Research Of Mine Explosion-proof And Intrinsically Safe Ultrasonic Ranging And Alarm System

In the process of coal mining, due to the complexity of environment, some transportation and production equipments are of collisions and other security threats to people and equipments around, and no distance alarm system can be used in the mine so far. To solve this problem, the ultrasonic ranging principle which is suitable for the mine environment is researched and an intrinsically safe distance alarm system is developed.A control alarm display center is used to control several ranging sensors in the distance alarm system. The ranging sensor is the technical core, in the paper the ultrasonic ranging theory is researched firstly. The principle and advantages of ultrasonic ranging, the temperature-sensitive and attenuation characteristics of ultrasonic are elaborated, and the principle, the classification and parameters like measuring range, dead zone, measure angle of ultrasonic transducer are introduced in the paper. The waterproof transmit&receive ultrasonic transducer is selected to adapt to the mine environment.To make the distance alarm system work safely in the mine, the DC18V explosive-proof and intrinsically safe power supply is used as its power source and parameters of control alarm display center and ranging sensor are strictly conform to the requirements of intrinsically safe. The intrinsically safe transducer driving circuit based on high-speed optoisolator is used in the ranging sensor instead of the commonly used waterproof transmit&receive ultrasonic transducer driving circuit based on boosting transformer. At the same time, the suitable receiving circuit is designed, in the receiving circuit three reverse operation amplifier circuits are used for the amplification of ultrasonic echo, resonance characteristic of transducer, parallel resonant characteristic of RLC circuit and band-pass characteristic of operational amplifier circuit are used to filtering the noise and interference of the echo signal. In addition, some steps are taken to weaken common mode interference of echo signal and avoid self-excitation of operational amplifier circuits. A diode is used to interdict background noise of amplified echo signal. Finally a peak-detect circuit and AD sampling function of microprocessor are used to detect the echo pulse and get the flight time of ultrasonic pulse after what the distance of obstacle can be figured out.In the software design of the ranging sensor, The I/O port low level interrupt function of microprocessor is used to receive range starting instruction, the timer function is used reasonably to implement transmitting of ultrasonic, timing of flight and transmitting of frequency signal.The control alarm display center controls range sensors based on MSP430F149microprocessor, which controls the beginning of range by command its I/O port to send low level pulse to range sensors, receives the obstacle distance frequency signal by using its I/O port interrupt function, drives the LCD12864screen to display the ranging result, and finally makes buzzer and LED send out sound-light alarm while the obstacle distance is lower than the warning distance.Finally measuring range, accuracy and thermal sensitivity of the range sensor are tested. The test result shows that the range sensor is of large measuring angle and small blind angle corner, its accuracy and thermal sensitivity can meet the requirements of range alarm system. The develop of intrinsically safe distance warning system achieves the distance alarm in the mine, the range sensor is of advantages of intrinsically safe, easily install, anti-interference, waterproof, dustproof so that it can be used in the mine. The range sensor is of great practical value.