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.