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Accurately Measuring Precision Resistors

I acquired a couple dozen Micro-Ohm 400 ohm, 0.1% resistors, and some other values. They've probably been around a decade or more, and/or may have been culled. In any case, I would like to check them to make sure they're within tolerance. I thought about doing this a couple ways:

Measuere them with a Fluke 4.5 digit meter, which hasn't been cal'd in decades, but it could give me an idea of how close they are to a common value, even if that value isn't exactly 400.

Measure them with a Leeds Northrup Wheatstone bridge. It's been around decades and hasn't been cal'd in a long time. But it's a bridge, so if there is any long-term drift, the resistors should drift the same way, assuming the resistors are all the same. My guess is they're wirewound, which is fairly stable. But there's grunge on the switch contacts, etc.

Make a bridge out of four of the 400 ohm resistors. Again, use this to compare them to one another, to see if they are all about the same resistance. If I apply a few dozen volts to the bridge, I should be able to measure a few millivolts, as long as I don't heat up the resistors too much and cause them to drift.

One other thought. I have a precision power supply with terminals on the back to allow me to hook up a resistance in series with the 1.000 mA constant current source. If it is 400 ohms, then I should measure 0.400 VDc output.

I realize that 0.1% is one part in a thousand, so that's 400 + or - 0.4 ohms. That's about the residual meter lead resistance I see in my meters. I don't have a standard resistance, traceable to the NIST or whatever. And I don't have a friend who's working at a cal lab. So I'm trying to make do with what limited resources I have to get the most accurate measurement. Any helpful advice would be appreciated. Thanks.

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You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it:
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Reply to
Watson A.Name - "Watt Sun, th
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Post your snail mail address, and I'll send you several .01% resistors, checked with a

6 1/2 digit DVM.
Reply to
The Phantom

Dark Remover\""

may

sure

resistors,

Which remindw me, I have some precision resistors made by Cinema Engineering out in the garage. I think some of them are that low a tolerance, but they're big ol' bobbins wound with lots of very fine wire. I'll have to dig around and check them out.

Reply to
Watson A.Name - "Watt Sun, th

The Phantom wrote: > Post your snail mail address, and I'll send you several .01% resistors, checked with a

I'm building a measure bridge, and I'd love two of these. How much do you want? I've turned "on" this address, so you can mail me at snipped-for-privacy@vidarlo.net

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MVH,
Vidar

www.bitsex.net
Reply to
Vidar Løkken

I'm curious as to the application for 400 ohm 0.1% resistors might be besides instrumentation? tnx

--

73 Hank WD5JFR "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...
Reply to
Henry Kolesnik 

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Conversation.
Reply to
John Fields

"Henry Kolesnik" wrote in news:xuU7e.2555$VA3.2543 @newssvr30.news.prodigy.com:

A long boring thread...

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Reply to
me

--- snipped-for-privacy@here.net ?

If it was boring for you, instead of just yawning and taking a superior position and going away with no comments, why did you feel that it was necessary for you to respond with a bogus address instead of not responding at all?

Because you think your opinion is important? It isn't, unless you can back it up with facts so, unless you can do that, piss off.

-- John Fields Professional Circuit Designer

Reply to
John Fields

Well, calibration, for one. And they can be used to make a closely balanced wheatstone bridge. But since these are wirewound, that's not too practical for AC work. Unless the inductance is as accurate as the resistance.

Also, education. One should learn how to make accurate measurements and minimize errors. And learn the capabilites and limitations of his test equipment.

But as I originally stated, my primary reason for measuring them accurately is to make sure they're not some out-of-tolerance culls that someone picked up ar a surplus parts place.

wrote

some

may

sure

in

common

around

if

way,

wirewound,

etc.

to

on

1.000 mA
0.400
0.4

or

I'm

Thanks.

Reply to
Watson A.Name - "Watt Sun, th

I took like to have accurate things to confirm something to hte nth degree. I'm still hoping that someone will come up with a trick to verify as you asked but by the looks of it, it can't be done.

--

73 Hank WD5JFR "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...
Reply to
Henry Kolesnik

degree.

you

Ummmmm.. I think I need some kind of instrument to understand what you said above. Or maybe I should just put a few 'pints' under my belt and I'd understand you more clearly. Speaking of pints under my belt, check this out. I assume by pints, they mean ale, since lager is German, IIRC.

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A real gut-buster! More here.

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wrote

be

not

the

and

test

that

[snip]
Reply to
Watson A.Name - "Watt Sun, th

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.

--

73 Hank WD5JFR

Reply to
Henry Kolesnik

You really have to have *something* you trust to start with. Two somethings makes it even easier.

I was thinking about finding *something*, and it seems to me, at least theoretically, that you could make a large set of resistors (or other things) of a given precision into a smaller set of resistors (or other things) with higher precision.

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). This is from the definition of Sample Normal Distribution. Assuming the 1 M resistors had a mean of 1 M, and a somewhat normal error distribution (it doesn't even have to be very close to normal), this should increase the precision by a factor of 10. What say you to the analysis?

Of course there may be other errors introduced in trying to connect 100 resistors in parallel. Details, details.

Now if I could just invent perpetual motion . . .

--
Barry

Heisenberg may have slept here.
Reply to
Barry Jones

degree.

precison

by the

1%.

of

100

Like getting the bus hot enough to solder all 100 of them, which then heats the other resistors up for a long time. Not so good.

But what if the testing machinery happens to be off a half percent that day, on the high side, and all of the resistors in your batch are ones made that day. Now your statistical curve is distorted significantly.

Maybe it's better to just scrounge a known good 0.1% resistor from a piece of equipment, and have it checked by a known accurate meter. Sort of like those sets of weights with the little ivory tweezers to pick them up. They are known standards, cal'd at a lab that can trace back to the standards at NIST or wherever. You don't use them day-to-day, just once in awhile to verify that your instruments are working properly.

Reply to
Watson A.Name - "Watt Sun, th

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. The conversion is straightforward, but you need some kind of absolute measure at some point in the procedure.

--

Stewart Pinkerton | Music is Art - Audio is Engineering
Reply to
Stewart Pinkerton

There is one fatal error often missed by those trying this trick - the excluded middle. If your chosen resistors represent the best available from that maker, then you may be in with a chance, but if they are not the top spec, then there's a good chance that they are 'selected seconds' which failed to make the top grade, and therefore there will be *no* examples close to nominal. Depending on the selection process, it's also possible that they will all be on one side of nominal.

Caveat experimentor!

--

Stewart Pinkerton | Music is Art - Audio is Engineering
Reply to
Stewart Pinkerton

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

--

73 Hank WD5JFR
Reply to
Henry Kolesnik

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.

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.

Reply to
Dave 

--
There were watches around 2500 years ago?^)
Reply to
John Fields

Less than a dollar, quantity 1, for 402R +/-0.1% 25ppm from stock (leaded, which I'd prefer for this purpose, 1206 or 0805).

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
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Reply to
Spehro Pefhany

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