Accelerometer using pulse-on-demand control

Abstract

A force balanced accelerometer system comprises an accelerometric sensor and a control system. The sensor comprises a conductive pendulum pivotably mounted between first and second electrode plates. The control system establishes a cycle period with three phases. In the first phase, the pendulum is electrically isolated in an electric field established between the electrodes. The pendulum is moved from a null position in response to inertial acceleration, and a pickoff signal indicative of the acceleration-responsive position is generated. The pickoff signal is fed into a sample-and-hold circuit and then into a servo compensation circuit, having proportional and integral control, so as to generate a force-indicative signal indicative of the magnitude and direction of the force required to restore the pendulum to the null position. At the start of the second phase, the electrode required to restore the pendulum to its null position, selected in accordance with the sign of the force-indicative signal, is maintained at a first fixed potential, while the pendulum and the other plate are switched to a second fixed potential. The second phase is maintained for a time period determined by the magnitude of the force-indicative signal, which time period is a measure of the sensed acceleration. At the end of the second phase, the third phase begins with the electrodes and pendulum switched to ground, until the cycle repeats. The cycle period and the timing of the phases are controlled by a microprocessor.