Studies On The Characteristics Of Electrical-Thermally Excited Resonant Micro-beam Pressure Sensor And Development Of The Portable Piezometer

Microstructure resonant pressure sensor is a device which measures the applied pressure by detecting the change of frequency of its mechanical resonator. It is showing broad application prospects for the advantage in its very small size, high accuracy and convenient interfacing with digital electronics. In this thesis, characteristics of the electrical-thermally excited resonant pressure sensor are investigated and an applied instrument is developed.Based on the theoretical analysis of the physical and mathematical models, the properties of sensitivity of the clamped-clamped beam resonator to the axial stress and the excitation signals are investigated. An open-loop test system is established to measure the resonant characters as the Q factor, amplitude-frequency characteristic and nonlinear performances, by using special lock-in amplification technology. In order to solve the problem of detecting dynamic relationships between various sensors' output frequency and their applied conditions, a close-loop system is designed and fabricated. In this system, the sensor's pressure sensitivity and temperature dependence are measured.The temperature characteristic is analyzed by studying the drift of excitation resistor and thermal-structural stress. FEA software simulations show that the difference in structure and materials between sensors will result in opposite temperature drift directions. It is also approved by the close-loop system test results. A software compensation method is employed for the pressure measurement in the close-loop system. The test results indicate that this method can reduce the output relative error of the close-loop system from 28% to less than 0.2% within the temperature range used.A novel portable piezometer, whose sensing unit is an electrical-thermally excited resonant micro-beam pressure sensor, is successfully designed and fabricated. Based on a embedded system, functions as signal linearization, temperature compensation and interfacing with PC are realized in the instrument. The full scale of the instrument is between OkPa~600kPa. By contrasting to the standard pressure gauge, the instrument is tested in the scale from lOOkPa to 450kPa: the output error is less than 0.5% and the measurement accuracy is between ?kPa in an applied temperature range from 0℃ to 60℃.