What are resolvers? Simply put, a resolver is a transformer with a fixed input winding and two rotating output windings placed orthogonal (i.e. at 90 degrees) to each other. Like a transformer, a resolver only works with AC voltages. If you add a third output winding and space them 120 degrees apart instead of 90 degrees, then the resolver becomes a synchro. So, synchros and resolvers are closely related and are often referred to as synchro-resolvers.

Resolvers are Super Precise

They are used in for instance robots, tools, weapons, ships, and airplanes as they are not only very precise but also extremely robust and reliable. They support wide temperature ranges and can handle shocks and vibrations. Resolvers excel in harsh environments.

If you put an AC voltage on the input winding of a resolver, a voltage develops on the output windings. However, as the output windings can rotate, the amplitude of the output voltage depend on the angle between an output winding and the input winding. One amplitude follows a sine wave, the other a cosine wave. From these amplitudes the angle between the rotating and fixed windings can be calculated. It is also possible to determine the rotation speed and its direction.

Resolvers are Repeaters

In this video we have a closer look at resolvers and, with the help of an old audio amplifier set two of them up as a master-slave repeater.