Accelerometer using pulse-on-demand control

For use with a force balanced instrument comprising a sensing mass that is displaced from a null position in response to a sensed inertial acceleration input to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of the sensing mass, a method of measuring acceleration, comprising the cyclical repetition of the steps of:

• (a) determining a fixed time period;
• (b) during a first predetermined interval within the time period, applying equal and opposite fixed potentials to the first and second plates, respectively, while the sensing mass is electrically isolated so as to assume a pickoff voltage that is indicative of its displacement from the null position;
• (c) applying the pickoff voltage to generate a force-indicative signal that indicates the magnitude and direction of the force needed to restore the sensing mass to the null position;
• (d) selecting one of the plates for the application of a restorative electrostatic force to the sensing mass, based upon the sign of the force-indicative signal;
• and
• (e) after the end of the first interval, applying a fixed potential to the selected plate for a second time interval within the fixed time period, the second interval having a duration that is proportional to the magnitude of the force-indicative signal, wherein the ratio of the duration of the second time interval to the fixed time period is a measure of the sensed inertial acceleration during the fixed time period.

In a force balanced instrument, of the type including a sensing mass that is displaced from a null position in response to a sensed inertial acceleration input to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of the sensing mass, the improvement comprising:

• first means for generating a clock signal representing a fixed time period;
• second means for applying a fixed positive voltage to the first plate and a fixed negative voltage to the second plate during a first time interval within the fixed time period;
• third means for generating a pickoff signal indicative of the magnitude and direction of the displacement of the sensing mass in response to a sensed acceleration input during the first time interval;
• fourth means, responsive to the pickoff signal, for generating a force-indicative signal indicative of the magnitude of an electrostatic restorative force required to restore the sensing mass to the null position;
• fifth means, responsive to the force-indicative signal, for (a) supplying a selected one of the first and second plates with a first fixed potential that applies the restorative force to the sensing mass, the restorative force being applied for a second time interval within the fixed time period, the duration of the second time interval being proportional to the magnitude of the force-indicative signal;
• and (b) electrically coupling the sensing mass and the unselected one of the first and second plates to a second fixed potential;
• and
• sixth means, responsive to the clock signal, for generating an output signal indicative of the ratio of the duration of the second time interval to the fixed time period, which ratio is a measure of the sensed acceleration input.