ABSTRACT
A sketch of the behavior of two resistance temperature transducers with increasing temperature is shown in Figure 2.1. The electrical resistance of a metal increases with temperature, since electrons in a metal, similar in behavior to the molecules in a gas, are more agitated at higher temperatures. This greater kinetic motion decreases individual electron mobility. Thus, under an applied electric field, net electron drift in response to the field is diminished. For platinum, this increase in resistivity with temperature is remarkably linear. Platinum resistance temperature detectors often consist of spirals of a very thin wire, designed to maximize the measured resistance (commonly 1000 at ooc). They are fragile but considered quite accurate. The Perkin-Elmer differential scanning calorimeter uses this
device as a sample and reference temperature transducer. A thermistor is a semiconducting device which has a neg-
ative coefficient of resistance with temperature, e.g. its resistance decreases with increasing temperature. The principles behind its operation follows.
