Accelerometer systems with self-testable features

Abstract

In recent years, substantial effort has been devoted to the design and fabrication of a new class of silicon sensors, the accelerometer. A number of companies have been working in the area to produce, for the first time, an accelerometer that is substantially more cost effective and with higher performance than previously possible. Careful electromechanical design and micromachining process development has allowed silicon accelerometers to be fabricated in volume.

Two questions that arise in ultra-high reliability applications, such as safe-and-arming, are whether the aceelerometer is free and working and whether the device is broken. A unique solution to these questions has been designed and implemented in a piezoresistive accelerometer; this approach allows the device to be tested by electrostatic deflection of the mass. A number of key advantages result from this configuration. Even though the spring constants of the device may vary from unit to unit or over temperature, and even though the piezoresistive coefficients vary over temperature, as long as the voltage and initial separation gap are held constant, the output will be proportional to a given acceleration. Applications for the self-testing technique are in temperature compensation, testability and uni-directional force-balance applications.

This approach of building testability into the sensor bridges the gap between the open-loop sensors now in production and the much more complex closed-loop force-balance devices.