Patent ID: 7633286
Filing Date: 2009-12-15
Classification: G01R

Abstract:
1. An electric current monitoring device arranged for measuring an electric current value of a signal current outputted to a two-wire transmission line by a measuring instrument that converts a physical quantity measured thereby to the signal current, comprising: an electric current detector inserted in the transmission line, for measuring an electric current value of the signal current outputted to the transmission line; a radio unit for radio-transmitting the electric current value measured by the electric current detector; and a supply voltage generator inserted in the transmission line, for outputting a voltage generated due to flow of the signal current through the transmission line; wherein the supply voltage generator includes: a transistor inserted in the transmission line and allowing the signal current to pass therethrough, a voltage detector connected to two electrodes of the transistor that is inserted in the transmission line, for detecting a voltage value of a voltage generated between the two electrodes due to flow of the signal current therebetween, a reference voltage generator connected to the two electrodes of the transistor, for outputting a predetermined reference voltage value, and a voltage comparator/regulator for comparing the reference voltage value outputted from the reference voltage generator with the voltage value detected by the voltage detector, and varying an internal resistance of the transistor to adjust the voltage between the two electrodes of the transistor to a predetermined voltage value, wherein the electric current detector and the radio unit are driven by the voltage outputted from the supply voltage generator.