10A1. General description. Self-synchronous transmitters and indicator units are used in the following I.C. systems:

Motor order telegraph system

Rudder angle indicator system

Bow and stern plane angle indicating systems

Underwater log system

Shaft revolution indicator system

Gyrocompass repeater system

Various fire control systems

Self-synchronous units are manufactured by various companies which refer to them by trade names such as Selsyns, Synchros, Auto syns, and Telmotors. The theory of operation is the same for all the various types of units. For brevity, they will be referred to as selsyns in the following text.

Thee are 2 basic designs of selsyn units, One employs a 3-phase motor and a single phase

  stator, the other employs a single-phase rotor and a 3-phase stator. Both are energized by 115 volts, 60 cycle, single-phase, alternating current. They will operate efficiently on a voltage and frequency variation of +- 10 percent. That is, they will operate in a voltage range of 103.5 volts to 126.5 volts and a frequency range of 54 cycles to 66 cycles. The 3-phase rotor, single-phase stator design is most commonly used in submarine equipment.

The indicators (motors) differ only mechanically from the generators (transmitters) in that a mechanism for dampening oscillations is mounted on the rotor shaft. Electrically, they are identical.

The type designations that the Navy uses for selsyn units indicate principally the size of the unit. Common types used in submarines are:

Types "A" and "B" transmitters (generators). Type "B" is larger than type "A."

Types "N" and "M" indicators (motors). Type "N" is larger than type "M."


Figure 10-1. Sectional view of type A transmitter.
Figure 10-1. Sectional view of type "A" transmitter.

Figure 10-2. Sectional view of type M indicator.
Figure 10-2. Sectional view of type "M" indicator.

10B1. Principle of operation. The following discussion is based on the 3-phase rotor, single-phase stator design (Figure 10-4).

The stator or fields of the transmitter and all indicators in the circuit are connected to the same supply. The 3-phase rotors are connected electrically. When the supply circuit is closed, a single-phase alternating current is impressed on the interconnected stators. The single-phase current in the stator windings, or primary circuits, induces voltages in the rotor windings, or secondary circuits. If the indicator rotors are in exact correspondence with the transmitter rotor, the voltage in phase 1 (R1) of the indicators is equal to the voltage in phase 1 of the transmitter. The same condition applies to phases 2 and 3 (R2 and R3). Because these voltages are balanced, no current will flow in these circuits. If the transmitter rotor is moved, the balance is destroyed. Currents then flow in the rotor

  circuits, setting up a torque. If the indicator rotor is free to turn, the reaction is a restoring of the original balance which results in the indicator rotor being, brought into agreement with the transmitter rotor.

10B2. Maintenance. a. General. The brushes and slip rings should be cleaned periodically with an approved solvent. Even though the silver slip rings and contacts may become discolored, the conductivity is not necessarily reduced. The ball bearings should be lubricated periodically with a small amount of light mineral oil. Sticky bearings, which may cause the indicators to move sluggishly or prevent them from following the transmitter accurately, should be repaired at once or the unit will burn out. The greater the displacement between transmitters and indicators, the greater the current flow. The dampener mechanism of the indicators should be inspected periodically to insure that its

Figure 10-3. Mechanical analogy of selsyn transmitter and indicator.
Figure 10-3. Mechanical analogy of selsyn transmitter and indicator.

Figure 10-4. Elementary wiring diagram of selsyn transmitter and indicators.
Figure 10-4. Elementary wiring diagram of selsyn transmitter and indicators.
action is not sluggish. All connections should be kept tight and the circuits kept clear of grounds. Should it become necessary to replace a unit, care must be taken to insure that all electrical circuits are connected in their proper relation. The following procedure will insure proper performance of instruments at all times:

1. If trouble develops in a system, always check the fuses and external wiring first. Inspect for short circuits, grounds, or opens before tampering with the instruments or selsyn units.

2. Check selsyn units for erratic or sticky operation.

3. See that all gears are tight on their shafts, and also that they are meshing properly.

4. Examine all bearings for dirt and free operation. Clean, and then lubricate them with a drop of fine, light oil.

5. Check the multipronged plug, jackboard, and the terminal bar solder connections for continuity.

  6. Instruments that must be opened to replace lamps or for other purposes should not be left open any longer than necessary. Take care that the ring light surfaces are not scratched. When replacing covers, make certain that the handle and rheostat shafts are properly aligned. The drain valve, which is at the lowest point of the instrument case, can be opened to remove moisture which may have condensed in the instrument. Opening of this drain valve will also equalize pressures during compartment air tests.

7. To replace self-synchronous motive power units, it is necessary to remove the entire interior mechanism and the jackboard internal wiring to the selsyn units.

CAUTION. When replacing a selsyn unit, the electrical zero marks on the unit must be aligned with the zero marks on the mounting plate and gears. (See Section 10B2c.)

b. Trouble indications. On page 137 is a table of conditions that may be encountered in the operation of selsyn units due to circuit derangements and mechanical troubles.


Figure 10-5. Elementary wiring diagram showing connections between selsyn transmitter and indicator.
Figure 10-5. Elementary wiring diagram showing connections between selsyn transmitter and indicator.

Trouble Indications Causes
Indicator pointers are 180 degrees out of position with the transmitter pointer. Reversed stator leads.
Indicators follow accurately as long as transmitter is moved along slowly. If transmitter is moved rapidly, indicators get out of position. Open stator lead.
Indicator moves erratically over dial. Open rotor lead.
Indicator is 120 degrees out to the right and rotates opposite to transmitter. Reversed R1 - R2
Indicator rotates opposite to transmitter rotation. Reversed R1 - R3
Indicator oscillates back and forth before coming to rest. Sticky damper.
Indicator does not follow accurately and has a pronounced hum Sticky bearings, bent shaft, or other misalignment.
Rotor operates as an induction motor The three rotor leads are shorted or connected together. Such a condition will quickly burn out the rotor winding.

c. Electrical zero setting. When a transmitter or an indicator is removed from an instrument and replaced, it is necessary to reset the arrow. The instructions given here assume that circuit MB is being set. The procedure is as follows:

1. Check to see that the transmitter arrow is at the center of the STOP position.

2. Install the new unit in position mechanically.

3. Cross connect S1 with R2 and S2 with R1 and R3 (see Figure 10-6).

4. Connect 115-volt, 60-cycle, single-phase, alternating current to leads marked MB and MBB. The rotor will now assume its electrical zero position.

  5. Loosen the setscrew that holds the arrow in position on the arrow collar and loosen the screws that hold the clamping collar.

6. Move the arrow to the center of the STOP position on the dial. Tighten the screws in the clamping collar, then tighten the setscrew that secures the arrow to the collar.

7. Replace the original external wires. The unit should now synchronize with the other units in the system.

NOTE. The electrical zero setting for instruments used in angle indicating systems should be made to center the indicating arrow on the 0 or zero position.

Figure 10-6. Selsyn connections for electrical zero.
Figure 10-6. Selsyn connections for electrical zero.


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