Flowmeter Selection
Reference data and engineering information about flowmeter selection for process control applications.
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Overview
Engineering reference data for Flowmeter Selection in process control.
Key Formulas
PID Controller
Proportional-Integral-Derivative control.
Transfer Function
First-order system.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Proportional gain | — | |
| Integral gain | 1/s | |
| Derivative gain | s | |
| Time constant | s |
Flowmeter Comparison
The following table provides a detailed comparison of common industrial flowmeter types, highlighting their operating principles, best-use scenarios, and performance characteristics.
9 rows
Flowmeter Type | Principle | Best Suited For | Not Suited For | Accuracy | Typical Rangeability | Pressure Drop | Required Upstream Diameters | Relative Cost | Effect of Viscosity | Moving Parts |
|---|---|---|---|---|---|---|---|---|---|---|
| Electromagnetic | Induction across magnetic field | Clean/dirty conductive liquids & slurries | Hydrocarbons, low-conductivity fluids, gases | ± 0.5 - 1% of rate | 40:1 | None | 5 | High | None | None |
| Coriolis (Mass) | Coriolis effect on vibrating tube | Clean/dirty liquids, gases, slurries; monitors concentration | High-pressure gas applications | ± 0.05 - 0.5% of rate | 10:1 | Low | None | High | None | None |
| Thermal (Mass) | Heat transfer from fluid | Clean/dirty liquids, some slurries | High-pressure gases | ± 1% of rate | 10:1 | Low | None | High | None | None |
| Orifice Plate | Differential pressure (ΔP) | Clean/dirty liquids, some slurries | Highly viscous fluids | ± 2 - 4% of scale | 4:1 | Medium (required) | 10-30 | Low | Significant | None |
| Turbine | Rotational speed of turbine | Clean viscous liquids & gases, turbulent flow | Corrosive fluids, fluids with solids | ± 0.25% of rate | 20:1 | Higher | 5-10 | Medium | Significant | Rotor |
| Ultrasonic (Transit-Time) | Frequency shift of ultrasonic pulses | Clean liquids | Gases, dirty fluids | ± 1 - 5% of full scale | 20:1 | Low | 5-30 | Medium | None | None |
| Ultrasonic (Doppler) | Frequency shift from suspended particles | Dirty liquids, slurries | Gases, clean liquids | ± 1 - 5% of full scale | 10:1 | Low | 5-30 | Medium | None | None |
| Vortex | Vortex shedding frequency | Clean/dirty liquids & gases, steam, turbulent flow | High-viscosity fluids | ± 1% of rate | 10:1 | Medium | 10-20 | Medium | Significant for high viscosity | None |
| Wedge | Differential pressure (ΔP) | Slurries & viscous liquids | Low-viscosity fluids | ± 0.5 - 5% of scale | 3:1 | Low to Medium (required) | 10-30 | Medium | Low | None |
Source: engineeringtoolbox.com
Key Selection Criteria
Fluid Properties:
- Conductivity: Required for electromagnetic meters.
- Cleanliness/Presence of Solids: Dictates choice between intrusive (turbine, orifice) and non-intrusive (ultrasonic) types.
- Viscosity: Affects differential pressure (DP) meters (orifice, wedge) and turbine meters significantly.
- Phase: Most meters are for liquids; some (vortex, turbine, thermal mass) also handle gases and steam.
Performance Requirements:
- Accuracy: Mass flow meters (Coriolis) offer the highest accuracy. DP meters (orifice) have lower accuracy but are robust and inexpensive.
- Rangeability (Turndown): Electromagnetic and turbine meters offer the widest operating ranges.
- Permanent Pressure Loss: DP meters (orifice) inherently cause a pressure drop. Non-intrusive meters (electromagnetic, ultrasonic) have minimal loss.
Installation & Cost:
- Upstream Straight Pipe: Critical for DP and turbine meters to ensure a stable flow profile. Not required for Coriolis or thermal mass meters.
- Relative Cost: Electromagnetic and Coriolis meters are high-cost but high-performance. Orifice plates are low-cost but require more maintenance and calibration.