flasher control switch in the vault control unit is
closed, the dc power interlock relay closes and
energizes the monitor lights in the tower control unit.
The unit responds in the same way as if the system
were in full operation and working well. For this
reason. the tower personnel must be notified when the
switch in the local/remote control unit is in the OFF
position. When the flasher control switch on the
local/remote control unit is in the OFF or LOCAL-ON
position, the red indicator lights tell you that the tower
control unit is not in full operation.
There is a monitor-sensing relay to monitor the
operation of the strobe lights. When all the light units
are working correctly, there will not be enough current
through the coil ofthe monitor-sensing relay to actuate
the relay. A variable adjustable resistor can be adjusted
so that there will be 7,333 ohms of resistance between
the monitor-sensing relay and ground. A resistance of
7,333 ohms equals three 22-kilohm resistors in series.
The monitoring circuit in each light unit has a 22-
kilohm resistor. So, if you take the three 22-kilohm
resistors out of the monitor control unit, the monitor-
sensing relay actuates when at least three light units
have ceased to work and their monitoring circuits are
grounded, as described earlier.
The sensitivity selector switch lets you reduce the
number of malfunctioning lights needed to actuate the
monitor-sensing relay by increasing the current
flowing through its coil. There are three 22-kilohm
resistors in the monitor control unit. Each of these three
resistors simulates the effect of a grounded monitor
connection to one of the lights.
If the monitor-sensing relay is tripped, the monitor
lights on the local/remote control unit will go out. At
the same time. the monitor lights in the tower control
unit go out and a buzzer sounds.
The adjustment for the sensitivity of the monitor
system is made at the monitor and control chassis in the
master sequence timer cabinet.
With all of the strobe lights operating and the
sensitivity selector switch in the No. 1 UNIT position,
the green monitor lamps should be on. If you turn the
strobe light units on and the monitor lights do not come
on, you need to adjust the sensitivity of the variable
resistor (sensitivity rheostat). You need a small
screwdriver to fit the slot in the rheostat shaft (No. 4).
Turn the shaft clockwise as far as it will go (about half a
turn). The green lamps should now be lit. Now, turn the
rheostat counterclockwise slowly until the green
lamps go out. Then turn the rheostat back clockwise
slowly and stop as soon as the green lamps light. Check
this setting by slipping a piece of paper between the
contacts of one of the timer switches. The monitor
lamps should go out. Remove the paper and turn the
control switch to OFF for a few seconds and then to
ON. The green lamps should now stay lit. Repeat this
procedure for different lamps and shift the rheostat
slightly if you need to until you find a setting that will
operate for any of the approach lights.
Change the sensitivity selector switch to the No. 2
UNIT position and repeat the procedure while
blocking two ofthe switches with pieces of paper. That
is like having two strobe light units out and should have
the same results as before. Restore the monitor lights
the same as before. Repeat the procedure with the
sensitivity switch in the No. 3 UNIT position while you
block three of the timer switches. Now, check the
operation ofthe monitor circuit with number 1, 2, and 3
strobe lights out.
When you find the correct setting of the rheostat,
no further adjustments should be needed. When your
base requires the selector switch to be on the No. 1
UNIT position, then, in proper operation, if one strobe
light fails, the alarm is silenced by just moving the
selector switch to the No. 2 UNIT position. The switch
is left in this position until the bad strobe light is fixed.
At that time, the selector is returned to the No. 1 UNIT
MASTER SEQUENCE TIMER.The master
sequence timer controls the order and rate of the
triggering impulses to the light units. The timer has two
camshafts driven by a motor (No. 12) through a
reduction gear. The cams actuate 30 contacts (No.
13)one for each light unitstaggered on the shafts
so that the contacts are closed in rapid succession as the
shafts turn. Note that although there are 30 contacts,
only 28 are used. Each ofthe 28 contacts is electrically
connected to one of the light units. Thus, when the
motor is energized, the contacts are momentarily
closed in a predetermined sequence twice each second.
That provides a series of 120-volt ac pulses to the
trigger relays in the lights. These pulses are known as
the timing circuit. Power for the 120-volt motor and the
120-volt timing pulses comes from the monitor and
control chassis. An elapsed time meter (No. 2) is
mounted next to the timer to show the total time the
equipment has been in use; thus it serves as a guide for
maintenance. Forty-five lightning arresters (No. 11)
are installed in the lower part of the cabinet to protect
the equipment from voltage surges on any ofthe lines.