Evolving EMC/EMI standards over the past many decades continue (or try) to keep pace with changes in technologies. The original EMI specifications were borne out of WWII, where tube technologies were the dominant state-of-the-art. This human being, as a boy, remembers Dad checking tubes at the ‘Radio Shack’ tube tester machine: “green for good” and “red for bad.” Today PNP junctions notwithstanding, tube amps are still highly prized in the audio world.
But I digress.
The first EMI specifications were initially developed because of concerns about interference to voice communications and focused on emissions to protect radio communications equipment jammed into cockpits and turrets. These specs were rapidly supplemented by susceptibility tests as it was realized that these little boxes of electron honey were vulnerable to outside pulses and spikes and continuous wave sources (or “noise” from other communications systems, radars, lightning, power, intentional jammers, etc.).
The EMI/EMC requirements converged over time and, for military equipment, MIL-STD 461 (circa 1967) emerged as the go-to for equipment procurement and performance. Over my now-mossy career, I’ve seen cited the A, B, C, D, E and the current MIL-STD-461G. You can find the legacy documents here: http://everyspec.com/MIL-STD/MIL-STD-0300-0499/MIL-STD-461_8678/
Work is being done on the next version of MIL-STD-461(H). Digressing again (and my silly opinion): It’s a little amusing—but understandable—that tests almost never get redacted, even though they were conceived during the times of tubes and concerns were principally for radio-audio interference. Anyway, the MIL-STD-461s address different levels of emissions and susceptibility (NOT immunity, mind you, as is used in the commercial parlance. Same shoes, different socks.) The companion document that addresses vibration, shock, temperature and humidity, etc., is found in MIL-STD 810H.
On the commercial aerospace side, the Radio Technical Commission for Aeronautics (RTCA) publishes EMC & Environmental standards for things that fly in friendly skies. The current requirements are examined in DO-160G. It is probably happenstance that the MIL and DO-160 versions are suffixed with a “G.” IDK, but my great-grandkids’ generation may be dealing with MIL-STD-461Z. Then what?
It is noted that there are many industry-generated specification for EMC/EMI-related applications. One such (heritage) spec, for example, is from Boeing (1974) that addresses upset/damage levels for transistor-based devices as well as suppression techniques, shielding and good design. EMP Electronic Design Handbook, AFWL-TR-74-58 is the document name and number. I’m not sure if this was ever updated; the requirements are probably superseded by the RTCA DO-160 document.
For things that go into outer space, in NASA’s realm, are addressed in the GEVS document series (General Environmental Verification Standard) that was initially issued at the onset of the Space Shuttle program. This document, like the DO-160 series addressed EMC and “Shake and Bake” requirements. (Image the thunderous roar of launch vehicle in the moments of ignition and liftoff…)
It must be mentioned that the MIL/Aerospace compliance requirements are often tailored to meet specific mission requirements and the services that use the widgets. It is not uncommon to see legacy specifications called out for specific programs. This is counter the commercial world where the path is tighter and an FCC/ISED/CE requirements for whatever-it-is is prescribed in the various published and adopted standards. Sometimes, it’s cut-and-paste, sometimes it is the specification writer that has some peccadillo.
Expect more to be added to the lexicon for all industries. We live in interesting times.
Image Credits:
Vintage Vacuum Tube Tester (EMC-205, circa 1945): Image by Joe Haupt via Wikimedia Commons, licensed under CC BY-SA 2.0.
Modern EMC/EMI Testing Equipment: Courtesy of Washington Laboratories, Ltd.
About the Author:
Mike Violette, P.E.
Director, Washington Laboratories
Mike is the Director of Washington Laboratories. He has over 40 years of experience in the field of EMC evaluation and product approvals and has overseen the development of engineering services companies in the US, Europe, and Asia. He is a Professional Engineer, registered in the State of Virginia. He has given numerous presentations on compliance topics and is a regular contributor to technical and trade magazines.
