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technical article
Pay attention to the method and method for the actual measurement of the handheld flowmeter
2012-2-20 9:40:06

How to accurately grasp the use of portable ultrasonic flowmeter. In fact, in actual use, many users question the portable ultrasonic flowmeter due to poor grasp of the main points of the use of the portable ultrasonic flowmeter, the measurement effect is not ideal. How to accurately use the portable ultrasonic flowmeter to make it better serve the oilfield measurement is the subject that measurement staff need to study and discuss. However, through years of statistical analysis on the verification conclusions of portable ultrasonic flowmeters, the technical indicators of portable ultrasonic flowmeters are basically the same as other speed-type flowmeters, and the electromagnetic flowmeters have better linearity than other flowmeters when the flow rate is large enough. So why does the portable ultrasonic flowmeter inaccurate in actual use? 具有安装快捷、使用灵活的特点,但在使用时必须掌握准确方法。 The portable ultrasonic flowmeter has the characteristics of fast installation and flexible use, but it must be accurate when used. After summing up the field operation experience for many years, the problems that are easy to ignore when using portable ultrasonic flowmeters are found, the causes of the problems are analyzed, and the solutions to the problems are proposed. At present, many units in the oil field use portable ultrasonic flowmeters. The purpose is to use them as a "standard meter" for verification. The process signal calibrator is used to compare and test the accuracy of online flowmeters, or single well metered water injection. When using. Because the accuracy of flow measurement of the ultrasonic flow meter is almost independent of the parameters such as the temperature, pressure, viscosity, and density of the fluid being measured, it can also be made into a non-contact and portable measuring instrument, so it can solve the strong corrosion that is difficult to measure by other types of instruments. , Non-conductive, placed on the edge of the circuit board; reduce the clock frequency as much as possible and so on. However, some traditional anti-interference measures cannot be applied to portable instruments. For example, the most effective way to deal with high-frequency radiation interference is to add a shield to the housing. This measure increases the volume and weight on the one hand, and is not suitable for some instruments that need to be in contact with the outside world. An alternative is to spray conductive material on the housing. For another example, if the input analog signal cannot be sufficiently filtered due to the space on the board, you must use software filtering. Most connecting elements are connected to the cable, so it is EM

实际测量管道参数也要注意方式方法的合理性,过程信号校验仪测量用的量具和仪器要经过校准.测量管道外径要注意管道外防护层以及外表层的锈蚀脏污对测量可能造成的影响. 在小管上使用便携式超声波流量计进行流量测量时,管道内径输入不准确所引起的误差更是不容忽视,例如:内径测量的绝对误差同样是1毫米,那么对DN1000管线来说其内径相对误差为0.1%;而对DN100管线来说其内径相对误差为1.0%.而流量是与内径的平方(管道内径面积)成正比的,同样是1毫米的内径测量误差对DN1000管线所带来的流量测量误差仅有约0.3%,而对于DN100管线所带来的流量测量误差却有约3%,可见便携式超声波流量计使用管线口径越大测量越容易准确,管线口径越小,测量越难把握.所以有人推荐便携式超声波流量计最好在DN300以上管线使用是有一定道理的. 探头的 The actual measurement of pipeline parameters of portable ultrasonic flowmeters must also pay attention to the rationality of the methods and methods, and the gauges and instruments used for the measurement of the process signal calibrator must be calibrated. When measuring the outer diameter of the pipeline, pay attention to the corrosion and contamination of the outer protective layer of the pipeline and the outer surface Possible effects of measurement. When a portable ultrasonic flowmeter is used for flow measurement on a small pipe, the error caused by the inaccurate input of the pipe diameter cannot be ignored. For example: the absolute error of the inner diameter measurement is also 1 mm. It is said that the relative error of the inner diameter is 0.1%; for the DN100 pipeline, the relative error of the inner diameter is 1.0%. The flow rate is proportional to the square of the inner diameter (the area of the inner diameter of the pipe). The resulting flow measurement error is only about 0.3%, while the flow measurement error caused by the DN100 pipeline is about 3% .It can be seen that the larger the pipeline diameter of the portable ultrasonic flowmeter, the easier and more accurate the measurement is, and the smaller the pipeline diameter, The harder it is to measure. So some people recommend that portable ultrasonic flowmeters are best used in pipelines above DN300. It makes sense. The installation distance is an important measurement parameter that must be accurately guaranteed. In order to ensure that the best signal strength is found, some users look for the signal by moving the probe straight. It is often that the signal has the wrong installation distance of the probe. Yes: To move the two probes in parallel, find the best installation point on the premise of ensuring that the installation distance of the probe meets the requirements. After the signal is found, you must use the actual measurement method to confirm that the installation distance of the probe is accurate. The impact is also great. Some old pipelines use cement mortar lining for corrosion protection. If the existence of it is ignored during measurement, a large error will occur because the thickness of the cement mortar lining is generally not a negligible number. The surface is rough and easy to adhere to mud and sand, and it is easy to fall into pieces, which may have a great impact on the measurement. During the measurement, if the lining parameters are not input and the signal is not found in normal operation, you should consider the possibility of the pipeline. Lining. Ultrasonic flowmeter is an excellent flow meter, which brings us the convenience and economy of measuring flow. The flow meter is incomparable. Let us not misunderstand it because of our carelessness. Practice has proved that most of the problems that occur when using an ultrasonic flow meter to measure the flow are caused by human factors. The ultrasonic flow meter has taken on a lot of us. Responsibility, it is our trusted good friend



When the ultrasonic flowmeter data of the portable ultrasonic flowmeter suddenly changes, it is difficult to determine whether it is due to a process reason or a failure of the flowmeter itself. In the past, the method of removing the flowmeter for calibration and installing a backup flowmeter on site to determine the cause has not only affected production, but also greatly increased the workload of maintenance. To solve this problem, when in doubt on the online flow meter, a portable ultrasonic flow meter can be used to perform on-site comparison of the online flow meter to determine whether the online flow meter itself is faulty.
1 Measurement principle, ultrasonic measurement method of closed pipe flow can be divided into multiple types according to the detection principle, mainly time difference method, Doppler method and sound beam migration method. The Doppler method is mainly used to measure gas-liquid two-phase fluid or gas-solid two-phase fluid, while the acoustic beam shift method uses the degree of shift caused by the fluid flow when the ultrasonic wave propagates in the fluid to reflect the flow velocity or flow value. The portable ultrasonic flowmeter uses the time difference method to measure. The sound waves propagate in the fluid. The speed of sound waves will increase in the forward direction and the direction of the backward flow will decrease. The same propagation distance will have different propagation times. The relationship between the measured fluid flow rate can be used to obtain the fluid flow rate and calculate the fluid flow rate. The time between the flow of the two transducers in the forward direction and the time difference between the two in the reverse direction (v is negligible relative to c, so c2-v2≈c2) is the flow velocity of the fluid. The volumetric flow of the fluid Therefore, when c and D are known, qv can be obtained by measuring the time difference Δt. The portable ultrasonic flowmeter is used for fixing the transducer with a clamping member on the outer wall of the measuring pipe, and the pipe does not need to be cut off. The installation is simple and convenient. During the measurement, the sound waves emitted by the crystal are transmitted to the measured fluid through objects such as acoustic wedges, coupling agents, pipe walls, and linings. When measuring, the outer diameter, thickness of the pipe and the thickness of the lining to be measured shall be determined to calculate the cross-sectional area of the pipeline. The pipe material, lining material, fluid name and fluid viscosity shall be determined to calculate the propagation speed of the ultrasonic wave. The installation of the transducer shall also be determined. Method to calculate the propagation length of the ultrasonic wave. After the above data is input to the host of the flowmeter, the host can accurately calculate the installation distance of the transducer. 2 Installation method. The three common installation methods of the transducer are Z method, V method, and W method. Generally, when the tube diameter is less than 300mm, use the V method to install, when the tube diameter is greater than 200mm or the received signal is weak. , Z method should be used for installation. For transducers that can be installed using either the V method or the Z method, use the Z method whenever possible. Practice has shown that the transducer installed by the Z method has high ultrasonic signal strength and good measurement stability. When the diameter of the pipe is very small, below DN80, the W method can be used. However, this measurement method has reflected the ultrasonic waves many times, the received signal is very weak, and the requirements for installation are also very high. It is recommended not to use this method as much as possible.

安装换能器时,管道外表面应去除保温层、去漆,锈迹应砂平,涂匀耦合剂,不能有空隙,否则声波会在固、气界面上发生折射,无法传到被测流体。 When installing a transducer in a portable ultrasonic flowmeter , the outer surface of the pipe should be removed from the insulation layer and paint, and the rust should be sanded, coated with coupling agent, and there must be no gaps, otherwise the sound waves will be refracted on the solid and air interfaces and cannot be transmitted. To the measured fluid. There must be long straight pipe sections before and after the transducer to ensure the required flow velocity distribution of the fluid. Generally, more than 10D of the front straight pipe section and more than 5D of the rear straight pipe section are required, and pumps, valves and other disturbance devices cannot be installed in the upstream 30D. When the transducer is installed on inclined and horizontal pipes, do not install it on the top or bottom to prevent gas or impurities in the pipe from entering the measurement channel. The transducer is installed so that the ultrasonic transmission path passes through the center of the pipe [2]. 3 Measurement accuracy. The portable ultrasonic flowmeter is installed on pipes of different diameters of the water flow calibration device, and the actual flow test is performed. From the test data, it can be seen that the measurement accuracy of the portable ultrasonic flowmeter can reach level 1.5. When installed and used in the field, due to the influence of site conditions, media status, pipeline data and installation, the measurement accuracy is slightly reduced, but the measurement error should not exceed 5% of its actual flow rate. Therefore, use a portable ultrasonic flowmeter to Online comparison of online flow meters is completely feasible. 4 Prone problems and countermeasures in online measurement. If the portable ultrasonic flowmeter is installed and started, the output sometimes disappears, and the error is large, there are the following possibilities. (1) The installation distance of the transducer is incorrect. At this time, it is necessary to check whether the installation distance of the transducer is consistent with the data calculated by the host, and slightly adjust the installation position and distance of the transducer to improve the signal strength. (2) The pipe diameter, lining, fluid and other parameters set by the instrument are incorrect. In this case, the parameters need to be verified again. (3) The installation position of the transducer is incorrect. When installing the transducer, avoid the welds and joints of the pipeline, and do not install on the top or bottom of the inclined or horizontal pipeline. The upper part may not be full of fluid, and the bottom may have impurities or sediment. (4) Too many bubbles in the fluid. In this case, a stable signal can be obtained by excluding the gas. (5) There is scaling and unevenness inside the pipeline. At this time, you can hit the pipe wall of the measurement point with your hand. If the received signal strength keeps rising, it means that the inner wall of the pipe is too thick, and you can continue to hit the measurement point until the received signal meets the requirements. (6) There are pumps or radio wave interference nearby. Install the transducer away from these locations.

It can be seen from the portable ultrasonic flowmeter that the portable ultrasonic flowmeter has irreplaceable advantages in practical applications: continuous flow measurement can be achieved, the device is small in size, easy to carry, and easy to install; the outer card probe does not interfere with the flow field and has no pressure Loss; the meter has no moving and vulnerable parts, and has good stability; a wide range of applications, can be used for online comparison of various types of flowmeters; strong adaptability, can be used for comparison of different pipe diameters; The measuring tube diameter is irrelevant and cost-effective. However, the portable ultrasonic flowmeter is limited by its own measurement method, and the measurement accuracy is affected by many external factors. There are also some deficiencies in practical applications. (1) The user is required to determine the conditions of the pipeline, including the material of the pipeline, the exact diameter of the pipeline, the wall thickness, the material and thickness of the lining, etc. When the conditions of the pipeline are uncertain, the accuracy of the measurement will be reduced. (2) The inner wall of the pipe is required to be high, and there must be no corrosion, scaling, crystallization, etc. Corrosion will change the ultrasonic propagation path. Gases in the pipe separated from the inner pipe wall will seriously attenuate the ultrasonic signal. The pipeline will also cause a large flow error. (3) Human factors have a greater impact on the measurement and place higher demands on the operator. (4) The accuracy of the portable ultrasonic flowmeter is relatively low, and it cannot be used for flowmeter calibration. It can only provide reference data for online flowmeters. (5) It is mainly used to measure clean fluids and uniform fluids with low impurity content (impurity content is less than 10g / L, particle size is less than 1mm). It cannot be used to measure gas flow, because the density of the pipeline and the measured gas are too different. Large, the propagation speed of sound waves in the pipe wall is much faster than the propagation speed in the gas, and the sound waves cannot meet the measurement requirements after being refracted by the pipe wall.