Investigation on Differrence of Radiated Emission Measurement Reproducibility between two EUTs at International RRT by Using CMAD as a Terminating Device for AC Mains Cable

The international round robin test (RRT) demonstrated that the site correlation improvement effect of a common-mode absorbing device (CMAD) varies depending on the equipment under test (EUT). This paper investigates the cause. The standard deviation of the common-mode current, when the termination condition was changed at the AC mains cable end, was obtained from the calculation by using 6-port network and the measurement by using the artificial EUT. The results indicated that the standard deviation was reduced when a high impedance was inserted between the EUT's frame and the protective earth (PE) wire. The results, based on the EUT used in RRT, indicated that the standard deviation of radiated emission was reduced by decoupling the PE wire from the frame. In conclusion, since the EUT's frame is directly connected to the PE wire in many cases, the effect of CMAD can be discounted.