1. Thermal Mass Principle (Most widely adopted, over 90% standard MFCs)
Divided into two types:
(1) Capillary laminar thermal type (traditional industrial MFC)
Gas splits into a main channel and a tiny bypass capillary. Two platinum coils wrap around the capillary: the upstream coil heats the gas, while the downstream coil detects temperature. Heat carried away by flowing gas creates a temperature difference proportional to mass flow. Readings are barely affected by gas temperature and pressure fluctuations.
- Pros: Wide measuring range, stable accuracy, fast response; standard for semiconductors, photovoltaics and labs.
- Cons: Capillary easily clogged by dust or oil; high cost for high-flow models.
(2) MEMS chip thermal type
Integrated heating and temperature-sensing resistors on a silicon MEMS chip with micro flow channels. Compact and low-cost, mainly for low-flow scenarios and portable equipment.
2. Coriolis Mass Principle
Gas passes through a vibrating bent measuring tube. Moving gas generates Coriolis force, producing a phase shift between tube sensors. The phase difference directly reflects mass flow rate without temperature/pressure compensation.
- Pros: True direct mass measurement, compatible with corrosive high-purity gases, high pressure resistance, suitable for large flow rates.
- Cons: Bulky, expensive, poor accuracy under ultra-low flow; rarely made into small-range MFCs, mostly used for large-bore gas mass flow meters.
3. Laminar Differential Pressure Principle
Based on Poiseuille’s law: under full laminar flow, pressure drop across a laminar element has a linear relationship with gas mass flow. A high-precision differential pressure sensor converts pressure signals into mass flow values.
- Pros: Robust structure, high temperature resistance, dust tolerance, cost-effective for large flow measurement.
- Cons: Strict laminar flow requirement; low accuracy under low pressure and tiny flow rates, applied to industrial purging and exhaust gas measurement.
Application Summary
- Thermal MFC: Standard for low & medium flow semiconductor, coating and laboratory processes
- Coriolis meter: High-precision large-flow measurement of rare or corrosive specialty gases
- Laminar differential pressure meter: Heavy industrial large-flow, high-temperature crude process gas measurement
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