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