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lsli09.4up - 09-1 Displacement and Proximity 09-1 09-2...

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09-1 09-1 Displacement and Proximity Displacement transducers measure the location of an object. Proximity transducers determine when an object is near. Criteria Used in Selection of Transducer How much force can transducer exert on object? Requirement can be as low as zero when the object is small or cannot be touched. What is the range of positions to be measured? How fast will the object be moving? What accuracy is required? 09-1 EE 4770 Lecture Transparency. Formatted 13:17, 10 February 1999 from lsli09. 09-1 09-2 09-2 Types of Displacement Transducers Potentiometer. Object moves tap on a variable resistor. Linear Variable Differential Transformer (LVDT). Object moves core of three-winding inductor. Capacitive Transducers. Object is either one plate of a capacitor, or moves the capacitor’s dielectric. Coded. Object moves surface covered with code marks. A transducer reads the code marks. There are many other ways to measure position ... these will not be covered individually but may be explained as part of problems. 09-2 EE 4770 Lecture Transparency. Formatted 13:17, 10 February 1999 from lsli09. 09-2 09-3 09-3 Potentiometers Symbol: Construction and Operation: Resistive material formed into either a strip or coil. An external object, through a mechanical linkage, moves the tap. Tap slides along resistive material. Tap and both ends of resistive material connected to leads. Miscellaneous Facts: These are built for instrumentation purposes. (Unlike the volume control on a radio.) Multiple-turn potentiometers can be made precise. (Percent calibration error less than 1%.) 09-3 EE 4770 Lecture Transparency. Formatted 13:17, 10 February 1999 from lsli09. 09-3 09-4 09-4 Desirable Characteristics Easy to read output. Linear response. Other responses also possible. Inexpensive. Undesirable Characteristics Adds friction to motion of object. Can wear out. Limited precision. Can only measure relatively large displacements. 09-4 EE 4770 Lecture Transparency. Formatted 13:17, 10 February 1999 from lsli09. 09-4
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09-5 09-5 Capacitive Displacement Transducers Symbol: no special symbol used. Two types discussed: moving plate and moving dielectric . Construction and Principle of Moving Plate Type: One plate of capacitor mounted to a fixed surface. The other plate mounted to the object. Capacitance changes with position of object. Possible ways of mounting and moving plates: Plates move normal to plane of plates. Plates move parallel to plane of plates. Plates, shaped like pie slices, rotate. Construction and Principle of Moving Dielectric Type: Both plates of capacitor mounted to a fixed surface. The dielectric mounted to an object. Capacitance changes with position of object. Possible ways of moving dielectric: Dielectric slides. Dielectric is a fluid that flows in and out of the capacitor.
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lsli09.4up - 09-1 Displacement and Proximity 09-1 09-2...

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