Using a thin wire instead of a resistor?

[Tony]

Many thanks to Spehro, Paul and John - it's always comforting to come
back here after a fruitless Google session.

And John - I'd certainly appreciate any curves on a.b.s.e if you are
able.

I understood that there were a number of grades of each, but it seemed
I could find compositions and occasionally limited TCR info, but never
together. The apparent effect of annealing isn't surprising; it
shouldn't be hard for us to anneal a batch at a time before assembly.

Our shunts won't normally carry any significant heating load, and
we're trying to cover -40C to +60C, so a peak no higher than 25C would
be best. Or maybe the wider ranges are where Constantan or Nikrothal
come in?

[...]
What about using a thin wire in place of a resistor?

It is a great way to make a resistor with a huge surge rating but a bad
temp-co.

The tempco is pretty good if you use manganin wire, and not so bad
with Constantan wire. Brass is not as bad as copper either.

I've been trying to find some decent data on the tempcos of Manganin,
Constantan and Nikrothal LX (or any other low TCR material) for a
while now - preferably a typical resistance vs temperature curve, but
the best I've been able to Google is that Manganin is either 10 or
15ppm/K, Constantan is either 20 or 74ppm/K (but over a wider range),
and Nikrothal LX may be 10 ppm/K - not quite enough consistency to
give me any confidence at all. Any chance you can point me to some
credible data (ideally over the range -40C to +60C)? Even better, a
trusted supplier? in Australia?

Tony (remove the "_" to reply by email)

Manganin has a parabolic curve of resistance vs temperature, peaking
at some temperature and falling off above or below. Within maybe 10
deg C of the peak, tc is only a few PPM. The peak temp depends on the
manganese composition and on the alloy's history - mechanical
stresses, like winding or fabrication, mess up the curve, and
annealing fixes it. You can buy "wire" manganin with zero tc (parabola
peak) near 25C, or "shunt" manganin with min tc around 80 c or
something, for big shunts that self-heat a lot. One alloy is "manganin
13" (13% manganese) and one is "manganin 12" but I can't remember
which is which.

I can post some data and curves to a.b.s.e. if anybody's interested. I
have that stuff at work.

John

Tony (remove the "_" to reply by email)

 

[Rene Tschaggelar]

Many thanks to Spehro, Paul and John - it's always comforting to come
back here after a fruitless Google session.

And John - I'd certainly appreciate any curves on a.b.s.e if you are
able.

I understood that there were a number of grades of each, but it seemed
I could find compositions and occasionally limited TCR info, but never
together. The apparent effect of annealing isn't surprising; it
shouldn't be hard for us to anneal a batch at a time before assembly.

Our shunts won't normally carry any significant heating load, and
we're trying to cover -40C to +60C, so a peak no higher than 25C would
be best. Or maybe the wider ranges are where Constantan or Nikrothal
come in?

You can always measure the temperature with an NTC and
calculate it out...

Rene

 

[Glen Walpert]

Many thanks to Spehro, Paul and John - it's always comforting to come
back here after a fruitless Google session.

And John - I'd certainly appreciate any curves on a.b.s.e if you are
able.

I understood that there were a number of grades of each, but it seemed
I could find compositions and occasionally limited TCR info, but never
together. The apparent effect of annealing isn't surprising; it
shouldn't be hard for us to anneal a batch at a time before assembly.

I just posted a .pdf of some generic electrical resistance alloy
properties to a.b.s.e., hopefully John can provide his specific data
also.