30 Dec
2004
30 Dec
'04
6:26 a.m.
Not really true. The manufacturing process and
resistor structure
is fundamentally different. Film resistors are generally an insulating
core, with spirals of the resistive stuff (thickness, width, and material
depend on the resistance of course) around the core. Then there's a
protective coating and marking around the outside.
There are a few applications where the spiral structure has undesired
inductive effects. But then there are different varieties of metal films,
some specifically low inductance.
If a film resistor is spec'd to work at 600 Volts, and it is having some
problems up there, I would say it's crummy.
I get the impression that the metal-film manufacturing
process has seen
all the benefits of manufacturing technology over the past few decades,
while the carbon composition process has had no improvement for like
fifty years. Mass-produced 0.1% metal film resistors are cheaper than
10% carbon composition units.
Yes, I agree. Carbon comp resistors are pretty much a dead technology.
All resistors drift over time :-). I will admit that
carbon compositions
are much more drifty with respect to just about everything
(time, temperature, heat cycling, humidity, phase
of the moon, etc.)
It is quite common (seen it with my own eyes, too) for a 40 year old
carbon comp resistor to drift over 20 percent, and that even includes the
five percent versions.
William Donzelli
aw288(a)osfn.org