You're right, I was talking nonsense. I stupidly took something someone at work told me at face value without thinking about it.

All resistors are much better than the tollerance - ever heard of six sigma?

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If you want that kind of calibrated precision don't forget to take into account the load condition the resistor will be working under. Thermal variance in a resistor will be significantly more important than generic component tolerance if there is a wide set of temperatures the resistor will be exposed to. You'll get two variance points, the resistors temperature rise from the current going through it and the ambient temperature from the rest of the circuit itself and their thermal linkages (air or heatsink) Heat sinking your resistor could reduce this effect, you could also insulate it with hot glue in a cold environment self heating would keep the temperature constant, the running temperature of the resistor just needs to be as close to constant as possible.

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I was just migrating all my stuff to a new computer, and ran across a resistance calculator program that I had forgotten I had. Very cool! It's free and available at:

Directory of /~rstevew/Public/Software

Look for Rescad.zip

It works for finding the nearest values, and series, parallel, and divider calculations. And you can choose from E6, E12, E24, E96, or E192 tolerance resistors.


Ken

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