DIY and use of EMI probes

To perform EMI measurement in a general laboratory, the easiest way is the near field test, and the detection distance requires less than 0.16λ. The radiation is still a pure magnetic field, so it can be picked up by magnetoelectric conversion. After sending the oscilloscope Waveform analysis and spectrum analysis can be performed. Probes to realize magnetoelectric conversion are a ring antenna, which is made as shown in the figure below, and the required wire is a 50Ω coaxial cable, and the connector is a BNC plug compatible with the ordinary oscilloscope. When using, it is necessary to let the antenna coil are parallel to the current ring on the circuit board, allowing the current generated by the current ring through the coil. Due to the distance from the distance, the degree of divergence of the magnetic field is higher, so to get a stronger signal, it is best to close the board, as shown below: Since only the change of the change in the changed current can be picked up, the radiation signal of the BUCK converter picked up by this antenna is shown in the blue waveform in the figure below. The following red waveform is the signal power spectrum obtained after the FFT conversion. . If you look at the voltage waveform of the Buck converter switch node in the time domain, it is still our common look: The holding coil is constant with respect to the height and position of the PCB, and the measurement is measured after a change in radiation conditions and compares the previous measurement data. You know if your improvement measures are effective. The radiation caused by the high frequency signal on the power cord often brings a large impact on the EMI level of the device, which can be measured by the high-frequency transformer shown below: Its production method is shown in the figure below: The material required except 50 Ω coaxial cables, as well as high frequency magnetic cores. The principle of this probe is the same as the appeal ring antenna, and the increased core can introduce the magnetic field generated by the current flowing through the wire to the secondary level of the transformer, and thus there can be a high gain. Measuring the difference current and common mode current principles on the power cord, the method is not the same, as shown below: All of the above appeared in the 13th issue of the Establishment Electronic News. The value of me is only rewritten together the contents of the original text, and the purpose is to make it easier and clear. There is another method of making another sensor in the newspaper. It is necessary to explore themselves. Considering that the reader is asking that the sensor is mainly involved, it is the type of sensor, so it is still possible to specifically Talking once. Reprinted from Richtektechnology.

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