TM 55-4920-428-13
SECTION Ill. TECHNICAL PRINCIPLES OF OPERATION
1-15. ELECTRICAL UNIT 145GS278-3.
1-16. Block Diagram (fig. 1-5).
a. The electrical unit includes No, 1 and No, 2 ILCA control circuits, No. 1 and No. 2 metering circuits,
power supply circuits, an undervoltage detector circuit, a hydraulic unit control circuit, a BITE circuit, automatic
range control circuit, and a digital voltmeter (DVM). The electrical parts of an ILCA or extensible link under test
are included in fig. 1-5 to show the interface,
b. No. 1 ILCA control circuit processes the signals associated with No. 1 extensible link. No. 2 circuit pro-
cesses the same type signals for No. 2 extensible link, Otherwise, th e two circuits are identical.
c. The ILCA control circuit is a servo system that provides a drive signal to the extensible link servo valve.
The servo system responds to five internally generated command signals selected by the FUNCTION SELECT
switch. When the FUNCTION SELECT switch is at SQ WAVE, CLSD LOOP, or BALANCE, the servo loop is
closed through feedback circuits from self and cross transducers. When the FUNCTION SELECT switch is at
HARDOVER EXTEND or HARDOVER RETRACT, the loop is open. When the loop is closed, self and cross
feedback signals are algebraically added to the command signal to ensure the extensible link is at the commanded
position. The command signals and their functions are as follows:
(1) The balance command signal drives the extensible link to its mechanical center.
(2) The closed loop command signal is generated at the VALVE CONTROL. This signal drives the exten-
sible link to any position between fully extended and fully retracted.
(3) The square wave command signal alternately extends and retracts the extensible link once every sec-
ond. Stroke is controlled by the SQ WAVE variable resistor.
(4) The hardover retract command signal drives the extensible link to maximum retract position. The
hardover extend command signal drives the extensible link to maximum extend position.
d. No. 1 metering circuit processes signals from No. 1 ILCA control circuit. No. 2 circuit processes the same
type signals from No. 2 metering circuit. Otherwise, the two circuits are identical.
e. The metering circuit selectively routes control circuit output signals and reference voltage to meter jacks on
the front panel. At the jacks they can be measured with external test equipment. ILCA output signals are selec-
tively routed to the DVM. Signals amplitude is reduced to the range of the DVM. The metering circuit also in-
eludes a 50-0-50 ua meter.
f. The power supply section includes three power supplies and four voltage regulators. These provide +28,
– 20, +20, – 12, +12, –7, +7, and +5 volts dc. The power supply section also includes a 400 Hz inverter. The
inverter is powered from 28 volts dc and supplies 13 volts ac 400 Hz.
g. An undervoltage detector circuit turns on the WARNING indicator when line voltage to the test set is less
than 105 volts ac.
h. The hydraulic unit control circuit includes two switches that close or open 115 volts ac circuits to the hy-
draulic unit.
i. The BITE circuit measures on the DVM the -20, +20, – 12, +12, and +5 volts dc power sources. It also
selectively provides simulated self and cross feedback signals to No. 1 and No. 2 ILCA control circuits. The de-
modulated feedback signals are measured on the DVM.
Change 3
1-15
