Inhibitors like trichloroethane and methylene chloride leave deposit on active bead that depresses gas readings while inhibitor is present
Sensor generally recovers most of original response once it is returned to fresh air
H2S functions as inhibitor BUT byproducts of catalytic oxidation become very corrosive if they build up on active bead in sensor
Corrosive effect can rapidly (and permanently) damage bead if not "cooked off" fast enough)
How efficiently bead "cooks off" contaminants is function of:
Temperature at which bead is operated
Size of the bead
Whether bead under continuous power versus pulsing the power rapidly on and off to save operating energy.
"Silicone resistant" vs. "standard" pellistor type LEL sensors
"Silicone resistant" combustible sensors have an external silicone filter capable of removing most silicone vapor before it can diffuse into the sensor
Silicone vapor is the most virulent of all combustible sensor poisons
Filter also slows or slightly reduces response to heavier hydrocarbons such as hexane, benzene, toluene, xylene, cumene, etc.
The heavier the compound, the greater the effect on response
Effects of hexamethyldisiloxane (HMDS) on pellistor sensor
