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Electromagnetic flowmeters, non-fulltube electromagnetic flowmeters must measure the liquid level in the tube while measuring the average flow rate. By using two excitation windings in forward and reverse series respectively, two different magnetic field strengths and magnetic field flow potentials measured under the magnetic field distribution are generated. The ratio between the two potentials has a certain function relationship with the height of the liquid level. In vortex flowmeters, the vortex frequency of vortex generators in vortex flowmeters is proportional to the flow rate. Ultrasonic flowmeters and ultrasonic mass flowmeters attempted to measure the acoustic impedance and density of the second parametric liquid using ultrasound on the basis of a time-of-flight ultrasonic volumetric flowmeter and calculated the mass flow rate.
Applications in a certain area where the application of mature meters is limited, after technological breakthroughs, the development of compatible and improved instruments has enabled rapid development in this area. The following sections discuss the progress of several flow meter applications.
1. Electromagnetic Flowmeters Non-full-tube electromagnetic flowmeters. Traditional electromagnetic flowmeters can only measure full-tube liquid flow. Non-full-tube electromagnetic flowmeters are used in the field of sewage discharge with free surface natural flow and improve measurement accuracy in this area. . The flow error of traditional non-full pipe or open channel flow is reduced from ± (3 ~ 5)% FS to ± (1 ~ 2)% FS.
Measuring liquids with lower conductivity, it is now possible to measure liquids that are 2 to 3 orders of magnitude lower than the conductivity threshold of traditional electromagnetic flowmeters, such as glycerol, ethylene glycol, etc., which could not be measured before. In addition, this type of instrument has almost no slurry noise and flow noise, nor does it produce noise caused by electrode surface effects. The inner surface of the lining is covered with a non-conductive layer such as grease, or a thin layer of insulating dirt does not affect the measurement.
Low-power and two-wire electromagnetic flowmeters have a relatively rapid development. The two-wire system does not require an additional external excitation circuit, and only uses 4mADC current to provide the power required by the instrument, usually only tens of milliwatts. Low-power electromagnetic flowmeters make it possible to use dry batteries or solar cells, making it easier to install electromagnetic flowmeters for places without mains power.
Two-dimensional (direction) electromagnetic flow meter and multi-point plug-in electromagnetic flowmeter, the ship's electromagnetic speedometer placed outside the hull is the prototype of plug-in electromagnetic flowmeter. Later, plug-in electromagnetic flowmeters have been developed in large and medium-sized pipelines, and they have also been used in open channels, called electromagnetic current meters. However, in river flow or hydraulic test models, not only the flow velocity but also the flow direction must be known. The two-dimensional electromagnetic flow rate, also known as the vector velocity meter, enables the electromagnetic flow meter family to enter the field of hydrological test applications.
In addition, the plug-in electromagnetic flowmeter also refers to the design idea of ​​the uniform velocity tube. Multiple electromagnetic flow velocity measurement units are placed on the insertion rod to improve the measurement accuracy, so that the plug-in electromagnetic flow is advantageous in the application of the large tube.
2. Thermal Mass Flowmeters Thermal mass flowmeters used to be thermally distributed in the past and used for small gas flow measurements. They are used in semiconductor industries, heat treatment furnaces, analytical instruments, and other flow measurement and control of hydrogen, oxygen, and ammonia. The amount of leakage is measured in the valve manufacturing process. In recent years, the use of intrusive and plug-in thermal flowmeters for heat dissipation in foreign countries and the development of large and medium-sized pipelines for environmental protection and process industries have developed rapidly. Radially arranged detection rods consisting of multiple groups of detection elements are more widely used in large and medium-sized HVAC (heated ventilation and air-conditioning) projects. They are also used in the monitoring of SO2 and NOX in large boiler intake air and flue gas displacement. Total emissions.
Although the small-scale liquid-mass thermal flowmeter has a history of more than 20 years, it has not been developed until recently in industrial applications. Now, several manufacturers have produced multi-type thermal distributed thermal flowmeters to market. At present, it is mainly used in experimental devices such as chemical, petrochemical and food industries. For example, the fixed flow ratio control in the liquid ratio system and the liquid flow measurement and control in the liquefied gas injection process.
Application of flow meter and its development trend
Application of Flow Meters and Their Development Trends In addition to sensing flow, flow detection elements or flow sensors may also experience other variables, and derive other functions therefrom. This simplifies the flow detection system and reduces the number of instruments and connecting lines. ,lower costs. The reduction of process piping openings reduces potential leakage failures.