Statistical evaluations of time-domain EMI measurements

In this paper we discuss the advantages and limitations of broad-band time-domain measurement techniques for electromagnetic interference (EMI). The digital processing of EMI measurements allows to emulate in real-time the various modes of conventional analogous equipment, e.g. peak-, average- RMS- and quasi-peak-detector modes. It is also possible to introduce new concepts of analysis, e.g. phase spectra, short-time spectra, statistical evaluation and FFT-based time-frequency analysis methods. Since time-domain techniques allow to process the amplitude and phase information of the whole signal spectrum in parallel, the measurement time may be reduced by at least one order of magnitude and the information obtained goes far beyond the information obtained with conventional analogue measurement systems. A time-domain electromagnetic interference (TDEMI) measurement system is presented. The signal processing algorithms and the results obtained with the system are discussed.