Abstract: This paper briefly introduces the structure of an insertion vortex flow meter and the calibration method for a point velocity meter type insertion vortex flow meter. The shortcomings of comparison methods using water pump flow and portable flow meters are analyzed, and a rapid table lookup method for calibration correction comparison of insertion vortex flow meters is proposed. An example demonstrates the effectiveness and feasibility of this method. Keywords: Insertion vortex flow meter; Comparison; Calibration correction comparison method Introduction Insertion vortex flow meters have significant advantages in measuring large-diameter flow rates due to their low price, light weight, low pressure loss, and ease of installation and maintenance. Currently, our company widely uses insertion vortex flow meters for measuring large-diameter water flow rates. With the implementation of various energy-saving and consumption-reducing measures in recent years, the accuracy requirements for water measurement data from various users have become increasingly stringent. There has been considerable internal debate regarding the accuracy of large-flow water measurement data within the company. Therefore, it is essential to find a simple and effective method as soon as possible to compare the measurement data of insertion vortex flow meters to correctly assess the accuracy of the instrument's measurement data. 1. Introduction to Insertion Vortex Flow Meters The insertion vortex flow meter is a point velocity meter type insertion flow meter. It consists of a measuring head, insertion rod, insertion structure, converter, and instrument housing (measuring pipe). When the measuring head is inserted into a specific position in the pipe (generally on the pipe axis or at the average flow velocity of the pipe), the local flow velocity of the medium at that point is measured. Then, the flow rate in the pipe is calculated based on the flow velocity distribution of the medium in the pipe and the geometric parameters of the instrument and the pipe. The measuring head of the insertion vortex flow meter is a pulse-frequency type. Its flow calculation formula is: qv=f/K (1) Where: qv is the volumetric flow rate, m3/s; f is the frequency of the flow meter, Hz; K is the instrument coefficient of the flow meter, 1/m3. 2. Calibration of Insertion Vortex Flow Meters There are two calibration methods for point velocity meter type insertion flow meters: flow meter method and velocity meter method. The flowmeter method calibrates the entire flowmeter. Its calibration equipment and methods are the same as for full-pipe flowmeters. However, because point velocity meter-type insertion flowmeters are often used for measuring large-diameter flow rates, their corresponding calibration equipment and costs are expensive, making them unsuitable for widespread use. They are only used in specific situations (such as arbitration of flowmeter measurement results by technical supervision departments, type approval tests of flowmeters, etc.). The velocity meter method calibrates the flowmeter's measuring head as a single flowmeter. First, the instrument coefficient K0 of the measuring head is measured. Then, correction factors are determined based on the fluid and pipeline conditions at the application site. Finally, the instrument coefficient K of the entire flowmeter is calculated based on the pipeline's cross-sectional area. For the standard calibration device used in the velocity meter method, a straight open channel is used for liquids, and a low-speed wind tunnel is used for gases. Most flowmeter manufacturers do not possess these two standard devices. In practice, a workaround is often used: calibrating the measuring head using a circular pipe flowmeter standard device to determine the measuring head's instrument coefficient K0. However, certain correction factors during the testing phase of this device must be determined simultaneously. The instrument coefficient K of a point velocity meter type insertion flow meter is usually calculated by correcting the instrument coefficient K0 of the calibrated measuring head. The formula for calculating and correcting the instrument coefficient K is: K = K0/(αβA) (2) Where: K0 is the instrument coefficient of the measuring head, 1/m3; α is the velocity distribution coefficient; β is the blockage coefficient; A is the cross-sectional area of ​​the measuring pipe, m2. 3 Comparison method of insertion vortex flow meter measurement data For a long time, the insertion vortex flow meters used by our company have been using the factory data of the instrument since they were put into use. After several cycles of use of the instrument, the measurement accuracy of the instrument may be affected by changes in the process and field environment, corrosion and wear of the measuring head by the medium, and deterioration of the performance of the instrument's electronic converter. Since the company does not have a standard device for calibrating insertion vortex flow meters, when the instrument measurement data error is large, the following methods are often used to make simple comparisons of the measurements. 3.1 Before comparing the flow rate of a water pump, when operators of the user unit have doubts about the measurement data of an insertion vortex flow meter, they often compare it with the rated flow rate at the "specified performance point" on the pump's nameplate or with the flow rate reading corresponding to the pump's typical pressure-flow characteristic curve. If the two flow rates are inconsistent, the instrument is considered inaccurate, and the instrument maintenance personnel are immediately notified for inspection. However, after the instrument maintenance personnel inspect, no abnormality is found in the instrument, leading to conflicting opinions and disputes. In fact, comparing the flow rate of a water pump with the instrument's flow rate often leads to misunderstandings because the pump's delivery flow rate is determined by the intersection of the pump's characteristic curve and the piping system's load characteristic curve. It varies with the operating load characteristics. The rated flow rate indicated on the pump's nameplate refers to the flow rate under a certain specified condition, and in most cases, the actual flow rate and the rated flow rate will not be consistent. Furthermore, the rated flow rate of water pumps is also specified to allow a tolerance of 4% to 8%. The head-flow characteristic curves of different water pumps of the same specification will also differ from the typical curves, and the delivered flow rates will not be the same. Even with the measured head-flow characteristic of a water pump, there may be an error of 2% to 3.5% between the flow rate value and the true value. Therefore, the flow rate value of a water pump cannot be used as the basis for judging the accuracy of a flow meter. However, cross-referencing can be used during daily operation. If abnormal changes occur in the difference, it can be considered a fault phenomenon, allowing for further inspection of the water pump, instruments, and piping system to determine the cause of the fault. 3.2 Using portable ultrasonic flow meters: In recent years, our company has successively introduced the American POLYSONICS DCT7088 and Japanese FUJI FLD/C portable ultrasonic flow meters to evaluate the flow conditions and energy/material balance of the pipeline network, or to check the operating status of other flow meters installed on the pipeline. To resolve the controversy surrounding the accuracy of high-flow-rate water metering data within the company, we attempted to use a portable ultrasonic flow meter to calculate water volume and then compared it with the measurement data from an insertion vortex flow meter. However, the portable ultrasonic flow meter, which uses the time-of-propagation method, requires calibration to calculate the flow area and propagation distance in the on-site pipeline. Its measurement error is not only related to factors such as the clamping position, pipeline characteristics (wall material and thickness, corrosion status, lining material and thickness), and acoustic coupling variations, but also to the technical skill level of the installation and commissioning personnel. Furthermore, its use is complex and difficult for general personnel to master. In practical use, the instrument's measurement results are unstable, and measurement accuracy cannot be guaranteed, making it difficult to provide effective data results. Therefore, the conditions for on-site comparison of measurement data from portable ultrasonic flow meters and insertion vortex flow meters are not yet mature and further exploration is needed to accumulate experience. 3.3 Calibration Correction Comparison Method for Insertion Vortex Flowmeters While theoretical analysis and measures such as maintenance and debugging can improve the field performance of insertion vortex flowmeters, the most convincing solution to disputes regarding the accuracy of flowmeter data ultimately relies on valid data. Our company currently possesses a static volumetric water flow calibration device with a maximum operating diameter of 300mm. We attempted to disassemble the insertion vortex flowmeter, which was the subject of considerable controversy in the field, and install it on a 300mm diameter pipeline of the calibration device. We calibrated the entire flowmeter using the flowmeter method, obtaining data through actual flow calibration. We then comprehensively analyzed the linearity, repeatability, and accuracy of the instrument under this diameter condition, assessed its performance, and further adjusted it to achieve optimal operating conditions. The current challenge is how to determine the instrument's field performance data when the geometric parameters of the installed pipeline differ from the experimental conditions. From the calculation correction formula for the instrument coefficient K (Formula 2), it can be seen that for the same insertion vortex flowmeter, its K0 value is uniquely determined at the same time. The instrument itself is not problematic after being calibrated and adjusted successfully on the flow calibration device (300mm diameter pipeline). Due to the different pipe diameter and other conditions at the installation site, the actual usage coefficient of the instrument is K′. K′ is only related to the α and β A parameters, so we can determine it through calculation and thus complete the comparison. 3.4 Quick Reference Method for Calibration Correction Comparison of Insertion Vortex Flowmeters Because calculating K′ through the formula is quite cumbersome and not easy for everyone to master, the author has compiled a quick reference comparison table based on his long-term accumulated experience (Note: This table is compiled based on data with D=300mm to calculate the comparison value for quick conversion), as shown in Tables 1 and 2. The insertion vortex flow meter was calibrated and tested using the flow meter method on a 300mm pipeline to determine the calibration coefficient K of the instrument when D=300mm. Then, by referring to Tables 1 and 2, the ratio of α β A under the actual operating pipe diameter condition to that under the 300mm pipe diameter condition can be obtained. This allows for the calculation of the instrument coefficient K′ under the actual operating pipe diameter condition, thus completing the calibration correction comparison of the insertion vortex flow meter. 3.5 Application Example of the Insertion Vortex Flow Meter Calibration Correction Comparison Method In our company's circulating water plant, the SX88-900L1B2 type insertion vortex flow meter (4~20mA analog output type) is used for water metering. For a long time, there has been considerable controversy regarding the measurement data of this meter. If the flow rate value of the water pump is used as the benchmark for comparison, the measurement error of the instrument is as high as 20%. Although it has been stated above that the flow rate value of the water pump cannot be used as the basis for judging the accuracy of the flow meter, they are still used interchangeably in daily operation. After careful inspection of the water pump, instruments, and their relationship by technicians, it was confirmed that the significant difference was caused by the instrument coefficient. The insertion-type vortex flowmeter was removed, and a series of operations were performed according to the calibration correction comparison method. Simultaneously, the amplifier was adjusted accordingly, yielding valid data: At the time of manufacture, based on the process conditions at the usage site, the factory calculated the instrument's maximum flow rate Qmax = 6000 m³/h and full-scale frequency fmax = 41.2 Hz. The entire flowmeter was calibrated using the flowmeter method on a 300 mm diameter pipeline. Through actual flow calibration, the instrument coefficient K = 202.951 was obtained. Then, by referring to Tables 1 and 2, the α (compared to the commonly used flow rate calculation) and β values ​​were obtained for the actual pipe diameter of 900 mm and 300 mm. The ratios of A and B are 1.016, 1.055, and 9.000, respectively. The corrected instrument coefficient K′ = K/(1.016 × 1.055 × 9.000) = 21.038 under a 900mm diameter condition is calculated. This is then converted to the actual maximum flow rate Qmax = 7050 m³/h at a full-scale frequency fmax = 41.2Hz, thus completing the calibration correction comparison for the insertion vortex flowmeter. Further estimation shows that the correction result has an error of approximately 0.5% compared to the traditional theoretical calculation, which meets the needs of on-site measurement. Furthermore, after the instrument is installed on-site, the gain and sensitivity of the instrument amplifier can be appropriately adjusted according to the actual situation to achieve optimal operating conditions, which is also very important. 4. Conclusion After a period of testing, it has been proven that using the calibration correction comparison method to obtain actual instrument usage data is effective and feasible. We applied this method to correct the instrument data of a batch of insertion vortex flowmeters with large measurement deviations, and this has been recognized by all parties, ensuring the accuracy of the company's large-flow water measurement data. Of course, since the measurement accuracy of insertion vortex flowmeters is greatly affected by the installation of on-site pipelines and instruments, and the calculation of the correction coefficient itself also has certain errors, many issues still need to be further explored.