ME 120 Course Review
Significant Figures and Rounding
• Correct number of sig figs after arithmetic operations:
o Addition/Subtraction
ƒ Least precise (fewest number of significant figures to the right of the
decimal point)
o Multiplication/Division
ƒ Maintaining precision
ƒ Fewest number of significant digits in operands (or alternate rule by
Mullins)
Accuracy, Error, and Calibration
• Error in measurement and the need to report the uncertainty associated with a
measurement
o Y ±Uy at X% confidence or (n:1) odds
o Systematic error
o Random error
• Calibration
o Independent and dependent variables
o Process of calibration
o Sensitivity
o Linearity
o Repeatability
o Hysteresis
• Resolution and accuracy (what is the difference?)
Uncertainty Analysis
• Uy = (by2 + py2)1/2
• Random errors are distributed (described by a distribution function, e.g., normal,
binomial, etc.)
• Population vs. sample
• Population and sample statistics
o Mean
o Standard deviation
o Variance
• Standard normal curve
o Areas correspond to probabilities
• Uncertainty bounds
o x = x ±t
S (at C% confidence)
true
α / 2,ν
x
where
xtrue is the true mean
x is the sample mean
tα / 2,ν is Student's t distribution with ν degrees of freedom
and α is the level of significance (and C=1-α )
BJ Furman | ME 120 Experimental Methods | ME120 Course Review.doc | 05DEC2006
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Uncertainty bounds, cont.
o Comparison of sample means
o Confidence interval on standard deviation
Calculating overall uncertainty
• Design-stage uncertainty (estimating uncertainty before any data is taken)
o Instrument resolution
o Instrument uncertainty from manufacturer’s data sheet (or prior information)
ƒ Use SRSS method
• Propagation of error in calculations that depend on measured values
Displacement Measurement (know their applications, capabilities, costs, etc.)
• LVDT and RVDT
• Encoders
o Incremental vs. absolute
o Quadrature output
• Potentiometers
• Hall Effect devices
• Capacitive sensors
• Eddy current sensor
Data Acquisition
• Analog and digital signals
o Average (DC) component of an analog signal
o RMS level
•
DAQ resolution fundamentally depends on the number of bits associated with the A/D
converter
o Be able to determine the resolution of the measurand
ƒ Will depend on the fundamental resolution of the A/D and the input range
selected for the DAQ device
• 2N bits are available to digitize (bin) the input range chosen
• Match input range of the DAQ to the signal!
•
Signal source type
o Grounded
o Floating
•
DAQ input configurations, their meanings, applications, advantages, disadvantages, when
to use, and when not to use
o Reference single-ended
o Non-referenced single-ended
o Differential
Dynamic Signal Analysis
• FFT
• Clipping
• Aliasing
o Calculating alias component
o Remedies to avoid aliasing
• Spectral leakage
o Windowing
BJ Furman | ME 120 Experimental Methods | ME120 Course Review.doc | 05DEC2006
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•
Effect of sample rate and number of samples on FFT results
Sound Measurement
• Speed of sound
• Sound pressure
• Sound power
• Sound intensity
• Sound pressure level
• Leq and SEL
• Measurement regions
• Sound intensity measurements
• Microphones
• Adding sound pressures
Motion Measurement
• Vibration measurement transducers
o Types and reasons why to choose one over another
Pressure Measurement
• Pressure measurement transducers
o Types and reasons why to choose one over another
Force, Torque, Stress, and Strain Measurement
• Strain gages
o Gage factor
o Strain gage circuits
o Consideration factors
Review Homeworks and Lab Experiments
• What were the big ideas?
Lab View
BJ Furman | ME 120 Experimental Methods | ME120 Course Review.doc | 05DEC2006
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