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°C to 962°C. 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°C to 1500°C. 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 kΩ (～31.5 mK) at 1500°C. It is concluded that the HTPRT made of a sapphire single crystal is anticipated to be an accurate contact thermometer at high temperatures.
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