Schematic Symbols

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.

Q.8 On the synchro schematic symbol, what indicates the angular displacement of the rotor?

SYNCHRO CONSTRUCTION

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.

ROTOR CONSTRUCTION

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.

This type of winding is frequently used in both transmitters and receivers.

The drum or wound rotor has coils wound in slots in a laminated core as shown in figure 1-6. This type of rotor is used in most synchro control transformers and differential units, and occasionally in torque transmitters. It may be wound continuously with a single length of wire or may have a group of coils connected in series. The single continuous winding provides a distributed winding effect for use in transmitters. When the rotor is wound with a group of coils connected in series, a concentrated winding effect is provided for use in control transformers. When used in differential units, the rotor is wound with three coils so their magnetic axes are 120 apart.

Figure 1-6. - Drum or wound rotor.

Both types of synchro rotors have their coils wound on laminated cores that are rigidly mounted on a shaft. To enable the excitation voltage to be applied to the rotor winding, two slip rings are mounted on one end of the shaft and insulated from the shaft to prevent shorting. An insulated terminal board, mounted on the end of the cylindrical frame, houses the brushes, which ride on the slip rings. These brushes provide continuous electrical contact to the rotor during its rotation. Also mounted on the rotor shaft are low-friction ball bearings, which permit the rotor to turn easily.

STATOR CONSTRUCTION

The stator of a synchro is a cylindrical structure of slotted laminations on which three Y-connected coils are wound with their axes 120 apart. In figure 1-7, view A shows a typical stator assembly consisting of the laminated stator, stator windings, and cylindrical frame; view B shows the stator lamination and the slots in which the windings are placed. Some synchros are constructed so both the stator and the rotor may be turned. Electrical connections to this type of stator are made through slip rings and brushes.

Figure 1-7A. - Typical stator

Figure 1-7B. - Stator lamination.

Now, refer to figure 1-4 for a view of a completed synchro assembly. The rotor has been placed in the stator assembly, and a terminal board has been added to provide a point at which internal and external connections can be made.

Q.9 What are the two major components of a synchro?
Q.10 Which of the two main types of rotors can have either a single winding or three Y-connected windings?
Q.11 How does the stator receive its voltage?
Q.12 Where are the external connections made on standard synchros?