At present, the development of flow measurement technology in China is getting faster and faster, and various advanced flow meters have been effectively applied in industrial production. However, different flow meters have certain differences in their performance and application scope. Ultrasonic flow meters can be widely used in various occasions and are suitable for multiple fields such as petroleum, chemical, gas, and sewage treatment.
Working principle of ultrasonic flowmeter
In the process of fluid propagation, the velocity of ultrasonic pulses is generally closely related to the fluid velocity, that is, the downstream velocity is greater than the upstream velocity. If there is a large time difference in pulse propagation, the flow rate will also increase accordingly. When performing operations, both upstream and downstream sensors emit certain ultrasonic pulses, but the two are different, mainly manifested as one being counter current and the other being counter current. Due to the influence of fluid, the arrival time of two pulse beams at the transducer will also have certain differences.
However, because the actual paths of the two are consistent, the difference in transmission time can also reflect the actual flow velocity of the fluid. When using the time difference method for measurement, two sensors need to be used for transmitting and receiving signals. When the sensor is installed in the pipeline, the two will implement acoustic signal communication, and during operation, they will transmit and receive. If the fluid inside the pipe is in a static state, the propagation time of forward and backward flow remains consistent. If the liquid is in a flowing state, the propagation time of the downstream signal will be lower than that of the upstream signal. During this process, the time difference between forward and backward propagation is proportional to the actual flow velocity.
According to the principle of signal detection, ultrasonic flow meters can be divided into propagation velocity difference methodTime difference method, phase difference method, and frequency difference method, Doppler method, cross-correlation method, etc.
Characteristics of Ultrasonic Flow Meter
When using an ultrasonic flowmeter, there are no obstacles present in the fluid, which will not affect the flow stream or cause any pressure loss. It can be applied to different fluids, especially those with high viscosity and strong corrosiveness. In addition, ultrasonic flow meters can also be effectively applied to gas flow, and have good advantages when measuring large-diameter flow.
1. The unique signal digital processing technology makes the instrument measurement signal more stable, has strong anti-interference ability, and measures more accurately.
2. No mechanical transmission components are easy to damage, maintenance free, and have a long lifespan.
3. The circuit is more optimized, with high integration, low power consumption, and high reliability.
4. Intelligent standard signal output, user-friendly human-machine interface, multiple secondary signal outputs.
5. Segmented small pipe diameter measurement is economical and convenient, with high measurement accuracy.
Advantages of Ultrasonic Flow Meter
Non contact measurement can be performed. As long as the transducer is installed outside the existing pipeline, an external clamp type ultrasonic flowmeter can be installed without stopping the cutoff pipeline, with no flow obstacles and no additional pressure loss.
The instrument coefficient of the flowmeter can be calculated based on the actual measured values of the pipeline and channel, as well as other geometric dimensions. Except for measuring pipe sections, actual flow calibration is usually not required.
Suitable for large circular and rectangular pipes, in principle not limited by pipe diameter, and the cost is basically independent of pipe diameter. For large pipelines, this is not only convenient, but can also be considered a preferred option in situations where actual flow inspection cannot be achieved. Doppler can measure more solid phasesThe measurement of liquids containing bubbles or non-conductive liquids is a supplement to electromagnetic flow meters, used for unobstructed flow measurement.
Due to its easy integration with testing methods such as speed area method of ammeter, tracer method, etc., it can solve some special measurement problemstopicFor example, severe distortion in measuring velocity distribution, Measurement of circular cross-section pipelines, etc. Some methods of propagation time（USF has the function of measuring the propagation time of sound waves and can measure the sound velocity of liquids to determine the type of liquid to be tested.
For example, if an oil tanker pumps oil ashore, it can verify whether it is measuring oil or water at the bottom of the tank. Ultrasonic flow meters have some of the advantages mentioned above, and therefore are receiving increasing attention. With the development of product series and generalization, instruments with different channel standards, high temperature resistance, explosion-proof, and humidity resistance have been made to adapt to flow measurement under different media, environments, and pipeline conditions.
Disadvantages and limitations of ultrasonic flow meters
The propagation time method can only be used for cleaning liquids and gases, and cannot measure liquids with suspended particles and bubbles exceeding a certain range; on the other hand,The Doppler method can only be used to measure liquids containing certain phases.
External clamping transducers should not be used for lining or pipelines with excessive scaling, and the lining (or rust proof layer) should not be peeled off from the inner pipe wall. If there is gas in the interlayer, ultrasonic signals can cause serious personal injury or severe pipeline corrosion (please change the ultrasonic wave transmission path).
In most cases, the measurement accuracy of Doppler method is not high. The existing varieties produced domestically cannot be used for diameters smaller thanDN25mm pipeline.
