A new high-temperature platinum resistance thermometer made of a sapphire single crystal

A high-temperature platinum resistance thermometer (HTPRT) was designed and fabricated, using a synthetic sapphire single crystal as sensor former, insulation and protection tube. Measurement data at several fixed points showed that the sapphire HTPRT satisfied the ITS-90 criteria as an interpolating thermometer in the temperature range from 0 degreesC to 962 degreesC. The temperature-resistance characteristic of the HTPRT was measured using a type S thermocouple. The data were fitted using a polynomial least squares fitting method, and showed a quadratic relationship in the temperature range from 500 degreesC to 1500 degreesC. The reproducibility of the Cu freezing point realized using the sapphire HTPRT was +/-19.2 mK and the HTPRT was very stable during the freezing experiments. The insulation resistance of the HTPRT decreased exponentially as the temperature increased, and was 63 kOmega (similar to 31.5 mK) at 1500 degreesC. It is concluded that the HTPRT made of a sapphire single crystal is anticipated to be an accurate contact thermometer at high temperatures.