Forty equally spaced teeth are machined on the
block serves as the junction for two thermocouple
flange at the forward end of the shaft. These
harnesses and the amplifier leads. It has eight
provide excitation for the speed sensor.
terminal connections and four terminals for each
of the two harnesses.
The housing encloses the shaft, supports the
forward end of the engine, and contains the mid-
Engine vibration is measured by a displace-
bearing assembly. The housing also provides the
ment type of vibration transducer. It is mounted
mounting for the speed sensor assembly and an
on the turbine rear bearing support at the 12
oil nozzle that lubricates the splines of the tapered
o'clock position. It provides a signal to a meter
coupling and shaft adapter. The mid-bearing
on the LOCOP.
assembly prevents the shaft from whipping.
Engine speed is measured by a magnetic
pickup. This is mounted in the PTO shaft housing
Besides the instruments that measure pressure
over the shaft exciter teeth. Passage of the exciter
and temperature of the engine's support systems
teeth under the magnetic pickup produces
and enclosure, several sensors monitor the engine
electrical impulses. These impulses are used by the
itself. These are the thermocouples, vibration
speed temp box for speed sensing. This, in turn,
sensor, and magnetic speed pickup.
is used for start sequencing, over- and underspeed
The thermocouples are wired in parallel to
protection, and speed monitoring.
provide an average TIT signal. This is amplified
by the turbine speed temperature box in the
LOCOP. This signal provides TIT indication and
SPEED GOVERNING SYSTEM
input to engine emergency shutdown functions.
The speed temperature box uses the magnetic
speed pickup signal for speed sensing and control
The Allison 501-K17 is a constant speed
during start. An alarm and automatic shutdown
engine. It is designed to maintain a speed (13,821
are provided for overspeed or underspeed. The
engine rpm) that will output a steady 60 Hz from
speed temp box also transmits a speed and
temperature signal for remote display of engine
required to keep electronic equipment and motors
speed and temperature on the DDIs.
operating properly. The Allison 501-K17 uses an
EG to maintain this constant speed. Two different
electronic control systems are used on the GTGSs.
Most model 104 GTGSs use the Woodward 2301
Eighteen dual-element, Chromel-Alumel ther-
control system. The model 139 GTGS and some
mocouple probes are mounted on the turbine inlet
model 104 GTGSs use the Woodward 9900-302
casing. The probes extend into the outlet of the
control system. Both model GTGSs use the
combustion liners at the turbine inlet. Each of the
Woodward EGB-2P electrohydraulic actuator.
probe elements is independent of the other,
Both systems normally operate on the EG. The
thereby providing two independent sampling
EG will maintain the frequency set by the
circuits. The thermocouple probe housing leading
operator. Once the frequency is set and the load
edges are air cooled to prolong probe life. To
is balanced between GTGSs in parallel, the
accomplish this, cooling air enters the probe cavity
governor system will maintain the set frequency
leading edge through a hole below the probe
and load balance.
shoulder. It flows through the probe and is
If failure of the EG control occurs, a
discharged through two small openings in the
mechanical flyweight governor will regulate the
bottom of the probe.
engine speed. The mechanical governor is set at
A thermocouple harness assembly has a right
a slightly higher speed than the EG. It will
and a left section. It is enclosed in channels that
are rigidly mounted on the turbine inlet case
mechanical governor prevents overspeed of the
forward flange. The harness incorporates separate
engine during an EG failure. It is set by a screw
leads for each thermocouple probe. A terminal
adjustment on the EG.