Nondispersive infrared sensor

It is non-dispersive in the fact that no dispersive element (e.g a prism or diffraction grating as is often present in other spectrometers) is used to separate out (like a monochromator) the broadband light into a narrow spectrum suitable for gas sensing.

Modern NDIR sensors may use Microelectromechanical systems (MEMs) or mid IR LED sources, with or without an optical filter.

Fourier transform infrared spectroscopy (FTIR), a more complex technology, scans a wide part of the spectrum, measuring many absorbing species simultaneously.

The low energy of MEMS emission means a sensitive detector circuit based on lock-in amplification is needed.

[5] Gases do not have a specific sensing wavelength, rather there are regions of the IR spectrum where there are typically many thousands of closely spaced absorption lines.