Factors affecting vortex flowmeter

by:Sure     2021-08-10
The measurement range of vortex flowmeter is relatively large, generally 10:1, but the lower limit of measurement is limited by many factors: Re>10000 is the most basic condition for the operation of vortex flowmeter. In addition, it is also limited by vortex energy. If the flow rate is low, the strength and rotation speed of the vortex are also low, and it is difficult to cause the sensing element to generate a response signal. The vortex frequency f is also small, which will also cause signal processing to occur. The measurement range of the vortex flowmeter is larger, generally 10:1. However, the lower limit of measurement is limited by many factors: Re>10000 is the most basic condition for the vortex flowmeter to work. In addition, it is also limited by the vortex energy. If the flow rate of the medium is low, the strength and rotation speed of the vortex are also low. It causes the sensor element to generate a response signal, and the vortex frequency f is also small, which also makes signal processing difficult. The upper limit of measurement is limited by the frequency response of the sensor (for example, the magnetic sensor generally does not exceed 400Hz) and the frequency of the circuit. Therefore, the flow rate range must be calculated and accounted for during the design, and the selection should be made according to the flow rate of the fluid. The environmental conditions at the use site are complicated. In addition to the environmental temperature, humidity, atmosphere and other conditions, electromagnetic interference should also be considered when selecting models. In strong interference, such as high-voltage power transmission stations, large-scale rectifier stations, etc., magnetic sensitive, piezoelectric stress type and other instruments cannot work normally or cannot accurately measure.  The temperature of the medium also has a great influence on the performance of the vortex flowmeter. For example, the pressure stress type vortex flowmeter cannot be used for a long time at 300℃, because its insulation resistance will drop from 10MΩ~10MΩ at room temperature to 1MΩ~10KΩ, and the output signal will become smaller, which will deteriorate the measurement characteristics. Magnetic sensitive or capacitive structure should be selected. In the measurement system, the sensor and converter should be installed separately to prevent long-term high temperature from affecting the reliability and service life of the instrument.   Vibration is also a big enemy of this type of instrument. Therefore, pay attention to avoid mechanical vibration, especially the transverse vibration of the pipe (vertical to the pipe axis and vertical vortex to generate the vibration of the body axis). This effect cannot be suppressed and eliminated in the flowmeter structure design. Since the vortex signal is also sensitive to the influence of the flow field, the length of the straight pipe section cannot guarantee the necessary flow conditions for the stable vortex street, it is not suitable for selection. Even the capacitive and ultrasonic types with strong vibration resistance can not be ignored to ensure that the fluid is a fully developed unidirectional flow. The history of vortex flowmeter is not very long, and it is currently in the process of research and development. Therefore, it is difficult to discuss its characteristics in a very specific and complete manner. Therefore, here is only a certain type of vortex flowmeter as an example to discuss its error characteristics, pressure loss characteristics and frequency characteristics.   Error characteristics of vortex flowmeter. This is an error calibration test for vortex flowmeters of the same caliber with air, water, and light oil. Due to the different viscosities of these three fluid media, their error characteristics are also different. However, it can be seen from the figure that, in addition to the large increase in the oil error in the range of Reynolds number Re less than 2×l04, when the Re number is within the range of 2×l04-3.5×l05, no matter which one The error characteristics of the medium are all within ±1%. This shows that the vortex flowmeter has a wide range of applications, and the accuracy is little affected by the medium. The frequency characteristic of vortex flowmeter. The vortex frequency is inversely proportional to the diameter and width of the vortex generator, and proportional to the flow velocity in the tube. It can be seen from the vortex flowmeter that, generally speaking, the larger the diameter of the flowmeter, the lower the vortex frequency generated; the smaller the diameter, the higher the vortex frequency generated. Pressure characteristics. Although the vibration energy of the fluid is only a part of the kinetic energy of the fluid, the pressure loss is inevitable. The greater the flow rate, the greater the pressure loss.
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