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How to choose the measuring point of ultrasonic flow meter

How to choose the measuring point of ultrasonic flow meter


Many users use ultrasonic flowmeters for the first time, because they do not know how to choose the appropriate measurement point, resulting in unsatisfactory debugging results or even impossible measurement, which reduces work efficiency. Today I will mainly introduce how to correctly select the measurement point when installing the ultrasonic flow meter.

1. First, choose a uniform and dense pipeline, which is easy for ultrasonic transmission.

2. Select a pipe section that is full of fluid in the pipe, such as a vertical pipe section (fluid flows upward) or a horizontal pipe section. For open or half-filled pipes, the flowmeter should be installed at the U-shaped pipe section. Avoid installation at the highest point in the piping system or on vertical pipes with free outlets (fluid flows downward).

3. Choose a pipe section with a smooth and clean surface. If there is rust, etc., you need to sand it with sandpaper to remove the rust and install the sensor. If it is a relatively old pipe, you must consider the scaling on the inner wall of the pipe. For pipe sections, fouling needs to be considered as a lining in order to achieve better measurement accuracy.

4. The installation point must be far away from interference sources such as valves, pumps, high-voltage electricity and frequency converters. The installation distance should be a straight pipe section that is more than 10 times the straight pipe diameter in the upstream and more than 5 times the straight pipe diameter in the downstream without any valves, elbows, variable diameters, etc.

5. The temperature and pressure of the measuring point are within the working range of the sensor.

6. When installing the external clip-on or plug-in sensor, it should be installed in the horizontal direction of the axial surface of the pipeline, and installed within a range of 45° from the horizontal position of the axis, so as to avoid the influence of phenomena such as dissatisfied pipes, air bubbles in the upper part, or precipitation in the lower part. The sensor measures normally. If the on-site environmental space limit cannot be installed horizontally, the sensor can be installed vertically or with an inclination angle under the condition that the pipeline is full and free of air bubbles.

Where is it not suitable to use the clamp-on ultrasonic flow meter?

The ultrasonic flow meter adopts the principle of time difference, and the change of time is proportional to the flow velocity of the liquid. When the flow rate is zero, the time required for the two sensors to emit and receive sound waves is exactly the same. When the medium is flowing, the planning and transmission time in the upstream direction is greater than that in the downstream direction The sound wave transmission time, according to the existing time difference, the calculation can obtain the conversion relationship between the flow velocity and the time difference, and the flow value can be obtained. The measurement medium is water, sewage, sea water, alcohol, various oils and other single uniform stable liquids that can transmit ultrasonic waves. Although low cost ultrasonic flow meters are widely used in petrochemical, electric power, tap water, power monitoring and other fields, external clamping devices are popular with users because they do not need to break the pipe, do not need to stop production, and are simple to protect the equipment. However, there are also some occasions. Clamp on ultrasonic flow meters cannot be used.

1. Pipeline environment: The clamp-on ultrasonic flow meter has relatively strict requirements on the pipeline, there must be no vibration, and there are relatively strict requirements for straight pipe sections. When installing, it is required to have a sufficient straight pipe section, and it should be kept away from strong interference places such as pumps, valves and strong magnetism. If the pipeline is used for a long time, there will be more and thick fouling on the inner wall, which will also affect the transmission of ultrasonic waves, hinder the reception of signals, reduce the signal strength, cause large measurement errors or cannot be measured without ultrasonic signals;

2. Not a single uniform and stable medium: when the measured medium contains more than 5% sediment particles, or when the bubble content is ≥ 20000ppm, the impurities prevent the absorption and transmission of ultrasonic waves, reduce the signal strength, and cause large measurement errors;

3. Non-wave-guiding media: According to the application principle of ultrasonic flow meters, custom ultrasonic flow meters can only measure liquids that transmit ultrasonic waves. For media that cannot conduct ultrasonic waves, ultrasonic flowmeters cannot be used to measure;

4. Frequency converter or high-voltage electromagnetic interference: It must be kept away from frequency converter and high-voltage electromagnetic interference source. If it cannot be avoided, the environment is not suitable for measurement with wholesale ultrasonic flow meter;

5. Pipe diameter < DN10mm, flow rate lower than 0.01M/S.

6. The fluid in the pipeline is not full of pipe;

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