Magnetic Sensor

Principle and Structure

Here the magnetic sensor is based on Hall effect. The effect is based on the interaction between moving electric carriers and an external magnetic field. In metal, these carriers are electrons. When an electron moves through a magnetic field, upon it acts a sideways force

where q is electronic charge, v is the speed of an electron, and B is the magnetic field.

Let us assume that a source of electric current is connected to the upper and lower ends of the strip (Fig. M1). The force F shifts moving electrons toward the right side of the strip which becomes more negative than the lift side. The sign and amplitude of the transverse Hall potential difference VH depends on both magnitude and directions of magnetic field and electric current. At a fixed temperature it is given by

where a is the angle between the magnetic field vector and Hall plate (Fig. M2), and h is the coefficient of overall sensitivity whose value depends on the plate material, its geometry, and its temperature.


Applications

The Hall effect sensor can be used to measure fuel level in a fuel tank (Fig. M3). The float has buoyancy in the fuel. It floats up as the fuel becomes more. The gap between the magnet and hall sensor will changed. It results in the changing of the output. The springs allow the float to move only vertically.