Tech 101 From Symmetry Electronics: Hall Effect Sensors

A Hall-effect sensor (Hall sensor for short) is a transducer that varies its output voltage as the magnetic field near it varies. Within a Hall sensor, current is applied along a thin strip of conductive material. In the presence of a magnetic field, the electrons line one edge of the strip inducing a change in voltage across the sides perpendicular to current flow.

In a Hall switch, the output reads high or low when the magnetic flux density around the sensor exceeds a certain pre-set threshold. A linear or rotational hall sensor with analog output has a hall voltage relative to the magnetic flux density around the sensor, typically linear until saturation. The threshold on these sensors is also pre-set. Besides an analog output, manufacturers offer sensors which have PWM, serial and SENT outputs for varying applications.

Linear Hall sensors can be used for current sensing applications and offer big advantages over resistive current sensing. When using a Hall sensor, the sensing circuit doesn’t have any direct electrical connection with the current being sensed. This means they are convenient in safety critical applications such as measuring currents in high-voltage circuits, and there are no insertion losses or power dissipation.

Most of Symmetry's Hall sensors offer user-programmable gain, offset, and temp compensation so a single sensor can be used for a number of applications. This also means the threshold and sensitivity of your design can be easily modified without modifying your hardware or the code on your controlling MCU.

When sensing linear or rotational position, a resistive potentiometer is commonly used. Unfortunately, potentiometers are prone to mechanical wear over time and are unstable and drift as temperature increases or decreases. Hall sensors alleviate these problems since there is no mechanical interaction between the sensor and the moving parts. They are also robust in harsh environments and can compensate for temperature drift.

Hall sensors can be used for sensing throttle, current, angle, speed and torque in robotics and industrial automation. Automotive applications include: buckle switch, throttle sensor, seat position, door handle position, door locks, steering torque, steering angle, gas and brake positions, powertrain valve position, and fluid leveling. Hall sensors can even be used to sense door location, water level, fan speed and fluid flow in your home appliances and white goods.

Featured products:

TDK-Micronas:

Low power Hall switches with wide supply voltage range and overvoltage protection
HAL15xy

High-precision linear Hall sensors with possible analog or PWM outputs and redundancy function
HAL24xy

Hall sensors for rotational or linear position detection based on 3D HAL Technology
HAL37xy family

Silicon Labs:

I2C Hall effect position and temperature sensor- Si7210

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