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Views: 55 Author: Site Editor Publish Time: 2021-08-26 Origin: Site
Electromagnetic flowmeter is a specific system composed of transmitter and converter. Insulation, number of shielding layers, distributed capacitance and cross-sectional area of conductor will all affect the measurement results of electromagnetic flowmeter.
Improper selection
The electrode and the lining are materials in direct contact with the medium. If we choose inappropriate electrode and liner materials, it will cause many problems, such as electrode scaling and corrosion, lining wear, scaling and deformation. These problems will lead to inaccurate measurement of industrial flowmeter and shorten the service life of magnetic flowmeter.
A. DC wave excitation
DC excitation is prone to electrode polarization and DC interference. Too high polarization voltage will block the input of the converter, and the converter of magnetometer can't amplify the normal signal. Therefore, we can't receive the reading displayed by the magnetic flowmeter.
B. AC sine wave excitation
AC sine wave excitation is easy to cause zero point vibration of electromagnetic flowmeter. Obviously, improper zero position will lead to inaccurate measurement.
Pipe Straight Run Requirements: Proper installation requires sufficient upstream and downstream straight pipe sections to ensure a stable flow profile. Typically, 5–10 times the pipe diameter (D) upstream and 2–5 times D downstream are recommended.
Improper Grounding & Shielding: Poor grounding can lead to signal noise and measurement instability. Proper grounding rings or electrodes help maintain accuracy.
Air Bubbles & Cavitation: Air bubbles in the fluid can cause signal fluctuations, leading to inaccurate readings.
Incorrect Sensor Orientation: The flow meter should be installed so that the electrodes are aligned horizontally to avoid trapping air or sediment.
Minimum Conductivity Requirement: Electromagnetic flow meters require a fluid conductivity of at least 2 µS/cm. If the conductivity is too low (e.g., distilled water, hydrocarbons, or gases), the meter will not function correctly.
Temperature & Pressure Effects: High temperatures (up to 180°C) can affect sensor materials, while pressure fluctuations can introduce pulsations in the flow, impacting accuracy.
Non-Homogeneous Fluids: Fluids with suspended solids or slurries may cause fluctuations, especially if deposition occurs on the electrodes
The electrode and lining materials should be selected based on the chemical composition, temperature, and abrasiveness of the liquid.
Common lining materials: PTFE, PFA, rubber, ceramic.
Common electrode materials: Stainless steel, Hastelloy, titanium, tantalum, platinum.
External magnetic fields or electrical noise can affect the signal processing. Proper shielding and grounding reduce the impact of EMI.
Flow disturbances caused by valves, bends, pumps, or reducers near the meter can affect accuracy. Using flow conditioners or positioning the meter properly helps maintain an ideal flow profile.
High temperatures can affect sensor and lining materials, leading to drift in measurements.
Pressure fluctuations can introduce flow variations that impact accuracy.
Advanced digital signal processing (DSP) improves accuracy by filtering noise.
Periodic calibration and verification help maintain accuracy over time. Factory calibration is typically performed using a high-precision reference standard.
Electromagnetic flow meters perform best within their specified flow velocity range (typically 0.2 to 15 m/s).
Operating too close to the minimum or maximum flow limits may reduce accuracy.
Range Ratio (Turndown Ratio): ARTang’s meters offer a range ratio of 1:100, meaning they maintain accuracy over a wide flow range.
Factory Calibration: Calibration must match actual operating conditions, with 0.2% or 0.5% accuracy being standard for high-precision applications.
Aging & Electrode Coating: Over time, deposits can form on the electrodes, leading to reduced accuracy. Regular cleaning and maintenance are required.
By ensuring proper installation, selecting the right meter, and minimizing external disturbances, you can maximize the accuracy of your electromagnetic flow meter. Would you like recommendations on improving accuracy in specific applications?
About ARTang
ARTang is a global leader in measurement instrumentation, services and solutions for industrial process engineering that energizes the transformation of society and industry to achieve a more productive, sustainable future. We provide process solutions for flow, level, pressure, analytics and digital communications, optimizing processes in terms of economic efficiency, safety & environmental impact.