Thermocouple Naming Convention
A thermocouple consists of two dissimilar metals, joined together at one end, which produce a small voltage when heated (or cooled). This voltage is measured and used to determine the temperature of the junction of the dissimilar metals. The voltage for any one temperature is unique to the combination of metals used. And the combination of metals used is assigned a letter under the Thermocouple Naming Convention.
This page on Thermocouple Naming Convention is an excerpt from the original
Thermocouple Materials webpage published by
Control And Instrumentation.com. It is produced here with their permission.
Letters Used for Naming Thermocouples
Thermocouples are available in different combinations of metals, usually refered to by a letter, e.g. type J thermocouple, type K etc. Each combination has a different temperature range and is therefore more suited to certain applications than others. Although it is worth noting that the maximum temperature varies with the diameter of the wire used in the thermocouple.
Guidance for the selection and use of devices for measuring temperature is given in the relevant sections of British Standards Specification, BS 1041, Temperature Measurement.
Thermocouple Type Chart
The following chart shows the thermocouple type, using the thermocouple naming convention, and the relevant junction materials and temperature ranges.
ASTM
Type |
Conductor
Combination |
Temperature Range |
| °F |
°C |
| B |
Platinum 30% Rhodium /
Platinum 6% Rhodium |
2500 to 3100 |
1370 to 1700 |
| E |
Nickel-chromium / Constantan |
32 to 1600 |
0 to 870 |
| J |
Iron / Constantan |
32 to 1400 |
0 to 760 |
| K |
Nickel-chromium / Nickel-aluminum |
32 to 2300 |
0 to 1260 |
| N |
Nicrosil / Nisil |
32 to 2300 |
0 to 1260 |
| R |
Platinum 13% Rhodium /
Platinum |
1600 to 2640 |
870 to 1450 |
| S |
Platinum 10% Rhodium /
Platinum |
1800 to 2640 |
980 to 1450 |
| T |
Copper / Constantan |
-75 to +700 |
-59 to +370 |
Type K Thermocouples
Type K are the most common thermocouple in the Oil & Gas, and refining industries due to their wide measuring range and low cost. They are occasionally referred to as Chromel-Alumel thermocouples, though this is a dated term. Note that for temperatures above about 750°C oxidation leads to drift and the need for recalibration.
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