Instructables

What is the tolerance in resistors?

Topic name is pretty much self explanatory. What is tolerance in resistors?

PADMA17523 years ago
If two resistance are inserted in to the circuit in series manner,what will happened to its tolerance.

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PKM6 years ago
I was told an interesting fact about resistor tolerance by my electronics teacher in school. Basically, you will never find a 5% tolerance resistor with the resistance it claims. Resistors are made to be, for instance, 50 ohms. Once the resistors have been made they are tested. Some of them may be 18 or 476 ohms, and they will be scrapped. Some are 48 or 53 ohms, and they are sold as "50 ohm 5% tolerance". If they are 50.02 ohm, however, they will be sold as "50 ohm 1% tolerance" resistors which get a higher price. The upshot of this is, if your resistors are available in 1% and 5%, then "5%" tolerance resistors will be between 1% and 5% different from their rated value. This may or may not be representative of current industrial practice, and might have been false but used as an example to teach us the value of testing your components for true rather than indicated value, but it's something to think about anyway. If the value of your resistors is crucial, test them until you find one suitable, or combine several to make a suitable value (only really works with resistors, capacitors and inductors).
gmoon PKM6 years ago
This may or may not be representative of current industrial practice, and might have been false...

Nope, I'd say it's true. It's called "cherry-picking," and happens broadly across the electronic industry.

It's how they decide speed or voltage rating for microcontrollers, and the military spec ICs, etc. They test a percentage of each batch (sometimes to failure) and the remaining "good stuff" gets up-rated.

(I believe it's how standard micro processors are speed rated, too.)

I had never considered the consequences for resistors, however--that it's highly unlikely the value would be within 1%....

Still, with the likeliest values probably @ 2% or 3%, that close enough for me.
Patrik PKM6 years ago
Makes sense - I wish they'd put a little "+" or "-" on the resistors though! :-D
The tolerance is the percentage of error that the reistor has. Most resistors will have one of three colors are no colors (+-20%, silver (+-10%), and gold (+-5%), although with other colors or with a 5-band, go to a place like wikipedia to find out. This means that you take the percentage x the ohms to get how far off it may be (i.e. 60 ohm with silver stripe would be anyhwere from 54 ohm to 66 ohm).