Infrared gas analysis

A method for detecting and quantitatively measuring a molecular species of gaseous material in a sample to be analyzed, comprising the steps of

• generating light in the form of incoherent infrared radiation;
• collecting, collimating and transmitting the light;
• filtering said light so as to selectively transmit light having a frequency range in the region of an absorption band for the molecular species to be detected;
• interferometrically filtering said filtered light and transmitting light at a plurality of discrete frequencies to form a plurality of fringes which provide a detectable signal by directing the light through a plurality of transmission windows regularly spaced in frequency, the frequency spacing between adjacent windows being equal substantially to the frequency difference between adjacent spectral lines of the absoprtion spectrum for the molecular species to be detected, and scanning said light to cause the transmission peaks for adjacent orders to coincide substantially with the spectral lines of said absorption spectrum, said signal having an intensity substantially equal to the sum of said fringes;
• transmitting said detectable signal through said gaseous material, whereby the intensity of said detectable signal changes in proportion to the concentration of said molecular species;
• and
• detecting and indicating the intensity change of said signal.

Apparatus for detecting and quantitatively measuring a molecular species of gaseous material in a sample to be analyzed comprising:

• a. light source means for generating incoherent infrared radiation, said light source means being adapted to emit light having a frequency range in the region of an absorption band for the molecular species to be detected;
• b. light conditioning means for collecting, collimating and transmitting said light;
• c. filtering means adapted to receive said light and transmit light having a plurality of discrete frequencies forming a plurality of fringes which provide a detectable signal, said filtering means having interference producing means for providing a plurality of transmission windows regularly spaced in frequency, the frequency spacing between adjacent windows being adjusted to equal substantially the frequency difference between adjacent spectral lines of the absorption spectrum for the molecular species to be detected, and scanning means for causing the transmission peaks for adjacent orders to coincide substantially with the spectral lines of said absorption spectrum, whereby said detectable signal has an intensity substantially equal to the sum of said fringes;
• e. means for transmitting said detectable signal through said gaseous material, whereby the intensity of said detectable signal changes in proportion to the concentration of said molecular species;
• f. signal conditioning means for converting to measureable form said intensity change;
• and
• g. detecting means for indicating the magnitude of said intensity change.