Hall effect sensors and current sensors

A hall effect sensor consists of a strip of metal that a current runs across. A stream of charged particles passing through a magnetic field will cause the beam to deflect from a straight line. If a conductor is placed in the magnetic field perpendicular to the electron flow, it will gather charge carriers and produce a voltage differential between the positive side of the metal strip and the negative side. This will produce a voltage differential that can be measured. The differential is called the Hall voltage, which is responsible for the phenomenon known as the Hall effect. This is illustrated in the following image. If a current is applied to a metal strip (as shown in the diagram) within a magnetic field, electrons will be attracted to one side of the strip, and holes to the other (see the curved line). This will induce an electric field that can be measured. If the field is strong enough, it will cancel out the magnetic force, and electrons will follow the straight line: 

Current sensors use the Hall effect for measuring the AC and DC currents of a system. There are two forms of current sensors: open loop, and closed loop. Closed loops are more expensive than open loop sensors, and are often used in battery-powered circuits.  

Typical uses of Hall sensors include position sensing, magnetometers, highly reliable switches, and water level detection. They are used in industrial sensors to measure the rotational velocity of different machines and motors. Additionally, these devices can be created very inexpensively, and can tolerate harsh environmental conditions.