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12 June 2015
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Flammable gas IR sensors – how they work

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.

IR sensors are reliable in a few environments that can cause pellistor-based sensors to function incorrectly or in some cases fail. In some industrial environments, pellistors are at risk of being poisoned or inhibited. This leaves worker on their shift unprotected. IR sensors are not susceptible so significantly enhance safety in these conditions.

For more information about the pro and cons of pellistor and IR sensors, read our blog “Are silicone implants degrading your gas detection?

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