Effects of Different Surroundings on the Stability of Standard Platinum Resistance Thermometers from 650°C through 1000°C

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Effects of Different Surroundings on the Stability of Standard Platinum Resistance Thermometers from 650°C through 1000°C (190.01 KB)

It was reported that standard platinum resistance thermometers (SPRTs) are contaminated when their sensors are close to base metals or alloys above 980°C. The Ni, Cr, and Fe ions seem to be able to permeate fused silica sheaths at high temperatures. In order to know if similar contamination occurs below 980°C, many SPRTs with different nominal resistances at 0.01°C (25.5, 2.5, and 0.25 ohms) were annealed in blocks of different materials (graphite, alumina, Inconel, and aluminum-bronze) from 500°C to 1000°C for more than 1000 hours. Our results showed no contamination at 660°C for any of the block materials investigated. There was no contamination discovered in the graphite and alumina blocks up to 1100°C. However, contamination began near 800°C in an Inconel block. The drift rates of Rtp of three SPRTs in an Inconel block were measured from 750°C to 1000°C.