In search of a new method to measure the resistivity of insulating solids

As an attempt to characterize the conductivity of solid insulating materials, the authors show that a step forward can be taken by extending the alternate square wave (ASW) method previously proposed-i.e. use of an alternate square wave of 10 V with variable half period from 0.1 s to 100 s (and even longer duration if necessary)-to record continuously transient currents down to 10/sup -15/ A. The capability of the measurement system has been checked by showing, in atmospheric air, the transition from the ohmic regime to the saturation regime, and by demonstrating that in the nonpolar liquid cyclohexane the ohmic regime takes place, as expected, in the range 0.1 s to 100 s. Measurements on commercial capacitors, using widely different insulating materials, and on polymer thick sheets have shown that perfectly reproducible results can be easily and quickly obtained. The new method has the special merit of overcoming the major inconvenience of the usual (and standardized) method of measurement of insulation resistance which is greatly affected by previous conditioning treatment.