LAB I1 Class Y Laboratory Measurements I1 Book(s) must be collected at VIA Lib Wednesday the...

LAB I1 Class Y

Laboratory Measurements I1Book(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:

• Measurement in engineering experimentation

• 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

• 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 MotionNewton's laws of motion are three physical laws:

• 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.

• 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.

• 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?• Force = M*A• 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.

• What is the acceleration of the car?• Acceleration = F/M• Acceleration = 13/10• Acceleration = 1.3 m/s2

General Characteristics of Measurement Systems

These three subsystems are quite obvious in most measuring devices.

SensingElement

Signal modification subsystem

Indicator or recorder

Measurand

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

Measurand Systematic error 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

• 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

• Systematic error = Average of readings – true value• = 6,03 Volt – 6,11 Volt • = -0,08 Volt

• Maximum random error = Reading that deviates the most – Average• = 5,96 Volt – 6,03 Volt• = -0,07 Volt