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I'm looking at an electrolytic capacitor (and old blue, Philips one used in electronics classes) and am wondering why it is printed with 4µ7-M.

I tried Googling, figuring that it was a common enough occurrence, but found nothing.

Is that supposed to be a 47µF cap? Why is the µ in the middle of the number? What is the -M for?

Thanks.

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  • \$\begingroup\$ Thanks guys. I'm not sure I have seen this before (although the answers do seem vaguely familiar). The explanations for it also make sense. Thanks again. \$\endgroup\$ – Synetech Dec 8 '10 at 6:08
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The "µ" symbol is put in place of the decimal point, 4µ7 translates to 4.7 µ farads.

Not too sure about the "-M" part tho - sorry

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    \$\begingroup\$ This is correct. You will also see this on some resistors were it will say 4k2 and mean 4.2k ohm. \$\endgroup\$ – Kellenjb Dec 6 '10 at 16:14
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    \$\begingroup\$ I suspect the M is probably some kind of indication of the dielectric temperature characteristic or voltage rating. It's probably a manufacturer specific code. \$\endgroup\$ – vicatcu Dec 6 '10 at 16:25
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Like Jim said, the µ indicates the place of the decimal point. This isn't restricted to capacitors, but also used for resistors and inductors:

resistor 31k6 = 31.6 kiloOhm
resistor 5M6 = 5.6 megaOhm
capacitor 2n2 = 2.2 nanoFarad
inductor 4µ7 = 4.7 microHenry

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    \$\begingroup\$ Beware people who use m for mega- and M for milli-. Not always that difficult to distinguish, but harder than (capital) S for seconds people. \$\endgroup\$ – Nick T Dec 6 '10 at 16:42
  • \$\begingroup\$ Good point, but most of the time this can be derived from context; 1m0 on an inductor will be milli rather than mega :-) \$\endgroup\$ – stevenvh Dec 6 '10 at 17:33
  • \$\begingroup\$ Most circuit simulation packages will also accept this format, but beware that they may not be case-sensitive, so a "1M0" resistor could work out as a 1.0 milliohm resistor, so use 1Meg in this case. \$\endgroup\$ – Martin Dec 6 '10 at 20:12
  • \$\begingroup\$ It gets even worse... Have you ever heard of a 100 uuF cap? That's micro-micro-farads. Nowadays, we call them picofarads. \$\endgroup\$ – Connor Wolf Dec 7 '10 at 0:37
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It caused less confusion than sometimes arose with a decimal point, which was missed sometimes when documents were copied or faxed. That's not such a problem these days, but it is in common use, especially here in Europe. I always use that notation.

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    \$\begingroup\$ I was more thinking about markings on components than documents, but you're right. However, in SMD markings a decimal point gets lost even more easily. \$\endgroup\$ – stevenvh Dec 6 '10 at 17:35
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    \$\begingroup\$ And in some European countries, a comma is used instead of a decimal point for the seperation of the fractional part, and a point is used for seperating out the thousand part instead of a comma. \$\endgroup\$ – Martin Dec 6 '10 at 20:14
  • \$\begingroup\$ @Martin: in everyday use the comma is used in all of Europe, except for the UK. But I've never seen it on components \$\endgroup\$ – Johan.A Aug 8 '13 at 9:23

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