1 Proposed issue The use of differential pressure principle for flow measurement is the most used in the world today, and it is also one of the most reliable flow measurement systems. The differential pressure flowmeters represented by orifice plates, nozzles, and venturi tubes have been successfully used in the industrial field for more than 100 years. In particular, the application of standard orifice plates has a long history. It occupies about 50% of the world's current level. 55% of the industrial flow measurement market. Orifice plate flowmeters are simple, reliable, and easy to process, but they also have the following limitations. Because of the above problems in orifice flowmeters, a new type of differential pressure equal flow tube flowmeter, the T-type Annubar flowmeter, gradually shows its superiority in practical applications. 2 Development of Annubar Flowmeter The Annubar flowmeter is a differential pressure equal velocity tube flow meter developed based on the principles of Bernoulli energy conservation and pitot tube measurement principles. It has experienced the three stages of development shown in Figure 1. The cross-section of the test rod of the original Annubar flowmeter is circular, and the K value of the flow coefficient of the circular Annubar flowmeter is found to be basically unchanged when the Reynolds number Re<1O5, and when it is between 106 and 108, K The value increases and is dispersed, with a dispersion of approximately ±10%. Further research shows that the above phenomenon is caused by the unfixed position of the separation point when the fluid flows through the round pipe; when Re<1O5, the separation angle between the separation point and the pipe center is 78 ゚. When Re>105, the separation angle is 130 ゚; When Re is between 105~108, the separation angle is in an undefined position between 78 ゚~130 ,, as shown in Fig. 2. Since the flow rate and the K value are proportional to the calculation formula of the Annubar flowmeter, the dispersion of ±10% of the K value will result in an error of ±10% in the flow measurement, while the dispersibility of the K value of the Annubar flowmeter is larger. The flow rate corresponding to the Reynolds number range is the normal flow rate of most gases in the pipeline. The outstanding advantage of the second-generation gems I (rhombic section) Anupuba flowmeter is that the position of the fluid separation point is fixed on the sharp inflection point on both sides of the diamond, thus solving the problem of unstable K value of the circular Annubar flowmeter. The measurement accuracy has been greatly improved. When the fluid flows through the edge of the Annubar sensor, vortices are generated. These eddies cause the vibration of the Annubar flow sensor, which produces a pulsating noise signal distortion, which affects the stability of the measurement. The second generation gem type II (improved diamond section) Annubar Flowmeter solves this problem. Whether it is an improved Nuba flowmeter with a diamond section or an oval, fan-shaped, bullet-type, wing-type, etc. developed on the basis of a circular annubar flowmeter The Nuba flowmeter has made great progress, but there are still the following problems. 3 T-type Annubar Flowmeter Features Compared with the conventional equal velocity tube flowmeter, the T-type Annubar flowmeter not only maintains the advantages of the improved diamond-shaped Annubar flowmeter, but also perfectly solves the above-mentioned actual problems, and its improvement. It is revolutionary. 3.1 Good anti-blocking properties The velocity distribution of fluid in each section of the pipeline is different. A precise speed flow meter needs to obtain the average speed of the fluid. In the past, the average speed flowmeter only had a few pressure taps and the sampling rate of the fluid was only about 6.5%. T-type Annubar flowmeter front high-pressure pressure notch across the entire pipe, to obtain more than 12 times the velocity of the fluid velocity sampling area than the previous uniform velocity tube flowmeter, its rate of sampling of fluids up to 85%, and thus get the most Good average speed measurement accuracy. The design of the T-type Annubar flowmeter across the entire high-pressure pressure notch of the pipeline also makes it have better resistance to blocking, and the adsorption of some impurities will not cause the measurement accuracy to occur on the conventional X-ray tube flowmeter. Catastrophic measurement error. The fluid flow of the T-type Annubar in the pipeline is shown in Fig. 3. From Fig. 3, it can be seen that the fluid can form a large high-pressure region on the front of the Annubar. The particles in the fluid deflect around this high-pressure region. , And flow away from the stagnant area of ​​the pressure relief port behind the T-type Annubar, so that impurities will not enter the interior of the Annubar, and get a good anti-blocking performance. 3.2 High precision and stability The K value is the most important characterization coefficient of the differential pressure flowmeter, which is crucial for measuring the stability of the flow range and directly related to the measurement accuracy of the flowmeter. It can be clearly seen from Fig. 4 that the K value of the T-type Annubar flowmeter can be kept constant in each Reynolds number range, completely solving the flow rate variation of all K-values ​​in all conventional X-ray tube flowmeters, especially in The problem of instability at low flow rates allows measurement accuracy to be within ±0.75%. This fundamentally ensures that the Annubar flowmeter can be accurately measured in a variety of fluid conditions. The improvement of the T-type Annubar flowmeter is very significant, and its repeatability is also very good, ± 0.1%. 3.3 outstanding signal to noise ratio and range ratio An important condition for the use of equal flow tube flowmeters is to make the differential pressure generated when measuring fluids large enough. The former anti-jamming ability of flowmeters is poor. At low flow rates, the signal-to-noise ratio of the output signal is too low. Distortion is great, and the accuracy and stability of the differential pressure measurement of the previous differential pressure transmitter are unsatisfactory. Under the same process conditions of the fluid, the differential pressure signal generated by the T-type Annubar flowmeter is more than 80% larger than that of conventional velocity flowmeters of various shapes. This not only improves the measurement accuracy, but also enables it to be used at other low flow rates. This feature gives it a turndown ratio of 10:1 to 20:1. As can be seen from Figure 5, the differential pressure signal output from the T-type Annubar flowmeter has a prominent signal-to-noise ratio, allowing the differential pressure transmitter to obtain a good differential pressure signal, resulting in a stable flow measurement. 3.4 Integrated Installation for Temperature and Pressure Compensation Due to the complexity of gas flow, gas flow meters are significantly inferior to liquid flow meters in terms of measurement accuracy, reliability, and the like. The flow measurement of gas is affected by changes in temperature and pressure. These factors have a serious impact on the accuracy and repeatability of the gas flow meter. Therefore, the measurement accuracy is improved by increasing the pressure and temperature compensation. Conventional fluid pressure and temperature compensation see formula (1) Where qm—the mass flow of the fluid; K basically changes with the change of flow rate, pressure, and temperature, and is not a constant. If only the flow coefficient at the normal flow rate is used in the temperature compensation formula, the measurement accuracy will be greatly reduced when the fluid working condition changes. It is also an important reason for the poor measurement accuracy of differential pressure flowmeters. In order to solve this fundamental problem, a multi-parameter flow transmitter is currently being demonstrated. This transmitter has built-in high-precision differential pressure transmitter, absolute pressure transmitter, temperature transmitter, high-speed CPU and large-capacity data memory. The memory stores the physical properties of various fluids that need to be used in the temperature compensation formula under different pressures and temperatures, including density, viscosity, gas constant, compression coefficient, constant volumetric heat, and other data. The actual working pressure varies according to the fluid. , Temperature, real-time, dynamic and most complete compensation calculation, to the greatest extent to eliminate the factors causing the flow measurement error. The steam flow measurement automatically determines whether the steam is saturated, unsaturated, or overheated and automatically performs compensation calculations. The combination of a multi-parameter flow transmitter and a T-type Annubar flowmeter solves the interference of gas pressure and temperature on measurement accuracy. The temperature sensor is built into the cavity of the T-type Annubar flowmeter, which is its sturdy casing. In this way, only one hole needs to be opened in the process pipe, and the measurement of differential pressure, pressure, and temperature is solved at the same time, and the integrated installation is realized. The measurement accuracy of the entire differential pressure flow measurement system is improved, and the investment cost of the entire flow measurement system is also greatly saved, which facilitates the construction. 3.5 Easy to install The front high-pressure tap of the T-type Annubar flowmeter spans the entire pipeline, which, while improving the average measurement accuracy of the fluid, also greatly reduces the installation requirements of the T-type Annubar flowmeter. It is allowed to have a deviation of ±5 ゚ in the three directions of X, Y, Z. The deviation of ±5 是 can be clearly judged by human eyes, and the installation personnel can more easily install and debug. 4 Problems to be aware of when using constant velocity tube flowmeters The mechanical dimensions of the Annubar flowmeter are tailored to the size of the pipe to be installed, and the flow measurement range is also calculated and calibrated based on the user-supplied flow data. Therefore, the provided flow data and pipe data must be correct, otherwise it will cause a large measurement error. The differential pressure produced by the differential pressure flowmeter is generally relatively small, the minimum may only be 20~30Pa, and the differential pressure signal generated by the constant flow tube flowmeter is closely related to the Reynolds number of the fluid working condition. The differential pressure measurement of less than 1 kPa, in particular the differential pressure of less than 0.5 kPa, requires special attention. Various constant velocity flowmeters have a very large fluctuation in K at such a low flow rate, affecting the measurement accuracy. Micro differential pressure measurement of less than 0.5 kPa requires the performance of the differential pressure transmitter to be very high. The performance of the equal flow tube flowmeter is an important parameter to measure the overall instrument. Although the T-type Annubar flowmeter has the nature of anti-blocking characteristics, the following situations require attention. 5 Concluding remarks As the average flow tube flow measurement technology matures and matures, its application prospects are broad. The T-type Annubar flowmeter not only has high stability and high measurement accuracy, but also integrates with a high-precision differential pressure transmitter, inherent anti-blocking characteristics, wide range ratio, low operating energy consumption, etc. It has a high application value. Entry Level Euphonium,Bb Flat Euphonium,Compensation Euphonium,Brass Instrument Euphonium ZhengOu Musical Instruments Co.,LTD , https://www.zomusical.com
a) The inlet edge of the orifice plate is easy to wear, the measurement accuracy is reduced, the performance is unstable, and it needs to be replaced regularly;
b) It is sensitive to dirty contaminated flow, moisture-containing gas and steam-containing medium, and it is prone to fouling, resulting in clogging of the pressure hole, causing measurement error;
c) The range ratio is relatively small, the signal to noise ratio in the differential pressure signal is low, the non-recoverable pressure loss is large, and installation and debugging are inconvenient;
d) In the application of large-diameter pipes, the price advantage is lost and the maintenance cost is high. 
a) The value of K is still not constant enough, especially when measured at low flow rates, which greatly affects the accuracy of the measurement of the Annubar flowmeter at low flow rates and low flow rates.
b) The generated differential pressure signal is relatively small, generally only 1~3kPa. When measuring the flow conditions with relatively low flow rates, even 20 to 50 Pa, there is no way to guarantee such low differential pressure, measurement accuracy and stability. Limits the use of Annubar flowmeters, especially in gas flow measurement applications.
c) Vulnerable to various interferences, resulting in a lower signal-to-noise ratio of the differential pressure signal and affecting the stability of the measurement.
d) Since the equal velocity tube flow meter is a fluid velocity taking type flow meter, according to the requirements of fluid mechanics research, it is necessary to sample the fluid velocity in a certain position in the pipe, so there is a higher requirement for the installation, in the X, Y, Z three axis The general direction does not require deviation greater than ±3 ゚, and it is very difficult to achieve such installation accuracy in the general field. 
(1)
K—flow coefficient;
Δp— differential pressure generated by the flowmeter;
P—pressure;
T—The temperature of the fluid.
a) Is there a sticky impurity in the fluid? If the fluid contains sticky impurities, the application of an X-ray tube flowmeter should be carefully considered. Viscous impurities stick to the sensor, which will greatly affect the measurement accuracy. Many flow meters are not suitable for applications under these conditions.
b) There is a lot of impurities in the fluid, and the device is operated intermittently, with frequent stopping and long time. During the time when the flow stops, the impurities may dry out and foul on the surface of the sensor, which will clog the pressure port for years.
c) Leading system leaks. Without the direct installation, the leak from the constant velocity tube flowmeter to the transmitter pressure piping system will cause fluid flow in the pressure plenum of the Annubar flowmeter. Although this flow is very small and the flow rate is very slow, over time, impurities can get into their interior and coalesce, causing clogging.