JPH0453553Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical fiber temperature sensor used for measuring the temperature of a high-temperature atmosphere such as the inside of a vacuum heat treatment furnace.

[Prior art] In an optical fiber temperature sensor, the light-receiving end at the tip of the fiber is set facing the target temperature measurement atmosphere, and the light transmitted within the fiber is guided from the light-receiving end to an external light-receiving element and the light intensity is measured. By measuring the above, temperature can be easily and accurately measured, and from this point of view, it is considered to be useful as a means for measuring temperature in high-temperature atmospheres such as the above-mentioned vacuum heat treatment furnace. In other words, if this type of temperature sensor is used, a small diameter (usually 1 mm)
It is only necessary to install an optical fiber (see below), which makes it easy to maintain airtightness of the temperature measurement atmosphere, and there is no need to provide an observation window as is required when using an optical pyrometer or radiation thermometer. Additionally, unlike thermocouples, they do not have the problems that frequently cause failures, and compared to thermocouples, they have many advantages, such as being able to measure temperatures up to a much higher temperature range.

[Problems to be solved by the invention] However, one problem when using an optical fiber temperature sensor to measure temperature in a high-temperature atmosphere is that the optical fiber (core) made of quartz glass etc. If it is kept at high temperatures for a long period of time, it may oxidize and gradually change in quality, causing its optical transmission ability to deteriorate over time. Furthermore, a similar phenomenon occurs in a temperature measurement mode in which an optical fiber is exposed to a corrosive gas atmosphere. If the optical transmission capacity of the optical fiber is reduced for such reasons, the sensitivity and temperature measurement accuracy will of course deteriorate.

The present invention focuses on the above-mentioned problems and provides an improved temperature sensor that does not deteriorate in performance due to deterioration of the optical fiber even when used in high-temperature atmosphere or corrosive gas for long periods of time. be.

[Means for Solving the Problems] In order to achieve this objective, the present invention inserts the required length of the tip end of the optical fiber into a protective tube whose inside is evacuated, and also inserts the light receiving end of the optical fiber into a protective tube whose inside is evacuated. , is characterized in that it is placed in the furnace close to the inner surface of the target provided at the tip of the protective tube.

[Function] In this way, if the tip of the optical fiber is inserted into the protective tube and the temperature is measured while the inside is evacuated, the heated tip of the optical fiber will not be exposed to oxygen-containing atmosphere or harmful temperature measurement. It is possible to cut off contact with atmospheric gases, and it is possible to reliably prevent performance deterioration due to oxidation and corrosion of the optical fiber.

In addition, this product evacuates the inside of the protective tube and eliminates the presence of gas that blocks the transmission of light.
The optical transmission efficiency of the optical fiber can be further improved.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

The drawing schematically shows, as an example, a case where the present invention is applied to an optical fiber temperature sensor used for measuring the temperature inside a vacuum heat treatment furnace. In the figure, reference numeral 1 denotes a vacuum heat treatment furnace, which is constructed by lining the inner surface of a furnace shell 2 with a heat insulating material 3. This vacuum furnace 1
is equipped with a heater 4 inside, and the heater 4 heats and raises the temperature of the processed material in the furnace.

An optical fiber type temperature sensor is attached to the vacuum furnace 1, which is constructed by combining an optical fiber 5 and a light receiving sensor 10 such as a silicon photocell. The optical fiber 5 has a length corresponding to the required length from the light receiving end 5a, which includes both the inner part of the furnace that is inserted into the furnace and is directly exposed to the high-temperature atmosphere, and the outer part of the furnace that is heated by heat conduction from that part. The distal end portion 5A is inserted into a hollow protective tube 6, and the protective tube 6 and the protective tube 6 are inserted into the furnace walls 2 and 3 and set. The protection tube 6 is made of a heat-resistant material such as stainless steel or Inconel, and has a cone-shaped target portion 6a at the tip that emits light depending on the temperature inside the furnace, and a base end and a bottom plate portion 6b, each integrally covered with a lid. The interior has an airtight structure. The optical fiber 5 is airtightly inserted into the protection tube 6 from the bottom plate portion 6b and passed through the inside in the axial direction, and the light receiving end 5a at the tip is placed at an appropriate distance from the back surface of the target portion 6a. It is positioned and fixed. In this case, this interval is set to such a distance that the field of view occupied by the light-receiving end 5a of the optical fiber 5 does not exceed the entire back surface of the target portion 6a, as shown by the broken line.

The protection tube 6, which is inserted into the furnace walls 2 and 3 with the optical fiber 5 inserted therein as described above, has an exhaust pipe 7 connected to one side of its proximal end that communicates with the inside. This exhaust pipe 7 is connected to a suction port 9a of a vacuum pump 9 via a socket 8 which can be switched open and closed. Further, the exhaust pipe 7 has a branch pipe portion 7 thereof.
a is connected through a valve 11 to a gas supply port 12a of a gas tank 12 that stores an appropriate inert gas.

Therefore, when measuring the temperature inside the furnace using such a temperature sensor, the protective tube 6 is inserted into the furnace together with the tip 5A of the optical fiber 5, and the target portion 6a at the tip is placed at an appropriate location facing the temperature measurement atmosphere. Deploy. Then, the target portion 6a of the protection tube 6 emits light in accordance with the temperature of the temperature measuring atmosphere, and the optical fiber 5 receives the light from the target portion 6 from the light receiving end 5a facing the back side thereof. The light transmitted within the optical fiber 5 is finally transmitted from the end thereof to the light receiving sensor 10 through the wavelength selection filter 10a, and the light is transmitted to the light receiving sensor 10 from the end thereof through the wavelength selection filter 10a.
Temperature is measured using emissivity as a factor.

At this time, the inside of the protection tube 6 has the vacuum pump 9
While operating the exhaust pipe 7, the exhaust pipe 7 is opened to evacuate the air and the air is replaced with a vacuum. Alternatively, after the vacuum treatment, the valve 11 may be opened from the gas tank 12 to introduce an inert gas to replace the inside of the protective tube 6 with the inert gas. In this way, if the temperature is measured while the inside of the protective tube 6 is replaced with a vacuum or an inert gas atmosphere, the tip 5A of the optical fiber 5 inserted into the inside that is heated directly or indirectly from the vacuum furnace 1 can be placed under a non-reactive atmosphere. In other words, since the temperature can be measured while completely isolating the heat-affected zone of the optical fiber 5 from the atmosphere and the gas in the furnace, the fiber core does not suffer from deterioration due to oxidation or corrosion, and therefore it can be used repeatedly or over a long period of time. Even if it is used, its temperature measurement performance will not deteriorate.

By evacuating the inside of the protective tube 6 in this way, it is easier to create a non-reactive atmosphere than when measuring by filling the inside of the protective tube 6 with gas. Since the light transmission efficiency of the optical fiber 5 is increased by eliminating the presence of the gas that causes this, the sensitivity and accuracy of the temperature sensor are further improved.

In the illustrated embodiment, the protection tube 6 is shown as having a relatively large size for convenience, but this has a diameter of 1
Since it is sufficient to pass through the optical fiber (core) 5 of mm or less, there is virtually no increase in diameter, and the simplicity of the facility in the case of the optical fiber type is not impaired. The protection tube 6 has the functions of simultaneously blocking disturbance light from entering the light-receiving end 5a of the optical fiber 5, and providing mechanical strength necessary for handling the tip 5A of the optical fiber 5. I am accomplishing it.

In addition, in the illustrated example, the distal end 5A of the optical fiber 5 is loosely inserted into the protective tube 6, but this may be done by making the inner diameter of the protective tube 6 smaller or by filling it with a filler so that it can be inserted into the protective tube 6. It can also improve familiarity.

[Effects of the invention] As described above, according to the invention, the required length of the tip of the optical fiber is inserted into a protective tube whose inside is evacuated, which effectively prevents performance degradation caused by oxidation and corrosion of the optical fiber. At the same time, it is possible to increase the light transmission efficiency of the optical fiber and effectively improve the sensitivity and accuracy of the temperature sensor.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view of an optical fiber temperature sensor showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Vacuum heat treatment furnace, 2...Furnace shell, 3...Insulating material, 4...Heater, 5...Optical fiber, 5a...
...Light receiving end, 5A...Tip, 6...Protective tube, 6a
...Target, 6b...Bottom plate part, 7...Exhaust pipe, 7a...Branch pipe part, 8...Kotoku, 9...Vacuum pump, 10...Light receiving sensor, 10a...Wavelength selection filter, 11... Valve, 12...Gas tank.

Claims (1)

[Scope of utility model registration request] The tip of the optical fiber is inserted into a protective tube whose inside is evacuated, and the light-receiving end of the optical fiber is placed in the furnace close to the inner surface of the target provided at the tip of the protective tube. Fiber optic temperature sensor.