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METROLOGY
MUKHTAR MALIKBY
TATiUC
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INTRODUCTION
Metrology is defined by the International Bureau ofWeights and Measures (BIPM) as "the science ofmeasurement, embracing
both experimental and theoretical determinations atany level ofuncertainty in any field of science andtechnology.
The ontologyand international vocabulary of
metrology (VIM) is maintained by the InternationalOrganisation for Standardisation.
http://en.wikipedia.org/wiki/International_Bureau_of_Weights_and_Measureshttp://en.wikipedia.org/wiki/International_Bureau_of_Weights_and_Measureshttp://en.wikipedia.org/wiki/Experimenthttp://en.wikipedia.org/wiki/Theoryhttp://en.wikipedia.org/wiki/Uncertaintyhttp://en.wikipedia.org/wiki/Ontology_(information_science)http://en.wikipedia.org/wiki/International_vocabulary_of_metrologyhttp://en.wikipedia.org/wiki/International_vocabulary_of_metrologyhttp://en.wikipedia.org/wiki/International_vocabulary_of_metrologyhttp://en.wikipedia.org/wiki/International_vocabulary_of_metrologyhttp://en.wikipedia.org/wiki/Ontology_(information_science)http://en.wikipedia.org/wiki/Uncertaintyhttp://en.wikipedia.org/wiki/Theoryhttp://en.wikipedia.org/wiki/Experimenthttp://en.wikipedia.org/wiki/International_Bureau_of_Weights_and_Measureshttp://en.wikipedia.org/wiki/International_Bureau_of_Weights_and_Measures7/27/2019 Me Trology 1
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CONCEPT
A core concept in metrology is metrologicaltraceability,[5] defined by the BIPM as "theproperty of the result of a measurement or
the value of a standard whereby it can berelated to stated references, usuallynational or international standards, through
an unbroken chain of comparisons, allhaving stated uncertainties."
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METROLOGY
The level of traceability establishes thelevel of comparability of the measurement:whether the result of a measurement can
be compared to the previous one, ameasurement result a year ago, or to theresult of a measurement performed
anywhere else in the world.
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METROLOGY
Traceability is most often obtainedby calibration, establishing the relationbetween the indication of a measuring
instrument and the value of ameasurement standard. These standardsare usually coordinated by national
metrological institutes: National Institute ofStandards and Technology, NationalPhysical Laboratory, UK, Physikalisch-
Technische Bundesanstalt, etc.
http://en.wikipedia.org/wiki/Traceabilityhttp://en.wikipedia.org/wiki/Calibrationhttp://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technologyhttp://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technologyhttp://en.wikipedia.org/wiki/National_Physical_Laboratory,_UKhttp://en.wikipedia.org/wiki/National_Physical_Laboratory,_UKhttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/Physikalisch-Technische_Bundesanstalthttp://en.wikipedia.org/wiki/National_Physical_Laboratory,_UKhttp://en.wikipedia.org/wiki/National_Physical_Laboratory,_UKhttp://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technologyhttp://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technologyhttp://en.wikipedia.org/wiki/Calibrationhttp://en.wikipedia.org/wiki/Traceability7/27/2019 Me Trology 1
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DEFINE
Traceability is used to extend measurement froma method that works in one regime to a differentmethod that works in a different regime, bycalibrating the two using an overlapping rangewhere both work. An example would be themeasurement of the spacing of atomic planes inthe same crystal specimen using both X-raysand an electron beam. Traceability also refers to
the methodology used to calibrate variousinstruments by relating them back to a primarystandard.[6]
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DEFINATION
Accuracy is the degree of exactness which the finalproduct corresponds to the measurement standard.
Precision refers to the ability of a measurement to beconsistently reproduced.
Reliability refers to the consistency of accurate resultsover consecutive measurements over time.
Traceability refers to the ongoing validations that themeasurement of the final product conforms to theoriginal standard of measurement.
http://en.wikipedia.org/wiki/Accuracyhttp://en.wikipedia.org/wiki/Accuracy_and_precisionhttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Traceabilityhttp://en.wikipedia.org/wiki/Traceabilityhttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Accuracy_and_precisionhttp://en.wikipedia.org/wiki/Accuracy7/27/2019 Me Trology 1
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TRUE ANALOGY
Dimensional Metrology is the science ofcalibrating and using physicalmeasurement equipment to quantify the
physical size of or distance from any givenobject. Inspection is a critical stepin product development and quality
control..
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METROLOGY
Dimensional Metrology requires the use ofa variety of physical scales to determinedimension, with the most accurate of these
being holographic etalons or laserinterferometers. The realization ofdimension using these accurate scale
technologies is the end goal ofdimensional metrologists
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PRECISE VS ACCURATE
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Metrology:The fabric of science and technology
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What is metrology?
The science of measurement(notweather!)
Metrology establishes the international
standards for measurement used by allcountries in the world in both science and
industry
Examples: distance, time, mass,temperature, voltage, values of physical andchemical constants
Wh i t l i t t
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Why is metrology importantand interesting?
Standard units and values of constantsneeded for all science
Technological standards make all technologywork better and can save lives: fire hydrant
standards
Measurement of constants can give fundamentalinsights into the universe: drift of fine structureconstant
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Who does metrology?
The Congress shall have Power Tofix the Standard of Weights and
Measures;
From Article I, section 8 of the U.SConstitution:
Government labs around the world.
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SI: The International System ofUnits
Length: meter (m)
Mass: kilogram (kg)
Time: second (s)
Electric current: ampere (A)
Thermodynamic temperature: kelvin (K)
Amount of substance: mole (mol)
Luminous intensity: candela (cd)
Seven base units: Lots of derived units:
Area: m2
Speed: m/s
Force: 1 newton = 1 kgm/s2
Voltage: 1 volt = 1 m2kg/s3A
Frequency: 1 hertz = 1/s
Power: 1 watt = 1 kgm2/s3
Electric Charge: 1 C = 1 As
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Hierarchy of units:Kings and queens of units:
Time, frequency, distance
Dukes and Earls:Current, voltage, resistance
Peasants:Mass, temperature, pressure,
luminosity
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Clocks: Atomic time
One part per quadrillion accuracy!!!
Accurate frequency gives accurate
distance and time.
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Artifact vs. quantum standards:
A metal bar:1889-1960 The meter is the length of the path
traveled by light in vacuum during
a time interval of 1/299,792,458 of
a second
The modern meter:
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The story of mass I:the modern kilogram
http://www.bipm.fr
The SI
kilogramdrifts!
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The story of mass II:possible replacements
Watt-balance
Avogadros numberMeasurement:Roundest object in
the world!
Goal: 10 parts perbillion accuracy
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Temperature: Kelvin, Celsius, andFahrenheit
294 K70 F21 C
273.15 K32 F0 C
77 K-321 F-196 C
4.2 K-452 F-269 C
0 K-459.67 F-273.15 C
Water freezes
Air liquefies
Helium liquefies
Room temperature
Absolute zero
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The kelvin: the SI unitThe kelvin, unit of thermodynamic temperature,
is the fraction 1/273.16 of the thermodynamictemperature of the triple point of water.
(0.006 atm)
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ITS-90: the practical realization ofthe kelvin
Platinum resistancestandard
Constant volume gasthermometer
PV=NkBT
Not primary!!!
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PLTS-2000: the low temperaturedefinition of the kelvin
Superconducting
fixed points
Helium-3 meltingpressure thermometer
Not primary, and very hard!!
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Electrical noise and temperature:The basic idea
All resistors make electrical noise proportional totemperature: hissing of a radio
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Electrical noise and temperature:applications of noise thermometry
By measuring the electrical noise of antennaspointed towards space, astronomers can measure
the background temperature of the universe!
(images courtesy ofNASA/WMAP Science Team)
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Why noise thermometry is hard:
Amplifiers add noise, and havecomplex behavior
Must be calibrated accurately to
measure temperature accurately
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The Shot Noise Thermometer
V
P
2 /B
k T e{
Relates temperature to voltage,
Simplifying amplifier calibration.
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The Shot Noise Thermometer:
Total cost of package
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ENGINEERING
&INSTRUMENTATION
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Engineering Metrology and
Instrumentation
Measurement Standards
Line-graduated Instruments
Measuring Straightness, Flatness, Roundnessand Profile
Coordinate Measuring and layout Machines
Gages
Optical Instruments Automated Measurement
Geometric Dimensioning and Tolerancing
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Engineering Metrology
Measurement of dimensions Length
Thickness Diameter
Taper
Angle
Flatness
profiles
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Engineering Metrology
Postprocess Inspection
In-process, on-line, real-time inspection
Dimensional Tolerances
The smaller tolerancehigh cost, but moreaccurate
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Measurement Standard
Inch, foot; based on human body 4000 B.C. Egypt; Kings Elbow=0.4633
m, 1.5 ft, 2 handspans, 6 hand-widths,24 finger-thickness
AD 1101 King Henry I yard (0.9144m) from his nose to the tip of his thumb
1528 French physician J.
Ferneldistance between Paris andAmiens
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Measurement Standard
1872, Meter(in Greek, metron tomeasure)- 1/10 of a millionth of thedistance between the North Pole andthe equator
Platinum (90%)-iridium (10%) X-shapedbar kept in controlled condition inParis39.37 in
In 1960, 1,650,763.73 wave length invacuum of the orange light given off byelectrically excited krypton 86.
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Measurement Standard
Sensitivity (Resolution); the smallestdifference in dimensions that theinstrument can detect or distinguish
Precision; the degree to which theinstrument gives repeatedmeasurements of the same standard(sometimes called accuracy)
Standard measuring temperature 20 0C
Instrument, gage
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Line-graduated Instruments
Graduated
marked to indicate acertain quantity
Rules; Steel rule (machinists rule), bar
or tape, [1 mm or 1/64 in] Vernier calipers; after P. Vernier 1600s,
caliper gages, [25 mm or 0.001 in],Withdigital readout
Micrometers; sensitivity[2.5 mm or0.0001 in],
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Line-graduated Instruments
Diffraction gratings; with two flat opticalglasses, interference fringes with 40lines/mm (1000 lines/in) gratings. [2.5
mm or 0.0001 in] Indirect-reading; dividers, calipers,
telescoping gage for holes and cavities.
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Comparative Length-Measuring Instruments
Also called deviation-type instruments Dial Indicator; using rack-and-pinion and
gear-train mechanism, accuracy [1 mm or 40min]
Electronic gage; using sensors (strain gage,inductance or capacitance), LVDT (Linear variable differential transformer) for
small displacement
Laser Scan micrometer; non-contactmeasurement; high temperature, too elasticor brittle material, on-line measuring, [0.125mm or 5 min]
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Other Measurements
Straightness; Knife edge, dial indicator,autocollimator (like a telescope with a lightbeam that bounces), Optical (transits andlaser)
Flatness; dial indicator, precision steelsquare, interferometry (if not flat, light fringesare curved)
Roundness; V-block with dial gage, read TIR(total indicator
reading)
Circular tracing; platform rotates
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Other Measurements
Profile Template, profile gage to check shape
conformity
Measuring screws and gear teeth Threaded plug gages, screw-pitch gages
(similar to radius gages), micrometer withcone shaped points, snap gages
Optical contour projector
Coordinate measuring machines
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Gages
Heat treated, stress-relieved alloy steels orfrom carbide
C.E. Johansson 1900s Gage blocks[0.05 mmor 2 min]
Grade 0.5 (AAA)-reference gage, very highprecision work
Grade 1 (AA)-laboratory grade, for calibration ofinstruments
Grade 2 (A+)-precision grade, tool room andinspection
Grade 3 (A)-working grade, use in production
Plug gage, GO gage, NOT-GO (NO-GO)
Pneumatic (air) gage
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Selection of Measuring Instruments
Accuracy The degree of agreement of the measured
dimension with its true magnitude
Magnification (amplification)
Precision
Resolution
the smallest dimension that can be read on aninstruments
Rules of 10(gage makers rule)
At least 10 times accurate than the tolerance
Sensitivity
Stability (drift); capability to maintain calibratedstatus
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Precision vs. Accuracy
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Tolerance
Tolerare; put up with, endure Impossible to make perfect parts
Too small tolerance, cost is high
Boeing 747-400 has 6 million parts,measurement of 28 features, 150 millionmeasurements
NIST (U.S. National Institute of Standard and
technology); tolerance shrink by a factor of 3every 10 yearsultraprecision ion-beammachining 0.001mm
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Importance of tolerance
Parts from the same machine can bedifferent
Speed of operation
Temperature Lubrication
Variation of incoming material
Other factors ISO system; definitions
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Definitions
Allowance; the specific difference indimensions between mating parts
Basic size; dimension from which limits ofsize are derived
Bilateral tolerance; deviation from the basicsize (+ or -)
Clearance; the space between mating parts
Clearance fit; fit that allows for rotation orsliding between mating parts
Datum; theoretically exact axis, point, line orplane
fi i i
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Definitions Feature; Physically identifiable portion of a
part, e.g. hole, slot, pin, chamfer Fit; the range of looseness or tightness
Geometric tolerancing; tolerances that involveshape features of the part
Hole-basis system; tolerances based on azero line on the hole
Interference; negative clearance
Interference fit International Tolerance grade (IT); a group of
tolerances that the same relative level ofaccuracy within a grade (varies depending on
basic size)
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Definition Limit dimension; Maximum and minimum dimension of a part,
MMC(maximum material condition); condition where a feature ofsize contains the maximum amount of material within the statedlimits of size
Nominal size;
Positional tolerancing; A system of specifying the true position,size, and form of the feature of a part, including allowablevariation
Shaft-based system;
Standard size
Transition fit; Fit with small clearance or interference that allowsfor accurate location of mating parts
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Tolerances
Unilateral tolerancing Zero line; reference line along the basic
size from which a range of tolerances
and deviations are specified. Limits and Fits
See the separate lecture note
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Micrometer
The micrometer is a basic precisionmeasuring tool. To a machinist, this tool isindispensable.
The engineer should also realize theimportance of being able to use this toolproperly. This discussion should help in
mastering the use of the common "Mike,"whether it is an outside, inside or depth type.
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MEASURING EQUIPMENTS
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LASER MEASURING TOOLS
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PRECISION MEASURING TOOLS
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DIGITAL MEASURING TOOLS
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