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Metrology:The fabric of science and technology

Lafe SpietzTMA class of 1990

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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

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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 fundamental

insights 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