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Specific Operation Methods
One method involves conducting a comprehensive annual inspection of the electromagnetic flowmeter. This includes visual checks, testing the converter's characteristics, calibrating the measurement value, measuring voltages at different points, checking insulation resistance, and verifying the circuit integrity. Adjusting the zero point is particularly important due to zero drift, but "online zero adjustment" requires stopping the fluid flow, which can be inconvenient. Therefore, online inspections often skip the sensor operation and focus only on the converter calibration, comparing results with historical data to determine if the instrument should continue to be used, repaired, or replaced.
Another method involves using online inspection to identify potential issues in systems where the medium cannot be stopped. This includes testing the converter with an analog annunciator and checking the sensor’s electrode inductive resistance, excitation coil insulation, and copper resistance. For systems where flow can be stopped, the inlet can be accessed to inspect and clean the lining and check the liquid level.
Key inspection areas include checking the zero point, separating the sensor, converter, and connecting cables. The technical requirements for a full machine zero check involve ensuring the measuring tube is filled with liquid and no flow is present. Many enterprises lack the conditions to perform this check, so they may instead focus on the converter’s zero adjustment. If the zero difference exceeds 5% of the full scale, further investigation is needed. Typically, the zero point deviation is less than 1%.
Checking the connection cables involves testing signal and excitation lines for conductivity and insulation resistance, as well as ensuring proper grounding of the shield layers. The converter inspection includes using standard instruments to replace the sensor and provide flow signals for zero adjustment and calibration. Comparing current readings with previous data helps assess performance.
For the flow sensor, the inspection involves evaluating the magnetic field strength, electrode liquid resistance, and insulation resistance. Measuring the excitation coil’s copper resistance helps detect short circuits, while checking the insulation resistance of the excitation circuit prevents interference. Electrode contact resistance measurements can reveal contamination or coating buildup, which may affect accuracy.
In addition, polarization voltage measurements can help identify electrode contamination, and checking the insulation between signal and excitation circuits ensures no interference is introduced. Insulation resistance and lining condition checks are essential for small-diameter sensors, while large ones may require internal access for inspection.
Author’s Recommendations for Effective Daily Inspection
To improve maintenance practices, companies should develop standardized inspection procedures based on ISO9001 guidelines. Larger organizations may create specific protocols for online verification and calibration. Promoting the use of specialized inspection tools, such as portable PCs and dedicated testing equipment, can enhance efficiency and accuracy. These tools allow for real-time data collection and analysis, making daily inspections more effective and reliable.
By implementing structured routines and advanced tools, companies can ensure the long-term performance and reliability of their electromagnetic flowmeters. This proactive approach not only reduces downtime but also improves overall process control and measurement accuracy.
Detailed analysis of two methods for daily maintenance of electromagnetic flowmeter
Introduction
The main objective of routine maintenance for electromagnetic flowmeters is to ensure or confirm that the device operates under controlled conditions. Routine maintenance is typically divided into two categories: online inspection and offline inspection. The primary goal of these inspections is to verify that the flow measurement values meet and maintain the expected performance standards. Electromagnetic flowmeters are widely used in industrial applications, especially for flow control, and they often measure corrosive or abrasive fluids. In practice, failures in these devices are commonly caused by corrosion leakage, insulation degradation, electrode contamination, or foreign matter adhering to the sensor.
Traditionally, periodic maintenance involves removing the flow sensor from the pipeline for inspection and calibration. However, to minimize damage to the lining during removal, it is common to first measure the insulation resistance on the pipeline to detect any abnormalities before deciding whether to remove the sensor for inspection or perform actual flow calibration. Companies that follow a strict quality management system like ISO9001 typically divide their maintenance tasks into three parts: one-third for online inspection, one-third for cleaning wetted parts after removal, and one-third for offline flow calibration.