A description of cryogenic temperature sensor characteristics by the weighted orthonormal polynomial expansion method: Germanium and platinum thermometer calibration test data approximation

We consider a new approximation of T=f(R) and R=g(T) functions for germanium (GRT) and platinum (PRT) cryogenic resistance thermometers from 1.2 to 85 K and from 14 to 325 K, respectively, using the weighted orthonormal polynomial expansion method (OPEM). The main aspect in this description is an evolving new type of weighting function referred to the specific material characteristics of the investigated cryogenic resistance temperature sensors. The OPEM fitting errors for GRT and PRT characteristics in the considered approximation within the whole useful temperature ranges determine the perspectives of our method in cryogenic thermometry. The proposed OPEM description of R and T functions of the investigated thermoresistors defines the hopefulness of our algorithm with respect to both the calibration of GRT and PRT sensors and the automation of thermal measurements at low temperatures. The demonstrated values of the OPEM fitting errors with the R function approximation as well as the evaluation of the first derivative dR/dT allow the OPEM to be successfully used for a generation of the interpolation tables with the resistance thermometer calibration. (C) 1996 American Institute of Physics.