Very often, when building various electrical generators or engines, it is required to determine the pole of the magnet. Almost every person, from school lessons in physics, knows that the magnet has two poles: the north (denoted by the blue letter "n") and the southern (designated in red and the letter "S").
This simple electronic detector will help you determine the name of the pole of the magnet. To do not build it, you do not need scarce details and components.
As a sensor, a liner sensor is applied in the detector, which can be dropped from an old cooler from the computer. Fortunately, such "good" is now in bulk.
As you know, computer fans are in their composition a brushless engine. Which consists of two windings on the anchor and the commuting element - the Hall sensor. This sensor switches the winding depending on the position of the movable magnetic ring located in the impeller.

Fan scheme


This element has four outputs. Two are meals, and two outlets on which there is food depending on the magnetic field. That is, the power supply may be only on one of the conclusions.

Magnetic detector scheme


For the location of the windings, we connect multicolored LEDs through a restrictive resistor. We will feed the entire scheme from the battery 3 volts of the type "Tablet".
Schema will collect on the dumping board. Withdraw the sensor a little on the outputs.



Check. The only disadvantage of this sensor is that the level is always present on one of the conclusions, regardless of the presence of a magnetic field. Therefore, I added a power button to switch the circuit with a source. As a result, it works like this: brought to the magnet, I pressed the button - the LED outlines the indicating field, all the button can be released.




I shoved the board into the housing from the flat marker. It turned out everything is very beautiful. As a result, I became the owner of such a pocket magnetic field indicator. In the farm to make it good.

This interesting device allows you to hear the world of electromagnetic radiation that surrounds us. It converts the fluctuations of the high frequency of radiation generated by a variety of electronic devices in the audience. You can use it near computers, tablets, mobile phones, etc. Thanks to him, you will be able to hear truly unique sounds created by the working electronics.

Principal electrical system

The scheme assumes the implementation of this effect with as the lowest number of radio elements. Further improvements and corrections are already at your discretion. Some parts of the details you can pick up for your needs, others are permanent.

Assembly process

The assembly assumes the use of a dummy board in size at least 15 x 24 holes, and special attention Addresses the location of the elements on it. The photographs show the recommended location of each of the radio elements and which links between them. The jumpers on the printed circuit board can be made from the cable fragments or cut off the legs from other elements (resistors, capacitors) that remained after they are installed.

First you need to hit the coils L1 and L2. Well push them away from each other, which will give us space and increase the stereo effect. These coils are a key element of the scheme - they behave like antennas that collect electromagnetic radiation from the environment.

After the coils sprinkle, C1 and C2 capacitors can be installed. Their container is 2.2 μF and determines the lower frequency of the slice of sounds, which will be heard in the headphones. The higher the tank value, the lower the sounds played in the system. Most of the powerful electromagnetic noise lies at a frequency of 50 Hz, so it makes sense to filter it.

Next, we solder the resistors of 1 com - R1 and R2. These resistors, together with R3 and R4 (390 com) determine the gain of the operational amplifier in the scheme. Inverting the voltage does not have a special value in our system.

Virtual Mass - Resistors R5 and R5 with a resistance of 100 com. They are a simple voltage divider, which in this case will divide the voltage of 9 V on half, so that from the point of view of the scheme it is powered by m / s-4.5 V and +4.5 V with respect to the virtual mass.

You can put in the panel operational amplifier any with standard outputs, for example OPA2134, NE5532, TL072 and others.

We connect the battery and headphones - now we can use this acoustic monitor for wiretapping electromagnetic fields. The battery can be glued to the scotch card.

Additional features

What can be added to increase the functionality? Volume control is two potentiometers between the output of the circuit and the headphone socket. Power switch - Now the scheme is on all the time until the battery is disconnected.

When testing it turned out that the device is very sensitive to the field source. You can hear, for example, how the screen is updated in a mobile phone, or how beautifully sings the USB cable during data transfer. The attached to the loudspeaker enabled works as an ordinary and completely accurate microphone, which collects the el-magnetic field of the operating speaker coil.

It is looking for a cable in the wall, on the trace detector manner. It is only necessary to raise the LC, increasing all 4 capacity up to 10 μF. The disadvantage is quite large noise and another signal is too weak - you need some additional power amplifier, such as on.

Video work detector RF

Discuss an artwork an unusual detector of electromagnetic fields

Scheme of experimental installation

Illustration: Kasper Jensen et al., 2016, ARXIV: 1601.03273

Danish and Russian scientists have developed a non-invasive method for measuring the magnetic field of individual nerves, which operates at room temperature and has a practically unlimited sensitivity. They reported on their work in the publication, which is available on the ARXIV.org website.

The signal is propagated by nerve fibers in the form of an electric potential of action. Registration of electrical activity of the nerves is critical to studying physiology nervous system and the diagnosis of its diseases. However, to measure the electric potential of the nerve fiber, it is necessary to combine it with a microelectrode, which requires surgical intervention. In addition, the electrode connect itself can distort the signal characteristics.

Therefore, the electrical activity of the nerves is measured by the magnetic field created by it. This field is very weak, and high-precision methods are required for its registration. Since the 1980s, this method served a magnetometry using a superconducting quantum interferometer (Skwid, from the English. Squid., SuperConductingQuantum.InterferenceDevice.). This method of bulk, expensive, requires cooling the conductor to ultra-low temperatures and can only measure the magnetic field of the nerve skipped through the detector helix, which makes it use in the clinic it is impossible.

The staff of the Copenhagen and St. Petersburg universities used in the work modified optical atomic magnetometer of its own development. The basis of its action is the ability of the atoms of gaseous cesium to polarize the light under the action of an external magnetic field (Cesium was selected due to the high pressure of its saturated steam, providing high measurement accuracy at room temperature). A laser is used as a source of polarizable light. The measurement of the magnetic field is carried out in two modes - constant and impulse. All this helped to achieve measurement accuracy limited only by quantum effects; The device is able to fix the magnetic fields with the inductance of less picotesla (10 -12 Tesla).

The sensor, which is a steam chamber with a cesium, has an internal diameter of 5.3 millimeters and a 0.85 millimeter wall thickness, which allows high-precision measurements at a distance of four millimeters from the nervous fiber, that is, for example, through the skin. The tests on the sedlicated nerve of the frog allowed at room temperature to register the electrical activity of nerve fibers and its changes in real time.

"Such a magnetometer is suitable for medical diagnostics in physiological and clinical areas as a fruit cardiography, registration of synaptic interactions in the retina of the eye and magnetorencephalography," write the authors of the study.

The manufacturer of the electromagnetic radiation detector GM3120 is the Chinese BENETECH company. The device manufactured by the firm is used to measure the intensity of electromagnetic fields. The application of the device allows you to qualitatively define physical quantities Voltage and current forces of electromagnetic radiation emanating from various objects and household appliances.

Detector from the manufacturer Benetech

The main direction of the specialization of BENETECH is associated with the production of measuring equipment. In any industries, various types of devices for measuring voltage, pressure, temperature and other parameters are used. These include:

  • manometers;
  • thermometers;
  • wattmeters;
  • luxometers;
  • multimeters, etc.

Benetech manufactures not only industrial, but also household types of devices. It belongs to them
considered detector. The device is suitable for controlling the level of electromagnetic radiation around the electrical equipment, power lines, household household appliances.

For ease of operation, the detector can be transferred in the pocket. Manufacturer is provided
The ability to install the device on a flat surface. The device is able to effectively identify
The presence of an electromagnetic field that has bad influence on human health.

The manufacturer is attached to the instruction for the device in English and Russian.

All documentation that comes in a set with the device is provided to the consumer in Chinese.

To facilitate the choice measuring device In the instructions are all specifications.

Benetech is an advanced manufacturer on the market.

The cost on which the household tester is implemented from this company is quite low.


The detector from this company can be purchased on various
Specialized sites or in supermarkets at a price of 1080 rubles. On the packaging of this product there is information about the manufacturer, its email address.

The model made in the Chinese version has hieroglyphs on the surface of the case.

The manufacturer delivers to the market and english version Devices. When buying a detector, hieroglyphs can not be given muchSince only numbers are needed on the device screen.

Benetech Meter Application Area

The main purpose of the tester is associated with the measurement of electromagnetic fields. This is the best
The known physical value arose at the stage of the nucleation of the universe. Visible light is the main form of the measured indicator under study.

Overview of electric and magnetic fields revealed that they are part of the spectrum of electromagnetic
Radiation, which is the following species:

  • static electric;
  • magnetic;
  • radio wave;
  • infrared;
  • x-ray.


The application area of \u200b\u200bthe device is considered:

  • measurement of the electromagnetic field tension (EMF), which is generated by power lines (LEP) or various species electronic technology;
  • detection of a hidden cable;
  • identifying the quality of grounding electrical equipment;
  • study of the level of radiation intensity emanating from electrical appliances at home;
  • study of the radiation situation next to power plants, high-voltage lines, plants, military facilities, airports.

SanPine 2.1.2.1002-00 Sets the maximum permissible hygienic standards. IN russian conditions The normal level of electromagnetic radiation is considered to be 10 mkl. In order to prevent the negative effects of the influence of the EMF factor by the World Health Organization (WHO), a safe level of this indicator is recommended, equal to 0.2 MTL. At the same time, uncertainty should be taken into account in the study effects of the effect of EMF.

Features of the detector


The tester is useful in that it is allowed to measure the intensity of electromagnetic radiation from domestic appliances and techniques.

The detector allows you to identify the presence of hidden wiring in the apartment.

Thanks to the built-in sensor, you can learn the test results, the optimality of which depends on the presence of 2 modes.

The display shows accurate digital data that is measured in the following units:

  • electrical field - V / m;
  • magnetic field - μT.


In the process of measurements, it can be noted that a slight increase in distance is able to reduce the field strength.

At the same time, household appliances with sufficient power transmits the electromagnetic field to the distance.

Thus, the detector from BENETECH,
Applied in everyday life and in industrial conditions, allows you to control electromagnetic radiation near electrical devices and other objects.

The use of the GM3120 instrument makes it possible not only to identify the location of the cable in advance, but also to choose a place where it is allowed to successfully pave a new wiring, drill the walls, install sockets.

Under the excessive and constant effects of the electric and magnetic field on the human body, the likelihood of developing certain diseases increases. According to the manufacturer, the device is indispensable for those who have diagnosed cardiovascular pathologies.

Exterior of the detector


Compact appearance The detector reminiscent of the usual multimeter ensures the quality of the applying of the device. The housing of the bright orange color has ribbed side parts. This allows you to conveniently hold the device in your hand.

The rear part of the tester with the plate of the main parameters of the device involves the presence of an element for the battery. It is a Croon type battery (9 V).

The case is made so that
Insert the battery is incorrectly impossible. The presence of a small monochrome display at the top of the tester allows you to identify indicators of physical quantities.


Under the screen on the instrument housing there are 3 buttons that ensure measurements. Above him
A frequency range is specified, within which measurements can be performed. There is also a place
For the name of the brand and the name of the meter model.

Under the tester screen, there is an inscription "Electromagnetic Radiation Tester". Translated from English
Language The word "RADIATION" means radiation. Fully inscription under the display is translated as "electromagnetic radiation tester", but the detector has nothing to do with radioactive instruments.

On the right of the inscription there is a red LED, which is working in conditions of exceeding the threshold in 40 V / m and / or 0.4 mkct. The LED begins to flash when the permissible norms are detected. When the sound is turned on, the device makes a picking signal.

Advantages and disadvantages of the device


The dignity of the device is that they can determine the electromagnetic radiation situation in the open air or indoors.

With this tester, only approximate physical quantities are detected, since it does not relate to professional measuring instruments.

The accuracy of the detector declared by the manufacturer does not allow to determine the power of the electromagnetic field without error.

The advantage of the tester is the ability to measure the power of the electromagnetic field transmitted by household appliances for a certain distance.

Using the device, you can measure electromagnetic radiation in the frequency range up to 2000 MHz, so the device is not able to respond to WiFi-radiation.

The tester has the following types of advantages allocating it among similar meters:

  • dual measurement mode EMF;
  • the presence of sound and light alarm;
  • the output of measurements in the form of text prompts;
  • display with three zones;
  • the ability to simultaneously display the results of measurements;
  • automatic alarm in case of exceeding safe values;
  • availability of battery charge indicator;
  • the ability to automatically turn off the screen backlight;
  • showing medium and peak measurements;
  • energy saving mode;
  • the "HOLD" function, which holds the display.

The right side of the display shows information about the mode of operation, the remaining battery charge.
You can make measurements in the dormant day. This is allowed due to uniform
illumination. She is not too bright, which makes her pleasant for sight. With side sides of the case
The meter has protruding elements that provide more convenient retention of the device in hand.

Specifications and equipment

Before buying a detector, it is better to get acquainted with its technical characteristics presented
In the instructions for the device. Unit of measure electric field is in / m, and magnetic -
mkl. The GM3120 detector model has the following functional and technical parameters for electrical and magnetic field measurements, respectively:

  • the measurement step is 1 V / m, 0.01 mkl;
  • the alarm has a threshold value of 40 V / m, 0.4 mkl.

Among the provided measurement parameters to which attention should be paid, stand out
The following ranges:

  • electric field - 1-1999 V / m;
  • magnetic field - 0.01-19.99 MTL;
  • frequencies (sampling time) - 5-3500 MHz;
  • operating temperatures - 0 ... + 50 ° C.

Test mode time is about 0.4 seconds. The device is capable of functioning in low conditions
Illumination and humidity no more than 80% at operating voltage 9 V (1 Croon Battery). The LCD display of the device has dimensions equal to 43x32 mm. The weight of the meter is 146 g, and its dimensions -
130x65x30 mm. The kit with the device in the original packaging includes instructions and batteries.

GM3120 meter operation principle

The principle of operation of the tester is based on identifying indicators related to the measurement of the following
The physical quantities per capita from the radiation object:

  • voltage caused by the occurrence of the electric field;
  • the current forces causing the appearance of a magnetic field.

The power of the electric field is measured in volts per meter (in / m), and magnetic - in amps per meter
(A / m). The electric field can be saved even if the device is turned off. As
Removal from the device This indicator decreases. The presence of an electric field is neutralized
Most building materials.

The top indicator on the display reflects the data on the presence of an electric field or low-frequency
radiation. Maximum readings is a threshold equal to 1999 V / m. According to the norms
Sanpina, the value of the maximum permissible level is 500 V / m. The greatest danger
represent objects that create a large voltage in the open space, for example,
LEP pillars.

The lower indicator on the instrument display allows you to define a magnetic field or high-frequency
Radiation measured in ICTL. This type of radiation comes from mobile phones, computers,
TVs, etc. The maximum level is considered to be 19.99 mkl (microtels). The presence of magnetic
The fields cannot be eliminated using most building materials.

Measurement of electromagnetic field

The heart of the measuring instrument is a single-chip microcontroller WT56F216 of the universal type. To the left of it is the display controller equipped with the possibility of managing the HT1621B memory. Above the microcontroller there is an operational amplifier 27m2c. All this can be found if you disassemble the device, removing the cover from the housing.

To turn on the meter, it will be necessary to collect it again. When he is ready for work, you can include it. At the same time, all the segments of the display begin to glow. The top of the screen shows the unit of measuring the electric field strength or "V / M" (volt per meter). At the bottom of the display, MKTL (Microtesla) is highlighted, that is, the unit, multiple TL, component of 0.000001 TL (Tesla). This is a unit of measurement of magnetic induction, magnetic induction flux density.

The display provides a red small LED. In case of exceeding the allowable level, it flashes in red. To carry out the measurement, the device must be turned on, and then bring to the maximum near distance To the household device upper face. In the end of the detector there is an antenna, so it needs to be directed by this particular thing to the object under study.

The device automatically makes a sound light, if the measurement result exceeds the safe
value. Below the display is 3 buttons:

  1. Button at the bottom. Includes / turns off the power of the device (screen backlight), for which the button is pressed and maintained.
  2. "HOLD / BEEP" button. Pressing briefly allows you to save the value on the screen at the moment, with a long press, the sound will be turned on / off when the installed norm is exceeded.
  3. Button "AVG / VPP". Translates the device to medium / peak values \u200b\u200bmode.

The AVG \\ VPP button ensures the measurement mode switching. If the VPP mode allows you to fix the maximum reading value on the screen, the AVG is provided for a dynamic measurement conducted by the tester. Indications may vary 3 times per second.
Review of the GM3120 detector used to measure the electromagnetic field, revealed the main
The advantages of this device.

Thus, the meter produced by the Chinese BENETECH company is a compact device. The device is safe for humans. It can be used to maintain its own health to eliminate sources of electromagnetic radiation, the norm of which exceeds the value installed by SanPiN.

What is this article

Magnetic field sensors are used to determine the magnetic field parameters. The principle of their action is based on four physical phenomena. The article describes the device of various types of magnetic field detectors. Advantages and disadvantages of each implementation.
You can also see other articles. For example, "The principle of operation of firmware for Brinell, Vickers and Rockwell" or "What is a non-destructive testing, where and how it is used."

Detection and measurement instruments of the magnetic field parameters are quite a lot, which they are used in many areas of both purely technical and household. These detectors are used in systems related to the tasks of navigation, measure the angle of rotation and direction of movement, the determination of the coordinates of the object, the recognition of "its own - someone else", etc.

The wide range of such sensors requires the use of various properties of the magnetic field to implement them. This paper discusses the principles of work that are laid in the magnetic field sensors:

  • using the effect of Vigand;
  • magnetorevatory;
  • induction;
  • hall operating on the effect;

Sensors Viganda

The sensor is based on the effect, open by American scientist vigand. The essence of the Vigand effect is manifested in the following. When making ferromagnetic wire to a magnetic field, it takes place spontaneous change in magnetic polarization. This phenomenon is observed when performing two conditions. The first - the wire must have a special chemical composition (52% cobalt, 10% vanadium - vicalala) and two-layer structure (drawing on the right). The second - the magnetic field strength should be higher than a specific threshold value - ignition threshold.

The moment of changes in the polarization of the wire can be observed using an inductance coil located next to the wire. The induction pulse of the voltage at its conclusions reaches several volts. When the direction of the magnetic field changes, the polarity of the induced pulses changes. Currently, the effect is explained by different speeds of reorientation of elementary magnets in a magnetic core and a magnetically solid sheath of the wire.

The design of the Vigand sensors comprises a coil of inductance and Vigand wire. When changing the location of the wire, the coil wound on it fixes this change.

The sensitive elements of Vigand are used in flow meters, speed sensors, angle of rotation and position. In addition, one of the most frequent applications of this element - the reading system of identification cards, which we all use daily. When applying the magnetized card, the field strength changes, to which the Vigand sensor reacts.

The advantages of the Vigand sensor include independence from the effect of external electrical and magnetic fields, a wide temperature range of operation (-80 ° ... + 260 ° C), operation without a power source.

Magnetic sensors of the magnetic function, the quality of the sensing element contain a magneticallyistor. The principle of operation of the sensor consists in the effect of changes in the ommic resistance of the material in the zone of the magnetic field. The most strongly of this effect is manifested in semiconductor materials. The change in their resistance can be several orders of magnitude more than that of metals.

The physical essence of the effect is as follows. When you find a semiconductor element with a flowing current in a magnetic field, Lorentz forces act on electrons. These forces cause the movement of the motion of charge carriers from straightforward, twist it and, therefore, lengthen it. And the elongation of the path between the conclusions of the semiconductor element is equivalent to changing its resistance.

In a magnetic field, the change in the length of the "path path" of electrons is due to the mutual position of the magnetization vectors of this field and the field of the flowing current. When the angle changes between the fields and the current vectors, resistance changes in proportion to.

Thus, the valid amount of the resistance of the sensor can be judged on the quantitative characteristic of the magnetic field.

Magnetoresistance strongly depends on the design of the magnetic resistor. Constructively, the magnetic field sensor represents a magnetic resistor consisting of a substrate with a semiconductor strip located on it. Conclusions are put on the strip.

To eliminate the effect of the Hall effect, the size of the semiconductor strip is maintained in certain tolerances - its width should be much longer. But such sensors have low resistance, so on one substrate placed the required number of strips and connect them sequentially.

With the same purpose, the sensor is often performed as a disk of Corbino. The sensor is powered by connecting to the outputs located in the center of the disk and by its circle. In the absence of a magnetic field, the current path is straightforward and directed from the center of the disk to the periphery by radius. If there is a magnetic field, the EDC Hall does not occur, since the disk does not have opposite faces. The resistance of the sensor changes - under the action of the Lorentz forces, the current path is curved.

Sensors of this type, due to high sensitivity, can measure minor changes in the state of the magnetic field and its direction. They are used in navigation systems, magnetometry, image recognition and object position determination.

Sensors of this type belong to the generator type of sensors. Designs and assignments of such sensors are different. They can be used to determine the parameters of variable and stationary magnetic fields. This review examines the principle of operation of the sensor operating in a constant magnetic field.

The principle of operation of induction sensors is based on the ability of an alternating magnetic field to induce electrical current in the conductor. In this case, the EDC induction appears in the conductor is proportional to the rate of changing the magnetic flux through it.

But in the stationary field the magnetic flow does not change. Therefore, to measure the parameters of a stationary magnetic field, sensors with a coil of inductance rotating from constant speed. In this case, the magnetic flux will change with a certain frequency. The voltage on the clips of the coil will be determined by the rate of change of flow (the number of revolutions of the coil) and the number of turns of the coil.

According to known data, the magnetic induction of a homogeneous magnetic field is easily calculated.

The sensor design is shown in the figure. It consists of a conductor as a coil of inductance located on the electric motor shaft. The tension from the rotating coil is carried out with the help of brushes. The output voltage at the conclusions of the coil represents an alternating voltage, the value of which is the greater the greater the speed of rotation of the inductance coil and the greater the magnetic induction of the field.

The magnetic field sensors on the Hall effect use the interaction phenomenon of moving electrical charges with a magnetic field.

The essence of the effect is illustrated by the pattern. Through the semiconductor plate, the plate flows from an external source.

The plate is in a magnetic field that penetrates it towards perpendicular to the current movement. In a magnetic field under the action of Lorentz, electrons deviate from straight movement. This force shifts them in the direction perpendicular to the direction of the magnetic field and the direction of the current.

In this case, the top edge of the electron plate will be greater than the lower, i.e. There is a difference in potentials. This potential difference is determined by the appearance of the output voltage - the liner voltage. Hall voltage is proportional to the current and induction of the magnetic field. With a constant value of the current via the plate, it is determined only by the value of the induction of the magnetic field (drawing on the left).

Sensitive elements for sensors are made of fine semiconductor plates or films. These elements are glued or sprayed on the substrate and are supplied with outputs for external connections.

The magnetic field sensors with such sensitive elements are characterized by high sensitivity and linear output. They are widely used in automation systems, in household appliances and optimization systems of various aggregates.