Tempco calcs

[Ian Fritz]

Hi Tony --

>    Yes, there are a number of really good linear metals, my company uses
> pure nickel wire to make temperature elements for our adiabatic machines
> but again, the problem is the low resistivity.  Something like 90 ohms
> per foot at some small gage.  Stuff is rediculously thin.

Are these for heaters? Just curious -- why not use Nichrome, Chromel
etc?

>    Anyway, I did some looking into buying bare wire, before I settled on
> Micro-ohm tempcos.  I forget where, but there is a good site with
> calculators and whatnot.  They had a number of different pure metal
> wires, and Platinum was one, but it had a coeff of 6000ppm, nearly twice
> what we'd normally use.

Hmm... I've never seen such a large number for Pt. The slope I got from
handbook data gives 3950 ppm/K. The IRC chips are speced at 3750+/-100
and I believe other manufacturers are similar.

>    The stuff that has the right coeff is not actually a pure metal but a
> combination of three.  Can't recall which, but if I dig up that site,
> I'll give it a post.

Please do. That would be much appreciated.

  Ian