A Proposal for a New Deviation Function in the IPTS-68 below 273 K

Abstract

The resistance ratios of platinum resistance thermometers from different manufacturers are compared a t many temperatures below 375 K. These resistance ratios can be interrelated by a function with six coefficients determined from the defining fixed point calibrations by the method of least squares. We suggest that this single function could replace the four deviation functions of the IPTS-68. Non-uniqueness in the temperature scale resulting from the imperfections both of this new, and of the IPTS-68 deviation functions are discussed. An even simpler deviation function is used to calibrate thermometers in the range 90 to 273 K. Moderately precise secondary calibrations are obtained over the whole temperature range using this simpler function together with comparisons with a calibrated thermometer a t only four temperatures. We show one way of smoothing the reference function of the IPTS-68 to make it more nearly resemble a real thermometer. The new six-coefficient function is then used to relate all thermometers to this smoothed reference function.

An evolutionary approach to updating the international temperature scale

“…The non-uniqueness of the scale below the ice point was clearly a concern [16][17][18]. However, such analyses are only as good as the quality of the data on which they are based.…”

“…Kemp et al [28,29] had been working for some time to improve the low-temperature interpolation, following-up on the approach introduced by Kirby et al [18]. The development of the ITS-90 reference function has been described by Kemp [30].…”

The Triple Point of Xenon as a Possible Defining Point on an International Temperature Scale

“…The chamber is of stainless steel and was made by machining two hemispheres of wall thickness 0.5 mm and welding them together. Each hemisphere has a central port (2) (3) machined in it. The upper port (2) is silver soldered to a length of 6 mmdiameter soft copper tubing (4).…”

“…Each hemisphere has a central port (2) (3) machined in it. The upper port (2) is silver soldered to a length of 6 mmdiameter soft copper tubing (4). the lower port ( 3) is silver soldered to a tube ( 5) 55 mm long, 3 mm in diameter with a wall thickness of 2 mm and having an internal volume of about 0.4 ml.…”

“…4. The cell ( 1) is enclosed in a thick copper radiation shield (2) and suspended from the top of the shield by thin stainless-steel straps so as to minimize heat conduction to the cell. The temperature of the radiation shield is electronically controlled [15] via a copper thermometer and a 200 SZ manganin heater (4) wound on the shield.…”