science

Synchro

Synchro is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Synchro rather than just read about it. In short: A synchro (also known as selsyn and by other brand names) 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 or transmitting rotation.

Key takeaways

Synchro belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Synchro to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Synchro from memory before moving on to harder problems.

Reference excerpt

A synchro (also known as selsyn and by other brand names) 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 or transmitting rotation. 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 voltages to appear between the Y-connected secondary windings fixed at 120 degrees to each other on the stator. The voltages are measured and used to determine the angle of the rotor relative to the stator.

Uses Synchro systems were first used in the control system of the Panama Canal in the early 1900s to transmit lock gate and valve stem positions, and water levels, to the control desks.

Fire-control system designs developed during World War II used synchros extensively, to transmit angular information from guns and sights to an analog fire control computer, and to transmit the desired gun position back to the gun location. Early systems just moved indicator dials, but with the advent of the amplidyne, as well as motor-driven high-powered hydraulic servos, the fire control system could directly control the positions of heavy guns. Smaller synchros are still used to remotely drive indicator gauges and as rotary position sensors for aircraft control surfaces, where the reliability of these rugged devices is needed. Digital devices such as the rotary encoder have replaced synchros in most other applications. Selsyn motors were widely used in motion picture equipment to synchronize movie cameras and sound recording equipment, before the advent of crystal oscillators and microelectronics. Large synchros were used on naval warships, such as destroyers, to operate the steering gear from the wheel on the bridge.

Synchro system types 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. Quite often, one system will perform both torque and control functions. Individual units are designed for use in either torque or control systems. Some torque units can be used as control units, but control units cannot replace torque units.

Synchro functional categories 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) 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.

… excerpt ends here. Continue reading the full article.

Illustrations

Synchro: Schematic of a synchro transducer. The complete circle represents the rotor. The solid bars represent the cores of the windings next to them. Power to the rotor is connected by slip rings and brushes, represented by the circles at the ends of the rotor winding. As shown, the rotor induces equal voltages in the 120° and 240° windings, and no voltage in the 0° winding. [Vex] does not necessarily need to be connected to the common lead of the stator star windings. — Schematic of a synchro transducer. The complete circle represents the rotor. The solid bars represent the cores of the windings next to them. Power to the rotor is connected by slip rings and brushes, represented by the circles at the ends of the rotor winding. As shown, the rotor induces equal voltages in the 120° and 240° windings, and no voltage in the 0° winding. [Vex] does not necessarily need to be connected to the common lead of the stator star windings.

Worked examples

Example 1 — a first encounter with Synchro

Start with the simplest possible case. Write down what Synchro claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Synchro before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Synchro ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Synchro

In research: Synchro appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Synchro in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Synchro is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric transformers, Transducers, so understanding it makes those chapters shorter.
In everyday life: Look for Synchro outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Synchro in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Synchro means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Synchro out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Synchro in simple terms?

Why does Synchro matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Synchro?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Synchro.