Problems with Ultrasonic Flowmeters in Use

First, there is no correct calibration or calibration of ultrasonic flowmeters. Any flowmeter needs to be calibrated or calibrated prior to use. Portable ultrasonic flowmeters are particularly important at this point. As we all know, portable ultrasonic flowmeters have three sets of probes (large, medium, and small) that can be selected to fit different diameter ranges. Each pair of probes and the host is a set of independent flowmeters in a sense. .

If the portable ultrasonic flowmeter is only calibrated or calibrated with a small probe on a small-diameter flow standard device, then if you use a large probe to measure the flow of a large pipe during use, you are using unverified or calibrated The measurement flow rate of the flowmeter can not be guaranteed, because the current technology level cannot guarantee the interchangeability of the probes, and the difference between the size probes is a variable that cannot be ignored.

Therefore, the correct method should be: based on the user's own use as a reference, as much as possible in the same or similar to the use of pipe diameter standard device on the flow of portable ultrasonic flow meter for the verification or calibration of multiple pipelines. At a minimum, ensure that each set of probes in the flowmeter configuration is calibrated.

The purpose of recording the test caliber and probe number on the certificate when verifying or calibrating the organization's certificate or calibration certificate is to prevent misunderstandings. The recognition that portable ultrasonic flowmeters are equivalent to other fixed-caliber flowmeters is wrong. It is also a reason why some users use portable ultrasonic flowmeters.

Meter correction factors are given on portable ultrasonic flowmeter verification or calibration certificates. All kinds of flowmeters will give a meter factor at the time of calibration because of principles, manufacturing, etc., but their names and expressions are different. The portable ultrasonic flowmeter is also equipped with multiple sets of probes, which are suitable for different calibers and may have several meter correction factors. When using a flow meter to measure flow, ensure that the meter correction factor is used correctly. Do not forget to use it and be careful not to mix it. It is a good habit to confirm that the meter correction coefficient set in the main unit is correct before formal measurement.

Second, ignoring the requirements of the flowmeter and the use of the environment requirements of any speed-type flowmeter on the measured flow of fluid within the pipeline are certain requirements, ultrasonic flowmeter is no exception. When the installation position of the flowmeter can not guarantee the straight pipe length requirements before and after, the measurement error caused by the instability of the flow field can not be ignored. Many users are limited by the meter's measuring well and measured at locations where the installation requirements cannot be met, resulting in increased measurement errors.

Time-lapse ultrasonic flowmeters are particularly sensitive to bubbles in water. Flowing bubbles can cause unstable flowmeter indications. If the accumulated gas exactly matches the probe's mounting position, the flowmeter will not work. Therefore, the installation of ultrasonic flowmeter should try to avoid the location of the pump outlet, the highest point of the pipeline and other susceptible to the impact of gas, the probe installation point should also try to avoid the upper and bottom of the pipeline, installed in the range of 45 degrees with the horizontal diameter , but also pay attention to avoid welds and other pipe defects.

Ultrasonic flowmeter installation environment should pay attention to avoid strong electromagnetic interference and vibration. In use, we found that under the high-voltage line, the vehicle intensive roadside, the use of cell phones or walkie-talkies near the host will have more or less impact on the measurement.

Third, can not accurately measure the pipeline parameters caused by measurement is not portable Ultrasonic flowmeter probe installed outside the pipeline, which directly measures the flow velocity of the fluid in the pipeline, flow is the product of flow rate and pipe flow area, and its pipe area and channel The length is calculated by the user's manual input of pipe 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 input a set of inaccurate pipeline parameters, the measurement result is inaccurate.

The best way to obtain pipeline parameters is to use actual measurement methods. Errors may occur in the way of accessing design drawings and inquiries to familiar personnel. Actual construction conditions often differ from design parameters, and manufacturing deviations from pipelines sometimes occur. It is also not negligible. The parameters such as the wall thickness of the pipe used for a period of time will also change with time.

The actual measurement of pipeline parameters should also pay attention to the rationality of methods and methods. The measuring tools and instruments used for measurement must be calibrated. When measuring the outer diameter of the pipe, pay attention to the possible influence of the rust and dirt on the outer protective layer of the pipe and the outer layer.

When the portable ultrasonic flowmeter is used for flow measurement on a small pipe diameter, the error caused by the inaccurate input of the pipe inner diameter cannot be ignored. For example, the absolute error of the inner diameter measurement is also 1 mm, so the inner diameter of the DN1000 pipeline is relatively small. The error is 0.1%; for the DN100 line, the relative error is 1.0%. The flow rate is proportional to the square of the inner diameter (diameter of the inner diameter of the pipe), and the measurement error of the inner diameter of 1 mm is only about 0.3% of the flow measurement error caused by the DN1000 pipeline, and the flow measurement brought by the DN100 pipeline. The error is about 3%. It can be seen that the larger the pipeline diameter is, the more easily and accurately the portable ultrasonic flowmeter is used. The smaller the pipeline diameter is, the more difficult the measurement is.

Therefore, it is recommended that portable ultrasonic flowmeters are best used in pipelines above DN300.

The installation distance of the probe is an important measurement parameter that must be accurately ensured. In order to ensure the best signal strength, some users use the method of moving a probe to find the signal, which is often the signal. The installation distance of the probe is not correct. The correct method is: to move two probes in parallel, to ensure that the installation distance of the probe meets the requirements of the premise to find the best installation point, after the signal to find a good way to use the measured method to confirm the installation of the probe is accurate.

The influence of the pipeline lining on the survey is also very large. Some old pipelines are preserved with cement mortar linings. If they are ignored during measurement, there will be great errors because the thickness of the cement mortar lining is generally not negligible. The number, coupled with the rough surface and easy adhesion of mud sand, and easy to fall off, may all have a great impact on the measurement. In the measurement, if no input lining parameters are input, if the normal operation is to find no signal, it should be considered that the pipeline may be lining.

Ultrasonic flowmeter is an excellent flow meter. It brings us the convenience and economy of measuring flow that other flowmeters cannot match. We should not misunderstand it because of our own carelessness. Practice has proved that using ultrasound. Most of the problems that occur when flowmeters measure flow are caused by human factors, so the above problems can no longer be ignored.