Abstract: The invention relates to a device for measuring the variation of a capacitive impedance, the dielectric of which consists of a lubricant, provided with an oscillator that supplies a signal having a predetermined frequency to the capacitive impedance by way of a bias impedance.The device according to the invention is characterized by a current measuring means delivering a signal depending on the current passing through the capacitive impedance to a converter the output of which delivers a direct current voltage signal coinciding with the instantaneous value of the capacitive impedance.