Let Us Know the Thermocouple Types

Base Metal Thermocouple Types

Noble Metal Thermocouple Types

Refractory Metal Thermocouple Types

 

Thermocouple Types

Several combinations of different materials are used for producing acceptable thermocouples, out of which, each has its own specific application-spectrum. But, the value of interchangeability as well as mass production economics leads to standardization, and a number of specific types are now readily available and cover most of the temperature as well as environmental applications.

Base Metal Thermocouple Types

These consist of some of the most common, and cost-efficient metals including copper, iron & nickel. The type E, type J, type K, type N, and type T belong to this group and they happen to be the most common ones.

  • E Type– This has a positive chromel leg (which is ninety percent of nickel and ten percent of chromium) and a negative constantan leg (which is five percent of nickel and 55 percent of copper) 
  • Type J – This has an iron-positive-leg & a Konstantin-negative-leg. 
  • K Type – This has a chromel positive leg (which is ninety percent of nickel and ten percent of chromium) and an Alumel negative leg (which is 95 percent of nickel and five percent of aluminum, silicon & manganese). 
  • Type N – This has a positive leg of Nicrosil (i.e. 74.1 percent nickel – 14.4 percent chromium – 1.4 percent silicon.0.1 percent magnesium) and a negative leg of Nisil (which is 95.6 percent of nickel to 4.4 percent of silicon). 
  • T-type – This has a positive leg of copper and a negative leg of constantan.

Noble Metal Thermocouple Types

They are made from wire made from precious metals such as Platinum & Rhodium. These can be utilized for oxidizing or for inert applications, & should be utilized with a ceramic protective tube outside of the thermocouple element. Such types of sensors are generally delicate and shouldn’t be utilized for applications that reduce or contain metal vapors. 

  • R Type – This is made with a positive leg of platinum or 13 percent rhodium & pure platinum negative-leg. Type R has the temperature ranging from 0°C to 1450°C (32°F – 2642°F) 
  • S Type – This is made from a positive leg of platinum or ten percent rhodium & a pure negative-leg of platinum. Type S has the temperature ranging from is 0°C to 1450°C (32°F to 2642°F) 
  • B Type – This is made from a positive leg of platinum or 30 percent rhodium.

Refractory Metal Thermocouple Types

They are made of wire made from the exotic metals tungsten 17 and rhenium. Such metals are a bit on the expensive side, hard to make, and wires made from such metals are quite brittle. So, such types of thermocouples are designed for use in vacuum ovens at very high temperatures and should not be used above 300°C in the presence of oxygen. Several different alloy combinations have been used in the past, but there is currently only one commonly used. 

  • C Type – This has a tungsten positive leg or five percent rhenium positive leg & a tungsten 26 percent rhenium negative leg. The temperature ranges from 0°C to 2320°C (32°F  to 4208°F). 
  • G Type – They are known technically as this – WM26Re. They have a combination of alloy with a positive lead of tungsten (W) and a negative lead of tungsten + 26 percent rhenium (W-26% Re). The max operating temp. of this is 0°C to 2320°C. 
  • D-Type – This is even called W3ReM25Re technically. It has a combination of alloy with a positive lead of tungsten plus 3 percent rhenium (W-3% Re) and a negative lead of tungsten plus 25 percent rhenium (W56% Re). The max operating temperature range is 0°C to 2320°C.

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