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Electromagnetic Flow Meters
Guide teacher: Dr. Ali Karimpour
Associate Professor
Ferdowsi University of Mashhad
Presented by: Leila Samizadeh
Lecture 12
Topics to be covered include
v
v
Flow Meter
Electromagnetic flow meter
u Introduction
u Application
u Specifications
u Advantage and Disadvantage
u Electrodes
u Excitation
u Example
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Dr. Ali Karimpour Sep 2014
Lecture 12
Flow Meter
Flow Meter: Flow measurement is the quantification of bulk fluid movement.
 Electromagnetic Flow Meter
 Oscillator Flow Meter
 Mass Flow Meter
 Thermal Mass Flow Meter
 Coriolis Mass Flow Meter
 Variable Area Flow Meter
 Ultrasonic Flow Meter
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Lecture 12
Flow Meter






Pitot Tube Flow Meter
Turbine-Type Flow Meter
Positive-Displacement Flow Meter
Open channel Flow Meter
Vortex Flow Meter
Rotameter
• Piston-Type
• Float-Type
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Lecture 12
How to choose?
Application
 Type of fluid
 Temperature
 Portable or Fixed
 Accuracy
 Price
 Cost of maintenance

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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
Flow Meter
 Electromagnetic flow meter
 Introduction
 Specifications
 Application
 Advantage and Disadvantage
 Electrodes
 Excitation
 Example

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Dr. Ali Karimpour Sep 2014
Lecture 12
Electromagnetic Flow Meter
The measuring principle of the electromagnetic flowmeter (Magmeter)
is based upon the Faraday's Law of electromagnetic induction.
 Following Faraday’s Law, flow of a conductive liquid through the
magnetic field will cause a voltage signal to be sensed by electrodes
located on the flow tube walls. When the fluid moves faster, more
voltage is generated.

E= B.V.L
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Dr. Ali Karimpour Sep 2014
Lecture 12
Electromagnetic Flow Meter
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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
v
v
Flow Meter
Electromagnetic flow meter
u Introduction
u Specifications
u Application
u Advantage and Disadvantage
u Electrodes
u Excitation
u Example
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Dr. Ali Karimpour Sep 2014
Lecture 12
Specifications

Just use for liquid with fluid conductivity greater than 5μS/cm

Does not usage for gases and Hydrocarbons

Run from 0.1 inch to 104 inches or more in diameter

Flow rate of 0.05 to 10 m/sec (0.15 to 33 ft/sec)

No moving parts or flow obstructions
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Lecture 12
WHY DOES WATER CONDUCT ELECTRICITY?
H2O itself is a stable molecule, and will not conduct electricity. So, why
does electricity flow in water?
 Besides H2O (water molecules), Ca2+ (Calcium ions) and Mg2+
(Magnesium ions) exist within water.

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Lecture 12
Accuracy

The real velocity in each cross section is the mean of whole point of
cross section.
This has best accuracy in other flowmeters.
 Accurate to +/-0.25% of reading.

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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
v
v
Flow Meter
Electromagnetic flow meter
u Introduction
u Application
u Specifications
u Advantage and Disadvantage
u Electrodes
u Excitation
u Example
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Dr. Ali Karimpour Sep 2014
Lecture 12
Applications
Sludge, Slurries, Sewage, Water and Waste water
 Building Automation (HVAC)
 Food & Beverage
 Chemical
 Pulp and paper
 Acids
 Mining, mineral processing

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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
v
v
Flow Meter
Electromagnetic flow meter
u Introduction
u Application
u Specifications
u Advantage and Disadvantage
u Electrodes
u Excitation
u Example
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Dr. Ali Karimpour Sep 2014
Lecture 12
Advantage
No moving parts or flow obstructions
 Accurate to +/-0.25% of reading
 Relatively unaffected by viscosity, temperature and pressure as long as
the magmeter is selected based on the process conditions
 Can respond well to rapid changes in flow

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Lecture 12
Disadvantage
Accuracy may be affected by air space in the pipe
 Water must contain a certain amount of Microsiemens (µS), giving it the
power to conduct heat and/or electricity
 Cannot detect gases and liquids without electrical conductivity

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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
Flow Meter
 Electromagnetic flow meter
 Introduction
 Application
 Specifications
 Advantage and Disadvantage
 Electrodes
 Excitation
 Example

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Dr. Ali Karimpour Sep 2014
Lecture 12
Electrodes
1)
2)
Contacting electrodes
 Its low cost.
 Its resistance to abrasion and wear.
 Its insensitivity to nuclear radiation.
 The ceramic tube cannot tolerate bending, tension, or sudden cooling
 Cannot handle oxidizing acids or hot and concentrated caustic
Non-contacting electrodes
 These designs are also better suited for severe coating applications.
 Non-contacting electrodes can "read" fluids having 100 times less
conductivity than required to actuate conventional flowtubes.
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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
Flow Meter
 Electromagnetic flow meter
 Introduction
 Application
 Specifications
 Advantage and Disadvantage
 Electrodes
 Excitation
 Example

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Lecture 12
Excitation type
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Dr. Ali Karimpour Sep 2014
Lecture 12
Excitation type
DC current excitation
 Used since 1832
 Used in liquid state metal flow measurement in nuclear energy
industry but has eddy current
 Did not immune to noise
 AC sine wave (50 or 60 Hz)
 Used since 1920, Commercialized in 1950
 Did not have a stable zero point
 Used a large amount of energy (300 W)
 immune to noise

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Dr. Ali Karimpour Sep 2014
Lecture 12
Excitation type


Low frequency dc rectangle
 Used since 1975
 Frequency is 6.25 Hz to 11 Hz
 Low zero-point drift
 less immune to noise
 The low sampling rates also made them sluggish when responding to rapidly
changing flow rates.
Tri-state low frequency dc
 Used since 1978
 Calibrate zero point
 Duty cycle is 1/2 that of rectangle
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Lecture 12
Excitation type

Dual-frequency excitation
 A low-frequency component of 6.25 Hz and a high-frequency
component of 75 Hz
 Can minimize serofluid noise
 Low zero-point drift
 Fast response
 Complex operation
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Lecture 12
Excitation type

Programmable pulse width
 Use microprocessor to control excitation pulse width and frequency
 Immune of noise
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Lecture 12
Excitation type
Not stable
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Lecture 12
An H-bridge controls the sensor coil excitation phase
 Excitation currents for electromagnetic flow meters tend to be quite large
relative to other flow techniques, with 125 mA to 250 mA.
 Current up to 500 mA or 1 A would be used for larger diameter pipes.
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Lecture 12
Linear regulated current sink
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Lecture 12
Reducing power consumption



Early magmeters needed a powerful magnetic field to create a signal
strong enough to be measured accurately.
Units that once drew 300 W can now operate with 10 W to 15 W.
These low-power units have some limitations. Check with your supplier,
but they typically require relatively high conductivity (10 µS to 20 µS)
for the process liquid .
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Lecture 12
Magnetic Flow Meter Piping Requirements
Always pipe an electromagnetic flowmeter so it is full of liquid.
 You can install magmeters in horizontal lines, but best practice calls for
installation in vertical lines with upwards flow.
 When installing magmeters, avoid downward flows.

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Dr. Ali Karimpour Sep 2014
Lecture 12
Grounding
If the pipeline is made of non-conducting materials, such as plastic these
stray ground potentials can cause significant measuring errors.
 If the pipeline is made of an unlined conducting material, the process
ground should be excellent.

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Dr. Ali Karimpour Sep 2014
Lecture 12
Topics to be covered include
Flow Meter
 Electromagnetic flow meter
 Introduction
 Application
 Specifications
 Advantage and Disadvantage
 Electrodes
 Excitation
 Example

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Lecture 12
OMEGA Magnetic Flow Meter
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Lecture 12
Example
 SPECIFICATIONS
Power: 12 to 24 Vdc, 250 mA
Flow Range: 0.28 to 20 ft/sec (0.08 to 6.09 m/sec)
Ambient Temperature: -17 to 72°C (0 to 160°F)
Fluid Temperature: 0 to 93°C (32 to 200°F)
Maximum Pressure: 13.8 bar (200 psi)
Minimum Conductivity: 20 µS/cm
Accuracy: ±1% of full scale
Output: Square wave pulse, opto isolated, This square wave signal can be
sent directly to a PLC, control or converted to 4 to 20 mA.
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‫‪Lecture 12‬‬
‫‪Exercises‬‬
‫‪ )1‬فلومترهای مغناطیس ی برای چه نوع ازسیاالت مناسب و نامناسب است؟ چرا؟‬
‫فلومتر های الکترومغناطیس ی فقط برای مایعاتی با قابلیت رسانایی باالتر از‪ 5μS/cm‬مناسب هستند و برای هیدرو کربن ها به دلیل نارسانایی و گازها بدلیل اغتشاش زیادشان‬
‫نامناسب هستند‪.‬‬
‫‪ )2‬مزایا فلومترهای مغناطیس ی را بیان کنید ؟‬
‫الف ) نداشتن قسمت ها‪ d‬متحرک و گردان در نتیجه نیازی چندانی به تعمیر و نگهداری ندارد‪.‬‬
‫ب ) دقت فوق العاده باالی این فلومتر نسبت به فلومترهای دیگر (‪)Accurate to +/-0.25% of reading‬‬
‫ج) حساسیت باالی نسبت به تغییر ناگهانی سرعت سیال دارد‪.‬‬
‫د) تاثیری بر سرعت‪ ،‬فشار‪ ،‬چگالی و چسبندگی مایع نمی گذارد‪.‬‬
‫‪ )3‬فلومترهای مغناطیس ی براساس چه قانون فیزیکی عمل می کند ؟ قانون را برای این فلومترها بیان کنید؟ فلومترهای الکترومغناطیس ی بر اساس قانون القا فارادی کار می کنند‪ .‬بر‬
‫اساس این قانون اگر یک جسم هادی درون یک میدان مغناطیس ی حرکت کند ‪ ،‬ولتاژ در دو سر هادی القا میشود‪ .‬این ولتاژ القایی متناسب با سرعت هادی خواهد بود‪.‬‬
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Lecture 12
REFERENCES
1)
2)
3)
4)
5)
http://cadillacmeter.com
http://www.omega.com
https://www.isa.org
http://www.analog.com
https://fa.wikipedia.org
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