Mass flow meters measure mass flow rate directly — the most fundamental flow quantity, unaffected by process temperature, pressure, or composition changes that would alter volumetric flow readings. Coriolis meters use the inertial forces of a vibrating tube — fluid flowing through a vibrating tube causes a Coriolis-induced phase shift between inlet and outlet tube deflection, proportional to mass flow; they also measure fluid density from the tube resonant frequency. Thermal mass flow meters heat the fluid stream and measure heat dissipation rate — mass flow rate is proportional to the energy required to maintain a fixed temperature difference between upstream and downstream sensors.
Coriolis: one or two bent or straight tubes are driven to vibrate at natural frequency by a drive coil. Fluid flowing through introduces Coriolis forces that cause the inlet half of the tube to lag and outlet half to lead the drive motion — the phase difference (time delay Δt between two position sensors) is directly proportional to mass flow rate. A second measurement: the tube resonant frequency shifts with fluid density — density is measured simultaneously to ±0.001 g/cm³. Thermal: a heater element raises the fluid temperature by ΔT; downstream temperature sensor measures heat carried away — at zero flow, heat diffuses symmetrically; flow carries heat downstream, creating an asymmetric temperature profile whose distortion is proportional to mass flow.
Challenges
Coriolis Tube Resonance Disruption from Entrained Gas or Two-Phase Flow
Gas bubbles in the vibrating tube disrupt resonance — drive energy increases; measurement becomes erratic above 2–3% gas void fraction.
Coriolis Zero Drift from Temperature Gradients or External Vibration
External pipeline vibration near tube resonant frequency shifts the zero point — periodic re-zeroing required.
Thermal Meter Response Time Lag at Sudden Flow Changes
Thermal sensor has a thermal time constant of 1–5 seconds — too slow for rapidly pulsing or batch-start flow events.
Coriolis Pressure Drop at High Viscosity (>1,000 cP) in Small Bore Tubes
Narrow bent-tube Coriolis design generates significant pressure drop with viscous fluids — limits application above 1,000 cP in small sizes.
Thermal Meter Fouling of Heated Sensor by Deposits or Biofilm
Deposits on the heater element change thermal resistance — calibration shifts; response decreases; false low reading.
Solutions
- Gas Entrained Service: Use Meter with Gas Void Fraction (GVF) Compensation Algorithm: Smart Coriolis with GVF compensation continues reliable measurement to 5% entrained gas — beyond that, use DP or vortex meter.
- Zero Verification and Reset During Process Shutdown (Quarterly Minimum): Zero check with closed valves and no flow — reset zero if drift exceeds 0.1% of maximum flow; trend over time detects pipeline vibration.
- Thermal Mass Meter with Fast Response Sensor (Thin-Film, Time Constant <0.5 s): Thin-film sensing element 10× faster than traditional — suitable for batch dosing and rapid-change flow applications.
- Straight-Tube Coriolis Design for High-Viscosity and Hygienic Service: Straight tube has lower pressure drop than bent tube — suitable for viscous fluids and easy CIP drain-down.
- Self-Monitoring (Diagnostics) Coriolis: Drive Gain, Tube Frequency, Balance Monitoring: Continuous self-diagnostics detect tube coating, corrosion, or mechanical damage — alerts maintenance before measurement failure.
Applications
- Pharmaceutical: API solution batch dosing and mass metering; excipient dispensing; sterile filling — Coriolis ±0.1% accuracy.
- Chemical: Polymer reaction feed metering; catalyst dosing; high-viscosity resin transfer — Coriolis mass + density.
- Food & Beverage: Ingredient dosing by mass; density measurement of beverages; Brix determination — Coriolis sanitary.
- Compressed Gas: Thermal mass for compressed air, nitrogen, CO₂ metering at low flows — no density compensation needed.
- Oil & Gas: Coriolis for fiscal metering and well test allocation — ±0.1% mass accuracy; density and volume also computed.
Models & Capacities
Mass Flow Meters (Coriolis and Thermal) — Models & Capacities | ||||||||||
Model / Type | Size DN [mm] | Mass Flow Range [kg/h] | Mass Accuracy [%] | Density Accuracy [g/cm³] | Max Viscosity [cP] | Temp Range [°C] | Max Pressure [bar] | Tube Config. | Output Signal | Weight [kg] |
Coriolis Micro | DN 1–DN 3 | 0.1–30 | ±0.1 | ±0.0005 | No limit | −50 to +200 | 350 | Micro bent | 4–20 mA + HART | 0.3 |
Coriolis Lab | DN 4–DN 8 | 1–200 | ±0.1 | ±0.001 | No limit | −50 to +200 | 350 | Bent tube | 4–20 mA + HART | 1.5 |
Coriolis Pilot | DN 10–DN 25 | 5–3,000 | ±0.1 | ±0.001 | No limit | −50 to +200 | 350 | Bent tube | 4–20 mA + HART/FF | 4 |
Coriolis Prod | DN 40–DN 80 | 500–80,000 | ±0.1 | ±0.001 | No limit | −50 to +200 | 100 | Dual bent | 4–20 mA + HART/FF | 18 |
Coriolis LP (large) | DN 100–DN 200 | 5,000–600,000 | ±0.1 | ±0.002 | No limit | −50 to +150 | 40 | Straight tube | 4–20 mA + HART/FF | 85 |
Coriolis Hygienic | DN 6–DN 50 | 5–15,000 | ±0.1 | ±0.001 | No limit | −50 to +150 | 40 | Bent/straight TC | 4–20 mA + HART + WirelessHART | 6 |
Thermal Mass (inline) | DN 6–DN 200 | 0.05–2,000 Nm³/h gas | ±1.5% FS | — | 1 | 0 to +60 | 100 | Inline probe | 4–20 mA + HART + relay | 1.5 |
Thermal Mass (insertion) | DN 50–DN 2,000 | 2–100,000 Nm³/h | ±2% FS | — | 1 | −20 to +80 | 16 | Insertion probe | 4–20 mA + Modbus | 2.5 |