Temperature sensor
A temperature sensor includes: a sheath tube; a pair of thermocouple wires inserted into the sheath tube; a temperature measuring junction of the pair of thermocouple wires; an insulating support disposed in the sheath tube; and a tip protective tube covering the outer periphery of a tip end of the sheath tube to surround the temperature measuring junction. The tip protective tube includes a base-end side tube portion and a tip-end side tube portion, the tip-end side tube portion having a diameter smaller than that of the base-end side tube portion. The tip-end side tube portion has a tip-end side portion filled with a first insulating filler in which the temperature measuring junction is buried. In the remaining part on the inside of the tip-end side tube portion, an air layer is formed.
1. A temperature sensor comprises:
a sheath tube;
a pair of thermocouple wires inserted into the sheath tube;
a temperature measuring junction formed by joining tip ends of a tip projecting portion of the pair of thermocouple wires with each other, the tip projecting portion being projected from the sheath tube;
an insulating support disposed in the sheath tube; and
a tip protective tube that covers an outer periphery of a tip-end of the sheath tube to surround the temperature measuring junction, wherein,
the tip protective tube includes
a base-end side tube portion that covers the outer periphery of the tip end of the sheath tube, and
a tip end-side tube portion formed at a position adjacent to a tip-end side of the base-end side tube portion, the tip-end side tube portion having a diameter smaller than a diameter of the base-end side tube portion, a tip end of the tip-end side tube portion being closed;
the tip-end side tube portion has a tip-end side portion filled with a first insulating filler, the first insulating filler burying the temperature measuring junction therein; and
the tip-end side tube portion has a portion adjacent to a base-end side of the first filler, the portion being formed with an air layer.
2. The temperature sensor according to claim 1 , wherein,
the tip-end side tube portion includes
a middle step portion connected to the base-end side tube portion, and
a tip portion formed at a position adjacent to a tip-end side of the middle step portion, the tip portion having a diameter smaller than a diameter of the middle step portion, the tip portion having a closed tip end; and
the temperature measuring junction is disposed inside the tip portion.
3. The temperature sensor according to claim 2 , wherein,
a base-end surface of the first filler is located inside the middle step portion.
4. The temperature sensor according to claim 1 , wherein,
a distance from the tip end of the sheath tube to a center of the temperature measuring junction is in a range of 5 to 15 mm;
a distance from the tip end of the sheath tube to the base-end surface of the first filler is in a range of 1 to 5 mm; and
a distance from the base end surface of the first filler to the center of the temperature measuring junction is in a range of 1 to 10 mm.
5. The temperature sensor according to claim 2 , wherein,
a distance from the tip end of the sheath tube to a center of the temperature measuring junction is in a range of 5 to 15 mm;
a distance from the tip end of the sheath tube to the base-end surface of the first filler is in a range of 1 to 5 mm; and
a distance from the base end surface of the first filler to the center of the temperature measuring junction is in a range of 1 to 10 mm.
6. The temperature sensor according to claim 3 , wherein,
a distance from the tip end of the sheath tube to a center of the temperature measuring junction is in a range of 5 to 15 mm;
a distance from the tip end of the sheath tube to the base-end surface of the first filler is in a range of 1 to 5 mm; and
a distance from the base end surface of the first filler to the center of the temperature measuring junction is in a range of 1 to 10 mm.
7. The temperature sensor according to claim 2 , wherein,
the tip-end side tube portion has an inner surface coated with an insulating material; and
a distance from a tip end of the temperature measuring junction to an inner tip end of the tip portion of the tip-end side tube portion is 0.1 mm or less.
8. The temperature sensor according to claim 3 , wherein,
the tip-end side tube portion has an inner surface coated with an insulating material; and
a distance from a tip end of the temperature measuring junction to an inner tip end of the tip portion of the tip-end side tube portion is 0.1 mm or less.
9. The temperature sensor according to claim 1 , wherein,
the first filler and the second filler are configured by
particle aggregates made of ceramics, and
a glass layer made of crystallized glass filling gaps between the particle aggregates.
10. The temperature sensor according to claim 1 , wherein:
a length of the air layer, extending from the tip end of the sheath tube to a base-end surface of the first filler in an axial direction of the air layer, is in a range of 1 to 5 mm.
11. The temperature sensor according to claim 2 , wherein:
the air layer is arranged inside the middle step portion, the middle step portion having a diameter smaller than that of the base-end side tube portion.
12. The temperature sensor according to claim 11 , wherein:
the air layer is further arranged in an inclined step portion between the middle step portion and the base-end side tube portion.