The table, below, summarizes some typical specifications for three popular transducers, information that is useful when selecting the transducer for a particular application. The transducer manufacturers can provide exact specifications for a particular transducer. An RTD has the highest stability of the temperature transducers mentioned, and its output is also very linear. Note, however, that connection lead resistance is automatically removed using the 4-wire method. A thermistor is constructed of material whose resistance changes non-linearly with changes in temperature.
Thermistors have a higher sensitivity than thermocouples or RTDs.
This makes the thermistor a good choice when measuring very small changes in temperature. Because of their high resistance, thermistors can be measured using a 2-wire resistance measurement method. A thermocouple converts temperature to an associated voltage level. When two wires composed of dissimilar metals are joined, a voltage is generated which is a function of the junction temperature and the types of metals in the thermocouple wire. Since the temperature characteristics of many dissimilar metals are well known, a conversion from the voltage generated to the temperature of the junction can be made.