Observe the assembly of piezoelectric components in the sound wedge. In addition, certain rubbers, plastics, and rubberwood can also be used as sound wedge materials.

The electronic circuit of an ultrasonic flowmeter includes transmission, reception, signal processing, and display circuits. The measured instantaneous flow and cumulative flow values are displayed in digital or analog form.

According to the principle of signal detection, ultrasonic flow meters can be roughly divided into propagation velocity difference method (including direct time difference method, time difference method, phase difference method, frequency difference method), beam offset method, Doppler method, correlation method, spatial filtering method, and noise method, as shown in the figure. Among them, the noise method has a simple principle and structure, is easy to measure and carry, is inexpensive but has low accuracy, and is suitable for use in situations where flow measurement accuracy is not high. Due to the fact that the basic principles of direct time difference method, time difference method, frequency difference method, and phase difference method all reflect the fluid velocity by measuring the difference in velocity between the forward and backward propagation of ultrasonic pulses, they are collectively referred to as propagation velocity difference method. The frequency difference method and time difference method overcome the errors caused by the variation of sound velocity with fluid temperature, and have high accuracy, so they are widely used. According to the different configuration methods of transducers, the propagation velocity difference can be divided into Z method (transmission method), V method (reflection method), X method (cross method), etc. The beam offset method uses the deviation of the propagation direction of the ultrasonic beam in the fluid with the change of fluid velocity to reflect the fluid velocity. At low flow velocities, the sensitivity is low and the applicability is limited. The Doppler method uses the principle of acoustic Doppler to measure the ultrasonic waves scattered by scatterers in non-uniform fluids

The Le frequency shift is used to determine fluid flow rate and is suitable for measuring fluid flow rates containing suspended particles, bubbles, and other substances. The correlation method uses relevant techniques to measure flow rate. In principle, the measurement accuracy of this method is independent of the sound velocity in the fluid, and therefore independent of fluid temperature, concentration, etc., resulting in high measurement accuracy and wide applicability. But the price of the correlators is expensive and the wiring is relatively complex. After the widespread application of microprocessors, this drawback can be overcome. The noise method (listening method) utilizes the principle that the noise generated during fluid flow in a pipeline is related to the flow velocity of the fluid, and represents the flow velocity or flow rate value by detecting the noise. The method is simple, the equipment price is cheap, but the accuracy is low.

The above methods each have their own characteristics, and should be selected based on factors such as the properties of the measured fluid, flow velocity distribution, pipeline installation location, and requirements for measurement accuracy. Generally speaking, due to the inability to maintain a constant temperature of the working fluid in industrial production, frequency and time difference methods are often used. The direct time difference method is only used when the pipe diameter is large. The general principle for selecting the installation method of the transducer is: when the fluid flows parallel to the pipe axis, the Z method is selected; When the flow direction is not parallel to the uranium tube or the installation location of the pipeline restricts the installation interval of the transducer, the V method or X method is used. When the flow field distribution is uneven and the straight pipe section in front of the meter is short, multi-channel (such as dual channel or four channel) can also be used to overcome the flow measurement error caused by flow velocity disturbance. The Doppler method is suitable for measuring two-phase flow and can avoid the drawbacks of blockage, wear, and adhesion caused by suspended particles or bubbles in conventional instruments, thus enabling rapid development. With the development of industry and the promotion of energy conservation, the transportation and application of coal oil mixture (COM) and coal cement mixture (CWM) fuels, as well as the development of energy-saving methods such as adding water to fuel oil for combustion assistance, have opened up broad prospects for the application of Doppler ultrasonic flow meters