IS barriers protect devices in hazardous areas
An intrinsic safety barrier is used to provide protection to a device mounted in a hazardous location. The basic components that make up most intrinsic safety barriers are a fuse, zener diodes, and a resistor and are shown below in this simple electrical diagram:
The circuit (or instrument) in the hazardous area operates normally until a fault condition occurs. In the illustration above, a fault voltage is applied to the terminals of the intrinsic safety barrier thus causing the zener diodes to “operate” and safely pass fault current to ground (rather than into the hazardous area). As a result of the fault current, the fuse will open and the complete loop maintains safety.
A simple analogy might include a steam engine with a pressure relief whistle. The steam engine operates normally until an overpressure situation causes pressure to be relieved in the form of excess steam.
The components used in a typical intrinsic safety barrier network perform much the same function. In the steam engine example, the engine continues to operate once the pressure has been relieved. In the case of an intrinsic safety barrier, this may or may not be the result since some IS barriers are designed to operate after the fault is removed while others will be rendered non-operational after a fault is applied. These situations obviously require further explanation, but I hope this simple example illustrates the basics of an intrinsic safety barrier.