Monolithic quartz structure vibrating beam accelerometer (VBA) prototype test results

This paper describes the test results obtained on prototype Vibrating Beam Accelerometers (VBA) being developed by Pressure Systems, Hampton, VA intended for applications requiring 0.1 to 1.0 mg bias stability and 10 to 100 ppm scale factor stability. The principle of operation is based on vibrating quartz beam technology whereby the frequency of vibration is modulated by an input acceleration. A unique feature of this instrument is that the vibrating beam, the vibration isolation mechanism, the proof mass, the proof mass suspension, and mounting means are all machined from a single piece of quartz crystal. The complete VBA uses two independent sensor packages within a common 1" D/spl times/1" L housing. This dual beam matched pair mechanization is arranged so that an input acceleration places one beam in tension and the other in compression. The VBA output is then taken as the difference frequency. Frequency differencing achieves common mode rejection of many error sources, including thermal and nonlinear effects. Several prototypes of the design just described were assembled and tested. The test results presented dramatically illustrate the effects of common mode rejection due to frequency differencing. For both linearity and thermal error effects, comparisons of both difference frequency and individual beam frequency data is presented to demonstrate error source reduction by a factor of twenty or more.