Abstract
A capsule-type standard platinum resistance thermometer was constructed, which is applicable to high accuracy measurements of heat capacity between 70K and 700K. A doubly coiled element is installed on a fused silica cross with strain-free construction in a platinum capsule, and four platinum leads are brought out through ceramic seals. After stability testing, the thermometer was calibrated based on the IPTS-68 by using standard calibration apparatus: It has an ice-point resistance of about 26.0Ω and a steam-point resistance ratio of 1.392 494 as determined by a d-c resistance bridge. A separate experiment for calibration was performed in the calorimeter (in situ), when an a-c resistance bridge and small-sized triple-point cells of Ga, In and Zn were employed. The resistance ratio at steam point was determined to be 1.392 543, being different from that obtained by the d-c measurement. The systematic errors in the a-c measurement of the thermometer resistance are evaluated by a couple of calibration experiments.
