As we all know, the formation of an explosion needs to meet three conditions, namely oxygen, explosive gas, and detonation source. Because air is everywhere, we have no control over oxygen. Therefore, the control of explosion can only start from the two aspects of explosive gas and detonation source. But there is another explosion-proof principle in the instrumentation industry: controlling the explosion range. Three common explosion-proof principles in instruments and meters: control explosive gases to artificially create a space without explosive gases in dangerous places (we call industrial sites that have the three conditions required for explosion at the same time dangerous places), and install instruments in it. The typical representative is the positive pressure explosion-proof method Exp. The working principle is: fill a sealed box with clean gas or inert gas that does not contain explosive gases, keep the air pressure inside the box slightly higher than the air pressure outside the box, and install the instrument inside the box. It is often used for explosion-proof re-line analysis instruments and positive-pressure explosion-proof instrument cabinets for placing computers, PLCs, operating stations or other instruments on-site. Controlling the explosion range artificially limits the explosion to a limited local range, so that the explosion within this range will not cause a larger explosion.

A typical representative is the explosion-proof explosion-proof method Exd. The working principle is: design a sufficiently strong shell for the instrument, and design, manufacture and install all interfaces strictly according to standards, so that the explosion that occurs inside the shell will not cause the explosion of dangerous gases (explosive gases) outside the shell. The design and manufacturing specifications for 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 explosion-proof electrical equipment and instruments are often very bulky and must be powered off for operation, but in many cases it is also the most effective method.

Controlling the detonation source artificially eliminates the detonation source, which not only eliminates sparks sufficient to detonate, but also eliminates surface temperature rise sufficient to detonate. The typical representative is the intrinsically safe explosion-proof method Exi. The working principle is: using safety barrier technology, the electric energy provided to the field instrument is limited to a safe range that neither generates sparks sufficient to detonate nor generates a temperature rise on the surface of the instrument sufficient to detonate. In accordance with international standards and my country's national standards, when any failure occurs in the equipment connected to the safety zone side of the safety barrier (voltage not exceeding 250V), intrinsically safe explosion-proof methods ensure explosion-proof safety at hazardous sites. Exia-level intrinsically safe equipment will not explode explosive gas mixtures when operating normally, when one fault occurs, or when two faults occur. Therefore, this method is the safest and most reliable explosion-proof method.