Permanent magnet assembly for moving coil instrument - has composite core incorporating moulded magnetic plastic ring ensuring homogeneous flux distribution

摘要

The permanent magnet assembly (1) for a moving coil instrument having a linear scale has a composite core formed by a central boss (6) of ferromagnetic material which in the preferred construction is surrounded by a ring (2) of moulded magnetic plastic which may either have isotropic properties or may be magnetised radially to provide a bipolar flux. The core (6.2) is concentric with a soft iron ring (3) which provides the return flux path leaving a uniform annular air gap (4) for the coil, and two slots (7) are moulded in the core (2) to enable its correct orientation within the instrument. ADVANTAGE - Provides homogeneous flux distribution of uniform density in air gap. Moulded core has inherently precise dimensions, obviating need for machining, and fixing means, together with type member etc., are readily moulded-in, giving reduced manufacturing costs.