Galvanometer way, no resistance, no pressure loss, no moving parts, no wear, no clogging risks. Practical application in the field, under the following conditions, the system is still working properly: the bond of nearly 100mm thickness dirty impurity inside wall of the pipe ①. ② water condensation inside the pipe. ③ transducer surface stickiness object covering 10mm thickness. Wide range of applications: ultrasonic gas flowmeter for a variety of work environments. In dirt, corrosive, viscous, heat, cold, vibration and other environmental long-term stability.