APPROXIMATING THE RESISTANCE-TEMPERATURE RELATIONSHIP OF PLATINUM RESISTANCE THERMOMETERS FROM 20 K TO 273 K

摘要

A platinum resistance thermometer (PRT) must be calibrated to accurately define the resistance-temperature relationship R(T). For the temperature range of 20 K to 273 K, this can be problematic due to the non-linearity of the R(T) and lack of convenient calibration media near 20 K. A method of approximating the R(T) has been developed based on a simple 3-point calibration using the boiling point of helium, boiling point of nitrogen, and ice point. This method has been investigated with laboratory grade and rugged aerospace sensor designs, including wire diameter between 8 and 80 μm. A correlation between resistance ratio values allows use of a standard ITS-90 interpolation formula with uncertainty less than 0.1 K over the range 20 K to 273 K.