Detection of Vortex Occurrence Frequency of Vortex Flow Meter

Abstract: The detection information of the vortex occurrence frequency of the vortex flowmeter meter is provided by the excellent flowmeter and flowmeter manufacturers and quotation manufacturers. The flow signal of the vortex flowmeter is reflected by the frequency of the vortex, so how to detect the vortex frequency is an important subject in the development of the vortex flowmeter. According to the current detection principle of vortex frequency signal, there are roughly two categories: 1. The vortex is detected after the vortex is generated. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the details of the detection article of the vortex occurrence frequency of the vortex flowmeter. The flow signal of the vortex flowmeter is reflected by the frequency of the vortex, so how to detect the vortex frequency is an important subject in the development of the vortex flowmeter. According to the current detection principle of vortex frequency signal, there are roughly two types: ① Detecting the frequency of flow change near the vortex generator after the vortex is generated, which is mainly completed by the thermal element; ② After detecting the vortex, the force is applied to the vortex generator. The frequency of change is mainly completed by piezoelectric sensitive elements. Below, we will discuss the specific examples of these two detection methods respectively. The first detection method takes the cylindrical vortex generator as an example, and its structure can be seen in Figure 3—9 is shown. There are pressure guiding holes on the surface of the cylinder, which communicate with the inner cavity of the cylinder. The cavity is divided into two parts by the partition wall, in the central part of the partition wall there is—A small hole, in which a platinum resistance wire for detecting fluid flow is installed. When the vortex is generated on the downstream side of the cylinder, the pressure under the cylinder is higher than that at the top due to the effect of lift. Under the action of the upper and lower pressure difference, the fluid under the cylinder enters the empty glue from the pressure guiding hole below the cylinder, passes through the small hole in the central part of the partition wall, flows through the platinum resistance wire, and flows out from the upper pressure guiding hole. If the platinum resistance wire is heated to a certain temperature value higher than the fluid temperature, when the fluid flows through the platinum resistance wire, it will take away heat and change its temperature, that is, change its resistance value. When a vortex is generated above the cylinder, the fluid enters from the upper pressure guide hole, flows out from the lower pressure guide hole, passes through the platinum resistance wire again, and changes its resistance value again. It can be seen from this that the change of resistance value corresponds to the change of flow, which also corresponds to the frequency of vortex. Therefore, the vortex frequency can be obtained by detecting the change frequency of the resistance of the platinum resistance wire, and then the flow value can be obtained. The circuit that converts the resistance value change of platinum resistance wire into electrical signal is shown in Figure 3—11 shown. In the circuit block diagram of the thermal detection method of the vortex flowmeter, A1 differentially amplifies the output of the platinum resistance wire on one arm of the bridge, and feeds back to the bridge through the output current of the power amplifier A2, so that the temperature of the platinum resistance wire is one higher than the fluid temperature. constant value. The second detection method takes the triangular column vortex generator as an example. Its structure can be seen in Figure 3—10 shown. Two elastic metal films are installed on both sides of the triangular column, which are also the poles of the capacitor, and the electrode plates are installed inside. The electrode plate and the metal film are filled with oil to transmit the pressure. In this way, when a vortex is generated under the triangle, and the pressure below is higher than the pressure above, the metal film under the triangle is pressed inward, and the metal film above pops out, changing the respective capacitances of the two capacitors. . In this way, corresponding to the alternately generated lift, the capacitances of the two groups of capacitors change differentially. Therefore, the change of capacitance corresponds to the change of lift force, which also corresponds to the frequency of occurrence of vortices. In this way, the vortex frequency can be obtained from the frequency of capacitance change, and then the flow value can be obtained. The block diagram of the circuit that converts the capacitance change into an electrical signal is shown in Figure 3—22 shown. The eddy detection sensor consists of two groups of metal films and electrode plates to form a differential change capacitor, which is placed on the electrostatic capacitance detection bridge, and is excited by the RF oscillation circuit. When the vortex is generated, the electrostatic capacity changes, which causes the bridge to be unbalanced. The unbalanced potential is amplified by the RF amplifier circuit, and the signal corresponding to the vortex frequency is obtained after detection. The signal is amplified and shaped into a rectangular wave, which is output by the constant current loop as a given current pulse. A feedback loop is used to compensate for bridge imbalances caused by temperature changes. Capacitive eddy frequency detector circuit block diagram Compared with the two detection methods, the first method has high sensitivity and a wider range of applicable frequencies, so the corresponding flow range is also wider. However, it has a fine structure and is easily affected by impurities in the fluid. The second method is solid and reliable in structure, and is widely used in industrial measurement. But since the lift force is proportional to the square of the flow velocity, that is, if the flow velocity increases 10 times, the lift force will change 100 times. Therefore, if the flowmeter is required to be suitable for a large flow range, but also to ensure that it has a certain degree of flexibility, this method is difficult. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Detection of Vortex Occurrence Frequency of Vortex Flow Meter'

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