EMI Sub-System Emission Limits Based on Statistic Analysis

Product EMI pre-compliance evaluation becomes more important nowadays than before owing to growing industrial trend in modular design, outsourcing and OEM. Pre-compliance testing involves measuring the radiated and power-port conducted emissions of a complex system at sub-system levels. Defining appropriate EMI limits at sub-system levels is crucial for the overall system compliance. Suppliers rely on product specifications to design the products. If a sub-system level limit specified is too conservative, the products would be EMI over designed. However, if a sub-system level limit specified is too loose, the system EMI compliance will be in jeopardy. This paper utilized the statistical modeling recommended by ITU to estimate the maximum increase in the radiated and power-line conducted emissions from a multi-unit system. The results are useful in determining appropriate product sub-system EMI limits and enhancing engineers´ judgment for compliance evaluation. The sub-system level limits based on statistic analysis provide plausible and rational criteria for subsystem level pre-compliance evaluation and prevent products from being over-designed.