Capacitive TransducesOutlineResourcesRelated Web PagesMajor Types and Uses of Capacitive TransducersCommon uses for Capacitive TransducersSpecificationsHow it worksHow it works-(continued)Slide 10Slide 11Slide 12Slide 13Slide 14LimitationsWhere to BuyCapacitive TransducesNoah A. SundbergECE 5320 MechatronicsAssignment #1OutlineResourcesRelated Web SitesMajor Types and Uses of Capacitive TransducersCommon uses for Capacitive TransducersSpecificationsHow it WorksExample-1Examples-2Examples-3Examples-4Example-5LimitationsWhere to BuyResourcesMechatronics Handbook, Robert H. Bishop, CRC Presswww.discovercircuits.com/resources/tutorials.htmlwww.capsense.com/capsense-wp.pdfMeasurement, Instrumentation, and Sensors Handbook CRCnetBase 1999, CRC PressRelated Web Pageswww.discovercircuits.com/resources/tutorials.htmlwww.capsense.com/capsense-wp.pdfhttp://nts2.balluff.com:8080/appsheet.nsf/7eac47c75cf0f2bc85256594006d701f/37c6ccfcce38150a852569b4006c5488?OpenDocumentMajor Types and Uses of Capacitive TransducersPossition SensorsCapacitive Displacement SensorsCapacitive Differential SensorsVariable Area Displacement SensorsAccelerometersDifferential-Capacitive AccelometerForceCapacitive Force TransducerTactile SensingProximity SensorsCommon uses for Capacitive TransducersMeasuring thicknesses with Capacitive GagingMost flowmeters measure force. Capacitors are common force sensors in these meters.Liquid Level-Measures liquid levels by measuring change in capacitance between two conductive platesMeasure consistancies based on variations of dialectric between two conducting plates-In oil refineries capacitive sensors measure the % of water in oilForce Sensor Capacitors are used as pressure sensitive light diming switches in many homesSpecificationsvery high resolutionhigh sensitivitylow power requirementsworks with high frequency dynamic measurementsCan detect 10^-4 displacementsCan detect both conductive and non conductive objectsDon’t very much with changes in Temperature or pressureCan be used in Noncontact sensingHow it worksCapacitive Transducers are plates seperated by a dielectric. Using the properties and knowledge of electric field and capacitance between separated charged plates we can retrieve information about the physical world. The distance between the plates and the type of the dielectric can both be used to measure the surroundings.How it works-(continued)Ader*e0C=er*e0*A/dHow it works-(continued)Example 1 -Proximity and distance measurementsC=er*e0*A/d where e0 is the permittivity constant and er is the permittivity of a specific substance, A is the area of the plates and D is the distance as the plates are separatedAs the plates separate there is a direct relation between the capacitance and the distance of the plates as is demonstrated in figure 1(from www.capsense.com/capsense-wp.pdf). This relationship can be used in sensing position and proximity by using the capacitance relationship to displacement Fig. 1How it works-(continued)Example 2 –Using the area of overlap can also be used to measure displacement. By measuring the capacitance we can also determine displacement because the capacitance of the object changes proportionally to the area of over lap. By measuring the capacitance the overlapped areas can be detected and the possition of the objects can be determined as is shown if figure 2 1(from www.capsense.com/capsense-wp.pdf) Fig. 2How it works-(continued)Example 3 -Force can be measured similarly to position, buy applying a force on the capacitor the distance between the plates change causing a change in the capacitance this capacitiance change is proportional to the force and therefore the capacitator can be used to measure forcedForce=0ΔdForce= ΔFHow it works-(continued)Example 4 –Thickness Gauging is done by knowing the distance between capacitors and the effective permittivity of the air gap between the plates. Using this you can determine the electric field, then by placing a nonmetallic object with a known permitivity the thickness of that object can be determinedHow it works-(continued)Example 5 –The same technique for Example 4 can be used to determine the percent of two substances in a mixture as long as the plate distance, area of plates, and both substances permitivity are known. After filling the space between the plates with a mixture of the two substances. The ratio of the two substances has is proportional to the capacitance that is measured.LimitationsSensitivity to failure when mishandledLimited range before signal to noise ratio is degrated5-500 VProximity sensing accurate to millimeter rangeWhere to BuyIFM Electronicswww.ifmefector.com/ifmus/web/capacitive.htmBalluffwww.balluff.com/products/Capacitive/default.htmwww.balluff.com/ShortForm/Capacitives.pdfSICKwww.sick.de/de/products/categories/industrial/capacitiveproximity/en.htmlAPLAChttp://www.aplac.com/products/a_pr_mems.htmRDP
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