According to different applications of ultrasonic flowmeters, it can be divided into fixed ultrasonic flowmeters and portable ultrasonic flowmeters.
的主要区别 The main differences between these two types of ultrasonic flowmeters
(1) Different applications
Fixed ultrasonic flowmeter is used to install in a fixed position to measure the flow of fluid in a specific pipeline for a long time without interruption; portable ultrasonic flowmeter has great mobility and is mainly used for
The fluid flow of different pipes is temporarily measured.
(2) Different power supply methods
The fixed ultrasonic flowmeter requires continuous operation for a long time, so it is necessary to use 220V AC or 24V DC power. The portable ultrasonic flowmeter can use either the on-site AC power supply or a built-in rechargeable battery.
Continuous working for 5-10 hours [hours], which greatly facilitates the need for temporary flow measurement in different occasions.
(3) Some functions are different
Due to the fixed type ultrasonic flowmeter, it usually has 4-20mA signal output and other functions for remote transmission display, but it can only store the parameters of one pipe; the portable ultrasonic flowmeter is only used to view the current flow on site
And the accumulated flow in a short time, so there is generally no output signal function, but in order to facilitate the measurement of different pipeline flow, it has a rich storage function, can simultaneously store dozens of different parameters of the pipeline for recall at any time.
2. The transducers have different power supply modes, which can be divided into three types: external type, plug-in type and tube type.
(1) External type
The external ultrasonic flowmeter is the earliest produced, the most familiar and widely used ultrasonic flowmeter. The installation of the transducer does not require the pipeline to be cut off.
(2) Pipe type
Some pipes due to sparse materials, poor sound guidance, or severe rust, gaps between the lining and the inner space of the pipe, cause serious attenuation of the ultrasonic signal, which cannot be measured normally with an external ultrasonic flowmeter, so pipe sections are generated.
Type ultrasonic flowmeter.
The tube-type ultrasonic flowmeter integrates the transducer and the measuring tube, and solves a difficult problem of the external-type flowmeter in the measurement. And the measurement accuracy is higher than other ultrasonic flowmeters, but it also sacrifices the external ultrasonic
The advantage of continuous flow installation of wave flowmeters requires the pipe to be cut to install the transducer.
The plug-in ultrasonic flowmeter is somewhere in between. During the installation, continuous flow can be performed. Special tools are used to punch holes in the water pipeline, and the transducer is inserted into the pipeline to complete the installation. Since the transducer is inside the pipe, its letter
The launch and acceptance of the signal only pass through the measured medium, not through the pipe wall and lining, so its measurement is not limited by the quality of the pipe and the lining material.
3.Selection of ultrasonic flowmeter
除上述各种类型外，近年来又出现了采用数字化电路的数字式超声波流量计，把换能器和转换器做在一起的一体式超声波流量计，等等。 In addition to the above types of ultrasonic flowmeters, digital ultrasonic flowmeters using digital circuits, integrated ultrasonic flowmeters with transducers and converters, and so on have appeared in recent years. Face the crowd
Many types of ultrasonic flowmeters, the user must reasonably select the type according to the actual situation and measurement needs.
When an ultrasonic wave propagates in a flowing fluid, it carries information about the velocity of the fluid. Therefore, the flow velocity of the fluid can be detected by the received ultrasonic wave, and then converted into a flow rate. According to the detection method, it can be divided into the propagation speed difference method,
Different types of ultrasonic flowmeters such as Doppler method, beam shift method, noise method and correlation method. Acoustic wave flowmeter is a type that has only been applied with the rapid development of integrated circuit technology in the past ten years.
Non-contact meters, suitable for measuring fluids that are difficult to contact and observe, as well as large pipe flow. It is linked with the water level gauge to measure the flow of open water. The use of ultrasonic flow is better than the need to install measuring elements in the fluid.
It will change the flow state of the fluid without additional resistance. The installation and maintenance of the meter can not affect the operation of the production pipeline, so it is an ideal energy-saving flow meter.
As we all know, the current industrial flow measurement generally has the problem of large pipe diameter and large flow measurement difficulty. This is because the general flow meter will bring difficulties in manufacturing and transportation with the increase of the measurement pipe diameter, increase the cost,
Increased energy loss, installation not only these disadvantages, ultrasonic flowmeters can be avoided. Because all kinds of ultrasonic flowmeters can be installed outside the pipe, non-contact flow measurement, the cost of the instrument is basically independent of the size of the pipe being measured, and other types
With the increase of the caliber, the cost of the flowmeter increases significantly, so the larger the caliber, the more superior the price-performance ratio of other types of flowmeters with the same function. Considered to be a better large-diameter flow meter, Doppler
Ultrasonic flowmeter can measure the flow of dual-phase medium, so it can be used for the measurement of dirty flows such as sewage and sewage. In power plants, portable ultrasonic flow meters are used to measure large diameters of water such as turbine water intake and steam turbine circulating water.
The flow rate is much more convenient than the previous peel tube anemometer. Ultrasonic flow-through juice can also be used for gas measurement. The applicable range of pipe diameter is from 2cm to 5m, and it can be used from a few meters wide open channel and underdrain to 500m wide river.
In addition, the accuracy of flow measurement of ultrasonic measuring instruments is hardly affected by parameters such as temperature, pressure, viscosity, and density of the fluid being measured. It can also be made into non-contact and portable measuring instruments, so it can solve the difficulties of other types of instruments.
To measure the flow of highly corrosive, non-conductive, radioactive and flammable and explosive media. In addition, in view of the characteristics of non-contact measurement, and equipped with reasonable electronic circuits, one instrument can adapt to a variety of pipe diameter measurement and a variety of flow
Measurement range measurement. The adaptability of ultrasonic flow meters is also unmatched by other instruments. The ultrasonic flowmeter has some of the advantages mentioned above, so it has been paid more and more attention to, and has developed into a series and universal product.
The standard, high-temperature, explosion-proof, and wet-type instruments of the channel are suitable for flow measurement of different media, different occasions and different pipeline conditions.
目前所存在的缺点主要是可测流体的温度范围受超声波换能铝及换能器与管道之间的耦合材料耐温程度的限制，以及高温下被测流体传声速度 The current shortcomings of ultrasonic flowmeters are mainly that the temperature range of the measurable fluid is limited by the temperature resistance of the ultrasonic transducer aluminum and the coupling material between the transducer and the pipe, and the sound transmission speed of the fluid under test at high temperatures.
Incomplete raw data. At present China can only be used to measure fluids below 200 ° C. In addition, the measuring circuit of the ultrasonic flowmeter is more complicated than the general flowmeter. This is because the flow rate of liquids in general industrial metrology is often several seconds per second.
Meters, and the propagation speed of sound waves in the liquid is about 1500 m / s. The change in the velocity (flow rate) of the measured fluid brings the maximum change in sound velocity to the order of 10-3. If the accuracy of measuring the flow velocity is 1%,
The measurement accuracy needs to be on the order of 10-5 to 10-6, so it must be completed with a complete measurement circuit. This is why the ultrasonic flowmeter can only be practically applied under the premise of the rapid development of integrated circuit technology.
Ultrasonic flowmeter consists of three parts: ultrasonic transducer, electronic circuit and flow display and accumulation system. The ultrasonic transmitting transducer converts electrical energy into ultrasonic energy and emits it into the fluid to be measured. The receiver receives
The obtained ultrasonic signal is amplified by the electronic circuit and converted into an electric signal representing the flow rate and is supplied to a display and integration meter for display and integration. This realizes the detection and display of the flow.
常用压电换能器。 Ultrasonic flow meters often use piezoelectric transducers. It uses the piezoelectric effect of piezoelectric materials and uses a suitable transmitting circuit to add electric energy to the piezoelectric element of the transmitting transducer, so that it generates ultrasonic vibration. Ultrasound
An angle is injected into the fluid to propagate, and then it is received by the receiving transducer and converted into electrical energy by the piezoelectric element for detection. The transmitting transducer uses the inverse piezoelectric effect of the piezoelectric element, while the receiving transducer uses the piezoelectric effect.
The piezoelectric element of the ultrasonic flowmeter transducer is often made into a circular sheet and vibrates along its thickness. The diameter of the sheet exceeds 10 times the thickness to ensure the directivity of the vibration. The piezoelectric element material mostly uses lead zirconate titanate. Fixed piezoelectric element
It is necessary for the ultrasonic wave to be injected into the fluid at an appropriate angle, and the element needs to be wedged into the vocal wedge to form the entire transducer (also called a probe). The material of the acoustic wedge not only requires high strength and aging resistance, but also requires energy loss after ultrasonic waves pass through the acoustic wedge.
If the loss is small, the transmission coefficient is close to 1. The commonly used acoustic wedge material is plexiglass because it is transparent, and the assembly of piezoelectric elements in the acoustic wedge can be observed. In addition, some rubber, plastic and bakelite can also be used as acoustic wedge materials.