In coal mine roof pressure monitoring system, the issues of wireless ZigBee sensors are not being long-lasting as designed and requiring frequent battery replacement. Hence, a wireless pressure sensor of hydraulic support based on LoRa technology is designed to address these problems. The wireless pressure sensor embedded LoRa module is installed on the hydraulic support to collect the pressure values of the front pillar, the rear pillar and the forepole. The measured liquid medium is pressurized to the piezoresistive element of the sensor through the pressure hole. The deformation of the piezoresistive element under pressure produces resistance change which is linearly related to pressure. The micro-control unit of the sensor measures the voltage which applied to the resistance and converts the voltage to the actual pressure value. The sensor achieves wireless long-range, low-power and high-reliability transmission of the coal mine roof pressure monitoring signal by using three methods: the direct sequence spread spectrum technology with high spread spectrum improves the sensitivity of the receiving end, achieves high signal gain and increases the communication distance; the forward error correction coding technology improves the transmission reliability; the sensor enters sleep mode to reduce the power consumption after collecting the pressure value of the hydraulic support and sending the data successfully. The test results show that the average power consumption of the sensor is 1.18 mA·h for 1 h and the theoretical endurance of the 5,000 mA·h lithium battery is 141 days. The sensor performance meets the need of coal mining. Comparing with ZigBee technology, LoRa shows better performance for long-range transmission and higher reliability.
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