20 Jan
1999
20 Jan
'99
1:17 a.m.
extremes,
things like the definition of a volt may be needed...
:-)... Possibly.. I think that might be going a bit far. I would hope
some other electrical books had survived.
If not, how would you define a 'volt'? In terms of the steps on a
microwave-excited Josephson Junction? It's reproducable, and
frequency/time is also easy to define. 
21 Jan
21 Jan
2:52 a.m.
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1:44 a.m.
At 11:52 AM 1/21/99 -0500, you wrote:
It was thus said that the Great Philip.Belben(a)pgen.com
once stated:
I thought length, mass (Kilogram), and time (seconds) were picked as the
basic SI units, and others, like temperature, were "secondary". For
electromagnetics,
a 4'th unit was required, sometimes an ampere (which can be defined from
mechanical variables), sometimes charge.
-Dave
I'd like to define it in terms of SI units, but the Kilogram is not too
easy (yet).
Really? The meter is defined (certain frequency of light from a certain
element for so many waves yada yada). Sea level is defined (don't know the
SI unit, but 780 millibars of pressure). Celcius is defined (0 is freezing
point of pure water at sea level, 100 boiling point of pure water at sea
level) and that's all you need to define the gram: one cubic centimeter of
water at 4C at sea level. That also gets you volume (liters).
4:25 a.m.
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22 Jan
22 Jan
5:15 a.m.
> > If not, how would you define a
'volt'? In terms of the steps on a
> > microwave-excited Josephson Junction? It's reproducable, and
> > frequency/time is also easy to define.
> I was thinking of defining it in terms of a
bandgap, such as used in
> precision reference "diodes".
I think a Josephson Junction is easier to make,
actually. The only real
problem is you need something around liquid helium temperature (you need
a superconducting metal IIRC). Apart from that, all the rest of the stuff
is pretty easy to make.
Of course for something like describing the supply
voltages and logic
thresholds of a chip, you don't need that much accuracy. Describing how
to make a weston standard cell and its voltage (at a given temperature)
would be massive overkill. I would think that describing how to make
_any_ common cell and specifying its open-circuit voltage would be good
enough.
Excuse me if I interupt, but you are talking about measuring
a specific voltage. But thats completly independant from the
definition. Only if you want to define Volt based on some
specific reproduceable effect - but thats not necesaty. To
get all electrical units you just need the 7 basic SI units
(Length, Weight, Time, Current, Temperature, Brightnes (?)
and Mol (sorry, no idea how to translate Stoffmasse)) and
only one is an electric unit (the Ampere). And only these
7 units have to be defined on specific, reproducable effects.
1V is defined as 1 kg m^2 / A s^2.
Gruss
H.
--
Ich denke, also bin ich, also gut
HRK
5:48 a.m.
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9468
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participants (5)
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ard＠p850ug1.demon.co.uk -
ddameron＠earthlink.net -
Hans.Franke＠mch20.sbs.de -
Philip.Belben＠pgen.com -
spc＠armigeron.com