The ultrasonic flow meter is a very convenient flow instrument to use, especially on large-diameter water supply pipelines. The portable ultrasonic flow meter can install the probe on the outer surface of the pipeline to achieve continuous flow measurement without damaging the original pipeline. Therefore, it is welcomed by the majority of users.
Ultrasonic flow meter has advantages that other flow meter cannot match. It will definitely become people's first choice flow meter for measuring flow in the near future. Here are a few advantages of ultrasonic flow meter for your reference:
1. The external clip-on ultrasonic flow meter can achieve non-contact flow measurement. Even if it is a plug-in or internally attached ultrasonic flow meter, its pressure loss is almost zero, and its convenience and economy in measuring flow are the best.
2. Ultrasonic flow meter can measure various media such as water, gas and oil, and its application fields are very broad.
3. The manufacturing cost of ultrasonic flow meter has almost nothing to do with the diameter. In large-diameter flow measurement situations, it has the comprehensive competitive advantages of reasonable price and easy installation and use.
4. The portable ultrasonic flow meter can measure flow on pipelines of various diameters and materials with one flow meter. It is the preferred type of flow meter used as a standard meter for online calibration, comparison or periodic verification.
5. Ultrasonic flow meter has the traceability and convenience of its flow measurement principle based on the two basic physical quantities of length and time. It is foreseeable that it will surpass flow meter with other principles and become the carrier of flow standards and even flow benchmarks.
6. The ultrasonic flow meter consumes very little energy in operation and can be easily powered by batteries for many years. In addition, the advanced intelligent host can facilitate network wireless communication, and its application prospects are even broader.
   The development prospects of ultrasonic flow meters are so promising, firstly, due to the inherent superiority of its flow measurement principle, and secondly, due to the rapid advancement of microelectronics technology.
   At present, the most widely used ultrasonic flow meter in the water supply industry is the portable ultrasonic flow meter for liquids. In actual use, many users do not have a good grasp of the key points of using the ultrasonic flow meter and the measurement results are not ideal, so they have various doubts about the ultrasonic flow meter: "Is this flow meter accurate?" Questions such as "Is this flow meter accurate?" have become hot topics in the industry.
The best platform to evaluate the quality of a flow meter is the flow standard device. Through statistics on the ultrasonic flow meter calibration conclusions over the past few years, we found that: the various indicators of the ultrasonic flow meter are comparable to other speed flow meters, and when the flow rate is large enough, its linearity is particularly good. So why do people feel that the measurement of ultrasonic flow meter is inaccurate during actual use? Through research and analysis, we found that users often ignore the following issues during use.
1. Failure to properly verify or calibrate the ultrasonic flow meter
Any flow meter needs to be verified or calibrated before use, and this is especially important for portable ultrasonic flow meters. As we all know, portable ultrasonic flow meters have three sets of probes to choose from (large, medium and small), which are suitable for different pipe diameter ranges. Each set of probes and the host are in a sense an independent flow meter.
If you only use a small probe to verify or calibrate a portable ultrasonic flow meter on a small diameter flow standard device, then if you use a large probe to measure the flow of a large pipe, it is equivalent to using an unverified or calibrated flow meter to measure the flow. The measurement accuracy cannot be guaranteed because the current technical level cannot guarantee the interchangeability of the probe, not to mention the difference between large and small probes is a variable that cannot be ignored.
Therefore, the correct method should be: based on the user's own usage conditions, try to verify or calibrate the portable ultrasonic flow meter on multiple pipelines on a flow standard device that is the same or close to the diameter of the pipeline being used. At least ensure that each set of probes configured in the flow meter is calibrated.
The purpose of the verification or calibration institution to record the experimental caliber and probe number on the certificate when issuing a verification or calibration certificate is to prevent misunderstandings. Those who equate portable ultrasonic flow meters with other fixed-caliber flow meters are wrong. This is also one of the reasons why some users cannot use portable ultrasonic flow meters.
The instrument correction factor will be given on the portable ultrasonic flow meter verification or calibration certificate. Various flow meter will give an instrument coefficient during calibration due to principles, manufacturing and other reasons, but the names and expressions are different. Portable ultrasonic flow meter are equipped with multiple sets of probes, suitable for different calibers, and may have several instrument correction factors. When using a flow meter to measure flow, be sure to use the instrument correction coefficient correctly. Don't forget to use it and be careful not to mix it. You should develop a good habit of confirming whether the instrument correction coefficient set in the host is correct before formal measurement.
2. Ignoring the requirements for the use conditions and environment of the flow meter
Any velocity flow meter has certain requirements for the flow field of the fluid in the pipe being measured, and ultrasonic flow meters are no exception. When the installation position of the flow meter cannot meet the length requirements of the straight pipe sections before and after it, the measurement error caused by the unstable flow field cannot be ignored. Many users are restricted by instrument measurement wells and measure at locations that cannot meet installation requirements, resulting in an increase in measurement errors.
The transit-time ultrasonic flow meter is particularly sensitive to bubbles mixed in the water. The flowing bubbles will cause the flow meter to become unstable. If the accumulated gas coincides with the installation position of the probe, the flow meter will not work. Therefore, the ultrasonic flow meter should be installed away from the outlet of the water pump, the highest point of the pipeline and other locations that are easily affected by gas. The installation point of the probe should also be installed away from the upper and bottom of the pipeline as much as possible, and should be installed within an angle of 45° to the horizontal diameter. Also, attention should be paid to avoiding pipeline defects such as welds.
The installation and use environment of the ultrasonic flow meter should be careful to avoid strong electromagnetic interference and vibration. During use, we found that under high-voltage lines, on the side of the road with dense vehicles, and the use of mobile phones or walkie-talkies near the host will have more or less impact on the measurement.
3. Failure to accurately measure pipeline parameters leads to inaccurate measurement
The portable ultrasonic flow meter probe is installed outside the pipe. It directly measures the flow rate of the fluid in the pipe. The flow rate is the product of the flow rate and the pipe flow area. The pipe area and sound channel length are calculated by the pipe parameters manually input by the user from the host. The accuracy of these parameters directly affects the measurement results. In other words: even if the flow meter measures the flow rate accurately, if you enter an inaccurate set of pipeline parameters, the measurement results will be inaccurate.
It is best to obtain pipeline parameters by actual measurement. There may be errors in obtaining design drawings and asking people familiar with the situation, because the actual construction situation is often different from the designed parameters. The manufacturing deviation of the pipeline is sometimes not negligible. Parameters such as the wall thickness of the pipeline that has been used for a period of time will also change significantly over time.
When actually measuring pipeline parameters, attention should also be paid to the rationality of methods, and the measuring tools and instruments used for measurement must be calibrated. When measuring the outer diameter of a pipe, attention should be paid to the possible effects of corrosion and dirt on the outer protective layer of the pipe and the outer surface on the measurement.
When using a portable ultrasonic flow meter for flow measurement on a small pipe diameter, the error caused by inaccurate input of the pipe inner diameter cannot be ignored. For example, if the absolute error of the inner diameter measurement is also 1 mm, then for a DN1000 pipeline, the relative error of the inner diameter is 0.1%; while for a 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 inner diameter area of ​​the pipe). The same 1 mm inner diameter measurement error brings only about 0.3% flow measurement error to the DN1000 pipeline, while the flow measurement error brought to the DN100 pipeline is about 3%. It can be seen that the larger the pipeline diameter used by the portable ultrasonic flow meter, the easier and more accurate the measurement will be. The smaller the pipeline diameter, the more difficult it will be to measure. Therefore, there is a certain reason why some people recommend that portable ultrasonic flow meters are best used in pipelines above DN300.
The installation distance of the probe is an important measurement parameter that must be accurately guaranteed. In order to ensure that the best signal strength is found, some users move a probe to find the signal. Often the signal has the wrong installation distance of the probe, and they lose sight of the other. The correct method is: move the two probes in parallel, and find the best installation point while ensuring that the installation distance of the probes meets the requirements. After the signal is found, you must use actual measurement to confirm that the installation distance of the probes is accurate.
Pipe lining also has a great impact on measurement. Some old pipelines use cement mortar lining for anti-corrosion. If you ignore its existence during measurement, it will produce a large error, because the thickness of the cement mortar lining is generally not a negligible number. In addition, its surface is rough and easy to adhere to mud and sand, and it is easy to fall off in pieces, which may have a great impact on the measurement. During measurement, if the lining parameters are not entered and no signal is found during normal operation, it should be considered that the pipeline may be lined.