Intrinsically Safe Barriers

The most important function of an intrinsically safe barrier is the use of it in the hazardous area. The barrier is a passive device, that is, it does not need any power source to function. It can be used to pass 4-20 mA at a nominal voltage of 24 V without any loss in power.

The barrier is made up of a wire wound resistor and zener diodes.

The wire wound resistors are used for limiting current and the zener diode is used to limiting the voltage.

A fuse will be used in series with the resistor. A high voltage is the main cause of explosion in hazardous areas if the fuse and resistor is used without zener diode. This can pass this high voltage in hazardous area before the fuse blows thereby causing the explosion in hazardous gas filled areas so that we cannot rely on just fuse, as only microsecond is needed to cause an explosion under the right condition.

Thus a zener diode which can limit the fluctuation in voltage can be used to bypass these voltages in hazardous areas. The zener diodes are generally connected in parallel to the circuit as shown below

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