The principle of pressure-temperature transducer of quartz crystal resonator

Abstract

This paper shows that the frequency and the force sensitivity of a quartz crystal resonator are in direct proportion to the order of overtone frequency if the resonator can be made to vibrate at different overtone frequencies in different circuits. This conclusion is tested and verified by experiment. This paper reports the success in experiment that makes the force transducer of circular plate crystal resonator, which has been designed with 3rd order overtone, 5 MHz thickness shear, vibrate at fundamental frequency, 3rd order overtone frequency, 5th order overtone frequency and 7th order overtone frequency separately in different circuits. An investigation has been made into the changing characteristics of both the frequency and sensitivity with the change of the overtone order. The experimental results show that both the frequency and the force sensitivity are in direct proportion to the order of overtone. This paper analyzes the feasibility and the limitations of the rising force sensitivity method, which is to make the designed resonator with smaller order of overtone frequency vibrate at higher order of overtone frequency. The principle of the pressure-temperature transducer is found to be based on the fact that a crystal resonator can be made to vibrate at differential order of overtone frequency in differential circuits, and on the fact that the sensitivity is a linear function of temperature when the resonator vibrates at an overtone frequency. The distinguished feature of this principle is that the transducer can be made up of only one resonator and is able to measure both pressure and temperature in fluid. This transducer uses the peculiar feature of temperature coefficient of sensitivity for avoiding the measurement error.