Making Sense of Sensors Part 8- Type R

Thermocouple Type R: Types R thermocouples, (Platinum vs. 13% Rhodium/Platinum), are usable up to 1480^°C (2,700^°F).

They are extremely stable but reducing atmospheres are particularly damaging. This type should be protected with a gas-tight ceramic tube and a secondary tube of alumina, aluminous porcelain, silicon carbide, or metal outer tube, as conditions require. Type R can deliver 15 percent more millivolt than Type S.

Thermocouples using noble metals are commonly employed in high temperature measurement and control, particularly for temperatures of 1093°C (2000°F) and higher. Type R thermocouples cover similar applications as Type S, but offer improved stability and a marginal increase in range. Consequently, Type R tends to be used in preference to Type S.

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. 

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

Considerations

Noble metal sensors are very costly. Elemental hydrogen, sulphur, and some other atomic contaminants must be excluded from type R. 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 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 9