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『How Electromagnetic Flow Meter Works: Applies Faraday’s law to interpret moving ionic fluids as an electric conductor generating proportional voltage signals.』Related information(v cone flow meter|rotary gas meter|gallon meter|gear meter|metal tube rotameter|glass tube rotameter|nutating disk meter|transit time ultrasonic flow meter|wedge flow meter|pd meters|hydraulic flow meter|ultrasonic water flow meter|water flow meter|air flow meter|magnetic water flow meter|oxygen flow meter|gas flow meter|argon flow meter|air velocity meter|gasoline flow meter|fuel flow meter|ultrasonic water meter|digital water meter|nitrogen flow meter|solid flow meter|Oxygen tank flow meter|digital water flow meter|diesel fuel flow meter|steam flow meter|02 flow meter|compressed air flow meter|oil flow meter|liquid flow meter)
How an Electromagnetic Flow Meter Works: Faraday Law and Ionic Fluid Signals
Quick Answer: An electromagnetic flow meter applies Faraday law of induction to a conductive liquid. Moving ionic fluids act as an electric conductor inside a magnetic field. The meter reads the voltage signal and converts it to flow rate. Silver Instruments supplies these meters for water, wastewater, chemical, food, and slurry lines from DN15 to DN3000.
Faraday Law Inside the Flow Tube
Two field coils sit on opposite sides of the flow tube. They generate a stable magnetic field across the pipe section. Two electrodes touch the fluid at 90 degrees to the magnetic field. When a conductive liquid moves through this field, it produces a voltage. This is the same Faraday law that applies to electric generators. The voltage appears at the electrodes. The signal is small. Most meters read between 1 and 5 millivolts at normal flow velocity.
The flow tube needs an insulating liner. The liner stops the voltage signal from shorting through the metal pipe. Common liner materials include PTFE, PFA, EPDM, rubber, and polyurethane. The liner choice depends on temperature, pressure, and chemical attack. A PTFE liner in a DN100 meter can handle 150 degree Celsius and 16 bar. A natural rubber liner often works in mining slurries up to 80 degree Celsius.
Why the Fluid Must Be Ionic
Faraday law only works if the fluid has free ions. Tap water, river water, wastewater, acids, caustic soda, beer, milk, and slurry all contain dissolved ions. The minimum conductivity for most industrial electromagnetic flow meters is 5 microsiemens per centimeter. Some high gain converters can work down to 0.5 microsiemens per centimeter. Pure water below 0.1 microsiemens per centimeter does not produce a stable signal. Oil, gas, and most hydrocarbons are non-conductive. They cannot be measured with this technology.
Here is a practical example. A desalination plant in Oman wanted to measure brine reject flow. The brine had conductivity above 20 millisiemens per centimeter. A DN300 electromagnetic flow meter with EPDM lining and Hastelloy C electrodes worked well. But the same plant asked us to meter demineralized water after the ion exchanger. The conductivity was 0.2 microsiemens per centimeter. The signal drifted. We changed the design to an ultrasonic flow meter instead.
Voltage Output and 4-20 mA HART Signals
The raw electrode signal is a few millivolts. The converter filters noise and amplifies the signal. The output is proportional to flow velocity. A typical meter provides 4-20 mA HART, pulse, frequency, and RS485 Modbus RTU. Some models include battery power and GPRS for remote sites. Accuracy is usually 0.5 percent of reading for flows between 0.1 and 15 meters per second. Repeatability is 0.1 percent. Flow rates below 0.1 meters per second can become unstable. The meter should be sized so normal flow sits between 1 and 5 meters per second.
Silver Instruments supplies electromagnetic flow meters with standard flange connections. Available sizes run from DN15 to DN3000. Pressure ratings include PN10, PN16, PN40, and ANSI 150. The converter can measure forward and reverse flow. Empty pipe detection is included on most remote display versions.
Installation Rules That Affect Accuracy
Installation is simple but specific. The pipe must remain full at all times. Air pockets break the circuit between electrode and fluid. The meter needs straight pipe upstream and downstream. We recommend 5 pipe diameters upstream and 3 diameters downstream for
We have seen this on customer sites many times. A water utility in Vietnam installed a DN400 electromagnetic flow meter in a drain line with a free fall after the meter. At low flow, the pipe was only 60 percent full. The meter gave unstable readings. The fix was simple. We moved the meter to a low point where the pipe stayed full and added a back pressure valve downstream. After that, the readings were stable at 0.5 percent deviation.
Recommended Models for Common Applications
Different fluids need different liners and electrodes. Clean water and wastewater normally use EPDM or hard rubber with 316L stainless steel electrodes. This combination is cost effective and lasts 10 years or more. Strong acids, alkalis, and chlorides often need PTFE or PFA lining. Electrodes should be tantalum, titanium, Hastelloy C, or platinum. Food and beverage lines use sanitary connections and PFA lining. Slurry and mining lines use natural rubber or polyurethane with tungsten carbide electrodes.
A palm oil producer in Indonesia needed a DN80 meter for crude palm oil. This fluid is non-conductive and cannot be measured by magnetic flow meter. In that case we supplied an oval gear flow meter for diesel and oil transfer instead. For a brewery in Thailand, a DN50 sanitary electromagnetic flow meter with PFA liner and 316L electrodes handled beer transfer at 3 meters per second. Temperature was 4 degrees Celsius. The meter held accuracy for two years without recalibration.
FAQ: Electromagnetic Flow Meter Working Principle and Selection
Can a magnetic flow meter measure pure water? No. The liquid needs enough dissolved ions. The normal minimum is 5 microsiemens per centimeter. For high purity water use an ultrasonic flow meter.
What is the best flow velocity for an electromagnetic flow meter? Keep normal flow between 1 and 5 meters per second. Below 0.1 meters per second the signal is weak. Above 15 meters per second the liner wears quickly.
Does an electromagnetic flow meter work with oil or gas? No. Oil and gas do not have enough conductivity. Use a Coriolis mass flow meter or vortex flow meter for those fluids.
What signals can I get from Silver Instruments electromagnetic flow meters? 4-20 mA HART, pulse, frequency, and RS485 Modbus RTU are standard. Some battery powered versions include GPRS or NB-IoT.
How do I get a price and quote? Send us your pipe size (DN), flow range (m3/h), pressure (bar), temperature (degree Celsius), and fluid type. We will reply with a selection, quote, and dimensional drawing within one working day.
Contact Silver Automation Instruments
We supply electromagnetic flow meters, ultrasonic flow meters, Coriolis mass flow meters, oval gear flow meters, vortex flow meters, thermal mass flow meters, pressure transmitters, and paperless recorders. Our customers are water and wastewater plants, chemical processors, food and beverage plants, mining operations, and marine systems across Southeast Asia, Oceania, Latin America, Africa, and the Middle East. Send us your flow range and pipe size. You will get a specific model recommendation instead of a generic brochure.
Tel: +86-25-68650347
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Website: flow-meter.com.au