Non-dispersive infrared (NDIR) sensors are increasingly being used in multi-sensor instruments to measure LEL combustible gas. But remember, no single type of sensor can detect all types of dangerous gases and vapors. Manufacturers offer different types of sensors to measure combustible gas and VOC vapors.
Non-dispersive infrared (NDIR) sensors measure gas as a function of the absorbance of infrared light. Molecules consist of atoms held together by bonds that can vibrate (stretch, bend or rotate) in three dimensions. When a chemical bond absorbs infrared radiation, the bond continues to vibrate at the same frequency but with greater amplitude after the transfer of energy. For infrared energy to be absorbed (that is, for vibrational energy to be transferred to the molecule), the frequency must match the frequency of the mode of vibration.