Resistor accuracy

I have two HV voltage dividers, each composed of 8x499kOhm+10kOhm resistors. Made of 0.1% resistors, because why not. That should result in 4.002MOhm end to end, in the range 3998..4006Ohms. A bit better, if the distributions are assumed to be Gaussian and added properly. But hey, not *that*:

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Since -- as they say -- there no accidents, just signs, what's the sign here? Have the factories been seized by six-sigma aliens and the lines silently switched to 0.01%? And they continue to sell "just"

0.1% because the market demands so? The meter is good, but not that good, either.

Needless to say the other divider provides exactly the same, rock-stable reading.

Best regards, Piotr

Reply to
Piotr Wyderski
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On a sunny day (Tue, 18 Jun 2019 09:13:30 +0200) it happened Piotr Wyderski wrote in :

The Russians have taken control of your meter? Shield it in tinfoil and try again.

Reply to
Jan Panteltje

Just a variation of Murphy's Law, when you don't care random things always fall out in your favour, and when you do care they never fall out in your favour (unless you expected that!).

Just tested an HP6629A, last calibrated in 2003, error at 49.5V was less than 6ppm - it was sold as a "Precision" version of that family but how did they know to match my meter :-)

MK

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Reply to
Michael Kellett

Michael Kellett wrote in news: snipped-for-privacy@giganews.com:

things

Like having an ON day or an OFF day when shooting pool. I go from making the shot and missing the scratch to making the scratch and missing the shot. The difference between the two, especially when doing multi-rail bank shots, is very slight and very chaotic. The amount of spin left on a ball after hitting a rail changes the angle it banks at. From the end rail, the side pocket 'window' is barely more than a ball wide. So the difference between hitting below or above the pocket or right on the money is very slight.

So small that I wonder how a man can hit tthat exact spot on the ball using just the right english on it to make it spin just so that when it hits that third rail, it squirrely-walks right into the pocket. One minute fraction off and it misses.

So when I do it consistently, I wonder how I can possibly be that accurate. I give all credit to Jesus or I (we) wouldn't even be here. But the shot precision... That I refer to as "The Harlem Globetrotter Effect". How could Meadowlark Lemon stand with his back to the hoop, talking to Howard Cosell at half court and toss a swish shot? ????????

You should see some of my pool shots. I shoot hard and once I am on and start getting exuberant, the balls start hopping all over the table. I shoot bank shots that come off the rail and jump to the pocket in mid air. The "hard shot" thing... I always get told I missed a shot because I shoot too hard. I always say nope. I missed because I missed the exact spot I needed to make it AT THAT SPEED. I shoot slow too, just when needed I shoot shots where the balls barely move at all. Shooting hard is how one gets the shot and brings the cue ball all the way around the table and back to where you need it for the next shot. Shooting hard should be part of any player's regimen. I also shoot when there are balls in the way. I can do a curl shot that is not masse, but is what got the otherwise hidden shot. I call it 'mild masse'. Matthew McConaughey would like my shooting style a lot.

Oh, and I do this all without even touching the table. My bridge hand is held in mid air on EVERY shot. I literally never touch the table if I can help it.

Reply to
DecadentLinuxUserNumeroUno

[and meter shows 4.002Mohm]

Have the factories been seized by six-sigma aliens and

More likely the resistors are laser-trimmed at room temperature, and the full specified range of temperatures would expand that deviation to something near the nominal tolerances.

Reply to
whit3rd

whit3rd wrote in news: snipped-for-privacy@googlegroups.com:

One would think that they get trimmed at an elevated temperature and with high potential electromotive pressure applied as well.

Reply to
DecadentLinuxUserNumeroUno

Zzzap!

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Reply to
Winfield Hill

0.1% R's are great! I'm use to my DMM showing 1.000 or 0.999. You've got four so in theory the error is down by 2 (sqrt 4). I don't have the patience (or good enough kit) to measure the distribution of values in 0.1% R's, but in 1% R's there is no Gaussian distribution. All the R's in one pac/ reel seem to be near some value...like 9.96k for 10 k.. and then a few outliers.

George H.

Reply to
George Herold

Even a blind pig finds an acorn once in a while.

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  Rick C. 

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Reply to
Rick C

You are pushing the accuracy of the meter.

But resistors are laser trimmed and are routinely 10x better than their specs.

The problem with a HV divider will be the voltage coefficient of the resistors. The higher the voltage, the lower the resistance. That can be a few PPM per volt for an exceptionally good resistor, up to hundreds of PPM/V. The series string helps.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

They're only as inaccurate as your meter. . . .

RL

Reply to
legg

The accuracy of the meter is specified as 1% at the 20M range, so the result is unreliable, sure thing. But for some odd reason the result matches the mathematically accurate value. Am I accidentally close to a factory calibration point or what? That's weird.

Hence 8. Good point, so the digital compensation would need to be more complex. I didn't know about this property, thanks, John. But the datasheet seems not to specify its value. It's a 25ppm 1206 part with

150V rating and my HV is 1kV most.

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Best regards, Piotr

Reply to
Piotr Wyderski

Thin films are better than cermets; carbon comp is the worst for voltage coefficient.

You might ask the manufacturer, and/or measure a few.

Trick: compare the output of the 8-resistor divider to a 2x16 array.

Or apply V (one stable power supply) and 2V (two supplies in series).

Or just use a very good DVM. The 2-supply trick can show if the DVM is linear.

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Reply to
John Larkin

I've found that at high voltage (>5kV) surface contamination of the resistor can give strange results. Much like what some here see with Meg ohm surface mounts and no clean flux. Clean Well and Bake at 85C to burn off organics (This is what Vishay recomends)

Cheers

Reply to
Martin Riddle

A legend in his own mind :-)

Reply to
Rheilly Phoull

It might be cheaper to run one production line making 0.01% resistors, rather than one make 0.1% and the other 0.01%. In that case, they'd mark some at 0.1% and some at 0.01%, and sell the latter at a higher price.

We find this kind of thing everywhere in manufacturing.

Many years ago, I determined that all I needed to do to install reversing lights on my car (it WAS many years ago), was fit the switch to the gear box, connect it to the existing loom, and put bulbs into the existing sockets. They had been omitted merely so that they could be included as part of a more expensive version.

Sylvia.

Reply to
Sylvia Else

Oscilloscopes typically are available in a range of bandwidths, the only difference being software. Buy the 200 MHz version, and later you can pay a lot for the passsword to upgrade it to 400.

Sometimes you can bargain to get the 500 MHz scope for the price of

350. It doesn't cost them anything.

FFT used to be an extra cost option, but competition has made it free.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Piotr Wyderski wrote in news:qeb5jh$1dmr$ snipped-for-privacy@gioia.aioe.org:

One reads high value resistances by using a high accuracy VOLTAGE meter. A nice 6.5 digit bench meter or such. Use two one for current and get a high accuracy shunt and use Ohms law to find the resistance.

Also, HV resistors are at a different value under HV 'pressure'.

At low voltages, one gets one reading, but once impressed upon at high voltage... That is where they operate, and that value is different "at voltage".

Ohmmeters are for basic value readings not particularly high accuracy inasmuch as the reading you get on LV resistors will be that reading in use. At least not for matching and culling purposes.

With high Ohm value, high voltage resistors, as the voltage across them increases, their resistance shifts a bit. Best determination of true value comes from applying a known voltage and reading the current and doing the math.

Reply to
DecadentLinuxUserNumeroUno

Martin Riddle wrote in news: snipped-for-privacy@4ax.com:

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Absolutely. I would recomend a brominated solvent wash. We had a

55 gallon drum of it. It was called Ensolv, but there are better.

Boeing Aerospace uses:

When we made HV supplies, the entire HV section had to be cleaned before potting, because... even "coffee breath" can cause a potting detachment, not to mention HV leakage path establishment.

That is exactly what happens in air as well. If ANY breath condensation, etc., etc., etc. is on them, they operate differntly than designed, because they are designed to operate properly only when 100% clean.

Reply to
DecadentLinuxUserNumeroUno

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