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Difference Between Mass Flow Meter and Magnetic Flow Meter: Direct Mass vs Induction
Quick Answer: A mass flow meter reads direct mass flow in kg/h or t/h. A magnetic flow meter reads volumetric flow and needs liquid conductivity above 5 µS/cm. Select mass flow for batching, custody transfer, or changing density. Select magnetic flow for water, wastewater, acids, and slurries with stable conductivity.
Direct Mass vs Induction: The Core Split
Mass flow meters, mostly Coriolis type, vibrate one or two tubes. The meter detects phase shift caused by fluid inertia. That signal gives direct mass flow. No density compensation is required. A magnetic flow meter works by induction. Coils create a magnetic field. Electrodes pick up voltage generated by a conductive liquid moving through that field. The output is volumetric flow. If you need mass flow from a magnetic meter, you must add density and temperature compensation.
Here is the thing. Many engineers skip this distinction during the selection stage. Later they find out a magnetic flow meter cannot correct for density swings in solvents or multi phase oils. We have seen this on customer sites many times.
Fluid Limits and Conductivity
Magnetic flow meters need a minimum conductivity. Most standard units require 5 µS/cm. Some can work at 0.05 µS/cm with special amplifiers. Pure oils, ultrapure water, and gases do not meet this requirement. Mass flow meters do not care about conductivity. They measure mass directly. They suit oils, LNG, syrups, and non conductive chemicals.
For high viscosity fluids above 200 cP, a Coriolis meter works well if pressure drop is managed. Magnetic flow meters can handle high viscosity too, but they still give volumetric data. In a food plant in Mexico, a chocolate syrup line used a magnetic flow meter and a separate density meter. We replaced both with one Coriolis meter. Cleaning cycles became faster and batch weight accuracy improved.
Accuracy and Repeatability
Coriolis mass flow meters often reach plus or minus 0.1 percent of rate for liquids and 0.35 percent for gas. Magnetic flow meters typically reach plus or minus 0.5 percent of rate. In custody transfer for crude oil in the Middle East, direct mass measurement is preferred. For large water distribution lines in Southeast Asia, magnetic flow meters are accepted because the cost per line is lower and accuracy demands are different.
A mass flow meter also records actual mass flow in kg/h. No need to convert from m3/h. For batch dosing of resins in a chemical plant, that removes one source of error.
Installation and Pipe Size
Magnetic flow meters are simple to install. A straight run of 5D upstream and 3D downstream is common. Grounding rings or electrodes are required. Coriolis mass flow meters need more support. They must be kept full of liquid. Vibration from nearby pumps harms accuracy. In tight skids, we often add pipe supports and flexible connectors.
Sizes matter. Magnetic flow meters run from DN15 to DN2000. Coriolis meters usually run from DN1 to DN300. Larger sizes get heavy and expensive. For a DN400 seawater line in a desalination plant, a magnetic flow meter is the practical choice. For a DN25 dosing line for chemicals, a Coriolis meter is compact and direct.
Cost and Maintenance
Magnetic flow meters are cheaper in large line sizes. A DN100 ma
In slurry service, magnetic flow meters with PTFE liner and 316L electrodes hold up well. Coriolis meters can handle abrasive fluids only if tube wall thickness is selected correctly. Most engineers skip this part. They select a standard wall and later face erosion in high velocity slurry lines.
Which One to Choose
Pick a magnetic flow meter when liquid conductivity is above 5 µS/cm, line size is DN50 or larger, and volumetric flow is acceptable. This covers water, wastewater, acids, caustic, and slurries. Pick a Coriolis mass flow meter when you need direct mass, batching, custody transfer, or when density changes often. This covers oils, solvents, syrups, and liquid gas.
For example, a paint manufacturer in Southeast Asia switched from magnetic flow to Coriolis on solvent batching. Batch weight error dropped from 2.1 percent to 0.3 percent. Last year a customer in Vietnam asked us for a seawater flow meter for desalination plant. They needed a magnetic flow meter with rubber liner and titanium electrodes. We supplied a DN300 unit with 4-20 mA HART output and IP68 sensors.
Outputs and Hazardous Areas
Both meter types support 4-20 mA HART, pulse, and Modbus. For oil and gas sites, request ATEX Zone 1 or IECEx certification. Silver Instruments supplies ATEX approved Coriolis and magnetic models with SS316, Hastelloy C, or PTFE wetted parts. Temperature ratings depend on process. Standard magnetic meters tolerate 120 °C with PTFE liner. Coriolis meters can handle 200 °C or higher with remote electronics.
FAQ: Mass Flow Meter vs Magnetic Flow Meter
Q: Can a magnetic flow meter measure mass flow?
A: Not directly. It measures volumetric flow. You need a density value and temperature compensation to calculate mass flow. A Coriolis meter gives mass flow directly.
Q: What is the minimum conductivity for a magnetic flow meter?
A: Standard meters need 5 µS/cm. Some low conductivity models work down to 0.05 µS/cm. Pure oils and gases are not suitable.
Q: Which meter is better for custody transfer?
A: Coriolis mass flow meters are often preferred because they measure direct mass. They also offer high accuracy around plus or minus 0.1 percent of rate.
Q: Can a magnetic flow meter handle sludge or slurry?
A: Yes. Use a PTFE or rubber liner and electrodes sized for the solid content. Magnetic flow meters work well in sludge and mining slurry because there is no obstruction.
Q: What should I send for a quote?
A: Send us your fluid name, pressure in bar, temperature in °C, pipe size in DN, and flow range. Also mention conductivity if you think it is low.
Contact Silver Automation Instruments for a direct comparison. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610. Send us your pressure in bar, temperature in °C, pipe size in DN, and flow range. We will reply with model options and price.
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