Electromagnetic flowmeters are widely used in industries such as environmental protection, water supply and drainage, and pharmaceuticals to measure the volumetric flow of conductive fluids. These flowmeters have become a mature product. However, improper maintenance and upkeep can affect their normal operation. Based on years of experience in selection, maintenance, and usage in a pharmaceutical company, the following summarizes the application of electromagnetic flowmeters in flow measurement and control processes:
Electromagnetic flowmeter precautions.
1. Importance of Proper Electrode Grounding
Proper grounding of electrodes is critical. A well-grounded system not only enhances the accuracy of the flowmeter but also extends its service life. For accurate operation, the measured medium must be at earth potential, typically achieved through grounding the pipeline or flange. If the process pipeline connected to the sensor is insulated from the measured medium (e.g., plastic pipelines or pipelines with insulating linings), grounding rings or sensors with grounding electrodes must be used to ensure the medium is at earth potential.
Case Study:
A pharmaceutical company encountered issues with flow measurement due to the high corrosiveness of dilute sulfuric acid. The company lined the transport pipeline with polytetrafluoroethylene (PTFE), which led to poor grounding of the sensor electrodes and caused the flowmeter to malfunction. The problem was resolved by installing a dedicated grounding device, restoring normal operation.
2. Conductivity Requirements of the Measured Fluid
Electromagnetic flowmeters are designed to measure the flow of conductive fluids. The fluid being measured must have a minimum conductivity of 5 μS/cm for accurate measurement.
Case Study:
During a routine shutdown and maintenance period, metrology personnel at the company used water as the test medium to verify the flowmeter’s accuracy using the gravimetric method. However, the flowmeter displayed no flow readings. Upon investigation, it was found that the conductivity of the pharmaceutical process water was below 3 μS/cm, too low for the device to function correctly.
This incident highlighted that electromagnetic flowmeters are suitable only for measuring fluids with conductivity ≥5 μS/cm, such as acids, bases, saline solutions, water, wastewater, corrosive liquids, slurry, pulp, and other conductive liquids. They cannot measure gases, steam, or ultra-pure water.
For water with conductivity ≤5 μS/cm and ≥3 μS/cm, you can contact us to customize an Electromagnetic Flowmeter for Low Conductivity Liquids (MTF-C).
Electromagnetic Flowmeter for Low Conductivity Liquids (MTF-C)
MTF-C is an electromagnetic flowmeter for measuring very low conductivity liquids (≥3 μS/cm). This flow meter is particularly suitable for applications with adhesive and greasy media that tend to form an insulating film.
- Available for low conductivity liquids ≥3 μS/cm
- Wide range of liners and electrode materials
- Colors and appearance can be customized as requested
- Also available in customer specific constructions
- No moving parts, no wear, no pressure loss
- Each flow meter is calibrated and assigned a unique serial number corresponding to all calibration data.
3. Maintenance and Care of Electromagnetic Flowmeters
Although electromagnetic flowmeters are highly reliable and rarely malfunction, their sensors are frequently exposed to fluids containing suspended solids or contaminants. Over time, electrode surfaces can become fouled, reducing performance or rendering the device inoperative if not cleaned regularly.
Case Study:
A company used a large-diameter electromagnetic flowmeter to measure wastewater discharge, achieving excellent results for nearly ten years. Installation, operation, and maintenance costs were minimal, and the device met the accuracy and reliability requirements. However, the medium and small-diameter electromagnetic flowmeters used for measuring tylosin column feed liquid—a challenging solid-liquid two-phase fluid—began to exhibit intermittent flow readings after two years of operation. Inspection revealed that deposits and scaling on the measurement tube walls had fouled the electrodes, forming passivation or oxidation layers. These insulated the electrodes, disrupting the measurement circuit.
Conclusion
Electromagnetic flowmeters play a critical role in flow measurement. To ensure optimal performance, attention must be given to the conductivity of the measured fluid, proper grounding of electrodes, corrosion resistance of electrodes, and routine cleaning to prevent passivation or contamination.
All instruments require regular maintenance, and electromagnetic flowmeters are no exception. Although these flowmeters are highly reliable, the constant exposure of sensor electrodes to liquids necessitates periodic cleaning to maintain measurement accuracy. It is generally recommended to clean the electrodes every year to year and a half to ensure optimal performance.
Metlan Magnetic Flow Meters
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