Study of the reliability and accuracy of thermistors for temperature measurements using transportable mercury triple point cells

Abstract

<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:arial;mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="">The triple point of high purity mercury filled in small sealed cells of borosilicate glass has been determined by using calibrated thermistors. The aim of the work is to check the accuracy of temperature measurement by using thermistors below zero degrees Celsius. Two small sealed cells were used. The first was filled with mercury purified at the thermometery laboratory of the National Institute for Standard (NIS) by chemical treatment followed by triple distillation (NIS sample). The second cell was filled with mercury of purity 99.9999% obtained from the National Institute for Standards and Technology (NIST), USA (NIST sample).The values obtained for the triple point of mercury are: -38.833±6.4 x 10^{-3 o}C and -38.834±6.4 x 10^{-3 o}C for the NIS and NIST samples, respectively. These two values are in good agreement with each other and reproduce well the value adopted by the International Temperature Scale of 1990 (ITS-90) for the triple point of mercury, which is -38.8344.C. The results obtained indicate that the method of purification used in the present work is suitable to obtain mercury of purity better than 99.999%. It indicates also that thermistors can be used for precise temperature measurement below zero degrees Celsius.</span>