Shanghai Kekun is engaged in the production of ultrasonic flowmeters for many years, and is quite familiar with various situations in the installation and use of external clamped ultrasonic flowmeters. FSV series ultrasonic flowmeters play a role in the production of medium-sized enterprises all over the country. In actual use, many users due to the use of ultrasonic flowmeter points are not good, the measurement effect is not ideal, often friends ask whether the ultrasonic flowmeter can be measured accurately? After communicating with our company's technology, we have a good understanding of the technical essentials and key factors needing attention for the installation and use of the external clamped ultrasonic flowmeter, and eliminate the misunderstanding of the measurement of the ultrasonic flowmeter. This article is aimed at customers often ask "Is this flowmeter accurate?" Such questions to make an explanation to friends, I hope to be helpful for friends who are selecting flowmeters or are using ultrasonic flowmeters.

The best platform to evaluate the quality of a flowmeter is the flow standard device, through the statistics of the ultrasonic flowmeter verification conclusions over the past few years, we found that the indicators of the ultrasonic flowmeter are comparable to other velocity flowmeters, and when the flow rate is large enough, its linearity is particularly good. So why do you feel that the ultrasonic flowmeter is not accurate in actual use? Through research and analysis, we find that users often ignore the following problems in use.

First, there is no correct verification or calibration of the ultrasonic flowmeter

Any flowmeter needs to be verified or calibrated before use, and portable ultrasonic flowmeters are particularly important in this regard. As we all know, the portable ultrasonic flowmeter has three sets of probes to choose from (large, medium and small), which are suitable for different pipe diameter ranges, and the combination of each set of probes and the host is in a sense a set of independent flowmeters.

If the portable ultrasonic flowmeter is only verified or calibrated with a small probe on the flow standard device with a small pipe diameter, then in use if you use a large probe to measure the flow of a large pipe, it is equal to that you are using an unverified or calibrated flowmeter to measure the flow, and its measurement accuracy cannot be guaranteed, because the current level of technology cannot guarantee the interchangeability of the probe. Moreover, the difference between the size of the probe is a variable that cannot be ignored.

Therefore, the correct method should be: based on the user's own use as a reference, as far as possible, the portable ultrasonic flowmeter is verified or calibrated on multiple pipelines on the flow standard device with the same caliber or close to the pipe used. At a minimum, ensure that each set of probes in the flowmeter configuration is checked.

The purpose of the verification or calibration institution is to record the experimental caliber and probe number on the certificate when issuing the verification or calibration certificate, which is to prevent misunderstandings, and the understanding that the portable ultrasonic flowmeter is equivalent to other fixed caliber flowmeters is wrong, which is also a reason why some users do not use portable ultrasonic flowmeters.

The calibration or calibration certificate of portable ultrasonic flowmeter will give the instrument correction factor. All kinds of flow meters will give an instrument coefficient when calibration because of principle, manufacturing and other reasons, but the name and form are different. The portable ultrasonic flowmeter is equipped with multiple probes and may have several meter correction factors for different calibers. When using the flow meter to measure the flow, it is necessary to ensure the correct use of the instrument correction factor, not to forget to use and pay attention not to mix, should develop a good habit of confirming whether the instrument correction factor set in the host before the formal measurement is correct.

Second, ignoring the requirements of the flowmeter use conditions and use environment

Any velocity flowmeter has certain requirements for the flow field of the fluid in the pipeline to be measured, and the ultrasonic flowmeter is no exception. When the installation position of the flowmeter can not ensure the length requirements of the front and back straight pipe section, the measurement error caused by the instability of the flow field can not be ignored. Due to the limitation of measuring Wells, many users can not meet the installation requirements of the position measurement, resulting in increased measurement errors.

The external clamped ultrasonic flowmeter is particularly sensitive to bubbles mixed in the water, and the subsequent flow of bubbles will cause the instability of the flowmeter value, and the accumulated gas will cause the flowmeter to fail to work if it coincides with the installation position of the probe. Therefore, the installation of ultrasonic flowmeter should try to avoid the pump outlet, the highest point of the pipeline and other positions susceptible to gas, the installation point of the probe should also try to avoid the upper and bottom of the pipeline, in the range of 45° Angle with the horizontal diameter, but also pay attention to avoid weld and other pipeline defects.

The installation and use of ultrasonic flowmeter environment should pay attention to avoid strong electromagnetic interference and vibration, in use, we found that under the high-voltage line, the roadside of dense vehicles, the use of mobile phones or walkie-talkies near the host will have a more or less impact on the measurement.

Third, can not accurately measure the pipeline parameters resulting in inaccurate measurement

The portable ultrasonic flowmeter probe is installed outside the pipeline, it directly measures the flow rate of the fluid in the pipeline, the flow rate is the product of the flow rate and the pipeline flow area, and the pipeline area and channel length are calculated by the user manually input the pipeline parameters, the accuracy of these parameters directly affects the measurement results. That is to say: even if the flow rate is measured accurately, if you enter an inaccurate set of pipe parameters, the measurement results are not accurate.

The best way to obtain pipeline parameters is to use the actual measurement method, and there may be errors in the way of looking up design drawing data and inquiring familiar with the situation, because the actual construction situation is often different from the design parameters, the manufacturing deviation of the pipeline is sometimes not negligible, and the parameters such as the wall thickness of the pipeline used for a period of time will also change over time.

The actual measurement of pipeline parameters should also pay attention to the rationality of the method, and the measuring tools and instruments used for measurement should be calibrated. When measuring the outer diameter of the pipeline, it is necessary to pay attention to the influence of the outer protective layer of the pipeline and the corrosion and dirt of the outer surface on the measurement.

The influence of pipeline lining on the measurement is also very great, some old pipe lines using cement mortar lining anti-corrosion, if it is ignored in the measurement, it will produce a great error, because the thickness of cement mortar lining is generally not a negligible number, plus its rough surface is easy to adhere to mud sand, easy to fall off in pieces, which may have a great impact on the measurement. When measuring, if there is no input lining parameter, the signal can not be found according to normal operation, it should be considered that the pipe may be lined.