Temperature sensor and temperature measuring device
A temperature sensor includes a pair of thermocouple wires, a temperature measuring junction formed by joining tip ends of the pair of thermocouple wires together, an outer tube having a tip end in which the temperature measuring junction is held, an insulator insulating the pair of thermocouple wires from the outer tube, and a glass seal filled in a base end of the outer tube. The pair of thermocouple wires disposed in the outer tube have surfaces where passive films are respectively formed due to the oxidization of the metallic materials on the surfaces of the pair of thermocouple wires.
1. A temperature sensor comprising:
a pair of thermocouple wires made of respective metallic materials different from each other;
a temperature measuring junction formed by joining tip ends of the pair of thermocouple wires together;
an outer tube made of a metallic material and having a tip end and a base end, the tip end holding the temperature measuring junction therein or having a tip end cover mounted thereto in which the temperature measuring junction is held, the base end allowing the pair of thermocouple wires to protrude therefrom;
an insulator made of an insulating material and disposed in the outer tube to insulate the pair of thermocouple wires from the outer tube and fix the pair of thermocouple wires to the outer tube; and
a glass seal made of a glass material and filled in at least either of the base end of the outer tube or a holder mounted to the base end of the outer tube to seal the outer tube, wherein
the pair of thermocouple wires disposed in the outer tube have surfaces where passive films are respectively formed on the surfaces of the pair of thermocouple wires due to oxidization of the metallic materials,
the pair of thermocouple wires from an N-type thermocouple;
the pair of thermocouple wires include a positive-leg thermocouple wire comprising Ni, Cr and Si;
the pair of thermocouple wires include a negative-leg thermocouple wire comprising Ni and Si;
the passive film formed on the surface of the positive-leg thermocouple wire comprises Cr-oxide or Ni-oxide at a highest content; and
the passive film formed on the surface of the negative-leg thermocouple wire comprises Ni-oxide at a highest content.
2. The temperature sensor according to claim 1 , wherein the passive films each have a thickness in a range of 0.3 μm to 10 μm.
3. The temperature sensor according to claim 1 , wherein the passive films are formed by oxidation of the surfaces of the pair of thermocouple wires prior to sealing the outer tube from inside thereof by the glass seal.
4. The temperature sensor according to claim 1 , wherein
the temperature sensor comprises the holder mounted to the base end of the outer tube; and
the glass seal is filled in the holder to seal the base end of the outer tube.
5. The temperature sensor according to claim 4 , wherein an inner diameter of the holder is larger than that of the outer tube.
6. The temperature sensor according to claim 4 , wherein the glass seal is filled in the holder up to a level of a maximum diameter of the holder.
7. A temperature measuring device comprising a temperature sensor and a control unit electrically connected to the temperature sensor and used for temperature measurement performed by the temperature sensor, wherein:
the temperature sensor comprises:
a pair of thermocouple wires made of respective metallic materials different from each other,
a temperature measuring junction formed by joining tip ends of the pair of thermocouple wires together,
an outer tube made of a metallic material and having a tip end and a base end, the tip end holding the temperature measuring junction therein or having a tip end cover mounted thereto in which the temperature measuring junction is held, the base end allowing the pair of thermocouple wires to protrude therefrom,
an insulator made of an insulating material and disposed in the outer tube to insulate the pair of thermocouple wires from the outer tube and fix the pair of thermocouple wires to the outer tube, and
a glass seal made of a glass material and filled in at least either of the base end of the outer tube or a holder mounted to the base end of the outer tube to seal the outer tube;
wherein the pair of thermocouple wires disposed in the outer tube have surfaces where passive films are respectively formed on the surfaces of the pair of thermocouple wires due to oxidization of the metallic materials; and
the control unit is configured to calculate an output temperature for the temperature sensor based on changes in electromotive force generated in the pair of thermocouple wires and correct for an error occurring in the output temperature due to the passive films being formed.