Physical Principles of Temperature Measurement
The type of thermocouple or resistance thermometer used depends on the respective requirements for accuracy, response, temperature range and chemical properties of the measuring task.
One advantage of thermocouples over resistance thermometers is the higher upper temperature limit of up to several thousand degrees Celsius. In contrast, however, they have poorer long-term stability and lower measuring accuracy.
Temperature Measurement with Thermocouples
The measurement of temperature using thermocouples is based on the thermoelectric effect discovered by Seebeck in 1821. Here it is assumed that a voltage can be measured at the free ends of two wires made of different materials that are connected together, if the temperature at the junction of the wires is different from that at the free ends.
The temperature difference between the temperature at the measuring point and the temperature at the connections of the measuring instrument is always decisive for the measurement.
The temperature at the measuring point can be determined by the measured thermoelectric emf. More detailed information can be found in the standard DIN EN 60584-1 "Thermoelectric voltages and limiting deviations", which lists the basic value series of thermocouples.
Temperature Measurement with Resistance Thermometers
at 0 °C. The resistance of a Pt1000 at 0 °C is called Pt100.
Basic value series Resistance Thermometer
|Temp. in [°C]||Pt100 in [Ω]||Pt 1000 in [Ω]|