CHAPTER V

_Annunciators_

=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.

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.

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_.

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.

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.

=Wiring up an Annunciator.= A diagram of the connections for an annunciator with a separate bell is given in Fig. 57. Where the bell is contained in the case a terminal will be generally found for connection.

The figure shows a wire running from the battery to one side of each push button. This is the common return, or battery wire, and saves installing two wires from each push. It should be larger, however, than the rest of the wires, generally about No. 16 B. & S.

All the wires for an annunciator should be run before connecting up. There are different methods of sorting out the wires at the annunciator. One way is to connect the wires (except of course common or battery return wires) to the drops in any order. Then an assistant travels from push to push and presses each button, noting the room numbers and the order in which they were visited.

As each drop falls, its number and order is noted.

Comparing this with the list made by the assistant will show the correct changes to make.

For instance, suppose pushes 1, 2, 3, 4, 5 and 6 were pressed in that order, and drops 3, 4, 5, 1, 2 and 6 fell in that order. Then the wires at the annunciator would be changed as follows: From 3 to 1, 4 to 2, 5 to 3, 1 to 4, and 2 to 5; 6 would already be in its right place.

Another way is to commence by twisting together say the wires at No. 1 push. Then go to the annunciator and touch each of the push wires to No. 1 drop until it falls. Then connect it, untwist the wires at No. 1, push and connect it up. Proceed to No. 2 and so on until all the pushes have been connected in turn.

In some cases it is desired to answer back to the person calling, or to be able to call any person from the annunciator.

A circuit like Fig. 58 answers the purpose of both annunciator call and return, or fire, call. This requires two wires from each room to the annunciator and a common return wire. By tracing out the circuit it will be seen that when a room push is pressed, the annunciator needle and bell indicate. And when one of the pushes near the annunciator is pressed, the corresponding room bell rings. The former circuit is from the push, along the common return wire, through bell and annunciator back to the push.

The fire call is from push up line to bell through bell along common return and through battery to the push.

The Western Electric single-wire system (Fig. 59) uses three-point pushes, two batteries and two return wires. Battery _A_ is for the annunciator circuit and battery _F_ for the fire, or return, call.

In each room the top contact and push spring contact are normally together.

If one of the pushes below the annunciator is pressed, battery _F_ is thrown in series with the bell in the room.

But when the room push is pressed its bell is cut out and the circuit becomes like an ordinary annunciator circuit.