How to Install Electric Bells, Annunciators, and Alarms. / Including Batteries, Wires and Wiring, Circuits, Pushes, Bells, Burglar Alarms, High and Low Water Alarms, Fire Alarms, Thermostats, Annunciators, and the Location and Remedying of Troubles

by Norman H. Schneider

The Annunciator.

The mechanism of an annunciator consists of electromagnets which allow shutters to drop or needles to move on the circuits being closed. A bell is also rung in most cases to call attention to the annunciator. The number of the circuit is marked on the shutter, or near the needle, either shutter or needle being replaced by a reset device, which may be mechanical or electrical.

Fig. 52

Annunciator drops are made in a variety of forms. [Fig. 52] illustrates the principle underlying nearly all of them.

When current flows through the magnet coils M, the armature A is attracted, and being pivoted at P, the lever hook H rises and allows the weighted shutter S to fall and display a number painted on its inside surface.

Fig. 53 Fig. 54

The needle drop in [Fig. 53] is one that has met with great favor and works as follows: the soft iron core of the magnet C has a hole drilled through it, in which turns the shaft S. An arrow or needle is attached at the front end over the face of the annunciator. A notched arm B is fixed on the rear end of the shaft and is held in a horizontal position by the end of armature A.

When the current flows around C, armature A turns on its pivot towards the core of C, as in [Fig. 54], unlocking B, which falls and thereby partly rotates shaft S and the arrow.

When it is desired to reset the arrow and arm, a button is pressed upwards, which raises a rod carrying an arm R. This latter arm in turn raises B to its former position, the heavy end of A falls, and its pointed end locks B.

Fig. 55

Pendulum, or swinging, signals are used in annunciator work, where there is a liability that the ordinary drop shutter would not be reset. They, however, only give a visible signal for a few seconds, and are therefore liable to be overlooked.

In [Fig. 55] a pivoted arm carrying a soft iron armature A and a thin plate B having a number on it is free to swing in front of an electromagnet M.

When the current flows in the electromagnet the armature is attracted, and upon the circuit being broken at the push, the armature is released and the arm swings to and fro.

The drops of an annunciator are wired up as in [Fig. 56].

Fig. 56

One end of each coil is attached to a common return wire C, the other end going to the push P. When P is depressed, the circuit of any drop is through M along C through bell, battery and up common battery wire W back to other contact of push P. Depressing any push does not therefore affect any other drop but the one controlled by it.