Quantifying the effect of scan rates in immunity testing

The authors quantify the effectiveness of tuned electromagnetic immunity tests carried out at specified scan rates, for example in accordance with the Generic European Immunity Standard IEC 801-3. Firstly, a method is described to determine test effectiveness for continuously tuned testing. The difference between manual `continuous sweep´ testing and automated `stepped frequency´ testing is discussed. A method for choosing the correct step sizes and dwell times for automated testing, which give an equally effective test, is derived. Specific examples are based on the scan rates defined in the IEC 801-3 immunity standard. Test effectiveness graphs are shown for ideal continuous tuning at the rates given. For equivalent stepped tuning tests, the number of frequency steps, step sizes and dwell times to meet the requirements of the specification are presented. Using these results the theoretically minimum test times for automated testing are derived and the implications of deviating from, or not specifying, step sizes and dwell times used during a test are discussed