Electromagnetic Flowmeter CRK2012

8/10/2019 Electromagnetic Flowmeter CRK2012

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Why use flow meters



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



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.



Quick Physics Lesson

Faradays Law of Induction

E = constant X B X D X V



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



Typical Magnetic flowmeter Sensor

configuration



How do mags work





Why Does It Work So Well ?



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.



Why are mags different then other

meters



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



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



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.



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.



Highlights (cont)

G. Bi-directional flow measurement

capability.

H. Meter system includes two

components:

– Detector (Flow Tube)

– Signal Amplifier (Electronic Converter)



Benefits to Good measurements



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).

Documents

Electromagnetic Flowmeter CRK2012