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EMC: COMPLIANCE TESTING


❱❱ Pre-compliance software can help reduce costs and lead times of electronic product


introduction; the Microrad NHT 3DL, inset, is a portable electromagnetic field analyser


DIY tests help avoid costly resubmissions


Effective pre-compliance testing can dramatically cut product development costs and lead times


but also to meet the stringent functional specifications for complex end products in industry, healthcare, telecommunications and the automotive industry, for example. Performing such testing in a certified test


A


house is costly but is a necessary expense before launching the product onto market. But what if it fails the test? Costs quickly mount when a “final” product goes back to the drawing board only to be retested at some later date. Such iterative approaches are not cost-effective and fail to meet competitive time-to-market aims. The alternative approach is to perform in-


house compliance testing, a method that’s becoming increasingly popular, especially with the availability of affordable laboratory equipment and software. Such tests can never be as precise as those performed in anechoic chambers equipped with high- precision antennas in a test house but they are extremely cost-effective in reducing the risk of product failure in final testing.


TYPES OF TESTING Electromagnetic interference (EMI) can be radiated (through the air) or conducted (along wires). EMC testing performs both tests. It also examines the product from the point of view of emissions given off and its susceptibility to received interference. Pre-compliance emissions testing requires


a spectrum analyser with EMC analysis software, a pre-amplier and antenna (for radiated emissions) and a line impedance stabilisation network (LISN) for conducted emissions. Immunity testing requires a signal generator and a set of probes. In all cases, since a high-cost anechoic chamber is unlikely to be available, great


care is needed when selecting the right testing environment so that results are not influenced by stray signals, such as emissions from anything other than the device under test or a signal from anything other than the signal generator. Radiated emissions tests can


be performed in large parking areas or empty conference rooms, for example, as it is crucial that transmissions from broadcast radio, TV or mobile phones don’t interact with the DUT or antennas.


TEST EQUIPMENT Advanced signal analysers are a key element in the test equipment needed for pre- compliance testing and some, like Keysight’s X-Series, are available with software such as the N6141A EMI measurement application, which contains a standard library of more than 25 measurement applications. The N6141A transforms the X-Series signal analysers into powerful EMI pre- compliance and diagnostic systems, providing easy-to-use data collection and analysis tools which facilitate rapid time-to- market for new designs. Other alternatives include the TekBox


EMCview pre-compliance PC-compatible software for simplifying the process of radiated and conducted emissions testing. EMCview complements an emissions test setup consisting of a spectrum analyser, an


LISN and an EMI-quiet TEM (transverse electromagnetic) cell. It has built-in amplitude correction and conversion coefficients for cables, amplifiers, attenuators, LISNs, TEM cells, antennas, RF current probes, striplines and capacitive coupling clamps. Software from other suppliers is also available


for the validation of RF designs, including SignalVu-PC from Tektronix. SignalVu-PC’s free base version has 17


signal analysis and real time spectrum analysis channels, with paid-for add-on options for EMI/EMC pre-compliance testing and de-bugging, as well as analysis of vector, pulsed and commercial wireless signals.


INTERFERENCE FREE VALIDATION Tools are available to help ensure tests can be performed in a valid way. One example is the Microrad NHT 3DL electromagnetic field analyser for measuring in both time and frequency domains. The hand-held device has a high-


resolution colour touch screen display and can be remotely controlled using Wi-Fi or fibre-optic connection, with the display shown on Windows and Android devices. The Microrad NHT 3DL analyser is particularly useful since it has been designed to operate in different modes, including as an area monitor. T&TH


April 2020 /// Testing & Test Houses /// 29


ttaining robust electromagnetic compatibility (EMC) is becoming increasingly necessary across all susceptible products, not only for standards compliance purposes


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