Knowledge
Sheath type thermocouple
What is a sheath thermocouple?
This is a thermocouple with airtight insulation and high-voltage resistance. It is filled with high-purity magnesia powder between a metal pipe (sheath) and a thermocouple wire.
It can also be bent without compromising the thermocouple elements.
Features of Sheath Thermocouple
1） Fast response speed
The integrated structure of the thermocouple wire, insulation material, and protective tube provides faster response than conventional protective tube-type thermocouples.
2） Excellent bending properties and impact resistance
It is more flexible than conventional protective tube-type thermocouples and can bend with a bend radius of at least twice the outer diameter of the sheath.
3） Excellent corrosion and pressure resistance
Magnesia powder (MgO) is densely compressed and filled in metal-pipe (sheathing), making it more airtight than conventional protective tube-type thermocouples, making it less likely to corrode due to external atmospheres and more resistant to pressures.
4） Wide temperature measuring range
Temperature can be measured from-200℃ to 1050℃ (1500℃ by using a sheath made of a special material).
Temperature measuring junction of sheath thermocouple
 Type I (grounding type) JIS code: G |
A shape in which thermocouple wire is directly welded to the tip of a sheath to make a temperature measuring junction. Fast response and suitable for temperature measurement under high temperature and high pressure. Since the wire is grounded to the sheath, it cannot be used in a hazardous place or a place where noise voltage is present. |
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 Type II (non-grounding type) JIS code: U |
The thermocouple wire is insulated from the sheath to make a temperature measuring junction. Response speed is inferior to that of a grounded type, but the change in thermoelectromotive force with time is minimal and it withstands long-term use. It is also unaffected by noise voltage and can be used in hazardous locations. |
 Types III (Exposed Type) |
Thermocouple wire is exposed from the sheath to form a temperature measuring contact. The response speed is the fastest of the three types, and it follows even a slight temperature change. However, because of its poor airtightness and mechanical strength, it cannot be used for a long time in a corrosive atmosphere or under high temperature and high pressure. |
