1.1.2.1 Continuous Harassment Voltage Test
The continuous harassment voltage measurement mainly measures the harassment voltage emitted along the power supply line to the grid, and the measurement frequency is 0.15 ~ 30 MHz. The measurement is generally carried out in the shielding chamber. An artificial power network (LISN or AMN) needs to be inserted between the grid and EUT when measuring, and the principle is shown in Figure 15. The action of AMN is to isolate the grid and EUT to make the measured harassment voltage.
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Figure 15: Basic structure of artificial power network
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Figure 16: 50Ω / 50 μH V-type AMN
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Figure 17: 150Ω δ type AMN
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Figure 18: Tolebelry device for harassment measurement arrangement
Only EUT is launched, no harassment of the grid does not mix. Another effect is to provide a stable impedance for the measurement because the impedance of the grid is uncertain, and the impedance is not the same, the voltage value of the EUT is also different, so it is necessary to specify a unified impedance, usually 50Ω. AMN is actually a two-way low-pass filter. The harassment in the grid is filtered out by a 50μH and 1.0μF filter, and the harassment of the EUT is not harassed. Due to the blocking of the 50μH filter, it is only possible to enter the grid. Enter the harassment meter by 0.1μF capacitor. The input impedance of the measuring instrument is 50 Ω, so the load impedance of EUT harass is about 50Ω. For a 50 Hz power supply, it is still possible to power the EUT via AMN. The AMN in Fig. 15 is only a basic structure, and the basic structure can form a V-type AMN for measuring the asymmetric harassment voltage of the phase line-ground wire and zero-ground wire in the power source, see Figure 16. It is also possible to form a δ type AMN, in addition to the measurement line-ground asymmetric harassment voltage, a symmetrical harassment voltage between the phase-zero line can also be measured, see Figure 17. The arrangement of EUT and AMN, the length and direction of the cable should be performed in accordance with the requirements of the standard. The AMN shell should be well grounded, otherwise it will affect the isolation between the grid and EUT. Figure 18 is a conductive diagram of a tail-based device.
1.1.2.2 Power Testing of Continuous Harassment
When the measurement frequency is raised to 30 MHz, the inductance in the artificial power network AMN is increased, so that it does not play a good isolation and filtering; so the power absorbing clamp should be measured. Structure of power suction jaw
Where C is a current probe, including a ferrite ring and a probe coil, the action is to measure the harassment of the power line. D is a ferrite ring, as a stable load of harassing common mode current, absorbs harassment power, and is used to isolate EUT and grid. If the ferrite ring D below 50 MHz cannot sufficiently play a radio frequency isolation, an auxiliary absorbent clamp f, which is also composed of a ferrite ring. E is also a ferrite ring group for absorbing the common mode current generated on the field in the current probe to avoid affecting the measurement. The measurement arrangement is shown in Fig. 19 (b), the test should be performed in the shield chamber, and the length of the power line should be greater than 6m, i.e., half-wavelength, and the length of the absorption clamp. For each test frequency point, the absorbent clamp should move along the power cord, find the maximum value, since the common mode current is in the form of a stand wave. The power absorbent clamp measurement system should be calibrated before, and the correction factor-frequency curve is obtained. The calibration arrangement is shown in Figure 20.
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Figure 20: Calibration arrangement of power absorbing clamp
When calibration, first enter the calibration signal directly into the measurement receiver, record the reading A '; then input the calibration signal to the calibration line, move the power absorbent clamp, find the first maximum, record the reading A; then get insertion loss L = A'-a. Because the harassment power DB (PW) is indicated, the reading of the measurement receiver is DB (μV). For the 50Ω system, the two are 17dB. For the sake of convenience, the manufacturer directly subtracts 17dB from the insertion loss, give a correction factor. So when measuring, as long as the reading of the measured receiver is plus the correction factor is harassed power.
It should be noted that the power absorbent clamp is a test on the power line, but the measurement is actually not transmitted, but the radiation emission is transmitted. The radiation emission of the EUT has two types, and one is an electromagnetic wave generated by differential mode currents in various current loops in the EUT, and the other is a common mode current radiation through the slit of the chassis housing. The common mode current radiation requires a common mode source and antenna. Due to the improper circuit design or wiring, an equivalent common mode source is formed inside the EUT; a part of the equivalent common model antenna is an external cable, and the other is often the interior of the EUT and Metal chassis. When the chassis size is close to the quarter-wavelength of the measured frequency, a part of the emission efficiency of the chassis as an equivalent common mode antenna will greatly improve, which is one of the reasons for the absorbent jaw method is not suitable for evaluating all of the radiation capabilities of EUT. In addition, if the EUT except for the power cord, there are other external cables, which may also have a common mode current radiation. So the absorption jaw method is used to evaluate the restrictions of all radiating capabilities: small EUT, 30 ~ 300MHz frequency segments, single cable connections. Of course, if the diagnostic test is performed with an absorbent jaw method, the above limit is not necessary, and the absorbent jaw method is the harassment power of the equivalent common mode source connected to the test cable, and is represented by a 50 Ω standard source. Since the test cable is equivalent to the radiation antenna, it is preferable that the connection cable between the test device, the absorbent clamp, and the measurement receiver is also available.
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Reprinted from -Wiku Electronic Market Network
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