Realization of the SI Unit Volt by Means of a Voltage Balance

A description is given of the measuring system set up at the PTB for the realization of the SI volt and the determination of the conversion factor K v by means of a voltage balance. The voltage balance comprises two cylindrical electrodes to generate the electrostatic force from the measuring voltage of 10.186 kV, and a substitution balance to measure the force by comparison with the force due to gravity acting on a 2 g mass. To achieve force equilibrium a small variable voltage is added to the constant measuring voltage. The measuring voltage is generated in a two-stage 1000-fold step-up and linked up with the asmaintained volt by using a transfer standard consisting of 10 saturated standard cells connected in series. The total relative uncertainty of K v is expected to be less than 4 parts in 10 7 .