Metrology: The fabric of science and technology

Lafe Spietz

TMA class of 1990

What is metrology?The science of measurement

(not weather!)Metrology establishes the international standards for measurement used by all

countries in the world in both science and industry

Examples: distance, time, mass, temperature, voltage, values of physical and chemical constants

Why is metrology importantand interesting?

• Standard units and values of constants needed for all science

Technological standards make all technology work better and can save lives: fire hydrant standards

Measurement of constants can give fundamental insights into the universe: drift of fine structure constant

Who does metrology?

“The Congress shall have Power To……fix the Standard of Weights and Measures;”

From Article I, section 8 of the U.S Constitution:

Government labs around the world.

SI: The International System of Units

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 kg·m/s2

Voltage: 1 volt = 1 m2·kg/s3·A

Frequency: 1 hertz = 1/s

Power: 1 watt = 1 kg·m2/s3

Electric Charge: 1 C = 1 A·s

Hierarchy of units:Kings and queens of units:

Time, frequency, distance

Dukes and Earls:Current, voltage, resistance

Peasants:Mass, temperature, pressure, luminosity

Clocks: Atomic timeOne part per quadrillion accuracy!!!

Accurate frequency gives accurate distance and time.

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:

The story of mass I: the modern kilogram

http://www.bipm.fr

The SI kilogram drifts!

The story of mass II: possible replacements

Watt-balance

Avogadro’s numberMeasurement:

Roundest object in the world!

Goal: 10 parts per billion accuracy

Temperature: Kelvin, Celsius, and Fahrenheit

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

The kelvin: the SI unitThe kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

(0.006 atm)

ITS-90: the practical realization of the kelvin

Platinum resistance standard

Constant volume gas thermometer

PV=NkBT

Not primary!!!

PLTS-2000: the low temperature definition of the kelvin

Superconducting fixed points

Helium-3 melting pressure thermometer

Not primary, and very hard!!

Electrical noise and temperature:The basic idea

All resistors make electrical noise proportional to temperature: hissing of a radio

Electrical noise and temperature:applications of noise thermometry

By measuring the electrical noise of antennas pointed towards space, astronomers can measure

the background temperature of the universe!

(images courtesy ofNASA/WMAP Science Team)

Why noise thermometry is hard:

Amplifiers add noise, and have complex behavior

Must be calibrated accurately to measure temperature accurately

The Shot Noise Thermometer

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P

2 /Bk T e

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Relates temperature to voltage, Simplifying amplifier calibration.

The Shot Noise Thermometer:

Total cost of package <10$

Tunnel Junction

Built-in Bias Tee(on-board SMTComponents)

Copper Plumbing parts

SMA Connectors for RF

Copper Tubing for DC lines

A new practical low temperature thermometer