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Determination of the Boltzmann Constant and new Definition of the Kelvin
Joachim FischerJoachim Fischer
Physikalisch-Technische BundesanstaltPhysikalisch Technische BundesanstaltBerlin, Germany
1 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Determination of the Boltzmann Constant and new Definition of the Kelvin
Contents
i l di f CCT/10 34including concerns of CCT/10-34
The Kelvin Definition
Impact
Implications of Changing the DefinitionImplications of Changing the Definition
Determination of the Boltzmann Constant
Summary and Outlook
2 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Standards and Scales
the scale:
triple point
the scale:additional fixed points and interpolating instrumentstemperatures from primary thermometers p p
of water
…H2 Ne O2 Ar Hg Ga In
primary thermometers
0273.16 × the unit
temperature intensive quantity
the unitthe unit
length extensive quantity
3 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
the scale
Definition of the Kelvin (1968)and triple point of water
“The Kelvin : fraction 1/273 16 of the1/273.16 of the thermodynamic temperature of triple
i t f t ”
(13. CGPM: Metrologia, 1968, 4, 43)
point of water”
T = 273 16 KTtpw = 273,16 K
p 611 66 PaWilliam Thomson,
definition = no uncertaintyptpw = 611,66 Pa the later
Lord Kelvin of Largs(1824-1907)
4 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Effects of D and 18O on TP temperature
0 04
0.05
) D0.02
) 18O
0.03
0.04
ffere
nce
(K)
0.015
ffere
nce
(K) O
10 mK
10 mK
0.02
pera
ture
dif
0.01
erqa
ture
dif 10 mK
0
0.01Tem
p
0.005
Tem
pe00.000 0.004 0.008 0.012
Mole fraction
00.00 0.02 0.04 0.06
Mole fraction
5 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Rod White, MSL N.Z.
Isotope effect, a material property
This substance is not available for filling of TPW cells
6 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
New definition based on Boltzmann constant k
system of “particles“thermal energy E per degree
of freedom
thermodynamic temperature T
E = ½kTk = conversion factor E = ½kTk = conversion factor
CODATA value of Boltzmann constant 2006:
k = R/NA = 1.3806504 (24) ·10-23 J/K u = 1.7·10-6 *)
7 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
A ( ) )*) Rev. Mod. Phys. 80 2008, 633
The Boltzmann Constant k and the kelvin
1/τ = dσ / dUBoltzmann: σ = ln P
entropymeasured in joulethermodynamic temperaturemeasured in kelvin
J1 38 10 20
Planck: S = k σ = k ln P 1/T = dS / dU
k = conversion factor 1.38x10-22
1.38x10-20
1.38x10-21
k conversion factor between energy and temperaturefixing the value of k :
1.38x10-23
1.38x10-24
1.38x10-25temperaturefixing the value of k : Boltzmann´s original i i ( 1)
1.38x10-26
8 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
intention (concern 1)P probabilityU internal energy
Wording
1. Reliable determination of k with different methods2 Fixing of the value of k2. Fixing of the value of k3. New definition of the kelvin like:
Explicit-unit definition
The kelvin is the change ofExplicit-constant definitionThe kelvin is the change of thermodynamic temperature Tthat results in a change of thermal
p f
The kelvin, unit of that results in a change of thermal energy kT by exactly 1.380 65X X × 10−23 joule, where
thermodynamic temperature, is such that the Boltzmann constant is exactly
Ludwig Boltzmann
k is the Boltzmann constantconstant is exactly1.380 65X X × 10−23 joule per kelvin.
9 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
g(1844 - 1906)
Determination of the Boltzmann Constant and new Definition of the Kelvin
Contents
The Kelvin Definition
Impact
Implications of Changing the DefinitionImplications of Changing the Definition
Determination of the Boltzmann Constant
Summary and Outlook
10 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Future uncertainties for high temperatures
0,35Best uncertainty
0,25
0,30Best uncertainty
ITS-90
At very low and very high temperatures there will
0,20n=1 (ITS-90
thermo-dynamic
At very low and very high temperatures there will be in future no need to reference back to the triple point of water
0,10
0,15 dynamicMain practical advantage of the new definition
0 00
0,05ITS-XX
0,001000 1500 2000 2500 3000 3500
Temperature / KBloembergen et al.
11 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
pTMCSI 2003, 291-296figure 2
The impact of a new definition of the kelvin
Short term:• the kelvin definition is independent• the kelvin definition is independent
of any material• no favoured fixed point • no favoured measurement method• no error propagation from TPW• thermodynamic measurementsthermodynamic measurements
and ITS-90 are coexisting • <20 K and >1300 K
thermodynamics are superiorthermodynamics are superior
Long term:
Ludwig Boltzmann
• With improvement of primary thermometry thermodynamic measurements may replace ITS-90
12 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
g(1844 - 1906)
y p
Determination of the Boltzmann Constant and new Definition of the Kelvin
Contents
The Kelvin Definition
Impact
Implications of Changing the DefinitionImplications of Changing the Definition
Determination of the Boltzmann Constant
Summary and Outlook
13 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
CCT WG4 Task Group (TG-SI) membersp ( )
Joachim Fischer (PTB) chairman( )Anatoly Pokhodun (VNIIM)Ken Hill (NRC)G h M hi (NPL)Graham Machin (NPL)Mike Moldover (NIST)Laurent Pitre (LNE/CNAM)Laurent Pitre (LNE/CNAM)Andrea Merlone (INRIM)Richard Davis (BIPM) Executive Secretary CCT( ) yOsamu Tamura (NMIJ)Hüseyin Ugur (CCT) President CCTR d Whit (MSL)Rod White (MSL)Inseok Yang (KRISS)Jintao Zhang (NIM)
14 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Jintao Zhang (NIM)
Status of ITS-90
For the foreseeable future :
Most temperature measurements in core temperature range (~ - 200 ºC … 960 ºC ) with SPRTs calibrated accord. to ITS-90( )
ITS-90 will remain intact, with defined values of T90 for all of the fixed points, including the TPW
Uncertainties in T will not changeUncertainties in T90 will not change
Dominated by uncertainties in the fixed-point realizations, y p ,
and the non-uniqueness of SPRTs, typically totalling < 1 mK
15 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Fixed points of ITS-90 ( table 1.2 red book )
T90
u(T90) / mK u(T) / mK u(Tk fixed) / mK
Cu (fp) 1357 77 K 15 60 60 1Cu (fp) 1357.77 K 15 60 60.1Au (fp) 1337.33 K 10 50 50.1 Ag (fp) 1234.93 K 1 40 40.1 Al (fp) 933 473 K 0 3 25 25 1
no changeat all
Al (fp) 933.473 K 0.3 25 25.1Zn (fp) 692.677 K 0.1 13 13.1 Sn (fp) 505.078 K 0.1 5 5.10 In (fp) 429 7485 K 0 1 3 3 11In (fp) 429.7485 K 0.1 3 3.11Ga (mp) 302.9146 K 0.05 1 1.15 H2O (tp) 273.16 K 0.02 0 0.49 Hg (tp) 234 3156 K 0 05 1 5 1 55Hg (tp) 234.3156 K 0.05 1.5 1.55Ar (tp) 83.8058 K 0.1 1.5 1.50 O2 (tp) 54.3584 K 0.1 1 1.00 Ne (t ) 24 5561 K 0 2 0 5 0 50Ne (tp) 24.5561 K 0.2 0.5 0.50e-H2 (vp) ≈20.3 K 0.2 0.5 0.50 e-H2 (vp) ≈17.0 K 0.2 0.5 0.50
H 13 8033 K 0 1 0 5 0 50
16 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
e-H2 (tp) 13.8033 K 0.1 0.5 0.504He (vp) 4.2221 K 0.1 0.3 0.30
Uncertainties in thermodynamic temperature
If 2002 CODATA recommended value of k were taken to beIf 2002 CODATA recommended value of k were taken to be exact and used to define the kelvin :
Uncertainty of k would be transferred to the value of TTPW
B t ti t f th l f T till 273 16 KBest estimate of the value of TTPW still 273.16 K,
but instead of being exact as result of definition of the kelvin :but instead of being exact as result of definition of the kelvin :
Uncertainty associated with estimate would become :
ur(TTPW) = 1.8 × 10−6, corresponds to 0.49 mK
17 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Error propagation from TPW
All thermodynamic measurements currently defined as ratios with respect to TPW :as ratios with respect to TPW :The 0.49 mK uncertainty propagates to all historicalthermodynamic temperature measurements
2,5
3,0 Temperatue range of SPRTs
1,5
2,0
t) /
mK
0,5
1,0
u (t
How well represents ITS-90 thermodynamic temperatures ?on
al
0,0
0,5
-250 0 250 500 750 1000
thermodynamic temperatures ?
addi
tio
18 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
temperature / °C
Fixed points of ITS-90 ( table 1.2 red book )
T90
u(T90) / mK u(T) / mK u(Tk fixed) / mK
Cu (f ) 1357 77 K 15 60 60 1Cu (fp) 1357.77 K 15 60 60.1Au (fp) 1337.33 K 10 50 50.1 Ag (fp) 1234.93 K 1 40 40.1 Al (f ) 933 473 K 0 3 25 25 1hAl (fp) 933.473 K 0.3 25 25.1Zn (fp) 692.677 K 0.1 13 13.1 Sn (fp) 505.078 K 0.1 5 5.10 I 429 7485 K 0 1 3 3 11
no changeat all
change > 0.1 mK
In (fp) 429.7485 K 0.1 3 3.11Ga (mp) 302.9146 K 0.05 1 1.15 H2O (tp) 273.16 K 0.02 0 0.49 H 234 3156 K 0 05 1 5 1 55Hg (tp) 234.3156 K 0.05 1.5 1.55Ar (tp) 83.8058 K 0.1 1.5 1.50 O2 (tp) 54.3584 K 0.1 1 1.00 N 24 5561 K 0 2 0 5 0 50Ne (tp) 24.5561 K 0.2 0.5 0.50e-H2 (vp) ≈20.3 K 0.2 0.5 0.50 e-H2 (vp) ≈17.0 K 0.2 0.5 0.50
19 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
e-H2 (tp) 13.8033 K 0.1 0.5 0.504He (vp) 4.2221 K 0.1 0.3 0.30
Uncertainties in thermodynamic temperature
⇒ TG-SI could not foresee any experiment where the slightly increased uncertainties of u(T ) would present a problemincreased uncertainties of u(Tk fixed) would present a problem
Any future changes in the temperature scale much smaller than y g ptolerances associated with current documentary standards for thermocouples and IPRTs :⇒ No requirement is anticipated for any future change in temperature scales to propagate to the documentary standards
Once k has been fixed in 2015 : TG-SI is not aware of any new technology for a primary thermometer providing a significantly gy p y p g g yimproved uncertainty u(TTPW) ⇒ no change of the assigned value of TTPW for the foreseeable f ( 2)
20 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
future (concern 2)
The Roles of the Mise en Pratique for the Definition of the Kelvin I
The mise en pratique (“practical realization”) for the definition of the kelvin (MeP-K) was created by the Consultative Committee for Thermometry(MeP K) was created by the Consultative Committee for Thermometry (CCT) in 2006 to give practitioners of thermometry a guide to the realization of the kelvin, i.e., measurement of temperature in kelvins, in accord with the International System of Units. y
The International Committee for Weights and Measures also foresaw that adoption of the proposed new definition of the kelvin would require a p p p qMeP-K
MeP-K will describe three categories of measurements:
- primary methods for measuring thermodynamic temperature T- formal approximations to T, in particular the International Temperature
S l f 1990 (ITS 90) d h P i i l T S l fScale of 1990 (ITS-90) and the Provisional Low Temperature Scale from0.9 mK to 1 K (PLTS-2000)
- indirect approximation methods that are neither primary nor defined ont t l t bl f ti ll l t i ti
21 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
a temperature scale, yet capable of exceptionally low uncertainties or increased reliability.
The Roles of the Mise en Pratique for the Definition of the Kelvin II (concern 3)( )
By providing a framework for primary methods and indirect methods, the MeP-K will foster development and application of new methods, such asMeP K will foster development and application of new methods, such as the use of absolute radiometry or high-temperature fixed points
MeP-K currently includes the text of the formal scales and a Technical Annex yof essential additional information
Next version will include recommended differences, T – T90, between the 90thermodynamic temperature and the temperature on the ITS-90 along with the associated uncertainty (ready for inclusion)
By documenting known ITS-90 biases, the MeP-K will support thermodynamically accurate measurements without mandating replacement of the ITS-90 in industry
In this way, the MeP-K provides the CCT with a mechanism to update and expand the thermometric methods in common use, without imposing on
22 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
industry the high costs of changing the International Temperature Scale
Schematic representation of relationship between MeP-K and other documents
SI D fi i iSI Definition
MeP-K
SI Brochure
MeP-KSection 3 Section 4 Section 5
Primary Methods Formal Approximations Indirect Approximations
Supplementary Guides
Supplementary Guides
ITS-90 Text
ITS-90 Technical
PLTS-2000 Text
Annex
ITS-90 Supplementary
I f ti
PLTS-2000 Supplementary
I f ti M P K 2006Information Information MeP-K 2006
on CCT webpagebox with solid border: prescriptive document
23 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
under preparationbox with solid border: prescriptive documentbox with dashed border: non-prescriptive guidance
Determination of the Boltzmann Constant and new Definition of the Kelvin
Contents
The Kelvin Definition
Impact
Implications of Changing the DefinitionImplications of Changing the Definition
Determination of the Boltzmann Constant
Summary and Outlook
24 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Determination of the Boltzmann constant for the redefinition of the kelvin
Coordinator:Physikalisch-TechnischeBundesanstalt
Partners:a t e sDanish FundamentalMetrology
Collaborators: Universidad de Valladolid
25 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Acoustic gas thermometryg ym atomic mass (40Ar)γ ratio of heat capacities cp/ cV = 5/3 for gas of single atomsu speed of sound
u02 = γ kT / m
u0 speed of sound
AGTL. Pitre, C. Guianvarc'h, F. Sparasci, A Guillou D Truong Y HermierA. Guillou, D. Truong, Y. Hermier, M. Himbert, C. R. Physique 10 (2009) 835-848
R.M. Gavioso,G. Benedetto, P.A. Giuliano Albo,transducer
receiver
, , ,D. Madonna Ripa, A. Merlone, C. Guianvarc`h,F. Moro, and R. Cuccaro, Metrologia 47 (2010) 387-409
Measured quantites: d
g ( )
sound frequency ν at resonancedimension d of resonatori ld d f d
d
26 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
yields speed of sound u0
Quasi-spherical cavity resonators
J.B. Mehl, M.R. Moldover,L. Pitre Metrologia 41, 2004,295 (QSCR)
Refractive index gas thermometry295 (QSCR)E.F. May, L. Pitre, J.B. Mehl,M.R. Moldover, J.W. Schmidt,Re Sci Instr m 75 2004
p = kT (n2 - 1) ε0 / α0Rev. Sci. Instrum. 75, 2004, 3307 (QSCR)J.W. Schmidt, R.M. Gavioso, E F May and M R Moldover
n refractive indexε0 electric constant, definedα0 atomic polarizability, known by theory
E.F. May, and M.R. Moldover,PRL 98, 254504, 2007 (RIGT) RIGT
QSCR enablemicrowave measurementto determine dimension
or RIGT: measurement of ε (p,T)
27 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
or RIGT: measurement of ε (p,T)of helium and argon QSCR
AGT preliminary results of spring 2010
Gavioso et al., Metrologia 47 387–409 (2010)
28 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
AGT
Dielectric constant gas thermometryg y
p = k T ε0(εr - 1) / α0ε0 electric constant, definedεr ≈ C(p)/C(0)
t i l i bilitα0 atomic polarizability,known by theory DCGT
Measured quantites:pressure p
C. Gaiser, B. Fellmuth and N. Haft, I t J Th h 29 2008 18
29 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
pressure pcapacitance ratio C(p)/C(0)
Int. J. Thermophys. 29 2008, 18
DCGT: Critical parameters
pressure: capacitance:piston gauge:
present uncertainty: 10 MPa u (p)/p = 5 ppm10 MPa u (p)/p = 5 ppmmain problem: uncertainty of area determination
co-operation withpressure lab
i 1 ppmaim: 1 ppm
co-operation with electricity lab:
present uncertainty:absolute: u (CN) 20 ppbrelative: u (CX /CN) 3 ppb
30 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
( X N) pp
aim: u (ΔCX / CX) 1 ppb
Doppler broadening thermometry
ΔνD = [2 kT /(mc02)]1/2⋅ν0
m atomic massc0 speed of light
DBT0 p g
C. Daussy, M. Guinet, A. Amy-Klein, K. Djerroud, Y. Hermier, S. B i d Ch J B dé d CBriaudeau, Ch.J. Bordé, and C. Chardonnet, Phys. Rev. Lett. 982007, 250801G Casa A Castrillo GG. Casa, A. Castrillo, G. Galzerano, R. Wehr, A. Merlone, D. Di Serafino, P. Laporta and L. Gianfrani Phys Rev Lett 100
ΔνD
Gianfrani, Phys. Rev. Lett. 1002008, 200801J. Petersen, J. Hald, Danish Fundamental Metrology
Measured quantites:doppler line width Δν
Fundamental Metrology
31 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
ν0
doppler line width ΔνDcentre wavelength ν0
University Paris North/LNEUniversities Naples and Milan/INRiMp
DBT
Paris: CO2 laser at 10 µm and ammonia cellNaples: 1.4 µm diode laser and water-vapour cell
Problems in line fitting at 10-4 to 10-5 leveldue to pressure effects
32 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Noise thermometry
<U2> = STΔf = 4 k T R Δf Nyquist´s Formula
bandwidth of detection systemswitched digital input correlator JNTvalid to order hf/2kT ~ 0.09 ppm at 1 MHz, 273 K
<U2>mean square noise voltage
resistance
R
relative method absolute method
33 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Zn fixed point : u = 2•10-5 (k=1)
k/h from Noise Power Ratios
Spectral density of thermal noise powerQuantum-Hall Ohm
Spectral density of electrical noise powerAC Josephson VoltageAC Josephson Voltage
Jifeng Qu, S. P. Benz, H. Rogalla and D R White Metrologia 46
X 0 003874 resistance in units of R
and D. R. White, Metrologia 46 (2009) 512–524
XR 0.003874 resistance in units of RK-90
T = 273.16 K temperature as realized in TPW cell
D2 = 1 47 ×10-6/N2 dimensionless number from digital synthesisD = 1.47…×10 6/N dimensionless number from digital synthesis
fs= DAC sampling frequency, 10 GHz (f1= Δf = fs/M)
M = 24×106 bits pattern repetition length (memory)
34 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
M 24×10 bits, pattern repetition length (memory)
N = number of Josephson junctions JNT
Determination of the Boltzmann Constant and new Definition of the Kelvin
Contents
The Kelvin Definition
Impact
Implications of Changing the DefinitionImplications of Changing the Definition
Determination of the Boltzmann Constant
Summary and Outlook
35 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
36 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Present state of k determinationconfidence interval = 68.3 %1,38075
Review of methods in F ll th G i Fi h
1,38070) DBTLPL
Fellmuth, Gaiser, Fischer,Meas. Sci. Technol. 17 2006, R145 - R159
1 38065 ( J
K-1
AGT NIST
RIGTNIST
CODATA 2006
LPL
1,38065
k x
1023
35 ppm
AGT
DCGTPTB
1,38060
DBTk =1
AGTLNE
INRiMNPL
1,380551985 1995 2005 2015
UniNAk =1
37 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
Year
Development of the achieved and envisaged relative standard uncertainties Δk/krelative standard uncertainties Δk/k
Method 2nd WS 2006 4th WS 2009 2013 possibility institute
AGT > 20 ppm 3 ppm 1 ppm CEM (UVa), INRiM, LNE/CNAM,NPL, NIM
DCGT 15 ppm - 2 ppm PTB
JNT - 25 ppm 5 ppm NIST, INRiM
DBT 200 ppm 37 ppm only Type A 10 ppm DFM, LNE/CNAM (LPL), INRiM
(UniNA2, PoliMI), UWA
38 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
2007 : Report to the CIPM on the implications of changing the definition of the base unit kelvin g g
that within the next four years there exists the possibility of achieving a reliable…that within the next four years there exists the possibility of achieving a reliable uncertainty of the value of k of order one part in 106 based on measurements applying different methods of primary thermometry. Thus, an improved value of the Boltzmann constant proposed for defining the kelvin would ideally have beenBoltzmann constant proposed for defining the kelvin would ideally have been determined by at least the two fundamentally different methods AGT and DCGTand be corroborated by other – preferably optical − measurements as TRT and DBT with larger uncertaintyDBT with larger uncertainty.
The TG-SI appreciates the considerable progress of ongoing experiments to determine the Boltzmann constant in order to corroborate the present value. It isdetermine the Boltzmann constant in order to corroborate the present value. It is assumed that the experiments currently underway to measure R or k will achieve consistent results by the end of 2010, so that the CODATA group can recommend in its 2010 constants adjustment a new value for k with a relative standard juncertainty about a factor of two smaller than the current ur of approximately 2×10−6. With the new definition of the kelvin adopted, this would result in a value of ur(TTPW) of about 1×10−6, corresponding to about 0.25 mK.
39 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
POSSIBLE CONSEQUENCES OF THE REDEFINION OF KELVIN AND RECOMENDATION TO CCT AND CIPM
CCT/10-34 by A. Phokodun, VNIIM:
…In view of the above said, as a member of the CCT Task Group investigating the consequences of a new definition of Kelvin based on the Boltzmann constant, I would suggest the CCT not to be over-hasty in adopting the new definition for the temperature unit of SI and, by the example the last meeting of the CCM in March 2010, to adopt a resolution stipulating that the redefinition of Kelvin should be conditioned by a number of criteria removing the above mentioned preoccupations.
40 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
2010 : RECOMMENDATION OF THE CCT SUBMITTED TO THE CIPM
RECOMMENDATION T2 (2010) Considerations for a new definition of the kelvin
The Consultative Committee for Thermometry (CCT) recalling its previous Report to the CIPM in 2007, entitled “Report to the CIPM on the implications of changing the definition of the base unit kelvin” TG SI/docs05 andimplications of changing the definition of the base unit kelvin , TG-SI/docs05, and considering
• further discussion at its 24th and 25th meetings held in 2008 and 2010, • recent progress in experimental determinations of the Boltzmann constant k as reported at• recent progress in experimental determinations of the Boltzmann constant, k, as reported at
the 3rd and 4th International Workshops on Progress in Determining the Boltzmann Constant held in 2008 and 2009 and
• other experimental progress allowing a mise en pratique for the new definition of the kelvinalready established and presently extended to cover direct measurement of thermodynamic y p y ytemperature,
noting
• that various experiments, such as acoustic gas thermometry, dielectric constant gas thermometry, Johnson noise thermometry, total radiation thermometry and Doppler broadening thermometry represent distinct routes to determining the Boltzmann constant,
• that the experiments currently underway to measure k need another two years before CODATA can recommend a robust value for k with a relative standard uncertainty about a f t f t ll th th t f i t l 2 10−6
41 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10
factor of two smaller than the current ur of approximately 2×10 6. • That a relative standard uncertainty of 1×10−6 in k corresponds to a standard uncertainty of
about 0.25 mK in the temperature of the triple point of water after the redefinition,
RECOMMENDATION OF THE CCT SUBMITTED TO THE CIPM (continued)( )
appreciating the considerable progress of ongoing experiments to determine the Boltzmann constant in order to improve confidence in the present value, recommendsrecommends
1. that before proceeding with the redefinition of the kelvin a relative standard uncertainty of the value of k of order one part in 106 be obtained, based on measurements applying different methods of primary thermometry,different methods of primary thermometry,
2. that these measurements ideally include at least two fundamentally different methods such
as acoustic gas thermometry and dielectric constant gas thermometry and be corroborated by other measurements such as Johnson noise thermometry, total radiation thermometry orby other measurements such as Johnson noise thermometry, total radiation thermometry orDoppler broadening thermometry,
3. that the CODATA recommended value be adopted for the Boltzmann constant.
42 50 years of efforts toward quantum SI, St. Petersburg, 6 Dec 10