An apparatus to measure the thermal conductivity of bulk samples at cryogenic temperatures is in use at LASA Laboratory since some years. The Magnex Scientific Ltd cryostat and the inner mechanical system realized at LASA, have maintained good performances during the time. On the contrary, the electrical connections have been damaged by the thermal cycles experienced, for this reason they have been replaced. The realization of the thermal sensors, AuFe (0.07% at.w.)-Cromel P thermocouples (TC), has been improved and standardized. A new electronic system, h/w and s/w, has been realized. The temperatures are acquired by a nanovoltmeter, while the measure parameters (pressures, cryogenic levels, etc) are acquired by a precision multiplexer. The acquisition, the storage and the readout of the data are managed in real time by LabView 8.5. The reliability of the measures and the quantity of the data have allowed a deeper study of instrumental phenomena as, for instance, the capacitive effect of the nitrogen level probe on the TC voltage and the relationship between the different thermal zero levels and the physical conditions of the apparatus.
Antonio et al. (Mon,) studied this question.