Each strobe light has four inputs from the rest of
the system: (1) 240 volts ac, (2) ground, (3) 120 volts
ac timing pulses at the rate of two per second, and (4) a
dc voltage connection to the monitor system. These
inputs are plugged into a cable through a four-pin
connector (No. 10). The unit steps up the 240-volt ac
input voltage to 1,460 volts ac with a transformer (No.
15) and passes this voltage through a full-wave
rectifier circuit of vacuum tubes (No. 13). The
resultant 2,000 volts dc is applied to the electrodes of a
flashtube and across the flash capacitor (No. 4).
The xenon-filled flashtube will fire only when
ionization is initiated by a trigger pulse of about 5,000
volts applied to its third electrode. This pulse is
supplied by a trigger coil. At the same time that the
flash capacitor is storing its charge, the trigger
capacitor is also being charged by the primary of the
trigger coil, which is an autotransformer, and cuts the
bleeder resistors in series out of the circuit. When the
l20-volt ac timing signal arrives, it is applied to the
coil of the trigger relay (No. 9), thus closing the relay
contacts, allowing the trigger capacitor to discharge
through the primary ofthe trigger coil. That generates
the necessary trigger pulse in the secondary of the
trigger coil, the flashtube fires, and the flash capacitor
discharges across the flashtube electrodes. The flash
capacitor discharges down to the deionization
potential of the flashtube, at which point the tube
becomes a nonconductor. The light-producing arc
ceases, and the charge cycle begins again.
The charge stored in the flash capacitor is a
potential safety hazard. To make sure that the
capacitor is discharged when the light unit is shut
off, provide a discharge circuit by a series of bleeder
relays. The bleeder relay (No. 5) closes this discharge
circuit when the power to the transformer is turned off.
The current that charges the flash capacitor creates
a pulse voltage in a surge resistor twice each second. A
part of this voltage is applied to a silicon rectifier
through a tap-off of the surge resistor. The rectified
voltage is then filtered and applied to the monitor relay.
The value of this voltage is sufficient to keep the
monitor relay energized when the unit is flashing
normally. When the unit stops operating because of a
component failure in the unit, the absence of the pulse
voltage at the surge resistor will allow the contacts of
the monitor relay to close. This action completes a
circuit from the monitor connection through a monitor
resistor of 22 kilohms to ground. The monitor and
control chassis react to the ground by warning the
Master Sequence Timer Cabinet
The master sequence timer cabinet has all of the
controls for the strobe light system except the tower
control unit. The cabinet is supplied from a 240-volt,
phase-to-ground circuit. Our discussion of how the
system operates is keyed to the numbered items in
LOCAL/REMOTE CONTROL UNIT.The
local/remote control unit (No. 1) gives you a way to
turn the system on locally or give control to the tower.
In the center of this unit is a control knob with three
positions: REMOTE/OFF/LOCAL-ON. There are
two red indicator lights above the control knob and two
green lights below it. When the control knob is in the
LOCAL-ON position, the system is turned on, and red
lights will glow to indicate that the system is on
LOCAL CONTROL. The green monitor lights should
burn unless there is a fault in the system; in which case,
they will go out. When the control knob is placed in the
REMOTE position, the system can be turned on and off
at the tower control unit. The red indicator lights will
go out, but the monitor lights will continue to work as
before. You should remember that the tower has no
control except when the switch is in REMOTE.
MONITOR AND CONTROL CHASSIS.The
monitor and control chassis has several functions.
They are as follows:
1. It de-energizes the monitor lights in both control
units when a set number of lights stop working.
2. It has a step-down transformer to supply the
voltages needed for control and indication.
3. It has a diode rectifier that supplies direct cur-
rent for relay operation.
4. It has the fuses that protect the master sequence
timer, the indicator circuits, and other components.
The main power transformer in the monitor and
control chassis is energized all the time from a local
240-volt ac supply. The secondary voltage from this
transformer energizes the indicator lamp transformer
and the transformer of the dc circuit. The indicator
lamp transformer supplies 12 volts ac to the indicator
lights in the local/remote control unit. The transformer
for the dc power will supply 95 volts ac to a bridge
rectifier that supplies 120 volts dc to the dc monitor
As long as the master control switch is on, power is
fed to the tower csontrol unit no matter what position
the local/remote control unit switch is in. When the