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Unformatted text preview: 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 13:26, 23 December 1997 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 13:26, 23 December 1997 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 13:26, 23 December 1997 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 13:26, 23 December 1997 from lsli09. 09-4 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....
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This note was uploaded on 11/28/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.
- Fall '99