![]() That lines up well with the metric system, which does everything by tens and was standard in electronics for as long as electronics has been around, even in places that still used other measurements for other things. Next there's the idea of having the numbers repeat with each "decade" or factor-of-ten interval. Now it makes sense to everyone in the business that it's a good thing for the standard list of resistor and capacitor values available from one manufacturer to be basically the same list of values available from some other manufacturer. People like Jean-Baptiste Vaquette de Gribeauval, Eli Whitney, and Marc Isambard Brunel are remembered for contributing to the introduction of interchangeability around the late 18th and early 19th Centuries (mostly for making muskets, cannon, and other military technology) it was revolutionary at the time. Today we take for granted that idea of "interchangeable parts," where things like screw threads are standardized so you could take the nut off one screw and thread it onto some other screw instead of all nuts and screws being made in pairs that have to be kept together. Moving away from the "craft" model of every manufactured thing being made from start to finish by one skilled individual meant there was a need to measure things and have all the things of a given model be the same as each other. This concept goes back to the Industrial Revolution - and it was one of the important defining factors in what the Industrial Revolution was all about. Why 47? Why not 46 or 48 - especially when 47 is a prime number and 48 has many small divisors, which would seem like it might be convenient? Here are some notes on the commonly-used numbers and where they come from.įirst of all, there's the question of having standard numbers of some sort at all. but for instance there also seems to be something special about the number 47, so you see many resistor values like 4.7kΩ, 47kΩ, 470kΩ, and capacitors like 0.47♟ and 470pF. You'll see power-of-ten sizes like 1kΩ, 10kΩ, 100kΩ and it's understandable that those would be "round" numbers it might be convenient to use and manufacture. You've probably noticed that although resistors and capacitors come in many different values, some of which seem like they could be randomly chosen, there's nonetheless some sort of logic to it. Preferred values for resistors and capacitors ![]()
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