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Measurement method of magnetic permeability
Release time:
2022-05-09
Source:
Www.fe2100.com Hunan Yongyi Technology Co., Ltd.
The permeability μ is one of the basic macroscopic physical quantities describing the magnetism of a substance. According to the nature of the applied magnetic field, the magnetic permeability is divided into static magnetic permeability, complex magnetic permeability and tensor magnetic permeability. The measurement methods of the three permeability are also different.
permeabilityμ is one of the basic macroscopic physical quantities describing the magnetism of a substance. According to the nature of the applied magnetic field, the magnetic permeability is divided into static magnetic permeability, complex magnetic permeability and tensor magnetic permeability. threeMeasurement method of magnetic permeabilityAlso different.
The static magnetic permeability is the ratio of the magnetic induction intensity B to H under the action of the static magnetic field H, that is, μ = B/H. Static permeability is generally measured with an impact galvanometer.Hunan Yongyi Technology Co., Ltd.DC Magnetic Testing System for FE-2100SD Soft Magnetic MaterialsIt is mainly used to measure the basic magnetization curve and hysteresis loop of various soft ferrite, pure iron, silicon steel, permalloy, amorphous and nanocrystalline ring-like or open-circuit strip soft magnetic materials under DC static state, and accurately measure the static magnetic characteristic parameters such as initial permeability μi, maximum permeability μm, saturation magnetic induction strength Bs, remanence Br and coercivity Hc. (only Bs and Hc are measured for open circuit measurement, and only permeability is tested for non-magnetic materials)
DC Magnetic Testing System for FE-2100SD Soft Magnetic Materials
The complex magnetic permeability is the ratio of the alternating magnetic induction intensity B to h under the action of the alternating magnetic field h. B and h often have different phases because μ is a complex number, I .e., μ = B/h = μ′-jμ″, where μ″ represents the magnetic loss of the material. When the frequency is from several Hz to tens of MHz, the coil is uniformly wound on the annular magnetic core made of the material to be measured, the inductance L and resistance R of the coil are measured, and the complex permeability is calculated by using the formula μ/μ0 = [(R-R0) jωL]/jωL0 = L/L0 (R-R0)/jωL0. where μ0 is the permeability of air, and L0 and R0 are the inductance and resistance of the same coil without a magnetic core, respectively. In the microwave frequency range of commonly used measurement methods are standing wave method and resonant cavity method.Hunan Yongyi Technology Co., Ltd.AC measuring device for FE-2100SA soft magnetic materialsIt can automatically measure the AC hysteresis loop, magnetization curve and loss curve of soft magnetic materials under dynamic (AC) conditions. Accurate measurement of residual magnetic Br, coercive force Hc, than the total loss Ps amplitude magnetic conductivity a, loss angle, inductive magnetic conductivity L, elastic magnetic conductivity, viscous magnetic conductivity, and Q value and other dynamic magnetic characteristics parameters. It provides powerful basic data for fully grasping the communication characteristics of materials.
AC measuring device for FE-2100SA soft magnetic materials
Speaking of the measurement of permeability μ, it seems very simple. Just wind a few turns of coil on the material sample ring, measure its inductance, and find a formula to calculate it. In fact, it is not the case. For the same sample ring, different instruments, different turns, different voltages or different frequencies may be used to measure different permeabilities. The reason for the great difference in test results is that not every tester has the energy to figure it out. This paper mainly discusses the influence of different test turns and calculation formula on permeability measurement.
Measurement method of magnetic permeability-effect of calculation formula
As we all know, the method of measuring magnetic permeability μ is generally to measure its inductance L by winding an N-turn coil on the sample ring. For a ring-shaped magnetic core with a smaller inner diameter, the inner diameter is not as easy to measure as the wall thickness. Their origin is to take the average magnetic path length of the ring as the magnetic path length of the magnetic core. The permeability calculated with them is called the ring permeability of the material. Some people say that the permeability measured by ring-type samples is called ring permeability, which is incorrect. In fact, the permeability of the ring is higher than the real permeability of the material, and the thicker the wall of the sample ring, the greater the error.
For the sample ring, under the same number of ampere-turns of magnetomotive force excitation, the magnetization field is not uniform in the radial direction. The closer to the outer side of the ring wall, the weaker the magnetic field. Under the condition that the magnetic permeability μ is constant throughout the sample ring, the magnetic flux density B of the ring is lower the closer to the outer side of the ring wall. In order to eliminate the influence of this uneven magnetization on the measurement, we regard the sample ring as consisting of an infinite number of thin-walled rings with a radius of r and an infinite wall thickness of dr.
If the sample rings are made of the same material, the calculated permeability is the true permeability of the material. It is slightly lower than its ring permeability.
Method of measurement of magnetic permeability-effect of the number of turns N of the test coil
Since the inductance L is proportional to the number of turns N2, it is reasonable to say that the calculated permeability μ should no longer be related to the number of turns N, but in fact it is often related.
Regarding the measurement of material permeability, the test frequency generally used is not high, and it is often tested at a frequency of 1kHz or 10kHz. The test signal is generally a sinusoidal signal, because the frequency is not high, the resistance part of the impedance of the sample surrounding the coil is negligible, and the winding coil is regarded as a pure inductance L connected to the measuring instrument. The test equivalent circuit is shown in the figure. The effective value of the voltage generated by the instrument signal source is U, and Ri is the output impedance of the signal source.
When measuring the magnetic permeability, the magnetization field strength in the sample ring is related to the number of turns of the test coil, and when the number of turns is a certain value, the magnetic field strength will reach the strongest value. The permeability of the material is closely related to the magnetization field strength, so the measurement of the permeability is related to the number of turns of the test coil. The effect of the number of turns on the magnetic permeability test is discussed in detail in conjunction with the figure.
Therefore, it is very important to use professional magnetic permeability measuring instruments. In the measurement of the DC characteristics of soft magnetic materials in the magnetization curve, the most difficult to test the exact amount or the initial permeability, with impact galvanometer or scanning method test error can reach tens of percent. However, at present, the simulated impact method is more used in China. It is difficult to control the repeatability in testing micro-devices and low remanence materials. A burr is tested. Although it has been smoothed, broken lines still appear continuously.
DC Measuring Device for FE-2100SD Soft Magnetic MaterialsOn the technology of inheriting the analog impact method, the impact waveform and signal are improved, and the integrator drift control technology is continuously improved, and the test point is optimized. And the system can perform excellent dB/dt control technology, high-resolution current control technology, magnetic flux sampling technology, and low drift control technology, so that the whole test is controlled. In the testing of micro components, low Br materials and iron powder core materials, it has obvious advantages over domestic and foreign counterparts. In 2014, it participated in the Berlin coil exhibition in Germany, which was affirmed by foreign enterprises and foreign counterparts. It has begun to provide this device for well-known foreign enterprises, and has been exported to scientific research institutes and enterprises in the United States, Germany, Israel, Russia and other countries.
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