A safety barrier, could be active and passive at same time. Imagine, for example, a loop powered pressure transmitter, placed in hazardous area,and connected to the DCS through a safety barrier. Since the transmitter is loop powered (passive), the safety barrier, in their transmitter or hazardous area terminals, must be “active”, due it has to supply energy for the loop powered device.
Furthermore, if the DCS field card is configured in active mode, providing the energy for the loop, our barrier, in their “safe area” terminals, must be passive (allowing current flow from-to DCS in same value that flows in the barrier-transmitter system).
In general, an active device, provides the necessary energy for the loop, an a passive device, is only a “receiver”, and the energy comes from other device (active device) in the loop (i.e. a transmitter with auxiliary power terminals, configured in active mode).