electromagnetic flowmeter crk2012
TRANSCRIPT
8/10/2019 Electromagnetic Flowmeter CRK2012
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8/10/2019 Electromagnetic Flowmeter CRK2012
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Why use flow meters
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Why Use Flow Meters
• Accurate flow 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
8/10/2019 Electromagnetic Flowmeter CRK2012
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How do mags Work?
• Any electrical conductor moving in a magnetic field willhave a voltage induced in it. (Faraday’s Law)
• The induced voltage is directly proportional to thestrength 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 conductorwill be directly proportional to the velocity of theconductor (flow stream).
• Flow detection is very dependent on the sensitivity ofthe instrument that measures the weak inducedvoltage.
8/10/2019 Electromagnetic Flowmeter CRK2012
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Quick Physics Lesson
Faradays Law of Induction
E = constant X B X D X V
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E = constant X B X D X V
B = Flux Density
D = Diameter of Pipe
v = Velocity of flow stream
Faraday’s Law
“A conductor moving through amagnetic field will induce an
electromotive force proportional
to the velocity of the conductor”
Operating Principle
8/10/2019 Electromagnetic Flowmeter CRK2012
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Typical Magnetic flowmeter Sensor
configuration
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How do mags work
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Why Does It Work So Well ?
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Accuracy and Repeatability
• 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 ownvelocity.
FLOW
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 pipeturbulences than force velocity type meter
technologies commonly found in agriculture.
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Why are mags different then other
meters
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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 accuratelymeasured with mag meters - velocity range 0.1-
39 fps• Cost of mags are competitively priced withtraditional mechanical meters and will typicallylast much longer
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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 voltrelationship
• Stray voltage or harmonics – Sensors in the meter used to detect voltage change do not know
the difference in stray voltage induced change or conductivefluid 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
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Mag meter highlights
A. Operates based on Faraday’s Law of
electromagnetic induction.
B. Completely open flow tube design:
– No moving parts
– No wear
– No maintenance
C. Not affected by the presence of solidparticles in the liquid. No strainer
required.
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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.
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Highlights (cont)
G. Bi-directional flow measurement
capability.
H. Meter system includes two
components:
– Detector (Flow Tube)
– Signal Amplifier (Electronic Converter)
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Benefits to Good measurements
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Quality measurements = Quality Data
• Initial cost is substantial but will reduce costs over timefor obtaining quality data.
• Quality data will provide higher level of certainty inoverall management of water resources.
• Data will allow users the ability to monitor irrigationsystem with high degree of accuracy.
• Data will provide feedback to users regarding wear onirrigation system and the ability to plan in advance formajor pump and motor servicing.
• Monitoring of pumping throughout a season willprovide feedback on aquifer response due to pumping(drawdown in the well).