Combined thermocouple-noise thermometry

The combined thermocouple-noise thermometer (TC-NT) unites the advantages of the thermocouple (simple measuring procedure, high sensitivity) with those of the noise thermometer (no decalibration, high absolute accuracy). With the combined thermometer, the TC in the sensor can be calibrated insitu. The advantage of this in situ calibration is that also all parasitic thermovoltages from inhomogeneous thermocouple wires in temperature gradients are calibrated and thus no measurement error arises. With the combined thermometer it is now possible for the first time to detect and eliminate in practice inhomogeneity errors (drifts). In order to clarify understanding of the basic effects, the modern theory of the thermocouple (generation of thermovoltage in the wires only in temperature gradients) is described as well as the principles of noise thermometry. (orig.)