Design Of Temperature Monitoring System For High Voltage Witchgear Based On SAW Sensor

Aiming at the disadvantages of the traditional temperature measurement method when facing with the high voltage, strong electromagnetic field, narrow space and other harsh environment of high voltage switchgear, a passive wireless temperature monitoring system based on SAW sensor is designed. The system is mainly composed of a resonant passive wireless temperature sensor and a high frequency interrogator based on the principles of radar.The main design ideas of the system:signal whose frequency can be modulated is generated by the interrogator to motivate interdigital transducer of sensor to generate saw, then the saw will overlap in the resonant cavity of the sensor. When the excitation signal stop, the superimposed saw will be converted to electrical signals by the interdigital transducer and radiated out through the sensor antenna. The echo signal of the sensor will then be received and sampled by the interrogator, and the amplitude of the echo signal is obtained at this frequency, then the interrogator will change the frequency of the excitation signal to ensure that the range of the resonant frequency change of the sensor caused by temperature is within the range of the excitation signal change. Since the external excitation signal frequency is consistent with the frequency of the SAW temperature sensor, the echo signal sensor will be the strongest, so a sweep cycle down, the resonance frequency of the temperature sensor is known, but also because the resonant frequency of the sensor has a linear relationship with the temperature, the interrogator can be drawn to the temperature of the node. The main research contents and achievements are as follows:(1) Deduced the propagation equation of SAW on piezoelectric materials and got the propagation characteristics of the SAW which can provide the basis for various SAW devices'preparation by deducing the propagation equation of SAW in piezoelectric materials.Simulated the frequency response and the impedance characteristic of IDT and the frequency response of the resonator by Matlab, and the results verified the correctness of the design of the sensor chip.Designed the impedance matching circuit of the sensor by tool of Smith chart. (The method is also suitable for the design of impedance matching circuit.)(2) Analysised and designed the circuit with the heip of ADIsimPLL and ADS2008, then drawed the circuits by Altium Designer, at last Compiled the program by Keil uVision4 and QUARTUS II, developed a high frequency interrogator The interrogator is able to produce the frequency of 434-436MHz and the step size of signal is 16KHz.(3) Analysied the source of the interference and the influence of the interference on the system and then proposed some effective anti-interference measurements form the aspects of hardware and software. Tested the performance of signal lauching circuit of interrogator by oscilloscope, then in order to test the the performance of signal receiving circuit of interrogator, used 10MHz sine signal and Arb signal generated by Signal generator to simulate the envelope of the sensor's echo signal. The Test results show that the designed interrogator achieves the desired effect.