Uncertainty Contributions in the Conducted Immunity Test

Conducted RF immunity testing to IEC 61000-4-6 requires the application of a stress voltage at a constant level across a wide frequency range. The coupling method chosen must be applicable to any type of construction. When the RF stress is applied it creates internal signals which may affect the desired operation to cause malfunction. This mechanism includes two particular sources of uncertainty associated with the actual applied stress. • The voltage or current induced at the relevant port depends on the choice of transducer, as the standard allows for three different types. Where any one of these three types may be chosen the failure stress level may depend on this choice. Since all three types are permitted it would be difficult to argue that one gave more ‘precise’ results than another. • Once the transducer has been selected for a conducted immunity test, the applied stress is determined by the impedances of the coupling source, the cable and the EUT. These in turn are affected not only by the design of each but also by the physical layout of the test set-up. The project described here investigates each of these issues.