Resistance Thermometer Theory and Practice

1. BASIC THEORY The electrical conductivity of a metal depends on the movement of electrons through its crystal lattice. Due to thermal excitation, the electrical resistance of a conductor varies according to its temperature and this forms the basic principals of resistance thermometry. The effect is most commonly exhibited as an increase in resistance with increasing temperature, a positive temperature coefficient of resistance. When utilising this effect for temperature measurement, a large value of temperature coefficient (the greatest possible change of resistance with temperature) is deal; however, stability of the characteristic over the short and long term is vital if practical use is to made of the conductor in question. The relationship between the temperature and the electrical resistance is usually non-linear and described by a higher order polynomial: