Improved electronic measurement of the Boltzmann constant by Johnson noise thermometry

The unit of thermodynamic temperature, the kelvin, will be redefined in 2018 by fixing the value of the Boltzmann constant, k. The present CODATA recommended value of k is determined predominantly by acoustic gas-thermometry results. To provide a value of k based on different physical principles, purely electronic measurements of k were performed by using a Johnson noise thermometer to compare the thermal noise power of a 200 Omega sensing resistor immersed in a triple-point-of-water cell to the noise power of a quantum-accurate pseudo-random noise waveform of nominally equal noise power. Measurements integrated over a bandwidth of 575 kHz and a total integration time of about 33 d gave a measured value of k = 1.3806513(53) x 10(-23) J K-1, for which the relative standard uncertainty is 3.9 x 10(-6) and the relative offset from the CODATA 2010 value is + 1.8 x 10(-6).