Views: 100 Author: Site Editor Publish Time: 2019-10-16 Origin: Site
Electric explosion proof instrument refers to the electric instrument which can be safely used in the environment with explosive mixture. In the design and manufacture of this kind of instrument, certain safety technical measures have been taken to ensure safe power supply, power consumption, detection and control in places with explosion danger such as petroleum and chemical industry. Next, I will introduce you some knowledge about explosion-proof instruments.
Explosive dangerous places are generally classified into 1 category and 2 categories. Class 1 places refer to places where flammable gases and air constitute explosive mixtures. Class 2 places refer to places where combustible dust and air constitute explosive mixtures. Class 1 is the most dangerous place. Explosion-proof instruments are designed for this condition. there are 0, 1 and 2 levels of electric explosion proof instruments according to the probability of explosive gases, vapors and air mixtures.
Flameproof electric explosion proof instrument will not cause explosive gas explosion outside the instrument even if the spark caused by the accident causes explosion inside the case. Flameproof instruments can be used in Class 1 and Class 2 locations. Instrument installation and maintenance can ensure safety, but when the shell is uncovered, it loses explosion-proof performance, so it can not open the shell for repair and adjustment in the case of power-on operation. After long-term use, it is difficult to maintain the gap of explosion-proof case due to wear and tear, so explosion-proof performance will gradually be lost. Flameproof instruments can not be used in explosive environments with high levels and groups.
The sparks produced by intrinsically safe circuits under normal and fault conditions and the temperatures reached do not cause explosive gas mixtures to explode. Normal state refers to the working state of electrical equipment under specified design conditions, including normal open and closed circuits. Fault state refers to short circuit, open circuit, grounding and power failure due to accidents. Modern intrinsically safe explosion-proof means the explosion-proof of the whole automation system. Explosion-proof system includes intrinsic safety and non-intrinsic safety circuits. The intrinsic safety circuit is installed in dangerous places, and the non-intrinsic safety circuit is installed in non-dangerous places. The explosion-proof safety grid is used between the two to prevent excessive energy from entering dangerous places. The whole instrument has intrinsically safe explosion-proof performance.
Explosion-proof instruments need to be selected according to the principle of reasonable use environment and economy. In general, the small-scale equipment used in explosive dangerous places, such as detection and measurement instruments, belongs to intrinsically safe type.
The intrinsically safe explosion-proof instrument mainly adopts four measures:
(1)The instrument adopts low working voltage and low working current.
(2)For instruments installed in dangerous places, the appropriate size of resistance, capacitance and inductance should be selected to ensure that the sparks generated during normal and failure are not enough to ignite explosive mixtures.
(3)Put explosion-proof safety grille at the entrance of non-dangerous places, prevent dangerous energy from entering dangerous places from safety places, and separate the circuits of dangerous places from non-dangerous places.
(4)Do not form too large distributed inductance and capacitance on the connecting wires of the instrument.
