Brief Introduction of Disturbance Power Measurement Method_Century Wisdom (Suzhou) Testing Technology Co., Ltd

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Brief Introduction of Disturbance Power Measurement Method

Release time:

2022-09-23 00:00

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　　Disturbance power measurement Use absorbing clamp measurement (ACMM) method of disturbance power in the frequency range of 30MHz-1000MHz. Mainly for small EUTs connected to only one mains lead (or other type of lead), such as household appliances and power tools.

　　The principle of absorbing clamp measurement: When the frequency exceeds 30MHz, the disturbance energy generated by the equipment propagates to the disturbed receiver through radiation. Experience has shown that most of the energy is radiated outwards from power and other wiring close to the equipment. Therefore, the disturbance level can be defined by the disturbance power on the power line and other connections of the equipment under test. This power is approximately equal to the measured value at the position of the maximum absorbed power by a suitable absorbing clamp set on these connections. The absorption clamp measurement method (ACMM) is an alternative to the radiation emission measurement method. ACMM uses absorption clamps to determine the disturbance power. The advantages of ACMM for radiation emission testing are mainly to shorten test time and save site costs (can be measured in a shielded room).

　　This article is based on CISPR14-1 (equivalent to GB4343.1) and CISPR16-2-2 (equivalent to GB/T6113.202) standards.

　　1. Measuring instrument requirements

　　The main test equipment required are: EMI measurement receiver, power absorption clamp (see Figure 1)

　　Figure 1 Schematic diagram of absorption clamp measurement method

　　2. Measurement site requirements

　　The site where ACMM is implemented is the Absorbent Clamp Test Site (ACTS). Chapter 4 of GB/T6113.103-2008 specifies ACTS in detail, and the site confirmation should be carried out according to the procedures stipulated in GB/T 6113.103-2008. ACTS can be indoor or outdoor installations, including the following devices (Figure 2);

　　-- Non-metallic test bench for placing EUT;

　　--Sliding rails for supporting the test line and absorbing forceps;

　　-- removable support or hook system for absorbing clamp test cables;

　　-- Auxiliary parts, such as ropes for moving the absorbent forceps.

　　3. EUT lead wire requirements

　　The length of the test lead shall be at least half the wavelength corresponding to the lowest frequency of measurement plus the additional length of the lead connected to the ground supply. Typical length of the lead is at least 7.5 m.

　　If the EUT has more than one lead wire, if possible, when measuring a certain lead wire, other lead wires (including connected auxiliary equipment) that do not need to be measured should be removed. If the leads cannot be removed, apply common-mode absorbing device (CMAD) isolation. The CMAD consisting of a large number of ferrite rings or other absorbing devices surrounds the leads and is placed close to the EUT enclosure. The isolated leads should be placed on the EUT test bench close to the EUT.

　　4. Test layout requirements

　　The EUT is divided into desktop and floor-standing equipment (see Figure 2 and Figure 3), and the layout of the EUT must meet the following requirements:

　　a) The EUT shall be placed on the test bench. For bench-top EUT, the height of the test bench shall be 0.8 m ± 0.05 m; the height of the support for floor-standing equipment shall be 0.1 m ± 0.01 m.

　　b) The EUT is placed on the EUT test bench as far as possible in the usual working position. The test line should be arranged facing the SRP of the absorbing clamp slide rail. If there is no regular operating position regulation, the EUT should be placed in the position where the test line is facing the slide rail of the absorbing clamp. The distance from the EUT unit to the SRP should be as short as possible.

　　Figure 2 Measurement layout of desktop EUT absorbing clamp

　　Figure 3 Floor-standing EUT absorption clamp measurement layout

　　5. Measurement procedure

　　For any lead wire connected to the EUT, the following measurement procedures shall be followed:

　　a) Pre-test at a fixed location

　　Absorbing clamps should be placed at a horizontal distance of 0.1 m from the SRP. EUT is switched on,. In this fixed position, the EUT performs a frequency scan in each relevant operating mode to find the operating mode which produces the maximum emission level. Final measurements were made in the mode that produced maximum emission. A peak detector is available for pre-testing. Pretests can also be used to obtain information on the type of disturbance (narrowband, wideband).

　　b) final test

　　The final test is performed based on the type of harassment identified in the pre-test. Depending on the type of harassment identified in the pre-test, two different final test procedures are provided below, either of which may be chosen:

　　1) Continuous moving measurement with fixed frequency absorbing clamp

　　2) The fixed absorbing clamp position receiver scans and measures in the frequency band

　　6. Determination of disturbance power

　　According to the measurement data of each lead wire under test, calculate the disturbance power P according to the following formula

　　P=V+F.

　　In the formula:

　　P—disturbance power, the unit is decibel picowatt [dB(pW)];

　　V—the voltage measured by the measuring receiver, the unit is decibel volts [dB(μV)];

　　F is the power clamp absorption clamp factor, in decibel picowatts per microvolt [dB(pW/μV)].

　　Note 1: The absorbing clamp factor is obtained with the 6 dB attenuator included

　　Obtain the power absorption clamp factor F from the measurement, input it into the EMC32 test software for correction, and the software can automatically calculate the disturbance power P value

　　7. Disturbance power limit

　　At present, CISPR14-1 (equivalent to GB4343.1) only stipulates the disturbance power limit of 30MHz-300MHz. There is no provision for the limit value of 300MHz-1000MHz.

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