Struggling to select the right mag meter size? The secret lies in matching pipe flow rates – not just pipe diameter.

Standard electromagnetic flow meters measure 0.3-10 m/s velocity (0.98-32.8 ft/s), with actual flow range determined by pipe size. For a DN100 (4") pipe, this equals 8.5-850 m³/h (50-5000 GPM). Measurement accuracy degrades below 0.3 m/s, while flows above 10 m/s risk liner damage.

Velocity vs Pipe Diameter Relationship

Here’s how to properly size your mag meter based on real process conditions.

What Is the Flow Range of the Electromagnetic Flow Meter?

Three key numbers define your mag meter’s operating envelope.

Critical ranges: 1) Minimum measurable flow (0.3 m/s), 2) Optimal range (1-5 m/s), 3) Maximum rated flow (10 m/s). Below minimum velocity, electrode signals become unreliable. Always size meters for normal flow near midpoint of their range (3 m/s ideal).

Recommended Flow Velocity Zones

Pipe sizing reference table:

Electromagnetic Flow Meter Diameter Selection Guide

Pipe Size (mm)	Flow Velocity (m/s)	Minimum Flow (m³/h)	Maximum Flow (m³/h)	Typical Applications
DN15 (½")	0.3-10	0.2	6.4	Chemical dosing
DN50 (2")	0.3-10	2.1	71	Process lines
DN100 (4")	0.3-10	8.5	850	Water treatment
DN200 (8")	0.3-10	34	3400	Main pipelines
DN400 (16")	0.3-10	136	13,600	Large water mains

What Is the Normal Range of a Flow Meter?

"Normal" depends entirely on your fluid properties and pipe configuration.

For water applications: Target 1-3 m/s (3.3-9.8 ft/s) for standard accuracy. Viscous fluids require higher velocities (≥1.5 m/s). Liner materials dictate maximum temperatures (PTFE: 100°C; ceramic: 150°C). Always verify chemical compatibility charts¹ before selection.

Velocity Requirements by Viscosity

Key selection factors:

Flow Meter Sizing Decision Matrix

Factor	Low Impact Range	Critical Threshold	Solution
Conductivity	>5 μS/cm	<1 μS/cm	Special electrodes
Solids content	<5% by volume	>10% abrasive	Ceramic liners
Temperature	0-80°C	>150°C	High-temp options
Pressure	<16 bar	>40 bar	Reinforced design
Bubble content	<5%	>15%	Upstream deaeration

What Is the Measuring Range of Ultrasonic Flow Meter?

Ultrasonic meters solve different challenges than mag meters.

Clamp-on ultrasonic meters measure 0.01-25 m/s (0.03-82 ft/s), with insertion types handling 0.3-12 m/s. Unlike mag meters, they work in non-conductive fluids² but require 10x pipe diameter straight runs and 100x particles/bubbles for reliable signals.

Technology Comparison Chart

Technology limitations comparison:

Flow Meter Technology Range Comparison

Parameter	Electromagnetic	Ultrasonic	Notes
Conductivity needed	>5 μS/cm	None	Ultrasonics win
Minimum velocity	0.3 m/s	0.01 m/s	Ultrasonics better
Maximum velocity	10 m/s	25 m/s	Ultrasonics win
Straight pipe needs	5-10D upstream	10-30D upstream	Mag meters easier
Solids tolerance	Medium	Low	EM better

What Is the Rangeability of a Flowmeter?

Rangeability determines how well one meter handles varying flows.

Mag meters offer 10:1 to 100:1 turndown (typical 20:1), meaning a meter rated 10-100 m³/h can measure down to 1 m³/h at reduced accuracy. Higher rangeability costs more – don’t overspecify if your process has stable flows.

Rangeability Visual Guide

Real-world examples:

Practical Rangeability Applications

Application	Flow Variation	Required Turndown	Recommended Type
Constant pump output	±10%	10:1	Standard mag meter
Batch processes	1:50	50:1	High-rangeability
Cooling water	1:20	20:1	Mid-range model
Chemical injection	1:200	100:1	Dual-range meter

Smarter Meter Selection Strategies

Avoid these three common sizing mistakes.

Mistake 1: Choosing pipe-size matched meter without flow data. Solution: Always size based on actual flow rates³, not pipe diameter. Mistake 2: Ignoring future expansion. Solution: Select for 130% of current max flow. Mistake 3: Underestimating low flows. Solution: For >10:1 turndown needs, consider two-meter installation.

Real-world Flow Patterns

Future-proofing considerations:

Long-Term Flow Meter Sizing Factors

Consideration	Short-Term View	Long-Term Solution
Capacity growth	Current flow +10%	Current flow +50%
Process changes	Single fluid	Multi-fluid capable
Maintenance access	Standard	Retractable design
Data integration	4-20mA output	Digital bus options
Environmental factors	Indoor rating	Explosion-proof

Conclusion

Electromagnetic flow meters typically handle 0.3-10 m/s velocities, translating to pipe-size dependent flow ranges. Proper sizing requires actual flow data, not just pipe dimensions. For highly variable flows, prioritize turndown ratio over maximum capacity.