ABSTRACT
This chapter focuses on the areas where the medical device designer has some control–circuit boards, circuit modules, and individual pieces of equipment. Grounding is probably the most important, yet least understood, aspect of Electromagnetic Interference (EMI). Every circuit is ultimately connected to one or more "grounds," so every circuit is affected by grounding EMI issues. Grounding cannot be left to chance–it must be designed in from the very beginning. Patient-connected medical devices impose some unique grounding constraints, due principally to power line leakage current limits. These limits are designed to prevent potentially lethal "microshocks." While these limits often pose severe constraints and make EMI even more difficult to control, safety must always take precedence. Leakage currents occur in many electrical and electronic devices. This leakage results from the power line voltage being impressed across "line-to-ground" capacitance, which results in a small amount of current flow through the capacitive reactance.
