High temperature fixed points for improved thermocouple calibrations
Project Description
The aim of the project is to develop robust high temperature fixed points for thermocouple calibration.
These developments will:
- reduce calibration uncertainty by a factor of 2 in the temperature region between the Cu freezing temperature and the Pd melting temperature
- avoid destruction of the thermocouple hot junction during calibration (as in wire bridge method)
- increase confidence in the calibration by having a fully assessed fixed point cell rather than relying on a piece of palladium wire of uncertain purity
- provide a means to compare national temperature measurement capability with lowest uncertainties
- enable selection of the most appropriate calibration method and temperature range required by the user
A management board will be established who will be responsible for setting up a formal project and ensuring its progress and continuous exchange of information.
The project will have 4 phases:
- Exchange of knowledge and methodology between partners building on the experience gained in the Himert project (eg to share knowledge concerning construction of Pt-Pd thermocouples and metal-carbon cells)
- Each partner to construct Pt-Pd thermocouples
- Each partner to construct two cobalt-carbon eutectic cells (1324 °C) suitable for contact thermometry, Assessment between partners of the devices developed. Two cells will be measured by radiation thermometry
- Disseminate to calibration activities
Learning from the above experience each partner will then construct and test at least one palladium-carbon eutectic cells (1492 °C) according to phases 3 and 4 above.
Expected duration : 4 years
Regular progress review meetings will be held (at least annually)
Final Report 2011-03-17
The E857 project is organised in five work packages (WP) :
- WP-1, construction of Pt/Pd thermocouples carefully stabilized for use at the metal-carbon eutectic point temperatures below,
- WP-2, development of sets of cells at the Co-C eutectic point (1324 °C)
- WP-3, development of sets of cells at the Pd-C eutectic point (1492 °C)
- WP-4, establishment of traceability to ITS-90
- WP-5, project management, meetings, future industrial dissemination plans
WP-1, -2 and -3 are inter-dependent.
Technical summary
WP-1(completed 2007): Each participating laboratory has constructed at least 3 Pt/Pd thermocouples. Their metrological performance in terms of thermoelectric stability and homogeneity were assessed in different ways. In 2007, the Pt/Pd thermocouples were used for local tests at the Co-C eutectic point. Thermocouples from LNE and NMIJ were selected for the Co-C comparison described below. The activities on Pt/Pd thermocouples carried out in this project have been presented at Tempmeko 2007 symposium and are reported in full details in the form of a paper (F. Edler, R. Morice, J. Pearce, in Proceedings of TEMPMEKO 2007, Int. J. Thermophys., doi:10.1007/s10765-007-0353-1).
WP-2 (completed 2009): Two cobalt-carbon cells have been constructed and locally tested in each laboratory. An inter-laboratory comparison of cells was performed to assess their stability and reproducibility. Each laboratory, including NMIJ, has provided one Co-C eutectic cell. The four cells and two Pt/Pd thermocouples (1xLNE, 1xNMIJ) were circulated to the laboratories in the following order: PTB, NPL, LNE, NMIJ, PTB. The melting temperatures of the Co-C eutectic fixed-point cells agree very well. All cells demonstrated good robustness. The results of the comparison of Co-C cells using Pt/Pd thermocouples are published in Metrologia : F Edler, R Morice, H Ogura, J Pearce, “Investigation of Co–C cells to improve thermocouple calibration”, Metrologia 47 (2010) 90–95.
WP-3 (completed 2010): A comparison of Pd-C eutectic cells has been carried out (participants PTB, NPL, LNE, NMIJ). Each participant constructed two Pd-C cells: one cell was circulated between the participants, the second cell was used as an internal check of the circulating cell before starting and at the end of the comparison. The four circulating cells were measured by each participant using a ‘local’ Pt/Pd thermocouple. The results showed an excellent agreement of the melting temperature of three Pd-C cells. A systematic difference by about -1.5 K was observed by using the PTB cell. Successive melt/freeze cycles resulted in a leakage of metal through the thermometer wells of some of the cells. Robustness of the Pd-C cell should be improved in the future, to constitute suitable fixed-point devices. Results will be published soon in Metrologia (2011).
WP-4 (completed 2009): At NPL non-contact measurement of a small Co-C and a small Pd-C cell made from the same batch of Co, Pd, and C as the contact thermometry cell has been performed. A Pd-C eutectic cell was measured at PTB using a LP3. Local assessments performed at NPL and LNE have been presented at Tempbeijing 2008 and published (two individual papers, in Acta Metrologica Sinica 29 (2009)) and at Tempmeko 2010, Int. J. Thermophys. (2011) DOI 10.1007/s10765-010-0892-8.
WP-5: A first review meeting was held 7 June 2006. Technical work performed in each laboratory was discussed as well as future work / time schedule. An International Workshop on High Temperature Fixed Point was organized at LNE 6-7 June 2006, gathering 63 participants from 14 countries.
The project and technical progress have been presented at Tempmeko 2007 symposium and published in the proceedings (R. Morice, F. Edler, J. Pearce, G. Machin, J. Fischer, J.R. Filtz, in Proceedings of TEMPMEKO 2007, Int. J. Thermophys., doi:10.1007/s10765-007-0356-y). Current research activities on HTFPs, including this work, were presented by the three laboratories at the NCSLI conference July-August 2007 (published in the journal Measure, March 2008). The final report of the ‘Quickstart’ EU project was submitted in March 2007 in the form of the above Tempmeko papers. A review meeting was held on May 25, 2007 (Lake Louise, Canada).
Other events related to this WP:
Review meeting, May 20th 2008, Paris (LNE, NMIJ, NPL, PTB
Technical exchanges and review, February 16, 2009, Berlin (PTB, LNE), February 18-19 2009, Teddington (NPL, LNE).