What are the types of thermocouple?


#1

Thermocouples are transducers used to measure temperature. When two dissimilar metals are connected together to form a junction. The junction creates a voltage difference across the wire when there is temperature difference is experienced at the junction. The classification is done based on the metal used and temperature range.

  • Base metal thermocouple

  • Noble metal thermocouple

  • Refractory metal thermocouple

Base metal thermocouple:

Thermocouple types K, J, E, T and N. Metals such as Nickel, Copper and Iron.

Type K:

Positive leg - Chromel, Negative leg - Alumel
Temperature range: -300 to 2300 Fahrenheit
Wire colour: yellow and red

Used in oxidizing and completely inert environment

Type E:

Positive leg - Chromel, Negative leg - Constantan
Temperature range: -300 to 1600 Fahrenheit
Wire colour: Purple and Red

It has the highest EMF Vs temperature values of all the commonly used thermocouples and can be used at sub-zero temperatures.

Type J:

Positive leg - Iron, Negative leg - Constantan
Temperature range: 32 to 1400 Fahrenheit
Wire colour: White and Red

Type J thermocouples can be used in a vacuum, oxidizing, reducing and inert atmospheres.

Type N:

Positive leg -Nicrosil, Negative leg - Nishil
Temperature range: 32 to 2300 Fahrenheit
Wire colour: Orange and Red

Type N is very similar to type K but is less susceptible to selective oxidation effects. Type N should not be used in a vacuum or in reducing atmospheres in an unsheathed condition.

Type T:

Positive leg - Copper, Negative leg - Constantan
Temperature range: 300to 700 Fahrenheit
Wire colour: Blue and Red

Type T thermocouples can be used in oxidizing, reducing or inert atmospheres.

Noble metal thermocouple:

Noble metal thermocouples uses expensive metals like Platinum and Rhodium . There are three types of noble metal thermocouples, Type B, R, S.

Type B:

Type B (Platinum/Platinum-30% Rhodium)
Temperature range: 32 - 3100 Fahrenheit
Wire colour: Gery and Red

Type R:

Type R (Platinum/Platinum-13% Rhodium)
Temperature range: 1000 - 2700 Fahrenheit
wire colour: Black and Red
The Type R is used in very high temperature applications.

Type S:

Type S (Platinum/Platinum-10% Rhodium)
Temperature range: 1000 - 2700 Fahrenheit
wire colour: Black and Red

Refractory Metal Thermocouples

These thermocouples are made of the exotic metals Tungsten and Rhenium, which are expensive, difficult to manufacture, brittle, and must be handled carefully. All of the refractory metal thermocouple has the same temperature range.

Type G:

Type G (Tungsten/Tungsten 26% Rhenium)
Temperature range: 32 - 4200 Fahrenheit
Wire colour: White with blue tracer and red

Type D:

Type D (Tungsten 3% Rhenium/Tungsten 26% Rhenium)
Temperature range : 32 - 4200 Fahrenheit
Wire colour: Type D: White with yellow tracer and red

Type C:

Type C (Tungsten 5% Rhenium/Tungsten 26% Rhenium)
Temperature range: : 32 - 4200 Fahrenheit
Wire colour: White with red tracer and red