Current measurement with magnetic sensors

Earth leakage current sensing devices and Hall effect current sensors are discussed. A closed loop device was developed for applications requiring greater accuracy and improved high frequency response. A secondary winding (typically 1000 turns) has current fed into it to oppose that of the primary current. Exact balance is detected by a zero output from the Hall element. The device in effect acts as a current transformer and the feedback current necessary to achieve zero balance is related to the current being monitored by the ratio of the number of primary to secondary turns. In order to achieve the high degree of sensitivity necessary for this method of operation a high permeability nickel-iron alloy is used for the magnetic core and indium antimonide for the Hall element