| Due to the unique characteristics such as passive, wireless, hostile environment durability and easy to realize sensor array, surface acoustic wave(SAW) sensors are especially suitable for online temperature measurement in electric power system.Aiming at temperature measurement of the power switch cabinet, passive and wireless temperature SAW sensor array is studied in this paper. It mainly includes three parts: the design of SAW sensor array, query of sensor array and calibration of sensor.The frequency division multiple access technology is adopted for SAW sensor array. Temperature sensitivity and temperature-frequency characteristic of SAW resonators are specially designed according to the permitted wireless bandwidth and the needed temperature measurement range. Then the cut orientation in quartz substrate and the metallization thickness of the electrodes are determined in the sensor array.The interrogation strategy of the sensor array in the transceiver is also introduced. The binary query algorithm based on the coherent demodulation echo signal is proposed so as to improve the interrogation speed. The fast Hartley transform(FHT) algorithm is used to estimate the frequency of the echoes, whose performance is compared with FFT algorithm. Besides, interpolation method is used to improve accuracy of frequency estimation with FHT algorithm.In this paper, in order to reduce the workload of calibration, based on frequency statistical characteristics of the echo signal, the relationship between the calibration accuracy and the number and position of temperature point is discussed by using Monte-Carlo simulation and the measurement accuracy of 1% within the full scale of sensor is realized. A “one-point calibration” method is proposed to eliminate the influence of position variation between the sensor reader and the sensor after installation. |
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