An explosion-proof displacement sensor has reached the highest level of explosion-proof standards and can be used directly in an environment filled with explosive gases.
The concept of explosion
An explosion is the sudden change of a substance from one situation to another, by physical or chemical change, and the release of immense energy. The rapid release of energy at speed will cause severe impact and damage to the surrounding objects.
The explosion must have three conditions:
1) Explosive substances: substances that can react with oxygen (air), including gases, liquids and solids. (gas: hydrogen, acetylene, methane, etc.); liquid: alcohol, gasoline; solid: dust, fiber dust, etc. )
2) oxygen: air.
3) ignition source: including open flame, electrical spark, mechanical spark, electrostatic spark, high temperature, chemical reaction, light energy, etc.
Why explosion-proof
Explosive substances: many production sites will attack some flammable substances. About two-thirds of the underground coal mines contain explosive substances; in the chemical industry, more than 80% of such production workshop areas have explosive substances. Oxygen: oxygen in natural air is ubiquitous. Light comes from: in the production process there are many use of electrical surface, a variety of electrical sparks will be friction out, mechanical wear sparks, static sparks, high temperature and so on inevitable, especially when the surface, electrical defects.
In fact, there are many industrial sites that satisfy the explosive conditions simultaneously. When the mixed concentration of explosive material and oxygen is within the explosive limit, if there is an explosive source, it will explode. Therefore, selection of explosion-proof is very necessary.
Principle of surface explosion protection
Hazard distinction in dangerous places:
The definition of explosive substances in China's standard North American Standard
Gases When in very normal conditions, explosive gas mixtures may also be connected or permanently present in Site 0 Div.1
Under normal circumstances, explosive gas mixtures may have 1 areas.
Explosive gas mixtures are not likely to occur under normal conditions, and only occasional or short-term occurrences of site 2 Div.2 under abnormal conditions.
Dust or fiber (CLASS II/III) under normal conditions, explosive dust or a mixture of combustible fibers and air may be connected, occurring repeatedly for a short time or for a long time in area 10 Div.1
Under normal conditions, explosive dust and combustible fiber-air mixture will not appear, but in abnormal circumstances, occasional or short-term occurrence of the site 11 Div.2
Applicability of explosion-proof measures to dangerous places:
Applicability of explosion protection to dangerous places:
Classification of explosive hazardous gases
According to the minimum spark heat that may be ignited, explosive gases are classified into four dangerous grades in China and most other countries and regions in Europe and the world, as follows:
Working condition, gas classification, representative gas, minimum detonating spark energy
Methane 0.280mJ under mine
Mines outside the factory II A propane 0.180mJ
II B ethylene 0.060mJ
II C hydrogen 0.019mJ
The United States and Canada first divide the explosives in the air into three CLASS (varieties): CLASS I gas and steam; CLASS II dust; CLASS III fiber; and then divide the gas and dust into red groups (groups):
Group name: representative gas or dust
A acetylene
B hydrogen
C ethylene
D propane
E metal dust
F coal dust
G grain dust
Gas temperature group distinction:
The surface temperature of the temperature group is more than that of the explosive gas.
T1 is less than 450 degrees hydrogen, acrylonitrile and so on 46 kinds.
T2 is less than 300 degrees, acetylene, ethylene and so on 47 kinds.
T3 or less than 200 degrees gasoline, 36 kinds of butenal, etc.
T4 is less than 135 degrees acetaldehyde, tetrafluoroethylene and 6 kinds.
T5 less than 100 C carbon disulfide
Ethyl nitrate and ethyl nitrite at T6 or less than 85 degrees C
Surface explosion-proof signs
The meaning of Ex (IA) II CT6 is:
Logo content symbol meaning
Explosion-proof statement Ex corresponds to a certain standard of explosion protection, temperature sensor such as our national standard.
The explosion-proof method ia selects ia grade intrinsic safety explosion-proof method, which can be installed in Zone 0.
Gas species II C is allowed to touch class II C explosive gas.
The surface temperature of the temperature group T6 does not exceed 85 degrees.
The meaning of Ex (IA) II C is:
Logo content symbol meaning
Explosion-proof statement Ex meets European standards for explosion-proof
The explosion-proof method ia selects ia grade intrinsic safety explosion-proof method, which can be installed in Zone 0.
Gas species II C is allowed to touch class II C explosive gas.
Note: there is no temperature category in the sign, indicating that the surface is not directly exposed to explosive gas.
Description of explosion-proof signs:
The explosive dangerous combustible substances in factories or mining areas are classified scientifically according to their ignition energy, the minimum ignition temperature and the time period of the existence of explosive dangerous gases on site, so as to determine the explosion-proof signs and methods of explosion-proof equipment on site.
Explosion-proof sign format:
Ex (IA) II CT4
Explosion-proof explosion-proof gas class temperature group
Description of explosion-proof level:
Class ia: Electrical equipment that does not light an explosive gas mixture during normal operation, one defect, and two defects.
When working normally, the safety factor is 2.
For one drawback, the safety factor is 1.5.
The two disadvantage is that the safety factor is 1.
Note: contact with spark must be flameproof enclosure, airtight enclosure or double running safety factor.
IB level:
Not in normal work and in a disadvantage.