Patent ID: 6466036
Filing Date: 2002-10-15
Classification: G01D,H03K

Abstract:
Apparatus for measuring the capacitance to ground of a plate, the apparatus comprising:at least three switching elements, each of the at least three switching elements having both a respective open state and a single respective closed state, each of the at least three switching elements electrically connected to one of two distinct reference voltages; a sample capacitor having two terminals, a proximal one of the two terminals connected to the plate by means not comprising one of the switching elements, the second terminal distal from the plate; a voltage measurement circuit connected to one of the terminals of the sample capacitor by means not comprising one of the switching elements, the measurement circuit comprising one of a logic gate and a voltage comparator; wherein: a first of the at least three switching elements connects the distal terminal of the sample capacitor to the first reference voltage when in its closed state and disconnects the distal terminal from the first reference voltage when in its open state; a second of the at least three switching elements connects the proximal terminal of the sample capacitor to the second reference voltage when in its closed state and disconnects the proximal terminal from the second reference voltage when in its open state; and the third of the at least three switching elements connects the distal terminal of the sample capacitor to the second reference voltage when in its closed state and disconnects the distal terminal from the second reference voltage when in its open state; the apparatus further comprising a controller for operating the at least three switching elements so that at any time at least one of the at least three switching elements is in its respective open state.