Classification and principle of toxic and harmful gas detectors
Gas sensors can be classified into three main categories based on their principles:
A) Gas sensors utilizing physical and chemical properties, such as semiconductor based (surface controlled, volume controlled, surface potential based), catalytic combustion based, solid thermal conductivity based, etc.
B) Gas sensors utilizing physical properties such as thermal conductivity, optical interference, infrared absorption, etc.
C) Gas sensors utilizing electrochemical properties, such as constant potential electrolysis, galvanic cell, diaphragm ion electrode, fixed electrolyte, etc.
According to the hazards, we classify toxic and harmful gases into two categories: combustible gases and toxic gases. Due to their different properties and hazards, their detection methods also vary.
Combustible gases are hazardous gases commonly encountered in industrial settings such as petrochemicals, mainly consisting of organic gases such as alkanes and certain inorganic gases such as carbon monoxide. Explosion of combustible gas
There must be certain conditions, which are: a certain concentration of combustible gas, a certain amount of oxygen, and sufficient heat to ignite their ignition source. These are the three essential elements of explosion, all of which are indispensable,
That is to say, the absence of any of these conditions will not cause a fire or explosion. When combustible gas
When steam, dust, and oxygen are mixed and reach a certain concentration, they encounter a certain
A fire source with high temperature will cause an explosion. We refer to the concentration at which combustible gases explode when exposed to a source of fire as the explosive concentration limit, abbreviated as the explosive limit, which is generally expressed in%. In fact, this
Mixtures do not explode at any mixing ratio and require a concentration range. When the concentration of combustible gas is below the LEL (minimum explosive limit) (insufficient concentration of combustible gas)
)When the concentration is higher than UEL (maximum explosive limit) (oxygen deficiency), no explosion will occur. The LEL and UEL of different combustible gases are different (see the introduction in the eighth issue),
This should be taken very seriously when calibrating instruments. For safety reasons, we should generally issue an alarm when the concentration of combustible gas is at 10% and 20% of the LEL, where 10% LEL is referred to.
Make a warning alert, while 20% LEL is called a danger alert. That's why we call the combustible gas detector LEL detector.
