Three basic control methods of instrument explosion-proof

To prevent explosions, it is necessary to avoid the existence of three conditions at the same time. Since oxygen (air) is everywhere, it is difficult to control. Therefore, the control of explosive gases and detonation sources are the two most common explosion-proof principles. In the instrument industry, there is another principle of explosion protection: controlling the explosion range.

Three common explosion-proof principles in the instrument:

1. Control explosive gas

Artificially create a space free of explosive gas in the dangerous place (we call the industrial site with the three conditions required for explosion at the same time as a dangerous place), install the instrument in it, the typical representative is the positive pressure explosion-proof method Exp.

The working principle is: in a sealed box, filled with clean gas or inert gas that does not contain explosive gas, and keep the pressure in the box slightly higher than the pressure outside the box, install the instrument in the box. Commonly used for explosion-proof analysis of re-line analysis instruments and positive pressure explosion-proof instrument cabinets that place computers, PLCs, operating stations or other instruments on the site.

2. Control the explosion range

Artificially limit the explosion to a limited local range, so that the explosion in this range will not cause a larger explosion. The typical representative is the explosion-proof explosion-proof method Exd.

The working principle is: design a sufficiently strong shell for the instrument, strictly design, manufacture and install all interfaces according to the standard, so that the explosion in the shell will not cause the explosion of dangerous gas (explosive gas) outside the shell. The design and manufacturing specifications of the explosion-proof and explosion-proof methods are extremely strict and the operating procedures for installation, wiring and maintenance are also very strict. This method determines that the explosion-proof electrical equipment and instruments are often very bulky and the operation must be powered off, but in many cases it is also the most effective method. Vortex flowmeter

3. Control the detonation source

Artificially eliminate the detonation source, not only eliminate the sparks enough to detonate, but also eliminate the surface temperature rise enough to detonate, the typical representative is the intrinsically safe explosion-proof method Exi.

The working principle is: use the safety barrier technology to limit the electrical energy provided to the field instrument to a safe range that can neither generate enough spark to detonate nor generate sufficient temperature rise of the instrument surface. According to international standards and China's national standards, when any failure occurs to the equipment connected to one side of the safety barrier safety zone (not more than 250V voltage), the intrinsically safe explosion-proof method ensures explosion-proof safety at hazardous sites. Ex ia-class intrinsically safe equipment will not cause explosive gas mixtures to explode during normal operation, one failure, or two failures. Therefore, this method is the most safe and reliable explosion-proof method.