Classification & Operating Principles of Toxic Gas Detectors
According to hazard characteristics, hazardous gases are divided into two major categories: combustible gases and toxic gases. Different properties and hazards correspond to different detection methods, and toxic gas detectors serve as professional testing instruments.
Combustible gases are common hazardous gases in petrochemical and other industrial sites, mainly including organic gases such as alkanes and certain inorganic gases like carbon monoxide. Three essential conditions are required for a combustible gas explosion: combustible gas at a specific concentration, sufficient oxygen, and an ignition source with adequate heat. These three elements are indispensable; fire or explosion cannot occur if any condition is missing. When combustible gas vapor or dust mixes with oxygen and reaches a certain concentration, explosion will be triggered upon contact with an ignition source of sufficient temperature.
The concentration range at which combustible gas explodes when exposed to an ignition source is defined as the explosive limit, generally expressed in %. Explosion only occurs within a specific concentration interval. No explosion will take place when the gas concentration is below the Lower Explosive Limit (LEL) due to insufficient combustible gas, or above the Upper Explosive Limit (UEL) due to insufficient oxygen. Each combustible gas has unique LEL and UEL values (refer to Issue 8), which must be fully considered during instrument calibration. For safety purposes, detectors are normally set to trigger alarms at 10% LEL and 20% LEL. The 10% LEL threshold is the warning alarm, while 20% LEL is the danger alarm. For this reason, combustible gas detectors are also known as LEL detectors.
Classification and Working Principles of Toxic Gas Detectors
A) Gas sensors based on physicochemical properties: semiconductor type (surface-controlled, volume-controlled, surface potential types), catalytic combustion type, solid thermal conductivity type, etc.
B) Gas sensors based on physical properties: thermal conductivity type, light interference type, infrared absorption type, etc.
C) Gas sensors based on electrochemical properties: controlled potential electrolysis type, galvanic cell type, membrane ion electrode type, solid electrolyte type, etc.
