The principle of the infrared measurement
uses the characteristic of gas to absorb light in some defined wavelenght
ranges (bands). Heteroatomic gases like CO2, CH4, NO2, and C2H2 can
be measured with infrared sensors.
A lamp or a heated wire is used to emit the infrared light. The
light passes through the measuring gas. The gas will absorb some
of the light, which loses intensity. The absorbtion of a small range
of wavelength is proportional to the measured gas concentration.
The loss of intensity is measured by sensors. At the same time the
reduction of intensity of other wavelengths where no absorption
of the measured gas took place is measured. This second measurement
is used as a reference signal. The accuracy of the measurement can
even be held if the intensity of the infrared lamp changes or a
mirror is dirty. |
