# Catalytic Bead Sensor #detection-technology #sensor #flammable-gas Catalytic bead sensors (pellistors) detect flammable gases through catalytic oxidation on heated beads. They are widely used for LEL detection in industrial environments. ## Principle - Two beads: one active (catalyzed), one passive (reference) - Active bead catalyzes oxidation of flammable gases - Heat from oxidation changes bead resistance - Difference between beads indicates gas concentration ## Advantages - Reliable detection of flammable gases - Good sensitivity to hydrocarbons - Proven technology with long history - Cost-effective for many applications ## Limitations - Susceptible to catalyst poisoning - Requires oxygen for operation - Affected by environmental conditions (temperature, humidity) - Signal drift over time (aging) ## Calibration - **Target Gas Calibration**: Preferred method using actual gas to be detected - **Cross-Calibration**: Using surrogate gas with calibration factors - Cross-calibration introduces uncertainty and should be avoided when possible - Calibration factors only valid for new sensors without stress history ## Autozero Function Automatic zero-point correction compensates for: - Long-term sensor drift - Day-night rhythm effects - Environmental parameter changes - Limited accuracy of double detector principle ## Applications - LEL monitoring in hazardous areas - Flammable gas detection - Industrial safety systems - Oil and gas facilities ## Related Concepts - [[Cross-Sensitivity]] - [[Gas Detection Calibration]]