Reliable operation conditions of capacitive inertial sensor for step and shock signals

For the operation of capacitive sensors, alternative electric testing signals are needed for detecting the variation of capacitance. Due to the electrostatic force, instability may occur; the seismic mass of the sensor can be pulled into contact with one of the static electrodes. In our previous work [Sens. Actuators A84 (2000) 213], the reliable operation range for a quasi-static signal (or for a heavily damped system) was considered for three capacitive accelerometer configurations: the single capacitor, the double-sided capacitor and the force-balanced configurations. The results show that the maximum inertial signal levels for reliable operation are significantly reduced by the electrostatic effect. In the present work, the reliable operation ranges for capacitive accelerometers with light damping for step and pulse signals are investigated. It is found that the electrostatic force imposes a significantly larger restriction on the inertial signal range than that on the quasi-static signal. The dependence of the critical acceleration on testing signal level is given both in expressions and in curves. The results show that the critical signal level of step inertial signal is smaller than that of quasi-static signals by a factor of 0.5-0.7. For pulse inertial signal, the reliable operation condition is dependent on the product of the amplitude and the time duration of the pulse. The maxima of the product for reliable operation are found by an energy approach. The results are given in analytical expressions and curves. For both signal types, the operation ranges are increased by the electro-mechanical feedback effect for accelerometers with a force-balanced configuration. (C) 2004 Elsevier B.V. All rights reserved.