Facility for the calibration of Pt/Pd thermocouples in the temperature range from 960 °C to 1500 °C

Abstract

Five Pt/Pd thermocouples, constructed and calibrated at IMGC at fixed points in the temperature range from 0 °C to the Ag point, were calibrated by comparison with the local primary standard radiation thermometer with the aim of replacing the presently used Pt/Pt–Rh alloy thermocouples as secondary reference standards up to 1500 °C. To fully exploit accuracy of Pt/Pd thermocouples, high-level calibration techniques need to be adopted. For this purpose, a new high-temperature three-zone furnace was arranged and characterized in order to obtain the best axial uniformity and a specially designed blackbody cavity was used as a transfer source for calibrating the thermocouples in the temperature range from 962 °C up to 1500 °C. At the end of the comparison measurements, additional calibrations at the Ag fixed point were made, in order to check the stability of the thermocouples' signals. A comparison between experimental results and the reference function is presented and an extrapolation of the fixed-point calibration data is analysed.

INRIM–NMC Comparison of Pt/Pd Calibration Above the Ag Point

“…Details of the INRIM thermocouple calibration facility against a radiation thermometer using a blackbody cavity as a transfer source are described in [1]. The facility is an improvement of what was used for developing the reference function of a Pt/Pd thermocouple from 800 • C to 1500 • C [6].…”

“…As such an arrangement allows calibration of Pt/Pd thermocouples against a radiation thermometer in an accurate manner [1], NMC also developed a similar facility to calibrate high-temperature thermocouples. With the aims of validating the respective measuring systems and fully exploiting the potential of Pt/Pd thermocouples up to 1500 • C, INRIM and NMC arranged a comparison of a Pt/Pd thermocouple and radiation thermometer based on such facilities.…”

The Combined Use of a Gas-Controlled Heat Pipe and a Copper Point to Improve the Calibration of Thermocouples up to 1100 ˚C

“…The cell was characterized using a group of five thermocouples: a Type S thermocouple, calibrated at ITS-90 fixed points up to the gold freezing point, and four Pt/Pd thermocouples, calibrated up to 1,500 • C by comparison with the standard radiation thermometer [6].…”

“…In fact, all the values of the emf measured by the thermocouples at the freezing plateaux give rise to calculated temperatures systematically below the temperature assigned by the ITS-90 to the copper fixed-point, i.e., 1084.62 • C: a difference of −0.09 • C was found for the Type S thermocouple, and an average difference of −0.14 • C, with a standard deviation of 0.08 • C, was found for the four Pt/Pd thermocouples. For the Pt/Pd thermocouples, the temperature was calculated using the reference function (now included in the ASTM E1751-00 standard [7]) and a deviation curve that was determined for each thermocouple from the calibration performed by comparison with the standard radiation thermometer [6]. The standard uncertainty of these two sensors was estimated to be 0.28 • C and 0.22 • C, for the Type S and Pt/Pd thermocouples, respectively.…”

“…Both a Type S thermocouple and one of the Pt/Pd thermocouples used in the present investigations, and referred to as Ea in [6], were included in the analysis. Firstly, the sealed copper cell was used to calibrate the Type S thermocouple that was previously calibrated in the laboratory for primary thermometers at the copper fixed-point.…”