When the electromagnetic flow meter leaves the factory, its accuracy has been calibrated by the calibration line.However, in the field of use, due to environmental conditions, fluid characteristics and the instrument itself, such as damage to components and other reasons caused by the instrument operation failure, it is necessary for the long-term use of the flow meter after a routine on-site calibration.As the sensor of the electromagnetic flow meter is installed on the pipeline, it is difficult to remove it and send it to the calibration line for inspection. At present, in the flow measurement range, the national and local regulations and other regulatory documents for on-line inspection of the large-diameter flow meter under the field conditions have not been found.In order to ensure the accuracy and reliability of the electromagnetic flow meter after fault repair and long-term use without affecting the daily production, the following online calibration methods:
1, the excitation coil of electromagnetic flow meter for safety insulation test, should be more than 20 m Ω.
2. Conduct copper resistance test on the electromagnetic flow meter excitation coil, which should be the same as the original factory value (at the same ambient temperature).
3. Test the resistance of the electrodes of the electromagnetic flow meter sensor to the ground. If the resistance value is between 2kf and 20kf, accompanied by charging and discharging phenomenon, the resistance of the two electrodes is similar, it is considered good.
4. Test the excitation current of the electromagnetic flow meter converter, observe the value of its output and the original current of the converter, and the error is no more than 0.25ma.
5. Test the analog output and frequency output of the electromagnetic flow meter converter, observe its linear change, and calculate its maximum linear error, which shall not exceed 0.5%.
6. For the electromagnetic flow meter above DN 1200mm, the push stage NB shall be tested, and the current error shall not exceed 12mA.