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

本文介绍了一种利用两个40 kHz超声波换能器在地下通风道壁面附近安装的风速计（以下简称超声波风速计）。风速计测量两个超声波脉冲波沿着和逆着气流传播的时间差。一个换能器位于另一个的上游，并且波的发射是同步的。超声波在上游和下游方向的传播时间是在同一路径上测量的。传播时间的差异与气流速度成正比。采用简单的合成电路，实现了模拟输出和记录系统。利用数字计数电路测量时间差，并根据风速对模拟量进行校准，在实验室进行了与风速相关的超声波风速计和热风速计的对比实验。从测量结果可以推测，它的测量误差在3%以内，其分辨率最小为0.03米/秒。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。估计平均速度的测量误差相对较小，并且可以检测流向。当车辆或工作人员通过测量点时，输出电压会突然增加或减少。利用这些输出特征，提出了一种识别超车的方法。超声换能器通过其振动表面的自清洁克服了灰尘的干扰。在地下矿井粉尘气流中的检查中，它已经运行了几个月而没有进行维护。

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.