EMI conducted interference test difference between LISN and three loop antenna

Electromagnetic interference is mainly divided into radiation type interference and conduction type interference. The electromagnetic interference transmitted through space belongs to radiation type, and the electromagnetic interference transmitted to the power grid through power lines belongs to conduction type According to IEC, CISPR, GB and other EMI specifications, conducted disturbance mainly measures the frequency range from 150kHz to 30MHz. Some product standards require measuring frequencies as low as 9KHz and as high as 108MHz.

When conducted interference test, in addition to EMI receiver or spectrum analyzer for pre compatibility test, must be used linear impedance stabilization network LISN, also known as artificial power network.

The artificial power network, also known as the line impedance stabilization network, can provide a specified impedance between the terminals of the tested equipment within the RF range, isolate the experimental circuit from the useless RF signals on the power supply, and then couple the interference voltage to the measurement receiver In the measurement of conducted and radiated emissions, LISN is connected between the tested equipment and the power supply, so that the test can be carried out according to the unified power impedance. Even if the test is carried out in different laboratories, it is comparable with each other. As shown in the following figure:

Equivalent circuit of LISN

There are two basic types of LISN: V-type networks coupled with asymmetric voltages and delta type networks coupled with symmetric and asymmetric voltages. The main indicators of LISN include: frequency range; Impedance; Partial pressure coefficient; Phase angle; Isolation, etc.

LISN has three main functions:
1. Provide a specified stable line impedance within the specified frequency range. According to the requirements of CISPR, the load impedance r of LISN is 50 Ω;
2. Isolate the power grid from the tested equipment: provide a pure power supply to EUT;
3. The interference signal generated by EUT is coupled to EMI receiver through coupling capacitance for measurement.

Antenna is the interference object of radiation emission. Antenna can be divided into dipole antenna and ring antenna; A loop antenna is a multi loop antenna that winds a metal wire into a certain shape, such as a circle, square, triangle, etc., and takes both ends of the conductor as the output end to wind multiple loops (such as spiral or overlapping winding).

Antennas can generate radio waves. These antennas can both transmit signals and receive signals (pick up noise). Therefore, as transmitting antennas, we should try to avoid interference from antennas; For the damaged device, try to avoid useless antenna generated by internal design, resulting in radio wave interference picked up The loop antenna is sensitive to current Many magnetic field detection devices based on Faraday’s law of electromagnetic induction use probe coils to pick up the magnetic field Ring antenna can both transmit and receive radio waves. Reducing the area of transmitting ring antenna is one of the effective methods to reduce interference Moreover, the magnetic field in the near field of the ring antenna is stronger, and the magnetic field decays faster with distance.

The European Union EMC certification en55015 test project, in the lighting industry, there are two methods to test EMI in 9khz-30mhz band. One is to use antenna and EMI receiver, which are based on cispr15, en55015 and gb17743 For low-frequency magnetic field equipment that may be generated by lighting fixtures, the three loop antenna specified in cispr16-1-4 shall be used to measure its low-frequency magnetic field radiation disturbance The test is mainly conducted by the three ring antenna and EMI receiver, and the test shall be conducted in the shielding room Note: the three loop antenna converts the low-frequency magnetic field components in X direction, Y direction and Z direction into RF signals, which are transmitted to EMI receiver through three channels of coaxial switch for measurement; The other is LISN test method, which needs EMI receiver + artificial power network +lisn and test software The conducted disturbance test system is used to measure the interference generated by the power port of lamps and lighting fixtures under normal working conditions. LISN realizes the isolation, sampling and impedance matching of RF signals, and provides an electrical channel for the EUT. The EMI receiver measures the RF signals, which are finally analyzed, processed and limited by the EMI test software The test shall be conducted in the shielding room.

Therefore, LISUN has launched the instrument matching with LISN and three loop antenna EMI receiver system for EMI (Electromagnetic Interference) radiation conduction or conducted emissions testing. The EMI-9KB EMI receiver is produced by the full closure structure and strong electro-conductibility material, which has high shielding effect. Due to the new technology for the EMI Test System, it solved the instrument self-EMI problem. The test results are according to the international format test report. The EMI Test System EMI-9KB fully meets CISPR15:2018, CISPR16-1, GB17743, FCC, EN55015 and EN55022.

EMI-9KB EMI Test Receiver

System Configurations:
• EMI-9KC Test System includes: EMI-9KC EMI Receiver built-in Attenuator (9K-1GHz), LISN-A Artificial Network Power (16A with RS-232 communicate), CDNE-M316 Coupling/Decoupling Network for Emission, 3pcs Isolation Transformers and cables.
• EMI-9KB Test System includes: EMI-9KB EMI Receiver (9K-300MHz), LISN-A Artificial Network Power (5A), CDNE-M316 Coupling/Decoupling Network for Emission, 3pcs Isolation Transformers, Attenuator and cables.
• EMI-9KA Test System includes: EMI-9KA EMI Receiver (9K-30MHz), LISN-A Artificial Network Power (5A), 3pcs Isolation Transformers, Attenuator and cables.

Option instruments to work with the EMI-9KC, EMI-9KB and EMI-9KA EMI receivers:
• LISUN LSP-500VARC/LSP-1KVARC Pure Sine Wave AC Power Source for EUT
• LISUN SDR-2000B Magnetic Shielding Cabinet for the EMI Receiver System
• LISUN VVLA-30M Three Loop Antenna to test 9k-30MHz Radiation
• LISUN AB-CLP Absorbing Clamp to test the Home Applications & motor tools

VVLA-30M_Three Loop Antenna

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

Our main products are Goniophotometer, Integrating Sphere, Spectroradiometer, Surge Generator, ESD Simulator Guns, EMI Receiver, EMC Test Equipment, Electrical Safety Tester, Environmental Chamber, Temperature Chamber, Climate Chamber, Thermal Chamber, Salt Spray Test, Dust Test Chamber, Waterproof Test, RoHS Test (EDXRF), Glow Wire Test and Needle Flame Test.

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