Thermic behaviour of electrical resistor passed by a constant DC is analysed both theoretical and numerical. This problem, a ill-posed one is changed in a well-posed one solving a parameter identification problem. The last problem is the principal subject of this paper. Numerical simulations presented here correspond to resistance temperature detector Pt-100. They lead to improving of resistance measurement error (and of temperature certainly for this particular case) through computational removing of error caused by thermic effects.