Why increasing immunity test levels is not sufficient for high-reliability and critical equipment

It is often assumed that passing an EM immunity test at 100% of the level of the worst-case disturbance that can occur over the lifecycle, and taking measurement uncertainties into account, will prove that the design of the tested equipment will almost never suffer from errors or malfunctions due to that dis-turbance in real life. Unfortunately, although the above is necessary when testing the EM immunity of equipment that must function with high relia-bility — such testing is insufficient to demonstrate that high-reliability, security, mission-critical or safety-critical equipment or systems will achieve tolerable failure levels over their life-cycles despite the EM disturbances in their environments. Part II of this paper explains why this is so, and Part III briefly introduces the techniques that are necessary for achieving sufficient confidence in EMC, when high reliability is required.