The VIA vibrating beam accelerometer: concept and performance

The micro-machined quartz vibrating beam accelerometer, VIA (Vibrating Inertial Accelerometer), has been developed in ONERA aiming at civil and military purposes. The present applications of this device are the guidance and the attitude control of tactical missiles as well as the aircraft inertial navigation. High accuracy, 10^-5 to 10^-6 of the measurement range, and low cost manufacturing are thus demanded. The VIA concept has been selected to meet these objectives. First, the monolithic configuration of the transducers is well suited to chemical etching process and miniaturization. Secondly, the choice of vibrating beams as sensitive elements, combined with excellent quartz mechanical properties, gives a very good stability of the scale factor. The performed optimisation of the transducer leads to a very good insulation of the active part, included a proof mass, a vibrating beam and two articulations, with respect to the mounting areas of the transducer. The insulation has been obtained by a flexible frame, inserted between the active part and the mounting areas. The VIA accelerometer is composed of two transducers and two oscillating loops. A differential arrangement is needed in order to reduce in particular the thermal sensitivity. The two beam frequencies are about 60 kHz and the accelerometer scale factor is 24 Hz/g