Thermocouple

The principle on which the modern thermocouple operates is derived from Seeback’s discovery that if a circuit is formed using two dissimilar metal Conductors with one junction at a higher temperature than other, then a current will flow in the circuit. The resultant emf. is proportional to the temperature difference between the junctions .


For many industries heating processes particularly those carried out at high temperature a Thermocouple is the most accurate convenient and simple method for temperature measurement.




Thermocouple Type & Temperature Range

TC Type

Name of Materials

Application Range

B

Platinum 30% Rhodium (+)

1200-1800°C

Platinum 6% Rhodium (-)

C

W5Re Tungsten 5% Rhenium (+)

1650 – 2315°C 

W26 Re Tungsten 26% Rhenium (-)

E

Chromel (+)

0-900°C 

Constantan (-)

J

Iron (+)

0-760°C 

Constantan (-)

K

Chromel (+)

0-1200 °C 

Alumel (-)

N

Nicrosil (+)

650-1260°C

Nisil (-)

R

Platinum 13% Rhodium (+)

870-1650°C 

Platinum (-)

S

Platinum 10% Rhodium (+)

980-1650°C

Platinum (-)

T

Copper (+)

-200°C - 350°C 

Copper (+)



PROTECTION SHEATHS


Seamless Tube And drilled bar stock

Type

Max. Temp (Recommended)

Remarks

SS304

870°C 

Most widely used low temperature sheath material.

Extensively used in food, beverage, chemical and other industries where corrosion resistance is required.

SS316

870°C 

Best corrosion resistance of the austenitic stainless steel grades. Widel used in the food and chemical industry

SS310

1150°C 

Mechanical and corrosion resistance,similar to but better than 304 S S .Very good heat resistance

446 SS  

1150°C  

Ferritic stainless steel which has good resistance to sulfurous atmospheres at high temperatures. corrosion resistance to nitric acid, sulfuric acid   and most alkalies.

INCONEL 600/601

1175°C  

 Good high temperature strength, corrosion resistance, resistance to chloride-ion stress corrosion cracking and oxidation resistance to high temperatures.

Metal Ceramic

1370°C

Used in Copper, Brass and Steel industry

Silicon Carbide

1650°C

Used in Aluminium Industry

Syalon®

1150°C

Used in aluminium Industry

Ceramic 610

1600°C

Excellent thermal mechanical and corrosion resistance.

Ceramic 710

1800°C

Excellent thermal mechanical and corrosion resistance.

*Standard thermocouple protection tube should be preheated to about 480 C before immersion in molten metal at 1100 C or higher.