EMC precompliance testing - prediction not correlation

Correlating measurement data is a task many EMC engineers face when performing precompliance testing. Correlation, creating a point-for-point similarity between two measurement systems, is often the approach taken to determine if product modifications are needed before performing an, often costly, compliance scan. However, correlation methodologies rely on calibration methods which are inadequate in determining point-for-point measurement similarity for devices with non-rigid structures. This inadequacy has been quantified as measurement uncertainty in various standards. The inability to correlate measurements absolutely is further exacerbated by alternate test environments and a lack of industry agreement on standard test procedures. The authors have developed a novel approach for determining the pass/fail status of an EUT from precompliance data taken from uncorrelated measurement systems. This simple and effective approach evaluates past compliance data and applies it to the current precompliance data set. The EMC engineer is thereby enabled accurately to predict if a unit will pass or fail the forthcoming compliance scan, regardless of site-to-site correlation.