An ultrasonic flowmeter (hereinafter referred to as USF) is an instrument that measures the volume flow by detecting the action of an ultrasonic beam (or ultrasonic pulse) when a fluid flows. This article focuses on the USF used to measure liquid flow in closed pipelines. The USF for closed pipelines is classified according to the measurement principle: ①propagation time method; ② Doppler effect method; ③ beam offset method; ④ correlation method; ⑤ noise method. This article will discuss the most widely used instruments of propagation time method and Doppler effect method. 1. Advantages: USF can be used for non-contact measurement. The USF clip-on transducer can be installed without stopping the flow and intercepting the pipe, as long as the transducer is installed outside the existing pipeline. This is a unique advantage of USF in industrial flow meters, so it can be used for mobility (ie, non-fixed-point fixed installation) measurement, which is suitable for the evaluation and determination of the flow status of the pipeline network USF is a measurement without flow obstruction and no additional pressure loss. The meter coefficient of the flowmeter can be calculated from the actual measurement pipeline and channel geometry, and it can be calibrated by dry method. Except for the measurement tube section type, there is generally no need for actual flow verification. USF is suitable for large circular pipes and rectangular pipes, and is not limited by the diameter of the pipe in principle, and its cost is basically independent of the diameter of the pipe. Not only does it bring convenience for large pipelines, it can be considered as the preferred option when real flow verification is not possible. Doppler USF can measure liquids with high solids content or bubbles. The USF can measure non-conductive liquids and is a supplement to the electromagnetic flowmeter in unobstructed flow measurement. Because it is easy to implement and combine with test methods (such as velocity-area method of velocimeter, tracer method, etc.), it can solve some special measurement problems, such as the measurement of severe distortion of velocity distribution and the measurement of non-circular cross-section pipes. Some USF propagation time methods have the function of measuring the propagation time of sound waves, that is, the sound velocity of liquid can be measured to determine the type of liquid measured. For example, if an oil tanker pumps oil products ashore, it is possible to check whether the measured oil products or silo bottom water. 2. Disadvantages: The propagation time method USF can only be used to clean liquids and gases, and cannot measure liquids with suspended particles and bubbles exceeding a certain range; on the contrary, the Doppler method USF can only be used to measure liquids with a certain out-of-phase. The USF of the outer clamp transducer cannot be used for lining or pipes with too thick scale, and can not be used for peeling of the lining (or rust layer) from the inner pipe wall (if the interlayer sandwiches gas, it will seriously attenuate the ultrasonic signal) or serious corrosion (Change the ultrasonic propagation path). In most cases, the Doppler method USF has low measurement accuracy. Existing domestically produced varieties cannot be used for pipes with a diameter less than DN25mm. Classical Handles,Zinc Alloy Dresser Knobs,Classical Wardrobe Handles,Classical Furniture Pulls Shenzhen Hongjingyuan Metal&Plastic Products Co., Ltd. , https://www.hjypull.com