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# Resistivity of tungsten down to -40degC

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#### cupoftea

Hi,
All web pages only give tungsten resistivity down to 20degC.
Do you know it down to -40degC?

Also, is this tungsten IR lamp have a filament made of tungsten?

..its "datasheet" doesnt say.

according to
Lide, D. CRC Handbook of Chemistry and Physics, 75 edition. CRC Press, 1995: 12.
at

"electrical resistivity of tungsten RW in n-ohm·m are given in
RW = 48.0 (1 + 4.8297 × 10−3 T + 1.663 × 10−6 T2)"

interesting unit - looks like nano ohm meters to me

this website talks about the temperature coefficient of resistivity

as does this one:

In a first order estimation, resistance of pure metals is proportional to absolute temperature, surely sufficient accurate for your problem.

All web pages only give tungsten resistivity down to 20degC.
Do you know it down to -40degC?
According to my extrapolation of the tungsten resistance curve, at -40°C it should be about 73% of the value at 20°C.
Also, is this tungsten IR lamp have a filament made of tungsten?
I would expect so, but it could also be an alloy like NiChrome, used in may heating elements such as toasters and stove tops.

Using @wwfeldman's link to the Physics Factbook, I plotted the data and an adequate trend using a 6th order Polynomial.

It has both the absolute Resistivity and the relative value referenced to R300K ( 27 °C)

You can use the ratio At -40 °C = 233 °K relative to your known value or the R/R300K .

Here is the equation for the R/R300K with x= °K and f(x) = R/R300K

Now the reduction in resistance with a constant voltage will raise the power dissipation and thus reduce the thermal colour temperature difference expected. But then I do not know the reason for your temperature.

It appears to have a resistivity ratio of 80% for R233/R273K or R-40C/R0C if you were wondering about the initial cold surge current for this PTC or positive tempco metal.

I suspect the reference IR lamp has a dominant visible temperature around 900 'K @ 500W if it is "ruby red" with most of the power in the IR spectrum.

I wonder what the spectral bandwidth is?

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