Tell about the selection and installation of vortex flowmeter in engineering

With the continuous development of microelectronics technology, the technical level of vortex flowmeters has also continued to develop. There are many models and types, and there are many foreign advanced products.Vortex flowmeters have many advantages that other flowmeters cannot match, such as high accuracy. Output digital signals, etc., but not as common as other flowmeters in industrial applications, not because its technical and performance indicators have not yet reached a satisfactory level, but because users lack application experience when selecting and using vortex flowmeters Caused.

1. Selection of vortex flowmeter

The choice of vortex flowmeter should be considered in combination with the characteristics of the process medium, such as the performance, economy, installation and environment of the flowmeter, which can be done by general professionals. This article introduces several issues that require special attention.

1.1 Choose according to the resistance to pipeline and fluid vibration

The vortex flowmeter is based on setting a resistance body in the fluid pipeline to generate a vortex, and measuring the frequency of the vortex to measure the flow. In industrial production, vibration is ubiquitous and unavoidable. The general industrial vibration frequency is mostly from a few Hz to a few kHz. The vortex frequency of the vortex flowmeter falls within this range. Vibration of pipes and fluids will inevitably affect the measurement of vortex flowmeters, so vortex flowmeters must have anti-vibration compensation.

Commonly used vortex flowmeters are capacitive, piezoelectric stress ultrasonic and other types. Currently these types have good vibration resistance, of which capacitive piezoelectric stress can only resist two-dimensional vibration. The vibration direction vibrates in the longitudinal direction (downstream direction) or parallel to the axis of the vortex generating body.It has anti-vibration capabilities and can basically be eliminated, but the ability to resist lateral (in line with the vortex lift direction) vibration is weak, while the ultrasonic type has anti-three-dimensional vibration. Therefore, in general occasions, the vibration acceleration is less than 1g, the vibration frequency is less than 500Hz, the amplitude is less than 21mm (there is a strong sense of vibration when you touch it, and you ca n’t hold it) .The three flowmeters can meet the requirements, but in occasions where the vibration is particularly strong or In the case of vibration in the lift direction, the ultrasonic flowmeter is more suitable.

1.2 Choose according to the measured medium

The general vortex flowmeter can measure the flow of gas liquid and steam medium, but due to the different characteristics of various media, the structure of the sensor is various, and its adaptability is also different. Piezoelectric stress and capacitance vortex flowmeters have a wide range of applications, but when measuring low-density and low-velocity gas flow, due to the limitation of vortex energy, the vortex is not strong. The low-capacity vortex flowmeter has two applications. The pressure guide hole is not easy to measure the stolen medium; although the ultrasonic type can measure the flow rate of the medium with low flow rate, it is more sensitive to pulsation; the specific conditions are as follows:

1) For fluids containing dust and solid particles or suspended matter in the medium, capacitive vortex flowmeters should not be used. Because there are two small pressure-guiding holes on both sides of the vortex generator, it is easy to block and make the output signal zero. All other types of flowmeters with pressure-guiding holes and capacitive flowmeters have a similar situation.

2) Although the ultrasonic vortex flowmeter has strong anti-vibration performance, the use temperature range is not as wide as the capacitive and piezoelectric stress type. The upper limit of the temperature measurement of the piezoelectric vortex flowmeter does not exceed 300 ℃. When exceeding, the output signal of the piezoelectric element decreases and the anti-interference ability is greatly reduced; the upper limit of the temperature measurement of the capacitive vortex flowmeter reaches 400 ℃, which has good high temperature resistance; and the upper limit of the temperature measurement of the ultrasonic vortex flowmeter No more than 200 ℃, if the temperature of the measured flow medium exceeds this range, the ultrasonic probe may be damaged. In addition, the ultrasonic vortex flowmeter should not be measured in a liquid containing too many bubbles or a liquid containing impurities, because a liquid with too many bubbles is difficult to pass through, which may cause difficulty in measurement or even impossible measurement. Impurities in the liquid will slow the reflection or absorption of ultrasonic waves and affect the accuracy of the measurement.

3) The choice of vortex flowmeter should not only consider the temperature of the measured medium, but also consider the temperature of the maintenance purge medium. The temperature of the measured medium of the vortex flowmeter may be normal temperature, but the pipeline needs to be purged with steam during maintenance, and the temperature of the steam is above 150 ℃. Street flowmeter, when overhauling the purge pipeline, it is possible to damage sensitive components

4) In the use state, if the measured medium has obvious pulsation, it is not suitable to choose ultrasonic vortex flowmeter. Because the ultrasonic vortex flowmeter is highly sensitive to small flows, it is used in such occasions, which will make the output signal unstable or even distorted.

5) When a large number of bubbles are mixed in the liquid, it is not suitable to use various vortex flowmeters

2. Installation of vortex flowmeter

The installation of the vortex flowmeter should consider the positioning of the flowmeter, the length of the upstream and downstream visual sections, the diameter of the pipe, environmental impact (temperature, electromagnetic radiation corrosion) vibration, valve installation, pipeline support and other factors. It is generally required that the flow caliber and the pipe diameter are the same and concentric. ). When the upstream resistance part is a valve or globe valve, the length of the upstream straight pipe section must be no less than 40D. The installation location of the flowmeter should avoid high-temperature corrosion electromagnetic radiation vibration source. When the vibration is strong, support should be considered to reduce The influence of amplitude. It is recommended to install the flowmeter downstream of the regulating valve when using the vortex flowmeter for control loop measurement. Usually in order to avoid vibration or some unpredictable reasons, install a throttle ring, expansion section or The storage tank partially absorbs the vibration and shock of the fluid, which is especially important in the control loop. If the vibration in a certain direction is predicted, the vortex flowmeter should be installed in a place where the vortex lift direction is consistent with the vibration direction. Ultrasonic vortex flowmeter When it is installed in a horizontal pipeline, the ultrasonic probe should be placed in the middle position on both sides of the horizontal pipeline (that is, the vortex generator is in the vertical position up and down) Doing that the aggregation prone bubbles above the pipe, the large foreign matter along the pipe they will interfere with the bottom flow over.

The sound wave is installed in the above way, which effectively avoids the above phenomenon to bring benefits to the measurement. Ensuring that the inner diameter of the pipeline is the same as the flowmeter diameter is the basic requirement of the manufacturer for the user to use the flowmeter. However, in actual use, it is shown that due to the different standards of the flowmeter diameter of foreign manufacturers, the standard inner diameter of the pipe is the same as the inner diameter of the national standard pipe in China. There are differences under the diameter. In addition, when the engineering diameter is the same, because the pressure level requirements are different, the wall thickness of the pipe is different. When users choose and install the vortex flowmeter, they often ignore the problem of pipe matching, which is likely to cause additional errors.