Edge correction in the determination of dielectric constant

An edge correction is often required in determining the dielectric constant of an insulating material by the capacitance method.Theoretical formulas by which the edge correction may be computed have been considered for a number of electrode arrangements.Some of these apply to circular electrodes and some to rectangular electrodes.The error in the dielectric constant which may arise from the use of these formulas is discussed for each of the different arrangements.The accuracies of the methods were experimentally determined by making measurements on the same specimens with the various arrangements of electrodes.The guard-ring arrangement was assumed to give the correct value of the dielectric constant, and the values obtained with the other arrangements were compared with it to determine their errors.Only two methods gave values which were in error by less than 1 percent.Both methods were for arrangements of electrodes in which one electrode was smaller than the other, one being for circular electrodes, the other for rectangular electrodes.Empirical equations were set up which gave values of the dielectric constant which were in error by less than 1 percent for all electrode arrangements, both for circular and rectangular electrodes.These equations are much simpler than the theoretical equations.