Thermal Strain Effects in Standard Platinum Resistance Thermometers

Seventeen standard platinum resistance thermometers from five commercial sources have been subjected to repeated thermal cycling over all or most of the range -196 °C to +650 °C to determine whether strain effects occur in the platinum sensors, and to what precision they affect temperature measurements. It is found that the resistance at the triple point of water, when measured repeatedly during thermal cycling, does undergo reversible changes in many thermometers that can be attributed to either elastic or anelastic strain. The magnitude of this resistance irreproducibility is usually between the equivalent of 0.1 m °C and 1.8 m °C near 0 °C. It is concluded that thermal strain effects pose a small, but significant, limitation on the ultimate performance of most of these thermometers.