NEETS Module 15 — Principles of Synchros, Servos, and Gyros
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Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview
of the information you are expected to learn in the chapter. The comprehensive check questions placed throughout
the chapters are based on the objectives. By successfully completing the Nonresident Training Course (NRTC), you
indicate that you have met the objectives and have learned the information. The learning objectives for this
chapter are listed below.
Upon completing this chapter, you will be able to:
the term "synchro."
2. State the primary purpose of a synchro.
3. Explain the importance of synchros
in naval equipment.
4. Name the two general classifications of synchros.
Explain the differences between torque and control synchros.
6. Name the seven functional
classes of synchros and list all inputs and outputs.
7. Name the two types of synchro
8. Interpret all synchro markings and identify the particular codes
9. Draw the five standard schematic symbols for synchros and identify all connections.
Describe the general construction and physical appearance of synchro rotors and stators.
Name the two common types of synchro rotors, giving an application of each.
12. List the
different synchro characteristics and give a brief explanation of each.
13. State the
advantage of using 400-Hz synchros over 60-Hz synchros.
14. Explain the operation of a basic
synchro transmitter and receiver.
15. State the difference between a synchro transmitter and a
16. List the basic components that compose a torque synchro system.
17. Explain the operation of a simple synchro transmission system.
18. Define the
term "correspondence" and explain how it is used in a simple synchro system.
19. Explain the
principle behind reversing the S1 and S3 leads on a synchro receiver and how this action affects receiver
20. Explain what happens when the rotor leads on a synchro transmitter or receiver are
21. State the purposes of differential synchros.
22. Name the two types of
differential synchros and give a brief explanation of each.
23. Explain the difference between
the torque differential transmitter and the torque differential receiver.
24. Name the
components that make up the TDX and the TDR synchro systems.
25. Explain how the two
differential synchro systems add and subtract.
26. State the wiring changes required to
convert the differential synchro systems from subtraction to addition.
27. State the purposes
and functions of control synchros.
28. Name the different types of control synchros.
29. Explain how the CX and CDX differ from the TX and TDX.
30. Explain the theory
and operation of a control transformer.
31. List the basic components that compose a control
32. Explain the operation of a control synchro system and how it is used to control a servo system.
33. State the purpose and function of the synchro capacitor.
34. Explain how
synchro capacitors improve the accuracy of synchro systems.
35. Explain the method used to
connect synchro capacitors in a circuit.
36. Define single and multispeed synchro systems.
37. State the purposes and functions of multispeed synchro systems.
38. Stale the
purposes for zeroing synchros.
39. Name three common synchro zeroing methods and give a brief
explanation of each.
40. Explain the different troubleshooting techniques used in isolating
synchro malfunctions and breakdowns.
Synchros play a very important role in the operation of Navy equipment. Synchros are found in just about every
weapon system, communication system, underwater detection system, and navigation system used in the Navy. The
importance of synchros is sometimes taken lightly because of their low failure rate. However, the technician who
understands the theory of operation and the alignment procedures for synchros is well ahead of the problem when a
malfunction does occur. The term "synchro" is an abbreviation of the word "synchronous." It is the name given to a
variety of rotary, electromechanical, position-sensing devices. Figure 1-1 shows a phantom view of typical
synchro. A synchro resembles a
small electrical motor in size and appearance and operates like a variable transformer. The synchro,
like the transformer, uses the principle of electromagnetic induction.
Figure 1-1.—Phantom view of a synchro.
Synchros are used primarily for the rapid and accurate transmission of information between equipment and
stations. Examples of such information are changes in course, speed, and range of targets or missiles; angular
displacement (position) of the ship's rudder; and changes in the speed and depth of torpedoes. This information
must be transmitted quickly and accurately. Synchros can provide this speed and accuracy. They are reliable,
adaptable, and compact. Figure 1-2 shows a simple synchro system that can be used to transmit different as of data
or information In this system, a single synchro transmitter furnishes information to two synchro receivers located
in distant spaces. Operators put information into the system by turning the handwheel. As the handwheel turns, its
attached gear rotates the transmitter shaft (which has a dial attached to indicate the value of the transmitted
information). As the synchro transmitter shaft turns, it converts the mechanical input into an electrical signal,
which is sent through interconnecting wiring to the two synchro receivers. The receiver shafts rotate in response
to the electrical signal from the transmitter. When these shafts turn, the dials attached to the shafts indicate
the transmitted information.
Figure 1-2.—Data transfer with synchros.
By studying the simple synchro system, you can see that information can be transmitted over long distances,
from space to space, and from equipment to equipment.
In addition to supplying data by positioning dials
and pointers, synchros are also used as control devices in servo systems. When the synchro and the servo are
combined, they work as a team to move and position heavy loads. The methods used to accomplish this are covered in
detail in the next chapter.
Q-1. What is the name given to a variety of rotary electromechanical,
position sensing devices?
Q-2. What is the primary purpose of a synchro system?
Synchros work in teams. Two or more synchros interconnected
electrically form a synchro system. There are two general classifications of synchro systems—TORQUE SYSTEMS AND
CONTROL SYSTEMS. Torque-synchro systems use torque synchros and control-synchro systems use control synchros. The
load dictates the type of synchro system, and thus the type of synchro.
Torque-synchro systems are
classified "torque" because they are mainly concerned with the torque or turning force required to move light
loads such as dials, pointers, or similar indicators. The positioning of these devices requires a relatively low
amount of torque. Control synchros are used in systems that are designed to move heavy loads such as gun
directors, radar antennas, and missile launchers.
In addition to the two general classifications, synchros are grouped into seven basic functional classes as shown
in table 1-1. Four of these are the torque type and three are the control type. Each synchro is described in the
table by name, abbreviation, input, output, and the other synchro units that may be connected to it. Generally,
torque and control synchros may not be interchanged. The functional operation of each of these seven synchros is
covered later in this text.
Table 1-1.—Synchro Information
Synchros are also classified according to their operating frequency. This classification was brought about by
the development of the 400-Hz synchro. Prior to this time, the 60-Hz synchro was the only one in use. Synchro
operating frequencies are covered in detail in the section on synchro characteristics.
Name the two general classifications of synchro systems.
Q-4. What is the difference between a
torque synchro and a control synchro? Q-5. Using table 1-1, name two synchros that provide a
STANDARD MARKINGS AND SYMBOLS
Synchros used in the Navy can be grouped into two broad
categories: MILITARY STANDARD SYNCHROS and PRESTANDARD NAVY SYNCHROS. Military standard synchros conform to
specifications that are uniform throughout the armed services. New varieties of equipment use synchros of this
type. Prestandard synchros were designed to meet Navy, rather than service-wide, specifications. Each category has
its own designation code for identification.
Military Standard Synchro Code
The military standard designation code
identifies standard synchros by their physical size, functional purpose, and supply voltage characteristics. The
code is alphanumerical and is broken down in the following manner. The first two digits indicate the diameter of
the synchro in tenths of an inch, to the next higher tenth. For example, a synchro with a diameter of 1.75 inches
has the numeral 18 as its first two digits. The first letter indicates the general function of the synchro and of
the synchro system-C for control or T for torque. The next letter indicates the specific function of the synchro,
If the letter B follows the specific function designation, the synchro has a rotatable stator. The last number
in the designation indicates the operating frequency-6 for 60 Hz and 4 for 400 Hz. The upper-case letter following
the frequency indicator is the modification designation. The letter "A" indicates that the synchro design is
original. The first modification is indicated by the letter "B." Succeeding modifications are indicated by the
letters "C," "D," and so on, except for the unused letters "I," "L," "O," and "Q."
For example, an 18TR6A
synchro is an original design, 60-Hz torque receiver with a diameter of between 1.71 and 1.80 inches.
synchro designated 16CTB4B is the first modification of a 400-Hz control transformer with a rotatable stator and a
diameter of between 1.51 and 1.60 inches.
All standard synchros are labeled with such a code. Synchros
used in circuits supplied by 26 volts are classified in the same way, except that the symbol 26V is prefixed to
the designator (for example, 26V-16CTB4A). Otherwise, a 115 volts source is assumed for the synchro system.
Navy Prestandard Synchro Code
The Navy prestandard designation code identifies prestandard synchros by size and function, using a number and
letter combination. Unlike the standard code, the number does not indicate directly the diameter of the synchro.
The number merely represents the approximate size of the synchro, increasing as the size increases. The
approximate size and weight of the five most common sizes are shown in the following table.
Note that prestandard size 1 is approximately the same size as standard size 23 (2.21 to 2.30 inches in
diameter). Prestandard size 3 is approximately the same size as standard size 31. Prestandard size 5 is
approximately the same size as standard size 37.
The letters used in the prestandard coding system
indicate the function, mounting, or special characteristics of the synchro as shown in the following chart.
Navy prestandard synchros are rarely used today. They have been replaced by the standard synchro. However, by
being familiar with the prestandard coding system, you will be able to identify the older synchros and make
correct replacements if necessary.
Q-6. What does the code 26V-11TX4D mean on a synchro
Q-7. Which of the two synchro designation codes is indicated by 5DG on a synchro nameplate?
Schematic symbols for synchros are drawn by various manufacturers in
many different ways. Only five symbols (as shown in figure 1-3), however, meet the standard military
specifications for schematic diagrams of synchros and synchro connections. When a symbol is used on a schematic,
it will be accompanied by the military abbreviation of one of the eight synchro functional classifications (TR,
TX, TDX, etc.).
The symbols shown in views A and B of figure 1-3 are used when it is necessary to show only the external
connections to a synchro, while those shown in views C, D, and E are used when it is important to see the
positional relationship between the rotor and stator. The letters R and S, in conjunction with an Arabic number,
are used to identify the rotor and stator connections; for example, R1, R2, S1, S2, and S3. The small arrow on the
rotor symbol indicates the angular displacement of the rotor; in figure 1-3 the displacement is zero degrees.
Figure 1-3A.—Schematic symbols for synchros.
Figure 1-3B.—Schematic symbols for synchros.
Figure 1-3C.—Schematic symbols for synchros.
Figure 1-3D.—Schematic symbols for synchros.
Figure 1-3E.—Schematic symbols for synchros.
Q8. On the synchro schematic symbol, what indicates the angular displacement of the rotor?
Figure 1-4 shows a cutaway view of a typical synchro. Having the knowledge of how a synchro is constructed
should enable you to better understand how synchros operate.
Figure 1-4.—Typical synchro assembly.
In this section we will discuss how rotors and stators are constructed and how the synchro is assembled. Each
synchro contains a rotor, similar in appearance to the armature in a motor, and a stator, which corresponds to the
field in a motor. The synchro stator is composed of three Y-connected windings (S1, S2, and S3). The rotor
is composed of one single winding (R1 and R2). As you can see in the figure, the rotor winding is free to turn
inside the stator. The rotor is usually the primary winding and receives its voltage (excitation) from an external
voltage source. The stator receives its voltage from the rotor by magnetic coupling.
There are two common types of synchro rotors in use-the SALIENT-POLE ROTOR and the DRUM or WOUND ROTOR. The
salient-pole rotor shown in figure 1-5 has a single coil wound on a laminated core. The core is shaped like a
"dumb-bell" or the letter "H."
Figure 1-5.—Salient-pole rotor.
Introduction to Matter, Energy, and Direct Current, Introduction
to Alternating Current and Transformers, Introduction to Circuit Protection,
Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading, Introduction to Generators and Motors,
Introduction to Electronic Emission, Tubes, and Power Supplies,
Introduction to Solid-State Devices and Power Supplies,
Introduction to Amplifiers, Introduction to
Wave-Generation and Wave-Shaping Circuits, Introduction to 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