A Study on the Stability of Standard Platinum Resistance Thermometer in the Temperature Range from 0°C through 720°C

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A Study on the Stability of Standard Platinum Resistance Thermometer in the Temperature Range from 0°C through 720°C (113.45 KB)

Stabilities of standard platinum resistance thermometers (SPRTs) were tested in the temperature range from 250°C to 720°C. The reason the SPRT stability should be tested not only at the maximum temperature but also at a few other temperatures is explained. Five specially made SPRTs with different filling gases were tested for this purpose. These SPRTs were annealed at four different temperatures (720°C, 675°C, 450°C, and 250°C) for up to 2000 hours. Two SPRTs with higher partial oxygen pressure showed excellent stabilities in the temperature range from 675°C to 720°C, and the total changes in their Rtp during annealing at 675°C for 200 hours were equivalent to less than 0.8 mK. But they were unstable at 250°C and 450°C with drift rates as high as 43 mK per 100 hours at 450°C. SPRTs with lower partial oxygen pressure showed very good stability in the temperature range from 250°C to 450°C, but the one with the lowest partial oxygen pressure showed upward drift in its Rtp in the temperature range from 675°C to 720°C. The factors which caused SPRT drifts were investigated and are discussed.