Time Domain Measurement System for Conducted EMI and CM/DM Noise Signal Separation

This article discusses how to use a digital oscilloscope to match the time-domain measurement computer-aided technique and Fourier transformation to measure the conducted EMI. Taking advantage of the multi-channel oscilloscope and the computer, it will deal with the Line and Neutral lines synchronization. It can mitigate the phase coherency problem to separate the common-mode (CM) and differential-mode (DM) EMI noise at the same time without any hardware implementations. Due to the time-domain measuring method, which allows the noise amplitude and phase in parallel processing for the whole spectrum range, measuring time is reduced. The computerized time-domain measurement environment is based upon the LabVIEW test and measurement system. The separation results are compared with the frequency-domain measurements. The proposed time-domain measured system can provide a user friendly and convincible approach for fast EMI measurement and countermeasures.