Effects of Varying the Length of Locally Grounded Cable on Radiated Emission as Per CISPR 25

Abstract

In this study, the ambiguity of the locally grounded wire length defined in the automotive EMI standard CISPR 25 is experimentally investigated. In-vehicle wire grounding conditions are divided into remotely grounded and locally grounded conditions based on the wire length of the battery negative terminal. In the locally grounded condition, the wire length of the battery negative terminal is specified as less than 200 mm; hence, different grounded wire lengths can be used when a tester performs measurements according to the specified locally grounded condition. Therefore, in this study, we simulated and measured the radiated emissions by changing the locally grounded wire length. We found that the radiated emission does not satisfy the EMI specification in a specific frequency band. In other words, it was confirmed that the locally grounded wire length could affect the pass/fail results of the tested products.