JP2006220469A - Temperature measurement apparatus using thermocouple and method for manufacturing thermocouple - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature measurement apparatus using a thermocouple which is easy to manufacture, is sturdy, and inexpensive and a manufacturing method allowing to manufacture the sturdy thermocouple used for the apparatus. <P>SOLUTION: The temperature measurement apparatus uses the thermocouple in which the tip of a first conducting wire and the tip of a second conducting wire, which is made of a different material from the first one, are brought into contact and are fixed to detect temperature of the place at which the part is positioned as electric potential. Parts with a predetermined length of the first conducting wire and the second conducting wire are formed in a tapered-shape such that their thickness gradually reduces toward their tip and are connectively fixed at the tip. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a temperature measuring device that measures temperature using a thermocouple and a method of manufacturing the thermocouple.

  Temperature measuring devices using thermocouples have been known for a long time. As one of them, a thermocouple with a very thin tip measuring portion as described in Patent Document 1 is known.

  In this thermocouple, a chromel wire of about 25 μm and an alumel wire are joined to one end of a chromel wire having a diameter of about 200 μm and the end of the alumel wire is overlapped, and the contact portion is fused or brought into contact with each other. It has a structure in which the temperature measuring part is melt-bonded so as to be spherical, and then rolled into a disk shape.

However, this thermocouple is manufactured by joining the tip of the chromel wire and the alumel wire, as well as joining a thin wire of 25 μm diameter of the same material to these 200 μm diameter wires, requiring a total of 3 joints. There was a problem that the process to do became complicated. In addition, these chromel wires and alumel wires have a problem that they are weak in strength because the thin wire portions are joined to the thick wire portions.
JP 2003-344178 A

  The present invention has been made in view of the problems of the conventional temperature measuring device using a thermocouple as described above, and a temperature measuring device using a thermocouple that is easy to manufacture, robust, and inexpensive, and to this device. An object of the present invention is to provide a production method capable of producing a robust thermocouple to be used.

  According to claim 1 of the present invention, the tip of the first conductor and the tip of the second conductor made of a material different from the first conductor are contacted and fixed, and the temperature at which this part is placed is detected as a potential difference. A temperature measuring device using a thermocouple, wherein a predetermined length portion of the tip of the first conductor and the tip of the second conductor is tapered gradually toward the tip and connected at the tip. A temperature measuring device using a thermocouple, characterized by being fixed.

  According to claim 5 of the present invention, there is provided a method of manufacturing a thermocouple for a temperature measuring device that detects the temperature at which this portion is placed as a potential difference by contacting and fixing the tips of the first and second conducting wires. Electrolytic polishing in which the tip portions of the coated first and second conductive wires are exposed by a predetermined length, and the portions are immersed in an electrolytic polishing liquid and subjected to electrolytic polishing so as to become thinner toward the tip. A temperature measuring device comprising: a step; and an electric welding step for fixing the first and second conductive wires in contact with each other by performing electric welding at a tip thinned by the electrolytic polishing step. A method of manufacturing a thermocouple is provided.

  The thermocouple described here is a phenomenon in which both ends of two different types of metal bodies are electrically connected to form a closed circuit, and this one end is heated to cause a thermoelectromotive force according to the temperature difference (Seebeck). This is a temperature sensor having a structure for measuring temperature by this thermoelectromotive force.

  According to the present invention, it is possible to obtain a temperature measuring device using a thermocouple that is simple and robust and inexpensive, and a manufacturing method that can manufacture a robust thermocouple used in this device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The device according to the present invention is a device that measures temperature using a thermocouple, detects the potential difference generated in correspondence with the temperature of the first conductor and the tip of the second conductor, and detects the potential difference. Measure. The first conductor and the second conductor in this case are referred to as thermocouple wires. The embodiment described below is an example in the case of using a chromel wire and an alumel wire as a thermocouple wire.

  FIG. 1 shows a configuration example of one embodiment of the present invention. In FIG. 1, 11 is an alloy mainly composed of nickel and chromium, so-called chromel wire, and 12 is a so-called alumel wire mainly composed of nickel. These chromel wires 11 and alumel wires 12 are, for example, 0.2 mm cross-sectional and circular wires. The types of these thermocouples according to JIS are B, R, S, N, K, E, J, and T. Although an embodiment in which the present invention is applied to a K-type thermocouple wire will be described here, the present invention is not limited to the K-type.

  These chromel wires 11 and alumel wires 12 are fixed at an insulating portion 13 near the ends.

  The chromel wire 11 and the alumel wire 12 protrude from the insulating portion 13 by about 15 mm, but this portion has a taper shape with a thick base and a thin tip. The original part has a diameter of about 200 μm and the tip thickness is about 20 μm. Thus, in order to make the chromel wire 11 and the alumel wire 12 into a tapered shape, an electrolytic polishing etching method is used as described in detail later.

  As shown in FIG. 1, the tapered chromel wire 11 (chromel wire tapered portion 11a) at the tip and the tapered alumel wire 12 (almel wire tapered portion 12a) at the tip are substantially parallel. It has become. As shown in FIG. 2 (a), the chromel wire tapered portion 11a and the alumel wire tapered portion 12a that are parallel to each other are brought close to each other and brought into contact with each other at the tip, and are fixed by electric welding. . FIG. 2B shows an enlarged view of the tip. As is apparent from this figure, the chromel wire 11 and the alumel wire 12 are overlapped at the tip and welded. Temperature measurement is performed by placing the temperature measuring contact 21 on the welded portion, that is, the portion to be measured.

  As shown in FIG. 4 described later, a predetermined DC voltage temperature detector is connected to the plus terminal 11b at the end of the chromel wire and the minus terminal 12b at the end of the alumel wire. These terminals may be integrated with a conductor connected to the DC voltage temperature detector.

  The insulating portion 13 is made of glass fiber, a fluorine resin insulator, a Teflon (registered trademark) resin insulator, or the like. When glass fiber is used for the insulating portion 13, for example, a glass fiber is spirally wound around each of the conductors of chromel wire and alumel wire to form a bundle in parallel, and the glass fiber is knitted and fixed to the outside. The shape is elliptical. In the case where a Teflon (registered trademark) resin insulator is used for the insulating portion 13, the conductors of the chromel wire and the alumel wire coated with Teflon (registered trademark) and insulated are bundled in parallel, and the outer side is teflon ( It is an elliptical shape that is covered and fixed with a registered trademark. The insulating portion 13 may not be provided specially.

  Here, the manufacturing method of the temperature measuring device of the present invention for tapering the chromel wire and the alumel wire will be described. First, the chromel wire 11 and the alumel wire 12 are cut to a required length. Next, in order to make the temperature measuring contact portion 21 very thin, a portion of the insulation coating about 15 mm from the tip is removed. The conductor portion from which the coating has been removed is exposed and divided into two parts so as not to touch each other. Further, in order to apply a voltage by making the temperature measuring contact portion extremely thin, an insulating coating portion of about 15 mm is removed from the tip on the opposite side, and the conducting wire is exposed.

  The electric resistance of the thermocouple wire was about 22 Ω (ohms) for the chromel wire and about 9 Ω for the alumel wire per 1 m actually measured.

  By the way, the chromel wire and the alumel wire have different electric resistances due to the difference in material. Chromel wire has higher resistance than alumel wire. Therefore, the current value flowing through each line is different, and the etching rate varies, and unevenness in thickness and length tends to occur. In order to eliminate such irregularities, a resistor 30 having a resistance value corresponding to the electrical resistance of the chromel wire is connected in series to the alumel wire, and the machining accuracy of the chromel wire and the alumel wire is maintained. In this example, a resistor 30 having a value of about 13Ω per meter is connected in series with the alumel wire. Of course, it is desirable to use a resistor having an appropriate value so that the unevenness does not occur depending on the alumel wire, chromel wire or the like to be used.

  Electropolishing and etching for tapering the tips of the chromel wire and the alumel wire are performed as follows. As the electrolytic polishing liquid 31, a mixed liquid of distilled water 1 is prepared for the ferric chloride solution “Baume 40 degrees” 1 and put in the electrolytic bath 32. The electrolytic bath 32 keeps the liquid temperature around 30 °. Titanium alloys are used as the cathodes 33a and 33b for electrolytic polishing. In order to ensure a stable voltage and current, a 12-volt storage battery is used as the electropolishing power source 34. The negative terminals of the electropolishing power supply 34 are connected to cathodes 33a and 33b, that is, titanium alloys.

  The plus terminal of the electropolishing power supply 34 is connected to the plus terminal of the chromel wire and the minus terminal of the alumel wire via the resistor 30. In addition, a voltmeter and an ammeter are provided (not shown) in order to constantly monitor the etching state.

  An automatic elevating device 35 that can raise and lower an object suspended by a holder is installed directly above the electrolytic cell 32. The thermocouple wire is hung on the above-mentioned holder of the automatic lifting device with the portion where the temperature measuring contact portion of the chromel wire and the alumel wire is made fine is down. It is preferable that this is lowered at a relatively fast speed of about 1 cm in about 5 seconds, and when it enters the electrolytic polishing liquid to a predetermined length, it is always moved up and down and not stopped in the electrolytic polishing liquid.

  When a switch (not shown) of the electropolishing power supply is turned on and a power supply (not shown) of the automatic lifting device 35 is turned on, the thermocouple wire moves up and down in the electropolishing liquid 31 and electropolishing is started. . Appropriate time is measured after the electropolishing is started, the wire is pulled up at a speed of about 1 cm in about 5 seconds, the diameter of the thermocouple wire is measured with a micrometer, and the tip of the chromel wire and the alumel wire is about 20 μm. Then, the electropolishing is finished. As it goes to the tip, the speed of melting by electrolytic polishing becomes faster, and the chromel wire and the alumel wire are tapered at the tip.

  When the wire diameter of the thermocouple wire is determined in this way, the portion touched by the electrolytic polishing liquid is neutralized and dried. An insulating part is provided on the thermocouple wire thus dried, and the tip portion is electrically welded and fixed, and a thermocouple measuring part used in the measuring apparatus of the present invention is obtained through performance inspection.

  In addition, since the error in the thickness of the thermocouple wire appears depending on the time required for etching due to the error in the temperature and concentration of the electropolishing liquid, the finish accuracy is confirmed at the initial stage, and the etching time of the automatic elevator is determined and set. After that, it is better to go into mass production.

  According to the above manufacturing method, the tip portion of the thermocouple wire having a predetermined length is tapered by electropolishing, and the tip portion is contact-fixed by electric welding, so that a simple and robust thermocouple can be manufactured. There are advantages.

  FIG. 4 shows a state of temperature measurement by the temperature measuring device according to the present invention. The chromel wire and the alumel wire are connected to the DC voltage temperature detector 42 by conducting wires 41a and 41b. The temperature measuring contact portion 21 is placed at a site to be measured, and the potential difference obtained through the chromel wire, the alumel wire, and the conducting wires 41a and 41b led from the temperature measuring contact portion 21 is converted into a potential difference by the DC voltage temperature detector 42. It will be detected and measured as temperature. The chromel wire and the alumel wire are detected by the DC voltage temperature detector 42 as a DC voltage (potential difference) of about mV, and the voltage is converted into temperature.

  According to the above-described temperature measuring device, only the temperature measuring contact portion is welded (contact fixed) and not welded at other portions, so that it is robust and does not require a step of fixing other portions in terms of process. Therefore, there is an advantage that a robust and inexpensive thermocouple can be obtained and an inexpensive temperature measuring device can be obtained.

  In the said embodiment, although the thickness of the alumel wire and the chromel wire was 200 μm, the thickness may be about 100 μm to 350 μm. The thickness of the tip of the wire forming the thermocouple is 20 μm in the above embodiment, but if it is too thin, it becomes mechanically weak. Therefore, it is preferable that the thickness is not less than about 50 μm. .

In more detail, generally commercially available thermocouple wire, in common to each insulating material, diameter 0.1 mm (cross sectional area 0.003 mm ^2), the diameter 0.2 mm (cross sectional area 0.03 mm ^2), the diameter 0. 32 mm (cross-sectional area 0.08 mm ² ) is available, but when a diameter of 0.1 mm or 0.2 mm is used, the tip has a thickness of 20 to 50 μm and a diameter of 0.32 mm. When used, the thickness of the tip is preferably about 30 to 50 μm.

  Further, the length of the tapered portion of the thermocouple wire is not limited to 15 mm, and is preferably in the range of about 10 to 30 mm.

  In the case of using a glass fiber-coated thermocouple wire by the temperature measuring device shown in FIG. 4, the measurement accuracy is about ± 2.5 ° C., the temperature measuring contact portion is from room temperature to 300 ° C., and the measurement temperature is as follows: It can be measured in the range from room temperature to 250 ° C. Further, when using a Teflon (registered trademark) resin-coated thermocouple wire, the measurement accuracy is about ± 2.5 ° C., the temperature measuring contact portion is −250 ° C. to + 300 ° C., and the measurement temperature is −250 ° C. to + 200 ° C. It can be measured in the range of ° C. In addition, when a fluororesin-coated thermocouple wire is used, the measurement accuracy can be measured in the range of −200 ° C. to 300 ° C. at the temperature measuring contact portion and the measurement temperature in the range of −200 ° C. to 260 ° C.

  Moreover, in the said embodiment, the case where a chromel wire and an alumel wire were used as a thermocouple wire was described. However, the thermocouple wire used in the present invention is not limited to the chromel wire and the alumel wire, but functions as a thermocouple by bringing two kinds of conductive wires into contact with each other, and generates a potential difference according to the temperature of the contact portion. Any conductive wire may be used.

The figure which shows the state before carrying out contact fixation of the front-end | tip of the thermocouple wire of the temperature measurement part vicinity of the temperature measuring device by one Embodiment of this invention. The figure which shows the state after connecting the front-end | tip part of the thermocouple wire of the temperature measuring device by one Embodiment of this invention. The figure for demonstrating the method to form the taper shape of the front-end | tip part of the thermocouple wire | wire of the temperature measuring device by one Embodiment of this invention. The figure for demonstrating the state which measures temperature with the temperature measuring device by one Embodiment of this invention.

Explanation of symbols

11 ... chromel wire,
12 ... Alumel wire,
11a, 12a ... tapered portion,
11b: Positive terminal,
12b ... negative terminal,
13: Insulating part,
31 ... Electropolishing liquid,
32 ... electrolytic cell,
33a, 33b ... cathode,
34 ... Electropolishing power source,
35 ... Automatic lifting device,
41a, 41b ... conducting wire,
42: DC voltage temperature detector.

Claims (6)

A temperature measuring device using a thermocouple that detects and detects the temperature at which this portion is placed as a potential difference by contacting and fixing the tip of the first conductor and the tip of a second conductor made of a material different from that of the first conductor. And
A thermocouple is used, characterized in that a predetermined length portion of the tip of the first conductor and the tip of the second conductor is tapered and gradually tapered toward the tip. A temperature measuring device.   The temperature measuring device using a thermocouple according to claim 1, wherein the first conducting wire is a chromel wire and the second conducting wire is an alumel wire.   The temperature measuring device using a thermocouple according to claim 2, wherein the length of each tapered portion of the first conducting wire and the second conducting wire is within approximately 10 mm to 30 mm.   4. The diameter of each of the first conductor and the second conductor is in a range of about 100 [mu] m to 350 [mu] m, and a diameter of a portion to be fixed in contact is in a range of about 20 [mu] m to 50 [mu] m. The temperature measuring apparatus using a thermocouple as described. A method of manufacturing a thermocouple of a temperature measuring device that detects and detects a temperature at which this portion is placed as a potential difference by contacting and fixing the tips of a first conductor and a second conductor,
An electropolishing step of exposing the tip portions of the first conductor and the second conductor covered by a predetermined length and soaking the portions in an electropolishing liquid so as to become thinner toward the tip. When,
An electric welding step in which the tip of the first conductor and the second conductor are contact-fixed by electrical welding at the tip thinned by the electrolytic polishing step;
A method of manufacturing a thermocouple for a temperature measuring device.   6. The method of manufacturing a thermocouple for a temperature measuring device according to claim 5, wherein the first conducting wire is a chromel wire and the second conducting wire is an alumel wire.

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