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 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

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

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

General Measurement System (3)

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

Important Terms in Measurement (2)

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

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

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

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

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