metrology: the fabric of science and technology lafe spietz tma class of 1990
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Metrology: The fabric of science and technology
Lafe Spietz
TMA class of 1990
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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
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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
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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.
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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
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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 timeOne 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 kilogram drifts!
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The story of mass II: possible replacements
Watt-balance
Avogadro’s numberMeasurement:
Roundest object in the world!
Goal: 10 parts per billion accuracy
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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
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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)
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ITS-90: the practical realization of the kelvin
Platinum resistance standard
Constant volume gas thermometer
PV=NkBT
Not primary!!!
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PLTS-2000: the low temperature definition of the kelvin
Superconducting fixed points
Helium-3 melting pressure thermometer
Not primary, and very hard!!
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Electrical noise and temperature:The basic idea
All resistors make electrical noise proportional to temperature: hissing of a radio
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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)
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Why noise thermometry is hard:
Amplifiers add noise, and have complex behavior
Must be calibrated accurately to measure temperature accurately
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The Shot Noise Thermometer
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Relates temperature to voltage, Simplifying amplifier calibration.
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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