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ME 220 Measurements & Sensors Mechanical Measurements Applications

ME 220 Measurements & Sensors Mechanical Measurements Applications. Chapters # 8, 9,10, 11 ( Figliola) and 18 (Beckwith). CH. # 8 Temperature Measurements. Thermometer. Thermometry based on thermal expansion Liquid-in-glass thermometers (accuracy from ±0.2 to ±2°C). Bimetallic Thermometers.

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ME 220 Measurements & Sensors Mechanical Measurements Applications

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  1. ME 220 Measurements & SensorsMechanical Measurements Applications Chapters # 8, 9,10, 11 ( Figliola) and 18 (Beckwith)

  2. CH. # 8 Temperature Measurements Thermometer Thermometry based on thermal expansion Liquid-in-glass thermometers (accuracy from ±0.2 to ±2°C)

  3. Bimetallic Thermometers If you take two metals with different thermal expansion coefficients and bond them together, they will bend in one direction

  4. Resistance Temperature Detectors RTD

  5. Thermistors Usually made of a semiconductor and have Much larger dR/dT (more sensitive) than RTD and has Fast Response

  6. Thermocouple (Thermoelectric)

  7. Thermoelectric Effects Seebeck effect: Generates voltages across two dissimilar materials when a temperature difference is present. Peltier effect: Moves heat through dissimilar materials when current is applied.

  8. Thermocouples Thermocouples measure the difference in temperature between two points. One of those points at a known temperature.

  9. Thermocouples in Series and in Parallel

  10. THERMOCOUPLE TIME CONSTANT • The conservation of energy: m cp dT / dt = h A (To – T) m : mass of thermocouple junction, Cp: specific heat of thermocouple junction h : heat transfer coefficient , A : surface area of thermocouple T : junction temperature , To : environs temperature θ =T – To / Ti - To Ti = initial measurement junction temperature, then the solution is θ = e (-t / τ ) The time constant for this process is τ = m cp /h A

  11. Error Sources in Temperature Measurements Conduction: Your probe can conduct heat to/from the environment to/from your desired measurement location

  12. Radiative Temperature Measurements (Pyrometry) Temperatures greater than 500ºC s = 5.67•10-8 W/m2K4

  13. Optical Pyrometer

  14. CH. # 9 Pressure and Velocity Measurements Dynamic Pressure = Total Pressure - Static Pressure Use of Manometers

  15. Pitot Tube Principles

  16. Deadweight Testers

  17. Elastic Pressure Transducers

  18. Bourdon Tube Gauge

  19. INCLINED MANOMETER

  20. Flow velocity measurementsThermal Anemometry

  21. Laser Doppler Anemometer (LDA)

  22. Particle Image Velocimetry (PIV)

  23. CH. # 10 Flow Measurements Turbine

  24. Obstruction Flow Meter

  25. Obstruction Meters

  26. Rotameter or Area meter

  27. Rotameter

  28. CH. # 11 Strain Measurements

  29. Strain Gauges The resistance across that conductor is Where r = conductor of resistivity If you strain this conductor axially, its length will increase while its cross sectional area will decrease. Taking the total differential of R,

  30. Gage factor For most strain gauges, n = 0.3. If the resistivity is not a function of strain, then F only depends on poisson’s ratio, and F ~ 1.6.

  31. Strain Gauge F and R are supplied by the manufacturer, and we measure ∆R.

  32. Strain Gage

  33. Strain Gage [Gage Factor = (∆R/R)/(∆L/L)& Young’s Modulus = (P/A) / (∆L/L) ]

  34. Strain Gage Bridge Circuit

  35. Wheatstone Bridge make R2 = R4 = R

  36. Multiple Gauge Bridge Most strain gauge measurement systems allow us to make 1, 2, 3 or all 4 legs of the bridge strain gauges. Eo Say that unstrained, all of these have the same value. If they are then strained, the resultant change is Eo is

  37. Multiple Gauges • All gauges have the same nominal resistance (generally true) • All gauges have matched gauge factors Eo

  38. Force Measurements

  39. Torque & Power Measurements Torque T = FR Power P = wT

  40. ACOUSTICS • Acoustics is the study of Sound. • Sound is caused by variations in Pressure transmitted through air or other materials. • The pressure, and the resulting sound, can vary in both Amplitude and Frequency. • Humans can detect sound over a wide range of frequencies and amplitudes.

  41. What is Sound? • Sound is a propagating disturbance in a fluid or in a solid. The disturbance travels as a longitudinal wave. • Airborne sound Sound in air is called airborne sound generated by a vibrating surface or a turbulent fluid stream. • Structure borne sound Sound in solids is generally called structure borne sound. • Sound: is measured by a microphone and has Amplitude and Frequency

  42. SOUND WAVESrapid pressure variation cycles of compressions and rarefactions

  43. SOUND WAVES • Sound energy is transmitted through air as a pressure wave. • Frequency : The frequency of a sound (cycles / sec.) hertz (Hz). f = 1/T (Hz) The range for human hearing is from 20 to 20.000 Hz. • Wavelength :The distance between analogous points of two successive waves. λ = c / f where c = speed of sound (m/s)f = frequency (Hz) Frequency (Hz) 63 125 250 500 1K 2K 4K 8K Wavelength (m) 5,46 2,75 1,38 0,69 0,34 0,17 0,085 0,043

  44. Frequency Independent of sound-pressure level.

  45. Speed of Sound and Wavelength The speed of sound in air = 344 m/s fn (Temp) The speed of sound in water = 1000 m/s The speed of sound in solid = 3000 m/s

  46. Sound Waves

  47. Pure Tone and Noise

  48. Human Ear

  49. External, Middle and Inner Ear

  50. Middle &Inner ear

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