Abstract: The average rate of the total pressure flowmeter back-pressure test and the number and location of holes, the test-profile shape, and other issues were discussed. Details on the average rate of several forms, is the use of the formula for calculating the flow measurement, analysis of various factors on the impact of measurement accuracy, the final product for the development of a concept.

Key words: both flow measurement of the impact of factors of speed


Average rate of flow meter measuring the components - both the speed (abroad said Annubar, literal translation Aniu Pakistan), is based on the principle of early Pitot tube gun developed, is developed by the late 1960s a new type of differential pressure flow measurement devices And started with the application of China's industrial scene, the mid-1970s there were more than 30 manufacturers to develop and produce. All of the advantages of speed, structure on a relatively simple (as shown in Figure 1), small pressure loss, installation, demolition facilitate and safeguard a small amount.


The flowmeters because of low production costs, low prices and therefore more popular in the market, the number of traffic it has occupied a place in the instrument. Especially because of its small pressure loss (compared with the orifice, only 5% of the Orifice Plate), greatly reducing the power consumption, energy-saving effect of significantly, and this energy crisis today, has its special significance. As the flow meter to a wide range, long-term stability (shown in Figure 2) have been greatly in recent years the development of a structure of several different forms of the flowmeter. However, improper use of the application of a number of problems arising in, making an objective requirement for the development of the status quo and have a lot of contradictions, many people hope that their application can be resolved, for which people have done a lot of unremitting efforts, made all speed of the flow Both of the oldest and youngest flowmeter, in energy, environmental protection and other measures have been tested in a wide range of applications

1 Average rate of flow sensors measuring principle

Average rate of flow sensors, by its structure of knowledge, it is a pipe inserted along the diameter of the hollow Jinzhu Gan, squarely in the direction of fluid flow paired with the pressure hole, is generally two pairs, but there are also a Or the right, aloof shape of 2007. Towards the flow of multi-point hole measuring the pressure is the pressure, and all of the pressure-connected, leads to an average total pressure p1, flow-back at the centre of a general open a hole, and the pressure of the same, leads to pressure p2 . The average rate is measured using the full pressure and fluid pressure to measure the difference between the velocity. The output of both speed differential ( p) and fluid average (v), based on the classic Bernoulli's equation that
1
In PHydrostatic pressure and all the differencePa
ѡFluid densitykg/m 3
kCorrection factor
If traffic to, its basic formula for calculating traffic

In qv The volume of fluid flowm 3 /s
qmThe quality of fluid flowkg/s
Working under both the speed of the flow coefficient
šWorking under the state of fluid flow, the flow-detection beam expansion coefficient
AWorking under the section of pipelinem 2
For different compression fluid=1 The fluid compressibilityţ1
All the pressure hole location, can strike a sub-area of law. In this way, the changes in flow speed of circumstances can have a better ability to adapt, as reflected by the error smaller. The so-called sub-area method is to split up into the pipeline section and the outer ring round the equivalent average velocity, the point is that the whole pressure-position, as shown in Figure 3.


All the pressure-opening position available Chebyshev seek numerical integration of the solution, shown in Figure 4, map r1 = 0.4597R, r2 = 0.8881R, r1, r2 to take centre-pressure pipeline from the centre Distance, R within a radius of the pipeline.
The point of this election method, whether the number or location, in recent years academics and the International Organization for Standardization have raised an objection that the tube should be divided into three regional mobile, click on the number of elections - Chebyshev (Log - Jchebycheff) method, therefore, the pressure should detect the location of the hole; r1 = 0.03754R; r2 = 0.7252R; r 3 = 0.9358R. This approach has been the International Organization for Standardization (ISO) in the closed pipeline flow measurement Committee (TC30) recognized, in the light of the above reasons, through the people's pilot study, the average rate of the total number of pressure-or proposed to use two pairs or three pairs Suitable.

Back-pressure test using a long hole is the result has been recognized both by regulating the speed of a potential flow, and the potential flow of the pipeline that is before the circumferential pressure points are equal, no lateral mobility. From this perspective, a back-pressure test holes have been sufficient, in order to prevent the flow of fluid in the detection process of obstruction-back-pressure test, the porous back-pressure from pressure, has begun to use the average rate of flow sensors, a word from Flow of basic formula tells us that as long as the effective detection of both speed of the output differential P, can detect the flow of fluid, which is both the velocity of flow sensors measuring principle.

2 Average rate of the structural form

Average rate of the structure is a hollow Jinzhu Gan, its profile shape of the product is the largest radio and diamond, the mid-1980s also used the wing-shaped cross section.
The average rate of the circular section, when the Reynolds number Re at 10 510 6 between, making the flow coefficient instability, it is the stability of the region in the Reynolds number Re <10 5 and Re> 10 6. This was mainly due to the resistance of circular section, its own existence of "resistance crisis" caused. Fluid flows through the tube when there is a separation of different points in the pipe caused Ying-fluid flow, in the pipe caused by pressure on the distribution of different, thus leading to a flow coefficient changes.
Diamond-shaped cross-section of the speed of both is to overcome the circular section of this flow coefficient designed to unstable regions. Diamond-shaped cross-section of both Reynolds number is the number of numerical Re, the separation of the same points are determined to better solve the average rate of flow sensors in detecting gas, steam flow instability in the area difficult. Average rate of use of diamond-shaped cross section, has already been identified by the total.
Wing-shaped cross section is to further reduce fluid by detecting when Ying-flow resistance, thereby reducing pressure loss. Actually, both in terms of speed, whether by radio or diamond-shaped cross section, can not restore the loss of pressure, are insignificant, accounting for only 2 percent of output differential pressure around, but in practical application process, the average rate of the Pressure P lower output it is a major weakness, when a wing-shaped cross section, can indeed reduce some resistance, but their output differential is smaller, and the circular section or diamond-shaped cross section compared to reduce the differential pressure 50 percent, due to the low differential pressure, work together to support the use of more expensive micro-differential pressure transmitter, and in these circumstances, making detection of instability, thus affecting its application.

3 Both the speed of the system components Flowmeter

As for (2) and type (3) below. Average rate of flow meter system is composed of real differential P measurement, this is all Differential Flowmeter in common, technology is common, that is, differential pressure transmitter used to P converted into the corresponding machinery Signal or signals can also be measured directly p and the corresponding treatment, the paper will not elaborate.

4 Application process of measuring accuracy of influential factors

Average rate of flow meter in the application process should pay attention to the issue, see the national verification protocols JJG640-94 differential pressure flowmeter testing protocols and related documents, the paper will not elaborate.

5 Concluding remarks

It should be noted that both speed of the flow meter from the design, manufacturing to installation, are very strict requirements, as long as one link in a little careless, can be a great error.
Traffic is no accurate measurement needs of the productive sector, no sector is also the issue of common concern. Average rate of flow meter to the next measurement applications play a role in raising the level of flow measurement is the road to take. Heat-average rate of flow meter is one of the ways, as shown in Figure 5.


Heat-average rate of flow meter consists of three parts, testing par, electronic circuits and flow with the plot of the show operator. Par Testing is a hollow metal tube, and in its allocation on a number of hot-wire sensor components. Electronic circuits and each corresponding to only heat-sensing device combination of silk, or a heat gun or wire.
Average rate of heat flow meter to the flow meter formula
(5)
In APipeline cross-sectional aream 2
nCross-section of the pipeline, such as Score
i Article i characteristic point of densitykg/m 3
i Article i characteristic point of the velocitym/s
Quality velocity (p ) for the calculation of
6
In:I for the current heating; R for hot-wire resistance; T for the hot wire temperature sensing devices; T0 as a gas temperature; tested for medium density; for fluid flow: 1, 2, m to experience constant.

References

1 Li Liang, such as trade, commonly used instrument Practical Guide, Beijing, China metering Press, 1988
2 Gross new industry, the average rate of flow meter application and development of automated instruments. 1986.17 (1)

2001-03-19 Received
About the author: Wang Liyong 27-year-old in 1995 and graduated from Harbin Institute of Technology Control professional.