Noise thermometry - an exact method of temperature measurement

The noise voltage above the clamps of a resistor is, according to Nyquist, proportional to the absolute temperature, to the frequency band width and the value of the resistor. Thermometers constructed on this principle have not been in use until today, especially because their measureing voltage is too low, and therefore relatively high efforts have to be made as far as electronics is concerned. The advantage of this method lies in the fact that the material of the resistor can be chosen freely, e.g. for measurements in nuclear reactors and the absolute calibration of the thermometer. After briefly describing the basic physical factors of the method, the essay deals with thermal elements, and requirements of electronics. In the laboratory measurement could reachan accuracy of 0.1% between 0 and 10000C. In total, measurements between 1% and 2500 K can be carried out with this instrument. In higher temperature regions the thermo-element and the thermometer are of approximately the same value, the latter showing a lower absolute error. The upper temperature limit might be conditioned by problems of insulation. Construction and function of a measurement device for industrial measurements are described. (orig./HP)