EMC TESTING & ANALYSIS: COMPATIBILITY
susceptibility rather than immunity, reflecting amore pessimistic or pragmatic attitude to EMC. “This glass-half-full/glass-half-empty
difference reflects the defence industry’s pragmatic view that EMC will affect their products and they want to know to what extent. Everything is susceptible and they want to quantify this,”Dorey toldme. The testing performed is designed to check intended product functions in an environment where there is a known transmitter.
EMC TESTING Testing is performed at all levels of the final product bill ofmaterials, including component, sub-assembly and system levels. REDaffects everything that has the ability of transmitting or receiving radio signals but there are also a lot of standards that relate to specific industries, such as automotivemanufacturing and the highly regulated defence and healthcare industries. On top of that, there is a whole different set of standards and regulations for the aerospace industry because of safety. “These industries have their own sets of
standards in addition to those which are generally applicable,” explainsDorey. “The EMC directives don’t relate to safety and aremore aligned towards stopping equipment frompolluting the radio spectrum.” Mains connected
equipment also needs to be checked for harmonics of up to 2kHz travelling back into themains plus voltage loads and flicker, so a comprehensive test plan is needed for all new products to ensure these test requirements are catered for withoutmaking repeated trips to the test laboratory.
Full product conformance certification requires a number of different tests
side effect of the design of the RAM(radio absorbentmaterial) wedges which are tuned for radio absorbance, not sound,” Dorey explains. RF receiving antennas are arranged
around the product tomeasure the radiated interference. These specialist antennas are designed to have a very wide frequency response, unlike a tuned TV ormobile phone antenna. Tests are performed in frequency ranges up to 6GHz as well as sometimes in the 6-18GHz or 18-40GHz range, which require different antennas. For standard testing,
EMISSIONS TESTING Tomeasure emissions, the product under test is placed into an anechoic chamber to block out any environmental factors that could influence the test results. According to Dorey, the controlled environment provided by the anechoic chamber consists of a faraday cage, which blocks out external factors and absorbent interior walls to stop radio reflections fromthe equipment itself. The wedge shaped absorbers on the walls
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give the facility the appearance of an acoustic chamber. “EMC chambers do absorb sound reflections so they seemto be acoustic in nature but this is really just a
36 /// Environmental Engineering /// August 2017 EMC standards
stop equipment polluting the
radio spectrum Peter Dorey of TÜV SÜD Product Service
IMMUNITY TESTING Immunity testing requires a reverse set up to that of emission testing using a signal generator, power amplifier and antennas used to transmit rather than receive a signal. These antennas need to produce signals across a wide frequency range at the appropriate power level, which ismuch higher than that in emission tests. Emission testing is about spectrum
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radiated frequencies are measured between 30MHz and 6GHz. The equipment is also wired into the network tomeasure conducted emissions. “Radiated frequencies lower than the 30MHz that the antennas can pick up are tested using conducted levels of interference since one implies the other,” explains Dorey. The signals received by the
antennas are fed into test receivers and spectrum analysers to build an EMC emission profile of the product under test.
protection and the levels aremeasured in microVolts. Immunity testing requires much higher levels,measured in Volts. Product performance needs to be monitored against criteria supplied by the manufacturer. Although it’s feasible to use the same antennas for both types of tests, there are sufficient differences to necessitate using different antennas for immunity testing. Similarly, the emissions testing chamber is normally different to that used for immunity testing as they need different anechoicmaterials. Other equipment needed includes a
turntable andmast, which are demanded by the standards, as well as equipment for other tests (transient interference, for example), such as lighting and electro static discharge (ESD). Sometimes tests can be performed on site
in the open air if the product is too big to be placed in a chamber. Emissions testing can be performed like this but background noise needs to be accounted for using subtractive analysis bymeasuring the background interference andmaking the same measurements with the product.However, emission thresholds are often very low level and can be drowned out by the background interference, rendering the test ineffective. It is not possible to carry out immunity
testing across the full spectrumin this way because it is illegal to transmit signals in this way outside of a chamber environment. It is only possible to do this using specific frequency bands using legal equipment likemobile phones but the scope is very limited. EE
To readmore online about EMC testing, scan the QR code or visit
http://goo.gl/AjZqxp
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