A magnetoresistive residual current sensor

This paper details the element topology and preliminary experimental results of a magnetoresistive sensor for use as a detector within Residual Current Devices (RCDs). The utilisation of thin film sensors provides the possibility of fabricating hybrid electrical safety devices with better cost/performance ratios than existing toroid technology. A serpentine meander path arrangement was photoetched from a Permalloy thin film to form the four arms of an electrical bridge. The results suggest that detection of a 5 A residual current with resolution of better than 1 mA is possible. Reliable detection of a 5 mA residual current fault is still possible whilst operating with standing (line) currents as high as 15 A in the circuit.