Effect of humidity on the calibration of the four-terminal-pair air-dielectric capacitance standards

In this work, the effect of relative humidity (RH) on two commercial four-terminal-pair (4TP) air-dielectric capacitance standards has been measured and analyzed. The capacitance is linearly proportional to the RH under 50% owing to the dependence of the dielectric constant of air on the RH. Over 50%, a clear dielectric dispersion has been observed. It is probable that this dispersion is caused by the interfacial polarization of the adsorbed water molecules on the oxidized aluminum electrodes. In calibration aspect, it is recommended to store at least for a day to stabilize the RH inside the standard and calibrate it at RH lower than 50%. The RH coefficient of the capacitance under 50% was estimated as 3 (μF/F)/% from the measurement.