SPEED CHANNEL MODULE.--The speed
modules by the motherboard. During
channel module maintains turbine speed at the
maintenance on the governor system, a jumper
wire must be used between two designated test
value selected by the operator. A magnetic pickup
points. This enables the LEDs on the circuit cards
unit (MPU) provides an ac signal that is
to illuminate.
proportional to turbine speed. The frequency
sensor circuits convert the MPU signal to a
FUEL LIMITER MODULE.--The fuel
proportional dc turbine speed signal. The speed
limiter module contains the circuits required
control compares the actual turbine speed signal
during turbine start and acceleration. The start
with the reference signal. The speed control
fuel schedule circuit controls the fuel flow to the
amplifiers then generate a voltage signal to
turbine during start. It monitors three signals from
maintain or correct turbine speed. The speed
the turbine--first TIT, second CIT, and third N1
control loop has the following inputs:
(speed voltage). The combination of the CIT and
N1 inputs produces corrected speed. Corrected
Master frequency trimmer
speed is the voltage from the speed frequency
Synchronizer
sensor corrected by the CIT temperature. Speed
correction results in increased fuel as CIT
Frequency sensor
decreases. Start fuel is decreased as a function of
TIT.
The output from the start fuel schedule is
Speed reference signal
applied to the HSS bus. The HSS bus is a
Load sensor
comparator circuit. It allows the highest signal
applied to the bus to pass. The other input to the
These speed error signals are input to the
HSS bus is the fuel limiter circuit. The fuel limiter
limits the maximum amount of fuel to the turbine
summing point. The stability amplifier applies the
as a function of speed. At rated or isochronous
summed signal to the speed control gain amplifier.
The control amplifiers provide proper tran-
speed, fuel is limited by the mechanical stop on
the fuel valve. When turbine speed is in the low-
sient response of the turbine. The stability
speed range, the fuel limiter signal is less than the
amplifiers control the time required to recover
start fuel schedule. So the fuel limiter signal is not
from a transient. The gain amplifiers control the
selected by the HSS bus. The output from the HSS
amplitude of the transient. Correct adjustment is
achieved when the time and off speed are both
bus is applied to the fuel limiter amplifier. This
amplifier then drives the LSS bus when its voltage
minimized without turbine instability.
is less than the speed or temperature control
The output for the speed control circuit is
inputs. The fuel limit mode LED illuminates when
applied to the low-signal select (LSS) bus. The
the fuel limiter module is controlling fuel.
LSS bus has diode inputs from the speed, tem-
The fuel limiter module has a deceleration
perature, LSS bus maximum limit clamp, and the
limiter circuit. The deceleration limiter controls
fuel filter control amplifiers. The bus allows the
lowest signal input to dominate the bus. The
the minimum fuel flow to the turbine. If fuel is
decreased too rapidly, a flameout will occur.
output of the LSS bus is applied to the input of
the high-signal select (HSS) bus. A speed control
During a start, the output of the LSS bus is high-
feedback signal is used so the control amplifier
signal selected. It has a fixed voltage when the
engine speed is below 8400 rpm. This voltage
can anticipate control of the LSS bus. This
limiter prevents the fuel valve from reaching the
provides for smooth transition between control
minimum fuel flow stop during start.
channels without excessive overshoot.
The acceleration temperature reference voltage
increases as the turbine speed increases during
POWER SUPPLY MODULE.--The power
acceleration. A CIT bias sets the reference lower
supply module provides isolated dc power for the
as the ambient temperature decreases. An
control circuits. The power supply converts +28
8400-rpm speed switch and a start/run latch are
volts dc to +12 volts dc and +R and R precision
used to select the temperature channel operating
reference voltages for use by the control circuits.
reference. Below 8400 rpm, the latch is set to the
The +12 volt dc and -12 volt dc voltages power
start mode. This selects the acceleration
the control electronics. The +R and R voltages
temperature reference and start TIT LED. When
are reference voltages where precise voltages are
the speed switch is above 8400 rpm and speed
required. The dc voltages are distributed to the
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