The Necessity and Method of Conducted Immunity Background Noise Measurement_Century Wisdom (Suzhou) Testing Technology Co., Ltd

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The Necessity and Method of Conducted Immunity Background Noise Measurement

Release time:

2022-06-16 00:00

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　　1 Introduction

　　In order to ensure the accuracy and repeatability of test results, some electromagnetic compatibility test items need to be carried out in a low and constant electromagnetic environment, which can bring great benefits to the improvement of measurement accuracy, measurement reliability and repeatability. to greater benefit.

　　Common test environments include open field, anechoic chamber, shielded room, TEM chamber, and general test site. Each environmental site has its own advantages and disadvantages. We need to select an appropriate environmental site for the test according to the characteristics and test requirements of the test project.

　　Conducted immunity test, there are currently two test sites in the industry: shielded room and unshielded room. The test environment in a shielded room must be better than that in a non-shielded room. Is it necessary to choose to test in a shielded room?

　　2 Do the standards and regulations have requirements for the environmental conditions of the conducted immunity test?

　　Let's take a look at the relevant descriptions of the environmental conditions of the conducted immunity test in the standards and regulations:

　　 ♦ The basic standard GB17626.6-2017 (IEC 61000-4-6: 2013) describes the electromagnetic environment requirements as follows:

　　 ♦ GB/T 6113.204-2008 (CISPR 16-2-4 2003) The environmental requirements for immunity test are as follows:

　　 ♦ CNAS accreditation document CNAS-CL16:2013 describes the electromagnetic environment requirements for conducted immunity test as follows:

　　It can be seen from the above standards and regulations that the standards and regulations have no mandatory requirements for the test environment of conducted immunity, but the actual electromagnetic environment cannot affect the test. Therefore, when we do not conduct the conduction immunity test in the shielding room, we must consider the influence of the electromagnetic environment of the site on the conduction immunity test.

　　3 How to confirm the conducted immunity test environment

　　When the conducted immunity test is performed in an unshielded room, the actual electromagnetic environment of the test may be more complicated, and the noise of some frequency bands/frequency points may reach or exceed the test level, thereby affecting the judgment of the test results.

　　The schematic diagram of the measurement layout of the conducted immunity electromagnetic environment background noise is as follows: the coupling network CDN and the signal generator are arranged/placed according to the actual test, the EUT port of the coupling network is connected to the input terminal of the receiver, the signal source has no output, and the receiver is in the The 0.15MHz-80MHz/230MHz frequency band measures the electromagnetic noise of the environment/system.

　　The ambient noise within the frequency band must be lower than level 1 (120dBuv).

Schematic diagram of the measurement layout for conducted immunity to ambient noise

　　According to the above arrangement, the measurement results are as follows, it can be seen that the electromagnetic environment brings a certain amount of electromagnetic noise to the test system:

Measured system/environmental noise

　　Disconnect the link between the receiver and the coupling network, the measured data are as follows:

Measured data when the receiver is not linked to the coupling network

　　4 Epilogue

　　In summary, when the conducted immunity test is not conducted in a shielded room, an environmental (background) test report is required according to CNAS-CL16:2013. According to the above measurement data, the external electromagnetic environment of the unshielded test site will affect the background noise of the conduction immunity system, and the complex electromagnetic environment will even affect the judgment of the test results.

　　Therefore, the conduction immunity test is recommended to be carried out in a shielded room, and the electromagnetic environment (background noise) of the site must be confirmed for the test site in a non-shielded room.

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