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ENT 164/4 SENSORS & MEASUREMENT

ENT 164/4 SENSORS & MEASUREMENT. Shazmin Aniza Abdul Shukor. Measurement. Reference books: Theory and Design for Mechanical Measurements, Richard S. Figliola & Donald E. Beasley, John Wiley & Sons

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ENT 164/4 SENSORS & MEASUREMENT

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  1. ENT 164/4SENSORS & MEASUREMENT Shazmin Aniza Abdul Shukor

  2. Measurement • Reference books: • Theory and Design for Mechanical Measurements, Richard S. Figliola & Donald E. Beasley, John Wiley & Sons • Mechanical Measurements, Thomas G. Beckwith, Roy D. Marangoni, John H. Lienhard V, Pearson International Edition • Process Control Instrumentation Technology, Curtis D. Johnson, Pearson International Edition

  3. General Measurement System (1) • Measurement = act of assigning a specific value to a physical variable (tool used for quantifying the measured variable)

  4. General Measurement System (2) • Sensor = a physical element – employs natural phenomenon – senses the variable being measured • Transducer = converts sensed information – detectable signal (electrical, mechanical, optical, etc) • Signal conditioning = convert transducer signal – desired magnitude • Output = indicates / records value measured • Feedback-control = interprets measured signal; makes decision

  5. General Measurement System (3)

  6. Important Terms in Measurement (1) • Variables = entities that influence the test • Independent variable = changed independently of other variables • Dependent variable = affected by changes in one / more variables • Extraneous variables = cannot be controlled during measurement, but affect the value of variable measured

  7. Important Terms in Measurement (2)

  8. Important Terms in Measurement (3) • Parameter = a functional grouping of variables • Noise = random variation of the value of the measured signal as a consequence of the variation of the extraneous variables • Calibration = applies a known input value to a measurement system for the purpose of observing the output

  9. Important Terms in Measurement (4) • Accuracy = closeness of agreement between the measured value and the true value • Error = difference between the measured value and the true value

  10. Standards • = reference value • Dimension = physical variable – describe aspect of physical system • Unit = quantitative measure of a dimension • E.g. mass (kg), time (s), length (m), temperature (K), current (A) • Derived units = association of dimensions and their units

  11. Problem • Identify the measurement stages for a room thermostat • Answer: • Sensor / transducer stage: Bimetallic thermometer • Output stage: Displacement of thermometer tip • Controller: Mercury contact switch

  12. Room Thermostat Thermometer coil with mercury switch attached The mercury switch

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