Development and Its Application of Flow Velocity Anemometer Using Ultrasonic Waves in Underground Airways

研制了在地下气道壁附近设置两个40 kHz超声波换能器的风速计（以下简称超声波风速计）。风速计测量沿气流和反气流的两个超声波脉冲波之间的传播时间差。一个换能器位于另一个的上游，并且波的传输是同步的。在同一路径上测量超声波在上游和下游方向的传播时间。旅行时间的差异与气流速度成正比。模拟输出和记录系统采用了简单的组成电路。并利用一个测量时间差的数字反电路，根据气流速度校准其模拟输出。用超声风速仪与实验室的热风速仪进行了风速的对比实验。从结果推测，其测量误差在3%以内，分辨率最低为0.03 m/s。在井下对超声波风速仪进行了试验研究。风速计不会成为过往车辆或工作人员通过其设置区域的障碍。估计平均流速的测量误差相对较小，并能检测出流向。当车辆或工人经过测量点时，输出电压会突然升高或降低。利用这些输出特征，提出了一种识别传球的方法。超声波换能器确实通过自我清洁其振动表面来克服灰尘的干扰。在对地下矿井粉尘气流进行检测时，已连续运行数月未进行维护。

The anemometer using with two 40 kHz ultrasonic transducers set near wall of underground airways (hereinafter called an ultrasonic anemometer) has been developed. The anemometer measures the difference in travel time between two ultrasonic pulsewaves along and against the airflow. One transducer is located upstream of the other and transmitting of the waves are synchronized. The travel times of the ultrasonic waves in the upstream and downstream directions are measured over the same path. The difference in travel time is proportional to the airflow velocity. Analogue output and recording system using a simple composition circuit was used. And a digital counter circuit to measure the time differences was utilized to calibrate its analogue output as against airflow velocity.Some experiments with ultrasonic anemometer related to airflow velocity were executed compared with a thermal anemometer at a laboratory. From the results, it is presumed that its measurement error is within 3% and its resolution is minimum 0.03 m/s.The ultrasonic anemometer has been investigated and examined at underground mine. The anemometer doesn't become an obstacle for passing vehicles or workers going through its setting area. The measurement error to estimate average velocity is relatively small and can detect flow direction. When vehicles or workers pass though the measurement point, sudden increase or decrease of output voltage occurs. Using with these output characteristics, a method is presented to recognize a passing. The ultrasonic transducer did overcome disturbances of dusts by self/cleaning of its vibrating surface. In case of the examination in dusty airflow of the underground mine, it has been operated for few months without a maintenance.