Magnetic flow meter working principle

Magnetic flow meters operate on Faraday’s Law of Electromagnetic Induction. Electrodes mounted on opposite sides of the flow meter body measure a voltage generated by the flow of a conductive liquid in a magnetic field. The voltage generated is proportional to the flow rate. The magnetic flow meter uses a full-sized pipe spool that is lined with one of several types of inert plastic materials. This makes the magnetic flow meter ideal for use in applications with dirty fluids, sewage, or slurries. Mathematically defined as E=k*B*D*V. The induced voltage (E) is directly proportional to the velocity (V) of the fluid moving through the magnetic field (B). The induced voltage is carried to the transmitter through the electrode circuit. The transmitter then converts this voltage into a quantifiable flow velocity. The volumetric flow rate of the fluid is calculated using this known velocity along with the area of the pipe.

How to Use Magnetic Flowmeters

    • Magnetic flowmeters measure the velocity of conductive liquids in pipes, such as water, acids, caustic, and slurries. Magnetic flowmeters can measure properly when the electrical conductivity of the liquid is greater than approximately 5μS/cm. Be careful because using magnetic flowmeters on fluids with low conductivity, such as deionized water, boiler feed water, or hydrocarbons, can cause the flowmeter to turn off and measure zero flow.
    • This flowmeter does not obstruct flow, so it can be applied to clean, sanitary, dirty, corrosive and abrasive liquids. Magnetic flowmeters can be applied to the flow of liquids that are conductive, so hydrocarbons and gases cannot be measured with this technology due to their non-conductive nature and gaseous state, respectively.
    • Magnetic flowmeters do not require much upstream and downstream straight run so they can be installed in relatively short meter runs. Magnetic flowmeters typically require 3-5 diameters of upstream straight run and 0-3 diameters of downstream straight run measured from the plane of the magnetic flowmeter electrodes.
    • Applications for dirty liquids are found in the water, wastewater, mining, mineral processing, power, pulp and paper, and chemical industries. Water and wastewater applications include custody transfer of liquids in force mains between water/wastewater districts. Magnetic flowmeters are used in water treatment plants to measure treated and untreated sewage, process water, water and chemicals. Mining and mineral process industry applications include process water and process slurry flows and heavy media flows.
    • With proper attention to materials of construction, the flow of highly corrosive liquids (such as acid and caustic) and abrasive slurries can be measured. Corrosive liquid applications are commonly found in the chemical industry processes, and in chemical feed systems used in most industries. Slurry applications are commonly found in the mining, mineral processing, pulp and paper, and wastewater industries.




  • Magnetic flowmeters are often used where the liquid is fed using gravity. Be sure that the orientation of the flowmeter is such that the flowmeter is filled with liquid. Failure to ensure that the flowmeter is filled with liquid can significantly affect the flow measurement.
  • Be especially careful when operating magnetic flowmeters in vacuum service because some magnetic flowmeter liners can collapse and be sucked into the pipeline in vacuum service, catastrophically damaging the flowmeter. Note that vacuum conditions can occur in pipes that seemingly are not exposed to vacuum service such as pipes in which a gas can condense (often under abnormal conditions). Similarly, excessive temperature in magnetic flowmeters (even briefly under abnormal conditions) can result in permanent flowmeter damage.

Application Cautions for Magnetic Flowmeters

  • Do not operate a magnetic flowmeter near its electrical conductivity limit because the flowmeter can turn off. Provide an allowance for changing composition and operating conditions that can change the electrical conductivity of the liquid.
  • In typical applications, magnetic flowmeters are sized so that the velocity at maximum flow is approximately 2-3 meters per second. Differential pressure constraints and/or process conditions may preclude application of this general guideline. For example, gravity fed pipes may require a larger magnetic flowmeter to reduce the pressure drop so as to allow the required amount of liquid to pass through the magnetic flowmeter without backing up the piping system. In this application, operating at the same flow rate in the larger flowmeter will result in a lower liquid velocity as compared to the smaller flowmeter.
  • For slurry service, be sure to size magnetic flowmeters to operate above the velocity at which solids settle (typically 1 ft/sec), in order to avoid filling the pipe with solids that can affect the measurement and potentially stop flow. Magnetic flowmeters for abrasive service are usually sized to operate at low velocity (typically below 3 ft/sec) to reduce wear. In abrasive slurry service, the flowmeter should be operated above the velocity at which solids will settle, despite increased wear. These issues may change the range of the flowmeter, so its size may be different than the size for an equivalent flow of clean water.
  • In order of usage, water/wastewater industry, chemical, food and beverage, oil and gas (although not for oil and gas fluids but in support of the processes), power, pulp and paper, metals and mining, and pharmaceutical.

Flow Range :-   

From 0.01 to 100,000 GPM (0.04 to 378.000 l/min)

Design Pressure :

Varies with pipe size; for a 4-in. (100-mm) unit, the maximum is 285 PSIG (20 bars); special units are available with pressure ratings up to 2500 PSIG (172 bars)

Design Temperature: –  

Up to 250 ° F (120 ° C) with Teflon   liners and up to 360 ° F (180 ° C) with ceramic liners.

Price :-

The least expensive designs are the probe versions that cost about $1500. A 1-in.(25-mm) ceramic tube unit can be obtained for under $2000. A 1-in. (25-mm) metallic wafer unit can be obtained for under $3000. An 8-in. (200-mm) flanged meter that has a Teflon liner and stainless electrodes and is provided with 4- to 20-mA DC output, grounding ring, and calibrator will cost about $8000.


Magnetic flow meter advantages and disadvantages

Advantage of Magnetic Flow meter :-

  • The electromagnetic flow meter provides rapid response to flow changes.
  • It provides linear wide range.
  • Measuring range setting can be optimized.
  • It has ability to measure reverse flow.
  • No additional pressure drops.
  • No obstruction is created to flow.
  • It is mainly suitable for hydraulic solid transport.
  • It is unaffected by changes in temperature, density, viscosity, concentration and electrical conductivity.

Disadvantage of Magnetic Flow meter : –

  • It is not suitable for low velocity.
  • It is more expensive.
  • It is suitable for fluids having conductivity greater than 20 micro ohm/cm.
  • Gas inclusion cause errors.

Magnetic Flow meter technical specification :-

 PROJECT 

 

GENERAL

OFFER REFERANCE TAG NO. : SERVICE:Bidder to indicate
 MAKE : MODELBidder to indicate
 PROCESS END CONNECTION[]Full Bore [] insertion type
 FLOW MEASUREMENTInstantaneous flow rate as well as totalized flow
 OUTPUTIsolated 4-20 mA DC with for volumetric flow
 ACCURACY[+ 1% []OTHERS
 FLOW TUBESS304
 REPEATABILITY[]+ 0.2% of calibrated span [] OTHERS
 RANGEABILITY[]10:1 [] OTHERS
 HART COMPATIBILITY[] YES [] NO
 RESPONSE TIME TO STEP CHANGE IN[] 20 MSEC MAX [] OTHERS
 INPUT 
 LOADLOOP RESISTANCE MAXIMUM 500 ohms
 CONTACTS(POTENTIAL FREE): 
 1) CONTACT RELAY OUTPUT FOR[] YES                   [] NO
 ALARM 
 2) NO. OF CONTACTS & RATING( if2 NO & 2 NC , 5A 230V AC
 applicable) 
TECHNICAL

 

DISPLAY/INDICATION:

 
 LOCAL DISPLAY OF FLOW METER WITH LCD SCREEN BACKLIGHT AND

 

[] YES                   [] NO

 KEYPAD. 
 TRANSMITTER:[] INTEGRAL TO FLOW METER [] SEPARATE
 

 

OPERATING VOLTAGE

[] 240V AC [] 24 V DC [] 110 VAC
 TOTALIZING FACILITIES[] YES                   [] NO
 SOFTWARE FEATURES:Compensation for any cross path errors.
 

 

DIAGNOSTICS:

False signal tolerance, Power supply failure,
  hardware failure.
 PROTECTION CLASS

 

[] IP-65 [] IP-68 [] OTHER

 POWER SUPPLY[] 2 WIRE LOOP POWER [] SEPARATE
  POWERED




 

 

ELECTRIC CONNECTION

 

PROCESS END CONNECTION

 

[] PLUG & SOCKET [] CABLE GLAND

Inline Flanged (with matching flange)

 

LINEAR

 

[]Hard Rubber [] OTHERS

 

MEDIUM

RATE OF FLOW (T/HR)

[]CW []ACW[]DMCW [] OTHERS NORMAL :
  MAXIMUM :
 OPERATING PRESS (Kg/cm2g) 
PROCESS DATADESIGN PRESS (Kg/cm2g) 
 OPERATING TEMP (Deg C) 
 DESIGN TEMP (Deg C) 
 PIPE LOCATION PIPE DIRECTION[] UNDERGROUND     []OVERGROUND [] HORIZONTAL      []VERTICAL

 

 

PIPE LINE DATA

PIPE SIZE (OD x THK) mm PIPE MATERIAL

 

AVAILABLE PIPE STRAIGHT LENGTH

 

 

 

 

SUPERVISION

SUPERVISION OF ERECTION & COMMISIONING

 

[] YES

 

[] NO

 




Electromagnetic Flow Meter Inspection and Test Plan 

This article provides you a electromagnetic flow meter inspection and test plan. This is a draft ITP and you need change it to meet your purchase order specification and requirements.

Electromagnetic Flow Meter Inspection and Test Plan TaskVendorTPI InspectionClient
Electromagnetic Flow Meter Checking of characteristics including the following items as minimum: body and connectionHWR
Electromagnetic Flow Meter Mill test reportsHRR
Electromagnetic Flow Meter Non-destructive examination, when specifiedHRR
Electromagnetic Flow Meter Pressure testHHR
Electromagnetic Flow Meter Performance test including: calibration and hysteresisHHR
Electromagnetic Flow Meter Insulation resistance testHWR
Electromagnetic Flow Meter Visual / Dimension InspectionHHR
Electromagnetic Flow Meter Documentation review prior to release(Final activity of Technical Inspection)HHR
Electromagnetic Flow Meter Pre-shipment InspectionHHR





H: Hold Point implies that relevant production activities shall not proceed until the continuation of work is permitted by Purchaser. (Notification req’d)

W: Witness point implies that Purchaser intends to witness the designated inspection feature. If Purchaser decides not to witness the relevant feature, production can proceed without permission of Purchaser. (Notification req’d)

S: Witness, but spot check basis. Initial operation will be witness point and subsequent operation will be witnessed at discretion of Purchaser considering the results of previous inspection. (Notification not req’d : Randam Inspection)

R: Review inspection & test records (Notification not req’d)

General Note :

1) Electromagnetic Flow Meter Witness/hold point by Code Inspector, when applied by Code /Local Regulation, is to comply with its requirements and to specify in Vendor’s ITP.

2) Type of Inspection by Electromagnetic Flow Meter Purchaser may be changed according to equipment criticality and vendor QC evaluation at job stage.

3) When requested in the requisition, detailed Electromagnetic Flow Meter ITP shall be submitted by Vendor.

4) Monitoring/Observation of Electromagnetic Flow Meter Vendor shop daily routine works (i.e.Storage of materials, Adherence to approved procedures, Testing tool calibration check, workmanship, cleanliness and etc.) shall be done by Purchaser during inspection visit.

5) 100% Electromagnetic Flow Meter inspection which is covered by the combination of witness / spot check / record review inspection & tests listed above and vendor’s original QC activity shall be confirmed by Purchaser’s inspector prior to shipment.

6) Unless otherwise specified in REQ., the Electromagnetic Flow Meter sampling Q’ty of ” S (Spot Witness Check) ” shall be as follows:

3 to 20→3Pcs(all if total 2 and less) , 21 to 50→5Pcs, 51 to 100→10Pcs,101 to 200→20Pcs, 201 to 300→30Pcs, 301 to 500→50Pcs

Minimum 25 pcs or more of the commodity shall be arranged for H/W/S inspection and test at one time inspector’s visit as much as practical.

7) Final Electromagnetic Flow Meter Visual Inspection/Documentation Review / Pre-Shipment Inspection may be combined within one time visit.



Electromagnetic Flow Meters Installation Guidelines :

1. Introduction To give the best performance, KROHNE flowmeters must be installed in a correct way. Important instructions should be taken into consideration, like the inlet and outlet length, pipe to be completely filled, direction of the flow, etc. Depending on the measuring principle of each device, the guidelines will differ. In this article we will explain the installation instructions for electromagnetic flow meters. The article cover the following topics:
  • Recommended installation positions for electromagnetic flow meters.
  • Installation guidelines for the WATERFLUX (special electromagnetic flow meter).
  2. Recommended installation positions
  1. An inlet section of at least 5 DN and outlet of at least 3DN is required.
  2. In case of T inlet in front of the device the distance will be doubled to 10 DN.
  3. Control valves must always be installed behind an electromagnetic flowmeter to prevent the sensor to run empty.
4. With electromagnetic flowmeters, it is important that the measuring tube is always completely full. For this reason, the measuring device should never be installed in an upper pipe elbow or a descending pipe line but preferably in front of risers or bent pipelines and elbows. This guarantees a completely full pipeline.
5. Do not install electromagnetic flowmeters directly in front of a free outlet as this does not assure that the pipe will be filled across the entire pipe cross-section.
6. External influences such as magnetic sources and vibrations should always be avoided.

Note

The inlet and outlet sections are measured from the middle of the measuring device, unlike measuring devices with other measuring principles which are measured from the flange.
3. WATERFLUX 3000
The waterflux is a special electromagnetic flowmeter for drinking water that can be installed without inlet and outlet sections.
  • For diameter (25:300) no inlet or outlet required (also the accuracy may decrease depending on the flow rate).
  •  In case of T section before the sensor. 

 Magnetic flowmeter Manufacturer

Magnetic Flow meter Manufacturers / VendorsCountryWebsitePhone No.
ABB AGGERMANYwww.abb.de+49 62143810
ABB LIMITEDUKwww.abb.com+44 1925741111
BOPP & REUTHER MESSTECHNIK GMBHGERMANYwww.burmt.de+49 6232657508
BROOK CROMPTON LARGE INDUSTRIAL MOTORSUKwww.brookcrompton.com+44 1484557200
EMERSONFRANCEwww.amm-marseille.com+33 491602263
EMERSONUKwww.frco.com+44 1162822822
ENDRESS & HAUSERGERMANYwww.endress.com+49 71562090
FUJI ELECTRIC CO LTD.JAPAN +81 425856201
KOBOLD MESSRING GMBHGERMANYwww.kobold.com+49 61922990
KROHNE MESSTECHNIK GMBH & Co. KGGERMANYwww.krohne.de+49 2033010
SIEMENSGERMANYwww.powergeneration.siemens.com+49 9131180
TOKYO KEISO CO.JAPANwww.tokyokeiso.co.jp+81 334311625
YAMATAKEJAPANwww.yamatake.com+81 334862111
YOKOGAWA ELECTRIC CORPU.A.E +973 17358100

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