How to verify the accuracy of electromagnetic flowmeter after zero point adjustment?

　　As a commonly used flow measurement instrument in industrial automation, the accuracy and stability of electromagnetic flowmeters are critical to the control of production processes and product quality. Zero adjustment is one of the important steps in the calibration of electromagnetic flowmeters and is used to eliminate the zero drift error when there is no flow passing through, thus ensuring the accuracy of the measurement. However, how to verify the accuracy after zero-point adjustment is an issue that needs to be explored in depth. In this paper, we will introduce in detail the accuracy verification method of electromagnetic flowmeter after zero point adjustment from various aspects, in order to provide valuable reference for practitioners in related fields.

　　First, the principle and purpose of zero adjustment

　　Zero adjustment is usually carried out after the installation of the flowmeter is completed and there is no flow flow in the pipeline. Through the flowmeter operator interface or debugging software, enter the zero adjustment function menu, confirm the current state of zero flow, and then start the zero adjustment procedure, the flowmeter will automatically calibrate and adjust the zero point. The purpose of this step is to eliminate the zero drift error caused by aging sensors, temperature changes, changes in fluid properties and other factors, to ensure that the flowmeter readings can be accurately zeroed in the zero flow state.

　　Second, the verification method is outlined

　　Verification of the accuracy of the electromagnetic flowmeter zero adjustment can be carried out from a variety of perspectives, including the use of standard flowmeter comparison, check the output signal of the flowmeter, analyse the flowmeter's measurement data and so on. The following will introduce several commonly used verification methods in detail.

　　1. Comparison using standard flow meters

　　This is the most direct and accurate verification method. Through the calibrated flowmeter before and after the series connection of a known accuracy of the standard flowmeter, so that the measured fluid flows through the two at the same time, to compare the difference between the two readings, so as to determine the error of the calibrated flowmeter. This method requires the construction of a special calibration device, and to ensure that the calibration environment meets the requirements, such as temperature, humidity, electromagnetic interference and so on. In practice, the following points need to be noted:

　　Choose a suitable standard flowmeter: the accuracy of the standard flowmeter should be higher than the calibrated flowmeter to ensure the accuracy of the calibration results.

　　Ensure solid connection and good sealing: avoid the influence of fluid leakage on the calibration results.

　　Multiple measurements to take the average value: to reduce the impact of random errors and improve the reliability of the calibration results.

　　2. Check the output signal of the flowmeter

　　The output signal of electromagnetic flowmeter usually includes analogue signal (such as 4-20mA) and digital signal (such as RS485). By checking the accuracy and stability of the output signal, you can indirectly verify the zero adjustment effect of the flowmeter.

　　Analogue signal check: using a signal generator or standard current source, the flowmeter will be connected to the signal test equipment, through the adjustment of the flowmeter's output parameters, so that the output signal in different flow points under the standard signal match.

　　Digital Signal Check: through the communication protocol and the corresponding debugging tools, check and modify the output data format, unit and numerical accuracy and other parameters to ensure that the output signal and the actual flow value to maintain an accurate correspondence.

　　3. Analyse the measurement data of the flowmeter

　　After the zero point adjustment, the accuracy can be verified by analysing the measurement data of the flowmeter. This includes checking the zero drift amount, measurement repeatability, measurement error and other indicators.

　　Zero drift amount: Over a period of time, the zero reading of the flowmeter is recorded periodically and the zero drift amount is calculated to assess the stability of the zero adjustment.

　　Measurement Repeatability: Under the same conditions, measure the same flow value several times, calculate the repeatability of the measurement results to assess the measurement stability of the flowmeter.

　　measurement error: the flowmeter will be connected to a known flow rate of the test system, compare the difference between the actual measured value and the standard value, calculate the measurement error, in order to assess the accuracy of the measurement of the flowmeter.

　　Third, the practical application of the notes

　　In verifying the accuracy of the electromagnetic flowmeter zero adjustment, you also need to pay attention to the following points:

　　Calibration environment selection: the calibration environment should be as close as possible to the actual conditions of use, in order to reduce the impact of environmental factors on the calibration results. For example, parameters such as temperature and pressure should be consistent with the actual working environment of the flowmeter.

　　Calibration cycle development: According to the frequency of use of the flowmeter and accuracy requirements, the development of a reasonable calibration cycle. For flowmeters with high accuracy requirements, the calibration cycle should be shortened to ensure that they are in good working condition for a long time.

　　Participation of professionals: Calibration work should be carried out by professionals with professional knowledge and skills to ensure the standardisation of the calibration process and the reliability of the results.

　　Fourth, the case study

　　The following is a practical case to illustrate how to verify the accuracy of the electromagnetic flowmeter after zero point adjustment.

　　A chemical plant uses an electromagnetic flowmeter to measure the flow of liquids in the production process. In the course of use, it was found that the zero drift of the flowmeter was large, resulting in inaccurate measurement. In order to solve this problem, the technicians carried out zero point adjustment of the flowmeter. After the adjustment was completed, the following methods were used for verification:

　　1. Use standard flowmeter comparison: before and after the flowmeter in series with a high-precision standard flowmeter, so that the measured liquid flows through both at the same time. By comparing the difference in readings between the two, it is found that the measurement error of the flowmeter near the zero point is less than ±1%, which meets the requirements for use.

　　2. check the output signal: the flowmeter will be connected to the signal test equipment to check the stability and accuracy of the analogue output signal (4-20mA). The accuracy of the output signal is verified by adjusting the parameters of the flowmeter so that the output signal matches the standard signal under different flow points.

　　3. Analysis of measurement data: Over a period of time, the zero reading of the flowmeter is regularly recorded and the zero drift is calculated. At the same time, the same flow rate value was measured several times under the same conditions to calculate the repeatability of the measurement results. The results show that the zero drift is small and stable, and the measurement repeatability is good.

　　V. Conclusion and outlook

　　Through the introduction and analysis of this paper, it can be seen that the accuracy verification of electromagnetic flowmeter after zero point adjustment is a complex and important process. By choosing the appropriate verification method, paying attention to the precautions in the practical application and analysing with specific cases, the accuracy and stability of electromagnetic flowmeter after zero point adjustment can be ensured.

　　In the future, with the continuous development of industrial automation technology, the application fields of electromagnetic flowmeter will be further expanded. In order to meet the demand for higher precision measurement, the research and development of electromagnetic flowmeter calibration technology should be strengthened to improve the accuracy and efficiency of calibration. At the same time, it should also strengthen the training and management of flowmeter users, improve their professional skills and quality, to ensure the correct use and maintenance of flowmeter.

　　In summary, the accuracy verification of electromagnetic flowmeter after zero point adjustment is an important step to ensure its measurement accuracy and stability. Through scientific verification methods and strict operational steps, can ensure that the electromagnetic flowmeter in industrial production to play a greater role for the production and development of enterprises to provide a strong guarantee.