防爆认证培训ATEX.ppt

Soh SC Insert footer information ATEX Atmosphere Explosives Classification of Hazardous Locations In US and Canada, hazardous locations are categorized into the following three classes, depending on the type of flammable substances present: Classification of Hazardous Locations Intrinsically Safe Systems Hazardous-Locations Apparatus Apparatus that are certified for use in hazardous locations are of two types—simple apparatus and intrinsically safe apparatus. Simple apparatus Simple apparatus are those devices in which none of the following values are exceeded: 1.5 V, 0.1 A or 25 mW. Practically speaking, simple apparatus are not able to generate or store energy sufficient to ignite a dangerous mixture. Thermocouples, resistance temperature detectors (RTDs), contacts, light-emitting diodes (LEDs) and photocells are part of this category and, due to their nature, do not require certification. Intrinsically safe apparatus The intrinsic safety of the apparatus must be guaranteed. This is accomplished by not permitting high energy levels, coming from connected apparatus or other circuits located in the same area, to be present in the hazardous location. Intrinsically Safe Systems The certification exemption cannot be applied to reactive circuits due to their capability of storing energy. Inductive components, relay coils or solenoid valves often can operate with energy levels much lower than the limits for intrinsic safety, but the energy released when the circuit is open can cause the ignition of the dangerous mixture. In the same way, a capacitive circuit can cause ignition during discharge of the capacitor. Those types of apparatus must be equipped with devices to reduce the released energy to safe levels. The solution for making an inductive component safe is to parallel-connect a semiconductor diode to the coil so that released energy can be absorbed. For capacitive components, a resistor must be series-connected to reduce the discharged current to a safe leve