A.C. magnetic fields exist throughout every EM site. For a given site, then, how does one predict when EM interference problems are likely to occur? Obviously, an accurate, meaningful magnetic field survey is the first step toward evaluating site EM magnetic field compatibility. Consequently, this article in our series will describe measurement equipment and techniques for achieving accurate, unambiguous magnetic field characterization.

In a previous article (Part II: “ACMF/EM Antipathy”, Microscopy Today, November ‘95), we examined several types of sources which produce alternating current magnetic fields (ACMFs). In near proximity, or at sufficiently high power levels, any of these sources (e.g., transformers, power cabling, ground currents, and/or combinations thereof) can affect EM operation. In this article, we will review specific instrumentation and methods for accurate magnetic field survey data collection and interpretation, a necessary prior step for EM interference prediction and resolution.