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What is EMC?

About EMC

Electromagnetic Compatibility (EMC) covers a broad discipline and touches the operation of equipment that greatly affects our modern lives.  In essence, the “goal of EMC” is the result of all electrical and electronics equipment operating in its environment properly and without a negative effect on the environment.

Early work in “RFI” or Radio Frequency Interference started in the 1930s, primarily with military systems and notably airplanes. The installation of radio equipment in early aircraft gave rise to noise problems in the radio receivers from ignition sources (spark plug noise) and related pulse and broadband interference sources, such as precipitation static (so-called “P-Static”). Other concerns, which continue today, include protection against lightning-induced energy which can threaten airborne, ground and sea-based equipment.

Over the years, RFI broaden to include such issues as immunity (susceptibility) to noise, such as lightning and pulsed threats.

The Military issued a number of standards for EMC performance. “The military first established EMI emission requirements for equipment in 1945 with JAN-I-225 that mandated measurement of conducted and radiated EMR in the frequency range 0.15–20 MHz. The first susceptibility requirement was introduced in 1950 in MIL-I-6181.” (Pierce). In 1967, the first versions of the MIL-STD-46X standards were issued (MIL-STD-461, MIL-STD-462 and MIL-STD-463). Eventually the -462 and -463 were merged into the same document with the “D” version of MIL-STD-461. This codified both the limits for measurements and the methods of measurement.

The development of standards to protect the spectrum was boosted in the early 1980s with the advent of home-based computing equipment and related electronics (such as video games, electronic controllers, appliances, etc.). The FCC’s first Rules that directly impacted digital electronics were issued in 1984 and are enshrined in Part 15 which was carved out in the early days of the FCC to cover ‘unlicensed operation.’ When the Rule-writers crafted the regulations after ‘The Telecommunications Act of 1934,’ most users of the spectrum were broadcasters (and amateurs). The broadcasters were set aside as “protected” users of the spectrum because they had, in principal, paid for the rights to use the spectrum in their allocated space.

The distribution of the spectrum in the early days is an interesting story in itself, with loads of political and influence peddling as eager market-makers battled for this precious resource. In any event, the FCC issued rules for digital devices that protected the licensed users. These regulations now affect the operation of billions of electronic devices, but only in terms of emissions from electronics devices. Immunity (with the exception of some regulated medical products) is largely left ‘to the market to decide,’ that is, if a device doesn’t work properly in its electromagnetic environment, it will be rejected as faulty.

Internationally, the European Union (EU) enacted broad sets of Directives as it tried to align its customs and trade regulations to create the ‘single market’ for goods and services. The EMC Directive was enacted in 1989 (89/336/EEC) and is one of the broadest directives that affect electronics. With an eye towards creating a baseline of quality in goods and services, a certain efficacy is demanded of products. The EMC Directive mandates that products that bear the CE Marking meet the “essential requirements” which include protection of the spectrum and proper operation in the intended environment. This was a ground-breaking regulation, really, as it created a global standard (essentially) for equipment performance. The EMC Directive has been updated over the years. The current Directive, EMC Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonization of the laws of the Member States relating to electromagnetic compatibility (recast) is applicable from 20 April 2016.

Other areas that are included under “EMC” include all manner of electromagnetic measurements. As EM phenomena extends from DC to nearly light (the upper end of the “radio frequency spectrum, at least according to standards writers, approaches 3000 GHz, above which optical models are more aptly applied for predicting and measuring EM phenomena). Thus, magnetic fields, static phenomena, transient behavior, all are grouped under the practice of EMC. Standards and practice do not only apply to equipment and measurements of conducted emissions, radiated emissions, conducted immunity and radiated immunity; the protection of human and animals is also part of the practice of EMC. Radiation hazards measurements, from large radiating structures such as antenna arrays all the way to mobile devices, are assessed against US and International standards. In the US, ANSI C95.1 is the guiding general limit, which closely aligns with requirements in the FCC Rules under 47 CFR 1.1307(b), 1.1310, 2.1091 and 2.1093.

Notes: History of Part 15 Rules:

1. Electromagnetic Compatibility (EMC) Requirements for Military and Commercial Equipment. James D. Pierce Jr. September 2009.