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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 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