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

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Presentation on theme: "ENT 164/4 SENSORS & MEASUREMENT Shazmin Aniza Abdul Shukor."— Presentation transcript:

1 ENT 164/4 SENSORS & 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


12 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

13 Room Thermostat The mercury switch Thermometer coil with mercury switch attached

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