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 TM 55-1905-220-14-1
1-65. RUDDER ANGLE INDICATOR AND TRANSMITTER.
a. The Rudder Angle Indicator equipment provides the helmsman with a constant visual indication of rudder position
and of the rate of rudder movement. It consists of a waterproof case containing a synchro receiver, a pointer driven by
the synchro rotor, a dial, three 115-volt dial lamps, a rheostat, and a terminal block.
b. The dial is graduated in one degree increments from 40 degrees right to 40 degrees left rudder. During daytime
operation, the dial indications 'are white against a black background. When illuminated, the dial indications are red
against a black background. The rheostat allows the operator to vary the intensity of illumination over a wide range.
c. The Rudder Angle Transmitter consists of a waterproof case which contains a terminal block and a synchro
transmitter operated through a pair of gears by an arm connected to the rudder stock.
d. Each synchro contains a Y connected stator and a single winding rotor. The rotor windings of the two synchros are
connected to 115 volt 60 cps supply. By transformer action across the rotor gap, the rotor excitation voltage induces a
voltage in each leg of the Y connected stator winding. The voltages are different for each leg and vary with the angular
orientation of the rotor. Starting at a point where the rotor field is parallel to any one of the legs of the stator, turning the
rotor one complete turn will cause the induced voltage in the stator leg to start at zero, rise to a maximum of 90 volts
when the rotor field is perpendicular to the stator winding, decrease to zero, decrease to -90 volts (out of phase) and then
return to zero at the end of the revolution. Each successive leg of the Y connected stator will pass through zero at a
shaft position 120 degrees away from the preceeding leg.
e. A transmitter and receiver synchro pair are operated by connecting the stator leads (S1 to S2, S3 to S3) together
and applying 115 volt excitations to both rotors (R1, R2). If the rotors are at different shaft angles, the voltages induced
in the rotor windings will be different. This difference in voltage will allow a circulating current to flow in each leg of the
stator winding. The currents in turn, set up a force which turns -the rotor.
f. At the point where both rotors are aligned, the stator voltages will be equal and opposite in all three legs of the
stator winding. The force turning the rotor will be zero and the synchros will remain at the position until the rotor is
turned.
g. This system sets up torques on both transmitter and receiver equally and in opposite rotations. However, since the
transmitter is restrained while the receiver is free to turn, the receiver will follow the transmitter. Thus, the pointer follows
exactly the movement of the rudder and gives a constant indication of rudder position.
1-103
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