Abstract：The calculable capacitor is a classical and fundamental experiment apparatus in precise electromagnetic measurements. It is followed the ‘new’ electromagnetic principle which is firstly introduced by Lampard D G and Thompson A E. The calculable capacitor is the AC impedance primary standard, and its the traceable source of the capacitance, inductance and AC impedance. It is a high-accuracy (at the level of 10-8) apparatus surpassed only by the quantum Josephson voltage and quantum Hall resistance experiments in the electromagnetic metrological field, and it is expected to reach the level of 10-9 through continual improvements and optimizations to improve the uncertainty level of electromagnetic metrology. The basic principle of the displacement measurement in calculable capacitor is presented, and impact factors, including Fabry-Perot interferometer locking, laser wavelength, residual index of refraction of air, cosine error and Gouy phase correction, are analyzed. Combining the repeatability of capacitance produced by calculable capacitor, a relative standard uncertainty of 4.7×10-9 is obtained.
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2022, Vol. 43 
