All the voltages, except for the 24-volt dc
rapid acceleration of the motor, which could allow
transducer (xdcr) power, are distributed directly
the motor to overshoot the desired PLA actuator
from the A2 assembly. The 24-volt dc power
position. Tachometer feedback reduces this
source for the PT2 and PT5.4 pressure transducers
problem. If the feedback signal was not present,
for both engines are distributed from the Al
the desired position would be passed. This would
assembly.
force the system to backtrack by turning the
motor in the other direction; it would eventually
PLA ACTUATOR ELECTRONICS
seesaw past the desired position a number of times
before it settled at the correct position. The
The main functions of this subsystem are
tachometer feedback anticipates the overshooting
to condition the command signal, compare it
of the correct position and acts as a braking
to the feedbacks from the actuator, and provide
system for the motor. This is the same function
the signal to drive the PLA actuator to the
that a compensating system in a hydraulic
commanded position. In conjunction with
governor provides.
the main functions, this subsystem provides
monitoring of certain system parameters for the
Slider Potentiometer
protection of the GTE and power train. The PLA
actuator electronics are identical in both model
The slider potentiometer provides a position
FSEEs. The major difference between the
feedback signal, which is proportional to the
actuator electronics of both models is location.
position of the PLA actuator shaft and MFC
I n the FSEE on the CG-, and DD-class
lever. It is a linear nonwire-wound variable
ships, the PLA actuator electronics are located
resistance whose potentiometer slider position is
in the A2 power supply set. In the FSEE on the
controlled by the actuator output shaft. Two gears
FFG-class ships, they are located in the A3 and
between the output shaft and the potentiometer
A4 dc power distribution assemblies.
increase the potentiometer's range of rotational
The PLA electronics are composed of three
movement by a factor of 2.27. The normal
PCBs (PWBs) per engine in the FSEE. These are
operating range of the actuator is about 100
the A, B, and C cards. The PLA actuator sends
degrees and the potentiometer 227 degrees. The
two signals back to the electronics. They are
potentiometer reference voltages are supplied
from electronics in the FSEE.
position feedback (potentiometer) and rate
feedback (tachometer). Besides the command
signal, these two signals provide most of the
Servomotor
information necessary for the electronics to place
the MFC at the correct position.
The dc servomotor is driven by the PLA
The potentiometer receives its reference
actuator drive signal from the PLA actuator
voltages from the PLA actuator electronics. The
electronics. The drive signal is developed by the
potentiometer slider takes a voltage proportionate
electronics in the FSEE. It is amplified and
to the actuator position from the potentiometer;
connected through the fail-to-idle relay. The
this voltage signal is connected to the control
motor's direction of rotation is determined by the
circuit. The voltage signal is used to compare with
polarity of the drive signal; its velocity is
the command signal and to generate an uplink
proportional to the drive signal amplitude. For
signal representative of actuator position. Also,
an input range of 23 to +23 volts, the motor
the position feedback is used within an idle
output shaft speed range is 0 to 900 rpm in either
position detection circuit; this circuit detects when
direction. The PLA actuator is reduced by a gear
the MFC is within 2 degrees of the normal idle
ratio of 55.64 to 1. This allows a speed range of
position and generates an uplink signal to indicate
0 to 16 rpm (0 to 96/second). It is also capable
when the MFC is at idle.
of running into mechanical stops at full voltage
Rate feedback is developed by the tachometer
and velocity and remain stalled without damage
attached to the motor shaft. The purpose of the
to the motor.
rate feedback is to control the response of the
PLA actuator during changes of MFC lever
Tachometer
position. When a large difference exists between
the commanded position and the actual position
The tachometer is a dc generator that is
of the PLA actuator, the drive signal to the
directly coupled to the motor shaft and outputs
servomotor is large. A large drive signal causes
a dc voltage proportional to the motor speed. The
2-53
