Control Systems

What is a Active Barrier ?

An active barrier uses transformers, optoisolators or relays to provide isolation between the hazardous area and the non-hazardous area.

It does not require an intrinsically safe ground connection. Either or both the hazardous area or the non-hazardous area signals may be grounded.

This may be the most logical barrier choice if a high quality I.S. grounding point is not available.

The below Figure shows a diagram of an active barrier. The barrier requires a 24 VDC power supply, and can typically drive larger loads than a loop powered zener barrier.

Active Barrier

Intrinsically safe systems should satisfy these requirements:

Ensure that there is a positive separation of intrinsically safe and non-intrinsically safe circuits. This prevents the ignition capable energy from intruding into the intrinsically safe circuit.
Separate conduit, panduit, cable trays, etc. should be used for I.S. wiring to keep it separate from the non-I.S. wiring. If conduit is used, it must be sealed per the applicable code. This is to prevent the conduit from becoming a means of conducting flammable material from the hazardous to the non-hazardous location. I.S. wiring must always be identified. This can be performed by tagging the wires, labelling the junction boxes, and/or color-coding the I.S. wires light blue.
Ensure that the entity parameters, upon which approval of the system is based, match up correctly.

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