Electronic Component Tolerances

Terry Casey · 2014-11-18T23:23:36+00:00

In a recent thread, component tolerances were discussed and there was a brief reference to E6 and E12 series. The concept of acceptable tolerances seems to be alien to many people, especially those who dabble with electronics for the first time. The availability of accurate digital meters compounds these problems. It is quite common to see posts in some forums on the lines of "I replaced R72 (100k) because it was reading high at 106.8k". Of course, if the resistor had a tolerance of ±10%, it would have been well within spec and it is quite possible that the replacement was even further from the nominal value but still within spec. In the days when everybody used analogue meters they would probably have noted that the pointer indicated 100k, near enough, and moved on ... Then there are these mysterious E numbers ... In the early days of electronics - or should I say the wireless? - manufacturing tolerances were so high that a simple 1,2,5,10... sequence was about the best that was reasonably possible. In fact, although improvements in resistor technology moved on quite rapidly, there is still a lot of vintage equipment about with capacitors that follow the 1,2,5 sequence* ... When it became viable to consistently produce resistors with a ±20% tolerance, a logarithmic or exponential series of values appeared. This was the E6 series, with values of 10, 15, 22, 33, 47 & 68 ohms and multiples of 10 thereafter. In time, as tolerances improved still further, the E12 series (±10%) and the E24 series (±5%) appeared. Anybody who thinks that the ranges of resistor values follow some weird random sequence might like to look at this drawing I produced which shows how neatly the values in the various ranges neatly dovetail together: * Some people seem to have great difficulty in grasping the concept that the 0.2µF and 0.5µF capacitors that they wish to replace can no longer be found and that all they are are offered are 0.22µF and 0.47µF components...

Nov 18, 2014 22 Replies

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Johny B Good 11 years ago

The smiley rather suggests you're taking the piss out of RS for misquoting a 4700µF 450v large can electrolytic HT smoothing capacitor as being a 12pF electrolytic capacitor.

Mind you, you seemed to have missed the typo on the price which seems to be inflated by an order of magnitude of error (at least when the cap in question is a low grade 2000 hour lifetime rated 85 deg C specimen). The pricing is all rather too Russ Andrewesque for my taste. :-)

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meow2222 11 years ago

or out of someone for thinking its 12pF

pretty normal for RS.

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whisky-dave 11 years ago

They aren't the sort of things I'd buy. How many 150Rs would you need to buy before finding one of 147.85 ohms ?

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