Resistance + Temperature, help!

Discussion in 'Homework Help' started by hive_world_junkie, Apr 4, 2012.

  1. hive_world_junkie

    Thread Starter New Member

    May 9, 2009
    Hello there,

    I am at a loss with a formula which calculates the resistance for a given temperature.

    R = Ro(1+at)

    I understand that this is only applicable for a temperature range of between 0 and 100C. Which is fine when i want to calculate the temperature change from 15C to 20C.

    I have the temp coefficient of copper at 20C = 0.0039
    and all the initial resistances i have calculated are at 20C using a resistivity value for copper in previous equations.

    However, I need something that will work with -55C

    Could somebody point me in the right direction with this as i can only find information on super conductivity which doesn't apply to this temperature or the level of my homework question.

    Any help information would be much appreciated.
  2. panic mode

    Senior Member

    Oct 10, 2011
    this is approximation of a nonlinear function so it's range is limited to temperatures close to reference. usually reference is room temperature so the given temperature coefficient can be used to either bigger or smaller temeperatures as long as they are 'reasonably close' to reference.
    but if you need precise data, you need to measure it yourself. if this is part of sensing device, you would perform calibration anyway.
    hive_world_junkie likes this.
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    Bearing in mind the limitations mentioned by the last contributor, i.e. that this is an approximate formula and only gives reasonable accuracy over a limited temperature range, it is not difficult to apply it to temperatures below 0°C.

    Your simple formula R = Ro (1 + at ) implies a reference temperature of 0C. In this case it is simply required to give t its negative value for sub-zero temperatures. The term "at" then becomes negative, and results in R becoming less than Ro.

    More generally for resistors the refence temperature may not be zero, temperatures around 25C being common. In this case a formula something like R = Rref (1 + a (t-tref)) might be used
    hive_world_junkie likes this.