Transcript Hall Effect Sensors - Utah State University

Hall Effect Sensors
Daniel Frei
Utah State University
ECE 5320
March 5, 2004
Outline
References used
 To Explore Further
 Major Applications
 What is the hall effect?
 How does this work?
 A Typical use: Honeywell’s magnetic
position Sensor:
 Major specifications
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Outline
Limitations
 What else do I need to know
 Conclusion
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References used:
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http://www.eeel.nist.gov/812/hall.html
http://www.micronas.com/products/overview/sen
sors/index.php
http://content.honeywell.com/sensing/prodinfo/so
lidstate/
Mechatronics Handbook, chapter 7. John C.
Brasunas,G. Mark Cushman ,Brook Lakew
1999, by CRC Press LLC
The Measurement Instrumentation and Sensors
Handbook, chapter 16-18. M. Anjanappa, K.
Datta, and T. Song, 2002 CRC Press LLC.
To Explore Further……..
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http://www.eeel.nist.gov/812/hall.html
http://www.micronas.com/products/overview/sen
sors/index.php
http://www.pha.jhu.edu/~qiuym/qhe/qhe.html
http://www.pha.jhu.edu/~qiuym/qhe/node2.html
http://www.warwick.ac.uk/~phsbm/qhe.htm
http://www.xs4all.nl/~skoric/quantum/
http://www.sypris.com/stm/content.asp?page_id
=678
Major Applications
Electromagnetic field
 Proximity
 Velocity
 Direction
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What is the hall effect?
Just the basics:
The change in magnetic field induces a
current, the change in intensity and
direction of the current can measure the
velocity and direction object producing the
magnetic field.
What is the Hall effect
“The basic physical principle underlying the Hall effect is
the Lorentz force. When an electron moves along a
direction perpendicular to an applied magnetic field, it
experiences a force acting normal to both directions
and moves in response to this force and the force
effected by the internal electric field. For an n-type,
bar-shaped semiconductor shown in Fig.1, the
carriers are predominately electrons of bulk density
n. We assume that a constant current I flows along
the x-axis from left to right in the presence of a zdirected magnetic field. Electrons subject to the
Lorentz force initially drift away from the current line
toward the negative y-axis, resulting in an excess
surface electrical charge on the side of the sample.
This charge results in the Hall voltage, a potential
drop across the two sides of the sample. “ (figure
one to the left)
From the
website:http://www.eeel.nist.gov/812/effe.htm#lore
What is the Hall effect
“This transverse voltage is the Hall voltage VH and its magnitude is
equal to IB/qnd, where I is the current, B is the magnetic field,
d is the sample thickness, and q (1.602 x 10-19 C) is the
elementary charge. In some cases, it is convenient to use
layer or sheet density (ns = nd) instead of bulk density. One
then obtains the equation
ns = IB/q|VH|.(1)
Thus, by measuring the Hall voltage VH and from the known
values of I, B, and q, one can determine the sheet density ns
of charge carriers in semiconductors. If the measurement
apparatus is set up as described later in Section III, the Hall
voltage is negative for n-type semiconductors and positive for
p-type semiconductors. The sheet resistance RS of the
semiconductor can be conveniently determined by use of the
van der Pauw resistivity measurement technique. Since sheet
resistance involves both sheet density and mobility, one can
determine the Hall mobility from the equation
µ = |VH|/RSIB = 1/(qnSRS).(2)
If the conducting layer thickness d is known, one can determine the
bulk resistivity
(r = RSd) and the bulk density
(n = nS/d). “
From the website:http://www.eeel.nist.gov/812/effe.htm#lore
How does this work???
“This sensor measures the thickness of nonferrous
materials with 1% accuracy by sandwiching the material
being measured between a magnetic probe on one side
and a small target steel ball on the other side [6].
It measures up to 10 mm. The Hall effect sensor is used to
measure the magnetic field, as a dc measurement; ac
Hall effect measurements can be made more precisely
because they eliminate bias and are done with less
noise”
From the website:http://www.eeel.nist.gov/812/effe.htm#lore
© 1999 by CRC Press LLC
In other words….????
As the magnetic field
between the sensor and a
metal ball changes the
sensor can measure it’s
proximity and direction by
measuring the direction
and intensity of the
current induced.
Picture is from:
http://www.micronas.com/products/overview/
sensors/index.php
A Typical use: Honeywell’s
magnetic position Sensor:
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“Position sensors are used in
applications that require accurate,
reliable outputs. They are found in
brushless DC motors, utility meters,
welding equipment, vending machines,
home appliances, computers, and so
on.”
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http://content.honeywell.com/sensing/p
rodinfo/solidstate/
Pictures: form
http://content.honeywell.com/sensing/p
rodinfo/solidstate/
and
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http://www.micronas.com/products/ove
rview/sensors/index.php
How Hall Effect sensors are
classified
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Switches
Sensors
Absolute field
Differential field
Special-Purpose
Picture From the
website:http://www.eeel.nist.gov/812/effe.ht
m#lore
Major specifications
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Range of about 6 mm
(Mechatronics handbook )
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Works on about 5v-6v
and about 4-10 mA
Temperature: from about
-40°C to about 150°C
Can work as sourse or
sink depending on the
type
Works on proximity to
other external magnet.
Picture From the
website:http://www.eeel.nist.gov/812/effe.ht
m#lore
Limitations
Sensor only devise
 Good only in close proximity
 Must have a reference point
 Magnetic field must be present
 Must be calibrated
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What else do I need to know
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Non-contact switching action
High resolution
Can Produce a digital output
Great motors
Where can I buy these?
http://content.honeywell.com/sensing/prodinfo/so
lidstate/
To Conclude……..
Hall effect sensors are good
for proximity, electromagnetic,
and direction sensors.