Direct Energy, 2018a

98 5.5 Applications of Hall Eect Devices
5.5 Applications of Hall Eect Devices
A Hall eect device is a simple device. It is essentially a piece of semiconductor
with leads connected and calibrated for use. For this reason, Hall
eect devices are inexpensive, small, and readily available. As with most
integrated circuits, these devices are durable and long lasting because they
have no mechanical moving parts [57].
Hall eect devices are available in two types: analog and digital. Analog
Hall eect devices are typically integrated with an amplier and circuitry
to make the output more linear [57]. Some devices also contain circuitry
to make the devices stable over a wider temperature range because the
output of Hall eect sensors may be slightly temperature dependent [57].
The operating output voltage range of these devices is often limited by the
amplier circuit as opposed to the Hall eect sensor [57]. Digital Hall eect
devices contain the Hall eect sensor integrated with additional circuitry
such as a comparator to produce a digital output [57].
Analog Hall eect devices are used to sense magnetic eld, temperature,
current, pressure, position, and other parameters [57]. To make a Hall
eect temperature sensor, for example, a magnet is mounted on a material
that contracts or expands in the presence of a temperature change. As
the magnet moves, it changes the magnetic eld in a nearby Hall eect
device and thereby generates a voltage across the Hall eect device. The
same eect can be used to measure pressure or other parameters using
a material that expands or contracts when the pressure changes or other
parameter changes. Current owing through a wire generates a magnetic
eld surrounding the wire. For this reason, the Hall eect can be used to
make an ammeter that can be mounted nearby, as opposed to in the path
of, the current.
Digital Hall eect devices are used as switches or as buttons in a keyboard.
If a small magnet is mounted in a button, a Hall eect device can
be used to sense when that magnet is pressed down near the Hall eect
sensor. Hall eect devices can also be used as proximity sensors to detect
the presence of nearby ferromagnetic objects [57]. Additionally, digital Hall
eect devices are used in magnetic card readers [57]. One of the most common
applications is in tachometers, devices that measure rotation speed.
To measure the rotation speed of a motor for example, the Hall eect sensor
is mounted near a ferromagnetic gear. See Fig. 5.2. As a gear tooth
passes the sensor, the magnetic eld at the sensor changes, and a voltage
is induced across the Hall eect device. Hall eect sensors are used
to measure rotation speed of motors, fans, tape machines, and disk drives
[57]. Relatedly, Hall eect devices are used as ow rate sensors. These