Reference

A catalytic bead burns the gas and measures the heat released; an infrared sensor measures the light the gas absorbs. Catalytic needs oxygen and can be poisoned but detects hydrogen. Infrared cannot be poisoned but is blind to hydrogen. This guide covers both principles and the specification decision that follows from them.

A poisoned catalytic bead sensor does not fault, blank or warn you. It reads low, silently, in a flammable atmosphere. This guide covers the compound classes that cause it, the difference between poisoning and inhibition, why calibration cannot fix it, and the daily function check that turns a silent failure into a visible one.

Cross-sensitivity is a sensor responding to a gas it was not built to measure, and it is not a defect but a property of the sensing chemistry itself. This guide covers the mechanism, the interference patterns crews actually meet, the under-reporting direction nobody expects, and how to diagnose a suspect alarm from clean air.