This document discusses synchros, which are electromechanical devices that produce an output voltage based on the angular position of the rotor rather than the rotor speed. There are four basic types: transmitters, receivers, transformers, and differentials. Transmitters convert mechanical rotation into electrical signals, with the voltage induced in the stator coils depending on the rotor angle. Receivers operate in reverse, using applied voltages to cause the rotor to align with the stator field. Differentials can measure the speed difference between a transmitter and receiver. The document provides examples and diagrams to illustrate the voltage relationships and functions of the different synchro components.

1. ICE 3015: CONTROL SYSTEM
COMPONENTS
Class 9: Synchros – Transmitters,
Differentials, Governing Equations
Dr. S. Meenatchisundaram
Email: meenasundar@gmail.com
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

2. Recall:
• Synchros are electromechanical devices which produce an
output voltage depending on angular position of the rotor and
not on rotor speed and it is different from a DC generator.
• The trade name for Synchros are Selsyn, Antosyn and Telesyn.
• Functionally, they resemble transformers whose primary to
secondary magnetic couplings may be varied by physically
changing the relative orientation of the two windings.
• The four basic types of Synchros
—transmitter
—receiver
—Transformers and
—Differentials
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

3. Transmitter:
• This is a mechanical to electrical transducer which consists of a
transformer core iron as stator shown in figure.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

4. Transmitter:
• The basic principle of the synchro is that the voltage induced in
the secondary depends on the angle at which the magnetic lines
of the flux cut the turns.
• This induced voltage will vary from a maximum of 1 when the two
windings are in line are parallel to 0 when they are perpendicular.
• Three poles, equally spaced at 120°are attached to the stator with
windings S1, S2, and S3.
• One end of each of three winding is connected internally to each
other to form a Y.
• The other ends are for external connection.
• Inside the core of the stator the rotor rotates with a single winding
brought out and connected through slip rings for unlimited rotation.
• The rotor is a primary winding and the stator is secondary winding.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

5. Transmitter:
• In the above figure, S2 and rotor are inline and maximum voltage
is induced in S2.
• The voltage induced in S1 and S3 are less.
• As the rotor rotates, the induced voltage will be
Es2 = K ER cos ɵ
Where,
Es2 – rms voltage in stator coil 2
ER – rms voltage in rotor
K – proportionality constant (depends on mag coupling & no. of turns)
ɵ - rotor angle in anti clockwise direction
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

6. Transmitter:
• The voltage induced in S1 and S3 can be given as
Es1 = K ER cos (ɵ+120°)
Es3 = K ER cos (ɵ-120°)
• The voltage between respective terminals can be given as,
Es31 = 3 K ER sin ɵ
Es12 = 3 K ER sin (ɵ - 120°)
Es23 = 3 K ER sin (ɵ + 120°)
• The waveform representation is shown in figure below
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

7. Transmitter:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

8. Example:
• The voltage applied to the rotor of a synchro transmitter is 28V rms. The
rotor shaft is moved 60°from the zero position towards clockwise direction.
Determine the stator voltages w.r.t the common stator connection for k=1.
Also determine the voltages between terminals S1 and S2, S2 and S3 and
S3 and S1. Take S2 as the reference winding.
Solution:
• Es2= K ER cos ɵ = 1 x 28 x cos 60°= 14V
• Es3= K ER cos (ɵ + 120°) = 1 x 28 x cos (60°+ 120°)= - 28V
• Es1= K ER cos (ɵ - 120°) = 1 x 28 x cos (60°- 120°)= 14V
• Es31= 3 K ER sin ɵ = 42V
• Es12= 3 K ER sin (ɵ - 120°) = - 42V
• Es23= 3 K ER sin (ɵ - 120°) = 0V
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

9. Receiver:
• In synchro transmitter, the terminal voltage is governed by angular
position of the rotor.
• In synchro receiver it is the reverse, that is, it will act as a voltage to
position transducer.
• A single phase voltage is applied to each of the three stator
winding and ac excitation to the rotor winding and mutual
repulsion gives the angle of the rotor shaft.
• Initially the magnetic field set by the stator and rotor windings cause
the rotor to be aligned in line with the stator winding S2.
• When the magnitudes of the stator voltages changed, the stator
current also changes. The resultant stator field changes direction,
causing the rotor field to follow it.
• As the rotor field follows the resultant stator field, the rotor shaft
starts to turn. Rotor motion is tampered by the fly wheel.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

10. Differentials:
• When the difference in shaft speed between the transmitter and
the receiver is required, we use differential synchro.
• There is hardly any difference between the construction of
synchronous generator and motor and between the differential
generator and motor except that the differential system has three
winding in the rotor also.
• In a differential generator, voltage is applied to the stator windings.
As the rotor turns, varying voltages are obtained at the rotor
terminals.
• In the differential motor, voltage applied to both rotor and stator.
The resultant magnetic field decide the position of the rotor.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

11. Differentials:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

12. References:
• Smarajit Ghosh, “Control Systems: Theory And Applications”,
Pearson Education India, 2004.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018