Abstract: A single-channel shunt-diode safety barrier for energizing a 2-wire transmitter, particularly for use in process control, incorporates within the barrier a floating d.c. power supply or its equivalent to enable the barrier to deliver into an earthed load a direct current substantially equal to that which it draws from the transmitter. The floating d.c. power supply is preferably derived from an external d.c. power source via a transformer or diode-pump circuit within the barrier itself. The barrier is enabled to pass superimposed digital or frequency signals in both directions to and from the transmitter.

Abstract: An electrical safety barrier which is adapted to pass a current returning from a hazardous area to a safe area but which will transmit negligible energy from the safe area to the hazardous area under fault conditions has in its return channel a fuse, shunt diodes and additional diodes. These additional diodes are either conventional rectifier diodes positioned at the safe-area end of the return channel or are Schottky diodes or diodes with a low forward voltage drop positioned at the hazardous-area end of the return channel.