K type thermocouple

Type K Thermocouple provides widest operating temperature range. It consist of positive leg which is non-magnetic and negative leg which is magnetic .In K Type Thermocouple  traditional base metal is used due to which it can work at high temperature and can provide widest operating temperature range. One of the constituent metal in K Type Thermocouple is Nickel, which is magnetic in nature.

The characteristic shown by K Type Thermocouple is that they undergo a deviation in output when magnetic material reaches its Curie Point, at around  185 °C. K Type  thermocouple  work very well in oxidizing atmosphere at temperatures up to 1260°C (2300°F) and its tolerance class is ± 1.5 K between -40 and 375 °C

K type thermocoupe colour code

Why To prefer K Type Thermocouple:

  • One of the major advantage of K type thermocouple over other thermocouple’s is it can function in rugged environmental condition & in various atmospheric .
  • It has integrated composition of Chromel and Alumel wires has a range of -270 °C to 1260 °C and an output of -6.4 to 9 mV over maximum temperature range.
  • Also known as general purpose thermocouple due to its wide range of
  • Type K has longer life than Type J as in Type J Fe (iron) wire oxidizes rapidly, especially at higher
  • They are inexpensive.
  • Have a fast response time
  • Small in size and are reliable.
  • Generally used at temperatures above 540 degrees C


In K Type Thermocouple positive leg is composed of 90% nickel, 10%chromium and a negative leg is composed of 95% nickel, 2% aluminum, 2% manganese and 1% silicon. These are the most common general purpose thermocouple with a sensitivity of approx 41µV/°C.

Type K Insulation Material:

In Type K Thermocouple mainly two type of insulation is used firstly Ceramic beads  insulation is used as it is a lightweight insulating product. It is made from high purity alumino-silicate materials. It has low thermal mass which means that it does not retain heat, low thermal conductivity and is an extremely effective insulation material as it can withstand high temperature of 1260 °C so it it best suited material for Type K thermocouple. Secondly compacted mineral insulation and outer metal sheath (MgO) is used. Magnesium Oxide has a high dielectric strength, responds quickly to temperature changes and is very durable. It has typical Composition of the Standard Quality MgO (97%) and the High Purity MgO and AI2O3. Magnesium Oxide insulation is recommended for K Type thermocouple when Thermocouple are to be immersed in liquids, high moisture, corrosive gases or high pressures.

Temperature Range:

To find appropriate range of thermocouple we should use appropriate wire because different wires measure various temperature ranges. Of the four major thermocouple types, type K covers the widest range :

  • Therocouple Wire grade  – 270 to 1260 degrees C
  • Extension wire 0 to 200 degrees C
Accuracy :-

+/- 2.2 to +/- 0.75 degrees C

EMF Vs Temperature Graph for K Type Thermocouple:

They are mostly used for applications at temperatures above 550 °C up to the maximum working pressure of the thermocouple.

  • They are used in many industries like Steel & Iron to monitor temperature & chemistry through out the steel making process.
  • Used for testing temperatures associated with process plants e.g. chemical production and petroleum refineries
  • Used for Testing of heating appliance safety
  • Type K is commonly used in nuclear applications because of its relative radiation hardness.

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