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.
NDIR-analyzer with one double tube for CO and another double tube for hydrocarbons
The main components of an NDIR sensor are an infrared (IR) 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 however some cross-sensitivity is inevitable. For instance, many measurements in the IR area are cross sensitive to H2Oso gases like CO2, SO2 and NO2 often initiate cross sensitivity in low concentrations.
The IR signal from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal.
NDIR sensors for carbon dioxide are often encountered in heating, ventilation, and air conditioning (HVAC) units.
Configurations with multiple filters, either on individual sensors or on a rotating wheel, allow simultaneous measurement at several chosen wavelengths.
Fourier transform infrared spectroscopy (FTIR), a more complex technology, scans a wide part of the spectrum, measuring many absorbing species simultaneously.
One of the problems of NDIR sensors are their large size and high cost, making them unsuitable for embedded applications integrated into other systems. Miniature IR sources based on microelectromechanical systems (MEMS) have been experimentally applied to NDIR systems since 2006 and is useful since 2016. The low energy of MEMS emission means a sensitive detector circuit based on lock-in amplification is needed. Other useful detectors include the photoacoustic gas sensorwhich use a MEMS microphone to detect IR-gas interactions.
Gases and their sensing wavelengths
O2 - 0.763 µm
CO2 - 4.26 µm, 2.7 µm, about 13 µm
carbon monoxide - 4.67 µm, 1.55 µm, 2.33 µm, 4.6 µm, 4.8 µm, 5.9 µm
NO - 5.3 µm, NO2 has to be reduced to NO and then they are measured together as NOx; NO also absorbs in ultraviolet at 195-230 nm, NO2 is measured at 350-450 nm; in situations where NO2 content is known to be low, it is often ignored and only NO is measured; also, 1.8 µm
NO2 - 6.17-6.43 µm, 15.4-16.3 µm, 496 nm
N2O - 7.73 µm (NO2 and SO2 interfere), 1.52 µm, 4.3 µm, 4.4 µm, about 8 µm
HNO3 - 5.81 µm
NH3 - 2.25 µm, 3.03 µm, 5.7 µm
H2S - 1.57 µm, 3.72 µm, 3.83 µm
SO2 - 7.35 µm, 19.25 µm
HF - 1.27 µm, 1.33 µm
HCl - 3.4 µm
HBr - 1.34 µm, 3.77 µm
HI - 4.39 µm
hydrocarbons - 3.3-3.5 µm, the C-H bond vibration
CH4 - 3.33 µm, 7.91±0.16 μm can also be used, 1.3 µm, 1.65 µm, 2.3 µm, 3.2-3.5 µm, about 7.7 µm
C2H2 - 3.07 µm
C3H8 - 1.68 µm, 3.3 µm
CH3Cl - 3.29 µm
H2O - 1.94 µm, 2.9 µm (CO2 interferes), 5.78±0.18 μm can also be used to eliminate CO2 interference, 1.3 µm, 1.4 µm, 1.8 µm
O3 - 9.0 µm, also 254 nm (UV)
H2O2 - 7.79 µm
alcohol mixtures - 9.5±0.45 μm
HCHO - 3.6 µm
HCOOH - 8.98 µm
COS - 4.87 µm
Infrared gas analyzer
Infrared point sensor
5. ^ Vincent, T.A.; Gardner, J.W. (November 2016). "A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels". Sensors and Actuators B: Chemical. 236: 954–964. doi:10.1016/j.snb.2016.04.016.
7. ^ Jump up to:a b c d e f g h i j k l m n o p q r s t u v w x Korotcenkov, Ghenadii (18 September 2013). Handbook of Gas Sensor Materials: Properties, Advantages and Shortcomings for Applications Volume 1: Conventional Approaches. Springer Science & Business Media. ISBN 9781461471653. Retrieved 16 April 2018 – via Google Books.
10. ^ Montgomery, Tami A.; Samuelsen, Gary S.; Muzio, Lawrence J. (1989). "Continuous Infrared Analysis of N2O in Combustion Products". JAPCA. 39 (5): 721–726. doi:10.1080/08940630.1989.10466559.
From Wikipedia, the free encyclopedia
The Q198 portable SF6 leak detector is designed with non-dispersive infrared technology (NDIR) principle. Q198 can detect extremely low concentration of SF6 gas, which can achieve the fastest response and reliable measurement even in the case of minimum leakage, which is an ideal choice for detecting leak location and leakage rate.