In writing, do I need to define an abbreviation when it is already an industry standard term?
Let us assume that your publisher / journal / conference / style manual has no restrictive guideline regarding abbreviations (otherwise, follow that guideline obviously in first place).

You do have to define every abbreviation. (As an example, I was confused yesterday by finding out that CRT is not only a cathode ray tube, but also the Chinese Remainder Theorem). Consider, e.g., the huge list at https://en.wikipedia.org/wiki/ADC . But you can do it in a clever, space-conserving way by


providing a list in an appendix,
defining them in footnotes on their first usage,
defining all of them in small size in a "preliminaries section" or in endnotes,
giving a reference to a standard Web site with the abbreviations you need,
giving a reference to your own Web page with the abbreviations you need, 
citing some electrical-engineering dictionary which defines them unambiguously the way you need,
…


Of course, pay attention that your paper reads well in first place; there may be no general advice on which of the above list items applies best to your paper.