title: Estimates of the difference between thermodynamic temperature and the International Temperature Scale of 1990 in the range 118 K to 303 K.
abstract: Using exceptionally accurate measurements of the speed of sound in argon, we have made estimates of the difference between thermodynamic temperature, T, and the temperature estimated using the International Temperature Scale of 1990, T90, in the range 118 K to 303 K. Thermodynamic temperature was estimated using the technique of relative primary acoustic thermometry in the NPL-Cranfield combined microwave and acoustic resonator. Our values of (T-T90) agree well with most recent estimates, but because we have taken data at closely spaced temperature intervals, the data reveal previously unseen detail. Most strikingly, we see undulations in (T-T90) below 273.16 K, and the discontinuity in the slope of (T-T90) at 273.16 K appears to have the opposite sign to that previously reported.
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: R
authors.initials: R
authors.lastname: Underwood
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK michael.depodesta@npl.co.uk.
authors.forename: M
authors.initials: M
authors.lastname: de Podesta
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: G
authors.initials: G
authors.lastname: Sutton
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: L
authors.initials: L
authors.lastname: Stanger
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: R
authors.initials: R
authors.lastname: Rusby
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: P
authors.initials: P
authors.lastname: Harris
authors.affiliation: School of Applied Sciences, Cranfield University, Cranfield MK43 0AL, UK.
authors.forename: P
authors.initials: P
authors.lastname: Morantz
authors.affiliation: National Physical Laboratory, Teddington TW11 0LW, UK.
authors.forename: G
authors.initials: G
authors.lastname: Machin
keywords: ITS-90; acoustic gas thermometry; primary thermometry