Methods for calibrating against the practical temperature scale in the region of 10–90°K

Conclusions

• 1. A method for correcting platinum thermometer scales against a standard scale by means of formula

  $$W_T = W_T^k + \sigma (1 + \eta )(1 - W_T^k ) - \frac{{\eta ^2 \sigma ^2 }}{{\eta \sigma + \nu W_T^k }}$$

  is suggested, where W ^K_T is a tabulated function of W ^st_T , and the latter is a function of temperature; σ, η andγ are constants obtained from calibrating the thermometer at the boiling points of helium, hydrogen and oxygen. The method is only applicable if these constants are positive. The error obtained after correction by this method of 10 different grades of platinum, which were experimentally investigated earlier [3], amounts to 0.01° in the range of 12–90°K for sufficiently pure grades of platinum (α>0.003923). For less pure grades of platinum the correction error amounts to several hundredths of a degree.

• 2. Experimentally obtained data [3] of thermometers made of 10 different grades of platinum were compared with the calculated data:

• a) Scales calculated by means of the Nernst formula with one constant and the Z-function method (with two constants) were compared with experimental data, thus determining the accuracy and range of applicability of these simple methods;

• b) scales of thermometer type IKh-4 calculated by more complex correction methods [5, 6, 7] were compared with experimental data, showing the insufficient accuracy of these methods for this type of platinum;

• c) the comparison of scales corrected by Barber's method [8] indicated the unsatisfactory degree of accuracy of this correction method in the 20–90°K range for sufficiently pure platinum. The correction accuracy at temperatures below 20°K is considerably worse than that obtained by the method suggested by the present author.