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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_Measures


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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."
http://en.wikipedia.org/wiki/Metrologyhttp://en.wikipedia.org/wiki/BIPMhttp://en.wikipedia.org/wiki/BIPMhttp://en.wikipedia.org/wiki/Metrology


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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/Traceability


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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]
http://en.wikipedia.org/wiki/Metrologyhttp://en.wikipedia.org/wiki/Metrology


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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/Accuracy


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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..
http://en.wikipedia.org/wiki/Product_developmenthttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Product_development


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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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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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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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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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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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