approximately 2,000 degrees Celsius;

a modulation amplitude of said microincandescent lamp being limited by inertia of said filament.

13. A system in accordance with claim 9, wherein:

said second radiation source is a microincandescent lamp with a tungsten filament sealed in a quartz bulb, said microincandescent lamp operates with a filament temperature of approximately 2,000 degrees Celsius;

a modulation amplitude of said microincandescent lamp being limited by inertia of said filament.

14. A system in accordance with claim 13, wherein:

said first spectral range includes characteristic wavelengths for a first set of gases and a reference wavelength;

said second spectral range includes characteristic wavelengths for a second set of gases;

said multispectral sensor and said infrared radiation detectors measure intensity of said characteristic wavelengths of said first and second set of gases and a reference wavelength after said combined radiation beam has passed through said gas flow;

said first set of gases include gaseous anesthetics;

said second set of gases include CO₂ and N₂ O.