M4 Basic Electronics

Synchro Systems

Postby easaman » 11 Jan 2016 17:23

A synchro is, in effect, a transformer whose primary-to-secondary coupling may be varied by physically changing the relative orientation of the two windings. Synchros are often used for measuring the angle of a rotating machine such as an antenna platform. In its general physical construction, it is much like an electric motor. The primary winding of the transformer, fixed to the rotor, is excited by an alternating current, which by electromagnetic induction, causes currents to flow in three Y-connected secondary windings fixed at 120 degrees to each other on the stator. The relative magnitudes of secondary currents are measured and used to determine the angle of the rotor relative to the stator, or the currents can be used to directly drive a receiver synchro that will rotate in unison with the synchro transmitter. In the latter case, the whole device may be called a selsyn (a portmanteau of self and synchronizing).
Simple two-synchro system.

There are two types of synchro systems: Torque systems and control systems.
In a torque system, a synchro will provide a low-power mechanical output sufficient to position an indicating device, actuate a sensitive switch or move light loads without power amplification. In simpler terms, a torque synchro system is a system in which the transmitted signal does the usable work. In such a system, accuracy on the order of one degree is attainable.
In a control system, a synchro will provide a voltage for conversion to torque through an amplifier and a servomotor. Control type synchros are used in applications that require large torques or high accuracy such as follow-up links and error detectors in servo, automatic control systems (such as an autopilot system). In simpler terms, a control synchro system is a system in which the transmitted signal controls a source of power which does the usable work.

A synchro will fall into one of eight functional categories.

Torque Transmitter (TX)
Input: Rotor positioned mechanically or manually by the information to be transmitted.
Output: Electrical output from stator identifying the rotor position supplied to a torque receiver, torque differential transmitter or a torque differential receiver.

Control Transmitter (CX)
Input: Same as TX.
Output: Electrical output same as TX but supplied to a control transformer or control differential transmitter.

Torque Differential Transmitter (TDX)
Input: TX output applied to stator; rotor positioned according to amount data from TX that must be modified.
Output: Electrical output from rotor (representing an angle equal to the algebraic sum or difference of rotor position angle and angular data from TX) supplied to torque receivers, another TDX, or a torque differential receiver.

Control Differential Transmitter (CDX)
Input: Same as TDX but data supplied by CX.
Output: Same as TDX but supplied to only a control transformer or another CDX.

Torque Receiver (TR)
Input: Electrical angle position data from TX or TDX supplied to stator.
Output: Rotor assumes position determined by electrical input supplied.

Torque Differential Receiver (TDR)
Input: Electrical data supplied from two TX's, two TDX's or from one TX and one TDX (one connected to the rotor and one connected to the stator).
Output: Rotor assumes position equal to the algebraic sum or difference of two angular inputs.

Control Transformer (CT)
Input: Electrical data from CX or CDX applied to stator. Rotor positioned mechanically or manually.
Output: Electrical output from rotor (proportional to sine of the difference between rotor angular position and electrical input angle.

Torque Receiver-Transmitter (TRX)
This synchro was designed as a torque receiver, but may be used as either a transmitter or receiver.
Input: Depending on the application, same as TX.
Output: Depending on the application, same as TX or TR.
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