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NNTP-Posting-Date: Sat, 27 Apr 2024 21:41:10 +0000
From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: Practical resistor accuracy distribution
Date: Sat, 27 Apr 2024 17:41:10 -0400
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On Sat, 27 Apr 2024 14:24:43 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:

>On Sat, 27 Apr 2024 16:47:29 -0400, Joe Gwinn <joegwinn@comcast.net>
>wrote:
>
>>On Fri, 26 Apr 2024 19:38:07 -0700, John Larkin
>><jjSNIPlarkin@highNONOlandtechnology.com> wrote:
>>
>>>On Fri, 26 Apr 2024 20:16:48 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>wrote:
>>>
>>>>On Sat, 27 Apr 2024 00:54:41 +0200, Klaus Vestergaard Kragelund
>>>><klauskvik@hotmail.com> wrote:
>>>>
>>>>>Hi
>>>>>
>>>>>I needed to look into distribution of accuracy of resistors.
>>>>>
>>>>>Vendors don't have any info, but luckily some nice people online have 
>>>>>done measurements:
>>>>>
>>>>><https://www.eevblog.com/forum/projects/smd-resistor-distributions/>
>>>>>
>>>>><https://lambdafox.com/resistor-tolerances/>
>>>>>
>>>>The thing to be aware of is that resistor value distributions are
>>>>often wildly non-Gaussian.  The classic example is where there are
>>>>grades, say 1%, 5%, and 20%.  The 5% group will often have a hole that
>>>>happens to match the 1% distribution perfectly.
>>>>
>>>>A lot of modern resistors are made with a relatively wide
>>>>distribution, and then machine-sorted into bins.  In this case, many
>>>>of the bins will have uniform distributions.  And so on.
>>>>
>>>>Joe Gwinn
>>>
>>>I suspect that they may laser trimmed and shipped, not binned.
>>>
>>>One batch on a reel could be very close to one another. 
>>
>>Also possible, and maybe a combination of both?
>>
>>But the fundamental point is that one must measure to be sure, unless
>>one is a large enough customer that the manufacturer will simply tell
>>you.
>>
>>Joe Gwinn
>
>We just assume that all 1% resistors are within 1%.
>
>We buy 0.1% and some 0.05% parts too. Since most of our products have
>software-based calibration, we mostly care about resistor tempcos, not
>so much tolerances.

Yes, and calibration will wash all those strange-distribution woes
away.

Joe Gwinn