Introduction to NDIR non-dispersive infrared gas detection technology

Gas also has characteristic absorption of infrared ray. When an infrared light source is used to illuminate the gas to be measured, part of the radiant energy carried by the infrared ray is absorbed by gas molecules, causing changes in the infrared spectrum. The absorbed gas is received and converted by two-way detectors. The measurement signal voltage that has absorbed infrared light and the reference signal voltage that has not absorbed this infrared light, and the gas concentration is inverted using Lambert-Beer's Law. The non-dispersive infrared absorption method can achieve accuracy in detecting gas content by calibrating experimental data and adding necessary constraints. Non-dispersive infrared (NDIR) technology used for gas measurement targets wavelength absorption in the infrared spectrum as a method of identifying specific gases. NDIR technology is suitable for detecting air pollutants from emission sources, such as carbon monoxide (CO), carbon dioxide (CO ˇ), sulfur dioxide (SO ˇ), nitrogen oxides (NOx), nitrous oxide (N ˇ O), ammonia (NH), hydrogen chloride (HCl), hydrogen fluoride (HF) and methane (CH).

Based on this theoretical basis, the NDIR infrared gas sensor uses a broad-spectrum infrared light source and has no grating or prism structure for splitting light, so it is called non-splitting infrared. The sensor consists of an infrared light source, an optical path, an infrared detector, circuitry and software. It adopts a dual-channel measurement scheme, combines a narrowband filter and two detectors, and calculates the concentration by comparing the detected optical signals. Compared with traditional electrochemical and single-channel measurement solutions, NDIR sensors have long service life, high detection accuracy, and less external influence.

One of the advantages of NDIR compared to other spectroscopy technologies isAnti-poisoning, no need for oxygen, excellent long-term stability, wide temperature range, measured concentration up to 100% vol。Infrared light sources with wavelengths in the 1 - 15 micron range can operate at lower temperatures than other light sources