Magnetooptical ammeter

A Kerr magnetooptical ammeter is described which uses a Permalloy thin film in order to make contact-free measurements of the current flowing through a conductor. The device is useful for current measurement in high-voltage lines. In this ammeter, the strength of the current is measured by measuring the position of a domain wall which traverses a narrow channel sensor composed of a Permalloy thin film under the stray magnetic field due to a current. Contact-free observation of the domain wall is achieved by means of a Kerr magnetooptical apparatus using a high-pressure mercury lamp as a light source. The easy axis of the Permalloy thin film is parallel to the stray magnetic field. The domain wall traverses a distance of 15 mm at 70 amperes. The size of the sensor is 0.5 by 20 mm.