A Novel Hollow Active Auxiliary Electrode Applied for the Vertical Calculable Cross Capacitor at NIM

To compensate the end effect error in a vertical calculable cross capacitor with a fixed and a movable guard electrode, two different methods, a nosepiece and a modified active auxiliary electrode, are usually adopted at National Measurement Institutes across the world. However, the latter electrical approach can be more difficult when assembling the mirrors in the resonant cavity of the Fabry-Perot laser interferometer. This paper describes a novel hollow active auxiliary electrode that can satisfy the optical requirements. The model test experimental results show that it has the same or better compensation effectiveness for the end effect error in comparison with the modified active auxiliary electrode.