A navigation grade micro-machined silicon accelerometer

The paper presents the initial results of AlliedSignal Inc. (formerly Sundstrand Data Control) Instrument System´s, development of a medium accuracy aircraft inertial navigation grade silicon accelerometer. This effort focused on developing a monolithic bulk-micromachined vibrating beam accelerometer. The accelerometer is designed such that an acceleration along the positive input axis places the vibrating beams in tension. Thus, the resonant frequency of the vibrating beams increase with applied acceleration. An electronic oscillator capacitively couples energy into the vibrating beams to keep them oscillating at their resonant frequency. The acceleration signal is then output from the oscillator as a frequency modulated square wave that can be sent directly to a digital interface. Performance data from the first AlliedSignal silicon vibrating beam accelerometer development program is presented. The data presented includes noise level, short term stability and tumble over temperature tests. This accelerometer is targeted to be incorporated into a system with one nautical-mile-per-hour navigational accuracy. This ambitious goal translates to an accelerometer with 50 μg, one sigma bias, and 50 ppm, one sigma long term scale factor accuracy. The data presented demonstrate the feasibility of meeting one-nautical-mile-per-hour accuracy with a vibrating beam micro-accelerometer. The cost savings offered by a micro-machined silicon accelerometer ensure that this technology will be pushed to its limit for application in inertial guidance systems