A Hall effect sensor (or simply Hall sensor) is a type of sensor which detects the presence and magnitude of a magnetic field using the

Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was dis ...

. The output

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

of a Hall sensor is directly proportional to the strength of the field. It is named for the American physicist Edwin Hall. Hall sensors are used for proximity sensing, positioning, speed detection, and current sensing applications. Frequently, a Hall sensor is combined with threshold detection to act as a binary

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

. Commonly seen in industrial applications such as the pictured

pneumatic cylinder Pneumatic cylinders (sometimes known as air cylinders) are mechanical devices which use the power of compressed gas to produce a force in a reciprocating linear motion. Like hydraulic cylinders, something forces a piston to move in the desir ...

, they are also used in consumer equipment; for example, some computer printers use them to detect missing paper and open covers. Some 3D printers use them to measure filament thickness. Hall sensors are commonly used to time the speed of wheels and shafts, such as for

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...

ignition timing In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need f ...

tachometer A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analo ...

s and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor peaks twice for each revolution. This arrangement is commonly used to regulate the speed of

disk drives Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are consi ...

Working principle

In a Hall sensor, a current is applied to a thin strip of metal. In the presence of a magnetic field perpendicular to the direction of the current, the charge carriers are deflected by the Lorentz force, producing a difference in

electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...

(

) between the two sides of the strip. This voltage difference (the Hall voltage) is proportional to the strength of the magnetic field. Hall effect sensors respond to static (non-changing) magnetic fields. This is a key difference from inductive sensors, which respond only to changes in fields.

Hall probe

A Hall probe is a device that uses a calibrated Hall effect sensor to directly measure the strength of a magnetic field. Since magnetic fields have a direction as well as a magnitude, the results from a Hall probe are dependent on the orientation, as well as the position, of the probe.

Materials

The key factor determining sensitivity of Hall effect sensors is high electron mobility. As a result, the following materials are especially suitable for Hall effect sensors: * gallium arsenide (GaAs), * indium arsenide (InAs), * indium phosphide (InP), *

indium antimonide Indium antimonide (InSb) is a crystalline compound made from the elements indium (In) and antimony (Sb). It is a narrow- gap semiconductor material from the III- V group used in infrared detectors, including thermal imaging cameras, FLIR systems ...

(InSb), *

graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.

Signal processing and interface

Hall sensors are linear

transducers A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and control ...

. Such sensors require a linear circuit for processing the sensor output signal. This circuit provides the drive voltage for the sensor and is used to amplify the output signal. In some cases, the linear circuit may cancel the offset voltage of Hall sensors. Moreover, AC modulation of the driving current may also reduce the influence of this offset voltage. Hall sensors with linear transducers are commonly integrated with digital electronics. This enables advanced corrections to the sensor characteristics (e.g. temperature-coefficient corrections) and digital interfacing to microprocessor systems. In some IC Hall sensors an integrated

DSP DSP may refer to: Computing * Digital signal processing, the mathematical manipulation of an information signal * Digital signal processor, a microprocessor designed for digital signal processing * Yamaha DSP-1, a proprietary digital signal ...

is used, which can allow more processing techniques directly within the sensor package. The Hall sensor interfaces may include input diagnostics, fault protection for transient conditions, and short/open-circuit detection. It may also provide and monitor the current to the Hall sensor itself. There are precision IC products available to handle these features.

Advantages and disadvantages

Hall sensors are capable of measuring a wide range of magnetic fields, and are sensitive to both the magnitude and orientation of the field. When used as electronic switches, they are less prone to mechanical failure, since there is no wear on physical parts. They can also be operated at higher frequencies than mechanical switches. Hall effect switches cannot be used in areas with high external magnetic fields. Hall sensors can be prone to thermal drift due to changes in environmental conditions, and to time drift over the lifetime of the sensor.

Applications

Position sensing

One of the most common industrial applications of Hall sensors used as binary switches is in position sensing. Hall sensors are also used in brushless DC motors to sense the position of the rotor and to switch the transistors in the right sequence. Another example of a Hall effect position sensor is the sensor used to detect whether a smartphone's cover is closed. See Galaxy S4 accessories.

Direct-current (DC) transformers

Hall sensors may be utilized for contactless measurements of

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...

current transformer A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary. Current transformers, along with volt ...

s. In such a case the Hall sensor is mounted in a gap in the magnetic core around the current conductor. As a result, the DC magnetic flux can be measured, and the DC current in the conductor can be calculated.

Automotive fuel-level indicator

Hall sensors are used in some automotive fuel-level indicators. The sensor is used to detect the position of a floating element within the fuel tank.

Keyboard switch

Hall effect switches for computer keyboards were developed in the late 1960s by Everett A. Vorthmann and Joseph T. Maupin at

Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...

. Due to high manufacturing costs these keyboards were often reserved for high-reliability applications such as aerospace and military. As mass-production costs have declined, an increasing number of consumer models have become available.

References

External links

*{{Commonscatinline, Hall sensors Magnetic devices Position sensors Transducers