Page 232 - Electromechanical Devices and Components Illustrated Sourcebook

194 Electromechanical Devices & Components Illustrated Sourcebook

One of the more common categories of electromechanical Mounting Holes
Point Set
equipment is acoustic devices. An acoustic device is a piece
of equipment that acts as an interface between electricity
Electromagnet
and sound waves. Therefore, any electromechanical device
that is intended to produce or detect sound and/or vibration Frame
Leaf Spring
is considered an acoustic device. Things like bells, alarms,
Ground Terminal (−) Power Terminal (+)
horns, loudspeakers, microphones, telephones, telegraphs,
and vibrators are all acoustic in nature. These devices are Figure 11-2 Buzzer
all around us in our day-to-day lives. We hear the telephone
when it rings, we pick it up and talk through the receiver.
A buzzer, as shown in Figure 11-2, is essentially the
We listen to our radios and television sets, thanks to loud-
same mechanism as the bell ringer. It operates on the same
speakers. When someone comes to our door, they press a
principle, except that the bell and clapper are deleted. A
button and we hear the door bell. Our microwave ovens
buzzer is generally specified in applications where back-
alert us to the completion of the heating cycle with a beep-
ground noise is low or in small, confined areas.
ing sound. And let’s not forget that annoying alarm clock
A two-tone door bell is an excellent example of the clever
next to our bed.
application of a solenoid coil. Figure 11-3 shows a typical
two–tone door bell. When the door bell button is depressed,
power is applied to the terminals and the plunger is pulled
Bells, Alarms, and Horns down, bouncing off the lower bar to generate the first tone.
When the button is released, the recoil spring pulls the plunger
There are a great many reasons to have audible signals that
up and it bounces off the upper bar to create the second tone.
will alert us to various situations within our environments. As
Alarm horn mechanisms are used for applications that
you stand talking to a coworker in the elevator, a gentle tone
require a very loud audible signal. These units were commonly
alerts you that you have arrived at your floor. The blaring siren
used to indicate diving and surfacing operations aboard sub-
of an emergency vehicle tells us to clear the way. The blast of
marines well into the 80s. Figure 11-4 shows a stylized
a Klaxon tells the submarine crew that they are about to dive.
schematic of an alarm horn mechanism. A metal diaphragm
Bells, alarms, and sirens are all around us and play an impor-
is attached to the base of a horn. A metal rivet is attached
tant role in our day-to-day lives.
to the center of the diaphragm. A motor-driven wheel, which
Figure 11-1 shows a typical electric bell ringer. A bell is
has a series of hammers around its circumference, is allowed
mounted to a base as shown. The base carries an electromag-
to impact the rivet. While the motor is running, the ham-
net, point set, and clapper arm. When power is applied to the
mering effect is amplified through the diaphragm and horn
terminals, the electromagnet pulls the clapper arm and the
combination.
clapper strikes the bell. At the same time, the point set is
Figure 11-5 shows a typical marine alarm horn. These
opened and the power to the magnet is disconnected. When
units are very robust and provide decades of service.
the power is disconnected, the clapper arm is forced back into
Additionally, there are very few environments that will effec-
its original position by the leaf spring. When the arm moves
tively drown out the noise produced by one of these devices.
back it closes the point set, which reconnects power to the
magnet. A repeating cycle is generated, ringing the bell for as
long as the power is connected to the terminals. Wooden Clapper
Second Tone Bar
Plunger
Mounting Holes
Recoil Spring
Terminal Strip
Coil
Base
First Tone Bar
Bell Clapper Bar Mounts
Clapper Arm Figure 11-3 Two-Tone Door Bell
Mounting Hole Metal Diaphragm Horn Throat Horn
Point Set
Hammers Sound Waves
Electromagnet
Base
Leaf Spring
Hammer
Ground Terminal (−) Power Terminal (+)
Wheel Anvil
Figure 11-1 Bell Ringer Figure 11-4 Alarm Horn Mechanism