The Engineer's Guide to Flow Measurement
Choosing the right flow meter is critical for efficiency, safety, and profitability. This guide simplifies the complex decision-making process.
Highest Turndown Ratio
Coriolis meters offer exceptional rangeability for processes with wide flow variations.
Peak Accuracy
Positive Displacement & Coriolis meters provide the highest accuracy for custody transfer.
Extreme Temperatures
Vortex and DP meters are built to handle high-temperature steam and gas applications.
Start Here: The Selection Gauntlet
Answer these fundamental questions to quickly narrow down your options. This decision tree guides you to the most likely candidates for your application.
→ Magmeter
→ Coriolis, PD, Turbine, Ultrasonic
→ Thermal Mass, Coriolis
→ Vortex, Turbine, DP
→ Vortex
→ DP Meter
Technology Deep Dive
Coriolis
Measures direct mass flow via tube vibration. The most accurate and versatile meter.
Best For: Custody Transfer, Viscous Fluids, Critical Processes
Accuracy: ±0.1%
Turndown: 100:1+
Pressure Drop: Medium
Electromagnetic
Uses Faraday's Law on conductive fluids. No obstruction, zero pressure drop.
Best For: Water, Wastewater, Slurries, Corrosive Liquids
Accuracy: ±0.2%
Turndown: ~40:1
Pressure Drop: None
Ultrasonic
Measures flow via sound waves. Non-invasive clamp-on models available.
Best For: Retrofits, Large Pipes, Clean (Transit-Time) or Dirty (Doppler) Liquids
Accuracy: ±1-2%
Turndown: ~30:1
Pressure Drop: None
Vortex
Measures frequency of vortices shed from an obstruction. Robust and reliable.
Best For: Steam, Gases, Clean Liquids, High Temps
Accuracy: ±0.75%
Turndown: ~20:1
Pressure Drop: Medium
Positive Displacement
Directly measures volume by trapping and counting fluid parcels. Excellent for viscous fluids.
Best For: Viscous Liquids (Oils, Syrups), Low Flows
Accuracy: ±0.1%
Turndown: ~100:1
Pressure Drop: High
Thermal Mass
Measures gas mass flow via heat transfer. Highly sensitive with great turndown.
Best For: Gas Monitoring (Air, Natural Gas), Low Flows
Accuracy: ±1%
Turndown: 100:1+
Pressure Drop: Low
Accuracy vs. Relative Cost
This chart plots the best-case accuracy against the typical initial cost. High-precision meters like Coriolis command a premium, while options like DP meters are cheaper but less accurate.
Turndown Ratio Comparison
A higher turndown ratio means the meter can accurately measure a wider range of flow rates. This is critical for processes with high variability.
Installation Headaches: Straight Pipe Requirements
Many meters require long, straight pipe runs upstream to ensure a stable flow profile for accurate measurement. This is a critical factor for installations in tight spaces. Meters are shown with their typical maximum upstream requirement.
Coriolis / PD
Electromagnetic
Turbine
Ultrasonic / DP
Vortex