Uncertainties and accuracies in EMC-testing

In this paper, the random- and systematic-errors are presented for EMC-measurements, including the measures that can be taken in order to minimize the uncertainty due to their effect. The probability density functions (PDF) are calculated for a normal distribution, a rectangular flat PDF and a U-shaped PDF which is function of the complex reflection coefficients of source and load due to impedance miss-match. The total combined standard uncertainty was then calculated via the appropriate sensitivity coefficients, when there is no correlation between any of the input estimates and must be determined in worst-case if correlation between any contributions is suspected. Normally the level of confidence for EMC-testing is 95%, with a coverage K-factor of 2. However a coverage factor K > 2 may be necessary for some exceptions depending on the ratio of the total combined uncertainty Uc(y) and system repeatability tests s, on a reference EUT (Equipment Under Test). This can be determined with a student-T distribution with a number of degrees of freedom l, depending on the ratio Uc(y)/s. The method was first developed for antenna-calibrations according to ANSI C63.5 at Laboratoria De Nayer and then implemented for EMC-tests including radiated emission and immunity, electrostatic discharge and conductive immunity.status: publishe