Accurately Measuring Precision Resistors

[Watson A.Name - \Watt Sun, the Dark Remover\]

Yes, I have my own doubts about attributing "man who have hole in
pocket feel cocky all day" to the great philosopher Kong fu zi.

As an aside from that, from what I've seen on the likes of Antiques
Roadshow, the ancient asian dress was just a simple pocketless pullover,
and they used a bag hung from their belt.

 

[Spehro Pefhany]

Oh, okay. I had no idea of how expensive they are, only that they
usually require some amount of manual labor, either in assembly or
testing. The ones I have are wirewound, and the Micro-Ohm website says
they are wound out ot wire that's as fine as .6 mil, which is 1/4 the
thickness of a human hair. Must be a very delicate and tedious
procedure.

The thin film type flow out of a resistor trimming machine in their
thousands much like 5% resistors do.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

Shame on you for not warning us that it would take 5 minutes to load
that image, even with the fuzzed out face.

Hey, Watt, it's 700K from a mini-snappy digital. That's a fraction of
a second on broadband. It's not like you're in Bangladesh or
something. I'll remember not to post links to any real hi-rez photos
from my digital SLR ;-)

Speaking of fuzzed out faces, I saw (not by choice, btw) the sketches of
Jacko's trial and they blurred out the faces of the witnesses. Pretty
sad when they have to go _that_ far.

I can see why the witnesses (or their parents/guardians if they were
minors) might not want to have their faces plastered all over the
papers.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

As an aside from that, from what I've seen on the likes of Antiques
Roadshow, the ancient asian dress was just a simple pocketless pullover,
and they used a bag hung from their belt.

Ancient garments that I've seen depicted were similar to that.
According to one web site, in Europe (and relatively recently compared
to Chinese history) pockets developed from people hanging the bag
(containing coins etc.) inside their garments to prevent theft. They
then added a slit to access the bag without disrobing and pockets
developed from that.



Best regards,
Spehro Pefhany

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

While theoretically true, this is practically useless information.

Absolutely not. Last week I needed a 0.1 ohm resistor, so I took out
the ref manual and looked at the wire tables, and found that 32 AWG has
162 milliohms per foot. This is a physical constant derived from Rho *
length / area. Rho for copper is 10.37 at 25 C. So I measured 7.4
inches of #32 wire and wound it around a 1W high value resistor, and it
measured very close to 0.1 ohm. Now I only have the problem that it has
..6 microhenry inductance.

The same can be done for a capacitor.

 

[BFoelsch]

Oh, okay. I had no idea of how expensive they are, only that they
usually require some amount of manual labor, either in assembly or
testing. The ones I have are wirewound, and the Micro-Ohm website says
they are wound out ot wire that's as fine as .6 mil, which is 1/4 the
thickness of a human hair. Must be a very delicate and tedious
procedure.

In this day and age, you can get remarkably accurate test equipment at a low
to reasonable cost. I used to screw around with the same sort of issues, so
I just went out and bought 2-3 pieces of decent test gear. You can get
multimeters with basic accuracies of .02% or better for about $500, a little
more if you want a big name. Once you get past about .1%, your test setup is
probably less accurate than the instrument anyway.

Something I have really grown to like is a "component tester," a dedicated
meter that measures (4 wire) ohms at DC and a few frequencies. It also
measures L and C and D and Q, and expresses losses as either parallel or
series R.

C.mon, Watt Sun. It's the 21st century. Treat yourself to some decent
equipment. Think of all the money you'll save by not burning out your
LEDs........

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hey, Watt, it's 700K from a mini-snappy digital. That's a fraction of
a second on broadband. It's not like you're in Bangladesh or
something. I'll remember not to post links to any real hi-rez photos
from my digital SLR ;-)

Great pic tho, worth the wait. Mor'n I can say for a lotta others. ;-)

I can see why the witnesses (or their parents/guardians if they were
minors) might not want to have their faces plastered all over the
papers.

But these were sketches......

Best regards,
Spehro Pefhany

http://www.speff.com

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

On Sun, 17 Apr 2005 09:18:18 -0700, the renowned "Watson A.Name -

Ancient garments that I've seen depicted were similar to that.
According to one web site, in Europe (and relatively recently compared
to Chinese history) pockets developed from people hanging the bag
(containing coins etc.) inside their garments to prevent theft. They
then added a slit to access the bag without disrobing and pockets
developed from that.

The following para is from
http://www.worldcollectorsnet.com/netsuke/

"Netsuke served both functional and aesthetic purposes. The tradtional
Japanese dress, the kimono had no pockets. The robes were hung together
by a broad sash (obi), so items that were needed to be carried were held
on a cord tucked under the sash. The hanging objects (sagemono) were
secured with carved toggles (netsuke). A sliding bead (ojime) was strung
on the cord between the netsuke and the sagemono to tighten or loosen
the opening of the sagemono.The best known accessory was the inro, a
small box used by the wealthy for carrying medicines and seals. Netsuke
were also used to secure purses, and were widely used to hold the
tobacco pouches that became almost universal with the introduction of
smoking in Japan."

 

[Spehro Pefhany]

Great pic tho, worth the wait. Mor'n I can say for a lotta others. ;-)


But these were sketches......

Unless they used the sketch artist who did the Unabomber sketches (old
SNL/Norm MacDonald reference) they probably bore a strong resemblance
to the actual people, no?


Best regards,
Spehro Pefhany

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

in message
In this day and age, you can get remarkably accurate test equipment at a low
to reasonable cost. I used to screw around with the same sort of issues, so
I just went out and bought 2-3 pieces of decent test gear. You can get
multimeters with basic accuracies of .02% or better for about $500, a little
more if you want a big name. Once you get past about .1%, your test setup is
probably less accurate than the instrument anyway.

Something I have really grown to like is a "component tester," a dedicated
meter that measures (4 wire) ohms at DC and a few frequencies. It also
measures L and C and D and Q, and expresses losses as either parallel or
series R.

C.mon, Watt Sun. It's the 21st century. Treat yourself to some decent
equipment. Think of all the money you'll save by not burning out your
LEDs........

Hey, c'mon, I got a (relatively) accurate Leeds & Northrup Wheatstone
bridge; it's fairly recent, due for recal in late 1968. ;-))

I got the Fluke 8600 decades ago, and it has earned its keep. I used a
Fluke differential voltmeter in the army, and that was a real tedious
PITA. So going to a DMM is like the best thing since sliced bread.

I think the best investment I've made in the last few yrs was the AADE
LC Meter IIb. It's great for those odd coils and caps.

But I think I should get a 'scope that's better than the ol' 15MHz one
that I now have. I can get a 100MHz one for a hundred or two on Ebay,
but a pair of decent stinkin' probes for it cost more than that!

Maybe I should spring for a scope that has the DMM pod on it, or has all
that buiilt-in and shows on the screen. I don't think I wanna get a
hend-held one because they're too easy to steal or drop. Besides, the
Fluke cable meter that I use at work had to have Ni-Cd batteries
replaced and they were $158 apiece.

 

[Rich Grise]

Confucius

Well, if what Confucius said is true, then NIST must not be certain of
the exact time. But NIST claims accuracy of something like 10^14 or so
over their numerous standards..

Perhaps it should be "Man with one watch is deceived into thinking he
knows the exact time.."

Ironically, a watch that's not even running shows the exact time twice
a day!

Cheers!
Rich

 

[Rich Grise]

That's not true. All electrical constants are based on physical
constants, and can be derived from them.

So, you're going to stand there and count 602,214,150,000,000,000,000,000
individual electrons?

Good Luck! ;-)
Rich

 

[Rich Grise]

Absolutely not. Last week I needed a 0.1 ohm resistor, so I took out
the ref manual and looked at the wire tables, and found that 32 AWG has
162 milliohms per foot. This is a physical constant derived from Rho *
length / area. Rho for copper is 10.37 at 25 C. So I measured 7.4
inches of #32 wire and wound it around a 1W high value resistor, and it
measured very close to 0.1 ohm. Now I only have the problem that it has
.6 microhenry inductance.

The same can be done for a capacitor.

Before winding it, bend the wire into a long, narrow "U" shape. Start
winding at the bend, in the middle of the form, and wind both ways. I
was told that this makes the inductances "cancel out". ;-)

Cheers!
Rich

 

[Michael A. Terrell]

Ironically, a watch that's not even running shows the exact time twice
a day!

Cheers!
Rich

Not digital watches. They just lay there and do nothing.

 

[Spehro Pefhany]

Not digital watches. They just lay there and do nothing.

I doubt anyone made a digital watch with the flip panels. ;-) But I
have noticed someone is making clocks like that again!


Best regards,
Spehro Pefhany

 

[John Fields]

Ironically, a watch that's not even running shows the exact time twice
a day!

 

[Barry Jones]

I doubt anyone made a digital watch with the flip panels. ;-) But I
have noticed someone is making clocks like that again!

Here's one:
<http://www.lares.dti.ne.jp/~yugo/storage/monocrafts_ver3/03/index.html>

 

[ehsjr]

On Sun, 17 Apr 2005 10:16:25 -0700, Watson A.Name - "Watt Sun, the Dark



Before winding it, bend the wire into a long, narrow "U" shape. Start
winding at the bend, in the middle of the form, and wind both ways. I
was told that this makes the inductances "cancel out". ;-)

Cheers!
Rich

It does when wound on a toroid. You wind 1/2 the turns in one
direction, form a U in the wire (as if you were making a
centertap) and wind the remaining turns in the opposite
direction. I've never done it with an air wound, but it
is a technique I've used on toroids.

Ed

 

[Stewart Pinkerton]

How did you know that the wire was *exactly* 32 AWG? How did you
terminate the resistor? How did you know the purity of the copper?
Note that basic 'tough pitch' copper does not have the same
resistivity as the ubiquitous OFHC wire, which does not have the same
resistivity as pure copper. Which did you have, and which was used to
build the wire tables you used?

With the same problems of accurate measurement of all parameters.

Before winding it, bend the wire into a long, narrow "U" shape. Start
winding at the bend, in the middle of the form, and wind both ways. I
was told that this makes the inductances "cancel out". ;-)

Yes, it's known as bifilar winding, and would drop the above resistor
to less than a nanoHenry with reasonable care.

 

[Winfield Hill]

Stewart Pinkerton wrote...

Yes, it's known as bifilar winding, and would drop the above resistor
to less than a nanoHenry with reasonable care.

Not simply bifilar. The reversal scheme is called an Aryton-Perry
winding, e.g., as in Ohmite's WN series of wirewound non-inductive
resistors, http://www.ohmite.com/catalog/pdf/whm-wnm.pdf And etc.
It's also made by winding a layer in one direction, adding insulation
and winding the next layer back in the opposite direction, with the
turns crossing every 180 degrees.