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.

Features:

• 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.

Features:

• 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.