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i see schematics with values such as .01uF among others... why out of all components are these not labeled using engineering notation

Edwin Fairchild
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    I thought micro (u), nano (n) and all were engineering notation (as opposed to scientific notation) – Marla Jul 11 '16 at 14:23
  • To be pedantic, .01uF should probably be labeled as 10nF. – brhans Jul 11 '16 at 14:26
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    thats exactly my point , .01uf is 10nf but i often see it labeled as .01 which is not engineering notation (1-999) – Edwin Fairchild Jul 11 '16 at 14:29
  • Because it is easier to say "everything is µF" and then not write µF all over the place? – PlasmaHH Jul 11 '16 at 14:32
  • I think this has cropped up before. – Andy aka Jul 11 '16 at 14:33
  • In the old days it was generally pF and µF. As the SI system became more widespread nF was more widely used. I like the 2n2, 4µ7, notation myself as it avoids errors due to missing the decimal point. – Transistor Jul 11 '16 at 14:34
  • Many schematics comes with a footnote, "all capacitance are in micro Farads unless otherwise stated"... Now you should understand. – soosai steven Jul 11 '16 at 14:35
  • Anyway, schematics are often not really following any special conventions, as designed and drawn by engineers(in the best case) of different levels. so you can find much weird stuff in them.. – Eugene Sh. Jul 11 '16 at 14:52
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    It's hard for dyslexic and sleep deprived to reliably distinguish u from n. Especially when reading schematic upsdide-down. </humor> – Nick Alexeev Jul 11 '16 at 15:03
  • @NickAlexeev: That may be part of why its a µ rather than a u. Hectofarad caps will not figure in most people's schematics. – hmakholm left over Monica Jul 11 '16 at 15:20
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    Nanofarads (and even picofarads) are a relatively recent invention. When I started in electronics, capacitors were either uF or uuF, so a schematic showing 0.01uF may have been drawn by an older engineer. – Peter Bennett Jul 11 '16 at 15:59
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    Interestingly, if you look at capacitors on DigiKey, they don't list values in nF. In their capacitance selection list, 10000pF is followed by 0.011uF. – Nick Alexeev Jul 11 '16 at 16:10
  • @Peter Bennet, pF was in common use in the sixties, at least for RF applications. – Chu Jul 11 '16 at 16:17

2 Answers2

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It is a matter of history, sadly. Capacitors where built well before the International System of measurement (SI) was established and some prefixes weren't used so much (e.g. nano).

For example, usually capacitors only used microfarad (sometimes written as \$MFD\$) and picofarad as units, this latter often written as micromicrofarad (\$\mu\mu F\$). Therefore \$10nF\$ could only be written as either \$10,000 pF\$ or \$0.01 \mu F\$.

Combine this with the need to encode other information on the smaller packages of the time (e.g. tolerance), and you end up with a metric ton of different encoding schemes, some more obscure than others.

Since old habits are hard to die, even in modern industry, the markings on the caps follow, in some way, the old tradition, where nanofarads "didn't exist".

LorenzoDonati4Ukraine-OnStrike
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The history of this is probably bound up in the technology of early capacitors. In the early days, capacitors were

  1. Electrolytic or oil-filled (generally larger than 1uF)
  2. Mica or NP0 (and other controlled tempco) ceramic types or air (some pF to hundreds of pF)
  3. Paper or film types, generally ranging from maybe 0.01uF to a few uF.

It probably seemed easier at the time for the engineers of old to use uF for all but RF applications, where pF were more appropriate.

Spehro Pefhany
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