milliamp signals. They are converted to 0- to
actuator electronics and a 0- to 10-volt signal for
5-volt signals for the torque computer. They are
uplink and display. Torque range is 5,000 to
also processed into 0- to 10-volt signals for
50,000 ft-lb. The computer also calculates
external use. The only temperature signal
horsepower as a function of PT speed and
processed by the FSEE is T2 . This signal comes
torque for shipboard monitoring.
from a platinum RTD. The electronics changes
the RTD signal to a 0- to 5-volt and a 0- to 10-volt
signal for the torque computer and uplink,
OVERSPEED SWITCH CONTROL
respectively.
The overspeed switch control circuits function
A dual tachometer system is mounted on the
to shut down the engine if a PT overspeed, PT
PT. This has a spur gear with 83 teeth which
underspeed, or a loss of control power to the
rotate past two sensors. The output of each
control circuits occurs. Two PCBs (PWBs) (the
D cards) of identical type are required per engine
sensor is a pulse train whose frequency is
for overspeed protection. Speed signal channels
directly proportional to the speed of the
turbine. The purpose for the two-speed signals is
A and B go to their own respective D cards. Each
reliability. One is the normal (channel A) signal,
card receives its signal from its own speed pickup
the other (channel B) is a backup in case the first
and controls both fuel valves. (Remember, there
fails. The speed signal is converted to voltages
are two fuel solenoid valves piped in series,
proportional to speed for purposes of torque
but wired in parallel.) This allows for two
independent speed channels and two independent
computer monitoring.
overspeed trips. The outputs of the overspeed
switch circuits are overspeed voltages, loss-of-
speed signal voltages, and a voltage for the fuel
TORQUE COMPUTER
shutdown valves. The following two test functions
The torque computer is a special-purpose
are provided:
computer used to calculate engine torque. It has
seven PCBs (PWBs) whose only function is to
1. Overspeed test function. Each board has
calculate the torque output of the PT. Five
the highest PT speed to ensure a proper test. When
inputs are necessary to the computer for the
you depress the test button, the overspeed
calculations. Four are 0- to 5-volt analog inputs
indicator on the GTE control console lights and
the fuel shutdown valves de-energize (close).
Pt 5 . 4 , T2 , and Np t. The fifth is a discrete
(ON/OFF) input to indicate whether bleed air is
2. Speed limit test function. When you
being diverted from the GG. If the bleed air valve
is open (ON), it will affect the efficiency of the
depress the speed limit test push button, the
electronics lowers the speed limit to 75 percent
engine and the torque output.
of the normal speed limit and permits testing
the speed limit circuitry without overspeeding
The torque computer is similar to many
the PT.
general-purpose computers of this size. The
computer performs internal calculations and
If the PT speed signals should become dis-
compares them to internally stored data tables.
connected or lost (Np t <100 rpm), the overspeed
From the tables, selected values are taken to be
switch opens. Both signals must be lost before the
used in further calculations to determine the final
fuel shutdown valves actuate.
value of torque. The torque calculated is accurate
to within 3,000 ft-lb.
To start the GTE, a method of bypassing the
When the turbine is at idle, the computer
loss of speed signal (Np t <100 rpm) shutoff is
provided. With the throttle position at a nominal
output is a torque value of about 5,000 ft-lb. This
30 degrees or below, a signal is generated that
set point is the basic value used to allow the
causes the loss of speed-signal function to be
electronics to operate accurately over a broad
bypassed. The throttle must remain below 30
range of operating conditions.
degrees until the PT exceeds 100 rpm. The signal
loss bypass function is deactivated whenever the
The output of the torque computer is a 0- to
throttle is above a nominal 30 degrees.
5-volt signal, which is the input to the PLA
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