The responsibilities of standards makers and test technicians in assessing EMC uncertainties

In EMC compliance testing most measurements have to be compared to a limit level. In most other fields of metrology the uncertainty is added to the measured result before comparing it to the limit, but this is a contentious issue in the field of EMC. In Europe, to assure common EMC test practice, a standard has been drafted, prEN50222, which states that measurement uncertainty was taken into account when setting the limit, therefore the measured result should be directly compared with the limit. This could be taken to absolve the technician from paying any attention to uncertainties. This is obviously undesirable because it could lead to widely dissimilar results at different test houses and ultimately legal disputes. This approach places the emphasis on the standards makers who then have to ensure that uncertainty tolerances are specified for all the equipment used and for the method used for each type of test. This creates a huge task for the standards makers and may lead to too many mandatory requirements which test houses may find undesirable. This paper looks at requirements to estimate uncertainties of measurement through the eyes of a test technician and then looks behind the scenes to the activities of standards makers whose aim is to ensure that EMC testing complies with the spirit of international documents on uncertainties