Towards an Electronic Kilogram

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Transcript Towards an Electronic Kilogram

Towards an Electronic
Kilogram
Physics 250
Victor Acosta
NOTE: Almost everything in this report was taken from NIST websites.
The Old Standard: "Le Gran K"
• Held In Sevres, France
• Only 1/7 SI units using physical artifact
• Δm/m = 30 ppb
Ideas for New Standard
• X-Rays in Si
– Avogadro’s #, NA
• 340 ppb (2003)
• Watt-balance: EM vs. G
– Planck Constant, h
• 52 ppb (2005)
Link to "invariant" quantum phenomena
The Watt Balance
• Balance Gravity
Force with EMF
• Find value for h,
Planck’s Constant
2R h
me
c
2
Physics
vz
z
F
I
z
Animation (if it works)
Measurements: Voltage
Hg Battery Stabilized I-Source
Zener Diode
Josephson Array Voltage
n fh
2e
Determine f with GPS Atomic clock
Measurements: Velocity
• 3 HeNe Laser systems give v and z
• Easily referenced to Meter standard:
• λHeNe = 632.99139822 nm
Measurement: Current
• Use DVM (Josephson ref.) to
measure V across R
• Get R via Quantum Hall Effect
DVM
Measurement: Gravity
• When scale is balanced
1
m
J
VJ
g v HeNe RH
• Easy to reference gravity!
• Use nearby gravimeter
• < 10 meters away
• Reference with HeNe, GPS
Watt-Balance UC
Basic references (error mode)
Mass (force)
Voltage, square error (current, voltage)
nW/W
15
2
Resistance (current)
10
Time, linear error (voltage, current, velocity)
0.5
Length (velocity)
3
Local gravity acceleration (force)
30
TOTAL RMS
52