Power Line Conducted Interference Measurement Differences Using U. S. and CISPR Line Impedance Stabilization Networks

Measurements of power line conducted interference are commonly made on commercial equipment throughout the world using line impedance stabilization network (LISN´s) in accordance with industrial and governmental procedures. Procedures in the United States applying to the 0.15-30 MHz frequency range specify an LISN that presents a frequency-dependent RF impedance to the equipment under test (EUT) whereas other national practices specify as LISN having an invariant 150-ohm impedance. This paper explores the expected measurement differences resulting from use of the two LISN´s for power line interference measurements. Calculated difference factors, which depend on the EUT power line RF-input impedance, are developed. The factors have utility in assessing expected conducted interference levels in one LISN measurement configuration, given the interference levels and impedance parameters of the other. Measurement differences, in addition to those introduced by the LISN, which are attributed to variations in specified field strength meter parameters (i. e., detector, bandwidth, mechanical time constants, etc.) are beyond the scope of this paper.