Noise thermometer

The electrical noise thermometer uses the voltage of the thermal resistance noise of a metal resistor to infer the absolute temperature directly. It is therefore a primary thermometer .

The thermal noise ( Johnson noise ) is caused by density fluctuations of the transport electrons due to their thermal movement. For sufficiently small frequencies f , the rms value of this voltage can be written as

${\displaystyle U_{R}={\sqrt {4k_{B}\cdot T\cdot R\cdot \Delta f}}}$

with the Boltzmann constant, the resistance, the bandwidth and the absolute temperature. ${\displaystyle k_{B}}$ ${\displaystyle R}$ ${\displaystyle \Delta f}$ ${\displaystyle T}$

In order to make this “useful noise voltage” accessible to a measurement and not to falsify it by the noise of an amplifier, the thermal noise voltage is amplified by means of two identical amplifiers and a cross-correlator .

Web links

• Physikalisch-Technische Bundesanstalt: Noise thermometer for low temperatures
• Jan Oliver Löfken: Noise thermometer measures temperature using tunneling electrons. On: Wissenschaft.de from June 21, 2003.