Figure 9-5.--Ionization principle.

field, a current will flow. Figure 9-5 illustrates this

RELAYS

principle. A potential from battery B is applied to plates

Relays are used in alarm, safety, and warning

P1 and P2. The air between the plates is ionized by the

systems to open and close circuits that may operate

radium. The charged particles move in the direction

audible and/or visual signals. Relays were discussed

indicated by the arrows. A sensitive galvanometers mea-

earlier in chapter 3 of this training manual.

sures the current, the value of which depends on the

strength of the radium source, and part of the ions and

electrons collide and neutralize each other. It is only

AUDIBLE AND VISUAL SIGNALS

when the potential reaches a certain limit that all of the

ions formed reach the plates. This is known as the

Audible and visual signals are used with the alarm,

saturation point. Beyond this point, the current remains

safety, and warning systems to alert personnel that an

virtually constant regardless of the increase of potential.

alarm condition exists. The types of signals and their

Only a change in the gas in the chamber will cause a

locations depend on the circuit they are used with.

change in the current flow when the unit is operating at

Audible and visual signals are also used with alarm

the saturation point.

panels and alarm switchboards, and as extension

The presence of combustion gas or smoke

signals in remote spaces.

particles between the plates will cause a sharp

decrease in current flow through the galvanometers.

AUDIBLE SIGNALS

This is true because the combustion gas and smoke

particles are many times larger and heavier than the

There are many types of audible signals in use on

air molecules and require a stronger radioactive source

board Navy ships. The type of signal used depends

to become ionized. Also, the ionized combustion gas

upon the noise level of the location and the kind of

and smoke particles are all neutralized by free

sound desired. The principle types of audible signals

electrons before reaching one of the plates.

are bells, buzzers, horns, sirens, and electronic signal

units.

Dual-Purpose Detectors

Dual-purpose detectors combine an ionization

Bells

detector and a mercury thermostat in the same circuit

in parallel.

Bells used with alarm, safety, and warning

systems are either ac or dc operated. Bells that are ac

operated have four types of gongs: circular 3-inch

diameter (type IC/B8S4), circular 4-inch diameter

(types IC/B5DF4 and IC/B5S5), circular 8-inch

diameter (types IC/B1S4 watertight and IC/B2S4

watertight explosion-proof), and cowbell (type

IC/B3S4). Figure 9-6 is an illustration of a type

IC/B3S4 bell.

Bells that are dc operated have three types of

gongs: circular 2 1/2-inch diameter (type IC/B1D4),

circular 8-inch diameter (type IC/B2D4), and cowbell

(type IC/E13D4). Figure 9-7 is an illustration of a type

IC/B2D4 bell.

Buzzers

Buzzers are used only in relatively quiet spaces,

There are two types of buzzers used with alarm, safety,

and warning systems, Type IC/Z1D4 is dc operated

and has make and break contacts. Type IC/Z1S4 is ac

operated and has no contacts. Figure 9-8 is an

Figure 9-5.--Ionization principle.

illustration of a type IC/Z1D4 buzzer.

9-8