How to detect the core of a high-frequency transformer? People who buy the core of a high-frequency transformer are afraid of buying a core made of low-grade materials. So how should the core be detected? This requires understanding some detection methods for the core of a high-frequency transformer.
If you want to figure out the core of a high-frequency transformer, you also need to know what materials are commonly used for the core. If you're interested, you can look into it. There are lots of different types of soft magnetic materials used for measuring magnetic properties. Because they're used in different ways, there are a lot of complex parameters that need to be measured. There are many different measurements and methods for each parameter, which is the most important part of measuring magnetic properties.
Measurement of DC magnetic properties
Different soft magnetic materials have different testing requirements depending on the material. For electrical pure iron and silicon steel, the main things measured are the amplitude magnetic induction intensity Bm under standard magnetic field strength (like B5, B10, B20, B50, B100) as well as maximum magnetic permeability μm and coercive force Hc. For Permalloy and amorphous match, they measure initial magnetic permeability μi, maximum magnetic permeability μm, Bs and Br; while for soft ferrite materials they also measure μi ,μm ,Bs and Br etc. Obviously if we try to measure these parameters under closed-circuit conditions we can control how well we use these materials (some materials are tested by open-circuit method). The most common methods include:
(A) Impact method:
For silicon steel, Epstein square rings are used, pure iron rods, weak magnetic materials and amorphous strips can be tested by solenoids, and other samples that can be processed into closed-circuit magnetic rings can be tested. The test samples are required to be strictly demagnetized to a neutral state. A commutated DC power supply and an impact galvanometer are used to record each test point. By calculating and drawing Bi and Hi on coordinate paper, the corresponding magnetic property parameters are obtained. It has been widely used before the 1990s. The instruments produced are: CC1, CC2 and CC4. This type of instrument has a classic test method, stable and reliable test, relatively cheap instrument price, and easy maintenance. The disadvantages are: the requirements for testers are quite high, the work of point-by-point testing is quite arduous, the speed is slow, and the non-instantaneous time error of pulses is difficult to overcome.
(B) Coercivity meter method:
It is a measurement method specially designed for pure iron rods, which only measures the Hcj parameter of the material. The test city first saturates the sample and then reverses the magnetic field. Under a certain magnetic field, the cast coil or sample is pulled away from the solenoid. If the external impact galvanometer at this time has no deflection, the corresponding reverse magnetic field is the Hcj of the sample. This measurement method can measure the Hcj of the material very well, with small equipment investment, practical, and no requirements for the shape of the material.
(C) DC hysteresis loop instrument method:
The test principle is the same as the measurement principle of the hysteresis loop of permanent magnetic materials. Mainly, greater efforts need to be made in the integrator, which can adopt various forms such as photoelectric amplification mutual inductor integration, resistance-capacitance integration, V-f conversion integration and electronic sampling integration. Domestic equipment includes: CL1, CL6-1, CL13 from Shanghai Sibiao Factory; foreign equipment includes Yokogawa 3257, LDJ AMH401, etc. Relatively speaking, the level of foreign integrators is much higher than that of domestic ones, and the control accuracy of B-speed feedback is also very high. This method has fast test speed, intuitive results and is easy to use. The disadvantage is that the test data of μi and μm are inaccurate, generally exceeding 20%.
(D) Simulation impact method:
It is currently the best test method for testing soft magnetic DC characteristics. It is essentially a computer simulation method of the artificial impact method. This method was jointly developed by the Chinese Academy of Metrology and Loudi Institute of Electronics in 1990. Products include: MATS-2000 magnetic material measuring device (discontinued), NIM-2000D magnetic material measuring device (Metrology Institute) and TYU-2000D soft magnetic DC automatic measuring instrument (Tianyu Electronics). This measurement method avoids the cross-interference of the circuit to the measurement circuit, effectively suppresses the drift of the integrator zero point, and also has a scanning test function.
Measurement methods of AC characteristics of soft magnetic materials
The methods for measuring AC hysteresis loops include oscilloscope method, ferromagnetometer method, sampling method, transient waveform storage method and computer-controlled AC magnetization characteristics test method. At present, the methods for measuring AC hysteresis loops in China are mainly: oscilloscope method and computer-controlled AC magnetization characteristics test method. The companies that use the oscilloscope method mainly include: Dajie Ande, Yanqin Nano and Zhuhai Gerun; the companies that use computer-controlled AC magnetization characteristics test method mainly include: China Institute of Metrology and Tianyu Electronics.
(A) Oscilloscope method:
The test frequency is 20Hz-1MHz, the operating frequency is wide, the equipment is simple and the operation is convenient. However, the test accuracy is low. The test method is to use a non-inductive resistor to sample the primary current and connect it to the X channel of the oscilloscope, and the Y channel is connected to the secondary voltage signal after RC integration or Miller integration. The BH curve can be directly observed from the oscilloscope. This method is suitable for comparative measurement of the same material, and the test speed is fast, but it cannot accurately measure the magnetic characteristic parameters of the material. In addition, since the integral constant and saturation magnetic induction are not closed-loop controlled, the corresponding parameters on the BH curve cannot represent the real data of the material and can be used for comparison.
(B) Ferromagnetic instrument method:
The ferromagnetic instrument method is also called the vector meter method, such as the domestic CL2 type measuring instrument. The measuring frequency is 45Hz-1000Hz. The equipment has a simple structure and is relatively easy to operate, but it can only record normal test curves. The design principle uses phase-sensitive rectification to measure the instantaneous value of voltage or current, as well as the phase of the two, and uses a recorder to depict the BH curve of the material. Bt=U2au/4f*N2*S, Ht=Umax/l*f*M, where M is the mutual inductance.
(C) Sampling method:
The sampling method uses a sampling conversion circuit to convert a high-speed changing voltage signal into a voltage signal with the same waveform but a very slow changing speed, and uses a low-speed AD for sampling. The test data is accurate, but the test frequency is up to 20kHz, which is difficult to adapt to the high-frequency measurement of magnetic materials.
(D) AC magnetization characteristics test method:
This method is a measurement method designed by making full use of the control and software processing capabilities of computers, and is also a vital direction for future product development. The design uses computers and sampling loops for closed-loop control, so that the entire measurement can be done at will. Once the measurement conditions are entered, the measurement process is automatically completed and the control can be automated. The measurement function is also very powerful, and it can almost achieve accurate measurement of all parameters of soft magnetic materials.
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Post time: Aug-23-2024