Active/Passive Barriers

Active Barriers can give you a complete signal isolation between the field device and the control room equipment as they use its own power source to convert the signal and relays it back to control room or field. Commonly used
isolation techniques are Transformers and octo-couplers (called galvanic isolation). The passive barriers cannot isolate the signals from the field to the control room or vice versa. They simply have Zenar barriers and resisters
forming a network to limit the voltage and current delivered to the field.