TM 11-5840-281-35/1
load winding reaches a minimum and the current
is applied 180 degrees out-of-phase with respect to the
increases sharply through resistor R8812.
The
first.
increased current results in an increased voltage drop
(5) The turn-on gates produced by the
across resistor R8812 which is coupled as a positive
second circuit are delivered to switch Q8801 coincident
gate through blocking diode CR8813 to the control gate
with the negative-going cycle of the A-phase voltage.
contact of silicon-controlled rectifier switch Q8802.
The circuits of magnetic amplifier AR8801 and gating
(2) Control of magnetic amplifier AR8801 is
switches Q8801 and Q8802 control the speed of azimuth
provided by the bias and control winding. The bias
drive motor B1002 in one direction of rotation. The
winding receives its input from the bias circuit and the
circuits of magnetic amplifier AR8802 gating switches
control winding receives the input from the electronic
Q8803 and Q8804 are identical and control the motor
control preamplifier. The bias circuit delivers a dc
speed in the opposite direction. The control windings of
current through the bias windings (pins 7 and 8) of
magnetic amplifiers AR8801 and AR8802 are in series,
magnetic amplifier AR8801, and develops a field that
but are connected opposite to each other so that one
opposes the field developed by the positive reference
direction of current flow acts as a forward-bias in one
cycle. The bias current is adjusted to keep the core of
magnetic amplifier, and a reverse-bias in the other.
magnetic amplifier AR8801 just below the point of
Secondary windings 3, 4, and 5 of transformer T8801,
saturation during the peak positive excursion of the
along with rectifier diodes CR8801 and CR8802, provide
reference voltage.
an independent bias supply whose output is proportional
(3) When an error current is delivered from
to the ac input of the magnetic amplifiers in case of
the electronic control preamplifier through the control
power variations. Electrolytic filter capacitor C8801 is
windings (pins 5 and 6 of magnetic amplifier AR8801), in
protected by regulator diode CR8803 from any reverse
the direction that aids the positive reference voltage field,
voltage which might result from the voltage induced in
the core of magnetic amplifier AR8801 saturates at the
the windings of magnetic amplifier AR8802. Control
peak of the reference voltage and a silicon-controlled
R8803 balances the bias current through the magnetic
rectifier turn-on gate is produced. As the error current is
amplifiers so that both are operating at the same point on
increased, the silicon-controlled rectifier turn-on gate is
their magnetic curve. BIAS ADJ control R8802 is used
produced earlier in the positive reference cycle.
to set the level of the bias current so that with zero
(4) In the case of zero error current, the
control current, the magnetic amplifiers are just out of
core does not reach saturation; however, a small positive
saturation at the peak of the positive7-ctrrent cycle and
voltage is still developed across resistor R8812, which
begin to saturate with a minimum allowable control
could be coupled through blocking diode CR8813 as a
current.
turn-on voltage.
To prevent this, diode CR8811
(6) The reference winding of azimuth drive
conducts during the full positive half-cycle through
motor B1002 requires a voltage which is 90 degrees
resistors R8814 and R8818. The current through R8813
from the A-phase control winding voltage.
produces a voltage of polarity which back-biases
Reference transformer T9001 on the azimuth drive motor
blocking diode CR8813 against the false turn-on voltage.
amplifier chassis is connected across the Band C-phase
Thus, switch Q8802 will be gated-on during the positive
legs of the primary power.
half-cycle of the ac reference voltage, completing the
Transformer T9001 is a tapped autotransformer used to
120 vac (phase A) circuit (through switch Q8802) to
reduce the amplitude of the reference voltage for the
motor control no. 1 winding. To utilize the negative half-
motor. When SCAN switch S1(6 on Radar Receiver-
cycle, a second load winding (pins 1 and 2) of magnetic
Transmitter RT-818/TPN-18 is placed to OFF, a low-
amplifier AR8801, and associated similar circuitry, is
voltage tap from transformer T9001 provides a low-
utilized to gate-on switch Q8801 during negative half-
voltage input to the reference sufficient to hold the motor
cycles. The second circuit is exposed to the same bias
and antenna in a fixed position with a minimum amount
and control fields as the first circuit and operates
of heat produced in the motor. When SCAN switch S106
identically to it, except that the reference voltage to the
is placed to ON, the second tap is used to provide the
second
load
winding
normal line voltage to the reference winding of the motor.
f. Remote Switching Control C-6989/TPN-18 Circuit (fig.
7-8 and 7-36). Remote Switching
2-27
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