Intrinsic Safety (IS)

Intrinsically safe device (Exi) defined as "equipment and wiring which is incapable of producing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixtures in its most easily ignited concentration." This is achieved by limiting the amount of power available to the  electric equipment in hazardous area to a level below that which will ignite the gases.As an example hydrogen requires 20- micro joules of energy for ignition, the intrinsically safe equipments are incapable of generating 20- micro joules of energy

In intrinsically safe circuits,a safety barrier is used in the safe area for prevent the high energy level passing into the hazardous area due to any fault.Basically there are  two types of intrinsically safety barriers; Zener barrier (passive devices) and Galvanic isolators  (active devices).Functionally, they achieve the same objective that is prevention of high energy level passing into the hazardous area.


Zener Barriers

Zener barriers are passive devices that contain zener diodes,resistors and fuse to limit excess voltage and current.The zener diodes in the zener barrier are connected in the revers direction.The breakdown voltage of the  diode is not exceeded in normal operation.if this voltage is exceeded due to a fault in non hazardous area,the diode start to conduct, causing the fuse to blow,thus preventing the transfer of unacceptable high energy into the hazardous area.

Galvanic Isolaters

Galvanic isolaters are active devices,these provides galvanic isolation between the hazardous  and safe area using transformers,opto isolatores or relays.