A DUAL-MODE THICKNESS-SHEAR QUARTZ PRESSURE SENSOR

Performance requirements of pressure and temperature sensors, especially from those used in oil-fields, are very demanding. Several years of effort have been devoted to the development of a dual-mode thickness-shear quartz pressure sensor to meet such requirements. The objective of this effort was to develop a sensor with an operating pressure range of 0.103.42 MPa (0-15 000 lb/in2); a temperature range of -10-degrees to 175-degrees-C, a pressure calibration accuracy of 6894.8 Pa (1 lb/in2), and resolution of 68.95 Pa (0.01 lb/in 2) with 1-s counter gate time. Doubly rotated cuts with piezoelectric coupling to both the B- and C- modes of vibration were investigated using the theoretical models proposed by Sinha, EerNisse, and Dulmet for predicting the pressure and temperature sensitivities of different designs. Experimental results were obtained for two sensor designs: one uses a cylindrical design with the SBTC-cut, and the other, called SPA, is a special design of resonator vibrating around 5 MHz without any activity dips (a particular orientation called WAD-cut is employed in this design). Pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in2) at 175-degrees-C is obtained. We briefly describe a theoretical study and general design considerations in the development of such sensors. Laboratory evaluation of the static and dynamic performances are discussed for the prototypes based on the SPA design.