TM 55-4920-328-13
3. Vertical tape indicator assembly 1A3. The
vertical tape indicator assembly (9, figure 122) is a rack-
mounted assembly used for display of operational
characteristics of an engine under test. The unit is
19.00 inches wide, 8.75 inches high, and 17.10 inches
deep, exclusive of the left and right track slides. Ten
vertical tape indicators are installed in the front panel.
Two connectors are mounted on the rear panel of the
unit. One connector, J1 is used for connection of 117v
ac, 60 Hz, 28v dc, and 26v ac, 400 Hz electrical power.
The second connector, J2, is used to connect external
signal circuits to the unit. Nine of the 10 vertical tape
indicators are provided for display of the following
engine parameters (the tenth unit, M2, is not used):
Horsepower - HP
Fuel Flow - Wf
Nl Speed
NII Speed
Torque Exhaust Gas Temperature-Ttg
Pressures (as applicable)
Pofo - Inlet Oil Pressure
P2brg - No. 2 Bearing Oil Pressure
Pogb -Gearbox Oil Pressure
PFM - Fuel Manifold Pressure
During a test, one of a number of engine performance
panels provided in the engine accessories is indexed to
the front panel of the vertical tape indicator assembly.
The selected engine performance panel has three
rectangular cutouts along the lower edge to accomodate
three-position switches used for selection of parameters
for different engines. The cutouts on each engine
performance panel are so arranged that each switch
must be in the correct position before the appropriate
panel can be indexed. The meters are designated M1
through M10, left to right. Six of the indicators are 0 to
5v dc voltmeters, the other four are synchro type
indicators. Four of the engine parameters displayed on
the unit which require signal conditioning are Nll speed,
horsepower, fuel flow, and torque. The torque signal is
input from torque elements having a full load capability
of either 5,000, 30,000 or 60,000 inch pounds,
depending on the torque elements used. All elements
exhibit a full scale output of 1.5 millivolts per volt of
excitation. With 12v dc; excitation, the full scale input is
equivalent to 18mv do. The input signal is amplified to
drive a 0 to 5v dc indicator. For horsepower display, 0v
dc represents 0 percent of Nll speed and 10v dc
represents 120 percent of Nll speed. Horsepower may
be calculated by multiplying Nll speed by torque and a
constant. One hundred percent of Nil speed represents
different rpm levels in different engines. Refer to the
applicable technical manual of overhaul instructions for
information on specific operating parameters. Fuel flow
input to the vertical scale indicator is in BCD code. 4
digits of 4 bits each, plus a common reference. Two
ranges are used when testing fuel flow in engines: 0 to
1,000 pph and 0 to 5,000 pph. A selector switch
determines the range to be used.
4.
Thermocouple
junction
1A9.
The
thermocouple junction (11, figure 1-22) is a standard-
width, rack-mounted unit used as a stable reference for
multi-channel thermocouple networks. The unit contains
24 reference thermocouples in a precisely controlled
temperature environment Four of the thermocouples are
used in high temperature Type K chromel-alumel
networks; the other 20 are used in low temperature Type
J iron-constantan networks. The unit is 19 inches wide,
3.50 inches high, and 8.20 inches deep. The unit
consists of a front panel with an on-off switch (13) and
heater indicator (12), a rear panel with matching
material input connections (24 pairs), and output
receptacle, a 0.75-ampere 3AG fuse and fuseholder
(See Table 1-6), and a three-conductor cable which
terminates
in
standard
terminal
lugs.
Internal
components of the unit include the 24 reference
thermocouples
imbedded
in
an
aluminum
block
enclosed in a heating element, a temperature sensing
mercury-in-glass thermostat, a safety thermostat for
overheat protection, a transformer and full wave bridge
rectifier, and solid state circuitry. When the on-off
switch is energized, rectified lIv dc power is supplied to
a 23-ohm fast warmup heater to raise the temperature
of the reference thermocouples to 150 °
F. When the
specified temperature is reached, a small amount of
current is by-passed through the mercury-in-glass
thermostat to change the bias of the transistor network
and remove the current from the heater. As the
temperature
lowers
around
the
reference
thermocouples, the mercury column contracts to
interrupt the circuit through the electrical bypass and
switch the current through the heater. This cycle
repeats every 10 to 20 seconds. The annunciator light
comes on when the sustaining heater is on line to
provide visual indication of temperature cycling. An
overheat
thermostat
in
the
circuitry
opens
at
approximately 170°F. This action connects a short
across the 117v ac input to cause the fuse to blow to
provide overheat protection of internal components.
5. Data multiplexer 1A5. The data mutliplexer
(14, figure 1-22) is a rack-mounted component used in
conjunction
with
the
switching
1-34
