Journal Archive

Platinum Metals Rev., 1968, 12, (1), 6

Self-heating in Platinum Resistance Thermometry

  • F. J. S.

Routine measurements of temperatures between −200 and +850°C are carried out with high accuracy using platinum resistance thermometers. However, the measuring current itself causes heating in the platinum element by an amount proportional to the square of the current. Measurements requiring extreme accuracy or those where the measuring current is larger than the usual few milliamperes thus require correction for the self-heating effect.

Dr W. Diehl, of Degussa, Hanau, has now shown (ETZ-B, 1967, 19, (22), 637–640) that the self-heating coefficient can be calculated by applying results of his tests on sealed platinum resistance elements. These tests measured the self-heating effect of such elements in still air, still water and running water. Using a test current of 3 milliamperes, results then were correct to within 0.008 to 0.024°C in still water and to within 0.06 to 0.11°C in still air at 20°C. Self-heating due to other currents can be calculated from the self-heating coefficients in the tables which Dr Diehl has produced.

None the less, for the greatest accuracy, it is recommended that the platinum element should have the lowest possible resistance and that its self-heating coefficient should be determined under conditions similar to those which it will meet in practice.

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