The ultrasonic flowmeter uses an external clamp type sensor to measure liquid flow rate. The installation process is extremely simple, with a fully Chinese human-machine interface that is easier to operate. Specially suitable for flow balance testing and flow monitoring: drinking water, river water, seawater, cooling water, hot water, industrial wastewater, lubricating oil

Working principle of ultrasonic flowmeter

According to the principle of signal detection, ultrasonic flowmeters can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method, and frequency difference method), beam offset method, Doppler method, cross-correlation method, spatial filtering method, and noise method.

1. Time difference method: measure the time difference caused by different propagation speeds during forward and backward propagation to calculate the velocity of the measured fluid.
   It uses two acoustic transmitters (SA and SB) and two acoustic receivers
   (RA and RB). Two sets of sound waves from the same source are transmitted separately between SA and RA, and between SB and RB. They are installed along the pipeline at a θ angle (generally θ=45 °) with the pipeline (as shown in Figure 1). Due to the acceleration of sound waves downstream by the fluid and the delay of sound waves upstream, the time difference between them is proportional to the flow velocity. It is also possible to measure the flow velocity by sending a sine signal to measure the phase shift between two sets of sound waves or by sending a frequency signal to measure the frequency difference.
2. Phase difference method: measures the calculation speed of phase difference caused by time difference during forward and backward propagation. Its transmitter sends a beam of sound waves along an axis perpendicular to the pipeline, and due to the fluid flow, the sound wave beam is offset downstream by a certain distance. The offset distance is proportional to the flow velocity.
3. Frequency difference method: a method of measuring the frequency difference between forward and backward propagation.
   When ultrasonic waves are transmitted in non-uniform fluids, scattering occurs. When there is relative motion between the fluid and the transmitter, a Doppler frequency shift occurs between the transmitted sound wave signal and the signal received after being scattered by the fluid. The Doppler shift is directly proportional to the fluid velocity. The area of the measured fluid in Figure 2-9 is located at the intersection of the transmitted beam and the received scattered beam. Require the beam to be very narrow, so that the angle θ between the two beams is not affected by the beam width. It is also possible to use only one converter as both a transmitter and a receiver, which is called single channel type.

Working characteristics of ultrasonic flowmeter

(1) Ultrasonic flow meters can be used for non-contact measurement. The clamp type transducer ultrasonic flowmeter does not require the installation of a stop flow pipe, as long as the transducer is installed outside the existing pipeline. This is a unique advantage of ultrasonic flow meters in industrial flow meters, making them suitable for mobile (i.e. non fixed installation) measurement and assessment of flow conditions in pipelines.
(2) Ultrasonic flowmeter is used for flow unobstructed measurement without additional pressure loss.
(3) Ultrasonic flow meters are suitable for large circular and rectangular pipelines, and are not limited by pipe diameter in principle. They can be considered as the preferred choice when real flow verification cannot be achieved.
(4) Ultrasonic flow meters can measure non-conductive liquids and are a supplement to electromagnetic flow meters in unobstructed flow measurement.
(5) Some propagation time method ultrasonic flow meters are equipped with the function of measuring the propagation time of sound waves, which can measure the sound velocity of liquids to determine the type of liquid being measured. For example, when an oil tanker pumps oil ashore, it can be verified whether the measured oil is the oil or the bottom water of the tank.
(6) The propagation time method ultrasonic flowmeter can only be used for cleaning liquids and gases.
(7) Ultrasonic flow meters with externally clamped transducers cannot be used for pipelines with thick lining or scaling, nor can they be used for pipelines with lining (or rust layer) peeling off from the inner pipe wall (if there is gas in the interlayer, it will seriously attenuate the ultrasonic signal) or severely corroded (changing the ultrasonic propagation path).

Ultrasonic flow meters are divided into three types: external clamp type, plug-in type, and pipe section type.

The external clamp type ultrasonic flowmeter is the earliest produced, most familiar to users, and widely used ultrasonic flowmeter. Installing the transducer does not require pipeline interruption, and can be used immediately. It fully reflects the characteristics of simple installation and convenient use of ultrasonic flowmeters.
Due to the sparse material, poor sound transmission, or severe corrosion of certain pipelines, as well as gaps between the lining and the interior space of the pipeline, ultrasonic signals are severely attenuated, making it impossible to measure with external ultrasonic flow meters. Therefore, pipe segment ultrasonic flow meters are produced. The pipe section ultrasonic flowmeter integrates the transducer and measuring tube, solving a difficulty in measurement for external mounted flowmeters, and has higher measurement accuracy than other ultrasonic flowmeters. However, it also sacrifices the advantage of continuous flow installation for external mounted ultrasonic flowmeters, requiring the installation of transducers by cutting open the pipeline.
The plug-in ultrasonic flowmeter is intermediate between the two mentioned above. During installation, it is possible to use specialized tools to drill holes in pipelines with water, insert the transducer into the pipeline, and complete the installation without interruption. Due to the fact that the transducer is located inside the pipeline, its signal transmission and reception only pass through the measured medium and not through the pipe wall and lining, so its measurement is not limited by the pipe quality and lining material.

Application of Ultrasonic Flow Meter

Various ultrasonic flow meters have been widely used in industrial production, commercial measurement, and water conservancy testing, such as:
In the measurement of raw water, tap water, reclaimed water, and sewage in the municipal industry, ultrasonic flow meters have the characteristics of large range ratio and no pressure loss, which improves the water transmission efficiency of the pipeline network while ensuring measurement accuracy;
In the flow measurement of water pipelines, channels, pump stations, and power stations in the water conservancy and hydropower industry, ultrasonic flow meters have the characteristics of large diameter, on-site installation, and online calibration, making accurate measurement possible. Simultaneously achieving equipment optimization and economic operation through metering of individual pumps and turbines;
In the measurement of industrial cooling circulating water, ultrasonic flow meters have achieved online continuous flow with pressure installation and online calibration;
Multi channel ultrasonic flow meters have achieved an accuracy (indication error) of over 0.2% in commercial metrology.
(1) The propagation time method is applied to clean, single-phase liquids and gases. Typical applications include factory discharge liquids, strange liquids, liquefied natural gas, etc;
(2) There is already good experience in the application of gas in the field of high-pressure natural gas;
(3) The Doppler method is suitable for two-phase fluids with relatively low heterogeneous content, such as untreated wastewater, factory discharge fluids, and dirty process fluids; Usually not suitable for very clean liquids.