ME 140L - Lecture 1 - Sensors

ME 140L - Lecture 1 - Sensors - MECHATRONICS LAB: ME 140L...

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MECHATRONICS LAB: ME 140L SENSORS http://www.automation.siemens.com/simatic-sensors/index_76.htm http://neat.com/products/electronics/pdf/EncoderBasics.pdf http://www.macrosensors.com/lvdt_macro_sensors/lvdt_tutorial/lvdt_primer.pdf Sensor: A device that responds to a stimulus, such as heat, light, or pressure, and generates a signal that can be measured. A. SENSOR SPECIFICATIONS Measurement Range : maximum range of quantity being measured Linearity : deviation of the measurement from a straight line Resolution : smallest change detected in the quantity being measured Sensitivity : ratio of output signal to measured property Bandwidth : range of frequencies that the sensor is capable of measuring Operating Temperature : temperature range of normal operating conditions Output Voltage : range of output voltage from sensor Repeatability (precision): ability of the sensor to provide measurements within a close distribution on the same quantity Also, ability of the measurement to be consistently reproduced Accuracy : ability to match the actual value of the quantity being measured—how close a measurement is the actual reading. High Accuracy, Low Repeatability High Repeatability, Low Accuracy
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B. POSITION SENSOR: Linear Variable Differential Transformer (LVDT) Faraday's Law: electric potential Change in the magnetic environment of a coil of wire causes an electromotive force (emf) to be ‘induced’ in the coil. This emf force represents energy per unit charge (voltage) and is not a "force"—but the term emf is retained for historical reasons. Transformer: the induced voltage is proportional to the ratio of the number of coil windings between primary (input) and secondary (output). where N is the number of coil windings and V is the voltage. LVDT: Electromechanical transducer that converts position into DC voltage. Movable cylindrical core of magnetically permeable material 3 wire coils: primary winding centered between a pair of identically wound secondary windings, symmetrically spaced about the primary. Primary coil establishes magnetic flux that is coupled to secondary coils through the core (Faraday’s Law).
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Basic Operation: LVDT Note: resistance to magnetic flux is larger in air than it is through iron Alternating current (1-10kHz) in primary coil establishes a magnetic flux—induces voltage in each secondary coil proportional to its mutual inductance with the primary via the core.
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This note was uploaded on 09/18/2011 for the course ME 140L taught by Professor Staff during the Fall '09 term at University of Texas at Austin.

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ME 140L - Lecture 1 - Sensors - MECHATRONICS LAB: ME 140L...

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