1. ME 220 Measurements & Sensors Mechanical 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 measurements Thermal 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 = 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. CH.# 18 Acoustic Measurement
Process, Machine or System
Sound Source with sound power W
Input
Sound Pressure
Measurement System
Sound Measurement
System
Output
Amplitude and
Frequency Data
Measured Sound Level
Noise is unwanted sound and should be reduced

41. 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.

42. 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

43. SOUND WAVES rapid pressure variation cycles of compressions and rarefactions

44. 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 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) K 2K 4K 8K Wavelength (m) 5,46 2,75 1,38 0,69 0,34 0,17 0,085 0,043

45. Frequency Independent of sound-pressure level.

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

47. Sound Waves

48. Pure Tone and Noise

49. Human Ear

50. External, Middle and Inner Ear

51. Middle &Inner ear

52. Hearing

53. Noise to Outside
From Machines such as Airplanes, Pumps, Compressors and generators.
From Air conditioning such as condensers, Chillers, Ventilation Opening, Louvers
Nose Control by: Relocation, Use of Vibration Damping, Use of Attenuator and Use of Enclosure.

54. Typical Noise Sources

55. The Decibel (dB) & Sound Power Level
dB = ten times the logarithm to base 10 of the ratio of two quantities.
Power Level = 10 log (w1 / w2) dB
where w1 and w2 are the two powers.
SWL = 10 log (sound power)/(ref. power)
Reference power  (Watt) = W, which is the threshold of hearing ( lowest detectable sound).

56. Sound Energy Decreases with (distance)2

57. Sound intensity Sound intensity, power per unit area.
The intensity passing a spherical surface around source in a free field is:
I = W / A = W / 4 π r2   = p2 / ρ c   (W/m2)
where
W = power     (W) A = area   ( m2) r = radius   (m) p = root mean square pressure  (N/m2) ρ = density     (kg/m3) c = velocity of sound   (m/s)
   
SOUND INTENSITY LEVEL LI = 10 log (I / I0)  (dB)
Where
Io = reference intensity  = W/m2.

58. Sound pressure level (SPL)
Sound measuring device respond to sound pressure .
Sound pressure level in decibels vary with distance from source.
SPL = 10 log (p2 / p02) = 20 log (p / p0)
where p= rms pressure (N/m2)
& po = 20x10-6 N/m2.
For Free Field : SWL=SPL +20 log r +11 dB

59. Sound Pressure Note the unit of the equation
The reference value used for calculating sound-pressure level is 2 ×10-5 Pa.
Note the unit of the equation

60. Sound Level Meter

61. Adding two sound pressure levels
Diff between 2-Levels Total= Larger +
0 or
2 or
4 or
10 or more
Total SPL =

62. Addition of two sound pressure levels

63. Noise criteria (NC)
1) NC relates SPL with frequency to show how SPL varies with frequency
2) The highest curve crossed by the data determines the NC rating. NC-39

64. A , B, and C - Weighting

65. A- Weighting (dBA)
The ear is less sensitive with decreasing frequency.
To simulate ear response use A weighting (dBA).
kHz 2kHz 4kHz
Fan Octave Band dB:
A-weighted :
81 dBA

66. SOUND INSULATION Reduction of Air-borne sound:
Source - Transmission Path- and Receiver
Air-borne noise and Structure-borne noise
Reduction of Air-borne sound:
- Relocation of source and/or receiver
- Use floating floors, Use absorbent material
- Use local insulation, and local attenuators
- Use fans with backward curved impellers
- Lined duct work and avoid crosstalk