Catalytic bead sensors (pellistors) detect flammable gases through catalytic oxidation on heated beads. They are widely used for LEL detection in industrial environments and represent a proven, cost-effective technology.
The principle involves two beads: one active (catalyzed) and one passive (reference). The active bead catalyzes oxidation of flammable gases, and the heat from oxidation changes bead resistance. The difference between beads indicates gas concentration.
Advantages include reliable detection of flammable gases, good sensitivity to hydrocarbons, proven technology with long history, and cost-effectiveness for many applications. However, they are susceptible to catalyst poisoning, require oxygen for operation, are affected by environmental conditions (temperature, humidity), and experience signal drift over time (aging).
Calibration is critical. Target gas calibration using the actual gas to be detected is preferred. Cross-calibration using surrogate gas introduces uncertainty and should be avoided when possible. Calibration factors are only valid for new sensors without stress history.
The autozero function provides automatic zero-point correction, compensating for long-term sensor drift, day-night rhythm effects, environmental parameter changes, and limited accuracy of double detector principle.
Applications include LEL monitoring in hazardous areas, flammable gas detection, industrial safety systems, and oil and gas facilities. Understanding cross-sensitivity and proper calibration ensures reliable operation.