Resolver (electrical)

A resolver is a type of rotary electrical transformer used for measuring degrees of rotation.

The exciter winding is located on the top; it is a coil of a turning (rotary) transformer.

This rotary transformer induces current in the rotor without wires or brushes to provide a direct electrical connection.

The two two-phase windings, fixed at right (90°) angles to each other on the stator, produce a sine and cosine feedback current.

This device may also appear in non-brushless type, i.e., only consisting in two lamination stacks, rotor and stator.

Resolvers can perform very accurate analog conversion from polar to rectangular coordinates.

When used with electronic driver amplifiers and feedback windings tightly coupled to the input windings, their accuracy is enhanced, and they can be cascaded ("resolver chains") to compute functions with several terms, perhaps of several angles, such as gun (position) orders corrected for ship's roll and pitch.

This allows for geared reduction of assemblies being rotated and improved accuracy from the resolver system.