Sheath type thermocouple generally shares the similar principle of protection tube type thermocouple. However, it has a different construction. It is filled with inorganic insulating material between the thin wire and the metal sheath, and it shares the same body as one. Inside the thin stainless steel pipe, thermocouple element is located, and then stainless pipe is filled with a MgO. Normally, thermocouple is used with a thermowell. The advantages over protection tube types are it has a faster response time, it has a broader temperature range (-200 ~ 1,600 ℃), longer life, it can be bended to install according to its required installation site condition, a better mechanical strength, and a better internal pressure control.