Intrinsic Safety (Ex i)
Intrinsic safety (Ex i) is a protection technique for electrical equipment in explosive atmospheres that limits the electrical and thermal energy in a circuit below the level that can ignite a specified gas or dust. Energy is restricted by associated apparatus, such as zener barriers or galvanically isolated barriers, located in the safe area. Protection levels are ia (suitable down to Zone 0), ib (down to Zone 1) and ic (Zone 2 only). The technique is widely used for transmitters, sensors, solenoid valves and other low-power instruments, and permits live maintenance. System design compares the entity parameters of field devices and associated apparatus (Ui/Uo, Ii/Io, Pi/Po, Ci/Co, Li/Lo), including cable capacitance and inductance. Equipment requirements are defined in IEC 60079-11 and installation in IEC 60079-14, with certification under ATEX or IECEx.
Examples
- Ex ia pressure transmitter in a Zone 0 area
- Isolated barrier for a 4–20 mA loop
- NAMUR proximity sensor in a hazardous area