US Patent 7633286 Electric current monitoring device

An electric current monitoring device is provided to be used in conjunction with a measuring instrument that converts a physical quantity measured thereby to a signal current and outputs the signal current to a two-wire transmission line. The electric current monitoring device includes an electric current detector inserted in the transmission line for measuring an electric current value of the signal current outputted to the transmission line, and a supply voltage generator inserted in the transmission line for outputting a voltage generated due to the flow of the signal current. The electric current detector is driven by the voltage outputted from the supply voltage generator.