Hall Sensor

Hall Effect Sensor is a small sensitive element that allows you to track changes in the magnetic field. The discovery has already turned 100 years old; the phenomenon underlying the principle of action has been known since 1879, but only in the last few decades have products become an integral part of the examples of technological advances.

Hall Effect

Edwin Hall showed that in the direction transverse to the magnetic field, an emf is generated in the conductor when DC current flows through it. In practice, it looks like the occurrence of potentials on the edges of a metal strip, when a magnet is brought to the strip. As a result, it becomes possible to record the fact of approaching the sensor. The potential difference depends mostly on:

1. The magnitude of the flowing direct current.
2. Magnetic field strength.
3. Mobility and concentration of charge carriers in the material.

Until the 1950s, when the microwave radiation recorder was first created, the Hall effect was not applied outside the laboratories. In the mass swimming launched by manufacturers of computer keyboards - concerns turned out to be interested in finding a contactless way of registering the position of the keys and found one in 1968.The solid-state sensor, invented in 1965 by Joe Mopin and Everett Wortman, greatly improved the characteristics of the equipment. Now the industry is experiencing an annual increase in the need for Hall sensors, an estimated top five of manufacturing companies collects $ 2 billion in revenue.

Today, Hall sensors use because of this feature - they are almost eternal, do not contain moving and rubbing parts. In the keyboard, it is not the sensitive element that breaks, but the controller. There are viruses that can reprogram a chip and infect a computer. .. via USB keyboards. By the way, the secret services have long adopted a method to spy, but there is simply no effective protection against vulnerability.

The Hall effect is manifested in the conductor, the stronger, the lower the carrier concentration and the greater the mobility. Metals( on the basis of which the phenomenon was first demonstrated) are not considered an ideal material for the creation of sensors. To a much greater extent, semiconductors are suitable for this purpose. At the same time, this greatly reduces the cost and increases the unification of mass production.

Let's see how the Hall sensor works. Imagine a semiconductor strip along which direct current flows. In the absence of external disturbances, an electric field is created inside, which sets in motion the charge carriers. Suppose now that lines of a constant magnetic field arise perpendicular to the surface of the strip. The emerging force of Lorentz will be the rule of the left hand to act on the process. Recall that the direction is determined as follows: “If you place your left hand in such a way that the magnetic field lines are perpendicular to your palm, and your outstretched fingers look in the direction of charge movement( in physics, positively charged particles, not negative electrons)will point in the direction of the action of the Lorentz force. "

There are no riddles in the Hall effect. The Lorentz formula was proposed a good dozen years later - in 1892 - before people found out that a plate of gold forms a potential difference at the ends when DC current flows. The influence of the magnetic field on the conductors in 1831 was clearly expressed by Michael Faraday, thanks to a secret admirer of which the world learned about generators and engines. It is still unknown who coined the first DC motor. When reversed running generator.

Hall Effect opened in 1879 at the base of Johns Hopkins University in Baltimore. Edwin tried to test the Kelvin theory, voiced thirty years earlier, was actively working to study the effect of a magnetic field on a gold plate. The scientist introduced a coefficient showing the effect produced depending on the product of the applied magnetic field and the flowing current. Obviously, the value depends on the material properties. The moment has already been discussed.

Hall Effects of Hall Sensors

Experts point out the following advantages of Hall sensors:

1. Long service life( for the keyboard - 30 billion clicks).
2. Lack of moving parts( solid-state electronics), which clearly simplifies the design with high demands on vibrations and shocks.
3. Ability to work at frequencies of change of the magnetic field up to 100 kHz.
4. Simple combination with the logical levels of digital technology signals.
5. Wide operating temperature range( from minus 40 to plus 150 degrees Celsius).
6. High measurement repeatability, which makes it easy to tare instruments based on Hall sensors.

Hall Sensors

Design During operation, traditional semiconductor materials — gallium and indium arsenides — perfectly manifested themselves. Typically, the Hall sensor is a small plate, to the opposite faces of which are paired electrodes. Feeding wide and located on the side of the rectangle. Where the signal is taken - the simplest point. In any scheme, a common point is marked( neutral wire, neutral), the sum of the contacts is three. Negative lines are combined.

Experts note that even in the absence of a magnetic field on the electrodes, there is usually a small signal. This is not due to the influence of our planet, as the readers will think. The potential along the side edge of the plate is unevenly distributed. And it is not always advisable to identify equivalent points. It is easier to tare electronics mated with the sensor, or to be guided by point pulses, which is often done in practice. Differential amplifiers are often used for correction( only a signal change is output).

sensor design The thickness of the conductor film is usually small, barely reaching 10 microns. For deposition on a substrate using the method of lithography. This allows you to create Hall sensors with a small sensitive area, which greatly and often improves the measurement accuracy, because the surface is small. In instruments, this is used to assess the positions of parts of mechanisms. However, small-sized sensors detect a relatively low response, measured in terms of W / T( the output power of the useful signal depending on the voltage of the magnetic field).For serial Hall sensors, the parameter usually ranges from 0.03 to 1.

In practice, this looks like a pulse generator. Suppose there are a number of magnets on the motor shaft of a washing machine, with a turn a certain number of peaks are produced. As a result, the electronic filling evaluates the rotational speed, the angular position of the rotor, which is used, for example, in valve engines( with electronic switching of the windings).

We digress and explain why the small Hall sensor has a weak response. The amplitude of the generated pulses depends on the flowing direct current, but it cannot be large, otherwise the conductor film( having a sufficiently large resistance) will overheat and burn. Therefore, valid values ​​(in amperes) range from 5 to 50 mA.

Application of Hall Sensors

1. Hall sensors are widely used in home appliances. An eloquent example is washing machines. Users break their minds, as in advanced models, the laundry is weighed. The network contains patents where it is proposed to solve the problem head-on with the help of springs or strain gauges. Such devices are not capable of great reliability, at the risk of constantly being subjected to deformations. In addition, a couple of bricks are hung on the tank, which means that the total weight of the structure is large, which imposes restrictions. In practice, in washing machines, the laundry is firstly moistened abundantly, then the total mass is estimated by the speed of the drum acceleration. This is the weighing of the laundry, which further determines the program of work of the equipment, the consumption of powder, water, rinse.
2. In computer keyboards Hall sensors first entered the mass production. Usually there is a sensitive element on the substrate, a magnet is mounted on the key. It is clear that there are no more springs inside the modern keyboard, and the elastic force is created by polymers with a high service life. The solution is extremely successful: it is not the sensor that breaks down and the mechanical part is not elastic, the controller fails.
3. The Hall sensor can be used to measure current( as in current tongs).The device can react to changes in the electromagnetic field surrounding the wire. A so-called excitation winding( inductance from copper wire) is created. The measured current is supplied to the taps; as a result, an electromagnetic wave is formed, a part is estimated by the Hall sensor. The response depends directly on the measured value. The calculation is carried out according to the formulas laid down, for example, in the controller. For accuracy, the instrument is calibrated by the manufacturer. And the advantages mentioned above remain, first of all - the absence of moving parts. Similarly, with the help of Hall sensors it becomes possible to measure power.
   

   The application of the sensor

4. Converting DC to AC voltage is considered an example of the creation of a generator. If the Hall sensor is in an alternating magnetic field, the voltage at the output repeats the shape. The efficiency of the device does not have a high value. But the design is simplified to the maximum, it becomes possible to directly transfer the shape of the magnetic field to the electric current.
5. In connection with the facts described above, we note that Hall sensors allow you to control the flow and full charge of batteries( by measuring the flowing current and integrating it over time).This causes the possibility of their wide application. For example, in cell phones( up to 37% of the market).But experts believe that the most promising direction is the segment of electric vehicles, where the issue of energy availability will be vital.
6. Due to the presence of the Earth’s magnetic field, it becomes possible to create compasses based on Hall sensors. The only problem is that the value in Tl is uneven over the surface of continents and continents, and the input of correction methods is required. Due to this effect, automatic image stabilization systems for video cameras of mobile devices sometimes work.
7. Little is known, but the automotive industry accounts for 52% of the yield from the release of Hall sensors. In this industry is required to measure the rotational speed of the wheels, crankshaft and camshaft. Readers have already guessed that the Hall sensor will help with determining the position of the throttle valve, steering. The automotive market has become the main driving force for the further improvement of devices. Some systems are considered the de facto standard( ASIC, ASSP, ESC / ESP, etc.) on the roar, and Hall sensors take an active part in them.