English Title：Working Principle of Portable Combustible Gas Detectors
Combustible gas detectors are installed in industrial and civil buildings. They respond to the concentration of single or multiple combustible gases.
Two types are widely used in daily practice: catalytic‑combustion combustible gas detectors and semiconductor‑type combustible gas detectors.
Semiconductor‑type detectors are mainly adopted in restaurants, hotels and domestic kitchens where coal gas, natural gas or liquefied petroleum gas are consumed. Catalytic‑combustion detectors are mostly used in industrial sites where combustible gas or vapor may leak.
The catalytic‑combustion combustible gas detector measures combustible‑gas concentration based on resistance variation of heated refractory platinum wire. When combustible gas enters the detector, oxidation reaction (flameless combustion) occurs on the platinum‑wire surface. Reaction heat raises platinum‑wire temperature and changes its resistivity. High ambient temperature will also alter platinum‑wire resistivity and cause measurement deviation.
The semiconductor‑type combustible gas detector determines gas concentration according to surface‑resistance change of semiconductor materials. It uses highly‑sensitive gas‑sensitive semiconductor elements. Under working condition, contact with combustible gas reduces semiconductor resistance, and the resistance drop corresponds to gas concentration.
A combustible gas detector consists of two functional parts: the sensing unit and the detection unit.
Principle of the detection unit: The detecting element, fixed resistors and zero‑adjustment potentiometer form a measuring bridge circuit. The bridge uses platinum‑wire‑based carrier catalytic elements. After power‑on, platinum wire heats up to operating temperature. Ambient gas reaches the element surface by natural diffusion or other means.
When no combustible gas exists in air, the bridge outputs zero. When combustible gas diffuses onto the detecting element, catalytic‑effect‑driven flameless combustion raises element temperature and platinum‑wire resistance. The bridge becomes unbalanced and outputs voltage signal proportional to combustible‑gas concentration. The signal is amplified and processed by analog‑to‑digital conversion, and combustible‑gas concentration is displayed on the liquid‑crystal screen.
An electrochemical gas detector is equipped with electrochemical sensors. Many gases possess electrochemical activity and can be oxidized or reduced electrochemically. The current generated by such reaction is proportional to gas concentration, so gas composition and concentration can be measured accordingly.
