Inductive Proximity SensorsOutlineReferencesTo Explore FurtherMajor ApplicationsTheory of OperationHow “Eddy Currents” WorkSlide 8Slide 9What can be measured?What is Lift-Off?Sensor Output in Proximity ApplicationsTypical Sensor OutputCalibrationApplicationsEncoder OutputApplications(Cont)Another ApplicationPower Systems ApplicationsTurbine Shaft Orbit MonitoringIllustration of Orbit MonitoringVibration MonitoringGeneral ApplicationsOther ApplicationsOther Applications(Cont)LimitationsConclusionInductive Proximity SensorsBrett AndersonECE 5230Assignment #1Outline1. To Explore Further2. Major Applications3. Theory of Operation4. Possible Measurements5. Sensor Outputs6. Applications7. ConclusionsReferenceswww.bently.comwww.allenbradley.comhttp://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/mutualinductance.htm www.davidson.com/auTo Explore FurtherAn interesting paper on applications: www.b ently.com/articles/apnotes/an047.asp Here is a great presentation on monitoring industrial systems: www.vibration.org/Meeting/0903/ Gearbox%20Spectral%20Components%20Presentation%20V2.pptMajor ApplicationsThe Eddy Current probe has many applications in industryThese applications are varied, but all require reliable, accurate resultsThese sensors are robust, and can typically handle extreme environmentsThese applications are discussed in greater detail in later slidesTheory of OperationThese sensors use mutual inductance between a known inductor and a conductive materialCommonly referred to as “eddy current” probesMutual inductance is a function of the distance between the inductor and the materialSource: http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/How “Eddy Currents” WorkAn inductive coil is placed near a conductive surfaceAn AC voltage (typically around 2Mhz) is applied to the coilMutual inductance begins to occurhttp://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/How “Eddy Currents” WorkThe coil generates a magnetic fieldCircular or “Eddy Currents” begin to flow in the conductive materialThese currents resemble an eddy in a stream of waterhttp://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/How “Eddy Currents” WorkThe Eddy Currents generate their own magnetic fieldThese fields have interaction with the coil through mutual inductanceThis leads to a measurable resultWhat can be measured?Electrical conductivity and magnetic permeability of the target materialThe amount of material cutting through the coils of the magnetic fieldThe condition of the material(whether it contains cracks or defectsLift-OffWhat is Lift-Off?Lift-Off is a very important measurement that can be made by Eddy Current SensorsIt represents the distance from the coil to the test materialThis leads to a great number of industrial, manufacturing, and other important applicationsSensor Output in Proximity ApplicationsA demodulator demodulates the signal from the sensor, and outputs a DC voltage which is proportional to the distance from the sensor to the conductive targetThis output voltage is linear over the specified range of the specific sensorTypical Sensor OutputProvides very high resolution output over ranges on the order of millimetersThe range an be increased depending on the application, but typically not more that several inchesCalibrationFrom the factory, most proximity probes are calibrated to measure 4140 steelBecause different materials have different conductivity and permeability, special calibration is needed to ensure accurate measurement of each specific materialThis usually involves some alteration of the signal conditioning and demodulation processSource: AllenBradly.comApplicationsCan be used as an encoder that monitors rotationCan measure thing like speed and accelerationSource: AllenBradly.comEncoder OutputThis is what the output looks like when being used as an encoderThe peaks represent the teeth on the sprocketSpeed and acceleration can be determined from this output dataSource: AllenBradly.comApplications(Cont)Used in Automated Assembly linesSensor detects each part as it passesProvides Accurate, Real-Time information about quantity and quality in manufacturing processesSource: AllenBradly.comAnother ApplicationInductive sensors monitor automated machineryThey can detect anything out of the ordinary and serve as a fail safe shutoff, which can save millions of dollars in preventing damage to malfunctioning machinery.Power Systems ApplicationsHigh Power turbines often operate in high temperature, strenuous environmentsInductive Sensors and be linked to a data system through a robust cable allowing for the monitoring of these systemsInformation gathered by these sensors can greatly add to the life and health of high power turbines and generatorsTurbine Shaft Orbit MonitoringTwo inductive sensors can be used to monitor the health of a turbineWhen placed 90 degrees apart, they can monitor the X and Y position of the shaft as it rotatesWhen bearing start to go out, the movement in the X and Y direction begins to increaseThis is detected by the sensors, and the bearings can be replaced before serious damage occursIllustration of Orbit MonitoringVibration MonitoringAn inductive sensor can monitor the vibration of a turbine shaftTypically, there is maximum limit that the shaft is allowed to vibrate, once that point is passed, the system is shut down to prevent serious damageGeneral ApplicationsGood for many short distance, high resolution applicationsCan be used to detect the presence or absence of conductive materialGood for long distance monitoring of machinery and industrial devicesUsually works well in extreme environmentsOther ApplicationsQuality ControlAutonomous removal of bad parts on an assembly lineReliable and consistent resultsOther Applications(Cont)Real-Time information on the position of railroad track switchesReliable due to resistance to changing conditionsLimitationsVery short range of measurementMaterial being measured must be conductiveTarget must be larger than the sensor tipCan only measure displacement in relation to the sensorConclusionInductive sensors operate on the principle of mutual inductionThey are useful in a wide variety of
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