是基于卡门涡街原理而研制成功的一种具有国际先进水平的新型流量计。 The vortex flowmeter produced by Dongxiang Instrument is a new type of internationally advanced flowmeter developed based on the Carmen vortex street principle. Because it has the advantages of other flowmeters, among many flow detection solutions, vortex flowmeters have high measurement accuracy, small pressure loss, easy installation, and are not affected by the physical properties of the measured medium. Characteristics such as transmission, application technology is becoming more and more perfect, especially in large pipe diameter and water, oil and other liquid media flow measurement applications are more widely used.
Advantages of vortex flowmeters Compared with throttle differential pressure flowmeters, vortex flowmeters have the following advantages.
① The structure is simple, firm and easy to install and maintain. No need for pressure lines and three valve groups, reducing leakage, blockage and freezing.
② The accuracy is high, generally ± (1 ～ 1.5)% R.
③ The measurement range is wide, the caliber is reasonably determined, and the range can reach 20: 1.
④ The pressure loss is small, about 1/4 to 1/2 of the throttling differential pressure flowmeter.
⑤ The output pulse signal is proportional to the flow rate, and there is no zero drift.
⑥ In a certain Reynolds number range, the output frequency is not affected by the fluid physical properties (density, viscosity) and composition, that is, the meter coefficient is only related to the shape and size of the vortex generator and the pipeline.
(2) Limitations of vortex flowmeter ① It is sensitive to the mechanical vibration of the pipeline, and should not be used in places with strong vibration.
② The larger the diameter, the lower the resolution. Generally, the flow meter is used below DN400 when the pipe is full.
③ When the fluid temperature is too high, the sensor is still difficult. Generally, the fluid temperature is ≤420 ° C.
④ When the fluid has pressure pulsation or flow pulsation, the displayed value is significantly higher, which has a greater impact, so it is not suitable for pulsating flow.
(3) Advantages of throttling differential pressure flow meter ① The standard orifice plate structure in the throttling differential pressure flow meter is easy to replicate, simple and firm, stable and reliable performance, and low price. Can be used without real-flow calibration, which is rare in flow meters.
② A wide range of applications. It is suitable for all single-phase fluids, and can also measure some mixed-phase flows, such as gas-solid, vapor-liquid, and solid-liquid.
③ Both high-temperature and high-pressure large diameter and small flow rate are applicable.
④ It is insensitive to vibration and has excellent anti-interference ability.
(4) Limitations of throttling differential pressure flowmeter ① The measurement accuracy is medium level in the flowmeter. Due to the complexity of many factors, it is difficult to improve the accuracy.
② The range is narrow. Due to the square relationship between the instrument signal (differential pressure) and the flow, the general range is only 3: 1 to 4: 1.
③ The requirements for on-site installation are high. If long straight pipe sections (referring to orifice plates and nozzles) are required, it is generally difficult to meet them.
④ The pressure line between the throttling device and the differential pressure display instrument is a weak link, which is prone to leakage, blockage, freezing, signal distortion and other faults.
The integrated throttling differential pressure flowmeter developed in recent years, although there is still a pressure-inducing pipeline, but the length is less than 1m, thereby reducing defects in this regard.
⑤ Large pressure loss (referring to orifice plate and nozzle).
Therefore, the choice of vortex flowmeter or orifice flowmeter should be selected according to the physical and chemical properties of the measured medium and flow range, but it is impossible to replace the orifice flowmeter with a vortex flowmeter. Thank you!
尽可能测量低流速、小流量，必须提高信噪比，即尽量提高有效流量信号的幅值而降低机械振动干扰信号的幅值。 In order for the vortex flowmeter to measure as low a flow velocity and a small flow as possible, the signal-to-noise ratio must be increased, that is, the amplitude of the effective flow signal should be maximized and the amplitude of the mechanical vibration interference signal should be reduced. Improving the structure shape of the fluid-impedance, so that the sensor can better receive the pulsating pressure of the vortex, and the effective signal amplitude can be increased. But a more effective method is to package two corresponding piezoelectric crystals on both sides of the vortex generator, that is, using a differential piezoelectric sensor and a differential amplifier circuit. Since the mechanical vibration forces on the two piezoelectric crystals are the same, and the fluid vortex is alternately generated on both sides of the fluid resistance, after differential amplification, the same mechanical vibration signals of the two piezoelectric crystals cancel and reduce each other. 2 The opposite flow signals of the bulk piezoelectric crystals are added and enhanced. Thus, the interference of mechanical vibration signals is greatly reduced.
The vortex flowmeter's obstructing fluid uses a piezoelectric crystal to detect the vortex frequency. The piezoelectric signal is amplified by an AC and a trigger to change the vortex frequency into a pulse signal. The pulse signal is sent to the secondary meter and the measured flow rate is displayed after conversion. Among them, the amplification factor K of the AC amplifier and the threshold voltage of the trigger can be adjusted. In order for the threshold voltage to block the interference signal and to ensure that the trigger can output a valid signal, the interference signal V must be less than the threshold voltage u, and the effective signal voltage E is greater than the threshold voltage u, that is, the working condition of the vortex flowmeter is: E> u > V The magnitude of the interference signal V determines the lower range limit of the vortex flowmeter. Therefore, expanding the lower range of the vortex flowmeter must start with reducing the interference signal. Adjusting the AC amplification factor K can only strengthen the output signal, but the lower limit of the range cannot be extended. Electromagnetic interference and mechanical vibration interference are important interference factors of the vortex flowmeter, which limits the decrease of the range and affects the Use in flow measurement. By designing optical isolation current-limiting anti-interference measures on the circuit, it can effectively solve the interference of the ground current and the main problem of anti-electromagnetic interference; the structural design uses differential piezoelectric sensors and differential amplifier circuits of dual piezoelectric crystals Can eliminate the interference of mechanical vibration. As a result of the above two anti-interference measures, the lower limit of the range of the vortex flowmeter can be extended to 1/2 to 1/3 of the lower limit of the original range.
的干扰问题在选择安装位置时，应注意以下几点： When selecting the installation location of the vortex flowmeter , the following points should be noted:
A. The installation position should be selected as far as possible without pipeline vibration or small vibration, and the vibration acceleration cannot be greater than 2g. If the vibration is large, vibration reduction measures should be taken;
B. There must be sufficient straight pipe sections upstream and downstream of the sensor C. The maintenance valve is installed upstream of the sensor, and the flow regulating valve is installed downstream of the sensor;
D. Try to choose a location that is convenient for installation and maintenance;
E. Choose a dry location;
F. The sensor can be installed on a horizontal pipe or a vertical pipe. Vortex flowmeters, but when installed on vertical pipes, the medium must flow from bottom to top.
G. The sensor should be installed indoors as much as possible, and must be waterproof when installed outdoors. The cable outside the amplifier box should be bent into a U-shape;
H. The sensor should be kept away from electrical noise, such as high-power inverters, high-power transformers, motors, and high-power wireless transceivers.