Moving iron instrument movement with linear characteristic - uses moving magnet core and stator yoke with air grap dependent on their relative positions

摘要

A moving iron instrument movement has the moving iron shaft taking up a position dependent on currents through the stator coils with a linear characteristic. A stator yoke consists of two, roughly U-shaped, elements mounted in a surrounding flux-carrying core with four coils - one on each leg of the yoke. - A moving iron permanent magnet rotor is mounted on a shaft centrally between the two pole pairs. The radii of curvature of the moving magnet are not the same as the pole pair faces, nor are they concentric with it. As a result, the air gaps between the rotor and stator are dependent on their relative positions and this is arranged to give a rotor angular position against stator coil current characteristic which is almost linear.