WO2007126255A1

WO2007126255A1 - Non-grounded type sheath thermocouple and method of manufacturing the same

Info

Publication number: WO2007126255A1
Application number: PCT/KR2007/002064
Authority: WO
Inventors: Sung Nam Hong
Original assignee: Sung Nam Hong
Priority date: 2006-04-27
Filing date: 2007-04-26
Publication date: 2007-11-08
Also published as: KR100767792B1

Abstract

The present invention relates to a non-grounded type sheath thermocouple and method of manufacturing the sheath thermocouple. A non-grounded type sheath thermocouple according to an embodiment of the present invention is constructed such that a pair of thermocouple element wires for temperature measurement are arranged in a sheath filled with an insulating material and a hot junction is formed by welding first ends of the thermocouple element wires while fully isolating the first ends from the sheath, and such that the hot junction is formed through welding in a hole formed in a direction from the front portion of the sheath thermocouple to the inside thereof at a predetermined depth. According to the construction, the productivity and product reliability of the non-grounded type sheath thermocouple can be improved.

Description

NON-GROUNDED TYPE SHEATH THERMOCOUPLE AND METHOD OF MANUFACTURING THE SAME

Technical Field

[1] The present invention relates, in general, to a sheath thermocouple and method of manufacturing the sheath thermocouple and, more particularly, to a non-grounded type sheath thermocouple, which has high productivity and reliability and excellent responsiveness, and a method of manufacturing the non-grounded type sheath thermocouple. Background Art

[2] Generally, a thermocouple is a device manufactured by joining both ends of two dissimilar metal lines to measure a temperature. In detail, a thermocouple is a device constructed such that, when both ends of two dissimilar metal conductors are electrically connected to each other and a temperature difference is applied to the ends, a Seebeck effect that causes current to flow in a circuit occurs and such that, at this time, the first ends (reference junction) of the metal conductors are maintained at constant temperature and the value of a thermoelectromotive force is measured, thus measuring the temperature of the second ends (hot junction).

[3] Since the thermocouple having these principles has a relatively simple structure and is capable of measuring temperature in a wide range from an ultra- low temperature of - 200⁰C to an ultra-high temperature of 3000⁰C, it has been widely used in medical temperature measurement as well as various types of industrial temperature measurement.

[4] Thermocouples are classified into a general thermocouple and a sheath thermocouple according to the protection type of the element wires of the thermocouples on which a hot junction is formed. The general thermocouple is formed by combining a separately manufactured protection tube, thermocouple element wires, an insulating tube, and an outlet box with each other. In contrast, the sheath thermocouple is formed by integrating a protection tube, thermocouple element wires, and an insulating material, such as magnesium oxide (MgO) into a single structure, and has characteristics, such as excellent mechanical durability and superior bendability, so that the sheath thermocouple is frequently used compared to the general thermocouple.

[5] Sheath thermocouples can be classified into a grounded type and a non-grounded type according to whether the element wires of a thermocouple are grounded against a metal protection tube (hereinafter referred to as a 'sheath'). The grounded type is a type in which the element wires of a thermocouple are directly welded to the front portion of a sheath and a hot junction is formed, and which has rapid responsiveness and is suitable for temperature measurement under the condition of a high temperature and a high voltage. The non-grounded type is a type in which the element wires of a thermocouple are fully isolated from a sheath and a hot junction is formed, and which has less time course change in a thermoelectromotive force and is robust to long-term use. Further, the non-grounded type sheath thermocouple can be safely used even in a danger area without being influenced by noise voltage. Furthermore, the non-grounded type sheath thermocouple is advantageous in that, when an insulating resistance meter is installed in a pair of element wires of the thermocouple, the insulating resistance of an insulating material can be conveniently measured. The present invention relates to the non-grounded type sheath thermocouple. [6] However, in the non-grounded type sheath thermocouple having the several advantages, as described above, a procedure of welding the fine element wires of a thermocouple to form a hot junction in the sheath is very difficult and complicated, so that most of the non-grounded type sheath thermocouples are currently imported from foreign countries in the form of expensive finished products. In particular, since there is a tendency for the external diameter of a sheath to reach a minimal size from 0.25 Φ to 0.5 Φ, highly advanced technology has been gradually required. Further, there occurs a problem in that, contact failures at the hot junction of the thermocouple element wires, etc. are detected after products have been completed, thus decreasing the productivity of sheath thermocouples and the reliability of products.

Disclosure of Invention

Technical Problem

[7] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a non-grounded type sheath thermocouple, which can improve the productivity and reliability of products.

[8] Another object of the present invention is to provide a method of manufacturing a non-grounded type sheath thermocouple, which can improve the productivity and reliability of products. Technical Solution

[9] In order to accomplish the above objects, the present invention provides a non- grounded type sheath thermocouple, comprising a pair of thermocouple element wires for temperature measurement arranged in a sheath filled with an insulating material, and a hot junction formed by welding first ends of the thermocouple element wires while fully isolating the first ends from the sheath, the hot junction having a structure formed through welding in a hole formed in a direction from a front portion of the sheath thermocouple to an inside of the sheath thermocouple at a predetermined depth.

[10] Further, the present invention provides a method of manufacturing a non-grounded type sheath thermocouple, comprising a first step of cutting the sheath thermocouple, in which a pair of thermocouple element wires for temperature measurement are installed in a sheath filled with an insulating material, at a predetermined length, and forming a first end of the sheath thermocouple as a plane, a second step of performing hole formation by forming a hole in a direction from the end, formed as the plane, to an inside of the sheath thermocouple at a predetermined depth, and a third step of concentrating both ends of the thermocouple element wires, which are within the sheath thermocouple and are exposed through hole formation, on a center of the sheath thermocouple, and welding the ends to each other.

[11] Preferably, the sheath may have an external diameter from 0.25mm to 0.5mm, and the hole may be formed at a depth from 0.5 mm to 1 mm from the front portion of the sheath thermocouple.

[12] Preferably, the method may further comprise a fourth step of performing a non- contact test after welding has been performed, thus determining whether a welding failure occurs; and a fifth step of welding a stopper to the front portion of the sheath thermocouple, thus sealing the sheath thermocouple. Brief Description of the Drawings

[13] FIG. 1 is a sectional view showing a sheath thermocouple according to an embodiment of the present invention; and

[14] FIG. 2 is a schematic flowchart of a method of manufacturing a sheath thermocouple according to an embodiment of the present invention. Best Mode for Carrying Out the Invention

[15] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[16] FIG. 1 is a sectional view showing a sheath thermocouple according to an embodiment of the present invention, and FIG. 2 is a schematic flowchart of a method of manufacturing a sheath thermocouple according to an embodiment of the present invention.

[17] Referring to FIG. 1, a non-grounded type sheath thermocouple 10 according to an embodiment of the present invention is constructed such that a pair of thermocouple element wires 11 and 12 for temperature measurement are arranged in a sheath 14 filled with an insulating material 13 and a hot junction 16 is formed by welding one ends (first ends) of the thermocouple element wires 11 and 12 while fully isolating the first ends from the sheath 14, and such that the hot junction 16 is formed through welding in a hole 17 formed in a direction from the front portion of the sheath thermocouple to the inside thereof at a predetermined depth.

[18] Referring to FIG. 2, the method of manufacturing a non-grounded type sheath thermocouple according to the present invention includes the first step SlO of cutting a sheath thermocouple, in which a pair of thermocouple element wires for temperature measurement are installed in the sheath filled with an insulating material at a predetermined length, and forming one end (first end) of the sheath thermocouple as a plane, the second step S20 of performing hole formation by forming a hole 17 in a direction from the end (first end), formed as the plane, to the inside of the sheath thermocouple, the third step S30 of concentrating both ends of the thermocouple element wires, which are within the sheath thermocouple and are exposed through hole formation, on the center of the sheath thermocouple, and of welding the ends to each other, the fourth step S40 of performing a non-contact test after welding has been performed, thus determining whether a welding failure occurs, and the fifth step S50 of welding a stopper to the front portion of the sheath thermocouple, thus sealing the sheath thermocouple.

[19] Hereinafter, respective steps are described in detail with reference to FIGS. 1 and 2.

The sheath thermocouple can be made of a material, such as a stainless steel, inconel, cupro-nickel, SUS304, or SUS316. Further, the external diameter of the sheath thermocouple is not especially limited, but the present invention can also use a fine sheath thermocouple having an external diameter of 0.25mm to 0.5mm. Hereinafter, in the embodiments, a description is made on the basis of the sheath thermocouple having an external diameter of 0.25mm or 0.5mm. The material and external diameter of the thermocouple element wires 11 and 12 are not especially limited, but the diameter of the thermocouple element wires 11 and 12 can be set to 0.045mm when the external diameter of the sheath 14 is 0.25mm. Further, the sheath thermocouple 10, in a semifinished state in which the pair of thermocouple element wires 11 and 12 for temperature measurement are arranged in the sheath 14 filled with the insulating material 13, can be used.

[20] At the first step SlO, the sheath thermocouple 10 is cut at a predetermined length to be suitable for application fields using a well-known wire cutting technique, etc. Next, the cut end (first end) is formed as a plane using a belt grinder or the like. At the opposite end (second end) of the sheath thermocouple, the insulating material 13 and the sheath 14 are removed to cause the ends of the thermocouple element wires 11 and 12 to be exposed using a wire stripper.

[21] Next, hole formation is performed by forming the hole 17 having a predetermined depth in a direction from the end (first end) of the sheath thermocouple, which is cut and formed as a plane, to the inside of the sheath thermocouple (at an inside diameter about 0.18mm or 0.3mm) using a micro drill at second step S20. In this way, after the inner space of the sheath thermocouple is secured by forming the hole 17, welding is performed, thus increasing welding efficiency and improving the reliability of products.

[22] Preferably, the depth of the hole 17 is set in such a way that a distance D from the end (first end) of the sheath thermocouple is set to 0.5mm to lmm. When the distance D is less than 0.5mm, there is a high probability that the thermocouple element wires 11 and 12 are grounded to the stopper 15, and when the distance D is greater than lmm, it is difficult to identify the thermocouple element wires 11 and 12 with the naked eye, and thus a welding operation is difficult.

[23] In the formed hole 17, the ends of the pair of the thermocouple element wires 11 and 12 are concentrated on the center of the sheath thermocouple. In this case, when a magnifying glass is used, a more precise operation is possible. Thereafter, the concentrated ends of the thermocouple element wires 11 and 12 are welded to each other, and thus the hot junction 16 is formed at third step S30. In this case, welding can be performed using a laser welder or an argon welder. It should be noted that the concentrated ends do not come into contact with the sheath.

[24] Next, in order to determine whether welding is precisely performed and a short circuit does not occur, a tester is connected to the second end of the sheath thermocouple, and a non-contact test is performed at fourth step S40. In this case, a multimeter, a buzzer tester, etc. can be used for the tester. The non-contact test is performed in the product manufacturing process in this way, thus improving the reliability and productivity of products.

[25] If there is no failure in the non-contact test, the stopper 15 is welded to the end (first end) of the sheath thermocouple, and thus the front portion of the sheath thermocouple is sealed at fifth step S50. In this case, the material of the stopper 15 is identical to that of the sheath 14, and welding can be performed through argon welding. After the stopper 15 has been welded, the multimeter or the buzzer tester is connected to the second end, and a non-contact test is performed again. If there is no failure in the non- contact test, the welded portion of the stopper 15 is smoothly processed using a belt grinder. As described above, the non-contact test is additionally performed, thus improving the reliability of products.

[26] Next, an insulating resistance tester is connected to the second end of the sheath thermocouple, and thus an insulating resistance test is performed. If insulating resistance cannot satisfy a reference value (more than 200MΩ at reference 500V), the sheath thermocouple is put in a dry furnace and is dried to obtain a predetermined insulating resistance value.

[27] Next, positive (+) and negative (-) terminals (wires) are respectively connected to the ends of the thermocouple element wires 11 and 12 which protrude from the second end. In this case, connection can be performed using silver brazing rod welding, spot welding, etc.

[28] The second end of the sheath thermocouple and portions thereof to be connected to the terminals (wires) are put in a sleeve (not shown), the second end of the sheath thermocouple is pressed using a hydraulic compressor, and the portions of the sheath thermocouple to be connected to the terminals (wires) are epoxy molded (18).

[29] Finally, if a temperature test is performed and thermocouple calibration is realized, a product is completed as a temperature sensor. The measurement of the thermoelec- tromotive force of the sheath thermocouple according to the present invention can be performed through a well-known moving coil type instrument, an electronic self- balancing instrument, a potentiometer, etc.

[30] The present invention can also be applied to medical instruments for medical treatment. For example, a high frequency wave is caused to flow through the surface of a sheath, so that various diseases, such as cancers or inflammations, can be treated, and so that temperature can be measured through thermocouple element wires within the sheath thermocouple. In this case, the sheath thermocouple according to the present invention has high product reliability and rapid temperature responsiveness, thus preventing the temperature of a treatment region from increasing.

[31] Further, the present invention can be used to prevent the overheating of semiconductor (IC chips and internal components of circuits) equipment, and to perform a performance test (at high temperature and low temperature) for semiconductor products.

[32] Since conventional products have large external diameters and low temperance responsiveness, they cannot sense fine variation in temperature and have low product reliability and productivity. Such a problem can be solved by the present invention. Further, the present invention is advantageous in that a temperature sensor device using the sheath thermocouple having high product reliability can be installed even in a portion in which a conventional temperature sensor device cannot be installed, or in a small and thin portion.

[33] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Industrial Applicability

[34] As described above, according to a non-grounded type sheath thermocouple and method of manufacturing the sheath thermocouple, the productivity and product reliability of non-grounded type sheath thermocouples can be improved. Therefore, the present invention can provide a sheath thermocouple having high reliability when temperature is measured in various fields, such as high frequency medical instruments or semiconductor manufacturing processes, and thus it is very useful.

Claims

[1] A non-grounded type sheath thermocouple, comprising: a pair of thermocouple element wires for temperature measurement arranged in a sheath filled with an insulating material; and a hot junction formed by welding first ends of the thermocouple element wires while fully isolating the first ends from the sheath, the hot junction having a structure formed through welding in a hole formed in a direction from a front portion of the sheath thermocouple to an inside of the sheath thermocouple at a predetermined depth.

[2] The non-grounded type sheath thermocouple according to claim 1, wherein the sheath has an external diameter from 0.25mm to 0.5mm.

[3] The non-grounded type sheath thermocouple according to claim 1 or 2, wherein the hole is formed at a depth from 0.5 mm to 1 mm from the front portion of the sheath thermocouple.

[4] A method of manufacturing a non-grounded type sheath thermocouple, comprising: a first step of cutting the sheath thermocouple, in which a pair of thermocouple element wires for temperature measurement are installed in a sheath filled with an insulating material, at a predetermined length, and forming a first end of the sheath thermocouple as a plane; a second step of performing hole formation by forming a hole in a direction from the end, formed as the plane, to an inside of the sheath thermocouple at a predetermined depth; and a third step of concentrating both ends of the thermocouple element wires, which are within the sheath thermocouple and are exposed through hole formation, on a center of the sheath thermocouple, and welding the ends to each other.

[5] The method according to claim 4, wherein the sheath has an external diameter from 0.25 mm to 0.5 mm.

[6] The method according to claim 5, wherein the hole is formed at a depth from 0.5 mm to 1 mm from a front portion of the sheath thermocouple.

[7] The method according to any of claims 4 to 6, further comprising: a fourth step of performing a non-contact test after welding has been performed, thus determining whether a welding failure occurs; and a fifth step of welding a stopper to the front portion of the sheath thermocouple, thus sealing the sheath thermocouple.