Realization of an SI traceable small force of 10 to 100 micro-Newton using an electrostatic measuring system
A small force of (10–100) micro-Newton traceable to the International System of Units (SI) has been realized using an electrostatic measuring system at the National Institute of Metrology, China. The key component of the measuring system is a pair of coaxial cylindrical electrodes. The inner electrode is suspended with the support of a self-balanced flexure hinge, while the outer electrode is attached to a piezoelectric moving stage. The stiffness of the self-balanced flexure hinge was also designed so as to be both sufficiently stable and sensitive to the small force applied to the inner electrode. Two sets of cameras were used to capture the shape of the electrodes and to obtain a better coaxial arrangement of the inner and outer electrodes. With the help of a capacitance bridge and a piezoelectric moving stage, the relative standard uncertainty of the capacitance gradient does not exceed 0.04 %. Associated with a laser interferometer and a DC voltage power source, the feedback system that controls the position of the inner electrode is responsible for the generation of a force of 10–100 micro-Newton. The standard uncertainty associated with the force of 100 micro-Newton does not exceed 0.1 %.
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