Type B thermocouple table: mV vs °C (0 to 1820 °C)

A type B thermocouple (platinum with 30% rhodium (+) and platinum with 6% rhodium (−)) produces a voltage that depends on the temperature difference between the measuring junction and the reference junction. The table follows the NIST (ITS-90) reference functions, with the reference junction at 0 °C.

Below about 50 °C the type B voltage is almost zero (slightly negative between 0 and about 40 °C) and does not identify the temperature. Type B is meant for high temperatures.

Type B thermocouple, reference junction at 0 °C

What about the cold junction?

In the field the reference junction sits at the transmitter or instrument terminals, almost never at 0 °C. So the voltage measured at the terminals is not the table value: the instrument compensates the cold junction. To check a mV reading, take the terminal temperature into account.

Calculated reference values, not measurements. The thermocouple tolerance depends on its class (IEC 60584-1) and is not in the table.