On Wed, 19 Nov 2014 00:51:36 +0000, Graham. wrote:

On Tue, 18 Nov 2014 23:23:36 -0000, Terry Casey
wrote:

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:

https://dl.dropboxusercontent.com/u/24301298/Res_Tolerance.png

* 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 ...

Bring back body-tip-spot resistors. That'll confuse 'em

I'd actually forgotten about them!



--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £30a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor