Isotech Copper Point SPRT

SPRT probe up to 1100 degrees Celcius

For years, the temperature calibration world has run into the problem of accurately measuring temperature at higher values. The ITS-90 specifies the SPRT to the freezing point of silver, 961.78°C. Thermocouples can be used at this temperature but it is difficult to detect small changes. For example, for a Type R thermocouple, the voltage sensitivity at the copper point is 14μV/°C; a change of 1μV corresponds to a temperature change of 71mK.

When thermocouples are used, electrical noise limits the ability to track small changes at the copper freezing plateau, and so Isotech has turned its attention to developing a new resistance thermometer that will allow better measurements to be made.

Isotech has a long history of producing SPRTs up to the silver point (model 96178). This experience was combined with new research to develop the new copper point SPRT (Model 108462).

Features SPRT Probe

Ro is nominally 0.25Ω, the same as the silver tip SPRT but the platinum winding is held in place on a new type of mandrel made of synthetic sapphire. Platinum “loves” to oxidize but “hates” reduced atmospheres. The mantle of the thermometer is alumina and it is filled with air and thus surrounded by 20% oxygen. In a unique way, the jacket is connected to a small air pump to keep the Model 108462 pressurized, so that any leaks go out, while maintaining an oxygen-rich atmosphere around the winding. This is what gives the thermometer its stability. The four platinum wires are separated with tubes of quartz glass and guided through four bores. During operation, the winding receives a prestress of +9 V DC through the enclosed ionizer.

After about 30 years of research, earlier results of which were officially presented at TEMPMEKO & ISHM 2010 and at the ninth International Temperature Symposium (ITS9), Isotech has now commercialized the design to allow other researchers to benefit from this technology as well.

For detailed specifications of this SPRT probe, please refer to the datasheet of the 108462 SPRT.

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