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Installation skills and suggestions for ultrasonic flowmeters

Author:    Source:    Date: 2021-05-26 16:02:15
Ultrasonic flowmeter is an indispensable measuring instrument for measuring the flow of liquid, acid, and alkali. The accuracy of the set point-to-point related flowmeter is currently generally used in two ultrasonic flowmeters, Doppler ultrasonic flowmeter and time difference ultrasonic flowmeter. The Doppler type uses the phase difference method to measure the flow velocity. That is to say, because a sound wave of a known frequency moves in the fluid, the liquid itself has a moving speed, so the frequency or phase of the ultrasonic wave between the two receivers (or transmitters) will change relatively. The velocity of the liquid can be obtained by measuring this relative change. The time difference type uses the time difference method to measure the flow rate. That is to say, the propagation time of a sound wave of a certain speed between two receivers (or transmitters) due to the flow of the fluid changes, and the flow velocity of the fluid can be obtained by measuring this relative change. The correct installation method is very important to the flowmeter. Rui Lingyi shares installation tips and suggestions for ultrasonic flowmeters.

   One, the correct installation position

The installation distance of the ultrasonic flowmeter should be within 10 times the straight pipe diameter upstream and 5 times the straight pipe diameter downstream. Choose valves, elbows, variable diameters and other uniform straight pipe sections. The installation point should be far away from the pump, high-voltage electricity, Interference sources such as inverters. It can be used for fixed and mobile measurements, installed with a special couplant, and will not damage the pipeline during installation. During installation, you can keep flushing, use special tools to punch holes in the pipe with water, insert the transducer into the pipe, and complete the installation. Because the converter is in the pipeline, its signal transmission and reception only pass through the measured medium, not the pipe wall and the lining, so its measurement is not restricted by the quality of the pipe and the lining, as shown in Figure 1.

   2. The initial installation must follow the following 9 points

   1. In mines where the measurement pipeline is relatively old, try not to use the dual-tone layer (v method) to install sensors. 1 sound layer) z method). With such an installation method, the ultrasonic waves emitted by the flow sensor of the ultrasonic flowmeter can be easily received by the measured flow sensor, which can ensure the signal strength of the main body of the ultrasonic flowmeter and ensure high-precision measurement values.

  2. When measuring a new tube, if there is paint or zinc tube, you can use roving to process the surface of the tube and then use fine yarn to continue processing. In this way, the installation point of the flow sensor of the ultrasonic flowmeter is smooth and flat, and the flow probe of the ultrasonic flowmeter can well contact the outer wall of the pipeline to be measured.

  3. When the pipe is in a vertical upward direction, it can be measured when the fluid in the pipe flows from bottom to top. When the liquid flows from top to bottom, this pipe is not suitable for collecting flow data.

  4. In addition, before collecting the flow data of a certain pipeline, you must measure the outer circumference of the pipeline (using a tape measure), wall thickness), thickness gauge), the temperature of the outer wall of the pipeline), surface temperature measuring instrument), etc. by yourself.

   5. Remove the thermal insulation and protective layer in the installation section, and brush the transducer clean along the wall of the installation site. Avoid partial depressions, smooth the protrusions, and brush the paint rust layer clean. 6. For vertically installed pipelines, when using the mono-channel propagation time method, the installation position of the sensor should be as far as possible in the plane of the bending axis of the upstream elbow to obtain an approximate average value after the flow field of the elbow is distorted.

  7. The sensor installation part and pipe wall reflection part of the ultrasonic flowmeter must avoid the interface and welding.

   8. The pipe lining and dirt layer at the installation place of the ultrasonic flowmeter's sensor glass should not be too thick. There should be no gaps between the lining, the rust layer and the pipe wall. When the pipeline is heavily rusted, you can use a hammer to shake the pipe wall to rust the wall and ensure the normal propagation of sound waves. However, care must be taken not to dent.

  9. There is enough couplant between the working surface of the sensor and the pipe wall, with air and solid particles, which cannot guarantee a good coupling.

   Three, installation tips

   The choice of installation pipe section has a great influence on the test accuracy. The selected pipe section should avoid the situation that has a great influence on the measurement accuracy of interference and eddy current. Generally, the selected pipe section should meet the following conditions:

   1. Do not install the machine in a place where water pumps, high-power radios, frequency conversions, that is, strong magnetic fields and vibration interference;

  2. Choose a pipe section with uniform and dense pipes that is convenient for ultrasonic transmission;

  3. Since there is a straight pipe section of sufficient length, the upstream straight pipe section of the installation point must be greater than 10D (Note: D=diameter), and the downstream must be greater than 5D, as shown in Figure 2;

  4. The distance between the upstream of the installation point and the pump needs to be 30D;

   5. The fluid should be filled with pipes;

  6. There must be enough space around the piping for easy operation by on-site personnel.

   Four, 3 requirements after installation

   1. Zero flow inspection

   When the liquid in the pipeline is still, there is no strong magnetic field interference around, and no strong vibration, the meter shows zero. At this time, the zero point is automatically set to eliminate the floating of the zero point. The small signal is cut off when driving, usually if the flow is less than 5% of the full flow, it is cut off automatically. At the same time, the zero point can also be adjusted through the menu.

  2, keyboard operation of the instrument panel

  Before starting the operation of the instrument, the parameters must first be set to be valid. For example, use the unit system, installation method, pipe diameter, pipe wall thickness, pipe material, pipe roughness, fluid type, distance between two probes, flow rate unit, minimum speed, maximum speed, etc. Only when all the parameters are correctly entered, the meter will correctly display the actual flow value

  3. Regular inspection of flowmeter

   In order to ensure the accuracy of the flowmeter, regular inspections are carried out. Usually, a higher-precision portable flow meter is used for direct comparison, and the measurement data is used to calculate: error = (measured value-standard value) / standard value, and the calculated relative error correction coefficient is used to meet the 2% error. Measurement requirements. The operation is simple and convenient, and can effectively improve the measurement accuracy.

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