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.
In gas detection terms, pellistors have been the primary technology for detecting flammable gases since the 60s. In most circumstances, with correct maintenance, pellistors are a reliable, cost-effective means of monitoring for combustible levels of flammable gases. However, there circumstances under which this technology may not be the best choice, and infrared (IR) technology should be considered instead.
Many of you will have come across hydrogen sulphide (H2S). If you have ever cracked a rotten egg the distinctive smell is H2S.
H2S is a hazardous gas that is found in many work environments, and even at low concentrations it is toxic. It can be a product of man-made process or a by-product of natural decomposition. From offshore oil production to sewerage works, petrochemical plants to farms and fishing vessels, H2S presents a real hazard to workers.
