What is Synchros

The Synchros is a particular kind of transducer that converts the angle of the shaft into an electric signal. Both an error detector and a rotary position sensor are employed. The shaft’s alignment issue is what causes the system error. The transmitter and the control transformer are the synchro’s two primary components.

Synchros System Types

The synchro system is of two types. They are

1. Control Type Synchro.
2. Torque Transmission Type Synchro.

Torque Transmission Type Synchros

Due to their low output torque, this type of synchro is used to drive very light loads, such as pointers. Driving the heavy loads requires the Synchro control type.

Control Type Synchros System

In positional control systems, the controls synchros is employed for error detection. Their systems are made up of two units. Those are

1. Synchro Transmitter
2. Synchro receiver

These two parts and the synchro always function together. So Below is a detailed explanation of the synchros transmitter and receiver.

Synchros Transmitter

They are built similarly to three-phase alternators. To minimize iron losses, the stator of the synchros is made of steel. The three phase windings fit into slots in the stator. The stator winding’s axes are kept 120 degrees apart from one another.

The AC voltage is applied to the rotor of the transmitter and it is expressed as

Where V_r – r.ms.value of rotor voltage
ω_c – carrier frequency

The stator winding coils are connected in a star pattern. The synchros’ dumbbell-shaped rotor has a concentric coil wound on it. Slip rings are used to apply the AC voltage to the rotor. The figure below illustrates the synchros’ constructional feature.

Consider the voltage is applied to the rotor of the transmitter as shown in the figure above. 

The rotor’s magnetizing current and an alternating flux are brought about by the voltage applied to it. The mutual induction of the rotor and stator flux causes the voltage to be induced in the stator winding. So The cosine of the angle between the rotor and the stator is equal to the flux linked in the stator winding. The stator winding induces the voltage.

So Let V_s1, V_s2, V_s3 be the voltages generated in the stator windings S₁, S₂, and S₃ respectively. The figure below shows the rotor position of the synchro transmitter. So The rotor axis makes an angle θ_r concerning the stator windings S₂.

The three terminals of the stator windings are

The variation in the stator terminal axis concerning the rotor is shown in the figure below.

The stator windings S2 generate the most current when the rotor angle is zero. The rotor’s zero position serves as a guide for calculating its angular position. So The stator winding of the control transformer, which is depicted in the above figure, receives the transmitter’s output. The transmitter and control transformer of the synchros are both subject to the same, large current. The air gap flux of the control transformer is established due to the circulating current.

The flux axis of the transmitter and the control transformer are positioned parallel to one another. So The cosine of the angle between the rotors of the transmitter and controller equals the voltage produced by the control transformer’s rotor. Voltage is specified as

Where φ – angular displacement between the rotor axes of transmitter and controller.
Φ – 90º the axis between the rotor of transmitter and control transformer is perpendicular to each other. So The above figure shows the zero position of the rotor of transmitter and receiver.

Consider the position of the rotor and the transmitter is changing in the same direction. So An angle θ_R deflects the rotor of the transmitter and that of the control transformer is kept θ_C. The total angular separation between the rotors is Φ = (90º – θ_R + θ_C)

The rotor terminal voltage of the Synchro transformer is given as 

So The small angular displacement between their rotor position is given as

Sin (θ_R – θ_C) = (θ_R – θ_C)

On substituting the value of angular displacement in equation (1) we get

The synchro transmitter and control transformer worked together to find the mistake. So The rotor shaft position of the control transformer and transmitter’s control transformer and transmitter are equal in the voltage equation above.

The differential amplifier receives the error signal before providing input to the servo motor. And So The control transformer’s rotor is turned by the servo motor’s gear.

So The output of the synchro error detector, which is a modulated signal, is shown in the above figure. So The misalignment between the rotor position and the carrier wave was visible in the modulating wave above.

Where K_s is the error detector.