[sci.electronics] Rational Capacitor Prefixes

vaso@mips.COM (Vaso Bovan) (08/23/89)

This is a plea to rationalize capacitor unit suffixes. Most postings
give capacitances in terms of pF or uF. Unfortunately, this often means
capacitances are are stated in inconvenient units. ie caps with the following
units are given 4700pF ; .0047uF ; .001uF !  It is a nuisance to have to count
the decimal places, but there is at least one situation where the "dot"
placement can actually cause mistakes: In photocopying schematics, "dots" are
added and taken away at random. 0.01uF might easily be mistaken for .001uF.

In conformance with good S.I. practice, the "nanofarad" is coming into wide
usage. (European schematics have long used nanofarads). eg .01uF becomes
10nF. 4700pF becomes 4.7nF. The ubiquitous .1uF (or 0.1uF) becomes 100nF. The
use of dot decimal places is not eliminated, but is substantially reduced.
(Yes, I know, for the purist it should be 47 nF (ie with a space), but that
often looks peculiar in non-proportional pitch.

Those who balk at nanofarads should consider it wasn't long ago that 
"puffs" were given as uuF, eg 47uuF.

ps  Another barbarity is to use pf and uf instead of pF and uF...

henry@utzoo.uucp (Henry Spencer) (08/23/89)

In article <26043@quacky.mips.COM> vaso@mips.COM (Vaso Bovan) writes:
>(Yes, I know, for the purist it should be 47 nF (ie with a space), but that
>often looks peculiar in non-proportional pitch.

Actually, for the purist it should be not a whole space but a narrow space;
troff "\|" is suitable.  But when reproducing that on a fixed-pitch device,
leaving out the space is probably better than widening it.
-- 
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

roy@phri.UUCP (Roy Smith) (08/24/89)

In article <26043@quacky.mips.COM> vaso@mips.COM (Vaso Bovan) writes:
> In conformance with good S.I. practice, the "nanofarad" is coming into wide
> usage. (European schematics have long used nanofarads).

	I remember once seing a (hand-drawn) schematic with a 10 nF cap on
it.  I was so convinced it was a mistake I tracked down the engineer who
drew it, had him dig out his copies, and confirm that, yes indeed, he meant
nanofarads.  That was, I think, about 7-8 years ago, and no, it wasn't a
european design.  But I do agree that nF should be a perfectly reasonable
unit and should be in general use.  Same goes for mF for milifarads.  I
will object, however, to centifarads and decifarads.

> Those who balk at nanofarads should consider it wasn't long ago that 
> "puffs" were given as uuF, eg 47uuF.

	Not to mention the even older MF and MMF for microfarads and
micromicrofarads.  BTW, is there any standardized rule which says u is for
micro.  The correct prefix is the greek mu, but since that's not an ascii
character, everybody uses the latin u, which looks similar.
-- 
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu
"The connector is the network"

scott@perle.UUCP (Scott Allen) (08/25/89)

In article <26043@quacky.mips.COM> vaso@mips.COM (Vaso Bovan) writes:
>This is a plea to rationalize capacitor unit suffixes. Most postings
>give capacitances in terms of pF or uF. Unfortunately, this often means
>capacitances are are stated in inconvenient units. ie caps with the following
>units are given 4700pF ; .0047uF ; .001uF !  It is a nuisance to have to count
>the decimal places, but there is at least one situation where the "dot"
>placement can actually cause mistakes: In photocopying schematics, "dots" are
>added and taken away at random. 0.01uF might easily be mistaken for .001uF.
>
[Remainder of article deleted]

I have often seen resistor values given by using the metric units
prefix in place of the decimal point. e.g: 4.7K ohms is given
as 4K7, 54.9Meg ohms is given as 54M9.

Could we not do the same with capacitors (or any other component)?
In the above examples: 4700pF = 4700p, .0047uF = u0047, .001uF = u001
The 'F' can be dropped as long as we know that it is a capacitor,
unless we want to give the value as a fraction of a Farad.
In this case an F is used in place of the decimal point: .01F = F01

-- 
========= *         Scott Allen          * UUCP:
P E R L E *      Perle Systems Ltd.      *  ...!uunet!mnetor!perle!scott
========= * Scarborough, Ontario, Canada *

bill@flash.UUCP (William Swan) (08/26/89)

In article <698@perle.UUCP> scott@perle.UUCP (Scott Allen) writes:
}I have often seen resistor values given by using the metric units
}prefix in place of the decimal point. e.g: 4.7K ohms is given
}as 4K7, 54.9Meg ohms is given as 54M9.
}
}Could we not do the same with capacitors (or any other component)?
}In the above examples: 4700pF = 4700p, .0047uF = u0047, .001uF = u001

It's already being done by at least one surface-mount cap manufacturer.
I was verifying some components for a prototype a couple days ago, and
found them marked in just ths fashion.


-- 
Bill Swan  entropy.ms.washington.edu!sigma!bill  Send postal address for info:
	Innocent but in prison in Washington State for 13.5 years:
	Ms. Debbie Runyan: incarcerated 01/1989, scheduled release 07/2002.
	                   In now:  0 years,  7 months,  0 weeks,  5 days.

ingoldsb@ctycal.COM (Terry Ingoldsby) (08/26/89)

In article <26043@quacky.mips.COM>, vaso@mips.COM (Vaso Bovan) writes:
> This is a plea to rationalize capacitor unit suffixes. Most postings
> give capacitances in terms of pF or uF. Unfortunately, this often means
...
> In conformance with good S.I. practice, the "nanofarad" is coming into wide
Another useful convention is to put the SI prefix where the decimal point
should go in resistor ratings (is it also used for caps?).

Eg.
  4.7 ohms   =   4R7
  4.7 K      =   4K7
  4.7 M      =   4M7

This is very useful when schematics are faded (ie. photocopied).




-- 
  Terry Ingoldsby                       ctycal!ingoldsb@calgary.UUCP
  Land Information Systems                           or
  The City of Calgary         ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb