Making Sense of Sensors Part 2- Type B

Thermocouple Type B: Platinum – 30% Rhodium (+) vs. Platinum – 6% Rhodium (-)

With a general application range from 870 – 1700°C (1600 – 3100°F), Type B thermocouple is recommended for use in clean air. 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.

Type B is more resistant than either type R or S to grain growth that could result in mechanical failure. Under some conditions, type B may also have less calibration drift than type R or S sensors that are subjected to the same use.

The type B sensor may be used for brief periods in a vacuum and is often seen in molten glass applications. It is also used extensively in the steel and iron industry to monitor temperatures and chemistry throughout the steel making process.

Considerations

Type B should not be used in reducing atmospheres, nor where exposed to nonmetallic or metallic vapors. This type of sensor is easily contaminated. Reducing atmospheres are particularly damaging to the calibration. Noble metal thermocouples should always be protected with a gas-tight ceramic tube, a secondary tube of alumina, and a silicon carbide or metal outer tube as conditions require. This type is not suitable for direct insertion into metallic protecting tubes.

A characteristic of type B is that they have a low electrical output, therefore are rarely used below 600°C.  As the output is virtually negligible up to 50°C, cold junction compensation is not usually required with this type.

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 3