Hall effect, named after the physicist Edwin Hall who discovered the phenomenon in 1879. He discovered if a conductor with current is placed perpendicular into a magnetic field a voltage difference is generated across the conductor. This voltage would later on be called the Hall voltage.
Without the presence of an external magnetic field will the charges within the current will flow in a straight line thru the conductor, but in the presence of a magnet field the charges flow will be curved by a force. This force is called Lorentz force, and the potential difference established by the curved charges in the current is called the Hall voltage.
Although Hall’s discovery was followed by successful experiments the practical usage of Hall effect was limited. This changed with the rise and continuous improvement of silicon semiconductors in the 1960s. The first hall effect sensors were a combination of hall effect sensor elements and amplifiers that evolved to the first integrated circuit hall switch.
Now hall effect integrated circuits are available with a wide variety of characteristics for different applications. Both the hall effect IC (the sensor chip) and hall effect transducers are commonly called hall effect sensor. Although the hall effect IC are very capable today, they are often integrated with a transducer. The transducer is equipped with voltage regulator, EMC safeguards, output calibration, mechanical enclosure of sensor and magnet, electrical connector etc.
Hall effect sensors are affected by two magnetic properties, magnetic flux density and polarity. Magnetic flux* is the field strength which affect the sensor and the polarity of the magnet decides the flux direction as it always travels from north to south. Correct configuration of sensor, magnet and orientation is key for accurate measurement as only vectors perpendicular to the sensor is sensed by the hall effect sensor element. Although this is true in theory and for basic one dimension-sensors, the development of two- and three dimension-sensors expands the practical implementation of magnet-sensor configuration. Continue reading for more about 2D- and 3D-sensors. Hall effect sensors are usually specified with a fixed magnet orientation ex. head on linear, overhead linear, rotary etc., and with a magnet flux value. In most hall effect transducers is this functionality built in by the manufacturer.
*Magnetic flux is the magnetic field thru a given area.
Switching and absolute sensors
The first hall effect sensors were switching sensors, the sensor switch when the magnet field strength passes the specified threshold value. Switching hall effect sensors can be used as a stand-alone sensor, a typical application is proximity switch. Or be integrated with an incremental transducer, by combining sensor element and magnet with special characteristics. Typical applications are magnetic encoders and gear tooth sensors.
The basic absolute analog sensor is a radiometric sensor, the output is proportional to the magnet field strength and orientation. This is the basic operation of all analog hall effect sensors, but today they are available in a wide range of options. Analog sensors are used in linear and rotary transducers that come with different characteristics such as output signal, programmable parametrics, supply voltage etc. Analog sensors are used in many applications such as linear positioning, steering-angle, clutch control etc.
2D and 3D sensors
Traditional one-dimension sensors only sense magnetic field perpendicular to the sensor element. This require precise positioning and motion of the magnet, the tolerance for airgap, magnet movement etc is low. As well as material properties such as variation in magnetic flux between magnets, temperature variations etc.
Two or three dimension sensors senses magnetic field in two or three dimensions; X,Y and Z. This is useful in true multi-dimension sensing in ex. joysticks. But also enables a more robust and accurate positioning in rotary and linear transducers.