New developments in standard thermometry at the IMGC

Abstract

Recent findings in precision platinum resistance and radiation thermometry at the Istituto di Metrologia "G. Colonnetti" are described. Two issues concern high-temperature platinum resistance thermometers. The first is the use of gas-controlled heat pipes for comparing these thermometers and the development of a novel approach to improve temperature stability and uniformity. The second deals with observations made at the freezing point of silver which suggest that humidity may lead to electric leakage. In radiation thermometry the main recent achievement has been the use of a photodiode-array thermometer to realize the ITS-90 above the silver point. Relative to single-detector thermometers, this new thermometer offers several advantages that are related to its spectral characteristics. Another issue of importance is the size-of-source effect (SSE). Practical rules for minimizing SSE errors in interlaboratory comparisons are given.

The “Temperature Amplifier”: an Innovative Application of Pressure-Controlled Heat-Pipes for Calibration of PRTs and Thermocouples

“…IMGC is working on the same topic and studied some years ago the association of Na and diphenyl heat-pipes for comparing thermometers [1]. …”

Towards new temperature standards for contact thermometry above 660 C

“…In order to improve the long-term stability and reproducibility in the sodium heat pipe, a novel approach was considered [2] that took advantage of the excellent reproducibility and stability of SPRTs below 400 C. It consisted of connecting a diphenyl heat pipe, operating below 400 C, to the pressure line of the sodium heat pipe, controlling the helium pressure by means of an SPRT in the diphenyl heat pipe. A temperature of 206 C in the diphenyl heat pipe results "amplified" to about 762 C in the sodium heat pipe.…”

“…The density of mercury vapour was derived from the literature [4]. For evaluation of the hydrostatic pressure gradient, the density of mercury vapour may also be approximated, possibly with sufficient accuracy, by use of the ideal gas law: (2) where is the pressure (8380 Pa), the molar weight (200.61 g mol -1 ), the universal gas constant (8.31451 J K -1 mol -1 ) and the absolute temperature ( 516 K). Figure 2 indicates that the measurement of the temperature distribution in the thermometer well of a gas-controlled heat pipe, by withdrawing or reintroducing the thermometer, induces small pressure changes because of shifts in the vapour-to-liquid ratio.…”