# Resolver Control Transmitter & Resolver Control Transformer

• In this article, principle, construction and working of resolver control transmitter and resolver control transformer is given.
• 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

### Principle of Resolver Control Transmitter

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

### Construction of Resolver Control Transmitter

• 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.

### Working of Resolver Control Transmitter

• When alternating supply ( Vr ) is given to reference winding, voltage induced in the stator SIN winding and stator COS winding.
• The 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