Catalytic Bead LEL Sensor

A sensor that contains two heated coils, connected by a Wheatstone bridge. One of the coils is treated with a catalyst to aid combustion. When a combustible gas passes through, the temperature increases at the catalyst-treated coil, changing the conductivity of that coil, causing a potential difference at the Wheatstone bridge. Measuring the change in potential difference enables the instrument to indicate the risk of explosion. A mesh filter is used to protect hazardous atmospheres from ignition. Gas has to permeate this mesh filter. Larger molecules have greater difficulty passing through the mesh filter, increasing the response time. Also, some gases burn hotter than others. LEL sensors are typically calibrated for methane, correction factors have to be applied for other gases.