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 important
and 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?
Government labs around the world.
From Article I, section 8 of the U.S
Constitution:
“The Congress shall have Power To…
…fix the Standard of Weights and
Measures;”
SI: The International System of
Units
Seven base units:
Lots of derived units:
Length: meter (m)
Area: m2
Mass: kilogram (kg)
Speed: m/s
Force: 1 newton = 1 kg·m/s2
Time: second (s)
Electric current: ampere (A)
Voltage: 1 volt = 1 m2·kg/s3·A
Frequency: 1 hertz = 1/s
Thermodynamic temperature: kelvin (K)
Power: 1 watt = 1 kg·m2/s3
Amount of substance: mole (mol)
Electric Charge: 1 C = 1 A·s
Luminous intensity: candela (cd)
Hierarchy of units:
Kings and queens of units:
Time, frequency, distance
Dukes and Earls:
Current, voltage, resistance
Peasants:
Mass, temperature, pressure,
luminosity
Clocks: Atomic time
One part per quadrillion accuracy!!!
Accurate frequency gives accurate
distance and time.
Artifact vs. quantum standards:
A metal bar:
1889-1960
The modern meter:
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 story of mass I:
the modern kilogram
The SI
kilogram
drifts!
http://www.bipm.fr
The story of mass II:
possible replacements
Goal: 10 parts per billion accuracy
Avogadro’s number
Measurement:
Roundest object in
the world!
Watt-balance
Temperature: Kelvin, Celsius, and
Fahrenheit
21 C
70 F
294 K
0C
32 F
273.15 K
Water freezes
-196 C
-321 F
77 K
Air liquefies
4.2 K
Helium liquefies
-269 C
-452 F
-273.15 C -459.67 F
0K
Room temperature
Absolute zero
The kelvin: the SI unit
The 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
PV=NkBT
Platinum resistance
standard
Not primary!!!
Constant volume gas
thermometer
PLTS-2000: the low temperature
definition of the kelvin
Not primary, and very hard!!
Helium-3 melting
pressure thermometer
Superconducting
fixed points
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
{
P
V
2kBT / e
Relates temperature to voltage,
Simplifying amplifier calibration.
The Shot Noise Thermometer:
A new practical low temperature thermometer
Copper Tubing for DC lines
SMA Connectors for RF
Copper Plumbing parts
Tunnel Junction
Built-in Bias Tee
(on-board SMT
Components)
Total cost of package <10$