Study of conducted emission measurement for equipment with multiple supply ports

It is common for the equipment under test (EUT) to have multiple input power ports. The International Commercial Standards on conducted emission (CE) specifies only about the measurement of the noise at individual power supply ports using line impedance stabilization network (LISN). The effect of the power supply ports other than the one which is tested, such as the noise getting on to the system via the other power supply ports or the low impedance path for the noise through the other ports bypassing the LISN, is often ignored. It is observed that the impedance at other power supply ports has a major influence on the noise measurement at the test port. In this paper effort is made to demonstrate the effect of other power supply ports on the test measurement. The measurement results with different configurations are presented here. The observations may be referred to the standard setting committee and considered for possible amendment in the standard during the revision.