Download Week35_LABI1Y_Presentation_1 - IT

LAB I1 Class Y
Laboratory Measurements I1
Book(s) must be collected at VIA Lib
Wednesday the 01-09-2010
between 4 and 6 pm..
Laboratory Measurements I1
Overview of the applications of experiments
and measurement systems:
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Measurement in engineering
experimentation
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Measurement in operational devices for
monitoring and control purposes
Measuring in engineering
experimentation
• Research experimentation
• Development experimentation
• Performance testing
Carbon fiber composit example
• Research experiments are uncertain
• Development programs usually have better
defined goals
• Performance testing is done on products
(Determine product life time)
Measurement in operational systems
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Airflow
Engine speed
Water temperature
Exhaust gas composition
…
Objective and overview
• A systematic approach includes carefull
planning and analytical design.
• This course provides the technical information
necessary to design an experimental system.
Dimensions and units
The four fundamental dimensions are:
length, time, mass and electric charge.
Numbers are meaningless for the physicist
without the correct use of units.
Newton's Laws of Motion
Newton's laws of motion are three physical laws:
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First Law: Every body remains in a state of rest or uniform motion (constant
velocity) unless it is acted upon by an external unbalanced force. This means that
in the absence of a non-zero net force, the center of mass of a body either remains
at rest, or moves at a constant speed in a straight line.
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Second Law: A body of mass m subject to a force F undergoes an acceleration a
that has the same direction as the force and a magnitude that is directly
proportional to the force and inversely proportional to the mass, i.e., F = ma.
Alternatively, the total force applied on a body is equal to the time derivative of
linear momentum of the body.
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Third Law: The mutual forces of action and reaction between two bodies are
equal, opposite and collinear. This means that whenever a first body exerts a force
F on a second body, the second body exerts a force −F on the first body. F and −F
are equal in magnitude and opposite in direction. This law is sometimes referred
to as the action-reaction law, with F called the "action" and −F the "reaction".
Newtons Second Law
• F=M*A, A=F/M
• F = Force = A push or pull
• M = Mass
• A = Acceleration = Speeding up, slowing down
or changing direction
• http://www.mansfieldct.org/schools/mms/hand/
Lawsnewton2law.htm
Newtons Second Law
• Mass = 5 kg
• Let’s assume that the wheels of a 5-kg car
apply 10 N of force. What is the net force if
friction and drag are negligible?
Newtons Second Law
• Mass = 5 kg
• Let’s assume that the wheels of a 5-kg car apply 10 N
of force. What is the net force if friction and drag are
negligible?
• The net force would equal 10 Newtons.
• What is the acceleration of the car?
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Force = M*A
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10 = 5*A
• Acceleration = 2 m/s2
Newtons Second Law
• Mass = 6 kg
• What is the net force if the wheels of the 5-kg
car apply 10 Newtons but a 1-kg parachute
applies 7 Newtons in the other direction?
Newtons Second Law
• Mass = 6 kg
• What is the net force if the wheels of the 5-kg car apply 10
Newtons but a 1-kg parachute applies 3 Newtons in the
other direction?
• The net force would equal 3 Newtons. The total mass = 6
kg.
• What is the acceleration of the car?
• Acceleration = F/M
• Acceleration = 3/6
•
Acceleration = 0.5 m/s2
Newtons Second Law
• Mass = 10 kg
• A rocket is added to the car and applies an additional force of
10 Newtons. The wheels still apply 10 N. What is the net force
if the parachute continues to apply 7 Newtons in the other
direction? The total mass of the car, rocket and parachute is
10 kg.
Newtons Second Law
• Mass = 10 kg
• A rocket is added to the car and applies an additional force of 10
Newtons. The wheels still apply 10 N. What is the net force if the
parachute continues to apply 7 Newtons in the other direction? The
total mass of the car, rocket and parachute is 10 kg.
• The net force would equal 13 Newtons. The total mass = 10 kg.
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What is the acceleration of the car?
Acceleration = F/M
Acceleration = 13/10
Acceleration = 1.3 m/s2
General Characteristics of
Measurement Systems
Measurand
Sensing
Element
Signal
modification
subsystem
Indicator or
recorder
These three subsystems are quite obvious in most measuring devices.
Measuring temperature
Which of those analog and digital thermometers is the most exact ?
Measuring temperature
• Use of a certified MIG (mercuri-in-glass)
thermometer is recognized as an accurate
standard; however, establishments may use
other methods or equipment to verify
accuracy of thermometers.
Validity of measurement
• It is very importent to the experiment that the
output of a measurement system truly states
the actual value of a measurand.
• The error of a measurement is defined as the
difference between the measurand and the
true value of the measurand
Error = measurand value – true value
Systematic and Random errors.
Systematic errors are consistent, repetable errors.
1. Calibration error.
2. Insertion of the measuring device alters
the measurand.
3. Measuring system is effected by variables
other than measurand.
Systematic error = average of readings – true value
Random errors are those caused by a lack of responsibility in the output of
the measuring system
Random error = reading that deviate the most – average of readings
Systematic and Random error
• Destinction between systematic and random
error.
True value
Range of random error
Systematic error
Measurand
Average of measured values
Example 2.1
• In a calibration test, 10 measurements using digital
voltmeter have been made of the voltage
a battery that is known to have a true voltage of 6,11
volt.
• The readings are : 5,98 V, 6,05 V, 6,10 V, 6,06 V, 5,99 V,
5,96 V, 6,02 V, 6,09 V, 6,03 V, 5,99 V.
• Estimate the systematic and maximum random errors
caused by the Voltmeter.
Solution for Example 2.1
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Average = add measurements and divide by the number of measurements
= (5,98+6,05+6,10+6,06+5,99+5,96+6,02+6,09+6,03+5,99)volt/10
= 6,03 Volt
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Systematic error = Average of readings – true value
= 6,03 Volt – 6,11 Volt
= -0,08 Volt
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Maximum random error = Reading that deviates the most – Average
= 5,96 Volt – 6,03 Volt
= -0,07 Volt