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2.3.3 Industrial platinum resistance thermometry

High precision platinum resistance thermometers used in the realization of ITS-90 are fragile and not suitable for general use. Rugged industrial platinum resistance thermometers, in which the platinum element is firmly held, are widely used and are manufactured to fit the following resistance/temperature relations:

   T(t) = R(0 °C) [1 + A₉₀t + B₉₀t² + C₉₀t³ (t − 100 °C)]

where

   A₉₀ = 3.9083 × 10⁻³ °C⁻¹

   B₉₀ = −5.775 × 10⁻⁷ °C⁻²

   C₉₀ = −4.183 × 10⁻¹² °C⁻⁴

   For t ≥ 0 °C the coefficient C₉₀ is set to zero. The normal temperature range for thermometers of this type extends from −200 °C to 600 °C but for some thermometers it extends up to 850 °C. The tolerances of manufacture and the accuracies to be expected for industrial platinum resistance thermometers are given in national and international standards such as BS 1904 and IEC 751.

T.J.Quinn

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