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

Outline Limitations What else do I need to know Conclusion

References used: sors/index.php sors/index.php lidstate/ 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 M. Anjanappa, K. Datta, and T. Song, 2002 CRC Press LLC.

To Explore Further…… sors/index.php sors/index.php =678

Major Applications Electromagnetic field Proximity Velocity Direction

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 z- directed 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)Fig.1 From the website:

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 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:

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: © 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: sensors/index.php

A Typical use: Honeywell’s magnetic position Sensor: “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.” - rodinfo/solidstate/ Pictures: form rodinfo/solidstate/ rodinfo/solidstate/ and rview/sensors/index.php rview/sensors/index.php

How Hall Effect sensors are classified Switches Sensors Absolute field Differential field Special-Purpose Picture From the website: m#lore

Major specifications Range of about 6 mm (Mechatronics handbook ) 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: m#lore

Limitations Sensor only devise Good only in close proximity Must have a reference point Magnetic field must be present Must be calibrated

What else do I need to know Non-contact switching action High resolution Can Produce a digital output Great motors Where can I buy these? - lidstate/ lidstate/

To Conclude…….. Hall effect sensors are good for proximity, electromagnetic, and direction sensors.