Optical gas analyzer

• US 5,739,535 A
• Filed: 10/10/1996
• Issued: 04/14/1998
• Est. Priority Date: 10/25/1995
• Status: Expired due to Fees

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Dragerwerk AG
• Inventors: Koch, Edmund, Al-Soufi, Wajih, Rosinke, Otto, Dreyer, Peter, Peter, Gerd
• Primary Examiner(s): Glick, Edward J.
• Assistant Examiner(s): Jiron, Darren M.
• Application Number:
  US08/731,204
• Time in Patent Office: 551 Days
• Field of Search: 250/339.13, 250/339.09, 250/343, 250/351, 250/338.3, 250/252.1 A, 250/252.1 R, 356/437
• US Class Current: 250/339.13
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

An optical gas analyzer for measuring the percentage of components in a gas phase by IR absorption, containing a power source, a measuring path containing the gas sample, a photoelectric receiver with an evaluation circuit arranged downstream of it, which receiver detects the IR radiation from the measuring path, and a plurality of filters, which can be introduced one after another into the beam path at a predetermined filter change frequency f, wherein measured signals belonging to the filters are sent by the receiver due to the radiation extinction in the measuring path, is to be improved such that different components in the gas sample can be detected in a simple manner and at good selectivity. To accomplish this object, the receiver is a pyroelectric detector, the evaluation circuit has elements for the evaluation of the voltage signal of the pyroelectric detector, the filter change frequency f is set at a value in the range of the declining branch of the frequency response of the voltage signal, and the pyroelectric detector is selected to be such that the declining branch of the voltage signal has a decline of -20 dB per decade.

Claims

1. An optical gas analyzer comprising:

a radiation source;

a measuring chamber capable of containing a gas sample, said measuring chamber receiving radiation from said radiation source;

a plurality of filters positionable in a beam path from said radiation source to said measuring chamber;

a photoelectric receiver receiving radiation from said radiation source through said measuring chamber, said photoelectric receiver generating a voltage signal in proportion to a received amount of said radiation, said voltage signal of said photoelectric receiver having a frequency response with a declining branch;

filter wheel means for moving said plurality of filters into and out of said beam path at a filter change frequency f, said filter change frequency f being in said declining branch of said frequency response.

2. An analyzer in accordance with claim 1, wherein:

said photoelectric receiver is a pyroelectric detector and said voltage signal of said pyroelectric detector is in proportion to IR radiation;

a first of said plurality of filters causes a first measured signal due to radiation extinction in said measuring chamber and a second of said plurality of filters causes a second measured signal for measuring anesthetics due to radiation extinction in said measuring chamber, said filters having wavelengths between 7 and 18 microns;

an evaluating circuit means connected to said photoelectric receiver and for evaluating said voltage signal.

3. An analyzer in accordance with claim 2, wherein:

said measured signals of said first and second filters are for measuring one of sevoflurane, desflurane, halothane, enflurane and isoflurane.

4. An analyzer in accordance with claim 2, wherein:

a third of said plurality of filters causes a third measured signal due to radiation extinction in said measuring chamber.

5. An analyzer in accordance with claim 2, wherein:

said evaluation circuit means includes a field-effect transistor (FET) positioned downstream of said pyroelectric detector and acts as an impedance converter with a high-ohmic gate resistor acting as a current-voltage converter.

6. An analyzer in accordance with claim 2, wherein:

a difference between said wavelengths of said plurality of filters is not less than 0.10 μ

m, and that a difference between a highest and lowest wavelength of said plurality of filters is less than 9 μ

m.

7. An analyzer in accordance with claim 2, wherein:

said first of said plurality of filters has a wavelength of substantially 8.21 μ

m, said second of said plurality of filters has a wavelength of substantially 8.4 μ

m, and a third of said plurality of filters has a wavelength of substantially 8.61 μ

m, said plurality of filters includes a reference filter for forming a reference measured signal for said measured signals.

8. An analyzer in accordance with claim 7, wherein:

a wavelength of said reference filter is substantially 10.5 μ

m.

9. An analyzer in accordance with claim 7, wherein:

said plurality of filters includes another reference filter with a wavelength of substantially 3.69 μ

m for forming another reference signal for measuring one of N₂ O and carbon dioxide.

10. An analyzer in accordance with claim 2, wherein:

a third of said plurality of filters has a wavelength of substantially 3.9 μ

m and is provided for measuring N₂ O.

11. An analyzer in accordance with claim 10, wherein:

a fourth of said plurality of filters has a wavelength of substantially 4.26 μ

m and is provided for measuring carbon dioxide.

12. An analyzer in accordance with claim 2, wherein:

a difference between said wavelengths of said plurality of filters is not less than 0.10 μ

m, and that a difference between a highest and lowest wavelength of said plurality of filters is less than 9 μ

m for measuring one of sevoflurane, desflurane, halothane, enflurane, or isoflurane.

13. An analyzer in accordance with claim 1, wherein:

a length of said measuring chamber is 5 to 15 mm.

14. An analyzer in accordance with claim 1, wherein:

said declining branch of the said voltage signal has a decline of -20 dB per decade.

15. A process for identification of a component in a gas sample from a group of N possible components, the process comprising the steps of:

providing an infrared gas analyzer with two filters and a measuring chamber;

generating a calibration curve for each of the N possible components by introducing respective gas samples containing a known percentage of a respective one of the N possible components into the said measuring path, recording measured signals with each of said filters and relating said measured signals to percentages as characteristic values;

recording at least one measured signal from the gas sample with each of said filters;

determining corresponding characteristic values of the N components for each said measured signal from said calibration curves;

selecting one of the N possible components at which the determined characteristic values for each filter are located within a predetermined tolerance range as the component to be identified.