IR Technology

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 some 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.
• Exposure to high levels of flammable gas can cause “sooting” of pellistors, reducing their sensitivity and potentially leading to failure Pellistors require oxygen to function. However, IR sensors can be relied on in applications such as fuel storage tanks where there is little or no oxygen, due to flushing with inert gas prior to maintenance or which still contain high levels of fuel vapours.
• The fail-safe nature of IR sensors, which automatically alert you to any fault, provides an additional layer of safety.

Gas-Pro IR measures in %LEL and has been certified for use in hazardous areas as defined by both ATEX/IECEx and UL.