And of course to some converting from the old notation to the more recent
nF randge is alien too, They obviously did not understand the decimal system
very well, though I do have to say that changing things like this seemed to
be totally pointless... pun intended.
There is also a tendency not to look what might have caused a problem. IE
they find a duff transistor, then put in a new one and it gets buggered as
well. In ogther words diagnostic tests should be done to see where issues
might be before sacrificing another transistor etc.
Brian
--
From the Sofa of Brian Gaff Reply address is active
"Terry Casey" wrote in message
...
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 ...
--
Terry
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