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Capacitive Transduces

Capacitive Transduces. Noah A. Sundberg ECE 5320 Mechatronics Assignment #1. Outline. Resources Related Web Sites Major Types and Uses of Capacitive Transducers Common uses for Capacitive Transducers Specifications How it Works Example-1 Examples-2 Examples-3 Examples-4 Example-5

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Capacitive Transduces

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  1. Capacitive Transduces Noah A. Sundberg ECE 5320 Mechatronics Assignment #1

  2. Outline • Resources • Related Web Sites • Major Types and Uses of Capacitive Transducers • Common uses for Capacitive Transducers • Specifications • How it Works • Example-1 • Examples-2 • Examples-3 • Examples-4 • Example-5 • Limitations • Where to Buy

  3. Resources • Mechatronics Handbook, Robert H. Bishop, CRC Press • www.discovercircuits.com/resources/tutorials.html • www.capsense.com/capsense-wp.pdf • Measurement, Instrumentation, and Sensors Handbook CRCnetBase 1999, CRC Press

  4. Related Web Pages • www.discovercircuits.com/resources/tutorials.html • www.capsense.com/capsense-wp.pdf • http://nts2.balluff.com:8080/appsheet.nsf/7eac47c75cf0f2bc85256594006d701f/37c6ccfcce38150a852569b4006c5488?OpenDocument

  5. Major Types and Uses of Capacitive Transducers • Possition Sensors • Capacitive Displacement Sensors • Capacitive Differential Sensors • Variable Area Displacement Sensors • Accelerometers • Differential-Capacitive Accelometer • Force • Capacitive Force Transducer • Tactile Sensing • Proximity Sensors

  6. Common uses for Capacitive Transducers • Measuring thicknesses with Capacitive Gaging • Most flowmeters measure force. Capacitors are common force sensors in these meters. • Liquid Level-Measures liquid levels by measuring change in capacitance between two conductive plates • Measure consistancies based on variations of dialectric between two conducting plates-In oil refineries capacitive sensors measure the % of water in oil • Force Sensor Capacitors are used as pressure sensitive light diming switches in many homes

  7. Specifications • very high resolution • high sensitivity • low power requirements • works with high frequency dynamic measurements • Can detect 10^-4 displacements • Can detect both conductive and non conductive objects • Don’t very much with changes in Temperature or pressure • Can be used in Noncontact sensing

  8. How it works Capacitive 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.

  9. How it works-(continued) C=er*e0*A/d A d er*e0

  10. How it works-(continued) Example 1 -Proximity and distance measurements C=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 separated As 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. 1

  11. How 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. 2

  12. How 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 force Force= ΔF Force=0 Δd d

  13. How 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 determined

  14. How 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.

  15. Limitations • Sensitivity to failure when mishandled • Limited range before signal to noise ratio is degrated • 5-500 V • Proximity sensing accurate to millimeter range

  16. Where to Buy • IFM Electronics www.ifmefector.com/ifmus/web/capacitive.htm • Balluff www.balluff.com/products/Capacitive/default.htm www.balluff.com/ShortForm/Capacitives.pdf • SICK www.sick.de/de/products/categories/industrial/capacitiveproximity/en.html • APLAC http://www.aplac.com/products/a_pr_mems.htm • RDP GROUP http://www.rdpelectrosense.com/displacement/sensagap/sensagap.htm

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