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The AM1968 Platinum Capsule SPRT covers temperatures from -260°C to 100°C. The capsule construction makes this SPRT a preferred primary standard for cryogenic applications and other applications where space is limited or stem conduction is a concern for a long stem SPRT.

The sensing element is made of pure platinum wires with a temperature coefficient of 0.003925 Ω/Ω/°C. The coiled platinum wires are mounted in a way that is strain free and are enclosed in a platinum capsule, which is sealed by glass. The special sealing glass has a thermal expansion coefficient that matches with that of the platinum wire to ensure the capsule SPRT is sealed permanently through the entire temperature range. A uniquely designed support structure provides excellent performances with regards to stability, mechanical shock resistance, and thermal cycle performance. This SPRT achieves a high level of stability and repeatability in performance, and fully meets the ITS-90 criteria for reference thermometers.