COMPARISON OF TEMPERATURE VALUES OF THE MERCURY TRIPLE POINT REALISED IN MINIATURE AND CONVENTIONAL CELLS.

摘要

Traditionally, the triple point of mercury (one of the ITS-90 fixed points, T_(90)=234.3156 K) is realised in glass cells similar to those used for the triple point of water, containing as much as (2÷3) kg of mercury. Now the technique of multi-compartment cells (multicells) is finding increasing appreciation. Thus, it would be desirable to realise also the triple point of mercury with such a device. This would allow to calibrate thermometers at all triple points used as cryogenic fixed points in at most two low-temperature runs (depending on the design of the multicell), without having to open the cryostat just to change single cells for every fixed point. With such an application in mind, a miniature cell was constructed and tested at INTiBS with a repeatability of better than 50 μK. It is a stainless-steel cell with an outer diameter of 5 mm and a length of 50 mm, sealed with only 7 g of mercury. In order to test for systematic errors, this miniature cell has now been compared with a triple-point cell of the traditional type. Three thermometers have been calibrated in the miniature cell and also in a traditional cell of IMGC.