Nondispersive infrared sensor

From Wikipedia, the free encyclopedia
  (Redirected from NDIR)
Jump to: navigation, search

A nondispersive infrared sensor (or NDIR sensor) is a simple spectroscopic sensor often used as a gas detector. It is nondispersive in the sense of optical dispersion since the infrared energy is allowed to pass through the atmospheric sampling chamber without deformation.[1]

NDIR-Analyzer with one double tube for CO and another double tube for hydrocarbons

Principle[edit]

The main components of an NDIR sensor are an infrared source (lamp), a sample chamber or light tube, a light filter and an infrared detector. The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas, typically nitrogen. The gas in the sample chamber causes absorption of specific wavelengths according to the Beer–Lambert law, and the attenuation of these wavelengths is measured by the detector to determine the gas concentration. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb.

Ideally other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector[2] however some cross-sensitivity is inevitable. For instance, many measurements in the IR area are cross sensitive to H2O so gases like CO2, SO2 and NO2 often initiate cross sensitivity in low concentrations[citation needed].

The IR signal from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal.[3]

Applications[edit]

References[edit]

External links[edit]