Introduction to the Differences in Thermocouple Types

Differences in thermocouple types
Although the maximum temperature varies with the diameter of the wires used in the thermocouple, each calibration has a different temperature range and environment. Although thermocouple calibration determines the temperature range, the maximum range is also limited by the diameter of the thermocouple wire due to the following factors. That is to say, very fine thermocouples may not reach the entire temperature range.
What are the accuracy and temperature range of various thermocouples?
It is important to remember that accuracy and range depend on the thermocouple alloy, measured temperature, sensor structure, sheath material, measured medium, medium state (liquid, solid, or gas), and thermocouple wire diameter (if exposed) or sheath diameter (if thermocouple wire is not exposed but has sheath).
The voltage output generated by the thermocouple can be correlated with the temperature measured by the thermocouple. The files in the table below provide the thermoelectric voltage and corresponding temperature for a given thermocouple type. Most documents also provide thermocouple temperature ranges, error limits, and environmental factors.
Why are K-type thermocouples so popular?
K-type thermocouples are so popular because of their wide temperature range and durability. The conductor materials used in K-type thermocouples are more chemically inert than T-type (copper) and J-type (iron). Although the output of the K-type thermocouple is slightly lower than that of the T-type, J-type, and E-type, it is higher than its closest competitor (N-type) and has a longer usage time.
How do I choose between different types?
Each thermocouple type has a designated color code defined in ANSI/ASTM E230 or IEC60584. The type can be identified by color, as follows:
Color code
In addition, some materials exhibit strong to weak magnetism:
J type positive (strong magnetic), K type positive (weak magnetic).
To determine polarity, connect a thermocouple to a voltmeter capable of measuring millivolts or microvolts and look for an increased output when slightly heating the tip.
How do I choose between different types?
Choosing the correct type of thermocouple is a matter of matching the thermocouple according to your measurement requirements. Here are some aspects to consider:
1. Temperature range: Different types of thermocouples have different temperature ranges. For example, the maximum temperature of the T-type and its copper feet is 370C or 700F. On the other hand, the K-type can be used up to 1260C or 2300F.
2. Wire size: When long-term measurement is required, the diameter of the thermocouple wire also needs to be considered. For example, the rated temperature of a T-type thermocouple is 370C/700F, but if your thermocouple uses # 14AWG wire (. 064 "diameter), its rated temperature is 370C/700F. If your thermocouple has # 30AWG wire, the temperature will drop to 150C/300F. More information can be found here (see table at the bottom of page H-7).
3. Accuracy: Among all base metal thermocouples, T-type thermocouples have the highest accuracy, at 1 ℃ or 0.75%, whichever is greater