On Sun, 05 Sep 2004 15:49:31 +1000, Tony wrote:
On Sat, 4 Sep 2004 14:35:48 -0400, "Arny Krueger"
wrote:
"Mike Rivers" wrote in message
news:znr1094259452k@trad
In article
writes:
Are you suggesting that they select the tempcos as well? or that it
always just happens that if a resistor is very close to its design
value, it automatically has a tighter tempco? Or that the makers lie
about the specs? Or have you just managed to find 0.1% resistors with
bad tempcos?
I have never been concerned with "tempcos" (I assume that's Australian
for temperature coefficient) for a device that will always be used at
room temperature.
Not to mention the fact that if the components of an attenuator are kept in
reasonbly close thermal contact with each other, their ratio, which sets the
attenuation, will remain the same, even if their values change with
temperature.
That's very true, and certainly for the mic attenuator and many other
applications, tempcos would not be an issue. But my comment was
directed at Mike's assertion that 0.1% resistors were simply selected
from 1% production, which I still don't believe to be true.
Tony (remove the "_" to reply by email)
You are right - it certainly isn't true. If it were, all resistors
other than the very best would have a bimodal distribution - a hole in
the middle where the best ones had been removed. They don't.
Typically resistor tolerance describes the width of the three-sigma
level of distribution, and that distribution tends to be normal. In
other words, resistors are "made" to the appropriate tolerance.
d
Pearce Consulting
http://www.pearce.uk.com