Development of a low temperature calibrator for the range -190 to -100 degree Celcius

Important results from the project

The aim of the project was to make it possible to transfer the international temperature scale, ITS-90, to industrial reference instruments from -190 °C to -100 °C with a measurement uncertainty better than ±0,01 °C. This was achieved by the development of new equipment, adapted to comparison calibrations within this range. The equipment has been tested within the temperature range to make sure it meets the requirements.

Expected long term effects

A low temperature calibrator was developed that consisted of a copper block suspended in a pressure container, surrounded by liquid nitrogen. The nitrogen cools down the block and a heating element heats it up to the desired temperature. A computational model was also developed to test how different parameters affect the result and initial tests were used to improve the design. Finally, measurements were made with a reference thermometer that showed that the cooling agreed with the model, that it was possible to reach the desired temperatures and that showed the stability of the system.

Approach and implementation

The project began by investigating existing solutions, both commercial and those developed at other metrological institutes. Existing equipment was also evaluated. A first design was then developed based on the investigation and a computational model was set up. Based on the calculations the design was updated and finally a first version was manufactured. After initial tests further changes were made to reduce temperature gradients in the copper block. Finally, measurements were made to test the performance of the equipment.