matching resistors to a schematic value

pro_crip · 1936

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Offline pro_crip

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on: March 19, 2011, 04:27:53 AM
This isn't really a tube question, more of a mathematical analysis. How many resistors would I have to buy to guarantee that a pair of them will perfectly (within 4 significant digits) match the value called for in the schematic? This is what I get for depending on excel too much. Thanks for listening.



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Offline Paul Joppa

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Reply #1 on: March 19, 2011, 05:39:16 AM
... How many resistors would I have to buy to guarantee that a pair of them will perfectly (within 4 significant digits) match the value called for in the schematic? ...
This is a statistical question. The answer is an infinite number; the best you can do is improve the probability that a pair will match - no guarantee is possible.

You are asking for 0.01% accuracy. On average I think you have a 50% chance that one out of a hundred 1% resistors will match a given value to 0.01%, so there must be a 25% chance that two out of 200 will do so. Beyond that, I don't remember enough of my probability and statistics education to answer.

You can buy 0.1% resistors pretty readily, but only in selected values.

Paul Joppa


Offline STURMJ

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Reply #2 on: March 19, 2011, 08:06:02 AM
Part Connexion carries prp resistors. They advertise 1% but the site says they may be closer to 0.1% . They are not expensive either, and they are made here in the mid-west USA!