MECHATRONICS LAB: ME 140L SENSORS http://www.automation.siemens.com/simatic-sensors/index_76.htmhttp://neat.com/products/electronics/pdf/EncoderBasics.pdfhttp://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 Nis the number of coil windings and Vis 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).