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 TM 55-1905-220-14-11
5-117. SHIP'S COURSE INDICATOR-MAINTENANCE INSTRUCTIONS (Continued).
If the control transformer rotor differs from this aligned or null position by an amount other than
180 electrical degrees, a voltage is induced in the (control transformer) rotor such that the phase of
the voltage indicates the direction of rotation from the aligned position. The magnitude of the voltage
is, for small angular rotations from the aligned position, proportional to the extent of angular
misalignment.
2
In the two-speed system the 36X control transformer passes through 72 nulls during a revolution of
the 1X dial. The servo circuit is controlled by the 1X speed synchro signal until the control
transformer signal is within +2.5 electrical degrees of position alignment. At this condition, the servo
circuit must switch to operate from the 36X synchro to provide fine position alignment.
(c) Anti-stickoff bias voltage.
1
The 36X control transformer determines the accuracy of the indicator, but because this synchro has
72 null positions for one revolution of the 1X indicator dial, the 1X synchro is used to determine the
proper null. The two synchro rotors are connected in shunt through a mixing network consisting of
pairs of diodes and two resistors. The mixing network performs three functions. First, it effectively
pens the 1X synchro rotor signal circuit whenever the indicator dial is within +2.5 degrees of null and
effectively closes the 36X synchro rotor signal circuits. Second, it limits or attenuates the 36X
synchro signal whenever the 36X synchro is more than +2.5 degrees from its null. Third, it keeps
synchro loading to its minimum allowable level.
2
The use of the mixing network anti-stickoff voltage eliminates every false null as an input signal to
the servo amplifier including the one at the 1800 point out of correspondence of the 1X synchro
control transformer. This null is eliminated by the effect of adding a 2.5 volt, 400 cps anti-stickoff
voltage in series with the 1X synchro rotor voltage, and shifting the phase of the 1X synchro voltage
by 2.5to bring the indicator null back to a true reading. The above procedure converts the 180out
of correspondence null point to an unstable (or decentering) null. If the coarse (1X), and fine (36X)
control transformers were adjusted to the same electrical zero as the electrical zero position of the
compass transmitters, there would be a position of the coarse control transformer shaft 180 degree
out of correspondence with the compass transmitter at which the rotor voltages of both the coarse
and fine control transformers
5-1308
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