Volume 4, Issue 3 (May 1976)
Guard-Gap Correction for Guarded-Electrode Measurements and Exact Equations for the Two-Fluid Method of Measuring Permittivity and Loss
Empirical equations are developed for evaluating the guard-gap correction for guarded electrodes, taking into account the ratio of gap width to electrode spacing, the ratio of the electrode thickness to the gap width, and the permittivities of the material in the gap and between the electrodes. Exact equations are then developed for calculating specimen permittivity, thickness, and dissipation factor from two-fluid measurements, for the first time taking into account the change in effective area when the specimen is inserted between the electrodes, the dissipation factor of the specimen, and that of the liquid. Series resistance and inductance and change in spacing of the electrodes between the first and second set of readings are also taken into account. The accuracy of the equations is estimated to be such that they will not significantly affect the accuracy of two-fluid measurements. Sample calculations are included.