Catalytic bead gas sensors - also called pellistors - detect flammable gas concentrations through oxidation on a heated catalytic bead element. A pair of matched platinum wire coils are embedded in ceramic beads - one (the detector) is coated with a catalytic material that promotes oxidation, the other (the compensator) is inactive. When flammable gas contacts the catalytic bead, it oxidises on the surface, raising bead temperature proportionally to gas concentration. The temperature difference changes a Wheatstone bridge circuit resistance, producing output proportional to % LEL. Catalytic bead sensors are calibrated in percent LEL for the target gas. Alarm setpoints are typically set at 10% LEL (early warning) and 20% LEL (evacuation and shutdown) to provide response well below the 100% LEL explosion threshold. Common calibrated gases include methane, propane, butane, hydrogen, ethylene, and acetylene. Sensor life is typically 2-4 years in clean air environments. Exposure to silicone vapour, lead compounds, or halogenated hydrocarbons can catalytically poison the bead, reducing sensitivity - making periodic bump testing and calibration essential maintenance requirements. ATEX and IECEx certified versions are available for Zones 1 and 2. Catalytic bead sensors are the standard first-stage detection technology in petrochemical plants, paint spray booths, LPG storage facilities, natural gas distribution facilities, laboratory environments with solvent or flammable gas use, and industrial processes involving combustible gas or vapour - wherever the proven simplicity and low cost of catalytic detection are appropriate for the application.
