Ultrasonic flowmeter guide to installation requirements and precautions

Ultrasonic flow meters installation precautions

1. When the direction of fluid in the pipeline is from bottom to top, ultrasonic flowmeter can be used to measure. If the flow direction of the liquid is from top to bottom, this pipeline is not suitable for measuring the flow rate with an ultrasonic flowmeter.

2. If the measured pipe diameter is lower than DN15, it is better to choose imported ultrasonic flowmeter. At present, the measurement accuracy of domestic ultrasonic flowmeter is difficult to meet the technical requirements for small pipe diameter measurement. When the measured medium is normal temperature, the domestic ultrasonic flowmeter can be selected. When the temperature is between 120 ℃ and 200 ℃, the imported ultrasonic flowmeter should be selected.

3. When the measurement pipeline is relatively old, try to install the probe using the single-layer (Z method) method, and do not use dual-channel and multi-channel (V, W method). Mono is easier to receive signals, less likely to generate false signals, and can ensure high-precision measurements.

4. The sensor installation place of the ultrasonic flowmeter and the reflection place of the pipe wall must avoid the interface and welding seam. At the same time, it is also necessary to avoid installing sensors in places with strong magnetic fields and vibration interference, such as pumps and high-power frequency conversion. To have a long enough straight pipe section, the straight pipe section upstream of the installation point must be greater than or equal to 10D (Note: D = the diameter of the pipe section), and the downstream must be greater than 5D.

5. The pipe lining or fouling layer where the sensor of the ultrasonic flowmeter is installed should not be too thick, otherwise it will affect the speed of sound propagation, which in turn affects the measurement accuracy. There should be no gaps between the lining, the rust layer and the pipe wall. For severely corroded pipes, the rust layer on the surface can be removed first to ensure the normal propagation of sound waves. There should be enough couplant between the working surface of the sensor and the pipe wall without air and solid particles to ensure good coupling.

6. Before measurement, it is necessary to measure the outer circumference of the pipe (with a tape measure), wall thickness (with a thickness gauge), and the temperature of the outer wall of the pipe (surface temperature measuring instrument), which can be more conducive to the parameter setting of the ultrasonic flowmeter. Make the measurement data more accurate. When encountering a pipeline with paint or coating, you can first use an angle grinder or a grinder to treat the surface layer of the pipeline, and then use sandpaper to smooth it, so as to ensure that the installation point of the flow sensor of the ultrasonic flowmeter is smooth and flat. , which is conducive to the benign contact between the probe and the pipeline.

7. The installation distance of the probe is an important measurement parameter to ensure the measurement accuracy. In order to find the best signal strength, use one of the probes to find the signal. However, it is often found that the signal is found, and the installation distance of the probe is not correct. The correct way to find the signal is to move the two probes in parallel at the same time, and find the best installation point on the premise that the installation distance of the probes meets the requirements. Determine the measurement position when the signal strength is large, and finally use the actual measurement method (usually the ultrasonic flowmeter has its own measurement function) to confirm that the installation distance of the probe is accurate.

Factors affecting the measurement accuracy of ultrasonic meter

The ultrasonic flowmeter uses the propagation velocity difference method to measure the water volume. Due to the influence of the on-site installation environment, pipeline material and parameters, sensor installation and other factors, the measurement accuracy is often lower than its nominal value, and sometimes the error is large.

1. The influence of the installation environment

When the ultrasonic flowmeter is installed, it is generally required that the upstream and downstream of the flowmeter have straight pipe sections with a diameter of 10 times and 5 times more, respectively, to ensure that the flow state of the measured medium meets the accuracy requirements of the instrument. installation location. Insufficient straight pipe section leads to different measurement errors. The downstream straight pipe has little effect on the accuracy. When the upstream side has more than three times the diameter of the straight pipe, it can be basically used. When the upstream straight pipe section is not enough, such as after the elbow, valve, pump valve When the table is used, it generally shows a positive error.

2. Influence of pipeline parameter input

After the ultrasonic flowmeter is installed, the meter needs to input parameters such as pipe diameter and pipe wall thickness. If the input parameters are changed while the pipe is fixed, the error of the pipe diameter input will increase the error of the measurement result by 2 times, and the pipe wall thickness input will be doubled. The error is positively correlated with the measurement error, but has little effect on the measurement result.

3. Influence of lining and pipe material

When the ultrasonic flowmeter measures the wrong input of the pipe material into the lining, it will also cause an error in the calculation of the installation distance of the probe, which will cause an error in the ultrasonic incident angle, reduce the measurement accuracy, and in severe cases, affect the signal and settings, so that the measurement cannot be performed. The influence of the pipe lining on the measurement is mainly due to the change of the actual pipe diameter. The lining reduces the cross-sectional area of the water, and the flow rate converted by the flow rate is correspondingly small. The measurement error is proportional to the change of the pipe cross-sectional area. If the lining is too thick and is ignored when setting or there is a gap with the pipe wall, detection or signal error generally occurs, so the lining material and thickness should be accurately and accurately input during measurement. The influence of pipeline and lining quality on the measurement is reflected in the difference in the propagation speed of sound waves in various media. If the actual sound speed of the material is greater than the set sound speed, the measurement result will be small, and vice versa.

4. Sensor installation

The ultrasonic flowmeter is divided into Z method, V method, X method, etc. according to the different measurement environments and measurement probes. The selection principle of the installation method of the measurement sensor is: when the water flows parallel to the pipe axis, choose the Z method for installation; when the flow direction When it is not parallel to the pipeline axis or the installation location of the pipeline restricts the installation interval of the transducer, the V method and the X method are used. The V method has a higher measurement accuracy than the Z method without affecting the signal reception. The distance between the two sensors has strict requirements, and must be installed according to the specified size. Different installation distances have different effects on the measurement accuracy, and some even have large errors.

5. Other external factors, couplants, signal cables

In the analysis of the operating characteristics of the ultrasonic flowmeter and the error analysis of the impact on the measurement of the portable ultrasonic flowmeter, it can be seen that to maximize the accuracy of the flowmeter measurement, the following points must be paid attention to: The wall surface where the sensor is installed is clean; The installation position of the sensor should be as far as possible in the plane of the bending axis of the upstream elbow, so as to obtain a closer average value after the smooth distortion of the elbow; the sensor installation and pipe wall reflection must avoid joints and welds; Pipe lining and scale layer should not be too thick; couplant must be used.