Wednesday, August 19, 2009

Temperature Coefficient for Electrical Resistivity

I remember telling someone in a forum about using stainless steel bolts as a shunt for use as a cheap current measurement. Someone else said that shunts are made with exotic (aka expensive) materials with very low thermal coefficients of resistance. I found this chart not too long ago and thought I would post it.

As you can see, stainless steel has a negligible coefficient. So, I feel vindicated. Stainless steel is exotic by the way. It is just mass produced and used for construction, thus making it pretty cheap.

Richard
at

2 comments:

  1. UnknownSeptember 7, 2015 at 10:41 AM

    Good blog by the way. A detail that will help if you have not already caught it: The above chart is thermal resistivity, not thermal coefficient of electrical resistivity. Aluminum resistance is 2.82 x10 (-8) ohm/meter (don't care at the moment) and the thermal coefficient of resistivity is 0.0039 /deg. K. The simple math is 0.0039 x delta T x 2.82. But the easy thing is to consider the 0.0039 as a variation on percent change. So we look at the coefficient of resistivity of the neat alloy Manganin - 0.000002 or about 2000 times better than aluminum or many other metals. 18-8 Stainless steel has a Tcoef of 0.00094, 4 x better than many metals but not great if the temperature varies too much. Decent shunts are available cheap on ebay.
    Neat stuff you do. Much appreciated.

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  2. UnknownSeptember 7, 2015 at 10:51 AM

    I retract my misinterpretation of your choice of graphs. Too many distractions. I need a shed or office. But real shunts are still better for tight tolerance measurements over wide temperatures. Feel free to dump both comments :)

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