Bilateral comparison of mercury triple point cells

Project Description

In Poland the national temperature standard in the temperature range from 13,8033 K up to 273,16 K has been established at INTiBS. The mercury triple point has been realized using a miniature mercury cell - designed and realized at INTiBS. It is difficult to provide an international comparison of the miniature cell and the typical large mercury cell used by the majority of NMIs.

INTiBS has now a new mercury cell (ISOTECH) which, after the bilateral comparison, will replace the miniature cell as the national temperature standard.

The bilateral comparison of mercury cells will be analogous to the bilateral comparison of water triple point cells (EUROMET Project 895).

The first set of measurements will be carried out at INTiBS. Two standard platinum resistance thermometers - one capsule type and one long stem - will be used for temperature measurements. The resistance of these thermometers is measured at the triple point of water, too. In the comparison, the values W(Hg) = R(TP_Hg)/R(TP_H2O) will be used.
The second set of measurements on the INTiBS mercury cell will be made at PTB. The cell will be compared with the PTB standard mercury cell, which was used for the CIPM Key Comparisons CCT-K2 and CCT-K3. During the comparison for the temperature measurements the SPRTs from INTiBS and PTB will be used.
Finally, on its return, the INTiBS mercury cell will be measured at INTiBS once again.

A final report of the comparison will be prepared by both partners.

Final Report 2011-03-15

The project was realized between 2006 and 2010.

Direct comparisons of the reference mercury cells of INTiBS (No. Hg220) and PTB (No. M090) were performed.

The two main results are:

• the mercury triple point cell no Hg 220 of INTiBS has a triple point temperature value which is lower than the national standard of PTB by 0,175(60) mK. Thus, its application for the calibration of precision platinum resistance thermometers according to the ITS - 90 at INTiBS  requires to apply a small correction.
• the results of the calibration of platinum resistance thermometers performed at INTiBS and PTB, respectively, coincide well within the combined uncertainty. This verifies the reliability of the uncertainty budgets established for the calibration by the both partners.

The final report is being prepared.