Why do electronic components have such odd values? (2021)
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Re: Why do electronic components have such odd values? (2021)
#2Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
Re: Why do electronic components have such odd values? (2021)
#3[deleted]
Re: Why do electronic components have such odd values? (2021)
#4Insightful article. Not something I had considered before, but also...isn't this just a fancy way of defining a geometric sequence thats convenient for values in base-10?
Re: Why do electronic components have such odd values? (2021)
#5Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
I also thought that was interesting. Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
Re: Why do electronic components have such odd values? (2021)
#6Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
I also thought that was interesting. Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
> Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
Neither.
Let R_{1, ideal}, R_{2, ideal} be the "ideal" resistances; both with the same tolerance t (in your example t = 0.05).
This means that the real resistances R_{1, real}, R_{2, real} satisfy
(1-t) R_{1, ideal} ≤ R_{1, real} ≤ (1+t) R_{1, ideal}
(1-t) R_{2, ideal} ≤ R_{2, real} ≤ (1+t) R_{2, ideal}
Adding these inequalities yields
(1-t) (R_{1, ideal} + R_{2, ideal}) ≤ R_{1, real} + R_{2, real} ≤ (1+t) (R_{1, ideal} + R_{2, ideal})
So connecting two resistors with identical tolerance in series simply keeps the tolerance identical.
Re: Why do electronic components have such odd values? (2021)
#7Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
I also thought that was interesting. Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
Fun fact is that afaik component values are often distributed in a bi-modal way because actually +-5% often means that they sorted out already the +-1% to sell as a different more expensive batch. At least it used to be that way. Wonder if it is still worth doing this in production. So I guess one could also measure to average things out otherwise the errors will stay the same relatively.
Re: Why do electronic components have such odd values? (2021)
#8Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
I also thought that was interesting. Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
tolerance should actually go down since the errors help cancel each other out.
reference: https://people.umass.edu/phys286/Propagating_uncertainty.pdf
disclaimer: it will be a relatively small effect for just two resitors
aleph's comment is also correct. the bounds they quote are a "wost-case" bound that is useful enough for real world applications. typically, you won't be connecting a sufficiently large number of resistors in series for this technicality to be useful enough for the additional work it causes.
Re: Why do electronic components have such odd values? (2021)
#9Earlier quoted context omitted.
I also thought that was interesting. Also, wouldn't the tolerance be doubled when you add them in series? Or does it still average out to +/- 5%?
tolerance should actually go down since the errors help cancel each other out. reference: https://people.umass.edu/phys286/Propagating_uncertainty.pdf disclaimer: it will be a relatively small effect for just two resitors aleph's comment is also correct. the bounds they quote are a "wost-case" bound that is useful enough for real world applications. typically, you won't be connecting a sufficiently large number of re…
Note that tolerance and uncertainty are different. Tolerance is a contract provided by the seller that a given resistor is within a specific range. Uncertainty is due to your imprecise measuring device (as they all are in practice).
You could take a 33k Ohm resister with 5% tolerance, and measure it at 33,100 +/- 200 Ohm. At that point, the tolerance provides no further value to you.
Re: Why do electronic components have such odd values? (2021)
#10Can someone explain the last paragraph? The author gives the example of trying to find a 70 Ohm resistor and how the 68 Ohm and 75 Ohm are a little off. They conclude by saying you should just use 33 and 47 Ohm resistors, but wouldn't that give an resistance of 80, not 70?
You are correct. Two of the comments on the article itself also mention this error.