Introduction:-
Type K Thermocouple provides the widest operating temperature range. It comprises of a positive leg which is non-attractive and a negative leg which is attractive. In K Type Thermocouple customary base metal is utilized because of which it can work high temperature and can give amplest working temperature range.
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 an oxidizing atmosphere at temperatures up to 1260°C (2300°F) and its tolerance class is ± 1.5 K between -40 and 375 °C.
Why prefer K Type Thermocouple:-
• One of the major advantages of K-type thermocouples over other thermocouples is it can function in rugged environmental conditions & in various atmospheres.
• It has an integrated composition of Chromel and Alumel wires has a range of -270 °C to 1260 °C and output of -6.4 to 54.9 mV over the maximum temperature range.
• Also known as general purpose thermocouple due to its wide range of temperature.
• Type K has a longer life than Type J as in Type J Fe (iron) wire oxidizes rapidly, especially at higher temperatures.
• They are inexpensive.
• Have a fast response time.
• Small in size and are reliable.
• Generally used at temperatures above 540 degrees C.
Composition:-
In K Type Thermocouple positive leg is made out of 90% nickel, 10%chromium, and a negative leg is made out of 95% nickel, 2% aluminum, 2% manganese, and 1% silicon. These are the most widely recognized broadly useful thermocouple with an affectability of approx 41µV/°C.Type K Insulation Material:-
In Type K Thermocouple mainly two types of insulation are used firstly Ceramic beads insulation is used as it is a lightweight insulating product. It is produced using high virtue alumino-silicate materials. It has a low warm mass which implies that it doesn't hold heat, low warm conductivity, and is an incredibly compelling protection material as it can withstand a high temperature of 1260 °C so it a most appropriate material for Type K thermocouple.
Also compacted mineral protection and external metal sheath (MgO) is utilized. Magnesium Oxide has a high dielectric quality, reacts rapidly to temperature changes, and is entirely sturdy. The regular composition having the standard quality Mgo with the purity MgO and AI203.
Magnesium Oxide protection is suggested for K Type thermocouple when Thermocouple are to be submerged in fluids, high dampness, destructive gases, or high weights. The thermocouple can be framed to arrive at in any case unavailable regions.
Temperature Range :-
To discover the fitting scope of thermocouples we should utilize proper wire in light of the fact that various wires measure different temperature ranges. Of the four significant thermocouple types, type K covers the largest reach:-
• Thermocouple grade wire, –454 to 2,300F (–270 to 1260°C)
• Extension wire, 32 to 392F (0 to 200°C)
Accuracy (whichever is greater):
• Standard: +/- 2.2°C or +/- .75%
• Special Limits of Error: +/- l.l°C or 0.4%
Tolerance Class:-
EMF Vs Temperature Graph for K Type Thermocouple:-
Pros And Cons:-
Pros
• To measure temperature it provides good linearity of emf.
• It provides good resistance against oxidation below 1000 °C (1600°F).
• Highly stable output.
• Comparitively cost-effective than other thermocouples.
Cons
• Not suitable for reducing atmosphere but can withstand metallic vapor.
• Aging of the emf characteristic, when compared to noble metal thermocouples (B, R, and S).
• Not suitable for vacuum applications due to vaporization of chromium in the positive element.
• Green-Rotis phenomenon may occur due to low oxygen level for the thermocouples which are used between 815°C to 1040°C (1500°F to 1900°F).
• Type K thermocouples should not be used in a Sulphuric environment since both elements will rapidly corrode and the negative element will eventually fail mechanically due to becoming brittle.
Uses:-
They are generally utilized for applications at temperatures over 550 °C up to the most extreme working weight of the thermocouple.
• They are used in many industries like Steel & Iron to monitor temperature & chemistry throughout 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.