Flow measurement technology is very different from the application of traditional measuring instruments. It is not simply about installing the flow meter and putting it into operation to achieve the measurement purpose. Two experts once conducted a survey on over a thousand flow meters installed on site and found that about 60% of the selected measurement methods were not the most suitable or correct. Among the remaining 40%, about half of them, although the measurement methods were suitable, had unreasonable on-site layout and installation, which resulted in corresponding measurement errors. Therefore, flow measurement is a strongly dependent measurement on usage conditions. In the laboratory, flow meters can achieve extremely high accuracy, but in the field of use, once there are significant changes in fluid or environmental conditions, not only can the accuracy be guaranteed, but normal measurement cannot even be carried out.

The error of a flowmeter during factory calibration is better than ± 0.5%, but it is not uncommon for the error of a new instrument to increase to ± 5% to ± 10% after installation and opening on site. There are various reasons for this situation, such as unreasonable selection, inappropriate range, insufficient length of upstream and downstream straight pipe sections, incorrect installation, significant deviation of fluid properties from the design state, operating conditions exceeding allowable values, pulsating flow effects, and harsh environmental conditions such as vibration. Many more can be cited. Therefore, flow measurement is a systematic problem, including detection devices, display devices, front and rear straight pipe sections, and auxiliary equipment. The research on application technology also includes the measurement object itself, and simply having good performance of the flowmeter itself cannot guarantee obtaining the required measurement results.

The goal of researching the application technology of flow measurement instruments is to use them correctly, mainly including the following specific contents.

1. Improve exemplary performance

In instrument equipment management, the definition of a leading example is: (total number of instruments - number of instruments not in normal use)/total number of instruments. Therefore, setting a good example is to reduce the number of instruments that cannot be put into normal use. In the design institute, the setting example of the measurement system designed by the self-control profession is one of the important indicators reflecting the quality of work and technical proficiency of the designers. Experienced and responsible designers can achieve a setting example of over 95%, and remote transmission of pressure gauges or rectification can achieve a setting example of over 95%. However, under the conditions of a market economy, engineering companies often implement a turnkey contracting approach for owners, requiring a set example of 100% instead of 95%. If the designed instrument system cannot be put into normal use, the engineering company is responsible for rectification or replacement of instruments, which means economic losses. Therefore, the research on instrument application technology has practical economic significance.

Setting an example is a comprehensive performance of the level of instrument application technology and the quality of the instrument itself. The matching, coordination, optimization of measurement methods and instruments with the measurement object and usage environment, as well as the design, selection, installation, and debugging processes prior to this, are all important factors that affect setting an example.

In recent years, the application technology of flow measurement instruments in China has made great progress, and the leading role of flow measurement instruments has been greatly improved. This is partly due to the significant improvement in the overall technical level of instrument personnel and the enhancement of their sense of responsibility. More importantly, the quality of instruments has been greatly improved compared to the planned economy era. The proportion of imported instruments and instruments assembled with advanced foreign technology is increasing, especially after the general implementation of intelligent instruments, the adjustable measurement range has been greatly expanded. Instruments that were previously unable to be put into normal use due to inappropriate measurement range selection can generally be put into use by changing the range.

2. Ensure measurement accuracy

The accuracy of flow measurement refers to the precision obtained by the flow measurement system, which is different from the accuracy of the flow meter itself. Just because the flowmeter itself has good performance and high accuracy, it may not necessarily achieve high measurement accuracy.

To ensure the accuracy of the flow measurement system, in addition to reasonable selection, correct installation and debugging, timely maintenance and upkeep, the application of intelligent technology to compensate and correct the errors that may be introduced in the measurement part is also an effective method. For example, compensating for the temperature expansion coefficient of liquids, compensating for the temperature, pressure, and compression coefficient of gases with stainless steel pressure gauges, compensating for the Reynolds number effect and flow expansion coefficient of differential pressure flow meters, compensating for the nonlinearity of flow coefficients of various flow meters, compensating for the temperature effect of volumetric flow meters and vortex flow meters, compensating for the velocity distribution of ultrasonic flow meters, etc. This compensation and correction is a systematic approach to eliminate or achieve basic elimination of inherent errors in the detection part that cannot be overcome by itself. Practice has shown that this method is simple, effective, and has great potential for development.