A Compensation Method With a Standard Square Wave for Precise DC Measurement of Mutual Inductance for Joule Balance

The precise dc-based measurement of the mutual inductance is one of the key issues in the Joule Balance method used to determine Planck´s constant h. Here, a new compensation method with a standard square wave is provided. The dc value of the mutual inductance is obtained by measuring the integral area of the induced voltage. To increase the accuracy of this integral method, we just accurately measure the residual area observed between the induced voltage of the mutual inductor and a synchronously generated standard square wave. Experimental results indicate that this approach is consistent with the previous frequency extrapolation method within 1 ppm. The measurement uncertainty is estimated to be about 0.22 μH/H for the 340-mH mutual inductor at room temperature. A better result of 0.1 ppm could be obtained when the superconducting coil is used.