Temperature Measurement

Type K Thermocouple

Type K thermocouple:

Type K thermocouple is the most commonly used thermocouple type, because it has the widest operating temperature range.

  • Leg Metal: Chromel, Alumel
  • Temperature Range: -270°C to 1260°C
  • Melting Point: 2550°F
  • Tolerance: +/-15K between -40°C to 375°C
  • Positive leg: Non magnetic, chromel
  • Negative leg: Magnetic, Alumel

Colour coding for K type thermocouple:

Why type K thermocouple are most commonly used?

  • Suitable for rugged environmental conditions
  • High temperature range and output of -6.4 to 54.9mV over maximum temperature.
  • Fast response
  • Small size
  • Reliable
  • K type thermocouple oxidize slowly so they has longer life.

Voltage vs Temperature graph for K type thermocouple:

Insulation used in type K thermocouple:

There are two types of thermocouple used for K type thermocouple, Ceramic and Magnesium oxide insulation.

Ceramic Insulation:

Ceramic insulation used for high-temperature applications, which can withstand high temperature of 1260°C.


  • Low thermal mass, which means it does not retain heat.
  • Light weight
  • Material: High pure Alumino silicate
  • High temperature capacity: 1260°C

Magnesium oxide:

Magnesium oxide is used in applications where thermocouples are immersed in liquid, in high moisture conditions, corrosive gases and high pressure conditions.


  • High dielectric strength
  • High speed responds
  • 97% High pure MgO and AI2O3.

Application of K type Thermocouple:

  • Type K thermocouples are used in many different kinds of environments such as water, mild chemical solutions, gases and dry regions for measurement. Motors, heaters for oil and boilers.
  • Used for testing of heating appliance safety
  • Commonly used in nuclear applications

Advantages of K type thermocouple:

  • Good linearity of EMF.
  • Good resistance against oxidation below 1000°C (1600°F)
  • Highly stable output.
  • Low cost

Disadvantages of K type thermocouple:

  • Not appropriate for reducting atmosphere, but will resist metallic vapor
  • Aging of the emf characteristic
  • Due to chromium vaporization in the positive element, not appropriate for vaccum applications.
  • Cannot be used in sulfuric environment, because both will corrode rapidly.


Instrumentation Engineer

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