_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.
[Illustration: 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.
[Illustration: 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_.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 57]
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.
[Illustration: FIG. 58]
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.
[Illustration: FIG. 59]
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.