The characteristics of explosion-proof instruments mainly include a reliable explosion-proof shell, which places instrument sensors, electronic circuits, and wiring terminals that may generate sparks and dangerous temperatures inside the explosion-proof shell, so that possible explosions inside the shell do not affect the surrounding flammable and explosive substances. Its design method is similar to that of explosion-proof electrical appliancesmotorBasically similar. The gap size and length of each mating surface (explosion-proof surface) of the shell must comply with the requirements of GB3836.2 standard. On the other hand, the shell has a certain mechanical strength and must reach 1.5 times the internal explosion reference pressure without damage or deformation. The design of explosion-proof instruments should pay attention to the following:


(1) Determine a reasonable shell structure

Due to the different application targets of explosion-proof instruments, such as temperature, pressure, material level, flow rate, mechanical quantity, etc., their original structure and form are not as single as motors and electrical appliances. Therefore, one or several explosion-proof enclosures are not used to replace them. According to the characteristics of the instrument, a specially designed shell that is compatible with the original structure should be used to achieve a shell that does not damage the original usage characteristics of the instrument and is economically reasonable and aesthetically pleasing; There are slender channels inside the shell cavity to avoid pressure overlap inside the cavity; The material of the shell can be made of new engineering plastics and lightweight alloys as much as possible to achieve a lightweight structure.

(2) Junction box structure

Explosion proof instruments should be designed with explosion-proof enclosures with junction boxes as much as possible, and the explosion-proof type of the junction box should also be explosion-proof. For industrial process control systems in China, the distance from field instruments to control rooms often ranges from a few hundred meters to several thousand meters. If explosion-proof instruments are directly introduced with cables or wires, the length of wiring left in the explosion-proof instruments cannot be estimated, and it brings inconvenience to users. If the explosion-proof type of the external junction box is made into an increased safety type or other type, the entire instrument should become a composite explosion-proof type, which will bring limitations to use.

Due to the low voltage and low current characteristics of explosion-proof instruments, the main chamber and junction box of explosion-proof instruments can be sealed with adhesive and sealing structures as much as possible, making the structure of explosion-proof instruments simple and easy to process.

(3) Indicator table structure

In order to enable on-site operators to timely understand the thermal parameters of industrial process control, it is required that explosion-proof instruments be equipped with indicator gauges. The indicator can be designed in the main chamber or junction box chamber of the instrument, but the transparent window should not exceed 100mm2, the thickness of the transparent glass should be greater than 8mm, and rubber sealing measures can be used to seal the outer shell.

(4) Zero adjustment structure

Most explosion-proof instruments require zero adjustment and calibration on site. The zero adjustment mechanical structure can adopt a cylindrical explosion-proof joint surface method. When using plastic or light alloy as the explosion-proof shell, a copper or steel shaft sleeve should be embedded to ensure frequent adjustment without wearing out the explosion-proof shell.