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Effect of Hall
      When an explorer with a flowing on him current is placed in the magnetic field so, that direction of current appears to the perpendicular magnetic lines of force, then the transversal electric field, proportional to work of closeness of magnetic stream and strength of electric current, appears. This effect arises up in explorers, however he is most substantial in semiconductors, where known under the name of effect of Hall.

semiconductor plate to which the magnetic field is attached with induction In is shown
                                           Fig. 1
   On a fig. 1 a semiconductor plate to which the magnetic field is attached with induction In is shown, perpendicular to the flowing through her current of I, and the arising up here electric field with tension of . Relation between magnetic induction, current and tension is determined as follows:

E = - RH (IB),

where   RH  = 1/ne     is a coefficient of Hall; is a number of charges,

flowing through unit of volume and formative an electric current in an explorer or semiconductor; is a charge of transmitter of charges.
    The effect of Hall is used in many types of transducers, intended for measuring of magnetic-field, and also in noncontact make - and - break devices.

See also:
Cryogenic Hall sensors
SENSORS OF PHYSICAL PARAMETERS
The application of the Hall effect in practice
The first industrial applications of the Hall effect found its way into life in the second half of the twentieth century. Today, slightly more than half of the share of the segment has to the automotive industry.
Often the sensor is included in the chip. Based on it released integrated crystal sensors to measure the angle of throttle position, steering, speed of rotation of the camshaft and the crankshaft. Widely the importance of technology in the work of valve engines, where the angular position of the rotor need to be commuting one way or the other winding. The measurement of the field doing the latest 3D sensors that determine not only angular, but linear position of the system of magnets. Until then simply recorded the presence or absence of an object in view. It is necessary for successful competition with magnetoresistive technology.

Today the rage are programmable design where the code can be entered a variety of functions. Sensors can be used in different ways. For example, the mutual position sensitive pad and magnet distinguish between the modes:

Frontal. In this case, the magnet is opposite the sensor, moving away from him or closer in a straight line. The field varies quadratically from distance and the law of the output signal from the cruise resembles a hyperbola. This is called unipolar, because the tension can't change.
Slide. In this case, between the sensing area and the magnet has a gap. This coordinate remains unchanged. And the magnet can slide parallel to the sensor in one axis. Field in this case does not change, and the dependence of the output signal from the coordinates is close to a Gaussian distribution. The direction of tension is not changing, therefore the mode is also called unipolar.
Bipolar slide. Sometimes you need to know which side had rejected a magnet. And not only to determine the distance. In this case, the horseshoe magnet is used. Accordingly, the poles evoke responses of different polarity. Which gave the name to the mode.
These modes are sometimes used in combination. For example, in the case when you need to precisely position the magnet relative to the sensors (via the actuators), the sensitivity of the equipment increases a steeper characteristic dependence of the output signal from the coordinates. This can be the magnets of the three stripes with alternating poles. Extreme descents of the graph obtained is flat, and the Central peak is quite pronounced. And this is achieved by precise positioning system.

To enhance the tension lines, making them more explicit directions apply the pole pieces. It's pieces of metal from a soft ferromagnetic alloys. As you approach thereto of the magnet the lines start to aspire to this area, forming a gap, where they will remain practically flat. If you put the Hall sensor, the sensitivity of the system can be significantly improved. With the same purpose are sometimes applied magnets the offsets that remain in one place and by themselves, can't trigger. But as you approach the moving part of the magnetic field density increases. This simplifies the operation and reduces the requirements to the sensitivity of the sensor.

Can we add that the structure of the output signal of the sensors are analog and digital. In the latter case, the system is easily interfaced with automation, and the measured signals does not lose precision, being transferred for processing.