[en] An error-functional expression is proposed to describe the adsorption characteristics with respect to the adsorption potential. An attempt is made to apply the expression to electrometric adsorption isotherms for water on aluminum oxide in an external alternating electric field from experiments using a moisture sensing capacitor. As results of the analyses, it is shown that electrometric parameters characterizing permittivities of adsorbent and adsorbed water depend on temperature, and statistic parameters characterizing the potential distribution vary with temperature. The dependency of the electrometric parameters are elucidated as polarizing behaviors of the adsorbent and adsorbed water in influence of temperature. The variation of the potential parameters are deduced from the temperature dependencies of the polar parameters because the polar adsorption force is caused by interaction of both polarizations of adsorbent and adsorbate; that is proved by linear correlations of the potential parameters with the product of both polar parameters. The expression is available as a calibration method for the moisture sensor; that is confirmed by evaluating differences between measured and calculated values. Moisture sensors of this type are recommendable for hygrometry in such as a tritium removal system, and its high reliability is obtained from calibration by the present method. (author)