Method and arrangement for determining the concentration of a gas component in a gas mixture

A method for non-dispersive analysis of gas mixtures for determining the concentration of such a first gas component in a gas mixture, whose absorbance may be influenced by other gas components of said gas mixture, said method comprising the steps of:

• (A) providing a radiation source emitting radiation over a wavelength range along a certain radiation path through the gas mixture;
• (B) providing to said radiation path a first extension radiation path with an optical first bandpass filter having a first transmission band within an absorption band of said first gas component;
• (C) providing a first detector for detecting a first intensity of radiation passing along said radiation path and said first extension radiation path, this first intensity producing a first measurement signal when the gas mixture in the radiation path is the gas mixture to be analyzed;
• (D) providing to said radiation path a selective beam splitter having a second transmission range, which comprises at least the first transmission band;
• (E) providing to said radiation path a second extension radiation path with an unlimited transmission;
• (F) providing a second detector for detecting a second intensity of radiation passing along said radiation path and said second extension radiation path, this second intensity producing a second measurement signal when the gas mixture in the radiation path is the gas mixture to be analyzed;
• (G) determining a concentration value for the first gas component in the gas mixture to be analyzed using a predetermined formula or predetermined formulas, which take(s) as inputs at least said first measurement signal and said second measurement signal;
• and
• (H) selecting the second transmission range so that it extends substantially or entirely outside the absorption bands of said first gas component and so that it comprises a second absorption band of a certain second gas component causing a distortion in the absorption band of said first gas component, the strength of the second absorption band being substantially less than the strength of the first absorption band.

An apparatus for providing an indication of the concentration of a first gas in a mixture of gases, said apparatus employing non-dispersive absorption measurement of radiation and comprising:

• a sample chamber for containing the gas mixture;
• a radiation source for transmitting radiation through the gas mixture;
• a first optical transmission band filter and a first radiation detector for detecting the intensity of the radiation exiting the sample chamber at a first transmission band, which comprises a first absorption spectrum band of the first gas;
• a second optical transmission band filter and a second detector for detecting the intensity of the radiation exiting the sample chamber at a second transmission band;
• concentration determination means, which are arranged to determine the concentration of the first gas in the gas mixture using a certain concentration formula or formulas and using the detected intensity of the radiation at the first transmission band and at the second transmission band, whereupon the second transmission band is substantially or entirely outside the absorption bands of said first gas component and comprises a second absorption band of a certain gas component causing a distortion in the absorption band of the first gas component, the strength of the second absorption band being substantially less than the strength of the first absorption band.

An apparatus for providing an indication of the concentration of a first gas in a mixture of gases, said apparatus employing non-dispersive absorption of radiation and comprising:

• a sample chamber for containing the gas mixture;
• a radiation source for transmitting radiation through the gas mixture;
• first radiation detector for detecting the intensity of the radiation exiting the sample chamber at a first wavelength range, which comprises a first absorption spectrum band of the first gas;
• second detector for detecting the intensity of the radiation exiting the sample chamber at a second wavelength range, which is substantially or entirely outside the first wavelength range;
• an optical transmission band filter, whose transmission band is one of the first and second wavelength ranges;
• concentration determining means, which are arranged to determine the concentration of the first gas in the gas mixture using a certain concentration formula and using the detected intensity of the radiation at the first wavelength range and at the second wavelength range;
• an optical blocking range filter, whose blocking range comprises at least the other of the first and second wavelength ranges and which is arranged at a certain angle so that it operates as a wavelength selective beam splitter reflecting radiation at the blocking range to one of the radiation detector means and transmitting radiation at least at the transmission band towards the other radiation detection means, and
• the second wavelength range is substantially outside the absorption bands of said first gas component and so that it comprises a second absorption band of a certain gas component causing a distortion in the absorption band of the first gas component, the strength of the second absorption band being substantially less than the strength of the first absorption band.