Transcript electromagnetic_flowmeters_Samizadeh

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
2
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
3
Dr. Ali Karimpour Sep 2014
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
4
Dr. Ali Karimpour Sep 2014
Lecture 12
How to choose?
Application
 Type of fluid
 Temperature
 Portable or Fixed
 Accuracy
 Price
 Cost of maintenance

5
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

6
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
7
Dr. Ali Karimpour Sep 2014
Lecture 12
Electromagnetic Flow Meter
8
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
9
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
10
Dr. Ali Karimpour Sep 2014
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.

11
Dr. Ali Karimpour Sep 2014
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.

12
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
13
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

14
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
15
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

16
Dr. Ali Karimpour Sep 2014
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

17
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

18
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.
19
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

20
Dr. Ali Karimpour Sep 2014
Lecture 12
Excitation type
21
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

22
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
23
Dr. Ali Karimpour Sep 2014
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
24
Dr. Ali Karimpour Sep 2014
Lecture 12
Excitation type

Programmable pulse width
 Use microprocessor to control excitation pulse width and frequency
 Immune of noise
25
Dr. Ali Karimpour Sep 2014
Lecture 12
Excitation type
Not stable
26
Dr. Ali Karimpour Sep 2014
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.
27
Dr. Ali Karimpour Sep 2014
Lecture 12
Linear regulated current sink
28
Dr. Ali Karimpour Sep 2014
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 .
29
Dr. Ali Karimpour Sep 2014
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.

30
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.

31
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

32
Dr. Ali Karimpour Sep 2014
Lecture 12
OMEGA Magnetic Flow Meter
33
Dr. Ali Karimpour Sep 2014
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.
34
Dr. Ali Karimpour Sep 2014
‫‪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.‬‬
‫‪35‬‬
‫‪Dr. Ali Karimpour Sep 2014‬‬
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
36
Dr. Ali Karimpour Sep 2014