Brett Anderson Sensor

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Inductive Proximity Sensors

Brett Anderson

ECE 5230

Assignment #1


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Outline

1. To Explore Further

2. Major Applications

3. Theory of Operation

4. Possible Measurements

5. Sensor Outputs 6. Applications

7. Conclusions


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References

www.bently.com

www.allenbradley.com

http://www.ndt-

ed.org/EducationResources/Community

College/EddyCurrents/Physics/mutualin

ductance.htm

www.davidson.com/au
http://www.bently.com/http://www.allenbradley.com/http://www.allenbradley.com/http://www.bently.com/


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To Explore Further

An interesting paper on applications:

www.bently.com/articles/apnotes/an04

7.aspHere is a great presentation on

monitoring industrial systems:

www.vibration.org/Meeting/0903/Gearbox%20Spectral%20Components

%20Presentation%20V2.ppt


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Major Applications

The Eddy Current probe has manyapplications in industry

These applications are varied, but allrequire reliable, accurate results

These sensors are robust, and can

typically handle extreme environments These applications are discussed in

greater detail in later slides


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Theory of Operation

These sensors use mutual inductancebetween a known inductor and a

conductive materialCommonly referred to as eddy current

probes

Mutual inductance is a function of thedistance between the inductor and thematerial


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Source: http://www.ndt-

ed.org/EducationResources/CommunityCollege/EddyCurrents/

How Eddy Currents Work

An inductive coil is

placed near a

conductive surfaceAn AC voltage

(typically around

2Mhz) is applied to

the coil

Mutual inductance

begins to occur


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http://www.ndt-



The coil generates a

magnetic field

Circular or EddyCurrents begin to

flow in the

conductive material

These currents

resemble an eddy in

a stream of water


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http://www.ndt-



The Eddy Currents

generate their own

magnetic field These fields have

interaction with the

coil through mutual

inductance

This leads to a

measurable result


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What can be measured?

Electrical conductivity and magnetic

permeability of the target material

The amount of material cutting throughthe coils of the magnetic field

The condition of the material(whether it

contains cracks or defects

Lift-Off


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What is Lift-Off?

Lift-Off is a very important measurementthat can be made by Eddy Current

Sensors It represents the distance from the coil

to the test material

This leads to a great number ofindustrial, manufacturing, and otherimportant applications


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Sensor Output in Proximity

ApplicationsA demodulator demodulates the signal

from the sensor, and outputs a DC

voltage which is proportional to thedistance from the sensor to the

conductive target

This output voltage is linear over thespecified range of the specific sensor


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Typical Sensor Output

Provides very highresolution outputover ranges on theorder of millimeters

The range an beincreaseddepending on theapplication, buttypically not morethat several inches


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Calibration

From the factory, most proximity probes are

calibrated to measure 4140 steel

Because different materials have differentconductivity and permeability, special

calibration is needed to ensure accurate

measurement of each specific material

This usually involves some alteration of the

signal conditioning and demodulation process


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Source: AllenBradly.com

Applications

Can be used as an

encoder that

monitors rotation Can measure thing

like speed and

acceleration


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Encoder Output

This is what the output

looks like when being

used as an encoder

The peaks represent

the teeth on the

sprocket

Speed and acceleration

can be determined fromthis output data


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Applications(Cont)

Used in AutomatedAssembly lines

Sensor detects eachpart as it passes

Provides Accurate,Real-Time

information aboutquantity and qualityin manufacturingprocesses


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Another Application

Inductive sensorsmonitor automatedmachinery

They can detectanything out of theordinary and serve as afail safe shutoff, whichcan save millions of

dollars in preventingdamage tomalfunctioningmachinery.


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Power Systems Applications

High Power turbines often operate in high

temperature, strenuous environments

Inductive Sensors and be linked to a datasystem through a robust cable allowing for

the monitoring of these systems

Information gathered by these sensors can

greatly add to the life and health of high

power turbines and generators


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Turbine Shaft Orbit Monitoring

Two inductive sensors can be used tomonitor the health of a turbine

When placed 90 degrees apart, they canmonitor the X and Y position of the shaft as itrotates

When bearing start to go out, the movement

in the X and Y direction begins to increase This is detected by the sensors, and the

bearings can be replaced before seriousdamage occurs


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Illustration of Orbit Monitoring


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Vibration Monitoring

An inductive sensor can

monitor the vibration of

a turbine shaft

Typically, there is

maximum limit that the

shaft is allowed to

vibrate, once that point

is passed, the system isshut down to prevent

serious damage


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General Applications

Good for many short distance, highresolution applications

Can be used to detect the presence orabsence of conductive material

Good for long distance monitoring ofmachinery and industrial devices

Usually works well in extremeenvironments


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Other Applications

Quality Control

Autonomous

removal of bad partson an assembly line

Reliable and

consistent results


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Other Applications(Cont)

Real-Time

information on the

position of railroadtrack switches

Reliable due to

resistance to

changing conditions


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Limitations

Very short range of measurement

Material being measured must be

conductive

Target must be larger than the sensor

tip

Can only measure displacement in

relation to the sensor


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Conclusion

Inductive sensors operate on the

principle of mutual induction

They are useful in a wide variety ofapplications

They provide high-resolution, reliable

outputsCan be used in varied conditions

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