Three different water triple point cells (Table 3) are used at METROSERT to represent the temperature of the triple point of water (TPW) according to the ITS-90 as the national reference.
The calibration points for the platinum resistance thermometers are selected as the approximate fixed point temperature values according to the defined sub-ranges of ITS-90 with additional temperature values between the fixed point temperatures.
General information: New standard reference tables for thermocouples are necessary as a result of the introduction of the new international temperature scale, ITS-90
, which interpolates between fixed points by means of a standard platinum resistance thermometer instead of thermocouples.
005 % from the corresponding ITS-90
is based on 17 temperature fixed points, to which certain temperatures are assigned.
Hart adds that Met/Temp II also enables users to perform ITS-90
coefficient and residual calculations and generate corresponding tables and reports.
PRTs may be read using the standard DIN curve or individually calibrated probes may use ITS-90
coefficients for higher accuracy.
These databooks are denoted as: 1 - Realising ITS-90
, Primary Laboratory; 2 - Secondary Laboratory Equipment; 3 - Industrial Laboratory Equipment; 4 - Blackbody and Thermocouple Reference Equipment; and 5 - Training and Services.
Within these documents, the differences in the realizations of the various fixed points in this range of the ITS-90
and the uncertainties of those differences are given for the 15 standards laboratories participating in the comparison.
This irreproducibility of temperature values is one type of so-called non-uniqueness of the ITS-90
and is an inherent limitation of the ITS-90
When it was developed, the ITS-90
represented thermodynamic temperatures as closely as possible.
New reference function for platinum-10 % rhodium versus platinum (type S) thermocouples based on the ITS-90
Part I: Experimental procedures, in Temperature, Its Measurement and Control in Science and Industry, Vol.