the comparative analysis between ‌Piston Flow Switches‌ and ‌Electromagnetic Flow Meters‌

Here is the professional English translation of the comparative analysis between ‌Piston Flow Switches‌ and ‌Electromagnetic Flow Meters‌, maintaining technical precision and structural clarity:

️ ‌I. Core Functional Differences‌

Feature‌ ‌Piston Flow Switch‌ ‌Electromagnetic Flow Meter‌

Primary Function‌ Detects if flow reaches preset threshold; outputs switching signal (ON/OFF) Measures flow value precisely; outputs continuous signal (e.g., 4-20mA, pulse)

Signal Type‌ Binary signal (relay contact, NPN/PNP) Analog or digital signal (instantaneous/totalized flow)

Typical Application‌ Pump start/stop control, dry-run alarm, safety interlock Process optimization, energy analysis, trade settlement

Accuracy‌ Lower (±5%–±10%)‌ High (±0.1%–±0.5%)‌

🔧 ‌II. Working Principle Comparison‌

Piston Flow Switch‌

Mechanical Trigger‌: Fluid drives an internal magnetic piston, actuating an external reed switch to open/close‌.

Compatible Media‌: Liquids/gases (low particulate), high-viscosity fluids (e.g., lubricating oil)‌.

Electromagnetic Flow Meter‌

Electromagnetic Induction‌: Based on Faraday’s law; conductive fluid cutting magnetic field generates voltage proportional to flow velocity‌.

Media Limitations‌: Only for liquids with conductivity ≥5μS/cm (e.g., water, acids/alkalis); incompatible with oils/gases‌.

📊 ‌III. Key Technical Parameters‌

Parameter‌ ‌Piston Flow Switch‌ ‌Electromagnetic Flow Meter‌

Response Time‌ Fast (milliseconds)‌ Slower (seconds)‌

Turndown Ratio‌ Narrow (1:5–1:10)‌ Wide (1:20–1:50)‌

Pressure Drop‌ Very low (≤0.3 Bar)‌ Moderate (pipe-size dependent)‌

Pressure Rating‌ Up to 100 Bar (SS housing)‌ Typically ≤40 Bar‌

🏭 ‌IV. Typical Application Scenarios‌

Piston Flow Switch Applications‌

Fire pump control: Activates pump when flow ≥20% setpoint‌.

Compressed air systems: Gas flow anomaly alarms‌.

Electromagnetic Flow Meter Applications‌

Wastewater plants: Precise flow measurement/billing‌.

Chemical processes: Corrosive media monitoring (e.g., acids/alkalis)‌.

️ ‌V. Key Selection Considerations‌

Piston Flow Switch‌

Vertical installation requires upward flow only‌ to prevent piston sedimentation‌.

Install ≥80-mesh filter to avoid debris jamming‌.

Electromagnetic Flow Meter‌

Full-pipe requirement‌: Incomplete filling or air bubbles cause measurement failure‌.

Avoid strong EMI‌: Motors/transformers disrupt magnetic field accuracy‌.

Summary‌: Piston flow switches are ‌cost-effective on-off controllers‌ for simple start/stop logic; electromagnetic flow meters are ‌high-precision instruments‌ for conductive liquid metering‌.

Key Terminology:

量程比 → ‌Turndown ratio‌

干簧管 → ‌Reed switch‌

法拉第定律 → ‌Faraday’s law‌

电导率 → ‌Conductivity‌

满管要求 → ‌Full-pipe requirement‌

电磁干扰 → ‌EMI (Electromagnetic Interference)‌

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