Improvement And Experiment Of Low Power Dielectric Measurement System

Dielectric measurement is widely used in industrial process control to detect product characteristics such as moisture content,density,thickness and toxin content.The research group has developed a low-power dielectric system for food safety detection.However,the system had a narrow frequency range,was easily disturbed by frequency interference.The dielectric constant calculation has not been done.In this thesis,the hardware and software of the original system were improved,and the new system based on the capacitance digital conversion technology was designed.The experiments were done for two systems.The forward channel of the original system was designed to improve the output signal amplitude.The power circuit was optimized by using the combination of DC / DC and LDO.The system resistance to power frequency interference and noise capacity was improved through separating digital and analog power;using metal shield,and designing ground plane design.The precision of spectrum analysis algorithm was improved by setting sampling frequency in different signal frequency range.The model of the sensor capacitance and the sample permittivity was established by the least squares fitting.In this thesis,the plates damage and plates dielectric constant measurement were carried out separately.The results show that the improved system has high stability in the sweep frequency,can detect the damaged plates effectively,the permittivity can be calculated steadily,the values decrease with the increase of frequency,and tend to stabilize gradually.A dielectric measurement system based on the AD7745 and MSP430 was developed.The system included capacitance digital conversion(CDC)module,capacitor input expansion module,human-computer interaction module and power management module.The system software included main monitoring program,initialization module,interrupt module,data acquisition module,human-computer interaction module and algorithm module.The capacitance conversion,read,dielectric constant calculation,display and other functions were achieved through the system software.The experimental results show that the system has a repeatability error of 0.0503 pF at 32 KHz.The system can distinguished the damaged plate accurately,the permittivity can be measured quickly and steadily.