Magnetometer / Magnetic Field Detector

The term magnetometer is used, among other things, for devices with which ferromagnetic materials or current-carrying lines are located due to their magnetic properties. These magnetometers often only give the user optical and / or acoustic signals. The intensity of these signals increases when the device is brought closer to the magnetic material. Highly sensitive magnetometers of this type can not only find concealed installation lines at a relatively short distance from the surface, but also, for example, duds, archaeological deposits or ore-bearing rock meters deep in the ground. In the following explanations, the term magnetometer is used exclusively for devices that display either the magnetic field strength in amperes per meter or the magnetic flux density (magnetic induction) in Tesla or Gauss.
There are natural magnetic fields independent of human activity, on the one hand through the earth's magnetic field and on the other hand through naturally occurring magnetic rocks such as magnetite, ferrite, pyrrhotite and columbite. We are constantly exposed to this magnetic radiation, regardless of the influence of modern technology. Unlike some animals, which are able to use the earth's magnetic field for orientation, we need tools to perceive and evaluate magnetic fields. In every magnetic field, forces act on electrons and magnetic materials. The strength of this effect can be measured with a magnetometer. When measuring, it must be taken into account that magnetic fields do not spread evenly in the room, depending on the respective source and any deflections. The spatial distribution of the magnetic field and the direction of the forces can be clearly illustrated by field lines. The closer the field lines are to each other, the higher the amount of magnetic flux density and the effect.

Many magnetometers can only detect a limited range of magnetic radiation with a single sensor. In particular, it should be noted that low-frequency and high-frequency magnetic fields differ greatly in their properties and are therefore usually recorded with different sensors. When evaluating the measurement results, it should be taken into account that different magnetic fields can overlap. Due to the mutual influence, the effect can be distorted, weakened or intensified in places.

Stationary magnetic fields, which are also called constant fields, are characterized by their constant strength and fixed alignment with the north and south poles. The earth's magnetic field has a comparatively low strength with 25 microtesla at the equator to 70 microtesla at the poles, but has been used for centuries for navigation with the compass. In Berlin the strength of the earth's magnetic field is 49 microtesla, in Karlsruhe 47 microtesla.
Artificial magnetic constant fields arise where direct current flows and on magnetized metal parts. Technical magnets made of ferromagnetic material are also known as permanent magnets. These permanent magnets come in different strengths and shapes, for example: cubes, cuboids, discs and ring magnets. The direction of magnetization is important for the technical application. The strength and orientation of these magnets can be checked with a magnetometer. Permanent magnets are used, for example, to transport or sort out ferromagnetic parts, as components in electric motors and loudspeakers, as counting marks in tachometers and as locking elements. In all of these functions, the magnet must achieve the desired field strength. Magnetometers can be used not only for checking permanent magnets, but also for checking incoming goods for material that may only be delivered with a low degree of magnetization.
According to the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, low-frequency magnetic fields are alternating fields that oscillate between 1 Hertz and 9,000 Hertz. In other publications, the low frequency range is also given as 0.1 Hertz to 1 Kilohertz. The range from 1 to 10 kilohertz is called the intermediate frequency range. The low-frequency fields include, for example, those generated by electrical power supply lines (50 Hertz) and rail electrification lines (16.7 Hertz). The magnetic flux density is measured with a magnetometer for low-frequency fields. For correct measurement, the sensor must be positioned in the direction of the field lines. If there are deviations from the direction, lower measured values ​​are displayed. If the direction of the field lines is not known, the magnetometer can be rotated at the measuring position along the various axes until the highest measured value is displayed. This also allows the direction of the field lines to be determined.
Strong magnetic fields can arise, for example, in the vicinity of electric motors, transformers (inverters, power supply units) and electrical heating devices, but also in the case of induction cookers. The strength decreases with increasing distance from the source. The magnetometer can be used to check the distance to the radiation source at which the prescribed or recommended guide values ​​are exceeded.
High-frequency magnetic fields are created when radio waves and microwaves are emitted, which we are constantly surrounded by in our technical world. In the case of high-frequency fields, the influencing electric and magnetic fields constantly change their direction (100,000 times and more often per second). Since they are closely linked to one another, one speaks of electromagnetic fields. The radiation exposure from radio applications, radio and television, cellular communications, WLAN, Bluetooth and other wireless networks can be measured with a magnetometer whose sensor is designed for high-frequency radiation. The electromagnetic radiation emitted by the base stations and transmitters on the human body is generally significantly lower than that of end devices such as cell phones and laptops.

There are magnetometers that measure the field strength separately for each of the three spatial axes with magnitude and direction and can then determine the resulting field strength. Many magnetometers can only detect one direction per measurement. With these devices, if the alignment of the field is not known, the magnetic sensor must be rotated in the various spatial directions to determine the maximum field strength.
Magnetometers with rod sensors are particularly suitable for some applications. When making your selection, you should pay attention to whether the field strength is measured axially or transversely to the rod. In general, with uniaxial measurement, the highest value is measured when the sensor is placed in the direction of the field lines and in the area of their greatest density. In the case of an axial sensor, the measuring rod should therefore be placed parallel to the field lines and, in the case of transverse measurement, at a right angle to them.

Some magnetometers have several sensors with which either different strengths of a frequency range or different frequency ranges can be covered. Stationary and low-frequency magnetic fields can often be detected with the same sensor. High-frequency fields are generally recorded with different sensors than low-frequency fields, so that a magnetometer for high and low-frequency fields usually has several sensors.
In particular, magnetometers that have a continuous measurement function are often equipped with a serial interface for transferring the measurement data to the PC. If the direct transfer of the measurement data is not possible, the internal memory of many devices can be used and read out later.