There are many terms in the magnet industry, tensile force, Gauss, magnetic flux, magnetic measurement, and so on. So today daisy will answer the question: What is magnetic measurement? What data is being tested?
What is magnetic measurement?
Magnetic measurement mainly refers to the measurement of magnetic field intensity, magnetic induction intensity, magnetic flux, magnetic permeability, hysteresis loss and eddy current loss of the medium and other basic magnetic parameters of the medium.
The classification of the magnetic field measurement：
The spatial magnetic flux density is proportional to the magnetic field intensity, and the measurement of the spatial magnetic field intensity is actually the measurement of the magnetic flux density. So what the magnetometer measures is actually the flux density. Magnetic field measurement is mainly carried out by magnetic measuring instruments. According to the properties of the measured magnetic field, magnetic field measurement can be divided into constant magnetic field measurement and variable magnetic field measurement.
Constant magnetic field measurement
For the measurement of the DC magnetic field that does not vary with time.The following seven types of measuring instruments are commonly used.
① moment magnetometer: referred to as magnetometer. The force effect of a magnetic field is used to measure the magnetic field strength or the magnetization of a material.
② Fluxmeter and impact galvanometer : used for impact method (see soft magnetic material measurement) to measure magnetic flux and magnetic flux density. When measuring, the magnetic flux in the detection coil must be artificially changed.
③ Rotating coil magnetometer: in the measured constant magnetic field, place a small detection coil and make it rotate at a constant speed. By measuring the electromotive force of the coil, the magnetic flux density or magnetic field strength can be calculated. The measurement range is 0.1 to 10 NTS. The error is 0.1 to 1%.The detection coil can also be suddenly flipped or quickly moved to the field free area to measure the magnetic flux density according to the impact method principle.
④ Fluxgate magnetometer: the core made of high permeability soft magnetic material is subjected to alternating and constant magnetic fields at the same time. Due to the nonlinearity of the magnetization curve and the core working in the asymmetric area of the curve, the voltage induced by the detection coil wound on the core contains even harmonic components, especially the second harmonic. This harmonic voltage is proportional to the constant magnetic field strength. By measuring the harmonic voltage of the detection coil, the magnetic field intensity is calculated.
⑤ Hall effect magneometer: The semiconductor rectangular sheet is placed in a magnetic field (flux density B) perpendicular to the sheet plane. If the DC current I is passed between the opposite end faces of the sheet, the electrodynamic force E is generated between the corresponding points on the other end faces (Hall effect). When I is constant, E has a proportional relationship with B, and the proportional coefficient is related to the width b, length l and thickness d of the sheet, as well as the material used. This property of materials is also called magnetic sensitivity. The magnetometer made of Hall effect can measure the value of magnetic flux density in the range of 1 microth to 10 microth. The error ranges from 0.1 to 5%. Hall plates can be made thin and small, can be extended into narrow gaps for measurement, and can also be used to measure non-uniform magnetic fields. In addition to Hall plates, there are also bismuth spiral, magnetic diode and so on.
⑥ Nuclear magnetic resonance magnetometer: the magnetic moment of the nucleus under the action of magnetic flux density B, will precession around the magnetic field direction, its precession frequency? 0=γB (γ is the gyromagnetic ratio, for a certain substance, it is a constant), if a small alternating magnetic field is applied in the direction perpendicular to B, when its frequency is equal to? When 0 is equal, resonance absorption phenomenon, that is, nuclear magnetic resonance, will occur. The magnetic flux density or magnetic field strength can be accurately calculated from the resonance frequency. The magnetometer has a measuring range of 0.1 milliverts to 10. The accuracy is very high, the error is less than 10-4 ~ 10-5, and it is commonly used to provide a standard magnetic field and as a calibration standard.
⑦ Magnetic potential meter: used to measure the magnetic potential difference between two points in space a and b, such as the uniform magnetic field, can be converted to the magnetic field strength at the place. Magnetic potential meters can also be used to measure the strength of the magnetic field inside a material. Because the tangential component of the magnetic field strength at the interface of the magnetic material is equal, the magnetic field strength measured by the magnetic potential meter along the surface space of the material is the tangential component of the magnetic field strength inside the material. The structure of the magnetic potential meter is to evenly wind a fine insulated wire on a non-magnetic soft tape or a hard piece, the former is called a soft magnetic potential meter; The latter is called a hard magnetic potential meter. The measuring instrument adopts impact galvanometer or flux meter. For a constant magnetic field, the magnetic flux linked to the magnetic potential meter must be changed during measurement. If the measured magnetic field is uniform, the magnetic field strength is converted from the magnetic potential difference. The magnetic potential meter can be calibrated in a standard uniform magnetic field and graduated according to the value of the magnetic field strength.
Variable magnetic field measurement
For measurements of alternating magnetic fields that vary with time.It is usually measured by using the electromagnetic induction effect to transform the magnetic quantity of the magnetic field into the electromotive force.
In the case of the alternating magnetic field with periodic monotonic rise and fall, the magnetic flux density can be measured by simply connecting the detection coil to the mean voltmeter. From the reading of the voltmeter, the maximum flux density Bm is the frequency, S is the effective cross section of the core, and N2 is the number of turns of the measuring coil. Hall plate can be used to measure the magnetic flux density directly. If I is kept as DC, the waveform of the output electromotive force E is the same as that of the magnetic flux density.
The value of magnetic flux density can be calculated by E. When measuring the magnetic field strength, if the average voltmeter is used as the measuring instrument of the magnetic potential meter, the maximum magnetic field strength can be converted according to the voltmeter reading, and it can also be calibrated in the uniform standard magnetic field.
Other magnetic field measurements：
1. Use the ampere force calculation formula "F=BIL" to measure magnetic induction intensity B
2. Use induced electromotive force to measure magnetic induction intensity B
3. The magnetic induction intensity B is measured by the relationship between the electric quantity of the circuit and the magnetic induction intensity when the induced electromotive force is generated
Helmholtz coils: two identical coils parallel to each other, and through the same direction of the current (I), the theoretical calculation shows that: when the coil spacing is equal to the coil radius, the total magnetic field of the two current carrying coils is uniform in a large range near the midpoint of the axis. This kind of magnetic field is widely used, especially in production and scientific research has greater use value, and is often used in the measurement standard of weak magnetic field.
The above is the magnetic measurement related content, I hope to help you. We are professional magnet manufacturers, if you have more questions or need to buy magnets, please consult us and provide your question and requirment.
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