When you're selecting a flow meter for your industrial process, two technologies often dominate the decision matrix: Coriolis and electromagnetic (magnetic) flow meters. Both are accurate, both are reliable, but they operate on fundamentally different principles and excel in different applications.
This guide compares these two technologies head-to-head so you can make an informed choice based on your specific requirements.
How They Work: Operating Principles
Coriolis Flow Meters
Coriolis metres measure mass flow directly by exploiting the Coriolis effect—a phenomenon where moving objects experience an apparent force when observed from a rotating reference frame. In practical terms:
- Fluid is forced through one or more vibrating tubes at a fixed frequency (typically 80–100 Hz)
- As mass flows through the vibrating tube, the Coriolis force deflects the fluid, causing a phase shift between the inlet and outlet vibrations
- This phase shift is proportional to mass flow rate
- Sensors detect the phase difference, which is converted directly to mass flow
Key advantage: Coriolis metres measure mass flow directly, eliminating the need for separate temperature and pressure compensation.
Electromagnetic Flow Meters
Electromagnetic (mag) metres rely on Faraday's law of electromagnetic induction:
- A magnetic field is generated perpendicular to the flow direction (typically between two coils)
- As conductive fluid passes through this field, it generates an electrical voltage (the motional EMF)
- This voltage is proportional to the volume flow rate: V = B × D × v (voltage = magnetic field × pipe diameter × fluid velocity)
- Electrodes sense this voltage, which is transmitted to an electronics module for flow calculation
Key advantage: Electromagnetic metres have no moving parts and minimal pressure loss, making them ideal for large-diameter applications.
Head-to-Head Comparison
Accuracy and Repeatability
Coriolis metres consistently outperform electromagnetic metres in accuracy. For custody transfer applications—where small measurement errors translate directly to financial loss—Coriolis is the preferred choice.
However, electromagnetic metres are perfectly adequate for most process control and monitoring applications.
- Coriolis: ±0.2% to ±0.5% of reading
- Electromagnetic: ±0.5% to ±2.0% of reading
Turndown Ratio
- Coriolis: Typically 10:1 to 20:1 turndown, with some manufacturers achieving up to 100:1 in laboratory conditions
- Electromagnetic: Typically 20:1 to 40:1 turndown under ideal conditions
Electromagnetic metres can handle wider flow ranges in a single installation, but Coriolis turndown is sufficient for most industrial processes.
Pressure Loss
- Coriolis: 0.5 to 2.0 bar across the metre body (fluid forced through tight, curved tubes)
- Electromagnetic: Minimal pressure drop, typically less than 0.1 bar (no obstruction to flow)
For applications where you're fighting pressure limitations (downstream consumers, long pipelines), electromagnetic metres reduce operational costs by eliminating the need for additional boosting equipment.
Viscosity and Fluid Properties
Coriolis metres work with any fluid—regardless of viscosity, density, or electrical conductivity. This includes:
- Heavy crude oil (1,000+ cP)
- Slurries and suspensions
- Cryogenic liquids
- Non-conductive fluids (pure water, organic solvents)
The operating principle is mass-based, so fluid properties don't affect measurement accuracy.
Electromagnetic metresrequire electrically conductive fluid (typically >5 µS/cm conductivity). They work poorly or not at all with:
- Pure water (unless treated)
- Distilled solvents
- Oils and hydrocarbons (unless conductive additives are present)
- Slurries with non-conductive particulates
Electromagnetic metres excel with water, aqueous solutions, and conductive slurries.
Cost
Coriolis: Capital cost of £3,000–£15,000+ (depending on line size and manufacturer). Typical for 1-inch to 2-inch lines: £5,000–£8,000.
Electromagnetic: Capital cost of £1,500–£8,000 (scales with pipe diameter). Typical for 1-inch line: £2,500–£4,000.
Electromagnetic metres are generally cheaper for smaller pipe diameters. However, for large-diameter installations (8+ inches), both technologies become cost-competitive due to the electromagnetic metre's size-dependent cost.
Maintenance and Longevity
Coriolis: No moving parts (the tubes vibrate, but this is controlled electronically). Minimal wear, typical service life: 15–20 years. Maintenance involves occasional verification calibration.
Electromagnetic: No moving parts or flow obstruction. Electrodes can corrode in harsh chemical environments. Typical service life: 10–15 years (lining degradation).
Coriolis metres tend to have longer, more predictable service lives.
When to Choose Coriolis
1. Custody Transfer and Allocation Metering
If you're measuring high-value product transfer between parties (oil and gas, chemicals, food ingredients), regulatory authorities typically mandate Coriolis for custody transfer. The accuracy and repeatability eliminate disputes over volume/mass discrepancies.
2. Multi-Phase Flow
Coriolis metres can handle gas-liquid mixtures directly. Electromagnetic metres cannot reliably measure gas content and would require separate technology.
3. High-Value Fluids Requiring Mass Accountability
When you need to charge customers by mass rather than volume (e.g., pharmaceutical ingredients, fine chemicals), Coriolis eliminates temperature and pressure correction, reducing disputes.
4. Non-Conductive Fluids
If your fluid is non-conductive (pure water, mineral oil, solvents), Coriolis is your only volumetric option. You cannot use electromagnetic.
5. Harsh Chemical or Slurry Applications
Coriolis metres tolerate abrasive slurries, corrosive chemicals, and extreme viscosities. If your process involves heavy sludge or chemical solvents, Coriolis won't degrade.
When to Choose Electromagnetic
1. Large Diameter Installations (>4 inches)
Electromagnetic metres scale more cost-effectively for large pipes. A 6-inch magnetic metre may cost £8,000; a 6-inch Coriolis metre may cost £20,000+.
2. Conductive Fluids with Minimal Pressure Loss Requirements
If you're measuring water, sewage, or conductive slurries and pressure loss is a constraint (long pipelines, downstream pressure limitations), electromagnetic metres reduce energy costs.
3. Water and Wastewater Applications
Water utilities, treatment plants, and irrigation systems favour electromagnetic metres because of cost, minimal maintenance, and proven reliability with conductive fluids.
4. High-Turndown Process Control
If you need to measure a wide flow range with minimal calibration adjustments, electromagnetic metres offer excellent turndown ratios (20:1–40:1).
5. Low Pressure Drop Requirements
Process lines with limited pressure budget (downstream equipment sensitive to backpressure) benefit from electromagnetic metres' negligible pressure loss.
Real-World Application Examples
Custody Transfer: Oil & Gas North Sea
A North Sea crude oil export facility measures crude from subsea wells. They use Coriolis metres (Emerson Micro Motion) because:
- Regulatory requirement: fiscal measurement must be ±0.2% accuracy minimum
- Multi-phase risk: wet crude with free gas requires mass-based measurement
- Custody handoff: accurate mass transfer is critical for revenue settlement
Water Treatment: UK Municipal Utility
A municipal water treatment plant measures potable water flow to distribution reservoirs. They use electromagnetic metres (Krohne OPTIFLUX) because:
- Fluid is conductive (treated, chlorinated water)
- Large pipe diameter (8 inches) makes electromagnetic cost-effective
- Pressure loss is unacceptable (adds pumping cost)
- High-turndown requirement: plant operates at 20%–100% capacity seasonally
Summary: Decision Tree
Choose Coriolis if:
- Accuracy >±0.5% is non-negotiable
- Fluid is non-conductive
- Multi-phase flow is present
- Mass accountability is critical
- Harsh chemical/slurry environment
Choose Electromagnetic if:
- Accuracy ±1%–2% is acceptable
- Fluid is conductive (water, aqueous solutions)
- Pipe diameter >4 inches
- Pressure loss must be minimised
- Capital cost is a primary constraint
Both technologies are mature, reliable, and proven. The choice comes down to your fluid, your accuracy mandate, and your budget.