Abstract: Differential capacitance is sensed by charging two capacitors to a voltage equal in magnitude but opposite in polarity during a short sampling period and discharging them in parallel during the remaining longer period of a pulse repetition cycle. In the preferred embodiment, an operational amplifier converts the charge difference to a voltage output signal. In an embodiment suitable for transducers, high sensitivity and low noise performance is obtained because of the output signal provided by the sensor is directly proportional to the excitation voltage, the excitation frequency and the value of a feedback resistor. This embodiment is also useful for proximity sensing in the presence of moisture and other ionic conductors, because the charging pulse can be of a short duration, typically 100 ns or less.

Abstract: A two degree of freedom (2 DOF) accelerometer comprising two imbalanced sensing modules (i.e., bar modules having an unbalance) is provided such that two sensing modules are located in the plane to be measured. The two imbalanced sensing modules have force balance and are used to measure linear and angular accelerations in two degrees of freedom. A single modular design is used for both of the axes. Each of the two individual sensing modules has a housing containing a proof mass for each measured output and a support of the proof mass with the support optimized for the sensitive axis selected for sensor output and having high rigidity in all other axes of the support. Also provided is electrostatic servo force balance technology. A proportional-integral-derivative (PID) controller is used to obtain a closed loop bandwidth of 1 kHz and a steady state error of zero for full scale accelerations up to 75 g's and 1000 rad/sec.sup.2.