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Old 7th September 2009, 11:25 AM   #1
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Default super noob question

First, I apologize for the ridiculous question, but here goes. What is the difference between a cap with a 47 nf value compared to a cap with say .047 microf value? I am assuming you can't substitute one for the other. What would happen if you did sub one for the other? How is the output changed?

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Old 7th September 2009, 03:47 PM   #2
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This should answer your question: http://openbookproject.net//electric.../DC/DC_13.html

unless you meant to ask if there is any difference in value between 47nf and 0.047uf ... there isn't.
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Old 7th September 2009, 05:05 PM   #3
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Quote:
Originally Posted by t_gaines View Post
What is the difference between a cap with a 47 nf value compared to a cap with say .047 microf value?
Same thing. It's like saying a wall is 6 feet high, or 2 yards high.
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Old 7th September 2009, 05:41 PM   #4
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Thanks for the article.

Next question then: if there is no difference, what possesses one to list 47nf vs. .047 microf on a schematic. Does it have more to do with availability? Thanks for your help.
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Old 7th September 2009, 07:35 PM   #5
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Engineers (in Europe at least) try to avoid using 0.xxx uF or writing 22000 pF We use 1-999 pF, 1-999 nF, 1-999 uF

This was really a super noob question but we are here for you
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Old 7th September 2009, 10:40 PM   #6
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It has nothing to do with availability - they are the same thing, it's just a different method of writing the numbers. Same as saying do you want twelve or a dozen?

On my own drawings, I prefer to use whatever notation requires fewest characters, so I'd choose to use 0u1 (i.e., 0.1uF) in place of 100n, but 10n in place of 0u01.
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Last edited by Steerpike; 7th September 2009 at 10:43 PM.
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Old 8th September 2009, 01:50 AM   #7
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Thanks! That helps a bunch. Now to just figure out what I did wrong on my circuit that prevents it from working. This is the part that is so frustrating'.
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Old 8th September 2009, 04:20 AM   #8
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I have been soldering for over 55 years now, and things have evolved. Nowdays we have units for every order of magnitude. terms like nano and pico were listed in reference books, but parts were never labeled that way, nor were schematics.

as was said above 47nf is just another way to say .047uf or 47000pf.

and .47nf is the same as 470pf.

COnvenience is part of it - having several ways to state something can be useful - but also different parts of the world tend to prefer certain conventions. And different industries have there preferences as well.

If you are dealing with higher frequency circuits where lots of parts are in pf. it might be less confusing to call out all the caps in pf instead of using two terms. So a list might have 220pf, 470pf, 82pf, 100pf, and 1200pf. If all the caps are in pf but one lonesome cap was written as 1.2nf or .22nf, someone could if not paying attention misread it as another pf. 2.2pf matters in RF circuits. So 2.2nf might be seen as 2.2pf just because all the other ones were. 2200pf removes that likelihood, however small a one it might be.

When I was learning, in the day of cps - cycles per second instead of Hertz - we didn't use picofarads, we used micro-micro farad. Means exactly the same thing. It was written uuf. Even earlier stuff was written mmf. Our "uf" is really the Greek letter "mu" not a "u." mu stands for micro. Long ago the "m" stood for micro. Hence uuf and mmf were the same. Nowdays we have caps of even several FARADs. 50 years ago, a whole farad was mostly just a concept. But a miili-farad would not be unreasonable to find presently. Today m means milli. But if you read a 50-60 year old schematic and see mmf and mf, it doesn;t refer to millifarads. it is just uf in disguise.

In the olden days it was not unusual to see a .00047 cap in a schematic.
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Old 8th September 2009, 04:39 AM   #9
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Another part of the puzzle is that in the old days, (before personal computers) schematics were drawn on paper and a recurring problem was guaranteeing legibility.
For example, often the decimal point (being just a dot on the page) would not be noticed.

That led to 2 conventions - replacing the decimal point with something else, e.g. writing 0u1 to mean 0.1uf, and omitting the unit altogether in favour of a common unit declared explicitly. e.g. "All capacitors in picofarads" would be written at the bottom of the schematic, and then they would mark a part 47000 (instead of 47nf).
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