Type E: The Type E thermocouple has a Chromel (Nickel-10% Chromium)
positive leg and a Constantan (Nickel- 45% Copper) negative leg. Type E has a
temperature range of -330 to 1600F, has the highest EMF Vs temperature values of
all the commonly used thermocouples, and can be used at sub-zero temperatures.
Type E thermocouples can be used in oxidizing or inert atmospheres, and should not
be used in sulfurous atmospheres, in a vacuum or in low oxygen environments where
selective oxidation will occur. The color code for TYPE E wire is purple and red.
Type J: The Type J thermocouple has an Iron positive leg and a Constantan
negative leg. Type J thermocouples can be used in vacuum, oxidizing, reducing and
inert atmospheres. Due to the oxidation (rusting) problems associated with the iron
leg, care must be used when using this thermocouple type in oxidizing environments
above 1000F. The temperature range for Type J is 32 to 1400F and it has a wire
color code of white and red.
Type K: The Type K thermocouple has a Chromel positive leg and an Alumel
(Nickel- 5% Aluminum and Silicon) negative leg. Type K is recommended for use
in oxidizing and completely inert environments. Because it’s oxidation resistance is
better than Types E, J, and T they find widest use at temperatures above 1000F.
Type K, like Type E should not be used in sulfurous atmospheres, in a vacuum or in
low oxygen environments where selective oxidation will occur. The temperature
range for Type K is -330 to 2300F and it’s wire color code is yellow and red.
Type N: The Type N thermocouple has a Nicrosil (Nickel-14% Chromium- 1.5%
Silicon) positive leg and a Nisil (Nickel- 4.5% Silicon- .1% Magnesium) negative
leg. Type N is very similar to TYPE K but is less susceptible to selective oxidation
effects. Type N should not be used in a vacuum or in reducing atmospheres in an
unsheathed condition. The temperature range is 32-2300 deg F and its wire color code
is orange and red.
Type T: The Type T thermocouple has a Copper positive leg and a Constantan
negative leg. Type T thermocouples can be used in oxidizing, reducing or inert
atmospheres, except the copper leg restricts their use in air or oxidizing environments
to 700F or below. The temperature range for Type T is -330 to 700F and it’s wire
color code is blue and red.
Noble Metal Thermocouples are another category of thermocouples and are made of
the expensive precious metals Platinum and Rhodium. There are three types of noble
Type B (Platinum/Platinum-30% Rhodium)
Type R (Platinum/Platinum-13% Rhodium)
Type S (Platinum/Platinum-10% Rhodium)
Types R and S have temperature ranges of 1000 to 2700F and Type B thermocouples have a temperature range of 32 to 3100F.
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