Type K thermocouple:
Type K thermocouple is the most commonly used thermocouple
- 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.
