TM 11-5855-250-12&P
assembly is energized, and the ignition circuits
has stopped or in an emergency situation.
(converter, igniter, and xenon lamp) become operational,
c. Relay Panel Assembly.
which causes the xenon lamp to light. Although the
The relay panel
xenon lamp is lighted, emission of light does not occur;
assembly contains the relays and circuitry necessary to
the metal blackout shield is in the path of the light beam
perform three functions: control of the searchlight modes
(E, fig. 1-10). When the SEARCHLIGHT power switch
of operation, automatic shutoff of the igniter assembly
and the converter assembly when the xenon lamp is fully
moved away from the path of the light beam and allows
lighted, and automatic limiting of the overdrive circuit to
emission of light to occur.
17.5 seconds 2.5. The searchlight modes of operation
are determined by the control voltages (28 volts dc)
b. Blower Motor. When the SEARCHLIGHT power
which the relay panel assembly receives from control
switch is set to STANDBY or ON, 28 volts dc is applied
boxes. The relay panel assembly causes the proper
to the blower motor and causes it to operate and cool the
drive motors to become energized; the drive motors, in
xenon lamp. Another circuit has been provided to insure
turn, place the metal blackout shield, the refractor, and
cooling of the xenon lamp after the searchlight has been
the infrared filter lens in their proper positions.
d. Ignition Circuits. When the SEARCHLIGHT
shut off. When the searchlight has been turned on for
approximately three to four minutes, the normal
power switch is set to STAND BY or ON, 28 volts dc is
temperature within the blower system will exceed 140 F
applied to the converter and igniter assemblies. The
(60 C). This action causes thermoswitch S7 to close,
converter assembly transforms the 28-volt dc input to a
330-Hertz (Hz), ac output plus a dc output, and supplies
applying 28 volts dc to the blower motor; therefore, when
these voltages to the igniter assembly. The igniter
the SEARCHLIGHT power switch is set to OFF, the
assembly steps up the ac voltage to 40 kv at a frequency
blower motor will continue to operate.
When the
from 2 to 8 megahertz (MHz) and applies this rf voltage,
temperature within the blower system falls below 130 F
in series with the dc voltage, to the xenon lamp. The rf
(54.4 C), thermoswitch S7 will open, and the blower
voltage causes the xenon gas to ionize and start lamp
motor will cease to operate. This additional cooling of
conduction.
The 55-volt dc signal increases the
the xenon lamp is required to prevent heat damage, and
temperature of the xenon gas which increases the level
is the reason why instructions specify use of the
of lamp conduction and, thereby, maintains lamp
SEARCHLIGHT power switch and not the main power
illumination. When illumination has been achieved, the
switch to shut off the searchlight. The main power switch
converter assembly shuts down, and lamp illumination is
is to be set to OFF only after the blower motor
sustained from the 28-volt dc source.
1-14
