It is possible to measure the characteristics of the magnetic field using both elementary systems and very complex technological solutions. It all depends on what measurements are being taken and what results are expected to be obtained. The simplest magnetic field sensors are reed switches. These elements change the state of the connected electrical circuit when exposed to a magnetic field. Reed switches are used everywhere, for example in door opening sensors.
Reed switches are very simple systems. You can also use a compass to get more information about the magnetic field. This is how the first magnetometers worked. But now the possibilities are much greater, because new systems have appeared, including common sensors that use the Hall effect.
The range of models of such sensors is extremely wide – from keyboards to assessing the closing or opening of a valve. Hall sensors are used in the contactless ignition system of gasoline engines, they are used to read the engine camshaft in order to determine the rotation parameters. The electronic control unit of the car, according to the readings of the sensor, determines the serviceability of the ignition and start system.
It all started with the work of Edwin Hall, who discovered the effect later named after him in 1978. The basic idea is simple: when a magnetic field is applied to a conductor through which an electric current passes, a voltage difference arises at the ends of the conductor when a current flows perpendicular to the field.
This effect is called the usual Hall effect, since there are other phenomena that are based on the interaction of a conductor, current and magnetic field.
Accordingly, sensors whose work is based on the Hall effect is just one of the varieties of modern magnetometers. There are many different types of sensors that use receiving inductors. They can rotate or Internet, scales or springs are also used to measure the strength of the magnetic field. It is even possible to detect a magnetic field using the optical properties of materials and the corresponding effects – for example, the Kerr or Faraday effect.
There are also very specific sensors that can be called exotic. They are based on measuring the proton resonance in hydrogen-rich compounds and substances like kerosene, or determining the energy state of gas molecules like cesium. There are also sensors with superconducting coils.
But it is precisely the Hall effect sensors that are the most inexpensive, small in size and very practical. As mentioned above, miniature Hall sensors are used in keyboards. It’s hard to imagine a keyboard based on superconducting sensors attached to the bottom of the keys.
Hall sensors are ideal when building speed control systems for anything from coolers to engines in technology. The sensors were used in deluxe video and cassette recorders. An example is Vega-MP122.
Hall sensors are also used in smartphones to solve a variety of tasks, including:
- The work of a digital compass, which is used in navigation programs and helps to increase the positioning speed.
- Optimization of the interaction of the device with various accessories, for example, magnetic cases.
- The use of the sensor in models with a folding design, to turn on and off the screen when opening or closing the lid.
How it works?
There are numerous videos online explaining the physical principles behind the Hall Effect. But you can understand without any videos – everything is relatively simple here. Imagine a conductor repeating a banknote in size and shape. The left and right sides are connected to a DC power source that flows through the conductor. If the conductor is in good condition, then without the influence of a magnetic field, the voltage at the top and bottom of the conductor will be close to zero.
But if a magnetic field appears in the system, the lines of which are located at right angles to the current flow, the Lorentz force begins to affect the electrons and holes in the conductor. The particles begin to deflect. Accordingly, electrons will collect on one side of the conductor, and they will not be on the other.
With a multimeter, you can measure the voltage at the top and bottom of the conductor. If you remove the magnetic field, then the voltage will again become almost zero.
In devices that use the Hall effect, another circuit is added, where a Hall voltage amplifier is usually present. Sometimes there is a bias voltage regulator. The digital output sensor can have a comparator and an output transistor.
All sensors are different
There are two main types of Hall sensors – these are digital sensors, which, in turn, are divided into unipolar and bipolar. And also analog sensors.
If you want to use a Hall sensor in your project, you need to understand in detail its basic characteristics. Transducers have frequency range limitations, plus some can be quite expensive. For example, Melexis has a 250 kHz device, this frequency is much higher than most similar systems. It will only work at 5V and 15mA.
The example datasheet shows that there are two varieties of this sensor – 7.5 mT (millitesla), the second – 20 mT. There is even a 60 mT version.
Hall sensors can be embedded in electronic circuits. For example, the ESP32 has its own Hall sensor, as shown in the video above.
Hall Effect Systems Design
As shown above, you can think of a lot of things. Another example is portable magnetometer, the board of which fits into a plastic box from under the Tic Tac. It makes it easier to trace electrical wiring in the wall or ceiling. One more example – coffee machine monitoringto estimate the number of cups of coffee prepared.