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15 Oct, 2013 1009 Views

EMI Measurement Application and Relative Test Standards

Recently, there have a new that the China Consumer Association announcement computer failure excessive radiation harassment, that easy to affect the power grid equipment and cause computer crash. The main reason is that computer power terminal radiation harassment beyond the limits specified in the national standard, and this harassment may interfere with other electronic devices work properly, especially sensitive electronic equipment. Along with the technical development, more and more digital and high speed electronic and electric devices are widely applied to vary industries. Those equipments push the society developing, and the same time they bring the electromagnetic pollution problem to the society. Electromagnetic pollution, water pollution and air pollution are the three big pollution sources for modern life. Go with series electromagnetic problem, the CISPR(International Special Committeeon RadioInterference) make the rules like the CISPR -16, CISPR-15; the European Committee for Standardization introduced EN55015 and EN55022. The main purpose for those standards is to limit radio disturbance and put forward the method of measurement of electronic and electric device, so that to decrease the society problem which brings by electromagnetic disturbance.

EMI(Electromagnetic Interference) included conducted interference and radiated interference. Conducted interference refers to the signal coupling through a conductive medium (interference) on an electric power network to another network; Radiated interference is the source of interference to its signal coupling through space (interference) to another radio network. In high-speed PCB and system design, the high-frequency signal line, the integrated circuit pins, various types of connectors so may become a source of interference with the antenna radiation characteristics, capable of emitting electromagnetic waves and affect other systems or to other subsystems within the system normal operation. As we know, the test object for EMC is electronic and electric device, among them, lighting is an important part which should do the EMC test naturally. Like FCC from America and CE from European Union, both of them request EMC measurement of LED lighting device. When talk about electromagnetic disturbance, generally it indicates two disturbance sources, one is conductive interference, it means that the disturbance signal will affect the EUT by conducting medium or public power supply; according to FCC, the LED lighting should do the conductive interference test at the frequency of 0.15MHz to 30MHz; but according to CE, it requests to do the test at the frequency of 9KHz to 30MHz. The other is radio disturbance, it means the disturbance signal will pass to electric network or device by the way of space coupling; according to FCC, the LED lighting should do the radio disturbance test at the frequency of 30MHz to 1GHz; but according to CE, it requests to do the test at the frequency of 30KHz to 300MHz.

In the lighting industry, when testing EMI frequency range at 9KHz~30MHz, there have two ways: The first is use Antenna and EMI Receiver which according to CISPR15, EN55015 and GB17743. For the low-frequency magnetic fields equipment which may produced by lighting luminaries, it need to adopt the provisions of tricyclic CISPR16-1-4 low frequency magnetic field antenna measurement radiation harassment. This need use three Loop Antenna and EMI receiver working together to measure it, and the testing must operate at inside of shielded room. Note: the three loop antenna made X direction, Y direction and Z direction’s low frequency magnetic field component converted to RF signal, and supplied to a receiver via three channels of EMI coaxial switch; The second way is use LISN, the testing system include EMI Receiver, Artificial Network Power, LISN and software. Conduction disturbance test system for measuring normal working light and lighting equipment’s harassmen which produced by power port. LISN achieve isolation RF signal, sampling, impedance matching, and provide electricity for EUT channel, EMI receiver for RF signal measurements and finally analyzed by EMI testing software, processing and sentenced limit. The testing must operate at inside of shielded room.

At the meantime, the testing EMI frequency range at 9KHz-300MHz will be use CDN. The CISPR15,EN55015 and GB17743 standards are also mentioned another way to measuring lighting equipment’s radiation harassment electric. that’s CDN common-mode terminal voltage method. The CDN test method include EMI Receiver, CDN and Attenuator, the testing can operate at inside of shielded room.

For EMI test, the International Special Committee on Radio Interference (CISPR) introduced CISPR-16 Radio Disturbance and Immunity Measuring Apparatus-Measuring Apparatus; for lighting industry, they introduced CISPR-15 Limits and Methods of Measurement of Radio Disturbance Characteristics of Electrical Lighting and Similar Equipments. Meanwhile, some countries push their own Lighting EMI test criterions according to their real situation, like EN55015-2007(quote CISPR-15) from EU counties, GB17743-1999 from China and etc. For EU countries, EN55015 is applied to the traditional lightings which radio disturbance field exceeds 1000Hz, like incandescent lamp luminaries, fluorescent lamp luminaries, self-ballasted lamps and etc. generally, the frequency of the traditional lamps will not exceed 30MHz, the corresponding radiated electromagnetic disturbance limit as table 1. But for LED lighting, the frequency will exceed 30MHz, so according to CE, the frequency scanning range should be from 30MHz to 300MHz.

Table 1:

Radiated Electromagnetic Disturbance Limits
Limits for Loop Diameter  Db (µA)
2m 3m 4m
9KHz to 70KHz 88 81 75
70KHz to 150KHz 88 to 58** 81 to 51** 75 to 45**
150KHz to 2.2 MHz 58 to 26** 51 to 22** 45 to 16**
2.2 MHz to 3.0MHz 58 51 45
3.0MHz to 30MHz 22 1.5 to 16*** 9 to 12***

Base on CISPR16, Lisun Group developed two EMI test systems. According to the standards for traditional Lightings and new LED lightings, the frequency scanning range is different. The scanning frequency for KH3962 EMI receiver is 9 KHz to 300MHz, which is applied to LED and traditional lighting test; the scanning frequency for KH3961 is 9 KHz to 30MHz, which is applied to traditional lighting test. Both of them input three data to judge if the EUT can pass the test or not, that is PK, QP and AV. And user is freely to setup the standards (like GB17743, FCC, EN55015, GB4343) directly in the software.

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