Time-domain Measurement Technique to Analyze Cyclic Short-Time Interference in Power Supply Networks

Conducted interference caused by equipment connected to power supply networks, and the interference in these networks, is conventionally measured using (slow) scanning tuned electromagnetic interference (EMI) receivers. A voltage sensor which separates common mode and differential mode in a threephase setup combined with a 8-channel digital oscilloscope allows measuring voltage and current via many samples in the three phases plus neutral. Using fast fourier transform for the data processing the conventional amplitude-as-function-of-frequency plots, similar to what would be obtained using conventional EM! receivers, can be generated. But with the presented measurement technique it is also possible to present time-frequency plots in a waterfall diagram. The time-domain measurement technique shows that the conducted noise is cyclic short-time interference.