Types and characteristics of Thermocouples

What is the difference between the thermocouple types? For which temperature range can the thermocouples be used?


In the following table you can see an overview of different types of thermocouples with general properties, the temperature range, material composition as well as advantages and areas of application. Information on the electrical voltage of thermocouples can be found in the table Thermoelectric voltage.

 

Thermocouple Types and Characteristics of Thermocouples

 

Thermocouple- types
--------------
Colour-
code

Characteristics of Thermocouples

 

General

 

Composition

 

Temperature range

 

Suitable application

 

Unsuitable application

Type E

 

 

 

 

base metal thermocouple

NiCr -CuNi
(nickel-chrome/copper-nickel)

single wires made of non precious metals

 

EP-leg:
89-90% nickel, 9-9.5% chrome, 0.5% silicium and iron balance: C, Mn, Nb, Co

EN-leg:
55% copper, 45% nickel approx. 0.1%, co balt, iron and manganese

 

-200°C/+700°C

 

  • in pure, oxidizing (air), or neutral atmosphere (inert gases)

  • high resistance against corrosion

  • small thermal conductivit

 

 

  • not sulphuric, reducing or alternately oxidizing, and reducing atmosphereu

  • do not apply in vacuum for a long time

 

Type J

 

 

 

 

base metal thermocouple

Fe - CuNi
(iron/copper-nickel)

single wires made of non precious metals

 

JP-leg:
99.5 % iron, approx. 0.25 % manganese, approx. 0.12 % copper, balance: other impurities

JN-leg:
55% copper, 45% nickel approx. 0.1%, cobalt, iron, and manganese

 

-180°C/+700°C

 

  • from 0 to 760°C in vacuum, oxidizing (air), reducing orinert atmosphere (inert gases)

 

 

  • temperatures below 0°C

  • sulphurous atmosphere above +500°C

  • above 760°C only with bigger wire diameters

 

Type K

 

 

 

 

 

base thermocouple

NiCr-Ni
(nickel-chrome/ nickel-aluminium)

single wires made of non precious metals

 

KP-leg:
89-90% nickel, 9-9.5% chrome, 0.5 % silicium and iron balance: C, Mn, Nb, Co

KN-leg:
95-96% nickel, 1-1.5% silicium, 1-2.3 % aluminium, 1-3.2% manganese, 0.5% cobalt, balance: Fe, Cu, Pb

 

-270°C/+1372°C

 

  • from 250°C to 1260°C in pure, oxidizing (air) and neutralatmosphere (inert gases)

  • for higher temperatures bigger wire diameters are recommended

 

 

  • between 250°C up to 600°C not suitable for exact measurements with quick temperature changes

  • not appropriate for a longer time with high temperatures in vacuum

  • do not apply with high temperatures in sulfurous, reducing or alternately oxidizing, and reducing atmoshere without protection

  • do not use in atmosphere favourizing "green mould" 

 

Type L

 

 

 

 

base thermocouple

Fe - CuNi
(iron/copper-nickel)

single wires made of non precious metals

 

LP-leg:
99.5 % iron, approx. 0.25 % manganese, approx. 0.12 % copper, ballance: other impurities

LN-leg:
55% copper, 45% nickel, approx. 0.1% cobalt, iron, and manganese

 

0°C/+900°C

 

  • from 0°C to 760°C in vacuum, oxidizing (air), reducing or inert atmosphere (inert gases)

  • above 500°C bigger wire diameters are recommended

 

 

  • Temperatures below 0°C

  • sulphurous atmosphere above +500°C

  • above 760°C only with bigger wire diameters

 

Type N

 

 

 

 

 

base thermocouple

NiCrSi - NiSi
(nickel-chrome-silicium/nickel-silicium-magnesium)

single wires made of non precious metals

 

NP-leg:
84% nickel, 14-14.4 % chrome, 1.3-1.6% silicium, ballance (not more than 0.1%): Mn, Fe, C, Co

NN-leg:
95 % nickel, 4.2-4.6 % silicium, 0.5-1.5 % magnesium, ballance: Fe, Co, Mn, C,
(altogether 0.1-0.3%

 

-270°C/+1300°C

 

  • from 300°C to 1260°C in pure, oxidizing (air) and neutral atmosphere (inert gases)

 

 

  •  do not use with high temperatures in sulphurous, reducing or alternately oxidizing, and reducing atmosphere without protection

  • do not use with high temperatures in vacuum

  • do not use in atmosphere faviourizing "green mould"

  • reducing atmosphere

 

Type R

 

 

 

 

base thermocouple

Pt13%Rh - Pt
(platinum 13% rhodium/ platinum)

single wires made of platinum and platinum - rhodium alloy

 

RP-leg:
platinum with 99.99% purity with a rhodium alloy (purity 99.98%) 13±0.05% rhodium portion

RN-leg:
platinum with 99.99% purity

 

-50°C/+1768.1°C
(melting point) recommended:
up to +1300°C

 

  • pure, oxidizing atmosphere (air), non aggresive (inert-) gases, and short-term in vacuum

  • above +1200°C type B more appropriate

 

 

  • reducing atmosphere umetal gases (for example plomb or zinc)

  • agressive vapours containing arsenic, phosphor or sulphur

  • do never use metal protecting tubes with higher temperatures

  • sensitive against impurities of impure metals

 

Type S

 

 

 

 

 

base thermocouple

Pt10%Rh - Pt
(platinum 10% Rhodium/ platinum)

single wires made of platinum and platinum - rhodium alloy

 

SP-leg:
platinum with 99.99% purity with a rhodium alloy (purity 99.98%) 10±0.05% rhodium portion


SN-leg:
platinum with 99.99% purity

 

-50°C/+1768.1°C
(melting point) recommended:
up to +1300°C

 

  • pure, oxidizing atmospheres (air), non agressive (inert-) gases, and short-term in vacuum

  • above +1200°C type B more appropriate

 

 

  • reducing atmosphere umetal gases (for example plomb or zinc)

  • agressive vapours containing arsenic, phosphor, or sulphur

  • do never use metal protecting tubes with higher temperatures

  • sensitive against impurities of impure metals

 

Type B

 

 

 

 

 

base thermocouple

Pt 30%Rh - Pt 6%Rh (platinum -0% rhodium/ platinum-6% rhodium)

single wires made of platinum and platinum - rhodium alloy

 

BP-leg:
platinum with 99.99% purity with a rhodium alloy (purity 99.98%) 29.60±0.2% rhodium portion

BN-leg:
platinum with 99.99% purity with a rhodium alloy (purity 99.98%) 6.12±0.02% rhodium portion

 

max. +1820°C
(melting point) ordinary up to
+1700°C

 

  • pure, oxidizing atmosphers

  • neutral atmospheres

  • vacuum

 

 

  • reducing atmosphere or such with agressive vapoursor impurities which react with metals of the platinum group, if it is not protected with a non metal protecting tube

 

Type T

 

 

 

base thermocouple

Cu - CuNi
(copper/copper-nickel)

single wires made of non precious metals

 

TP-leg:
99.95% copper, 0.02-0.07% oxygen, 0.01% impurities

TN-leg:
55% copper, 45% nickelapprox. 0.1% cobalt, iron, and manganese

 

-270°C/+400°C

 

  • from -200°C to 370°C in vacuum, oxidizing (air), reducing or inert atmosphere (inert gases)

  • with higher temperatures bigger wire diameters are recommended

 

 

  • above +370°C not appropriate in a hydrogen atmosphere

  • not appropriate in radioactive environment

 

Type U

 

 

 

 

Unedelmetall-base thermocouple

Cu - CuNi (copper/copper-nickel)

single wires made of non precious metals

 

UP-leg:
99.95% copper, 0.02-0.07% oxygen, 0.01% impurities

UN-leg:
55% copper, 45% nickel approx. 0.1% cobalt, iron, and manganese

 

0°C/+600°C
(+400°C)

 

  • from -200°C to 370°C in vacuum, oxidizing (air), reducing or inert atmosphere (inert gases)

  • with higher temperatures bigger wire diameters are recommended

 

 

  • above +370°C not appropriate in a hydrogen atmosphere

  • not appropriate in radioactive environment

 

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