Types of Resolver



  • Synchro is often referred as cousin of resolver. 
  • People often interchange term for resolver as motion feedback sensors, transducer sensors, encoders and rotary position sensors. 
  • The application of resolver in the military, product packaging plants and stamping press lines.
  • There are two types of resolvers : 

        ( 1 ) Resolver control transmitter
        ( 2 ) Resolver control transformer

Resolver control transmitter


  • It is a rotary transformer in which magnitude of stator energy varies sinusoidally as the shaft rotates.


  • There are two windings in the resolver in which one primary winding or reference winding and two secondary windings ( SIN winding and COS winding ). 
  • The primary winding or reference winding is embedded in the rotor and supply given to it via rotary transformer. 
  • There are two windings embedded in stator slots which are at 90 degree mechanically displaced. 
  • An alternating supply is given to reference winding by rotary transformer, no need of brushes and slip rings.


  • When alternating supply ( Vr ) is given to reference winding, voltage induced in the stator SIN winding and stator COS winding. ( Two windings are displaced at 90 degree so it is called as SIN winding and COS winding ). 
  • The magnitude of the induced voltage depends upon multiplication of reference voltage and SIN or COS angle of input shaft from electrical zero ( EZ ) point.

       VS = Vr Sin θ

       VC = Vr Cos θ

  • The rotor shaft position θ depends upon SIN winding and COS winding.

       Tan θ = VS / VC

  • The ratio of two voltage represents absolute position of shaft.

        Shaft position of rotor θ = Tan – 1 ( VC / VS )


Electrical Zero Position

  • When rated alternating voltage is given to the rotor winding at rotor initial position ( zero degree ), zero voltage induced in the stator SIN winding ( SIN 0 degree = 0 ) and maximum voltage induced in the stator COS winding ( COS 0 degree = 1 ), this position is called as electrical zero ( EZ ) position.

Resolver control transformer

  • It has two stator winding ( SIN winding and COS winding ) and one rotor winding. 
  • The rotor output voltage is directly proportional to sine of angle difference between input angle of stator and mechanical position of shaft.
  • The rotor voltage is directly proportional to Sin ( Φ – θ )

        Where θ = Reference position of shaft

                  Φ = Stator input angle


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