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Electromagnetic Flowmeter

Electromagnetic Flowmeter. Why use flow meters What is a magnetic flow meter How do they work How are the different from other meters Items that will impact the use of mag meters Benefits of good measurements. Why use flow meters. Why Use Flow Meters.

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Electromagnetic Flowmeter

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  1. Electromagnetic Flowmeter • Why use flow meters • What is a magnetic flow meter • How do they work • How are the different from other meters • Items that will impact the use of mag meters • Benefits of good measurements

  2. Why use flow meters

  3. Why Use Flow Meters • Accurateflow measurements eliminates guess work in water usage measurements • Guess work includes, pivot package, PCC work, acreage and crop water requirements • Provides only accurate means for measurement on complex irrigation systems • Will help to better manage irrigation system and save time, water and money

  4. How do mags Work? • Any electrical conductor moving in a magnetic field will have a voltage induced in it. (Faraday’s Law) • The induced voltage is directly proportional to the strength of the magnetic field, and the speed of the conductor moving through the field. • If the conductor is a fluid flowing through a fixed magnetic field, the voltage induced in the conductor will be directly proportional to the velocity of the conductor (flow stream). • Flow detection is very dependent on the sensitivity of the instrument that measures the weak induced voltage.

  5. Quick Physics LessonFaradays Law of Induction E = constant X B X D X V

  6. Operating Principle Faraday’s Law “A conductor moving through a magnetic field will induce an electromotive force proportional to the velocity of the conductor” E = constant X B X D X V B = Flux Density D = Diameter of Pipe v = Velocity of flow stream

  7. Typical Magnetic flowmeter Sensor configuration

  8. How do mags work

  9. Why Does It Work So Well ?

  10. Accuracy and Repeatability A Mag Meter averages the sum of the voltage of all particles: The result - a Mag Meter will produce superior accuracy and repeatability and is significantly less affected by pipe turbulences than force velocity type meter technologies commonly found in agriculture. • The voltage induced is a good average of the flow velocity because: • Water is made up of many particles. • Each particle generates a voltage based on its own velocity.

  11. Why are mags different then other meters

  12. Mags vs. Force Velocity meters • No moving parts = No mechanical failure • Minimal pressure loss across meter • Mechanical meters need enough energy in the water to accurately measure flows • Low flow measurements = large errors in accuracy • Low flow measurements are accurately measured with mag meters - velocity range 0.1-39 fps • Cost of mags are competitively priced with traditional mechanical meters and will typically last much longer

  13. Items that will affect mag meters • Significant amounts of air entrained in the water. • Air and water have diabolically different conductive properties and entrained air will change the velocity to induced volt relationship • Stray voltage or harmonics • Sensors in the meter used to detect voltage change do not know the difference in stray voltage induced change or conductive fluid induced change in the magnetic field • Partially filled pipe flow • Assumption with all closed conduit measurement is that the cross-sectional area is constant- Q = (Velocity)(Cross-sectional area) • Submergence must occur at all times for meter to work properly

  14. Mag meter highlights • Operates based on Faraday’s Law of electromagnetic induction. • Completely open flow tube design: • No moving parts • No wear • No maintenance • Not affected by the presence of solid particles in the liquid. No strainer required.

  15. Highlights (cont) • D. Operates in any meter orientation as long as the pipe is full • Horizontal • Vertical • Incline Piping • E. Minimum Head Loss: Equal to a section of pipe of the same length. • F. Minimum Piping Requirements: Three diameters of straight pipe upstream of the meter and two diameters downstream.

  16. Highlights (cont) • G. Bi-directional flow measurement capability. • H. Meter system includes two components: • Detector (Flow Tube) • Signal Amplifier (Electronic Converter)

  17. Benefits to Good measurements

  18. Quality measurements = Quality Data • Initial cost is substantial but will reduce costs over time for obtaining quality data. • Quality data will provide higher level of certainty in overall management of water resources. • Data will allow users the ability to monitor irrigation system with high degree of accuracy. • Data will provide feedback to users regarding wear on irrigation system and the ability to plan in advance for major pump and motor servicing. • Monitoring of pumping throughout a season will provide feedback on aquifer response due to pumping (drawdown in the well).

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