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Making Sense of Sensors Part 9- Type S

Tc Type SThermocouple Type S: Platinum/10% Rhodium positive leg, and a pure platinum negative leg.

The temperature range for Type S is 0 – 1450°C (32 – 2642°F) and the colour code is black for positive and red for negative. Thermocouples using noble metals are commonly employed in high temperature measurement and control, particularly for temperatures of 1093°C (2,000°F) and higher.

In general, thermocouples employing platinum in combination with platinum-rhodium alloys, gold, or palladium have been found to be the most reproducible of all the various types. They are resistant to oxidation in air, and because of their high melting points, can be used up to very high temperatures. Due to its high stability, type S is used as the standard of calibration for the melting point of gold (1064.43°C).

Some typical applications for type S are: heat treating and control sensors, semiconductor industry, glass manufacturing, ferrous and non-ferrous metals


Noble metal sensors are very costly. Elemental hydrogen, sulphur, and some other atomic contaminants, must be excluded from type S. If these contaminants are not totally excluded, then significant calibration drift, embrittlement, and failure of the thermocouple wire will occur. In addition, certain elements act as catalysts and must also be excluded from the vicinity of the thermocouple wires.

Low sensitivity (10 µV/°C) and high cost makes them unsuitable for general purpose use.

For assistance in choosing the proper sensor for your process, please contact us and our Temperature and Process Engineers will be happy to assist you!


Continue reading… Part 10