SYNCHROS In Control System Engineering || Synchro Error Detector || Synchro Pair Characteristics

Topic and core message

A synchro is an electromechanical, inductive device (a rotating transformer) that converts mechanical angular position into electrical voltages — and vice versa. A typical synchro system pairs a synchro transmitter with a synchro control transformer (receiver) to detect angular error and provide a control signal for position-control systems.

A synchro converts mechanical angular position into electrical signals (and back). A transmitter + control transformer pair forms an error detector that produces an error signal proportional to angular displacement for closed‑loop position control.

Key concepts and definitions

• Synchro: an electromechanical, inductive device (rotating transformer) that produces output voltages dependent on rotor angular position — an electromagnetic transducer converting mechanical angle ↔ electrical signals.
• Synchro pair / error detector: the combination of a synchro transmitter and a synchro control transformer (receiver) used to detect angular difference (error) and provide a control signal for position control.
• Principle of operation: transformer action (Faraday’s law). Rotor excitation produces a rotating magnetic field that induces voltages in stator windings whose amplitudes depend on rotor angle.

Classification

• Control-type (control synchro)
  • Used for error detection, position control and heavy-load motion (e.g., gun directors, missile launchers, undersea detectors).
  • Control transformers/receivers often have cylindrical rotors for a uniform air gap and stable impedance.
• Torque-transmission type
  • Used for light-load torque transmission (e.g., dials, pointers, indicators).

Main components

Synchro transmitter

• Construction: rotor (commonly a dumbbell shape or similar) and a stator with three windings (S1, S2, S3) placed 120° apart.
• Operation in transmitter: rotor is typically the primary (given AC excitation) and the stator windings are the secondaries where voltages are induced.
• Induced stator voltages depend on rotor RMS excitation (Er), a coupling constant K, and rotor angle θ.
• Example (from video transcript; watch for caption errors):
  • Es1 = K · Er · cos(θ + 120°)
  • Es2 = K · Er · cos(θ)
  • Es3 = K · Er · cos(θ − 120°)
• Terminal (stator-to-stator) voltages can be written in forms involving √3·K·Er and shifted sine functions (e.g., E31 = √3·K·Er·sin θ, etc.).
• Waveforms: individual stator voltages are 120° apart; terminal-to-terminal voltages are similarly shifted.

Synchro control transformer (receiver)

• Construction: usually a cylindrical rotor (uniform air gap) and stator windings (S1, S2, S3).
• Operation in receiver: stator acts as the primary (fed from the transmitter) and the rotor is the secondary (output taken to the load).
• Connections: transmitter stator terminals are connected to the receiver stator terminals (S1↔S1, S2↔S2, S3↔S3).
• The receiver rotor shaft is mechanically coupled to the load (the position to be controlled).

Operation — stepwise

Synchro transmitter operation

1. Apply AC excitation to the rotor winding (rotor current flows).
2. Rotor produces magnetic flux that links the stator windings.
3. By transformer action, voltages are induced in stator windings; their magnitudes depend on rotor angle θ.

Synchro pair / error detector operation

1. Connect corresponding stator terminals of transmitter and control transformer (S1↔S1, S2↔S2, S3↔S3).
2. The transmitter supplies the receiver stator with equal-magnitude, phase-shifted voltages.
3. The receiver rotor sees a resultant induced voltage whose amplitude (the error signal) depends on the angular displacement φ between the transmitter rotor and the receiver rotor.
4. That induced rotor voltage is treated as the error signal: it is amplified (AC/differential amplifier) and fed to a servo (servo motor + gearing).
5. The servo moves the load/receiver rotor until the angular error is reduced (error signal goes to zero or the desired value), achieving closed-loop position control.

Relationship between signals and angular difference: the error amplitude is proportional to the transmitter excitation and to a trigonometric function of the angular difference φ (commonly a sine or cosine dependence). Exact algebraic forms should be checked against a reliable reference if precise formulas are required.

Representative equations (from video; verify before use)

• Stator voltages induced in transmitter:
  • Es1 = K·Er·cos(θ + 120°)
  • Es2 = K·Er·cos(θ)
  • Es3 = K·Er·cos(θ − 120°)
• Terminal voltages between stator coils: typically of the form √3·K·Er·sin(θ + phase)
• Control transformer (qualitative output):
  • Vout(t) ≈ K·VT·sin(ωt + φ) — described as proportional to angular displacement φ.

Note: captions/transcript in the source contained inconsistencies. Use a textbook or manufacturer datasheet for exact expressions.

Applications

• Position control systems (servo control)
• Remote position sensing and signaling
• Torque transmission for indicators and dials
• Error detection and position comparison (synchro pairs)
• Naval/navigation equipment, weapon aiming, underwater detection, industrial and aerospace positioning

Advantages

• Robust and reliable; low failure rate
• Self-synchronizing: speed/operation largely independent of load
• Long life expectancy
• Capable of measuring very small angular displacements
• Some designs eliminate the need for slip rings for rotor excitation

Disadvantages

• Higher cost per kW compared with induction machines
• Rotor excitation required in some designs
• May be less economical than alternative technologies for some applications

Takeaway / conclusion

Synchros are robust electromechanical transformers used to convert angular position into electrical signals and to detect angular differences. A transmitter paired with a control transformer acts as an error detector producing an error signal proportional to angular displacement; that signal can be amplified and used to drive servos for precise position control. The system’s construction, voltage relationships, operating sequence, classifications, and pros/cons make synchros useful in many industrial, naval, and aerospace applications.

Speakers / sources featured

• Single unnamed presenter/narrator (video lecturer)
• Background music; no other identified speakers