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Introduction to Test Equipment
Navy Electricity and Electronics Training Series (NEETS)
Chapter 1:  Pages 1-71 through 1-78

NEETS   Module 15 − Principles of Synchros, Servos, and Gyros

Pages i, 1−1, 1−11, 1−21, 1−31, 1−41, 1−51, 1−61, 1−71, 2−1, 2−11, 2−21, 2−31, 3−1, 3−11, 3−21, 4−1, Index



The TX-TDX-TR System performs subtraction when the system contains standard synchro connections. Addition can also be performed with this system by reversing the S1 and S3 leads between the TX and the TDX, and the R1 and R3 leads between the TDX and the TR. Remember, this system works like a basic synchro system when the rotor of the TDX is on 0º; in this condition the TR rotor follows the TX rotor exactly.


The TX-TDR-TX System performs subtraction when the system contains standard synchro connections. Addition can also be performed with this system when the R1 and R3 leads between the TDR rotor and TX No. 2 are reversed.


CONTROL SYNCHRO Systems contain control synchros and are used to control large amounts of power with a high degree of accuracy. These synchro systems control servos that generate the required power to move heavy loads.


CONTROL SYNCHROS are of three different types: the control transmitter (CX), the control transformer (CT), and the control differential transmitter (CDX). The CX and the CDX are identical to the TX and the TDX except for higher impedance windings. In theory, the CX and CDX are the same as the TX and TDX, respectively.


The CONTROL Transformer (CT) is a synchro device that compares two signals, the electrical signal applied to its stator, and the mechanical signal applied to its rotor. The output is an electrical voltage, which is taken from the rotor winding and used to control some form of power amplifying device. The phase and amplitude of the output voltage depend on the angular position of the rotor with respect to the magnetic field of the stator.


Control Transformer (CT) - RF Cafe


ERROR Signal is the name given to the electrical output of a CT. The reason is that the electrical output voltage represents the amount and direction that the CX and CT rotors are out of correspondence. It is this error signal that eventually is used in moving the load in a typical servo system.






Error Signal - RF Cafe


The SYNCHRO Capacitor is a unit containing three delta-connected capacitors. It is used in synchro systems containing either differential transmitters or CTs. The addition of the synchro capacitor to these systems greatly reduces the stator current and therefore increases the accuracy of the systems.


Synchro Capacitor - RF Cafe


The SPEED of DATA Transmission is simply the number of times a synchro transmitter rotor must turn to transmit a full range of values. You refer to the speed of data transmission as being 1- speed, 2-speed, 36-speed, or some other definite numerical ratio.


MULTIsPEED SYNCHRO Systems transmit a wide range of data at different speeds and still maintain a high degree of accuracy. To indicate the number of different speeds at which data is transmitted, refer to the system as being a single-speed, dual-speed, or tri-speed synchro system.


a DOUBLE RECEIVER consists of a fine and a coarse receiver enclosed in a common housing. It has a two-shaft output (one inside the other), and its operation may be likened to the hour and minute hands of a clock.






Double Receiver - RF Cafe


STICKofF Voltage is a low voltage used in multispeed synchro systems that contain CTs to prevent false synchronizations. The voltage is usually obtained from a small transformer and applied across the rotor terminals of the coarse CT.


Stickoff Voltage - RF Cafe


ELECTRICAL ZERO is the reference point for alignment of all synchro units.




SYNCHRO ZEROING Methods are various and depend upon the facilities and tools available, and how the synchros are connected in the system. Some of the more common zeroing methods are the voltmeter, the electric-lock, and the synchro-tester methods.


The VOLTMETER ZEROING METHOD is the most accurate and requires a precision voltmeter. This method has two major steps-the coarse or approximate setting and the fine setting. The coarse setting ensures the synchro is not zeroed 180º away from its reference. This setting may be approximated physically by aligning two marks on the synchro. The fine setting is where the synchro is precisely set on

0º .


Voltmeter Zeroing Method - RF Cafe


ELECTRICAL-LOCK ZEROING METHOD is perhaps the fastest. However, this method can be used only if the rotors of the synchros are free to turn and the leads are accessible. For this reason, this method is usually used on TRs.


Electrical-Lock Zeroing Method - RF Cafe




The SYNCHRO-TESTER ZEROING METHOD is potentially less accurate than the voltmeter or electric lock methods. This is because the dial on the tester is difficult to read and may slip from its locked position.


The synchro tester is nothing more than a synchro receiver on which a calibrated dial is mounted. The tester is used primarily for locating defective synchros but does provide a method for zeroing synchros.


Synchro-Tester Zeroing Method - RF Cafe


TROUBLE INDICATORS are signal lights used to aid maintenance personnel in locating synchro trouble quickly. These lights are usually mounted on a central control board and connected to different synchro systems. The lights indicate either overload conditions or blown fuses.


Trouble Indicators - RF Cafe


SYNCHRO TROUBLESHOOTING is the locating or diagnosing of synchro malfunctions or breakdown by means of systematic checking or analysis. This is done by using trouble indicators, trouble tables furnished by manufacturers, known operating voltages as references, and synchro testers.






Answers to Questions Q1. Through Q76.


A-1.   The synchro.


A-2.   Precise and rapid transmission of data between equipment and stations.


A-3.   Torque and control.


A-4.   a torque synchro is used for light loads and a control synchro is used in systems desired to move heavy loads.


A-5.   The torque receiver (TR) and the torque differential receiver (TDR).


A-6.   It is the third modification of a 26-volt 400-hertz (torque) synchro transmitter whose body diameter is between 1.01 and 1.10 inches.


A-7.   The Navy prestandard designation code.


A-8.   The position of the arrow.


A-9.   The rotor and the stator.


A-10.   The drum or wound rotor.


A-11.   By the magnetic coupling from the rotor.


A-12.   At the terminal board.


A-13.   The number and type of synchro receivers, the mechanical loads on these receivers and the operating temperatures of both the transmitter and receivers.


A-14.   a measure of how much load a machine can turn.


A-15.   Ounce-inches.


A-16.   Aircraft.


A-17.   When it is overloaded.


A-18.   Synchros have one primary winding that can be turned through 360º and three secondary windings spaced 120º apart.


A-19.   The transmitter is in its zero-position when the rotor is aligned with the S2 stator winding.


A-20.   When the rotor coil is aligned with the stator coil.


A-21.   The amplitude of the primary voltage, the turns ratio, and the angular displacement between the rotor and the stator winding.


A-22.   a synchro receiver uses some form of damping to retard excessive oscillations or spinning.


A-23.   Mechanical damping.


A-24.   a synchro transmitter and a synchro receiver.


A-25.   The rotor leads.




A-26.   The voltages are equal and oppose each other.


A-27.   Signal.


A-28.   1 and S3.


A-29.   The rotor leads on either the transmitter or the receiver are reversed.


A-30.   Differential synchros can handle more signals than regular synchros and also perform addition and subtraction functions.


A-31.   The TDX and the TDR.


A-32.   Their application: a TDX has one electrical and one mechanical input with an electrical output.


A-33.   The way the differential synchro is connected in a system is the deciding factor on whether the unit adds or subtracts its inputs.


A-34.   When the TDX rotor is on 0º.


A-35.   240º.


A-36.   80º.


A-37.   The S1 and S3 leads are reversed between the TX and the TDX, and the R1 and R3 leads are reversed between the TDX rotor and the TR.


A-38.   The R1 and R3 leads between the TDR rotor and the TX to which it is connected.


A-39.   Clockwise.


A-40.   a control synchro.


A-41.   CX, CT, and CDX.


A-42.   The CX and CDX have higher impedance windings.


A-43.   The rotor is specially wound, it is never connected to an ac supply, and its output is always applied to a high-impedance load.


A-44.   They are perpendicular to each other.


A-45.   The voltage is maximum and in phase with the ac excitation voltage to the CX.


A-46.   Error signal.


A-47.   When the CX and CT rotors are in correspondence.


A-48.   To improve overall synchro system accuracy by reducing stator currents.


A-49.   TDXs, CDXs, and Cts.


A-50.   Magnetizing current.


A-51.   They are delta-connected across the stator windings.




A-52.   To keep the connections as short as possible in order to maintain system.


A-53.   a dual or double-speed synchro system.


A-54.   Greater accuracy without the loss of self-synchronous operation.


A-55.   The gear ratio between the two transmitters.


A-56.   a tri-speed synchro system.


A-57.   If one of the receivers goes bad the entire unit must be replaced.


A-58.   It is used in synchro systems to prevent false synchronizations.


A-59.   Electrical zero.


A-60.   The voltmeter method.


A-61.   A61.It ensures the synchro is on 0º, not 180º.


A-62.   a TR is zeroed when electrical zero voltages exist across its stator windings at the same time its rotor is on zero or on its mechanical reference position.


A-63.   Approximately 37 volts.


A-64.   Never leave the circuit energized for more than 2 minutes.


A-65.   To ensure that it did not move off zero while it was being clamped.


A-66.   Zero or minimum voltage.


A-67.   The coarse synchro.


A-68.   The electrical lock method.


A-69.   It can be used only if the leads of the synchro are accessible and the rotor is free to turn.


A-70.   The synchro under test is not on electrical zero.


A-71.   Replace it.


A-72.   Improper wiring and misalignment.


A-73.   An overload indicator.


A-74.   The transmitter or main bus.


A-75.   150º  and 330º


A-76.   use only one receiver so as not to overload the tester.




NEETS Modules
- Matter, Energy, and Direct Current
- Alternating Current and Transformers
- Circuit Protection, Control, and Measurement
- Electrical Conductors, Wiring Techniques, and Schematic Reading
- Generators and Motors
- Electronic Emission, Tubes, and Power Supplies
- Solid-State Devices and Power Supplies
- Amplifiers
- Wave-Generation and Wave-Shaping Circuits
- Wave Propagation, Transmission Lines, and Antennas
- Microwave Principles
- Modulation Principles
- Introduction to Number Systems and Logic Circuits
- - Introduction to Microelectronics
- Principles of Synchros, Servos, and Gyros
- Introduction to Test Equipment
- Radio-Frequency Communications Principles
- Radar Principles
- The Technician's Handbook, Master Glossary
- Test Methods and Practices
- Introduction to Digital Computers
- Magnetic Recording
- Introduction to Fiber Optics
Note: Navy Electricity and Electronics Training Series (NEETS) content is U.S. Navy property in the public domain.
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