Accurately Measuring Precision Resistors

[BFoelsch]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:116526nt9ip6bd7@corp.supernews.com...

"Dave" <nospam@nowhere.com> wrote in message
news:42625bea@212.67.96.135...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

For example, suppose you have 100 1 M resistors with a precision of

1%.

If you connect them all in parallel, you'd have an equivalent 10K
resistor, but it's standard deviation will have decreased by a
factor

of

sqrt(100).

As someone said, that only works if the originals are normally
distributed. If they were different makes then it might be valid, but
otherwise no chance.


Maybe it's better to just scrounge a known good 0.1% resistor from a
piece of equipment,

I don't think you will find 0.1% resistors are that expensive.

About $5 last time I checked. So buying a few is not exatly going to
break the bank.

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 Su]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:hc3561l9kmm62v796gef4g00ak22r4i0m2@4ax.com...

On Sun, 17 Apr 2005 09:11:16 -0700, the renowned "Watson A.Name -
\"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote:



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 ;-)

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

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.

But these were sketches......

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the
reward"
speff@interlog.com Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com

 

[Watson A.Name - \"Watt Su]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:9i4561d77gg0s549hfkdk865bsp2r6cucu@4ax.com...

On Sun, 17 Apr 2005 09:18:18 -0700, the renowned "Watson A.Name -
\"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote:

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.

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."

Best regards,
Spehro Pefhany
--

 

[Spehro Pefhany]

On Sun, 17 Apr 2005 13:07:07 -0700, the renowned "Watson A.Name -
\"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote:

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:hc3561l9kmm62v796gef4g00ak22r4i0m2@4ax.com...
On Sun, 17 Apr 2005 09:11:16 -0700, the renowned "Watson A.Name -
\"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote:



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 ;-)

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

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.

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
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Watson A.Name - \"Watt Su]

"BFoelsch" <BFoelsch@comcast.ditch.this.net> wrote in message
news:y8WdnbOM5Pe2AP_fRVn-qQ@giganews.com...

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote
in message news:116526nt9ip6bd7@corp.supernews.com...

"Dave" <nospam@nowhere.com> wrote in message
news:42625bea@212.67.96.135...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

For example, suppose you have 100 1 M resistors with a precision
of

1%.

If you connect them all in parallel, you'd have an equivalent
10K
resistor, but it's standard deviation will have decreased by a
factor

of

sqrt(100).

As someone said, that only works if the originals are normally
distributed. If they were different makes then it might be valid,
but
otherwise no chance.


Maybe it's better to just scrounge a known good 0.1% resistor
from a
piece of equipment,

I don't think you will find 0.1% resistors are that expensive.

About $5 last time I checked. So buying a few is not exatly going
to
break the bank.

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........

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]

On Sun, 17 Apr 2005 08:48:05 -0700, Watson A.Name - "Watt Sun, the Dark

"Henry Kolesnik" <kolesnik@sbcglobal.net> wrote in message
....
"Man with one watch knows exact time, man with two, not sure."
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]

On Sun, 17 Apr 2005 08:43:17 -0700, Watson A.Name - "Watt Sun, the Dark
Remover" wrote:

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
news:b55461d9b3f7g8bbr4kv8v7f0vgt3rl6rh@4ax.com...
On Sat, 16 Apr 2005 17:20:01 GMT, "Henry Kolesnik"
kolesnik@sbcglobal.net> wrote:


I too like to have accurate things to confirm something to the nth
degree.
I'm still hoping that someone will come up with a trick to verify a
precison
resistor with stuff you already may have as you initially asked. But
by the
looks of it, it can't be done.

Unfortunately, there *are* no tricks. In order to verify any given
electrical quantity to a high degree of precision, you must already be
in possession of a highly precise electrical quantity, be it voltage,
current or resistance.

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]

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

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
On Sun, 17 Apr 2005 08:43:17 -0700, "Watson A.Name - \"Watt Sun, the
"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
On Sat, 16 Apr 2005 17:20:01 GMT, "Henry Kolesnik"
....
I too like to have accurate things to confirm something to the
nth
degree.
I'm still hoping that someone will come up with a trick to verify
a
precison
resistor with stuff you already may have as you initially asked.
But
by the
looks of it, it can't be done.

Unfortunately, there *are* no tricks. In order to verify any given
electrical quantity to a high degree of precision, you must already
be
in possession of a highly precise electrical quantity, be it
voltage,
current or resistance.

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

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.

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

 

[Spehro Pefhany]

On Mon, 18 Apr 2005 19:11:18 GMT, the renowned "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Rich Grise wrote:

On Sun, 17 Apr 2005 08:48:05 -0700, Watson A.Name - "Watt Sun, the Dark
"Henry Kolesnik" <kolesnik@sbcglobal.net> wrote in message
...
"Man with one watch knows exact time, man with two, not sure."
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

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
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[John Fields]

On Mon, 18 Apr 2005 15:28:37 GMT, Rich Grise <richgrise@example.net>
wrote:

On Sun, 17 Apr 2005 08:48:05 -0700, Watson A.Name - "Watt Sun, the Dark
"Henry Kolesnik" <kolesnik@sbcglobal.net> wrote in message
...
"Man with one watch knows exact time, man with two, not sure."
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!

---
Not always. Check abse where your name is in the subject line.

--
John Fields
Professional Circuit Designer

 

[Barry Jones]

Spehro Pefhany wrote:

On Mon, 18 Apr 2005 19:11:18 GMT, the renowned "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:



Rich Grise wrote:


On Sun, 17 Apr 2005 08:48:05 -0700, Watson A.Name - "Watt Sun, the Dark


"Henry Kolesnik" <kolesnik@sbcglobal.net> wrote in message


...


"Man with one watch knows exact time, man with two, not sure."


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


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!


Here's one:

<http://www.lares.dti.ne.jp/~yugo/storage/monocrafts_ver3/03/index.html>
--
Barry

 

[ehsjr]

Rich Grise wrote:

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

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message

On Sun, 17 Apr 2005 08:43:17 -0700, "Watson A.Name - \"Watt Sun, the

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message

On Sat, 16 Apr 2005 17:20:01 GMT, "Henry Kolesnik"

...

I too like to have accurate things to confirm something to the

nth

degree.

I'm still hoping that someone will come up with a trick to verify

a

precison

resistor with stuff you already may have as you initially asked.

But

by the

looks of it, it can't be done.

Unfortunately, there *are* no tricks. In order to verify any given
electrical quantity to a high degree of precision, you must already

be

in possession of a highly precise electrical quantity, be it

voltage,

current or resistance.

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

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.


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]

On Mon, 18 Apr 2005 15:35:02 GMT, Rich Grise <richgrise@example.net>
wrote:

On Sun, 17 Apr 2005 10:16:25 -0700, Watson A.Name - "Watt Sun, the Dark
"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
On Sun, 17 Apr 2005 08:43:17 -0700, "Watson A.Name - \"Watt Sun, the
"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
On Sat, 16 Apr 2005 17:20:01 GMT, "Henry Kolesnik"
...
I too like to have accurate things to confirm something to the
nth
degree.
I'm still hoping that someone will come up with a trick to verify
a
precison
resistor with stuff you already may have as you initially asked.
But
by the
looks of it, it can't be done.

Unfortunately, there *are* no tricks. In order to verify any given
electrical quantity to a high degree of precision, you must already
be
in possession of a highly precise electrical quantity, be it
voltage,
current or resistance.

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

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.

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?

The same can be done for a capacitor.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

 

[Winfield Hill]

Stewart Pinkerton wrote...

Rich Grise wrote:

Watson A.Name wrote:
... Last week I needed a 0.1 ohm resistor, ... so I measured 7.4
inches of #32 wire and wound it around a 1W high value resistor.
Now I only have the problem that it has 0.6 microhenry inductance.

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.

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.


--
Thanks,
- Win

 

[Tom MacIntyre]

On Mon, 18 Apr 2005 17:57:31 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Mon, 18 Apr 2005 15:28:37 GMT, Rich Grise <richgrise@example.net
wrote:

On Sun, 17 Apr 2005 08:48:05 -0700, Watson A.Name - "Watt Sun, the Dark
"Henry Kolesnik" <kolesnik@sbcglobal.net> wrote in message
...
"Man with one watch knows exact time, man with two, not sure."
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!

---
Not always. Check abse where your name is in the subject line.

I'm coming in late here, but I always sort of liked the band Chicago's
assessment of this.

Tom