Working Principle

The electromagnetic flowmeter operates based on Faraday's Law of Electromagnetic Induction, which states that a conductor moving through a magnetic field generates an electromotive force (EMF). Key implementation steps:  

1.Magnetic Field Generation: A pair of excitation coils in the flowmeter's measurement tube generates a uniform magnetic field perpendicular to the fluid flow direction when energized.  

2. Conductive Fluid Flow: The measured liquid (with conductivity ≥5 μS/cm) flows through the magnetic field, acting as a conductor cutting magnetic lines.  

3. EMF Generation: Charged ions in the fluid induce an EMF (E) between electrodes perpendicular to both the magnetic field and flow direction:  

-k: Instrument constant  

-B: Magnetic flux density  

-D: Pipe inner diameter  

-v: Average fluid velocity 

4. Flow Calculation: By measuring (E) and combining it with the pipe’s cross-sectional area , the flow rate is calculated as (Q = v*A).  

Core Components

1. Measurement Tube: Lined with insulating materials (e.g., PTFE, rubber) to prevent electrode shorting and resist corrosion.  

2. Electrodes: Material selection (e.g., Hastelloy, titanium, platinum-iridium) depends on fluid properties.  

3. Excitation Coils: Generate uniform magnetic fields, critical for accuracy.  

4. Transmitter: Processes electrode signals into standard outputs (4–20 mA or digital signals).  

Advantages

- No moving parts, high reliability, low maintenance.  

- Wide measurement range (turndown ratio up to 100:1).  

- Unaffected by fluid density, viscosity, temperature, or pressure.  

- Bidirectional flow measurement with zero pressure loss.  

Limitations

- Requires conductive liquids (≥5 μS/cm); unsuitable for gases, oils, or pure water.  

- Installation demands full-pipe flow and straight pipe sections (typically 5D upstream, 3D downstream).  

- Higher cost, especially for large-diameter pipes.