Figure 9-16.--High-temperature alarm circuit.

armature is located directly in front of the coil and is

supervisory drum shows a yellow section when it is

hinged between the side members of the frame. An

de-energized. The two relays are in series with a

insulated roller attached to the upper pm-t of the armat-

sensing device.

ure engages the contact spring. A helical coil spring

When the circuit is in normal operation, the

maintains the armature in the open position when the

supervisory relay is energized. The supervisory

coil is de-energized. The contacts are open when the coil

resistor (a 7000-ohm, 5-watt resistor, connected

is de-energized or in a normal condition, and closed

across the terminals of the last sensor or detector)

when energized or in an alarm condition.

associated with the contact maker is in the circuit.

The indicator drum is located in front of the arma-

While the alarm relay is also in the circuit, it is not

ture and is pivoted between the sides of the frame (fig.

sufficiently energized to operate the armature and

9-15). The drum is connected to the armature by a short

close the contacts. When a contact maker closes, it

link, and rotates when the armature operates. The face

short-circuits the supervisory resistor for that circuit,

of the drum protrudes slightly through the panel to be

causing an increase in current. This increase in current

visible. The part of the drum visible when operated is

increases the magnetic energy of the alarm relay to a

painted red, the rest of the drum is grey.

point where it will operate its armature, closing the

The supervisory relay is similar in design and con-

alarm relay contacts, energizing the alarm bell. When

struction to the alarm relay. However, the number of

the alarm relay operates, it also rotates the target drum

turns on the coils and the contact arrangement are

to red, indicating the circuit is in an alarm condition.

different. The supervisory relay is equipped with one

pair of contacts. Note that when the armature (1) of the

Since the normal operating current is just

alarm relay operates, it rotates the target drum (5)

sufficient to hold the supervisory relay armature

through an eccentric, and closes the contacts for the

operated, an open circuit will cause the supervisory

audible alarms by moving the roller (3). However, the

relay to drop out. This, in turn, closes the supervisory

supervisory-target relay is designed to be normally op-

contacts, energizing a buzzer and rotating the

erated; its alarm contact is closed when the relay is

supervisory target drum to yellow, indicating the

de-energized, and open when energized.

circuit with a problem.

The magnetic coil of the supervisory relay is wound

The current flowing under normal conditions

with 14,500 turns of wire and has a resistance of 1350

(supervisory relay operated, supervisory resistor in the

ohms.

circuit, alarm relay not operated) is approximately

The line unit test switch is a three-position, four-

0.012 amperes. If a contact maker closes, shunting the

pole, rotary switch. The switch is not adjustable and

supervisory resistor, the current flow will rise to

should require no maintenance.

approximately 0.043 amperes, which is sufficient to

operate the alarm relay.

Normal Operation

An extension signal relay is also in the alarm

circuit (fig. 9-16). When the alarm relay contacts

The alarm drum has a red section that rolls into

view when the alarm-target relay is operated. The

close, the alarm bell is energized by the extension

Figure 9-16.--High-temperature alarm circuit.

9-14