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 TM 9-1270-219-13&P
to 50 knots, is displayed by lateral and fore-aft direction
input
current
and
voltage
to
provide
over-current
indicators, each mounted on a single radius arm and driven
and
over-voltage
protection.
A
25kHz
square
wave
from a dc torquer motor via a 4:1 reduction gear. The
oscillator drives two inverter transistors which provide the
intersection of the two direction indicators is related to the
output transformer primary with an 80 Vac pk-pk square
circular scale to obtain total airspeed.
wave. The ac is next stepped down to required secondary
voltages by the output transformer and rectifier assembly.
a. A three-position flag motor is used to indicate
either status (GOOD) (matt black), status (FAIL) (red
(1) V o l t a g e O u t p u t s . After the power supply has
and black diagonal stripes) or (OVER-RANGE) (O/R). The
started, a relay switches the source of supply for the +10
display surface is illuminated by miniature 5 Vdc red
Vdc from the helicopter 28 Vdc supply to a secondary on
lamps mounted in a recess behind the front cover.
the transformer. This allows greater tolerance of helicopter
Examples of displayed information for various flight
28
Vdc
fluctuations
and
reduces
power
consumption.
conditions are shown in figure 1-29.
Voltage outputs are as follows:
b . The torquer motor is mounted on a pointer drive
1 5 Vdc analog supply.
a s s e m b l y . A double sided printed circuit board attached
5 Vdc TTL logic supply.
to
this
assembly
carries
the
control
electronics.
INJ current microprocessor supply
C o n n e c t i o n s to the LAI are made via a 19-pin socket on
(derived from 5 Vdc supply).
the rear of the instrument.
1 5 Vdc LAI supply (current limited to 1.0A).
L A I F u n c t i o n a l D e s c r i p t i o n . A block diagram of
t h e LAI is included as figure 1-30. Positional feedback is
(2) P e r f o r m a n c e . Output voltages and currents are
obtained from a potentiometer which is integral with the
maintained
to
within
2%,
with
input
voltages
varying
torquer-motor. This feedback signal is compared with the
between
10
Vdc
and
80
Vdc
under
steady
state
input signal and fed to a high gain amplifier. The feedback
conditions.
s i g n a l is phase-shifted and used to provide rate damping.
This rate damping provides optimum response to large
(a) The main (+80 Vdc) supply is monitored for
input signal changes (e.g. at switch on) and also improves
under-voltage
only,
as
over-voltage
and
short
circuit
the
low
vibration
immunity
of
the
indicator.
over-current protection are inherent in the boost regulator
design.
a. The forward channel has an over-range (O/R)
indication
which
is
displayed
by
the
three
position
(b) This monitoring provides a fail signal to the
i n d i c a t o r when the forward airspeed input to the indicator
EPU
status
indicator.
is in excess of 50 knots.
(3) P o l a r i t y R e v e r s a l P r o t e c t i o n . Supply
polarity
b . The indicator has built-in failure monitor circuits
reversal protection is provided by diode protection on the
which flag a failure if the indicators fail to respond to an
28 Vdc input to the EPU.
i n p u t . This fail signal will be repeated on the EPU, but
will not affect the operation of any other LRU in the
ADS. In addition the indicator monitors the ADS Fail
LAI
Physical
Description.
The LAI (Fig. 1-28) is
s i g n a l and displays a failure to the pilot if the system
h o u s e d in a standard 3 inch instrument case, fitted at the
shows fail.
top center of the pilot's instrument panel. Low airspeed, up
1-30
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