Here is our final video in the series illustrating the working of hydrocarbon gas detecting sensors. This time, we show the basic mode of operation of an infrared (IR) sensor for flammable gases.
Infrared emitters within the sensor each generate beams of IR light . Each beam is of equal intensity and is deflected by a mirror within the sensor on to a photo-receiver, which measures the level of IR received. The “measuring” beam, with a frequency of around 3.3μm, is absorbed by hydrocarbon gas molecules, so the beam intensity is reduced . The “reference” beam (around 3.0μm) is not absorbed, so arrives at the receiver at full strength. The %LEL of gas present is determined by the difference in intensity between the beams measured by the photo-receiver.