Working Principle, Maintenance and Servicing of Portable Combustible Gas Detectors
Combustible gas detectors are installed in industrial and civil buildings. They are detectors responding to the concentration of single or multiple combustible gases.
Two types of combustible gas detectors are widely used in daily applications: catalytic‑type combustible gas detectors and semiconductor‑type combustible gas detectors.
Semiconductor‑type combustible gas detectors are mainly adopted in restaurants, hotels, domestic kitchens and other sites using coal gas, natural gas and liquefied petroleum gas. Catalytic‑type combustible gas detectors are mostly used in industrial sites where combustible gas and combustible vapor are released.
The catalytic‑type combustible gas detector measures combustible gas concentration by means of resistance variation of heated refractory platinum wire.
When combustible gas enters the detector, oxidation reaction (flameless combustion) occurs on the surface of platinum wire. The generated heat raises the temperature of platinum wire and changes its resistivity. Therefore, factors such as high ambient temperature will alter platinum‑wire temperature and resistivity, leading to deviation in detection data.
The semiconductor‑type combustible gas detector determines combustible gas concentration based on surface resistance change of semiconductor materials.
It adopts highly sensitive gas‑sensitive semiconductor components. Under working condition, its resistance drops upon contact with combustible gas, and the resistance drop value corresponds to combustible gas concentration.
A combustible gas detector consists of detection unit and sensing unit, with both detection and sensing functions.
For the detection unit, the sensor forms a measuring bridge circuit together with detection elements, fixed resistors and zero‑adjustment potentiometers. The bridge takes platinum wire as carrier catalytic element. After power‑on, platinum wire is heated to working temperature, and air reaches the element surface through natural diffusion or other approaches.
When no combustible gas exists in the air, the bridge outputs zero signal. When combustible gas diffuses to the detection element, flameless combustion takes place due to catalytic effect, raising the temperature and resistance of the detection platinum wire. The bridge circuit becomes unbalanced and outputs a voltage signal proportional to combustible gas concentration. The signal is amplified and converted via 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 feature electrochemical activity and can be oxidized or reduced electrochemically. The current generated from such reaction is proportional to gas concentration, so gas composition and concentration can be measured through this reaction.
