philip keebler

Wireless technology is experiencing explosive growth. More than just devices of the same kind, there is a proliferation of applications that take advantage of wireless connectivity, using it in new and novel ways. Wireless technology itself is developing and radio access technologies are becoming increasingly complex and sophisticated. The result is that today’s electromagnetic environment is changing. This means that old test methods and limits are no longer adequate to insure systems have adequate electromagnetic immunity.

The use of exclusion zones to keep wireless transmission devices (WTDs) (e.g., radio walkie-talkies, cellular phones, etc) from being too close to instrumentation and control (I&C) equipment and system cabinets containing this equipment remains a primary concern in existing and advanced (future) nuclear power plants. In Part 1 of this article, a background and history of how exclusion zones were developed and implemented in these plants was presented along with their advantages and limitations. In Part 2, presented here, the elements of the exclusion zone strategy are discussed followed by the demonstration of a concept often used in studying the electromagnetic compatibility (EMC) immunity of modern electronic systems. This concept—called layered immunity—is key to understanding the parts of a system where EMC system immunity must be applied. The initial thought that readers must accept before proceeding to read and understand this concept described in this article is that system immunity involves other parts of the system besides just the immunity of the individual piece of equipment requiring protection.

Today’s end-use electronic equipment has a number of characteristics that require protection from the electromagnetic environment. These characteristics include the growing use of digital electronics (still with a layer of analog electronics); multiple inputs and outputs for power, data, controls and indicators; ventilation for air flow and thermal management; and small openings for accessories. Few pieces of equipment use only one microprocessor. Multiple digital packages (i.e., integrated circuits) are used for small and large amounts of memory, signal processing, and input/output control just to name a few. The days of having just one power cord and a few knobs for control have long since past.