Figure 7-15.--Block diagram of the flight crash alarm module.

AMPLIFIER OSCILLATOR POWER

frequency and 1500 cycles per second for the high

SWITCHES.-- These switches provide power to the

frequency. In either case, clockwise rotation of the pots

two power supplies and relay power supply located in

will increase frequency and counterclockwise rotation

the control rack and the power amplifiers and blowers

will decrease frequency.

located in the power rack. During normal operation,

FLIGHT CRASH ALARM.-- The flight crash

these switches are in the ON position.

alarm consists of a phase shift oscillator that controls the

AMPLIFIER CHANNEL SELECTOR

frequency of a relaxation oscillator through a varistor

SWITCH.-- Three choices of channel operation are

network and an amplifier stage producing a siren tone.

available in this system: (1) 1MC-A/6MC-B, (2)

Figure 7-15 is a block diagram of a flight crash alarm

1MC-A/6MC-A, and (3) 1MC-B/6MC-B. Selection is

module. Operation of the flight crash alarm contact

accomplished by operation of the AMPLIFIER

maker supplies -30 volts dc through relay K501 to all

CHANNEL SELECTOR switch. Channel A is normally

stages of the circuit.

used for circuit 1MC operation, and channel B is

Resistor R7 (not shown) is a trimpot used in the

normally used for circuit 6MC operation. Should one

circuit to adjust the frequency limits of the siren tone.

channel fail during operation, the switch can be

Clockwise rotation of the pot will raise the frequency of

positioned to the operational channel, thus putting both

Q503, while counterclockwise rotation will decrease it.

circuit 1MC and circuit 6MC on the same charnel.

The normal setting produces a frequency varying

Under this condition, however, circuit 1MC has priority

between 750 cycles per second and 1750 cycles per

over circuit 6MC. Figure 7-16 is a simplified system

second.

switching diagram showing the AMPLIFIER

CHANNEL SELECTOR switch in the 1MC-A/6MC-B

position.

Switching and Transfer Controls and

OSCILLATOR GROUP SELECTOR

Indicators

SWITCH.-- Selection of either group of alarms is

accomplished by operation of the OSCILLATOR

The switching and transfer controls on the front of

GROUP SELECTOR switch. Should any alarm module

the control rack consist of the amplifier oscillator power

within either oscillator group fail during operation, the

switches, the amplifier channel selector switch, the

switch can be positioned to the operational group.

oscillator group selector switch, the microphone control

During normal operation, this switch is in the NO. 1

station disconnect switches, the loudspeaker group

position.

disconnect switches, visual disc switch, and various test

M I C R O P H O N E CONTROL STATION

switches. Indicators on the front of the control rack

DISCONNECT SWITCHES.-- There are six mi-

consist of a power available lamp, blown-fuse

indicators, and a test meter.

crophone control station disconnect switches, one for

Figure 7-15.--Block diagram of the flight crash alarm module.

7-14