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'[EE] Metric units'
2006\02\16@114022 by Timothy Weber

face picon face
[changed the subject line from 'Linear power supply blowing it's diodes']

Gerhard Fiedler wrote:
>
> And believe me, the USA /is/ going metric. The sooner it gets there, the
> easier it will be. It's just a matter of time, and the longer that twilight
> zone lasts, the worse.

You know, since the last discussion here about metric in the USA, I
resolved to be more diligent about using metric whenever possible.

Then I tried to order some hardware online.  I believe I already had
some metric standoffs that were exactly as long as I wanted them to be
for a project; all the ones I could find measured in inches were a
little too short or a little too long.  Now I just wanted some nuts and
bolts to fit them.

Well... it was a long search... I'm sure it could have been longer, and
they're out there somewhere, but I just couldn't find any metric nuts
and bolts!

This probably has more to do with me trying to buy hardware from
electronics places, to combine with other orders and save on shipping,
than anything else.  But I eventually redesigned the project so it would
fit with English standoffs and bought a pile of 4-40 screw hardware.

I thought it was an interesting data point.
--
Timothy J. Weber
http://timothyweber.org

2006\02\16@124649 by Rob Robson

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face
> Well... it was a long search... I'm sure it could have been longer, and
> they're out there somewhere, but I just couldn't find any metric nuts
> and bolts!
>

There are metric nuts and bolts in the Digi-Key catalogue, but I'm not sure
who pays the tax on them.

RR


2006\02\16@125724 by peiserma

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piclist-bounces@mit.edu wrote:
> Well... it was a long search... I'm sure it could have been
> longer, and they're out there somewhere, but I just couldn't
> find any metric nuts and bolts!

<http://www.fastenal.com/web/home.ex>

they may even have a store near you.

2006\02\16@133654 by Gerhard Fiedler

picon face
Timothy Weber wrote:

> Gerhard Fiedler wrote:
>>
>> And believe me, the USA /is/ going metric. The sooner it gets there, the
>> easier it will be. It's just a matter of time, and the longer that twilight
>> zone lasts, the worse.
>
> You know, since the last discussion here about metric in the USA, I
> resolved to be more diligent about using metric whenever possible.
>
> Then I tried to order some hardware online. [...] Well... it was a long
> search...

I know; there doesn't seem to be the same variety on the market for metric
hardware. Given the simple fact that most of the US automotive industry is
already metric, this is strange. (But most of the US automotive
/aftermarket/ industry uses imperial hardware... go figure :)  Maybe asking
for it at your preferred distributors and manufacturers tells them that the
time is ripe to stock some metric stuff.

OTOH, when I google for 'metric hardware online' a number of promising
links come up. Maryland Metrics is one that seems to have quite a
selection, but I find their site confusing. As always, McMaster-Carr has of
course quite a bit :)


I've also been involved recently with some mechanic work in the USA, and
the people who do it seem to mostly basically refuse to work in metric
units.

I still stand by my opinion that attitudes like this are just prolonging
the confusion with the dual system while not avoiding the inevitable move
to metric.

Gerhard

2006\02\16@142129 by Timothy Weber

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Rob Robson wrote:
> There are metric nuts and bolts in the Digi-Key catalogue, but I'm not sure
> who pays the tax on them.

Sure enough, they do have some.  I guess I wasn't using the right search
terms - or maybe I wasn't doing a Digi-Key order for anything else at
that point and it seemed silly to pay $5 handling + shipping for a dozen
nuts and bolts.

spam_OUTpeisermaTakeThisOuTspamridgid.com wrote:
> <http://www.fastenal.com/web/home.ex>
>
> they may even have a store near you.

Weird - they do!  It's all of 9 blocks away, though; don't know if I can
walk *that* far.  ;)  Thanks!

So maybe this is more about my poor Googling skills than anything else.
 But I guess my point was that whatever electronics parts store I was
already ordering from that time *did* have the equivalent Imperial
parts.  As well as lots of other kinds of standoffs, spacers, etc. that
I can get with 4-40 thread.

and Gerhard Fiedler wrote:
> I've also been involved recently with some mechanic work in the USA, and
> the people who do it seem to mostly basically refuse to work in metric
> units.
>
> I still stand by my opinion that attitudes like this are just prolonging
> the confusion with the dual system while not avoiding the inevitable move
> to metric.

I agree, if it's just "No, we don't do that here," that's silly.
--
Timothy J. Weber
http://timothyweber.org

2006\02\16@151522 by Danny Sauer

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face
Gerhard wrote regarding 'Re: [EE] Metric units' on Thu, Feb 16 at 12:40:
> hardware. Given the simple fact that most of the US automotive industry is
> already metric, this is strange. (But most of the US automotive
> /aftermarket/ industry uses imperial hardware... go figure :)

People that work on their own cars and need to buy hardware are
usually working on older stuff - which is still at least patially
imperial, wheras the dealer doesn't need generic hardware.  At least,
that's my crummy theory...

> I still stand by my opinion that attitudes like this are just prolonging
> the confusion with the dual system while not avoiding the inevitable move
> to metric.

Bah, if we hold out long enough, this metric "fad" will eventually
fade away.  I'm sure of it. :)

--Danny, annoyed at the need to own duplicate sets of wrenches and
sockets in various depths and configurations

2006\02\17@070042 by Gerhard Fiedler

picon face
William ChopsWestfield wrote in the thread "[EE] Linear power supply
blowing it's diodes":

> except that few typewriters have proper greek "mu" characters,
> so mF has been used to mean "microfarads" at various times

Specs written against typewriter limitations can (and should) be corrected
when transformed into electronic media (and that's what /we/ are using
here).

>From the beginning (and that's been ages) 'm' has been short for 'milli'.
Whoever used that for 'micro' doesn't really care much about unambiguity.
The much more common 'u' for 'micro' is less prone to error. (Of course, if
more of the in English-speaking countries common email clients understood
Unicode and the charset headers and dealt with them properly, at least in
email we wouldn't have to resort to that sort of thing. And once you start
talking about atoms, the 'u' for 'micro' is not a good thing anymore. But
that doesn't make the 'm' a better choice.)

The same argument could be made against the use of 'M' for 'mega' and 'm'
for 'milli' -- several people have used 'm' for mega and 'M' for milli, not
because of typewriter or ASCII limitations, but because of simple "I don't
care about standards" attitude. This practice doesn't seem to cause a
feeling that these letters are not good to be used.

It's just as simple as that... you want to be understood, you should use
the proper units. And that's not just the ramblings of a (to the US)
foreigner -- the US government has a rather good guide for the proper use
of units:

http://physics.nist.gov/cuu/Units/
http://physics.nist.gov/Pubs/SP811/contents.html

The style rules are not just for sissies. They are the result of many
people thinking and discussing about avoiding ambiguities. And as always,
this standard may take this to an extreme that's not necessary in everyday
communication, but knowing about it is definitely an enhancement.


> becides, this was 0.1F, so why not 1 dF or 10 cF

Entirely possible, even though it may look strange. As long as you write
your quantities correctly, anybody (with a minimum of a technical
background) should be able to understand it. I'd rather read a technical
spec with unusual but correctly written quantities than one with more or
less commonly used wrong spellings (like 'ma' or 'MA' for 'milliampere' or
the 'mF' for 'microfarad' you mentioned).


The one thing I wonder about this is why it's only in the US that this
seems to be a problem. I've seen no other country that has this sort of
desperate reluctance to standardize, and these discussions about whether or
not it's a good idea to use 'm' for 'milli' seem to pop up mainly in the
US. (This is not an attack against the USA, this is just an observation.
People seem to have a different attitude towards standards that make
sense...) But then, the inch is standardized on the international
definition of the meter, for a century or longer now (which probably few
know), so as long as it's hidden, it's accepted :)

Gerhard

2006\02\17@090119 by Alan B. Pearce

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>>From the beginning (and that's been ages)
>>'m' has been short for 'milli'.

>Whoever used that for 'micro' doesn't really care
>much about unambiguity. The much more common 'u'
>for 'micro' is less prone to error.

Agreed, and that is my preferential usage as well, when using normal ASCII
characters.

>The same argument could be made against the use
>of 'M' for 'mega' and 'm' for 'milli' -- several
>people have used 'm' for mega and 'M' for milli,

It has not been a problem until the last couple of decades, as the unit that
'm' or 'M' is being used for is normally ascertainable by simple inspection.
I would hate to see a Megahenry inductor - if an 'm' or 'M' is used, then it
would be reasonable to expect it to be millihenry.

In capacitors it is only (relatively) recently that capacitor values have
climbed to the millifarad range, so the use of 'm' could reasonably have
been taken to be microfarad.

the use of 'm' or 'M' when dealing with resistors again can normally put one
in the correct range by inspection, although again it is only since
semiconductors started doing "real" power things in the 60's and later that
milliohm resistors really got used.

The use of 'm' and 'M' for measuring current could also be confusing, except
that for most people if there is a current of Megamps flowing, then
milliamps are of no interest as it would be down in the leakage current
noise level, and if milliamps is your normal current, then if there are
Megamps around, you are in big strife. The number of people who would use
the two extremes will be very small, and I suspect these people will be very
well versed in using the correct prefix.

2006\02\17@090757 by Danny Sauer

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Gerhard wrote regarding '[EE] Metric units' on Fri, Feb 17 at 06:06:
[...]
> The one thing I wonder about this is why it's only in the US that
> this seems to be a problem. I've seen no other country that has this
> sort of desperate reluctance to standardize, and these discussions
> about whether or not it's a good idea to use 'm' for 'milli' seem to
> pop up mainly in the US.

Who argues that?  Doesn't everyone use m for milli (except those
idiots who type in all caps, all the time)?  For what it's worth, it's
never even occurred to me to read mF as microfarads, or to type it as
anything but uF - and I've never been outside of the USA.  Or rather,
the closest I've been is driving through the Florida Keys, and those
bridges are still in the USA.  Not that there's any reason to write
one millifarad as anything other than "1000 uF" anyway, considering
the units those devices are usually marked with... :)  May as well use
roman numerals, too, so there's no obvious way to tell if the author
means one thousand or ten thousand.  M MF.  Just look at how
beautifully concise that is!

Using whatever abbrev. for for micro one wants is fine - in one's own
notes.  If trying to communicate, though, it would do one well to
remember that standards are standards for a reason.  The main reason
is the enablement of effective communication.

--Danny, avoiding "FWIW" because it's not a well-known standard :(

2006\02\17@093344 by peiserma

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piclist-bounces@mit.edu wrote:
>>> From the beginning (and that's been ages) 'm' has been short for
>>> 'milli'.
>
>> Whoever used that for 'micro' doesn't really care much about
>> unambiguity. The much more common 'u'
>> for 'micro' is less prone to error.
>
> Agreed, and that is my preferential usage as well, when using normal
> ASCII characters.

and then there are wonderfully braindead software packages (like mine)
that force you to use capital letter when assigning attributes to
components.

For example, if I want an attribute on a capacitor called "power rating"
I cannot say "250 mW" because it WONT LET ME USE LOWER CASE.

same with caps, I can't write "100 pF", but have to write "100 PF"

There's a way around it, but its tedious, so I just resign myself to
saying "1/4 W"

2006\02\17@110908 by w d myrick

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Danny,  Sixty years ago mF was always micro microfarads.
I think that all usage today comes from that.  This  I think
came about like conventional current flow, a guess
as to what to use and was wrong.  when you use it for 40
to 50 years it is hard to change.  The person who uses all caps
is about as bad as one who uses all lower case.

Derward

<snip>


> Using whatever abbrev. for for micro one wants is fine - in one's own
> notes.  If trying to communicate, though, it would do one well to
> remember that standards are standards for a reason.  The main reason
> is the enablement of effective communication.
>
> --Danny, avoiding "FWIW" because it's not a well-known standard :(
> --

2006\02\17@111420 by w d myrick

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Danny,  I had an error  it was microfarads not micro microfarads.

Derward  

<snip>

2006\02\17@151433 by Gerhard Fiedler

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Danny Sauer wrote:

> Who argues that?  Doesn't everyone use m for milli (except those
> idiots who type in all caps, all the time)?  

It seems you haven't read all the responses here... I responded to a post
questioning the understandability of mF as millifarad due to different uses
for 'm' in (apparently ancient) US history -- when 'm' was meant to be
(sometimes) 'micro' and 'mm' could have been 'pico'...

Gerhard

2006\02\17@152443 by Gerhard Fiedler

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w d myrick wrote:

> Danny,  Sixty years ago mF was always micro microfarads. I think that all
> usage today comes from that.  This  I think came about like conventional
> current flow, a guess as to what to use and was wrong.  when you use it
> for 40 to 50 years it is hard to change.  

That's true, and exactly my point: the longer it takes, the harder it gets.

There's been a pretty good standard in use for about 50 years, adopted by
the US in the seventies -- that's 30 years now. It was less hard to change
back then... :)

Gerhard

2006\02\17@155053 by William Chops Westfield

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On Feb 17, 2006, at 4:00 AM, Gerhard Fiedler wrote:

> you want to be understood, you should use the proper units.

So you should NEVER use a micro prefix in electronic media unless
you're certain both your software and the audience's software can
properly represent and present a greek mu?   That doesn't mean using
a mu that some random software vendor stuck in a an unused slot of
a common font, either.  It's got to be something standardized.
(unicode is probably OK.  How widely implemented IS unicode?  I
thought it also go stuck behind the "it's so much easier to use
vendor-defined fonts" trap...)

> The one thing I wonder about this is why it's only in the US
> that this seems to be a problem.

Probably because the US was generating reams of printed schematics
back before whatever metrification we've done, with no mu's on our
typewriters, back when "m" was no more ambiguous than "u" is now...

BillW

2006\02\17@160952 by David VanHorn

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>
> Probably because the US was generating reams of printed schematics
> back before whatever metrification we've done, with no mu's on our
> typewriters, back when "m" was no more ambiguous than "u" is now...


I do remember the days of CPS and mmF and mF, but now I think everyone uses
uF and pF and even nF

2006\02\17@173116 by Jinx

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> but now I think everyone uses uF and pF and even nF

You say "even" as though nF is not common. Perhaps not in US-
based usage (and I do tend to notice that in US schematics), but
for UK-based cultures it's been around for a long time. It's the
equivalent of the "k" bridge between units (ie pF) and mega (ie uF).
Once you get to using "n" on a regular basis it's not hard to tell at
a glance that 2n2 (and capacitors are often marked 2n2, or 222,
which is yet another convention) is 0.0022uF or 2200pF. Sometimes
usage depends on the context. For radio or HF work you might
find 2200pF is more appropriate than 2n2 if comparing caps in
parts of the circuit, eg 4700pF is easier to relate to 100pF without
that extra mental step

2006\02\17@183352 by William Chops Westfield

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On Feb 17, 2006, at 1:09 PM, David VanHorn wrote:

> I do remember the days of CPS and mmF and mF, but now I
> think everyone uses uF and pF and even nF...

I don't THINK that ANYONE is arguing that "mF" should be
(or is) widely used today.  It's just that it WAS used enough
in the past that its appearance in a schematic would introduce
some amount of ambiguity (especially since millifarads are so
uncommonly used, even in the relative rare circumstances where
they COULD be used.)

BillW

2006\02\17@185401 by Gerhard Fiedler

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William ChopsWestfield wrote:

>> you want to be understood, you should use the proper units.
>
> So you should NEVER use a micro prefix in electronic media unless you're
> certain both your software and the audience's software can properly
> represent and present a greek mu?   That doesn't mean using a mu that
> some random software vendor stuck in a an unused slot of a common font,
> either.  It's got to be something standardized. (unicode is probably OK.
>  How widely implemented IS unicode?  

I don't know about your work environment, but every current decent online
program understands Unicode. Its more common versions, in addition to a
number of 8-bit ISO fonts (not vendor-specific fonts), are in pretty
widespread use. The charset element of the Content-Type header is also
well-defined and understood by all decent and remotely current and
standard-conform browsers and email/newsreaders.

The Windows NT family of OSes understands Unicode, and so do most
applications running on it. I'm sure most decent Linux/Unix programs
understand it. Mainframe programs from the 60ies or 70ies or DOS WordStar
don't... Ever since I left Win 3.1 behind I've never had problems
exchanging texts with accented characters, or the Greek lowercase mu.
Again, this problem -- if it is really one -- seems to be restricted to the
USA (not sure about other English-speaking countries).

The common ISO fonts (ISO 8859) are well-defined. Even if some program
should not have support for the specific encoding being used, it is
possible to translate that easily into Unicode (if it's in some sort of
generic text format like XML or HTML).

So far my newsreader tells me that this message uses the us-ascii charset
(default), because I haven't yet used anything beyond 7-bit ASCII. Now I'll
insert that dreaded Greek lower case mu "µ" and the charset switched to
iso-8859-1 (could have been utf-8 or whatever; that's just the preference
of my newsreader, and it would switch to utf-8 if I inserted a character
that's not in iso-8859-1). This message will get sent out with the
Content-Type header set to something like "text/plain; charset=ISO-8859-1".
Every email and news client should be able to understand and display this
correctly; it's one of the more common standardized codepages. (It's not a
vendor standard, it's an ISO standard, and the Content-Type header is
clearly defined for ages in an RFC.) And if yours doesn't, you should
switch to one that does... IMO of course :)

And even if you have to stick to 7-bit ASCII for some reason, 'm' for
'micro' is simply a bad choice. I'm not sure what really is to discuss with
that... 'm' is 'milli'. That's one of the few universally known
conventions. Using 'm' for 'micro' is asking for communication trouble.


>> The one thing I wonder about this is why it's only in the US
>> that this seems to be a problem.
>
> Probably because the US was generating reams of printed schematics back
> before whatever metrification we've done, with no mu's on our
> typewriters, back when "m" was no more ambiguous than "u" is now...

I'm not so sure this argument makes sense. Where did the convention that
'micro' means 10^-6 come from? I'm pretty sure it came from the same place
the convention that 'milli' means 10^-3 came from. So whoever knew about
micro knew about milli (or could and should have known), and also that 'm'
was the agreed-upon abbreviation for 'milli'. Which made it pretty obvious
IMO that 'm' was, even at that time, a bad choice as abbreviation for
'micro'. If you cherish unambiguity, that is.

Also, the standards I'm talking about have been around for fifty years and
are officially adopted in the USA for at least thirty years. Still sticking
to what has been done 50 years ago... Most did switch to using
semiconductors in electronics by now, even though they did not show up in
the reams of schematics from "back then", from 50 years ago :)

Gerhard

2006\02\17@201729 by William Chops Westfield

face picon face

On Feb 17, 2006, at 3:53 PM, Gerhard Fiedler wrote:

> So whoever knew about micro knew about milli (or could and should have
> known), and also that 'm' was the agreed-upon abbreviation for
> 'milli'. Which made it pretty obvious IMO that 'm' was, even at that
> time, a bad choice as abbreviation for 'micro'.

Look, you're arguing about what things SHOULD be, and I'm just
trying to deal with the way they ARE.

Do a web search for "mf capacitor."  Restrict the search to your
favorite metric country if you want.  Check out how often it means
micro, and how often it means milli...

It doesn't matter what it should be.  It doesn't matter whose
fault it is.  "mF" *is* ambiguous.  Don't use it if you want to
be widely understood...

www.physics.ncsu.edu/courses/py208/208testsF98/208test2F98.html
www.engr.colostate.edu/~dga/mechatronics/lab_components.html
www.mhs-science.org.uk/U6/capacitor_exercise.htm
http://www.doctronics.co.uk/4015.htm
www.maplin.co.uk/searchpages/2200_MF_CAPACITOR.htm
http://symek.de/g/ifd970.html
http://www.walter-fendt.de/ph14e/osccirc.htm
www.kaut.de/pdf/Ersatz/SAP-KRV93EH-C.pdf
http://www.jencam.de/pdf/XC-ST50-Pixel.pdf
http://www.scantec.de/Whitepaper/TDK/embedded-modem-designs.pdf

(I especially like the examples from physics classes, where
the problems are not connected enough to reality to have much of a
clue whether the author mean milli or micro.  Sigh.)

BillW

2006\02\17@214141 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

>> So whoever knew about micro knew about milli (or could and should have
>> known), and also that 'm' was the agreed-upon abbreviation for
>> 'milli'. Which made it pretty obvious IMO that 'm' was, even at that
>> time, a bad choice as abbreviation for 'micro'.
>
> Look, you're arguing about what things SHOULD be, and I'm just
> trying to deal with the way they ARE.

No. I'm not saying how they should be, I'm saying how they are. You can
turn and twist that as you want, the international standard says that 'm'
/is/ 'milli', not that it should be 'milli'. The few who don't care about
international standards just don't make enough of a difference, especially
since they don't really care about communicating themselves (if they did,
they'd use standards :)


> Do a web search for "mf capacitor."  Restrict the search to your
> favorite metric country if you want.  Check out how often it means
> micro, and how often it means milli...

Search for 'mf kondensator' and set language to German. (Restricting to a
country, e.g. '.de' domains, doesn't help much, because what you get are
English texts from .de domain sites -- with the same problem.) I didn't do
an exhaustive search, but I didn't come up with much 'micro' hits (some,
but they were generally inconsistent anyway, like one who uses both mF and
uF for microfarad on the same page). What I found though are quite a number
of 'MF's that seem to mean microfarad. I guess this means that sellers
can't necessarily be trusted to be experts in what they are selling -- they
mostly are experts in how to make money out of it. I'm not sure I want to
start basing my spec nomenclature on 'commercial literature' of this sort.

There seems to be this problem that a few programs seem to insist in
displaying the 'µ' (lower case mu) as 'm' (instead of displaying a square
or whatever is displayed when the character can't be displayed). I don't
know which ones this are; this was claimed in a previous discussion here.
Anyway, to follow this logic, one also would have to stop speaking about
milliamperes, and assume that everything 'ma' or similar is meant to be
'microampere' (since it could be a properly written mu that got wrongly
converted to an 'm').

If one can't sensibly distinguish (abbreviated) millifarad from microfarad,
how can one distinguish milliampere from microampere? Or, the other way
'round, if one can distinguish milliampere from microampere, why can't one
distinguish millifarad from microfarad? It is correct that capacitors in mF
ranges (or F ranges) were rare twenty (or fifty) years ago, but so were
SOIC cases. I just use them, and call them what they are.

Gerhard

2006\02\18@060833 by Howard Winter

face
flavicon
picon face
Bill,

On Fri, 17 Feb 2006 17:17:26 -0800, William "Chops" Westfield wrote:

>...
> Do a web search for "mf capacitor."  Restrict the search to your
> favorite metric country if you want.  Check out how often it means
> micro, and how often it means milli...
>...
>... http://www.maplin.co.uk/searchpages/2200_MF_CAPACITOR.htm

This one's a bit unfair - it's a search-result screen, where someone searched the Maplin site for 2200 MF
CAPACITOR, and didn't find any exact matches, so it's showing a near-miss that doesn't contain "MF" - that
hardly counts as a hit!  I'm not even sure they would have used capitals - the search engine may have
capitalised it.

And I've just tried a UK-Google search for "mf capacitor" and found that it gives hits where the mu character
is used, as if someone at Google has decided that "m" a synonym for mu, so I'm not sure how valid is your
assertion above.

Personally I've never seen mF used for microfarads in Britain - if the mu character isn't available the
convention is to use u.  I wonder why this hasn't been made a more formal standard, since it's the only
non-typewriter character that's used as a scaling factor - you can go all the way from a to T (what comes
after Tera?) with only mu being the odd one out.

Cheers,


Howard Winter
St.Albans, England


2006\02\18@064450 by Jinx

face picon face
(what comes after Tera?)

http://math.ucr.edu/home/baez/physics/Administrivia/notation.html

Bottom of page

2006\02\18@090918 by Howard Winter

face
flavicon
picon face
Jinx,

On Sun, 19 Feb 2006 00:44:49 +1300, Jinx wrote:

> (what comes after Tera?)
>
> math.ucr.edu/home/baez/physics/Administrivia/notation.html
>
> Bottom of page

Thanks for that, and sorry for being too busy (lazy?) to look them up myself.  Interesting that I could
remember femto and atto (1964) but not Peta and Exa (1975).  I think I probably learned them in about 1972!

But it does show two anomalies that annoy me:  the single exception to the typewriter-characters that I
mentioned (mu), and the fact that "k" really ought to be "K" to indicate that its greater than one.  I ignore
the non-3 powers (c, d, D, h) because I think they're unnecessary, so other than k the lower case letters are
less than one and the capitals are greater.  I can easily go from millimetres to metres with no need for
centimetres!  In fact I've just realised that I do - I just checked a tape-measure and it's marked in cm with
mm divisions, but I always "read" it in mm.  

Incidentally, do you use feet and inches down under?  We still use both somewhat (clothes sizes are in inches,
timber is in mm but using close approximations to the actual inch sizes so floorboards are 19x144, not 20x150)
and rulers and tape-measures have both.  I was a tad suprised that in the US tape measures only have inches -
I thought they'd have both since they are "in the process of metrication", at least officially.

Cheers,


Howard Winter
St.Albans, England


2006\02\18@143548 by Bob Barr

flavicon
face
On Sat, 18 Feb 2006 14:09:15 +0000 (GMT), "Howard Winter" wrote:

<snip>

>  I was a tad suprised that in the US tape measures only have inches -
>I thought they'd have both since they are "in the process of metrication", at least officially.
>

Oh, we're inching our way toward the metric system but we've got many
yards. perhaps miles, to go. :=)


Regards, Bob

2006\02\18@150221 by Dwayne Reid

flavicon
face
At 07:41 PM 2/17/2006, Gerhard Fiedler wrote:

>If one can't sensibly distinguish (abbreviated) millifarad from microfarad,
>how can one distinguish milliampere from microampere? Or, the other way
>'round, if one can distinguish milliampere from microampere, why can't one
>distinguish millifarad from microfarad? It is correct that capacitors in mF
>ranges (or F ranges) were rare twenty (or fifty) years ago, but so were
>SOIC cases. I just use them, and call them what they are.

Some of the (really) old schematics I used to deal with were pretty
consistent:  they contained both "mf" and "mmf" designations.  But I
don't remember that usage continuing past the mid 1960's.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam@spam@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2006\02\18@161141 by William Chops Westfield

face picon face

On Feb 18, 2006, at 3:08 AM, Howard Winter wrote:

>> ... http://www.maplin.co.uk/searchpages/2200_MF_CAPACITOR.htm
>
> This one's a bit unfair

Oops.  I meant to remove that one...


> And I've just tried a UK-Google search for "mf capacitor" and
> found that it gives hits where the mu character is used

Yes, especially in PDF files,  but not all of them, and I tried
not to include any of those in the examples I quoted.

A number of the examples I found were in media where mu might
be unavailable: usenet, assorted online forums, etc.  Still, I
stand by my point: regardless of whether mF is technically
ambiguous, it has become linguisticly ambiguous...

BillW

2006\02\18@164643 by Jinx

face picon face
> it's marked in cm with mm divisions, but I always "read" it in mm

I think the only time I ever hear centimetres any more is in "the man
is described as stocky, 178cm tall and police say he should not be
approached". At one time they'd helpfully include "that's 5'10". I
can imagine 5'10" tall - I can't do 178cm

> Incidentally, do you use feet and inches down under?

Hmmm, "down under". Now there's somewhere that centimteres
sound so much more impressive

Well, people still say "mileage" (but not mpg - it's litres/100km). Don't
think "kilometreage" will ever catch on. "Six feet under" ? In general
NZ uses metric but I still keep a 10ths ruler handy for PCBs

> timber is in mm but using close approximations to the actual inch
> sizes so floorboards are 19x144, not 20x150)

I can still ask for and get 2 x 4 timber or an 8 x 4 panel (although
the assistant will invariably tell me that it's 2440 x 1220)

> and rulers and tape-measures have both.  I was a tad suprised
> that in the US tape measures only have inches - I thought they'd
> have both since they are "in the process of metrication", at least
> officially

My mother had a dress-making tape with both and that was bought
in the UK in the late 60s, just pre-dismalisation

I have a couple of steel rulers with 64ths, but use them only for
comparison measurements. That could be part of the problem.
An imperial ruler might have 5ths (you've reminded me of a
wooden ruler we used at school that had 5ths, aaah happy days),
10ths, 8ths, 16ths and so on. At least in mm you're going to be
using the same units as everyone else

2006\02\18@170330 by Jinx

face picon face
> "k" really ought to be "K" to indicate that its greater than one

Presumably K(elvin) and H(enry) were taken first and/or decided
upon as SI units, bumping the lesser uses down to k and h

http://en.wikipedia.org/wiki/Kelvin

http://en.wikipedia.org/wiki/Henry_%28inductance%29

http://en.wikipedia.org/wiki/SI

"The one exception is the litre, whose original symbol "l" is dangerously
similar to the numeral "1". The NIST recommends that "L" be used instead,
a usage which is common in the U.S., Canada and Australia, and has been
accepted as an alternative by the CGPM"

Don't know if I could ever get used to "L" for litre. Just looks too....big.
But I might get used to it quicker than GM for g on a box of cornflakes


2006\02\18@171838 by Gerhard Fiedler

picon face
Jinx wrote:

> (what comes after Tera?)
>
> math.ucr.edu/home/baez/physics/Administrivia/notation.html
>
> Bottom of page

This table shows what comes after tera, but WRT the one-letter symbol it's
a bit odd: suggesting 'm' for both milli and micro doesn't work well. It's
also not the standard, even though it's a university site. Even the
non-technical and non-scientific Wikipedia is smarter here:
http://en.wikipedia.org/wiki/Micro

And whoever thinks that in the 50ies or 60ies the use of 'm' for 'micro'
was understandable because 'milli' was not yet around should look at this:
http://en.wikipedia.org/wiki/Milli -- they claim that 'milli' was adopted
in 1795 :)  Not sure this really holds true, but it definitely is older
that most of us here.

Gerhard

2006\02\18@173007 by Jinx

face picon face
> http://math.ucr.edu/home/baez/physics/Administrivia/notation.html

> This table shows what comes after tera, but WRT the one-letter
> symbol it's a bit odd: suggesting 'm' for both milli and micro doesn't
> work well. It's also not the standard

I don't see any suggestion there of using m for milli and micro. I see

milli      10^-3    m                 milliampere    mille, thousand in
Latin
micro      10^-6    m (Greek mu)      microohm       mikros, small in Greek

2006\02\18@173141 by Jinx

face picon face
Howard, I wrote

> Presumably K(elvin) and H(enry) were taken first and/or decided
> upon as SI units, bumping the lesser uses down to k and h

I have never used the phrase "k and h" ever, and can't believe I
didn't manage to work in something from "Being For The Benefit
Of Mr Kite"

"Messers K. and H. assure the public
their production will be second to none"

2006\02\18@174121 by Jinx

face picon face
>> suggesting 'm' for both milli and micro doesn't work well

> milli      10^-3    m
> micro      10^-6    m (Greek mu)

Gerhard, I will backtrack on what I said. A bit. On the web page
and what I copied/pasted I see the "mu" character. In the sent mail
it has changed to "m". You must have seen "m" in your browser. In
the source for that page

<FONT FACE="Symbol">m</FONT> (Greek mu)

2006\02\18@213038 by Peter Todd

picon face
On Fri, Feb 17, 2006 at 09:53:50PM -0200, Gerhard Fiedler wrote:
> I don't know about your work environment, but every current decent online
> program understands Unicode. Its more common versions, in addition to a
> number of 8-bit ISO fonts (not vendor-specific fonts), are in pretty
> widespread use. The charset element of the Content-Type header is also
> well-defined and understood by all decent and remotely current and
> standard-conform browsers and email/newsreaders.
>
> The Windows NT family of OSes understands Unicode, and so do most
> applications running on it. I'm sure most decent Linux/Unix programs
> understand it. Mainframe programs from the 60ies or 70ies or DOS WordStar
> don't... Ever since I left Win 3.1 behind I've never had problems
> exchanging texts with accented characters, or the Greek lowercase mu.
> Again, this problem -- if it is really one -- seems to be restricted to the
> USA (not sure about other English-speaking countries).
>
> The common ISO fonts (ISO 8859) are well-defined. Even if some program
> should not have support for the specific encoding being used, it is
> possible to translate that easily into Unicode (if it's in some sort of
> generic text format like XML or HTML).

Wikpedia makes extensive use of unicode in it's entries involving
foreign languages and the like. Being a wikipedia addict I've used it on
all sorts of modernish computers in many environments while I've been
procrastinating. I can say I rarely see computers that don't display
almost everything correctly.  Some really obscure parts of unicode may
break, like oddball multi-character entities used for some Arab
languages, but for the most part everything just works.


It's a major, major change from just a few years ago. So older computers
will probably fail, but anything shipped in the past 3-4 years will
probably be just fine.

> So far my newsreader tells me that this message uses the us-ascii charset
> (default), because I haven't yet used anything beyond 7-bit ASCII. Now I'll
> insert that dreaded Greek lower case mu "µ" and the charset switched to

Datapoint: That µ turns up just fine in my default Linux console...

--
petespamKILLspampetertodd.ca http://www.petertodd.ca

2006\02\18@215949 by William Chops Westfield

face picon face
> ...but every current decent online program understands Unicode.

Hmm.  Anyone know how to enter a 'mu' in an Eagle component value?

BillW

2006\02\18@221250 by Peter Todd

picon face
On Sat, Feb 18, 2006 at 06:59:47PM -0800, William Chops Westfield wrote:
> > ...but every current decent online program understands Unicode.
>
> Hmm.  Anyone know how to enter a 'mu' in an Eagle component value?

Have you tried cut-n-paste from another application? I just tried it on
my copy of eagle on Linux, and it worked. Same way I can enter in this µ

Do that enough and one single µ will have quite the family of
descendents...

--
.....peteKILLspamspam.....petertodd.ca http://www.petertodd.ca

2006\02\19@073709 by Russell McMahon

face
flavicon
face
> But I might get used to it quicker than GM for g on a box of
> cornflakes

No no no !
That means the corn has been genetically modified.
(Most has these days - even if they don't label it with GM. Or, more
correctly, most batches of corn you buy will have some GM content).



       RM

2006\02\19@085908 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

>> ...but every current decent online program understands Unicode.
>
> Hmm.  Anyone know how to enter a 'mu' in an Eagle component value?

This is platform-specific (and also to some degree program-specific, as
there are some programs that provide additional UI features, to the ones
the platform provides.)

I could tell you how to do that on a recent Windows system (there are a
number of different ways), but your headers tell me you are using Apple.

Gerhard

2006\02\19@090532 by Gerhard Fiedler

picon face
Jinx wrote:

>>> suggesting 'm' for both milli and micro doesn't work well
>
>> milli      10^-3    m
>> micro      10^-6    m (Greek mu)
>
> Gerhard, I will backtrack on what I said. A bit. On the web page
> and what I copied/pasted I see the "mu" character. In the sent mail
> it has changed to "m". You must have seen "m" in your browser. In
> the source for that page
>
> <FONT FACE="Symbol">m</FONT> (Greek mu)

Here we go... this is non-standard HTML. It is relying on platform-specific
(Windows in this case) non-standard fonts.

Of the three browsers I have available (on WinXP), IE and Mozilla use the
specified platform-specific font to display the intended mu, whereas Opera
doesn't use the font specification and displays an m instead. I used
Opera... :)

The proper way to program this in HTML would be to simply use the
appropriate entity "&mu;" instead of the sequence "<FONT
FACE="Symbol">m</FONT>". This is not platform-specific and would work
across (standard-compliant) browsers and platforms -- and be correct HTML.


Come to think of it, it may be that the unlucky use of the Symbol font is
the source of many intended 'mu's appearing as 'm's. Just don't use it if
you want to share your documents. It's a left-over from the early 80ies and
before, when Unicode wasn't widely available. Want to insert a mu into a
Word (or other) document? Use the appropriate character from the standard
(Unicode) font you are already using, not the one from the Symbol font. If
the font you're using doesn't have a mu (AFAIK that's rare), use another
Unicode font that has it. Don't use the Symbol font...


As usual, the problem lies with too many programmers and documenters not
being aware of 'i18n', the existence of various platforms and related
problems. ('i18n' is short for 'internationalization', coming from the Java
camp AFAIK. The '18' symbolizes the 18 left-out letters.) Many just don't
care enough to get familiar with these issues on their own and only do it
when forced.

"Don't ever use anything platform-specific on a public web site. Use
standard HTML whenever possible." These are two basic web design rules, and
whoever wrote this page never heard of them. I would expect a little more
diligence from somebody writing a manual about of all things notation in
scientific online publications.


Just for fun (and some education), look at the w3.org validator output for
this page:
<http://validator.w3.org/check?uri=http%3A%2F%2Fmath.ucr.edu%2Fhome%2Fbaez%2Fphysics%2FAdministrivia%2Fnotation.html>

(Long link, you may have to recompose it.)

- The first comment is "No Character Encoding Found! Falling back to
UTF-8." A clear indication that the author didn't care about any font
encoding questions. If it were meant to be utf-8, there would have been no
need to use the Symbol font in the first place.
- The second comment is "No DOCTYPE found". A clear indication that the
author didn't care about HTML standard compliance. Adding the appropriate
DOCTYPE to define what kind of document you're writing is the first thing
you do when creating a standard-compliant HTML document.
- The error 2 shows a second problem with the way they want to display the
mu: the font tag is not allowed where they used it. (The validator doesn't
know about the characteristics of the Symbol font, so it doesn't say that
it's a bad thing. It doesn't check these things; it only checks for HTML
compliance.)

Concluding... a completely screwed-up page that should have never passed a
minimum of quality assurance :)


For a counter-example, run http://en.wikipedia.org/wiki/Unicode through the
above validator... The page starts with a proper !DOCTYPE tag, and has as
first header tag the Content-Type definition "<meta
http-equiv="Content-Type" content="text/html; charset=utf-8" />". This is
one of the reasons why it works here... It's not impossible; you just have
to care about it.

Gerhard

2006\02\19@091734 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

> A number of the examples I found were in media where mu might be
> unavailable: usenet, assorted online forums, etc.  

Especially in those places, mu should be available. On the Internet, all
the necessary standards are in place for a long time to represent mu
correctly and platform-independently. Pretty much all web server script
languages have ready-made functions to convert user input into the
appropriate HTML entities. Character sets are well-defined, and so are the
ways to define which one is used. Browsers and newsreaders handle that and
display that correctly. It's only not available when there's a bug, or an
inept programmer :)


> Still, I stand by my point: regardless of whether mF is technically
> ambiguous, it has become linguisticly ambiguous...

If I understand you correctly, you make one point with two supporting
arguments. The point is that 'm' as multiplier should be avoided, for both
'milli' and 'micro'. The two arguments are:
1- Up until the 60ies, it was common in the US to use mF to mean
microfarad. Therefore mF is now ambiguous.
2- Some documenters and programmers don't know how to handle font and
encoding issues properly, so sometimes an 'm' appears where a mu was
intended to be.

I vote for discarding the first argument. This was just a very unlucky
non-standard use, and it's almost half a century behind us now. This
practice simply didn't make any sense back then, doesn't make any sense now
and people should be, if needed, forced to adapt. (You don't like
non-standard web sites that work only in IE on Windows, do you? I'm pretty
sure you prefer standard-compliant web sites that can be viewed properly on
a MacOS X system with Mozilla :)


The second argument doesn't affect only the question uF vs mF; it affects
all micro/milli quantities (and it affects the ohm, too: in one of the
links you collected, the Greek capital omega got shown as W -- resulting in
a 10 kW resistor... :)

So (if I discard the first argument) is the suggestion to never use the 'm'
multiplier again (as in mA, mH, mm, mV, and yes, mF) because it could be
mistaken for micro? In all these cases, both milli and micro are in ranges
generally used. In some, even mega is used occasionally, additionally
creating confusion due to people who seem to think that everything
technical is in capitals (or in lower case :).

So, I still ask: if you think it's linguistically not possible to
distinguish mF from uF properly, why is it possible to distinguish mA from
uA, mV from uV, mH from uH, mm from um?


BTW, in Germany, mF seems to be in widespread use (as millifarad, not as
microfarad). To find them, of course you need to look for texts in German,
not for English texts on .de domain sites :)

Gerhard

2006\02\19@110652 by olin piclist

face picon face
Gerhard Fiedler wrote:
> Especially in those places, mu should be available. On the Internet,
> all the necessary standards are in place for a long time to represent
> mu correctly and platform-independently. Pretty much all web server
> script languages have ready-made functions to convert user input into
> the appropriate HTML entities. Character sets are well-defined, and
> so are the ways to define which one is used. Browsers and newsreaders
> handle that and display that correctly. It's only not available when
> there's a bug, or an inept programmer :)

I've been watching this debate on the sidelines for a while, but you're
constant complaining about how everyone that doesn't follow the standards is
inept is getting me fed up enough to respond.

Most things that we have today evolved via a long list of individual
decisions that largely made sense *** at the time and context the decision
was made ***.  This process doesn't always lead to the optimal end result.
The end result is merely the result we ended up with, just like with
biological evolution.  And it's also not a final answer as things will
continue to evolve.  Just because it's not what we wish it were or because
we can imagine a better result doesn't make the individual decisions wrong
for the most part (this is not to say there aren't occasional bonehead
decisions along the way, but mostly that's not the case).

Look at the use of the metric system in the US.  I think a lot of people
would agree that metric is a better system on the whole and it would be a
benefit if everyone used it (the english system has some benefits too, but
let's stipulate metric is better for this discussion).  However, that
doesn't make it stupid to buy a set of english wrenches.  My first set of
tools were all english because my first car was a 1972 Ford Pinto which
required english tools.  I bought that car for a variety of reasons, and
whether it required english or metric tools wasn't on the list of criteria.
Meanwhile I have acquired metric equivalents of most dimensional tools
because occasionally I run into metric hardware.

Now think about a mechanic who has 1000s of $$ of english tools because
that's what was required for the cars he works on.  Along come cars with
metric hardware.  Is this guy going to be happy to go out and spend another
$1000 on metric tools?  No, but he'll probably do it while grumbling all the
time.  He probably buys only what he needs in metric.  He grew up with
english and probably thinks in inches and feet.  If he's going to build
something himself, it will probably be in english units.

What about people building a few things on the side in their basement?  They
have a large collection of english tools.  What kind of bolts and nuts do
you think they are going to buy when they get to the hardware store?  I do
this too.  I've got a good feeling what #4 or #10-32 or 1/4-20 machine screw
is.  Yes, I could convert that to metric and find an equivalent metric size,
but when I'm working on something in my basement why should I?  That's what
I grew up with, so that's what I think in, and converting requires more
mental work.  So what are the hardware stores going to stock?  Whatever
their customers demand, right?  So why should I buy a stock of metric
hardware when I've already got a nice stock of english hardware and it's
more available anyway?  (Actually metric hardware is available too, but not
quite as widespread as english.)

So who's doing anything stupid here?  Everybody is just doing what makes
more sense for them each little decision along the way.  Eventually things
will change as more and more stuff gets manufactured in volume using metric.
Cars are just about all metric now.  Kids newly learning auto mechanics will
probably be more exposed to metric and eventually there will be a generation
that thinks in metric because that's what they were exposed to when they
grew up.  It all takes time.  Just about all scientific work is done in
metric, most large industries are metric, the military is all metric,
electronic measurements have always been metric, there's just the minor
problem of 300 million people not having grown up that way.

If you were Outer Vulgaria and woke up at the end of world war II taking a
leap from ox carts to cars in a span of 5 years, it's no big deal to decide
to standardise "about that long" with a meter.  It's a lot more trouble for
a technologically advanced society like the US that already has an
entrenched system and existing infrastructure.

As for capacitance, I've never understood why that was the only value where
milli and nano were skipped.  When I grew up it was all micro or pico, with
pico sometimes called micro-micro.  Rarely I did see mF mean micro-farads,
but I haven't seen that for a very long time.  The old timers I dealt with
when I was learning only ever used micro and pico farads, but I grew up with
enough metric to think that was silly.  I make it a point to use milli and
nano farads whenever appropriate, partly because I've deliberately taught
myself to think that way and partly because I want to get the world used to
it.  I've only ever once run into a problem with this.  There is a 1mF
capacitor in the EasyProg, and the guy who put the kits together took that
to mean 1uF even though there were other caps labeled with uF and that I had
pointed that out to him ahead of time.  He had to retrofit a bunch of kits
with 1mF capacitors for free.  I think of this as one small victory, because
I doubt he's going to make that mistake again.

As for the mu symbol, I've looked upside down, inside out, and sideways at
my keyboard and I don't see one.  Yes, there may be a way to make a mu
symbol with a bunch of keystrokes, but I don't know that off the top of my
head and it would be too much hassle anyway.  Using "u" for mu is a well
accepted and very common practise.  I'm quite sure that when I write "22uF"
every last person reading this knows exactly what it means.  Yes there is of
course a unicode character for mu, and also in the iso-latin-whatever
character set.  But in reality if it's not ASCII it's either not safe or too
much of a hassle.

Unicode is a big pain in the butt because it takes 16 bits per character.
I've got a huge amount of software that uses 8 bits/character.  This means I
intend to ignore unicode to the largest extent possible.  It also means that
new software I write will not use unicode since it will be layered on many
existing utility routines that all use 8 bit characters.  And if I'm adding
to the utility routines, I'm going to stick to 8 bit characters because else
I couldn't make incremental changes.  So my software is going to use 8 bit
characters for a long time yet to come, hopefully that will be good enough
for as long as I'm around.  Since the iso-latin-whatever character set fits
in 8 bits and it's a superset of ASCII, and it contains all the character
that I know how to use, the really really good reason to switch to unicode
is just missing.  Maybe the coming economic pre-eminence of China will
change this.  When writing HTML and I think about it and I have time, I do
use the "&mu;" construct for mu.  That's OK since it's guaranteed to work in
all browsers (part of the HTML definition), I can remember it, and the
resulting file still uses 8 bit characters.

> You don't like non-standard web sites that work only in IE
> on Windows, do you?

Actually I couldn't care less since I use IE.  Again you are forgetting that
everyone makes individual decisions that are the best for them at the time.

> I'm pretty sure you prefer standard-compliant web sites that can
> be viewed properly on a MacOS X system with Mozilla :)

No, I don't give a crap as long as the web sites look right in *my* browser,
which happens to be MSIE.

However when I write web pages that I want a wide audience to see, I try to
stick to lowest level common HTML.  But that's because in that case it's in
my interest.

Again, my main point is that you are whining about people doing things
different from how collectively you think it should be done, but ignoring
what is in each individual person's best interest.  Yes, it might be good if
we could all suddenly use the same standard, but who's going to pay for
that, and why should I pay if I don't perceive the value to me outweighs my
cost?  Are you willing to go thru a few 100000 lines of my source code and
convert every last character reference to unicode?  I didn't think so, so
stop whining about it already and stop calling me inept for not doing it.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\19@121753 by Peter

picon face

On Sat, 18 Feb 2006, Dwayne Reid wrote:

> At 07:41 PM 2/17/2006, Gerhard Fiedler wrote:
>
>> If one can't sensibly distinguish (abbreviated) millifarad from microfarad,
>> how can one distinguish milliampere from microampere? Or, the other way
>> 'round, if one can distinguish milliampere from microampere, why can't one
>> distinguish millifarad from microfarad? It is correct that capacitors in mF
>> ranges (or F ranges) were rare twenty (or fifty) years ago, but so were
>> SOIC cases. I just use them, and call them what they are.
>
> Some of the (really) old schematics I used to deal with were pretty
> consistent:  they contained both "mf" and "mmf" designations.  But I don't
> remember that usage continuing past the mid 1960's.

But what is a 'cm' ? There used to be schematics with 'cm' units on
caps. What is a 'cm' ?

Peter

2006\02\19@124015 by Metis Adrastea

picon face
2006/2/19, Peter <EraseMEplpspam_OUTspamTakeThisOuTactcom.co.il>:
> But what is a 'cm' ? There used to be schematics with 'cm' units on
> caps. What is a 'cm' ?

maybe a centimeter?

--
He comentado ya que tengo un blog? O:-)
http://metisadrastea.blogspot.com/

2006\02\19@124610 by Tomas Larsson

flavicon
face

> But what is a 'cm' ? There used to be schematics with 'cm'
> units on caps. What is a 'cm' ?
>
> Peter
Centi-meters, the length of the cap? Lol.


2006\02\19@130553 by Spehro Pefhany

picon face
At 07:17 PM 2/19/2006 +0200, you wrote:

>On Sat, 18 Feb 2006, Dwayne Reid wrote:
>
> > At 07:41 PM 2/17/2006, Gerhard Fiedler wrote:
> >
> >> If one can't sensibly distinguish (abbreviated) millifarad from
> microfarad,
> >> how can one distinguish milliampere from microampere? Or, the other way
> >> 'round, if one can distinguish milliampere from microampere, why can't one
> >> distinguish millifarad from microfarad? It is correct that capacitors
> in mF
> >> ranges (or F ranges) were rare twenty (or fifty) years ago, but so were
> >> SOIC cases. I just use them, and call them what they are.
> >
> > Some of the (really) old schematics I used to deal with were pretty
> > consistent:  they contained both "mf" and "mmf" designations.  But I don't
> > remember that usage continuing past the mid 1960's.
>
>But what is a 'cm' ? There used to be schematics with 'cm' units on
>caps. What is a 'cm' ?

It *Italian*?

I'll take a WAG (helped a bit by a web search since I know about 15 words of
Italian, not including food-related terms) and say it's not units but
"motor run capacitor", "condensatore di marcia" or something like dat.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2006\02\19@134424 by Tomas Larsson

flavicon
face
Imperial is a pain in the arse, when it comes to PCB design.
It seems that most editors has imperial units as base units in the database,
and that creates round-off problem when working in metric.
Since most Chip manufacturers is moving from imperial to metric it creates a
problem.



With best regards

Tomas Larsson
Sweden
http://www.naks.mine.nu for downloads etc.
ftp://ktl.mine.nu for uploads. Or use the free http://www.yousendit.com service.

Verus Amicus Est Tamquam Alter Idem


2006\02\19@141026 by olin piclist

face picon face
Tomas Larsson wrote:
> Imperial is a pain in the arse, when it comes to PCB design.
> It seems that most editors has imperial units as base units in the
> database, and that creates round-off problem when working in metric.
> Since most Chip manufacturers is moving from imperial to metric it
> creates a problem.

All CAD where I've looked into this use an integer representation that is a
sub-multiple of both mm and mil.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\19@142226 by Bob Axtell

face picon face
Olin Lathrop wrote:

>Tomas Larsson wrote:
>  
>
>>Imperial is a pain in the arse, when it comes to PCB design.
>>It seems that most editors has imperial units as base units in the
>>database, and that creates round-off problem when working in metric.
>>Since most Chip manufacturers is moving from imperial to metric it
>>creates a problem.
>>    
>>
>
>All CAD where I've looked into this use an integer representation that is a
>sub-multiple of both mm and mil.
>
>
>******************************************************************
>Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
>consultant in 2004 program year.  http://www.embedinc.com/products
>  
>
I've never encountered a rounding probem either , even good ole DOS Tango
could go to .01 mm without any problems...

Most genuine CAD programs use a very deep math unit

--Bob



--
Note: To protect our network,
attachments must be sent to
@spam@attachKILLspamspamengineer.cotse.net .
1-520-850-1673 USA/Canada
http://beam.to/azengineer

2006\02\19@144318 by Spehro Pefhany

picon face
At 12:22 PM 2/19/2006 -0700, you wrote:
{Quote hidden}

Real CAD (rather than the PCB variety) tends to use floating point math
with algorithms to detect when things are effectively in contact even if
the numbers are off by a bit.

The old, old EDA programs seemed to use integer units of mils, since they
crapped out at about +/-32" (16 bit representation).

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
KILLspamspeffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2006\02\19@144624 by w d myrick

picon face
Olin,  I think you did a good job on this.

As one that has been in electronics for 69 years I grew up with mf used for
microfarad and mmf  as micromicrofarad .  I have changed to the new
(correct)
notation.  Even though I have changed I still revert to the old way at
times.
As one that taught electronics, from basic concepts through microwaves for
four
years, and has a BS in electronics Engineering( Microwave and RF options)
and have designed all types of electronic equipment from consumer through
the
USA space program (the guidance and command system on Saturn SA5) I feel
that I am not stupid when I sometimes revert to the mf notation.  I still
own a
small Co. that manufacture three products and do custom design of any thing
a
customer wants in the way of electronics. With all of this if I still
occasional us mf or
mmf  but I don't think this means I don't care, It just means I had 40 years
that way and
the old notation just slips in at times.  However the equipment I design
now days
is used mostly local so it does not impact too many people.

Derward Myrick



{Original Message removed}

2006\02\19@144712 by Tomas Larsson

flavicon
face
{Quote hidden}

In My experience, the problems do apear when you have to switch between
metric and imperial, and use both system in the same database.


2006\02\19@154344 by Gerhard Fiedler

picon face
Olin,

I think we are more in agreement than not, regarding SI and attitudes
towards it. In the below I snipped lots, since it's a long post and I agree
with much of it. I'm not sure though what made you think I didn't.


Olin Lathrop wrote:

> I've been watching this debate on the sidelines for a while, but you're
> constant complaining about how everyone that doesn't follow the
> standards is inept is getting me fed up enough to respond.

It seems you didn't understand at least some of what I wrote. I never
called anyone "inept". You write that again later... not sure why.

> That's what I grew up with, so that's what I think in, and converting
> requires more mental work.  So what are the hardware stores going to
> stock?  Whatever their customers demand, right?  So why should I buy a
> stock of metric hardware when I've already got a nice stock of english
> hardware and it's more available anyway?  (Actually metric hardware is
> available too, but not quite as widespread as english.)

A side note: If you're talking about threaded hardware when you talk about
'English hardware', I don't think you're talking about English threads.
AFAIK, the threads common in the USA are UTS threads; a standard that
didn't seem to catch on in the UK. They use either metric or BA.


I'm not sure about your work environment, but the shops I've seen recently
usually have both sets of tools and stocked hardware: metric and
imperial/UTS.

In a neutral world, either would be fine. (I think the metric makes more
sense, but that' a different question and we agree on that.) However,
having both in your shop if you don't need it is not that smart. You see a
threaded hole. By your experience you know from the size what thread it
might be. Works if you know whether it's metric or imperial, but if you
don't know which one it is, it gets a bit trickier. So you imagine that
it's a #4 thread -- but no, it's an M3 thread. If you only had M3, that
wouldn't happen. (It wouldn't happen either if you only had #4, but that's
not more than wishful thinking, with the rest of the world using M3.)

That's just one example why it is obviously more difficult and more costly
to work with both systems in parallel. Why stock both #4 and M3 screws when
they are about the same size? The thing is that sooner or later you will
need M3 screws, so it /may/ be a smarter move to get that done earlier --
before you spend the next $1000 in imperial/UTS tools. You can't control
what others do, but you can control what you use.


> So who's doing anything stupid here?  

I don't know -- you tell me. I didn't say that anybody does anything
stupid. Please don't try to project your harsh judgment into my head and
stick to quotes from me if you want to talk about what I wrote.


> If you were Outer Vulgaria and woke up at the end of world war II taking
> a leap from ox carts to cars in a span of 5 years, it's no big deal to
> decide to standardise "about that long" with a meter.  

Now this is a pet peeve of mine :)  It seems some people in the USA think
that because during the 50ies the USA became the leading nation in science
and industry, people in Europe ate bananas from the trees before that (to
exaggerate a bit :). That's not quite so. By the 50ies, when most of Europe
went metric, Europe had an industrial park and a scientific community just
as developed as the USA. By the time European companies went metric, they
had just as much pre-metric baggage as USA companies. The only difference
is that European governments and companies saw the potential of
international cooperation and the need of international standards for that
earlier than USA companies, and jumped on the SI bandwagon earlier (the
companies) or with more grip (the governments).

> It's a lot more trouble for a technologically advanced society like the
> US that already has an entrenched system and existing infrastructure.

That's true, and holds just as well for Germany, France, Great Britain,
Sweden and the many other countries that were already industrially well
developed by the time they adopted the SI. If you'll look through my
previous messages, I did /not/ compare the situation in the USA to the
situation in "Outer Vulgaria"; if I compared anything, I used countries
that were just as developed as the USA by the time they went metric.

People like Bohr, Einstein, Heisenberg, Planck and companies like Siemens,
Bosch, Mercedes-Benz, Volkswagen, BASF, BMW did not operate in an
industrial vacuum. In the 50ies, Europe was arguably as developed as the
USA, technologically and industrially. (Sorry if the list above is quite
Germany-centered, but that's what comes to my mind. I'm sure there are just
as significant examples for many other European countries.)


> I make it a point to use milli and nano farads whenever appropriate,
> partly because I've deliberately taught myself to think that way and
> partly because I want to get the world used to it.  

This is exactly my point. I may write it with other words, and I definitely
have a different angle on many things, but the base line is this. So what's
the problem?

> I think of this as one small victory, because I doubt he's going to make
> that mistake again.

:)  And I think it is not wasted. This is exactly the sort of attitude that
I think is missing. He, OTOH, if he's not smart, may think you are a
metrics-whino :)


> As for the mu symbol, I've looked upside down, inside out, and sideways
> at my keyboard and I don't see one.  Yes, there may be a way to make a
> mu symbol with a bunch of keystrokes,

Two, to be exact. The same number it takes to write an uppercase 'L'.

> but I don't know that off the top of my head and it would be too much
> hassle anyway.  Using "u" for mu is a well accepted and very common
> practise.  

I don't know what you read from me that make you think otherwise, but
that's exactly what I'm saying. There's no need to avoid the 'm' for
'milli' (as advocated by others because some people like to use 'm' for
'micro') -- everybody who's worth his money would use either the (correct)
mu or the (IMO acceptable) 'u' for 'micro' and use the 'm' for 'milli'.

> But in reality if it's not ASCII it's either not safe or too much of a
> hassle.

See, this is one of the problems that only seem to exist in the USA. The
rest of the world does not have a problem with non-ASCII characters and use
them on a daily basis. I'm sitting right here in Brazil, writing and
reading Portuguese, German and English texts every day without problem.
Most of it is not covered by ASCII. No safety problems, neither hassles.
Just a little bit of knowledge.

(And again, as mentioned several times, I'm pretty sure you are using
Unicode, maybe without knowing it.)


> Unicode is a big pain in the butt because it takes 16 bits per character.

I'm not sure what you know about Unicode, but this is wrong. Maybe you read
up a bit on Unicode before you write about it and spread disinformation?


Just for the eventual lurker: Unicode comes in a number of different
encodings. There was a time, some time ago, where the whole Unicode code
space fit into 16 bits, and that's where Olin's misconception may come
from. But this is not the case anymore; 32 bits are now necessary.

But the number of bits required to represent every code point are not
necessarily the number of bits to represent each individual code point.
Non-linear encodings have been used for a long time, because some code
points are much more frequent than others and therefore it's more efficient
to represent them with fewer bits.

Check out <http://en.wikipedia.org/wiki/Unicode>, especially the section
<en.wikipedia.org/wiki/Unicode#Storage.2C_transfer.2C_and_processing>.
The default in many situations is UTF-8, which uses only one byte for the
printable characters in the ASCII range (and the same encoding).


So the whining that occasionally can be heard about Unicode needing 16 bit
per ASCII character is just lack of knowledge -- 16 bits are not enough to
/enumerate/ the code space, and in most cases 8 bits are enough to /encode/
a character :)


> the really really good reason to switch to unicode is just missing.  

Why are you so defensive here? Did I say anything about anybody switching
to Unicode? The only thing about Unicode I said was that if somebody wants
to use the mu character in newsgroups, email or web, it is easily possible
because the standards are there and widely used. The proof is that you can
read this mu: 'µ'. (Not exactly Unicode in the message source, but what
happens is that the ISO-8859-1 character that gets sent gets then mapped by
your newsreader into the appropriate code point in your Unicode font. You
may not know it, but you may be using Unicode <g>. Check out the fonts in
your system: most of them are probably Unicode.)


> When writing HTML and I think about it and I have time, I do use the
> "&mu;" construct for mu.  That's OK since it's guaranteed to work in all
> browsers (part of the HTML definition), I can remember it, and the
> resulting file still uses 8 bit characters.

That's exactly what I said. Use stuff that works. Again, I don't see what
your problem is with what I wrote.

A side note: General 8-bit characters (especially Windows fonts) are /not/
guaranteed to work platform-independently. If you want to use anything
other than the default UTF-8 (which includes 7-bit ASCII) on the web, you
need to specify the character set.


>> You don't like non-standard web sites that work only in IE on Windows,
>> do you?
>
> Actually I couldn't care less since I use IE.

That was written as a response to a message to Bill. He apparently doesn't
use IE on Windows. I'm sure you don't like sites that only work on Mozilla
on MacOSX, right? :)  Standards do make sense; they are the reason we can
exchange messages and browse the web in the first place.


> Again you are forgetting that everyone makes individual decisions that
> are the best for them at the time.

It's a bit (not much though) besides the point, but I'm sure that this is
/not/ the case. Not everybody (not me, not you, not anybody else) only
makes decisions that are the best. We all make mistakes. Using the Windows
Symbol font in a public web site of an educational institution and
therefore causing the abbreviation of 'micro' to show up as 'm' on a
significant portion of the browsers is such a mistake, not an "individual
decision that [is] the best for them" at any time.

Besides, I never forgot that...


> Again, my main point is that you are whining about people doing things
> different from how collectively you think it should be done, but ignoring
> what is in each individual person's best interest.

No. I'm not whining, I'm not talking about what I think collectively should
be done (that would go far OT :) and I don't ignore what may be in each
individual's interest.

I'm not whining. I'm arguing against the whiners that always say that it's
soooo much more difficult for companies and people in the USA to go metric.
It was difficult for every single one of the companies and people in Europe
when they did it fifty years ago. There were people with tools in their
basements in Europe before 1950, just as in the USA. There were engineers
that grew up with different measurement systems, just like in the USA.
There were huge amounts of company history and blueprints in other units,
just as in the USA. The only difference is that they did it back then,
unlike their counterparts in the USA.

> Yes, it might be good if we could all suddenly use the same standard, but
> who's going to pay for that, and why should I pay if I don't perceive
> the value to me outweighs my cost?  

Here's the fallacy. It's more expensive to keep the dual system, and the
amount wasted on that adds up every year it will take to move over. It's as
simple as that. The conversion cost may show up in the budget of a company
as "$1.000.000 spent once on metrication efforts", but the cost of keeping
the dual system in place won't show up as "$100.000 per year spent on
multi-measurement system support".

So yes, the short-sighted advantage is with staying with what works and is
in place. Judging management by quarterly results reinforces this. But
since the move is inevitable (and I'm not sure you agree, but you seem to),
it's simply a matter of continuing a waste of money to delay the move, in
many situations.

(Just as the additional effort you spent -- on your side and on your
associate's side who you taught that lesson -- by teaching him that mF
means millifarad. This was a cost factor, and you could have avoided it by
not using mF and sticking to uF, as Bill suggests. You didn't, you spent
the effort, and you did it because you thought that's the right thing to do
and that it's cheaper in the long run. I agree completely. I just take this
a bit further, maybe...)


The other thing is: if the US automotive (and a few other) industries think
that it's cheaper to go metric (they definitely had to convert /a lot/ of
existing documentation and change stock), it may not be so far off to think
that it'd be cheaper for many others, too, and that some of the main
reasons they didn't do it are just not thinking about it, and sometimes
mental (and other) laziness.


> Are you willing to go thru a few 100000 lines of my source code and
> convert every last character reference to unicode?  I didn't think so,

Again, I never said anybody should convert all existing programs to
Unicode. This seems to be something that tripped your fuse. Please /read/
my stuff. I try to write good, clear English that everybody should be able
to understand. I try to make the points clearly. I try not to call people
names, and rather stick to facts and mark my opinions clearly as such where
I mention them. AFAIK I /never/ in this thread said that anybody should
convert any code to Unicode. I said about Unicode that it's well supported
in the online media like www, newsgroups and email so that there's no
reason not to use Unicode characters. If you think you can find the passage
where I said that you (or anybody) should convert existing applications to
Unicode, that would be helpful.

You seem to be using OE6, probably on a Win2k or WinXP system, and if that
is correct, your system supports Unicode -- you /are/ using Unicode, as far
as your interface to me is concerned. So you weren't really addressed with
the comments to that effect...


> so stop whining about it already and stop calling me inept for not doing
> it.

Again, I never said that you should convert any of your code to Unicode,
and I definitely never called you inept. I would definitely like to see the
quote you took that from.

Gerhard

2006\02\19@172404 by Peter Todd

picon face
On Sun, Feb 19, 2006 at 02:10:21PM -0500, Olin Lathrop wrote:
> Tomas Larsson wrote:
> > Imperial is a pain in the arse, when it comes to PCB design.
> > It seems that most editors has imperial units as base units in the
> > database, and that creates round-off problem when working in metric.
> > Since most Chip manufacturers is moving from imperial to metric it
> > creates a problem.
>
> All CAD where I've looked into this use an integer representation that is a
> sub-multiple of both mm and mil.

Using 0.1mm as your base unit would do you just fine as the inch is
defined as exactly 25.4mm.

That said real machining can easilly go down to tolerences as tight as
+-0.01mm, so you'd want am much smaller base unit than 0.1mm.

--
TakeThisOuTpeteEraseMEspamspam_OUTpetertodd.ca http://www.petertodd.ca

2006\02\19@175201 by Tomas Larsson

flavicon
face
Well, for instance, if you ar working with the TQFP-packages with a lead
pitch of 0.5mm that equals 0.019685039 inch, and it seems that its rounded
to 0.02 inch which equals to 0.508 mm and having 20 of those pins gives at
least an error of 0.16 mm.

With best regards

Tomas Larsson
Sweden
http://www.naks.mine.nu for downloads etc.
ftp://ktl.mine.nu for uploads. Or use the free http://www.yousendit.com service.

Verus Amicus Est Tamquam Alter Idem

> {Original Message removed}

2006\02\19@192623 by Gerhard Fiedler

picon face
Peter Todd wrote:

>> All CAD where I've looked into this use an integer representation that is a
>> sub-multiple of both mm and mil.

Can that work? What base unit would that be? I don't think such a number
exists.

> Using 0.1mm as your base unit would do you just fine as the inch is
> defined as exactly 25.4mm.

/If/ you use a metric base unit -- because the inch is defined based on a
metric unit, as you say. That's why conversions from inch to metric units
always result in numbers with a limited (and easy to determine) number of
decimals: the conversions are multiplications.

You're in more trouble if you're using a base unit defined in inches. Then
the conversions become divisions, with the problems Tomas mentioned.

Gerhard

2006\02\19@192623 by Gerhard Fiedler

picon face
Peter Todd wrote:

>> All CAD where I've looked into this use an integer representation that is a
>> sub-multiple of both mm and mil.

Can that work? What base unit would that be? I don't think such a number
exists.

> Using 0.1mm as your base unit would do you just fine as the inch is
> defined as exactly 25.4mm.

/If/ you use a metric base unit -- because the inch is defined based on a
metric unit, as you say. That's why conversions from inch to metric units
always result in numbers with a limited (and easy to determine) number of
decimals: the conversions are multiplications.

You're in more trouble if you're using a base unit defined in inches. Then
the conversions become divisions, with the problems Tomas mentioned.

Gerhard

2006\02\19@203904 by olin piclist

face picon face
Gerhard Fiedler wrote:
> It seems you didn't understand at least some of what I wrote. I never
> called anyone "inept".

I don't have a copy of your message and the archive server hasn't caught up
to that message yet, but you said one explanation for lack of unicode was
inept programmers.

> The thing is that sooner
> or later you will need M3 screws, so it /may/ be a smarter move to
> get that done earlier -- before you spend the next $1000 in
> imperial/UTS tools.

Probably not though.  It's not going to be a sudden all or nothing
switchover.  This will be driven by necessity one little piece at a time.

> I don't know -- you tell me. I didn't say that anybody does anything
> stupid.

Actually you did ("inept") and with your general tone of "why don't these
idiots just drop what they're doing and switch to metric already".

> It seems some people in the USA
> think that because during the 50ies the USA became the leading nation
> in science and industry, people in Europe ate bananas from the trees
> before that

Nah, not me.  I didn't think banana trees grew in Europe. ;-)

>> But in reality if it's not ASCII it's either not safe or too much of
>> a hassle.
>
> See, this is one of the problems that only seem to exist in the USA.
> The rest of the world does not have a problem with non-ASCII
> characters and use them on a daily basis.

That's because the rest of the world uses all those silly umlauts and such
;-)

Remember, ASCII stands for American Standard Code for Information
Interchange.  It's not surprising it suits us pretty well.  Early computers
were primarily developed in England and the US.  Umlauts, accents, and 27
different Icelandic characters weren't on the priority list when ASCII was
invented.  I can understand why others might not like ASCII, but it works
fine for me.

>> Unicode is a big pain in the butt because it takes 16 bits per
>> character.
>
> I'm not sure what you know about Unicode, but this is wrong.

It's been a few years since I looked into it, but the Windows API has (at
least used to) have one definition for a normal character data type and
another to support unicode.  If I remember right, it was called WCHAR (for
wide character I think).  Whatever it was called was 16 bits wide while
normal characters were 8 bits wide.  Maybe that has changed in the last few
years (I'd be surprised), but it was definitely true at one time.

>> the really really good reason to switch to unicode is just missing.
>
> Why are you so defensive here? Did I say anything about anybody
> switching to Unicode?

Yes.  You attributed lack of unicode support to inept programmers.

> That was written as a response to a message to Bill. He apparently
> doesn't use IE on Windows. I'm sure you don't like sites that only
> work on Mozilla on MacOSX, right? :)

Possibly, but I don't have to worry about that since no serious web designer
is not going to not test his web page with MSIE.

> It was difficult for every single one of the companies and
> people in Europe when they did it fifty years ago. There were people
> with tools in their basements in Europe before 1950, just as in the
> USA. There were engineers that grew up with different measurement
> systems, just like in the USA.
> There were huge amounts of company history and blueprints in other
> units, just as in the USA. The only difference is that they did it
> back then, unlike their counterparts in the USA.

That doesn't make a synchronized sudden switch the right answer, nor does it
prove that it was the right answer for Europe back then.

{Quote hidden}

This is the part of your argument that pisses me off.  You are basically
saying that everyone who doesn't switchover wholesale now is stupid.
There's a lot more to it than "simply a matter of continuing to waste
money".  It really comes down to two things, available resources and return
on investment.  If you don't have the $1M to switch over, then it's not an
option whether you'd like to or not.  But let's say the funds are available.
It then becomes a question of "how can I spend this $1M to get the best
return?".  In your example, the ROI is about 10 years.  That's very long.
If that $1M can instead be spent on something that yields a ROI in 18
months, then that's a much better investment.  The world is never perfect,
but you have to intelligently chose what to address and what to live with.
In many cases the cost to switching to metric is substantial and the payback
small.  Without careful analisys you can't say whether switching makes sense
or not.

This is why the switchover is going to be slowly phased in, as has already
been done in getting to where we are, which is over half way in my opinion.
It will be driven, as it has been, by many individual decisions about supply
and demand and market pressure.  And that's exactly how it should be.  Let
the capitalist system do it's job.

> (Just as the additional effort you spent -- on your side and on your
> associate's side who you taught that lesson -- by teaching him that mF
> means millifarad. This was a cost factor, and you could have avoided
> it by not using mF and sticking to uF, as Bill suggests. You didn't,
> you spent
> the effort, and you did it because you thought that's the right thing
> to do and that it's cheaper in the long run.

No, it probably wasn't.  However my cost was small (the supplier had to fix
it, not me), so I could afford to base the decision on ideology instead of
practicality.  Also remember that it wasn't planned that it work out the way
it did.

> The other thing is: if the US automotive (and a few other) industries
> think that it's cheaper to go metric (they definitely had to convert
> /a lot/ of existing documentation and change stock), it may not be so
> far off to think that it'd be cheaper for many others, too, and that
> some of the main
> reasons they didn't do it are just not thinking about it, and
> sometimes mental (and other) laziness.

There you go again.  Now people who don't switch because you think they
should are "lazy".  You are once again ignoring the many good reasons not to
switch.  Companies will largely do what's to their advantage.  I can
understand why it's to the advantage of large heavy-iron companies to switch
to metric, but that doesn't automatically make it a good idea for everyone
else, at least not yet.  That will come as the switch trickles down.  Some
have enough to gain now so they switch.  That may make it attractive for
their suppliers to switch when it previously wasn't.  Now the tradeoff is
tipped a little more for their suppliers, and so on.  That doesn't make
those who haven't switch lazy or stupid.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\19@204432 by olin piclist

face picon face
Gerhard Fiedler wrote:
>>> All CAD where I've looked into this use an integer representation
>>> that is a sub-multiple of both mm and mil.
>
> Can that work? What base unit would that be? I don't think such a
> number exists.

It certainly exists and some CAD systems use exactly this method.  As
someone else already pointed out, 100um is a sub-multiple of both a mm (10)
and inch (254).  By factoring out the common 2, you get 200um as a base unit
for both (1/5 mm and 1/127 inch).  You can keep scaling that down until you
get the resolution you want.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\19@212906 by Tomas Larsson

flavicon
face
There is a huge difference between a CAD-system and PCB-design software.
A CAD system such as AutoCad and similar are using the aproach that you
always use the scale 1:1 wich means that one drawing-unit equals one
real-world-unit so it does not matter if you are using metric or imperial.
The reason is that you normaly want the drawing on paper, so you scale it at
print-out, or let the CAM-SW handle the rounding, CAD SW do not work with
1/2" representation but with 12,7 representation and when translating the
drawing, especially a mecanical one, you normaly don't work with 0.01 mm
tolerances, which means that rounding is quit easy and non-destructive.

PCB-design software on the other hand does work in absolute measurements
i.e. the database is basad on either mm or inch and not drawing units. And
when working on a scale of 0.01 mm or even less tolerances, scaling is an
issue, and the same thing applies, it dont work with 1/2" but rater 0.5 in =
12,7 mm and as I mentioned earlier its, a quite difference between 0,508 mm
and 0,5 mm, its nearly a 2% rounding error.

With best regards

Tomas Larsson
Sweden
http://www.naks.mine.nu for downloads etc.
ftp://ktl.mine.nu for uploads. Or use the free http://www.yousendit.com service.

Verus Amicus Est Tamquam Alter Idem

> {Original Message removed}

2006\02\19@222548 by Gerhard Fiedler

picon face
Olin Lathrop wrote:

>>>> All CAD where I've looked into this use an integer representation
>>>> that is a sub-multiple of both mm and mil.
>>
>> Can that work? What base unit would that be? I don't think such a
>> number exists.
>
> It certainly exists and some CAD systems use exactly this method.  As
> someone else already pointed out, 100um is a sub-multiple of both a mm (10)
> and inch (254).  By factoring out the common 2, you get 200um as a base unit
> for both (1/5 mm and 1/127 inch).  You can keep scaling that down until you
> get the resolution you want.

Ok, yes of course :)  The original poster said (see above) "a sub-multiple
of both mm and mil". That would then have to be 200 nm.

This means that the system needs to use a metric unit as base unit. This
works. I'm just not sure that all systems use a metric base unit. The ones
who don't probably have more trouble.

Gerhard

2006\02\20@072353 by olin piclist

face picon face
Gerhard Fiedler wrote:
> This means that the system needs to use a metric unit as base unit.

No, only that the base unit can be multiplied by an integer to get exactly
the smallest measure you care about in either system.  This base unit can
therefore be expressed as a rational fraction in either system.  That's the
point.  In the example cited, the base unit is 1/5 mm and 1/127 inch.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\20@073125 by Lembit Soobik

flavicon
face
Now that you mention it, I remember that unit. it was used afaik pretty
seldom and IIRC, it pF.
The explanation was something like two two disks ?? size and 1 cm apart
would make a 1 pF capacitor. Sorry, but that was half century ago.
Lembit

>
> But what is a 'cm' ? There used to be schematics with 'cm' units on
> caps. What is a 'cm' ?
>
> Peter
> --

2006\02\20@073127 by Enrico Schuerrer

picon face

----- Original Message -----
From: "Olin Lathrop" <RemoveMEolin_piclistspamTakeThisOuTembedinc.com>
To: "Microcontroller discussion list - Public." <piclistEraseMEspam.....mit.edu>
Sent: Monday, February 20, 2006 2:39 AM
Subject: Re: [EE] Metric units


> Gerhard Fiedler wrote:
> > It seems some people in the USA
> > think that because during the 50ies the USA became the leading nation
> > in science and industry, people in Europe ate bananas from the trees
> > before that
>
> Nah, not me.  I didn't think banana trees grew in Europe. ;-)

Tremendous :-) There are European countries where banana trees are growing -
but believe me, we weren't in the trees ;-). And this bananas don't matter
if the measurement units are inch or mm - the curvature is regulated by EU
law, so it is mm ;-)

Enrico

2006\02\20@090421 by Tomas Larsson

flavicon
face

> -----Original Message-----
> From: EraseMEpiclist-bouncesspammit.edu
> [RemoveMEpiclist-bouncesEraseMEspamEraseMEmit.edu] On Behalf Of Olin Lathrop
> Sent: Monday, February 20, 2006 1:25 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Metric units
>
> Gerhard Fiedler wrote:
> > This means that the system needs to use a metric unit as base unit.
>
> No, only that the base unit can be multiplied by an integer
> to get exactly the smallest measure you care about in either
> system.  This base unit can therefore be expressed as a
> rational fraction in either system.  That's the point.  In
> the example cited, the base unit is 1/5 mm and 1/127 inch.
>
That's how AutoCad and similar CAD-Systems work.

But not PCB-Cad systems, since they use either mm or inch as base unit.

PCB-Cad is not a proper Cad-system but more a merge of CAM-CAD-CAE, and
since the CAM is in there, they need to work in "real world units" such as
mm or inch.

By design Cad-systems like AutoCad were designe to be as generic as
possible, it doesn't matter if you are designing nano-robots or skyscrapers,
you use the same software, one DU could represent in nanometer or one meter,
it's up to the designer to choose, the scaling is done at print-out because
you might want the result in different scales, or when the file is fed to
the CAM-system, which translates the du-based database to the requirements
of the actual NC-Machine. There I no way, by looking on a CAD-Drawing to
know whether a line is 1 mm or 1 km, you have to know by experience and what
type of design it is to tell what measurment system is used. As an example,
looking on a drawing on a building and measuring a door, you find that the
door is near 800 units wide, by experience and the knowledge that this is a
building I can assume that the door is 800 mm wide, not 800 m nor 800 nm.
You have to be careful though, when importing "Blocks" or symbols, because
you need to know how they were created, to scale them properly.


In PCB-Cad , by design, they are targeted to a very specific task, to create
a PCB, and we can assume that the maximum size of that pcb probably would
bee 1 by 1 meter or so, furthermore the output from the system will allways
be at scale 1:1, nothing else would be useful. Then by history the databases
where designed around the common measurement 1 mil and multiples of it since
most component-sizes once were based on mil's.
Since the system and libraries use a common system of measurement, there is
no risk of scaling when adding symbols.
Given that measurements whithin the database is based on a realworld sizes,
and it can only be one system in the database, there will be scaling errors
when using a different measurement system.
Finally all vectors are represented with integers, hense 0.2 inch will be
200 mil equals 5,08 mm and 5mm will not be 196,8503937007874015748031496063
mil, because its not an integer, but rounded to 200 mil and there you have
the scaling error.



With best regards

Tomas Larsson
Sweden
http://www.naks.mine.nu for downloads etc.
ftp://ktl.mine.nu for uploads. Or use the free http://www.yousendit.com service.

Verus Amicus Est Tamquam Alter Idem


2006\02\20@101506 by olin piclist

face picon face
Tomas Larsson wrote:
> Given that measurements whithin the database is based on a realworld
> sizes, and it can only be one system in the database, there will be
> scaling errors when using a different measurement system.

There are no scaling errors since measurements are stored as integers in the
base unit.  The only error will be roundoff to the nearest multiple of the
base unit.  However, the base unit is deliberately chosen to express all the
common human units to the customary precision exactly.

For example, we've already determined that 1/5 mm = 1/127 inch is the
largest base unit in which whole mm and inches can be expressed exactly.
This mm/inch common base unit can be further divided by any integer and
maintain this property.  Suppose we decide that our system must be able to
express mils (1/1000 inch) and .01mm exactly.  The largest base unit that
can do that is 1000 times smaller than the previous example, which is 1/5000
mm = 1/127000 inch.  If coordinates are stored as 32 bit integers, this
gives a range of about +-2 furlongs.  Given that's way more than necessary
for designing PC boards by any stretch of the imagination, you could chose
to provide another digit of exact representation by making the base unit
another 10x smaller.  That means any multiple of .0001 inch or .001 mm can
be expressed exactly without any roundoff or conversion error, and you still
have a coordinate range of +- 214 millifurlongs, 8.5 rods, 7 trucklengths,
or whatever your favorite measure of distance is.

Every electrical CAD system where I've looked into this uses this method.
For example, the Eagle base unit is 1/10000 mm = 1/254000 inch.  This means
a user can enter coordinates down to 1/2 mil and still have them represented
exactly and without any error if they were converted to mm.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\20@121359 by Robert Ammerman

picon face
>>  I was a tad suprised that in the US tape measures only have inches -
>>I thought they'd have both since they are "in the process of metrication",
>>at least officially.
>>

I am in the US and have a combination metric/inch tape measure. However, I
had to go out of my way to get it, actually buying it from one of my
customers which is in the science/math educational supply business. They
sell it to schools to help teach metric.

When I use it for woodworking (cabinet making) I often use the metric side
of it.

However, when using it for construction/remodeling work, I nearly always use
the feet/inch markings.

Bob Ammerman
RAm Systems

2006\02\20@123509 by David VanHorn

picon face
Between building codes and inertia, I think construction will end up like
chemistry, full of obsolete names and referents.

Why isn't lime, lime flavored, or at least green?  :)

2006\02\20@133004 by Peter

picon face


On Sun, 19 Feb 2006, Spehro Pefhany wrote:

>> But what is a 'cm' ? There used to be schematics with 'cm' units on
>> caps. What is a 'cm' ?
>
> It *Italian*?

No, no. You would have caps in a radio, say tuning cap, of 1000cm. I
suspect it is close to the pF. One theory I have is that it would be the
equivalent plate capacitor with 1mm separation in air (or vacuum), and
1cm^2 which is about 0.82pF. Come to think of it, this makes sense. Once
upon a time real men made their own capacitors and coils so this would
have been be a very practical measure for everyday use.

Peter

2006\02\20@145216 by William Killian

flavicon
face
According to this link cm would mean "Molded Case" as opposed to "Dipped
Case" style.

http://xtronics.com/kits/ccode.htm

while here I cm of capacitance is 1.11pF

http://www.du.edu/~jcalvert/phys/caps.htm

I guess it would depend upon whether the schematic in question had no
Farad rating along with the letters CM and whether the CM had a number
with it.

> {Original Message removed}

2006\02\20@184624 by Juan Cubillo

flavicon
face
How can you make your own caps? Aren't they huge???

-----Original Message-----
From: "Peter"<RemoveMEplpspam_OUTspamKILLspamactcom.co.il>
Sent: 2/20/2006 12:27:11 PM
To: "Microcontroller discussion list - Public."<RemoveMEpiclistTakeThisOuTspamspammit.edu>
Cc:
Subject: Re: [EE] Metric units



On Sun, 19 Feb 2006, Spehro Pefhany wrote:

>> But what is a 'cm' ? There used to be schematics with 'cm' units on
>> caps. What is a 'cm' ?
>
> It *Italian*?

No, no. You would have caps in a radio, say tuning cap, of 1000cm. I
suspect it is close to the pF. One theory I have is that it would be the
equivalent plate capacitor with 1mm separation in air (or vacuum), and
1cm^2 which is about 0.82pF. Come to think of it, this makes sense. Once
upon a time real men made their own capacitors and coils so this would
have been be a very practical measure for everyday use.

Peter

2006\02\20@193516 by David VanHorn

picon face
On 2/20/06, Juan Cubillo <EraseMEjacubillorospamspamspamBeGonecostarricense.cr> wrote:

> How can you make your own caps? Aren't they huge???


Two metal plates, some air space between, voila, you have a cap.
A microfarad cap built this way is huge. A picofarad isn't.
1500pF, built from double-sided FR4 circuit board material is a few square
inches.

I have caps that are a screwdriver adjustable metallic disc with ceramic
insulators supporting this disc near another disc.

I also have "Vaccuum variables" that withstand higher voltages since they
are in a vaccuum.

Variable caps are built in a similar way, rotating one or more plates of
metal so that they are close to, or far from, a second set of plates that
don't move.

2006\02\20@194254 by Gerhard Fiedler

picon face
part 1 874 bytes content-type:text/plain; charset="big5" (decoded quoted-printable)

Juan Cubillo wrote:

> How can you make your own caps? Aren't they huge???

Not sure you've seen the short wave tuning caps they used to use (and
possibly still use): just a bunch of metal plates, every other plate
connected to one end, the in-betweens to the other end, and the tuning knob
turns the one set of plates in and out of the other set, modifying the
active area.

For two parallel plates, the capacity is

C = ` a / d

with
C: capacity
`: dielectric constant
a: area
d: distance

(For simplicity, all in SI units :)

` is around 8.9 pF/m for air. Most dielectric materials are in the range of
up to 100 times this value, some over 1000 times.

So an air capacitor with 100 cm^2 area and 1 cm distance would have 8.9 pF.
You can put that in your pocket; not sure it counts as "huge" :)

Gerhard



part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\02\20@212301 by Jinx

face picon face


> How can you make your own caps? Aren't they huge???

Depends on the value. A tuner in a transistor might be 60-160pF
and be 20mm square. Thin metal plates separated by insulating
plastic film. Similar to a trimmer cap of a few pF. An air tuner, like
you might find in a valve set, is a lot larger perhaps a 50mm cube,
generally still well under 1000pF. No reason you couldn't make
your own fairly compact caps from coiled plastic/cooking foil

2006\02\21@151329 by Peter

picon face

On Mon, 20 Feb 2006, William Killian wrote:

> while here I cm of capacitance is 1.11pF
>
> http://www.du.edu/~jcalvert/phys/caps.htm

Ok, that's the one. The esu based capacitance unit is a cm. I wonder
what they were thinking when they chose it (naw, we're never going to go
metric so using cm for capacitance will never bother anybody).

Peter

2006\02\21@154402 by Peter

picon face


On Mon, 20 Feb 2006, Juan Cubillo wrote:

> How can you make your own caps? Aren't they huge???

Not really. A 'twiddlecap' made by twisting two insulated wires together
can go to about 30pF before it is too large.

A plate capacitor with PVC dielectric (saran wrap) can go pretty far (it
can be 100pF/cm^2 of plate with 10um saran).

Simple electrolytic capacitors can be made using an aluminium can (coke
etc) and water (boiled in) plus salt water as electrolyte.

None of these parts are 'good' by todays standards but if you are trying
to prove a point or tech some kids new tricks it may be interesting to
try them.

Resistors of low value can be made from pencil graphite, with wire
wrapped around the ends for low value (<1kOhm), and from paper
'scribbled' thickly with graphite for high values (>100kOhms).

Peter

> {Original Message removed}

2006\02\21@182336 by Gerhard Fiedler

picon face
Peter wrote:

>> http://www.du.edu/~jcalvert/phys/caps.htm

> I wonder what they were thinking when they chose it (naw, we're never
> going to go metric so using cm for capacitance will never bother
> anybody).

Given the name they gave the unit of capacitance ('centimetre'), the
abbreviation 'cm' makes perfectly sense :)

Gerhard

2006\02\22@050613 by Russell McMahon

face
flavicon
face
Seriously useful capacitors for extremely high voltages can be made
with glass jars and foil.
"Leyden jars" no less.
Capacitance values are lowish but useful in typical applications.


>> How can you make your own caps? Aren't they huge???

> Not really. A 'twiddlecap' made by twisting two insulated wires
> together
> can go to about 30pF before it is too large.

> A plate capacitor with PVC dielectric (saran wrap) can go pretty far
> (it
> can be 100pF/cm^2 of plate with 10um saran).

2006\02\22@154018 by Peter

picon face

On Tue, 21 Feb 2006, Gerhard Fiedler wrote:

> Peter wrote:
>
>>> http://www.du.edu/~jcalvert/phys/caps.htm
>
>> I wonder what they were thinking when they chose it (naw, we're never
>> going to go metric so using cm for capacitance will never bother
>> anybody).
>
> Given the name they gave the unit of capacitance ('centimetre'), the
> abbreviation 'cm' makes perfectly sense :)

Maybe Coulomb's apparatus caused centimetre-sized deviations on the
scale on the wall and that's where it comes from. An Englishman would
have used inches. A German would have used Zoll.

Peter

2006\02\22@160002 by Peter
picon face


On Wed, 22 Feb 2006, Russell McMahon wrote:

> Seriously useful capacitors for extremely high voltages can be made with
> glass jars and foil.
> "Leyden jars" no less.
> Capacitance values are lowish but useful in typical applications.

Maybe but plate caps (or wrapped foil) are much better for this imo ;-)

Peter

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