Simplified beam splitter for IR gas sensor

• US 8,586,930 B2
• Filed: 09/23/2009
• Issued: 11/19/2013
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Haveri, Heikki, Weckstrom, Kurt Peter
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Vu, Midny
• Application Number:
  US12/565,099
• Publication Number:
  US 20100078563A1
• Time in Patent Office: 1,518 Days
• Field of Search: 250/343
• US Class Current: 250/343
• CPC Class Codes: G01J 3/427 Dual wavelengths spectrometry
• CPC Class Codes: G01N 2021/3177 Use of spatially separated filters in simultaneous way
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A non-dispersive single beam detection assembly in an infrared gas analyzer. The detection assembly comprises radiation source(s) providing infrared radiation, a measuring chamber, and a physical beam splitter for dividing said radiation beam into a reflected beam portion and a transmitted beam portion, or for combining a reflected beam portion and a transmitted beam portion into said radiation beam. A measuring detector receives one beam portions, and a reference detector receives another beam portion. Alternatively a measuring/reference detector receives both beam portions. Said transmitted beam portion has a first spectral intensity peak at shorter wavelengths with a first peak wavelength, and said reflected beam portion has a second spectral intensity peak at longer wavelengths with a second peak wavelength. There is a wavelength gap between said second peak wavelength and said first peak wavelength, which gap corresponds a wavelength shift of an optical interference filter with said second peak wavelength as tilted from its perpendicular position to an angled position. Said wavelength gap is at maximum 10% of the second peak wavelength, and at minimum 0.5% of the second peak wavelength.

Claims

1. A non-dispersive single beam detection assembly in an infrared gas analyzer, the assembly comprising:

one wide-band radiation source providing infrared radiation as a beam;

a measuring chamber for a gas mixture with a gas component to be measured;

a physical beam splitter for dividing said radiation beam transmitted through the measuring chamber into a reflected beam portion and a transmitted beam portion;

a measuring detector positioned to receive the reflected beam portion, and a reference detector positioned to receive the transmitted beam portion;

wherein the detection assembly comprises;

a pair of dielectric optical pass-band filters having the same peak wavelength and the same half-bandwidth when perpendicular to the radiation direction, one of the dielectric optical filters positioned to be the physical beam splitter dividing the infrared radiation as a beam, and another of the dielectric optical filters positioned to be an analyzing filter between the physical beam splitter and the measurement detector, wherein said transmitted beam portion has a first spectral intensity peak at shorter wavelengths with a first peak wavelength and a first half-bandwidth, and said reflected beam portion after the analyzing filter has a second spectral intensity peak at longer wavelengths with a second peak wavelength and a second half-bandwidth; and

there is a wavelength gap between said second peak wavelength and said first peak wavelength, which wavelength gap corresponds to one wide-band to a wavelength shift of an optical interference filter with said second peak wavelength as tilted from its perpendicular position to an angled position between 30° and

60°

in respect to radiation direction; and

said wavelength gap is at maximum 10% of the second peak wavelength, and at minimum 0.5% of the second peak wavelength.

2. A non-dispersive single beam detection assembly according to claim 1, wherein an arithmetic sum of the first half-bandwidth and the second half-bandwidth is smaller than two times the wavelength gap.

3. A non-dispersive single beam detection assembly according to claim 1, wherein said dielectric optical filters are narrow-band dielectric optical filters having a second half-bandwidth smaller than 5% of the second peak wavelength, or at maximum 3% of the second peak wavelength.

4. A non-dispersive single beam detection assembly according to claim 1, wherein said second peak wavelength and said second half-bandwidth match with an absorption peak of the gas component to be measured.

5. A non-dispersive single beam detection assembly according to claim 1, wherein said wide-band source has a half-bandwidth larger than the wavelength gap between said second peak wavelength and said first peak wavelength.

6. A non-dispersive single beam detection assembly according to claim 3, wherein said wide-band source has a half-bandwidth larger than the first half-bandwidth, or larger than the second half-bandwidth.

7. An infrared gas analyzer, comprising a non-dispersive single beam detection assembly according to claim 1, wherein said infrared gas analyzer has one measuring chamber for gas mixture, and at least two non-dispersive single beam detection assemblies wherein their infrared radiation pass as beam(s) to said one measuring chamber, whereupon:

in a first non-dispersive single beam detection assembly said second peak wavelength and said second half-bandwidth match with an absorption peak of a first gas component to be measured; and

in a second non-dispersive single beam detection assembly said second peak wavelength and said second half-bandwidth match with an absorption peak of a second gas component to be measured.

8. A non-dispersive single beam detection assembly in an infrared gas analyzer, the assembly comprising:

one or two wide-band radiation sources providing infrared radiation as a beam;

a measuring chamber for a gas mixture with a gas component to be measured;

a physical beam splitter for combining a reflected beam portion and a transmitted beam portion into the radiation beam;

a measuring/reference detector positioned to receive both the reflected beam portion, and the transmitted beam portion that is then transmitted through the measuring chamber;

wherein the detection assembly comprises;

a pair of dielectric optical pass-band filters having the same peak wavelength and the same half-bandwidth when perpendicular to the radiation direction, one of the dielectric optical filters positioned to be the physical beam splitter combining the infrared radiation to a beam, and another of the dielectric optical filters positioned to be an analyzing filter between the physical beam splitter and the radiation source for the reflected beam portion; and

a chopper unit connected to the one or two wide-band radiation sources and to the measuring/reference detector swapping the reflected beam portion and the transmitted beam portion, wherein the transmitted beam portion has a first spectral intensity peak at shorter wavelengths with a first peak wavelength and a first half-bandwidth, and said reflected beam portion has a second spectral intensity peak at longer wavelengths with a second peak wavelength and a second half-bandwidth; and

there is a wavelength gap between said second peak wavelength and said first peak wavelength, which wavelength gap corresponds to a wavelength shift of an optical interference filter with said second peak wavelength as tilted from its perpendicular position to an angled position between 30° and

60°

in respect to a radiation direction; and

said wavelength gap is at maximum 10% of the second peak wavelength, and at minimum 0.5% of the second peak wavelength.

9. A non-dispersive single beam detection assembly according to claim 8, wherein an arithmetic sum of the first half-bandwidth and the second half-bandwidth is smaller than two times the wavelength gap.

10. A non-dispersive single beam detection assembly according to claim 9, wherein said dielectric optical filters are narrow-band dielectric optical filters having a second half-bandwidth smaller than 5% of the second peak wavelength, or at maximum 3% of the second peak wavelength.

11. A non-dispersive single beam detection assembly according to claim 9, wherein said second peak wavelength and said second half-bandwidth match with an absorption peak of the gas component to be measured.

12. A non-dispersive single beam detection assembly according to claim 9, wherein said wide-band source has a half-bandwidth larger than the wavelength gap between said second peak wavelength and said first peak wavelength.

13. A non-dispersive single beam detection assembly according to claim 9, wherein said wide-band source has a half-bandwidth larger than the first half-bandwidth, or larger than the second half-bandwidth.