forward air seals. At this point it is called balance
to a corresponding electric signal. The sensor
piston air.
information is transmitted to the controls, either
directly or through the FSEE. The controls use
the sensor information for GTE monitoring,
Balance Piston Air
alarming, and control sequencing. A majority of
these sensors, along with their location/function,
On the LM2500 GTE, balance piston air (or
are described in the following paragraphs.
pressure balance air) is ninth-stage air that is bled
into a balance chamber to reduce the aft loading
on the No. 7B bearing. This air applies force to
Pressure is sensed by a total pressure probe
the face of a rotor disk in the direction opposite
mounted in the compressor front frame at the 12
the thrust load to reduce the axial load applied
o'clock position. Pressure is piped to a transducer
to the thrust bearing by the rotor thrust. This
mounted on the bottom of the enclosure base. The
increases the thrust-bearing life. The balance
electrical output signal from the transducer is sent
piston principle is shown in figure 2-52.
to the FSEE signal conditioner and torque
computer electronics. Output signals from the
Thirteenth-Stage Air
FSEE are sent to the controls.
Thirteenth-stage air is bled from the com-
Power Turbine Inlet Total Pressure
pressor through holes in the thirteenth-stage vane
(Pt 5 . 4)--Pressure is sensed by five total pressure
bases and compressor casing into an external
probes located circumferentially in the turbine mid
manifold. The air is piped through the compressor
frame. Pressure is piped to a transducer mounted
rear frame casing and into the HP turbine
on the bottom of the enclosure base. The
shrouds. The air then flows through and cools the
electrical output signal from the transducer is
second-stage turbine nozzle. Some of the air
sent to the FSEE signal conditioner and torque
exits through nozzle-trailing edge holes. The
computer electronics. An output signal from the
remaining air is used for cooling the interstage
FSEE is sent to the controls.
seal, the aft side of the first-stage blade shanks,
and the front side of the second-stage shanks.
Compressor Inlet Temperature (T2)--
Temperature is sensed by a platinum RTD
Sixteenth-Stage Air
penetrating the enclosure inlet barrier wall at the
lower left corner. The signal from the RTD is
Sixteenth-stage compressor discharge bleed air
sent to the FSEE signal conditioner and torque
is bled through holes in the inner wall of the
computer electronics. An output signal from the
compressor rear frame and out through Nos. 3,
FSEE is sent to the controls.
4, 8, and 9 frame struts. It is then piped to the
bleed air valve. The bleed air valve operates
NOTE: Only Pt 2, P5 . 4, and T2 (which are
electrically to provide air to the ship's bleed air
torque computer inputs) are signal conditioned
system. High-pressure turbine rotor and blade
in the FSEE. Signals from the following instru-
cooling air is extracted internally through the
mentation go to the controls where they are signal
aft stationary air seal and holes in the forward
conditioned and used for monitoring, control,
end of the rotor front shaft. The remaining
alarm, and shutdown as noted.
compressor discharge bleed air is used for
cooling the combustion liner and first-stage HP
Power Turbine Speed (Np t)--Npt is sensed
turbine nozzle vanes.
by two magnetic pickups in the turbine rear frame.
The signal from the magnetic pickups is sent to
the controls to the FSEE signal conditioner and
ENGINE INSTRUMENTATION
torque computer electronics, The controls use the
signal for PT speed meter displays and PT
The GT assembly is instrumented with sensors
overspeed alarm generation.
that provide for remote monitoring of the engine,
module, and LOSCA. Temperature, vibration,
and speed sensors give an electrical output signal
generator speed is sensed by a single magnetic
directly. However, pressure sensors use base-
pickup located on the top left side of the aft TGB
mounted transducers to convert a pressure level
(AGB).
2-47
