An apparatus of one embodiment includes a sensor and a controller. The sensor has first and second electrodes separated by an insulator. The controller includes measurement circuitry, a processor, and a memory comprising logic. The logic is operable to disconnect the second electrode from the measurement circuitry, induce a current on the second electrode by applying voltage to the first electrode, apply charge to the second electrode, connect the second electrode to the measurement circuitry after applying the charge to the second electrode, and determine a capacitance value associated with the second electrode.