Page:Popular Science Monthly Volume 89.djvu/293

Five Examples of Alarm Work

THIS may be done by arranging the circuits as shown in Figs, a, b, c, d, e. Usually when it is necessary to employ a constant ringing method on a call system, an annunciator is also installed and a point provided on the annunciator for each place where a call is turned in. This is shown in all of the diagrams.

An image should appear at this position in the text.Wiring diagrams of a five-bell electric annunciator system

In Fig. (a), a constant ringing bell is used. This type of bell is a combination of the vibrating bell and the automatic drop. Its operation is as follows: the circuit is taken through the push-button and a point on the annunciator, then through the coils in the bell and back through the battery. This causes the armature to be drawn in and allows the drop to fall, completing another circuit through the bell, the connection being from line to bell to line. This will cause the bell to ring as long as there is enough current in the battery.

In Fig. (b) practically the same operation takes place except that the bell and the drop are separate.

In Fig. (c) the diagram is based on another principle. When the push-button is closed, current flows through the coil of the relay. The bell is prallel with the relay. This will cause the armature to be drawn up,

closing the circuit through the armature of the relay and the frame. This will close a circuit through the coils on the relay and the bell continually. As there is a circuit through the coils the armature will be drawn up and held there as long as the current Hows.

In Fig. (d) is illustrated a closed-circuit alarm. To be adapted to a call system it must be connected as shown in Fig. (e) . The current flows through the contacts and the coils of the relay to the armature of the relay to the frame of the relay and back to the battery. The platinum point of the relay is toward the coils and the armature must be drawn over toward the coils before the circuit is complete. Once completed it will be held by the action of the armature. A switch is provided for closing the circuit. The bell is connected across another battery, although it could be connected through the same one. The current for the bell passes through the armature of the relay and the extra platinum joint on the relay which is insulated from the frame. As the circuit through the contacts is broken, the spring will pull the armature away from the contact point toward the coil and against the contact point to which the bell is connected.