Types and working principles of flowmeters

Abstract: Information on the types and working principles of flowmeters is provided by excellent flowmeter and flowmeter manufacturers. In 1738, the Swiss Daniel Bernoulli used the differential pressure method to measure the water flow based on the Bernoulli equation; later, the Italian Venturi studied the flow measurement with a Venturi tube, and published the results in 1791; 1886 In 2009, the American Herschel used a Ventura. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the types and working principles of flowmeters. Types of Flowmeters Flowmeter Principles·Based on the Bernoulli equation, Bernoulli used the differential pressure method to measure the water flow; later, the Italian Venturi used a Venturi tube to measure the flow, and published the results in 1791; in 1886, the American Herschel used Venturi tubes make practical devices for measuring the flow of water. In the early to mid-20th century, the original measurement principles gradually matured, and people began to explore new measurement principles. Since 1910, the United States began to develop trough flowmeters for measuring water flow in open ditches. In 1922, Parshall reformed the original Churi sink into the Parshall sink. From 1911 to 1912, the Hungarian-American Carmen proposed a new theory of the Karman vortex street; in the 1930s, a method of using sound waves to measure the flow velocity of liquids and gases appeared again, but there was no great progress until the Second World War. It was not until 1955 that the Maxson flowmeter using the acoustic cycle method was used to measure the flow of aviation fuel. In 1945, Colin successfully measured blood flow with an alternating magnetic field. After the 1960s, measuring instruments began to develop in the direction of precision and miniaturization. For example, in order to improve the accuracy of differential pressure instruments, force balance differential pressure transmitters and capacitive differential pressure transmitters have appeared; in order to miniaturize the sensors of electromagnetic flowmeters and improve the signal-to-noise ratio, the use of non-uniform magnetic fields has appeared. and electromagnetic flowmeters with low frequency excitation. In addition, practical Karman vortex flowmeters with wide measuring ranges and no moving detection parts appeared in the 1970s. Flow measuring instrument Flow measuring instrument is an industrial automation instrument used to measure the flow of fluids such as liquid, gas or steam in pipes or open trenches, also known as flow meters. Flow refers to the amount of fluid flowing through the effective section of the pipe per unit time. The amount of fluid expressed in volume is called volume flow, and the unit is meters? /hour, liter/hour, etc.; the quantity of fluid expressed by mass is called mass flow, and the unit is ton/hour, kilogram/hour, etc. With the rapid development of integrated circuit technology, ultrasonic (wave) flowmeters with phase-locked loop technology have also been widely used. The wide application of microcomputers has further improved the ability of flow measurement. For example, after the application of microcomputers in laser Doppler flowmeters, more complex signals can be processed. Flow can be indirectly measured by various physical phenomena, so there are many kinds of flow measuring instruments. According to the measurement method, the flowmeter has differential pressure type, variable area type, volume type, velocity type and electromagnetic type. Differential pressure flowmeter is a type of flow measuring instrument that is widely used, accounting for about 70% of the total number of flow measuring instruments. It consists of a throttling device and a differential pressure gauge. When the fluid filled with the circular tube flows through the throttling member (such as an orifice plate), the flow beam forms a local contraction at the orifice plate. There is a pressure difference between the front and rear of the plate, which is proportional to the square of the flow. Instruments for measuring differential pressure include strain, capacitive and vibrating wire differential pressure transmitters, as well as dual bellows differential pressure gauges. Such instruments are easy to debug and have been standardized. As long as the throttling device is matched with the differential pressure gauge, it can be used to measure the flow of the fluid. The main form of variable area flowmeter is a rotary (float) flowmeter, which is composed of a conical glass tube and a float, and the float can move up and down in a vertically installed conical glass tube. When the fluid to be measured flows through the annular gap between the tube wall and the float from bottom to top, the float is lifted upward, and the area of ​​the annular gap between the tube and the float increases until the force formed by the pressure difference on both sides of the float is equal to the gravity of the float. , the float is in an equilibrium position. When the flow changes, the force formed by the pressure difference on both sides of the float also changes, so that the float is rebalanced in a new position, and the height of the float is the reading of the flowmeter. Turbine flowmeter is composed of sensor and display instrument. The sensor is mainly composed of magnetoelectric induction converter and turbine. As the fluid flows through the sensor, it passes through the front deflector and then spins a turbine made of ferromagnetic material. The rotating turbine cuts the magnetic field lines of the magnetoelectric induction converter on the solid shell, and the magnetic resistance in the magnetic circuit changes periodically, thereby inducing an alternating current signal. The frequency of the signal is proportional to the volume flow of the measured fluid. The output signal of the sensor is amplified by the preamplifier and then sent to the display instrument for flow indication and accumulation. The turbine speed signal can also be detected by converters such as photoelectric effect and Hall effect. The electromagnetic flowmeter is composed of sensors, converters and display instruments, and works according to Faraday's law of electromagnetic induction. The Karman vortex flowmeter is to place a bluff column (cylinder or triangular column, etc.) in the fluid, and within a certain Reynolds number range, a regular vortex will be generated alternately on both sides behind the column.

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