Principles of determining the explosion-proof mark
Determining the explosion-proof mark of a product according to the expected use conditions of the product is the key to ensuring the economical and reasonable indicators of electrical equipment design. In general, the following factors need to be considered in determining the explosion-proof mark to make the determined explosion-proof mark more economical and reasonable.
- (1) Consider whether the possible installation position of the product at the production site is zone 0 or zone 1 to determine whether the explosion-proof level is ia or ib. It has nothing to do with gas type and gas temperature group.
- (2) Consider the types of gases that may occur at the production site of the product installation, and use one of the most ignitable gases, check Table B of the Appendix to GB383611-2000, "Examples of Flammable Gases, Vapors, Levels, and Temperature Groups", and determine It belongs to IIA, IIB or IIC. It has nothing to do with gas concentration or frequency of occurrence. For example, in practice, the gas group cannot be classified as IIB because the probability of occurrence of hydrogen in hazardous locations containing hydrogen is small.
- (3) Considering the lowest temperature group in the gas that may occur at the production site of the product installation, check Table B in the Appendix to GB383611-2000, "Examples of Flammable Gases, Vapors, Levels, and Temperature Groups", and determine that they belong to T1, T2, T3, and T4 , T5 or T6.
In short, when determining the explosion-proof mark of a product, various specific factors in the actual application requirements should be comprehensively considered to make the determined explosion-proof mark economical, reasonable, safe and reliable. Of course, the most ideal situation is to set the explosion-proof mark as ExiaⅡCT6. However, if the explosion-proof mark is set too high, the product circuit may not meet the design requirements of intrinsic safety. For this reason, especially for some dedicated meters, the explosion-proof mark of the meter should be determined according to the medium, environment and place where the meter is actually used. For example, for oil measuring or measuring instruments, it is generally sufficient to set the explosion-proof mark of the instrument as ExiaⅡBT4. It can be applied to a variety of possible oil hazardous locations, including applications in Zone 0 hazardous locations.
GB383611-2000 Appendix B "Gases and vapors are classified according to maximum test safety clearance (MESG) and minimum ignition current (MIC)". It lists the classification and grouping of 153 gas or vapor explosive mixtures.
The intrinsically safe instrument with explosion-proof mark ExiaⅡBT4 can cover more than 97% of applicable hazardous gas. If the instrument is designed as ExiaⅡBT6, then the applicable gas of the instrument is only one more than the original, but in order to increase the surface temperature group of the instrument from T4 (135 ° C) to T6 (85 ° C), it may be necessary to increase the The power of each heating element or increase the heat sink of the element will inevitably lead to an increase in the cost of the instrument or an increase in the volume, and even cause a decline in the performance of the instrument. Therefore, the determination of the explosion-proof mark of the instrument must also take into account factors such as actual use conditions and design costs, and it cannot unilaterally increase the explosion-proof level of the instrument. The determination of the explosion-proof mark of explosion-proof electrical equipment for flammable dust environments is different from electrical equipment for explosive gas environments. As far as the type of dust explosion protection currently accepted in China, the determination of the explosion-proof mark of the equipment usually only needs to know the area where the equipment is actually used, the dust characteristics that may exist (conductive or non-conductive), the ignition temperature of the dust, and the dust accumulation. The selection principle of airborne dust equipment requires that the explosion-proof mark of the corresponding equipment be determined.
Mystone 's explosion-proof products are SC910N and SC910 combustible gas detectors. Different gases can be used for gas detection by replacing sensors.