Brushless encoders are devices for measuring angle. They are sometimes referred to as brushless resolvers, rotationally variable differential transformers (RVDTs) or inductive encoders. As with brushless motors, brushless encoders have no electrical connection to the rotor and hence do not require any electrical contacts, slip-rings or brushes.
This contrasts with brushed devices such as synchros or some resolvers in which the rotor is supplied with AC signal by the host system. As the active rotor displaces relative to other windings, the amount of inductive coupling varies in proportion to angular displacement.
Brushless encoders offer the advantages of long life and the eradication of periodic service or maintenance. The most popular form of brushless encoder is the inductive encoder or incoder. Incoders use the same basic physic as brushless resolvers :- a passive rotor varies the inductive coupling to a stator according to its angular displacement. The advantage of the inductive encoder is high levels of reliability, accuracy and long life in harsh conditions. Incoders are typically described as ‘fit and forget’ devices.