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8/12/2019 M.E projects PSE

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3D FINITE ELEMENT ANALYSIS OF A FLUXSET

MAGNETIC FIELD SENSOR


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Organization Aim of the Project.

Abstract

Fluxset sensor operating principle

Finite Element Analysis

Calculation of Flux Model of a Fluxset sensor

Meshing

STATIC ANALYSIS Flux distribution plot for various Values of Current


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Aim of the Project

To Model a Magnetic Field Sensor

To Provide Steady-State and Transient Analysis for the

Sensor using Finite Element Method .

To Detect the crack using Fluxset magnetic field sensor


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Abstract

A 3D model of a Fluxset sensor serving to measuremagnetic field are analyzed by the finite element method.

In steady state and transient Analysis, the voltage inducedin the pick-up coil is obtained by computing the flux of thecore of the sensor for several values of exciting currents

and external field.

Detection of crack using the principle of eddy currentNon-destructive testing


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The sensor is made of two solenoids wound on each other. The innerand outer solenoids are called excitation solenoids and pick-upsolenoid.

In the middle of the sensor, a ribbon shaped core is located. The core ismade of very good soft magnetic material with high initial permeabilityand low saturation.

When a current is passed through the excitation solenoid, the corebecome magnetized.

The magnetic induction of this core changes in the presence of externalmagnetic field.

The pick-up solenoid outputs a signal that is coupled through the corefrom the excitation solenoid.

The output of the sensor is proportional to the difference between thevoltage induced in the pick-up and excitation solenoids.


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In the presence of External field,

Before saturation of the core, external field is channeled through thecore producing a high flux due to its high permeability.

At the end of saturation the core permeability falls away and causingthe flux to collapse.

During next half cycle of the excitation waveform the core recoversfrom saturation ,and the flux due to external field is once again at a highlevel until the core saturates in the opposite direction.

A Pick-up coil placed around the core will pick-up these flux changes,the sign of the induced voltage indicating the flux collapse or recovery.


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Pre-processing:It includes the material characteristic modeling, meshing and setting upboundary conditions.

Problem editing:

The magnetization characteristic for the core material, the type of solver

to be used and the tolerance during numerical iterations are specifiedduring problem editing.

Problem solving:

The output of the solver will be a digital version of the magnetic field.

Post Processing:

The mathematical solution which is in the form of nodal potential valueis processed to obtain specific results such as flux linkage, losses etc..,


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Calculation of Flux

To determine the magnetic field distribution in the Fluxset sensor:

The magnetic vector potential A and current density J vector have onlyaxially directed components and flux has X-Y components.

As the reluctivity of the magnetic materials is field dependent andgives the magnetic vector potential A over the cross section.

The magnetic induction B is

B=curl A.

The area enclosed by the coil is

=B.ds


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Calculation of Flux

The expression of the flux will be

Using Stokestheorem,

If the vector potential of the coil sides of the coil is denote as Ar andAlrespectively, then the flux

= l(Ar-Al)

= curlA.ds

S

= A.dlS


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Model of a Fluxset sensor


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3D Model of a Fluxset sensor


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Meshing


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Static Analysis

FLUX PLOT FOR THE FLUXSET SENSOR

Flux distribution in Fluxset sensor for current 1mA

Flux distribution in Fluxset sensor for current 2mA


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Transient Analysis

SENSOR UNDER EXTERNAL FIELD

For simulation of sensor response under external

magnetic field, sensor is placed inside a

solenoid.

For generation of external magnetic field, a DC

current is applied to external solenoid. By varying

this DC current, external field can be changed.


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Model of a Fluxset sensor with external

Magnetic field


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Core saturation in a Fluxset sensor

In the presence of External field without excitation

when core is not saturated by excitation, external

field is concentrating in the core as it has very

high permeability and hence offers very low

reluctance path.


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In the presence of External field with excitation,

when core is saturated by excitation, external

field is not flowing through the core, as core is

already in saturation mode and hence offered

reluctance is very high.


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In the presence of excitation without external field,

The saturation of core without external field is same as that of the core

with external field and excitation .when the core is saturated by

excitation, the external field is not flowing through the core hence

offered reluctance is high.


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Result for Transient Analysis


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Eddy current testing

Simple Coil above a metal surface When an AC current flows in a coil in close proximity to a conducting

surface the magnetic field of the coil will induce circulating (eddy)

currents in that surface. The magnitude and phase of the eddy currents

will affect the loading on the coil and thus its impedance.


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Eddy current testing

Simple Coil above a cracked metal surface

Assume that there is a deep crack in the surface immediately

underneath the coil. This will interrupt or reduce the eddy current flow,

thus decreasing the loading on the coil and increasing its effective

impedance.


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Eddy current testing In eddy current testing, by monitoring the voltage across the coil in

such an arrangement we can detect changes in the material of interest.

That cracks must interrupt the surface eddy current flow to be detected.

Cracks lying parallel to the current path will not cause any significant

interruption and may not be detected


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2D Model of a Fluxset sensor with

metallic plate


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Flux distribution of a Fluxset sensor with

crack in the metallic plate


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Applications of Eddy current testing

Sorting of materials with different heat treatment,microstructure etc.

Detection of flaws / defects in metallic plates, tubes,

rods and bars.

Measurement of non-conductive and conductivecoating thickness.

Measurement of electrical conductivity and magneticpermeability.


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Advantages of Eddy Current Testing

Eddy current test can nearly all metallic materials.

High inspection speeds possible.

Eddy current test can readily detect very shallow and tight surfacefatigue cracks and stress corrosion cracks.

High temperature and on-line testing is possible.

Non-contact / remote / inaccessible testing is possible.

Recording and analysis of inspection data is possible (Computer basedinstruments / systems available with data acquisition, storage, analysisand database management).


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Inference Flux distribution for a Fluxset sensor for various values of excitation

current has been done.

Modeling of a Fluxset sensor with and without external field has been

done.

Static and transient analysis of a Fluxset sensor for various values

external field and excitation current has been done.

Detection of crack from the distorsion of eddy current has beenanalyzed using Eddy current Non-destructive testing.


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References

1.Kurt Preis,Numerical Simulation and Design of a Fluxset Sensor byFinite Element Method, IEEE Transactions onmagnetics,Vol.34,pp:3475-3478,september .1998.

2.Mauricio Bochner, Optimization of the Magnetic Properties ofMaterials for Fluxgate Sensors,Material research,Vol.11,No.2,145-149,April 2008.

3.Rio de Janeiro, Fluxgate Sensor with a special Ring-Core,Szezecin university of technology, Institute of control engineering,September, 17-22,2006.

4.Raffaelle Albanese, Assessment of performance for Fluxset sensorcore,Electromagnetic Non-destructive Evaluation(III),IOS Press.


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