• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Electrical Engineering News and Products

Electronics Engineering Resources, Articles, Forums, Tear Down Videos and Technical Electronics How-To's

  • Products / Components
    • Analog ICs
    • Battery Power
    • Connectors
    • Microcontrollers
    • Power Electronics
    • Sensors
    • Test and Measurement
    • Wire / Cable
  • Applications
    • 5G
    • Automotive/Transportation
    • EV Engineering
    • Industrial
    • IoT
    • Medical
    • Telecommunications
    • Wearables
    • Wireless
  • Learn
    • eBooks / Handbooks
    • EE Training Days
    • Tutorials
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • White Papers
    • Educational Assets
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • Podcasts
    • DesignFast
  • Videos
    • EE Videos and Interviews
    • Teardown Videos
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • Bill’s Blogs
  • Advertise
  • Subscribe

What are Hall effect sensors?

August 16, 2016 By Chris Francis 2 Comments

Magnetic sensors are typically Hall effect sensors (named after Edwin Hall who discovered the effect in 1879), whereby a small voltage difference can be measured across a conductor with current flowing through it when a perpendicular magnetic field is applied. They are available as small, integrated solutions with signal or multiple outputs, and analog or digital outputs. The magnetic field normally comes from a magnet. While the earth’s magnetic field can be detected, it isn’t usually wanted and could be a nuisance. For that reason, strong magnets and low sensitivity hall sensors are used.

Hall effect sensors figure 1
The Allegro Microsystems A139x range is an example of a single axis linear output sensor with analog output.

The different versions have different sensitivities, giving an output proportional to the magnetic field. The effect of the earth’s magnetic field will be small — the sensitivity is only up to 10mV/Gauss and the earth’s magnetic field is never more than 1 Gauss on the earth’s surface. They are intended to be used with an applied magnet. Bear in mind that the direction of the magnetic field is important. With a single axis hall effect sensor the maximum sensitivity will be when the magnetic field is perpendicular to the current flow. If the magnetic field is in line with the current flow you will detect nothing. Also, there will be a small signal present depending on the device orientation due to the earth’s magnetic field.

Hall effect sensors fig 2

A multi-axis sensor will give a signal whatever the orientation of the magnetic field and you will be able to detect the orientation of the magnetic field. The Infineon TLV493D above is one example of a 3D magnetic sensor. It has an I≤C interface and very low current consumption, as low as 10µA when operating. While the current consumption of the A139x series at 3.2mA seems very high by comparison, the Infineon device is already strobing the sensor at 10Hz to save power. While measuring, the TLV493D will consume 3.7mA. With a hall sensor, the voltage detected is proportional to the current flowing so ultra-low power consumption is difficult to achieve. While the signal can be amplified, you will have more problems with a offsets and noise when you start with a very small signal. As a result, the sensors typically rely on strobing the sensor to keep power consumption low. This is a typical design practice in battery operated equipment.

One use for magnetic sensors is for non-contact position detectors. A control element such as a joystick or knob with an embedded magnet can provide a linear (or rotary) control signal. An alternative for a rotary control would be an optical encoder, although they tend to have a quadrature output which will require something to continuously monitor the outputs to detect movement. Also, rotary encoders for user controls are not usually absolute, although they can have a zero position index. The current consumption of an optical encoder is often quite high and being incremental. You would have to be very careful if you wanted to strobe it without risking missing pulses.

An example of a rotary optical encoder would be the Bourns EN series, but they are expensive. A magnetic sensor based control can be tiny with devices often only 2mm or 3mm across. You need a tiny magnet and system for holding and moving the magnet so it is not a “complete” solution compared to an optical encoder which will take a standard control knob. Magnetic sensors are relatively inexpensive – often less than $1.

Some hall sensors are actually switches such as the Allegro Microsystems A122x series. They have an open drain output and various versions with different switching thresholds. They are “latching” so once turned on with a north pole, they need an equally strong south pole to turn them off. This behavior makes them only suitable for certain applications.

Hall effect sensors figure 3

More general purpose devices are the Allegro A110x series which don’t need the opposite polarity to release them, but they do have hysteresis to prevent output chatter. You can use them where you want to detect if something is open or closed, such as a refrigerator door.

Another class of Hall-based sensor is used for detecting gear teeth for speed measurement of motors and for automobile ABS sensors such as the Allegro ATS642LSH. They incorporate a magnet so a passing ferrous metal can be detected as it disturbs the magnetic field reaching the hall sensor.

AMS AG in Germany offer a range of magnetic sensors for rotary and linear position measurement. The also sell magnets which include multipole magnet strips such as the AS5000-MS20-150. That magnet is 300mm long and has 150 poles making construction of long linear sensors possible.

iC-Haus, also in Germany, make a range of magnetic encoder and interpolator ICs which will perform up to 16-bit sine/cosine interpolation for making very high-resolution encoders. The simple hall sensor seems to have found quite a variety of uses.

 

You Might Also Like

Filed Under: Featured, MEMS & Sensors, Sensors Tagged With: allegromicrosystems, amsag, basics, Bourns, FAQ, icHaus, infineon

Reader Interactions

Comments

  1. Phil-S says

    August 29, 2016 at 2:06 pm

    One of the most useful sensors, especially for utility meters like water and gas.
    Infineon do some very small outline, low power types, ideal for battery applications

    Log in to Reply

Leave a Reply Cancel reply

You must be logged in to post a comment.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Primary Sidebar

EE Engineering Training Days

engineering

Featured Contributions

Integrating MEMS technology into next-gen vehicle safety features

Five challenges for developing next-generation ADAS and autonomous vehicles

Robust design for Variable Frequency Drives and starters

Meeting demand for hidden wearables via Schottky rectifiers

GaN reliability milestones break through the silicon ceiling

More Featured Contributions

EE Tech Toolbox

“ee
Tech Toolbox: 5G Technology
This Tech Toolbox covers the basics of 5G technology plus a story about how engineers designed and built a prototype DSL router mostly from old cellphone parts. Download this first 5G/wired/wireless communications Tech Toolbox to learn more!

EE Learning Center

EE Learning Center
“ee
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.
“bills
contribute

R&D World Podcasts

R&D 100 Episode 10
See More >

Sponsored Content

Designing for Serviceability: The Role of Interconnects in HVAC Maintenance

From Control Boards to Comfort: How Signal Integrity Drives HVAC Innovation

Built to Withstand: Sealing and Thermal Protection in HVAC Sub-Systems

Revolutionizing Manufacturing with Smart Factories

Smarter HVAC Starts at the Sub-System Level

Empowering aerospace E/E design and innovation through Siemens Xcelerator and Capital in the Cloud

More Sponsored Content >>

RSS Current EDABoard.com discussions

  • The Analog Gods Hate Me
  • Apc 650 upa
  • CST Studio RAM error
  • MCP23017 what is the typical output voltage at logic Hi?
  • Battery Deep Discharge – IC Workarounds?

RSS Current Electro-Tech-Online.com Discussions

  • Simple LED Analog Clock Idea
  • The Analog Gods Hate Me
  • Wideband matching an electrically short bowtie antenna; 50 ohm, 434 MHz
  • PIC KIT 3 not able to program dsPIC
  • Parts required for a personal project
Search Millions of Parts from Thousands of Suppliers.

Search Now!
design fast globle

Footer

EE World Online

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDABoard Forums
  • Electro-Tech-Online Forums
  • Engineer's Garage
  • EV Engineering
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips

EE WORLD ONLINE

  • Subscribe to our newsletter
  • Teardown Videos
  • Advertise with us
  • Contact us
  • About Us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy