There are two calibration methods for plug-in vortex flowmeters.

There are two calibration methods for plug-in vortex flowmeters.


The composition of the plug-in vortex flowmeter and the calibration method of the point-flow meter type plug-in vortex flowmeter are briefly introduced. The shortcomings of the pump flow ratio comparison and the portable super flowmeter comparison method are briefly analyzed. The fast calibration method of the calibration correction ratio of the plug-in vortex flowmeter is proposed. The example proves that the method is effective and feasible.

Key words: plug-in vortex flowmeter;
Calibration correction

introduction

Due to its low price, light weight, small pressure loss, easy installation and maintenance, the plug-in vortex flowmeter has outstanding advantages in the measurement of large-diameter flow. At present, the measurement of large-diameter water flow is widely used in our company. Plug-in vortex flowmeter. With the implementation of various energy conservation and consumption reduction measures in recent years, the accuracy requirements of water consumption measurement data by various users have become higher and higher. The accuracy of the internal measurement data of large flow water has been controversial, so it must be As soon as possible, find a simple and effective method to compare the measurement data of the plug-in vortex flowmeter to correctly evaluate the accuracy of the metering data.

1 Introduction to the plug-in vortex flowmeter

The plug-in vortex flowmeter is a point flow meter type plug-in flowmeter consisting of a measuring head, an insertion rod, an insertion structure, a converter, and a meter housing (measuring pipe).

When the measuring head is inserted into a specific position in the pipeline (generally on the pipeline axis or the average flow velocity of the pipeline), the local flow velocity of the medium is measured, and then calculated according to the flow velocity distribution of the medium in the pipeline and the geometric parameters of the instrument and the pipeline. The value of the flow within the pipe.

The measuring head of the plug-in vortex flowmeter is a pulse-frequency type. The flow calculation formula is:

Qv=f/K (1)

Where: qv is the volume flow, m3/s; f is the frequency of the flowmeter, Hz; K is the meter factor of the flowmeter, 1/m3.

2 Calibration of the plug-in vortex flowmeter

There are two calibration methods for point flow meter type plug-in flow meters: flow meter method and flow meter method.

The flowmeter method is to calibrate the entire flowmeter. The calibration equipment and method are the same as the full-tube flowmeter. However, since the point flowmeter type plug-in flowmeter is often used for the measurement of large-diameter flow, its corresponding calibration equipment and The calibration cost is expensive and cannot be universally used. It can only be used in certain specific situations (such as the technical supervision department's arbitration of flowmeter measurement results, flowmeter stereotype test, etc.).

The flow meter method is to calibrate the flowmeter's measuring head as a flow meter. Firstly, the meter coefficient K0 of the measuring head is measured, and then the correction coefficient is determined according to the fluid and pipeline conditions at the use site, and then the meter coefficient K of the entire flow meter is calculated according to the cross-sectional area of ​​the pipeline. For the standard calibration device used in the flow meter method, the medium is a straight liquid tank and the gas is a low speed wind tunnel.

Generally, the flowmeter manufacturer does not have the above two standard devices. In practice, the variable pipe method is used to calibrate the measuring head to determine the meter coefficient K0 of the measuring head, but the test stage of the device must be determined at the same time. Some correction factors.

The meter coefficient K of the point flow meter type plug-in flowmeter is usually calculated by the calibration of the metering factor K0 of the calibration head. The calculation formula for the meter coefficient K is:

K = K0/(αβA) (2)

Where: K0 is the meter factor of the measuring head, 1/m3; α is the velocity distribution coefficient; β is the blocking coefficient; A is the cross-sectional area of ​​the measuring pipe, m2.

3 Insertion type vortex flowmeter measurement data comparison method

For a long time, the plug-in vortex flowmeter used by our company has been using the instrument's factory data since the time of commissioning. After several periods of use of the instrument, due to changes in the process and the on-site environment, the medium is corroded to the measuring head. The measurement accuracy of the meter may be affected by the wear and the deterioration of the performance of the instrument electronic converter. Since the company does not have the standard device for verifying the inserted vortex flowmeter, when the instrument measurement data error is large, the following methods are often used to make a simple comparison.

3.1 Water pump flow ratio comparison

Previously, when the operator of the unit used to have doubts about the measurement data of the plug-in vortex flowmeter, it was often carried out with the rated flow rate of the “specified performance point” on the pump nameplate or the flow reading corresponding to the typical pressure-flow characteristic curve of the pump. If the two flow values ​​are inconsistent, the instrument is considered to be inaccurate, and the instrument maintenance personnel are immediately notified to check. However, after the instrument maintenance personnel check, the instrument is not found to be abnormal, so both parties hold their own opinions and cause disputes.

In fact, the pump flow ratio is often misunderstood by the meter flow value, because the pump delivery flow rate is determined by the intersection of the pump characteristic curve and the piping load characteristic curve, which varies with the running load characteristics, and is indicated on the pump nameplate. The rated flow rate refers to the flow rate under a certain specified condition, and in most cases the actual flow rate and the rated flow rate, and in most cases, the actual flow rate and the rated flow rate are not consistent. In addition, the rated flow rate of the pump is also allowed to have a tolerance of 4% to 8%. The head-flow characteristic curve and the typical curve of each pump of the same specification will also have corresponding differences, and the delivery flow rate will be different, even if It is the measured head-flow characteristic of the pump. There may be an error of 2%~3.5% between the flow value and the actual value. Therefore, the flow value of the pump cannot be used as the basis for determining whether the flow meter is accurate or not. However, it can be cross-referenced during daily operation. If there is an abnormal change in the difference, it can be used as a fault phenomenon to further check the water pump, instrument and piping system to determine the cause of the failure.

3.2 Comparison with portable ultrasonic flowmeters

In recent years, our company has introduced the United States Polysonic POLYSONICS DCT7088, Japan Fuji FUJI FLD/C portable ultrasonic flowmeter for evaluating the flow condition and energy/material balance of the pipe network, or used as a verification pipeline installed. The health of other flow meters. In order to solve the dispute about the accuracy of the company's internal large-flow water metering data, we have tried to use the portable ultrasonic flowmeter to calculate the water volume, and further use it to compare with the measured data of the plug-in vortex flowmeter. However, the portable ultrasonic meter that uses the propagation time method to measure the flow area and the propagation distance of the pipeline involved in the calculation by calibration is not only related to the clamping position, the characteristics of the pipeline such as the material and thickness of the pipe wall, the corrosion condition, the lining material. It is related to the thickness and the change of acoustic coupling. It is also related to the technical level of the installation and debugging personnel. The use is more complicated and the general personnel are not easy to master. In actual use, the measurement results of the instrument are unstable, the measurement accuracy cannot be guaranteed, and it is difficult to provide effective. Data results. Therefore, the conditions for on-site comparison of the measurement data of the portable ultrasonic flowmeter and the plug-in vortex flowmeter are currently immature, and further exploration is needed to accumulate experience.

3.3 Calibration correction method for plug-in vortex flowmeter

Although the on-site use of the plug-in vortex flowmeter can be improved through corresponding theoretical analysis, overhaul, commissioning, etc., the dispute over the accuracy of the metering data of the flow meter is finally solved, and the most convincing is valid data.

Our company currently has a static volumetric water flow calibration device with a maximum working diameter of 300mm. We tried to remove the controversial plug-in vortex flowmeter on the site, installed it on the 300mm diameter pipeline of the calibration device, calibrated the entire flowmeter with the flowmeter method, and obtained the data through the actual flow calibration. Analyze the linearity, repeatability and accuracy of the instrument under this caliber condition, and analyze whether the instrument's performance is qualified, and further make relevant debugging to make the instrument reach the best use state.

The question now is, how to determine the use data of the instrument in the field when the geometric parameters of the installation pipeline are different from the experimental conditions? From the calculation formula of formula K (formula 2), it can be known that for the same plug-in vortex flowmeter, the K0 value is uniquely determined at the same time, and is calibrated and debugged by the flow calibration device (300mm diameter pipeline). The instrument itself is not problematic. The actual use factor of the instrument is K' due to different conditions such as the diameter of the installation site. K' is only related to the αβ A parameter, so we can determine by calculation to complete the comparison.

3.4 Calibration correction of insert vortex flowmeter

Because the calculation of K' by the formula is quite cumbersome and difficult to be mastered by everyone, the author has compiled a quick comparison comparison table based on some experience and experience accumulated by himself for a long time. (Note: This table is compiled based on the data of D=300mm, so that Quick conversion), as listed in Table 1, Table 2.



Using the flowmeter method, the plug-in vortex flowmeter is calibrated and debugged in the 300mm pipeline, and the calibration coefficient K of the instrument when D=300mm is determined. Then, by looking up Table 1, Table 2, the actual pipe diameter can be obtained. The ratio of α β A under the condition of 300 mm pipe diameter is converted into the meter coefficient K′ of the instrument under the actual use of the caliber condition, thereby completing the calibration correction comparison of the plug-in vortex flowmeter.

3.5 Application example of calibration calibrating method for plug-in vortex flowmeter

The SX88-900L1B2 plug-in vortex flowmeter (4~20mA analog output type) is used for water metering in our circulating water plant. The long-term circulating water plant has great controversy on the measurement data of this meter. The flow value is used as a reference comparison and the measurement error of the meter is as high as 20%. Although the flow values ​​of the pumps cannot be used as the basis for determining the accuracy of the flow meters, they are used interchangeably in daily operation. After careful inspection of the pump, instrument and relationship by the technician, it is confirmed that the apparent difference between the two is caused by the meter factor.

The plug-in vortex flowmeter is removed, and a series of operations are performed according to the calibration correction method. At the same time, the amplifier is debugged accordingly, and valid data is obtained. The meter calculates the maximum flow rate Qmax of the instrument according to the process conditions at the factory. =6000m3/h, full-scale frequency fmax=41.2Hz; installed on the pipeline of 300mm diameter, the whole flowmeter is calibrated by flowmeter method, and the meter coefficient K=202.951 is obtained by real-flow calibration, and then the table is checked. Table 2 shows that the ratio of α (compared to the commonly used flow rate of the instrument), β, and A under the condition of the pipe diameter of 900 mm and the diameter of 300 mm is 1.016, 1.055, and 9.00 respectively, and the calculated instrument is in the condition of 900 mm. The following meter coefficient K'=K/(1.016×1.055×9.000)=21.038, and then converted to the full-scale frequency fmax=41.2Hz, the actual maximum flow rate of the instrument Qmax=7050m3/h is the calibration of the plug-in vortex flowmeter. Correct the comparison. After further estimation, the correction result is about 0.5% compared with the traditional theory, which can meet the measurement needs of the site.

In addition, after the instrument is installed on the site, it is also very important to properly debug the gain and sensitivity of the instrumentation amplifier according to the actual situation, so that the instrument can reach the optimal operating state.

4 Conclusion

After a period of experimentation, it is proved that it is effective and feasible to obtain the actual use data of the instrument by using the calibration correction comparison method. We applied this method to correct the instrument data of a batch of vortex flowmeters with large deviations in measurement data, and obtained the approval of all parties to ensure the accuracy of the company's large-flow water metering data. Of course, since the measurement accuracy of the plug-in vortex flowmeter is greatly affected by the installation of the pipeline and the instrument, there are certain errors in the calculation of the correction coefficient itself, so there are many problems to be further explored.

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