Figure 4-52.--Type E ship's course indicator

40.129

Figure 4-52.--Type E ship's course indicator (designed for bulkhead mounting).

the 180 point, the servo would drive away from this

The use of the mixing network eliminates every

false null; but, because the 36X voltage has control, it

false null except the one at the 180 point of the

drives the servo toward this 180 point. The 36X

indicator dial. This null is eliminated by adding a 2.5-

error voltage (negative between 175 and 180) tends

volt, 400-Hz, antistickoff voltage in series with the 1X

to drive the servo to an increased angle (180). The

synchro rotor voltage, and shifting the phase of the

36X voltage is positive between 180 and 185, and

1X synchro voltage by 2.5 to bring the indicator null

tends to drive the servo to a decreased angle (180),

back to a true reading. This procedure converts the

the same point. In other words, if this condition were

180 point to an unstable (or recentering) null. If the

tolerated, the servo would lock in at a false null.

coarse (1X) and fine (36X) control transformers were

installed (adjusted to the same electrical zero as the

To remove this condition (false null), an

electrical zero position of the compass transmitters),

antistickoff voltage of 2.5 volts is obtained from a

there would be a position of the coarse control

transformer in the amplifier unit and applied to the

transformer shaft 180 out of correspondence with

coarse error voltage. This voltage is applied either in

the compass transmitter, at which the rotor volt ages

phase or 180 out of phase with the 1X error voltage

of both the coarse and fine control transformers

and is sufficient to shift the IX error signal null

would again both equal zero. Thus, the coarse

points 2.5. The resultant voltage does not pass

synchro system provides two null points in a complete

through the zero reference position of the 36XCT

cycle. Regarding the coarse control transformer

voltage. To restore the resultant voltage to the zero

(1XCT), its null at the 180 point is an unstable null,

reference position, the 1XCT stator is shifted 2.5 in

because if the shaft were on either side of that point,

its housing. Thus, the resultant 1X error voltage is

by an infinitesimal angle, the servo would drive

shifted a total of 5, which corresponds to 180

toward the correct null, 180 away. The fine synchro

rotation (36 x 1X) of the 36X synchro.

has 72 null positions or 36 times as many as the

coarse synchro system. If only the fine control

With antistickoff bias, the false null at the 180

transformer (36XCT) were connected in the system,

point cannot be attained by virtue of the 36X or 1X

there would be 36 positions of the transmitter shaft

error signal on either side of this point, both being of

that would produce a stable null error voltage. Only

such polarity as to drive in the same direction to the

one of these 36 positions is desired, that position

real null at zero degrees. The 36X error signal drives

being the point where the 1XCT also provides a stable

2.5 toward the correct null and then the mixing

null.

network switching to the 1X error signal, which

drives to 2.5 of the zero degree null position.

The mixing network switches the fine error signal

into the servoamplifier when the error is small

As the 2.5 point is reached, the mixing

(output of the coarse synchro is small) and introduces

circuit automatically shifts the amplifier input

the coarse error signal to the amplifier when the

signal from the 1X synchro to the 36X synchro.

error is large (output of the coarse synchro is large).

This signal, with amplifier output and motor

The coarse error signal can be small enough at the

torque reacting accordingly, is reduced as the

180 point to result in the tine error signal being fed

servo approaches null. The final null position is

into the servo, through the action of the mixing

reached at the point of minimum 36X synchro

network. If only the 1X error voltage were applied at

4-59