By hmimcu 
The Hall sensor is a magnetic field sensor made according to the Hall effect. The Hall effect is a kind of magnetoelectric effect, which was discovered by Hall (A.H.Hall, 1855-1938) in 1879 when he was studying the conductive mechanism of metals. Later, it was found that semiconductors and conductive fluids also have this effect, and the Hall effect of semiconductors is much stronger than that of metals. Various Hall elements made of this phenomenon are widely used in industrial automation technology, detection technology and information processing, etc. aspect. The Hall effect is a basic method for studying the properties of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine important parameters such as the conductivity type, carrier concentration, and carrier mobility of semiconductor materials.
How Hall Sensors Work
There is a Hall semiconductor sheet in the magnetic field, and a constant current I passes through the sheet from A to B. Under the action of the Lorentz force, the electron flow of I shifts to one side when passing through the Hall semiconductor, causing the sheet to generate a potential difference in the CD direction, which is the so-called Hall voltage.
The Hall voltage changes with the strength of the magnetic field. The stronger the magnetic field, the higher the voltage, the weaker the magnetic field, and the lower the voltage. The Hall voltage is very small, usually only a few millivolts, but it is amplified by the amplifier in the integrated circuit. This voltage can be amplified enough to output a stronger signal. If the Hall integrated circuit is used as a sensor, it is necessary to use a mechanical method to change the magnetic induction intensity. The method shown in Figure 1 below is to use a rotating impeller as a switch to control the magnetic flux. When the impeller blade is in the air gap between the magnet and the Hall integrated circuit, the magnetic field deviates from the integrated chip, and the Hall voltage disappears. In this way, the change of the output voltage of the Hall integrated circuit can indicate a certain position of the impeller drive shaft. Using this working principle, the Hall integrated circuit chip can be used as an ignition timing sensor. Hall effect sensors are passive sensors that require an external power source to work, which allows them to detect low-speed operation.
Classification of Hall sensors
Hall sensors are divided into linear Hall sensors and switch Hall sensors. Hall devices have many advantages. They have firm structure, small size, light weight, long life, easy installation, low power consumption, high frequency (up to 1MHZ), vibration resistance, and are not afraid of dust, oil, water vapor and salt spray, etc. contamination or corrosion. The Hall linear device has high precision and good linearity; the Hall switch device has no contact, no wear, clear output waveform, no jitter, no bounce, and high position repeatability.
(1) The switch-type Hall sensor is composed of a voltage regulator, a Hall element, a differential amplifier, a Schmitt trigger and an output stage, and it outputs digital quantities. There is also a special form of switch-type Hall sensor called a key-lock Hall sensor.
(2) The linear Hall sensor is composed of a Hall element, a linear amplifier and an emitter follower, and it outputs an analog value.
Linear Hall sensors can be divided into open-loop and closed-loop. Closed-loop Hall sensors are also called zero-flux Hall sensors. Linear Hall sensors are mainly used for AC and DC current and voltage measurements.
Application of Hall Sensor
Hall sensor technology has a wide range of applications in the automotive industry, including powertrain, body control, traction control, and anti-lock braking systems. In order to meet the needs of different systems, Hall sensors have three forms: switch type, analog sensor and digital sensor. Hall sensors can be made of metal and semiconductor. The change of effect quality depends on the material of the conductor, which will directly affect Positive ions and electrons flowing through the sensor.
The automotive industry typically uses three semiconductor materials for the manufacture of Hall elements: gallium arsenide, indium antimonide, and indium arsenide. The most commonly used semiconductor material is indium arsenide. The form of the Hall sensor determines the difference in the amplifier circuit, and its output should adapt to the controlled device. This output may be analog, such as an accelerator position sensor or a throttle position sensor, or it may be digital. Such as a crankshaft or camshaft position sensor, when the Hall element is used for an analog sensor, this sensor can be used for a temperature gauge in an air conditioning system or a throttle position sensor in a power control system.
The Hall element is connected to a differential amplifier, and the amplifier is connected to an NPN transistor. The magnet is fixed on the rotating shaft, and when the shaft is rotating, the magnetic field on the Hall element is strengthened. The Hall voltage generated by it is proportional to the strength of the magnetic field. When the Hall element is used for digital signals, such as crankshaft position sensor, camshaft position sensor or vehicle speed sensor, the circuit must be changed first. The Hall element is connected with the differential amplifier, and the differential amplifier is connected with the Schmitt trigger. in this configuration. The sensor outputs an on or off signal. In most automotive circuits, the Hall sensor is a current sink or grounds the signal circuit. To do the job, an NPN transistor is needed connected to the output of the Schmitt trigger. The magnetic field passes through the Hall element, and a blade on a trigger wheel passes between the magnetic field and the Hall element.