Simplified beam splitter for IR gas sensor
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.
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.