Instrumentation • Electronics
Fig. 3. A Ford focus being tested at MIRA’s anechoic EMC chamber.
anything from six to 10 hours. German auto makers have recently founded a work council for development and testing of electric vehicles, tabling an amendment to CISPR 25 which includes tests for radiated emissions on a vehicle battery, converter and electric motor, as well as components. “You have to think about impedance not only at the
battery terminals but also at the terminations for the high voltage lines and communications lines,” explains Ralf Benecke, electric vehicle EMC expert at Intertek in Germany.
Measuring attenuation
“Within CISPR 25 there are five tests for measuring attenuation for both high and low voltage systems because you have to ensure that disturbances from the high voltage system are not propagating through the low voltage system into the rest of the car. “We reduce the time to measure such emissions by using
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powerful methods such as fast Fourier transform (FFT) analysis, because in hybrid cars for example, the electric motor might be used to boost acceleration for a just a few seconds when overtaking.” A normal scan will monitor a bandwidth of 30-100MHz,
but when there are high voltage pulses on the electrical network they need to be tested using high bandwidth test equipment from the likes of Rohde & Schwarz and Agilent to ensure that components will be able to withstand such pulses. The test requirements will be defined in the functional performance specification by the auto maker, the customer and component manufacturer. Daniel Griffin, business stream manager at Intertek
Testing & Certification in the UK, adds: “A lot of resources also go into testing batteries, which has to be carried out in a reinforced bunker because of the risk of explosion because we try to simulate a fault in the battery which causes it to erupt and leak noxious gas. We then sample the gas to measure what is in it.” ●
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