The product has three functions: measuring average flow velocity, measuring water depth, measuring water temperature, and can display cross-sectional flow rate. The water temperature measurement uses a temperature probe, the water depth measurement uses an imported high-precision pressure sensor, and the flow velocity measurement is obtained by emitting and receiving ultrasonic wave signals through an ultrasonic probe (transducer) and performing corresponding calculation processing. Average flow velocity measurement: The measurement of flow velocity is obtained by emitting and receiving ultrasonic wave signals through an ultrasonic probe (transducer) and performing corresponding calculation and processing: transducer 1 emits ultrasonic signals with a frequency of f1, which are emitted from underwater to the water surface at a certain angle. After encountering suspended particles or bubbles in the water, the frequency shifts and is reflected to transducer 2 at the frequency of f2, which is known as Doppler. The difference between f2 and f1 is the Doppler frequency difference fd. Assuming the fluid flow velocity is v, the ultrasonic velocity is c, and the Doppler frequency shift fd is proportional to the fluid flow velocity v. There are a large number of impurity particles and bubbles in the water, and each reflected particle corresponds to a Doppler frequency shift fd. The flow velocity of these large particles can be calculated by conversion, and the average of these particles can be obtained. Flow velocity refers to the average flow velocity of the fluid.