Apparatus developed for measurement of the resistivity of highly insulating liquids

An apparatus developed for measurement of the resistivity of highly insulating liquids is presented. The principle of the apparatus is to measure the conduction current flowing through the liquid sample subjected to a highly stable AC trapezoidal voltage (100 V, 1 Hz). The current is detected after a convenient delay (to avoid surge currents of charge and discharge). This low-cost apparatus can be used either in the laboratory or in a factory, to make production controls, or aging, at some distance and in different points (thanks to separate measurement units). The instrument, called a resistivity meter for liquids, can detect 10^-12 A, and then measure 10¹⁴ Omega . For a liquid of relative permittivity 2, filling a cell of approximately 20 pF, the highest measurable resistivity is in the range 10¹⁶ to 10¹⁷ Omega cm (which would correspond to tan delta of 10^-6 to 10^-7, at 50 to 60 Hz).