METHOD FOR REALIZING LIFESPAN EXTENSION OF THERMOCOUPLE WIRE AGAINST BREAKAGE

Abstract

Instead of a single-element sheathed thermocouple, a sheathed thermocouple is used in which: two pairs of thermocouple wires are enclosed in a metal sheath while being embedded in an inorganic insulating material powder, the thermocouple wires being made of the same materials as and having a diameter that is 90% or greater of or substantially equal to the diameter of thermocouple wires of the single-element sheathed thermocouple, and the metal sheath being made of the same material and having the same outer diameter and wall thickness as a metal sheath of the single-element sheathed thermocouple; only one pair of the two pairs of thermocouple wires are joined to each other at leading ends to form a measuring junction; and a base end of the metal sheath is sealed with a seal with the pair of thermocouple wires joined to each other at the leading ends passing therethrough.

Claims

1. A method for realizing lifespan extension of a thermocouple wire against breakage, as a measure against breakage of a thermocouple wire of a single-element sheathed thermocouple in which a pair of thermocouple wires that have substantially the same diameter and that are joined to each other at leading ends to form a measuring junction are enclosed in a metal sheath while being embedded in an inorganic insulating material powder, and a base end of the metal sheath is sealed in a state in which the thermocouple wires pass therethrough, the breakage occurring when the single-element sheathed thermocouple is used in an environment subjected to repeated heating and cooling, the method comprising: using, instead of the single-element sheathed thermocouple, a sheathed thermocouple in which: two pairs of thermocouple wires are enclosed in a metal sheath while being embedded in an inorganic insulating material powder, the two pairs of thermocouple wires being made of the same materials as the pair of thermocouple wires of the single-element sheathed thermocouple and having a diameter that is 90% or greater of or substantially equal to that of the pair of thermocouple wires of the single-element sheathed thermocouple, and the metal sheath being made of the same material and having the same outer diameter and wall thickness as the metal sheath of the single-element sheathed thermocouple; one pair of thermocouple wires, of the two pairs of thermocouple wires, are joined to each other at leading ends to form a measuring junction; and a base end of the metal sheath is sealed in a state in which the pair of thermocouple wires that are joined to each other at the leading ends pass therethrough; and performing temperature measurement using the pair of thermocouple wires that are joined to each other at the leading ends.

2. The method for realizing lifespan extension of a thermocouple wire against breakage according to claim 1, wherein, in the sheathed thermocouple that is used instead of the single-element sheathed thermocouple in order to extend the lifespan of a thermocouple wire against breakage, not only one pair of thermocouple wires, of the two pairs of thermocouple wires, are joined to each other at the leading ends to form the measuring junction, but also the other pair of thermocouple wires are joined to each other at leading ends to form a measuring junction, and the base end of the metal sheath is sealed in a state in which not only the one pair of thermocouple wires but also the other pair of thermocouple wires pass therethrough, and temperature measurement is performed using either pair of thermocouple wires of the two pairs of thermocouple wires.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1A is a cross-sectional view, taken along the radial direction, of a wire-breakage-prevention sheathed thermocouple, excluding a leading end portion and base end portion thereof.

[0034] FIG. 1B is a cross-sectional view taken along line A-Ain FIG. 1A.

[0035] FIG. 1C is a cross-sectional view taken along line B-B in FIG. 1A

[0036] FIG. 2A is a cross-sectional view, taken along the radial direction, of a single-element sheathed thermocouple, excluding a leading end portion and base end portion thereof.

[0037] FIG. 2B is a cross-sectional view taken along line C-C in FIG. 2A

[0038] FIG. 2C is a cross-sectional view, taken along the longitudinal direction, of an MI cable from which the single-element sheathed thermocouple is formed.

[0039] FIG. 3A is a cross-sectional view, taken along the radial direction, of a double-element sheathed thermocouple, excluding a leading end portion and base end portion thereof.

[0040] FIG. 3B shows a D-D cross section and an E-E cross section of the double-element sheathed thermocouple in FIG. 3A

[0041] FIG. 3C is a cross-sectional view, taken along the radial direction, of a triple-element sheathed thermocouple, excluding a leading end portion and base end portion thereof.

[0042] FIG. 4A is a cross-sectional view, taken along the radial direction, of a sheathed thermocouple with breakage-preventing wires, excluding a leading end portion and base end portion thereof.

[0043] FIG. 4B is a cross-sectional view taken along line F-F in FIG. 4A.

[0044] FIG. 4C is a cross-sectional view taken along line G-G in FIG. 4A.

DESCRIPTION OF THE EMBODIMENTS

[0045] An embodiment of the present invention will be described with reference to FIGS. 1A to 1C, and also with reference to the above-described FIGS. 2A to 2C and 3A to 3C, as appropriate. FIG. 1A is a cross-sectional view, taken along the radial direction, of a wire-breakage-prevention sheathed thermocouple embodying the present invention, excluding the leading end portion and base end portion thereof, FIG. 1B is a cross-sectional view taken along line A-Ain FIG. 1A, and FIG. 1C is a cross-sectional view taken along line B-B in FIG. 1A.

[0046] If a single-element sheathed thermocouple 2 shown in FIGS. 2A and 2B, in which a pair of thermocouple wires 28 that have substantially the same diameter and that are joined to each other at leading ends to form a measuring junction 29 are enclosed in a metal sheath 27 while being embedded in an inorganic insulating material powder 210, and a base end of the metal sheath 27 is sealed in a state in which the thermocouple wires 28 pass therethrough, is used in an environment subjected to repeated heating and cooling, the enclosed thermocouple wires 28 may break.

[0047] As a measure against this breakage, instead of the single-element sheathed thermocouple 2, a wire-breakage-prevention sheathed thermocouple 1 shown in FIGS. 1A to 1C is used in which two pairs of thermocouple wires 8 are enclosed in a metal sheath 7 while being embedded in an inorganic insulating material powder 10, the thermocouple wires 8 being made of the same materials as the thermocouple wires 28 of the single-element sheathed thermocouple 2 shown in FIGS. 2A to 2C, and having a diameter that is 90% or greater of the diameter of the thermocouple wires 28, and the metal sheath 7 being made of the same material and having substantially the same outer diameter and wall thickness as the metal sheath 27 of the single-element sheathed thermocouple 2 in FIGS. 2A to 2C, only one pair of thermocouple wires 8 of the two pairs of thermocouple wires 8 are joined to each other at leading ends to form a measuring junction 9, and a base end of the metal sheath 7 is sealed with a seal 12 in a state in which the pair of thermocouple wires 8 that are joined to each other at the leading ends pass therethrough. Thus, the thermocouple wire lifespan until breakage occurs is extended.

[0048] As described above, if a metal that has a greater linear expansion coefficient than the linear expansion coefficients of the thermocouple wires is used for the metal sheath, tensile stress is repeatedly generated in the thermocouple wires in an environment subjected to repeated heating and cooling, causing breakage of the thermocouple wires, and even if the linear expansion coefficient of the metal sheath is not greater than those of the thermocouple wires, tensile stress is repeatedly generated in the thermocouple wires in an environment subjected to repeated extremely rapid heating, causing breakage of the thermocouple wires.

[0049] Moreover, as described above, the tensile stress that is generated in the thermocouple wires 8 of the wire-breakage-prevention sheathed thermocouple 1 is reduced at most to approximately 62% of the replaced single-element sheathed thermocouple 2, and the number of cycles of heating and cooling until the thermocouple wires 8 break is significantly increased, and lifespan extension can be achieved accordingly.

[0050] Next, the wire-breakage-prevention sheathed thermocouple 1 in FIGS. 1A to 1C structurally differs from a double-element sheathed thermocouple 4 shown in FIGS. 3A and 3B in that, in the double-element sheathed thermocouple 4, each pair of thermocouple wires 48 of the two pairs of thermocouple wires 48 are joined to each other at leading ends to form a measuring junction 49, and an end of a metal sheath 47 is sealed with a seal 412 in a state in which the two pairs of thermocouple wires 48 pass therethrough, whereas, in the wire-breakage-prevention sheathed thermocouple 1, only one pair of thermocouple wires 8 of the two pairs of thermocouple wires 8 are joined to each other at the leading ends to form the measuring junction 9, and only the pair of thermocouple wires 8 that are joined to each other at the leading ends pass through the seal 12 at the end of the metal sheath 7. In the wire-breakage-prevention sheathed thermocouple 1, the temperature measurement is performed using this pair of thermocouple wires 8 that are joined to each other at the leading ends.

[0051] In this embodiment, the outer diameters of the metal sheath 27 of the single-element sheathed thermocouple 2 and the metal sheath 7 of the wire-breakage-prevention sheathed thermocouple 1 are specifically set to be the following three different values: 4.8 mm, 6.4 mm, and 8.0 mm. With respect to the cross-sectional dimensions of a single-element sheathed thermocouple and a double-element sheathed thermocouple that are commercially available, examples regarding those from two companies A and B are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Single-element sheathed thermocouple Double-element sheathed thermocouple Metal sheath Metal sheath Thermocouple Metal sheath Metal sheath Thermocouple Outer diameter Wall thickness wires Diameter Outer diameter Wall thickness wires Diameter Company A 4.8 mm 0.53 mm 0.79 mm 4.8 mm 0.53 mm 0.74 mm 6.4 mm 0.74 mm 1.04 mm 6.4 mm 0.74 mm 0.97 mm 8.0 mm 0.91 mm 1.30 mm 8.0 mm 0.91 mm 1.22 mm Company B 4.8 mm 0.72 mm 0.76 mm 4.8 mm 0.72 mm 0.76 mm 6.4 mm 0.93 mm 1.00 mm 6.4 mm 0.93 mm 1.00 mm 8.0 mm 1.16 mm 1.30 mm 8.0 mm 1.16 mm 1.30 mm

[0052] To give examples of the materials, the thermocouple wires 8 may be K-type thermocouple wires, the metal sheath 7 may be made of SUS 316, and the inorganic insulating material powder 10 may be magnesia. The materials are, of course, not limited to these materials.

[0053] As shown in Table 1, when the metal sheaths have the same outer diameter, the wall thickness of the metal sheath of the single-element sheathed thermocouple and the wall thickness of the metal sheath of the double-element sheathed thermocouple are the same, with respect to both of the companies A and B, and the diameter of the thermocouple wires of the double-element sheathed thermocouple from the company A is 90% or greater of that of the single-element sheathed thermocouple from that company, while the diameter of the thermocouple wires of the double-element sheathed thermocouple from the company B is the same as that of the single-element sheathed thermocouple from that company.

[0054] This means that, at the production stage of the wire-breakage-prevention sheathed thermocouple 1 of this embodiment, the same MI cable as the MI cable from which a commercially available double-element sheathed thermocouple is formed can be used to form the wire-breakage-prevention sheathed thermocouple 1, and the wire-breakage-prevention sheathed thermocouple 1 can be produced by performing a process for processing a commercially available double-element sheathed thermocouple, excluding the step of joining a pair of thermocouple wires to each other at the leading ends, in the processing of the leading end portion, and the step of making that pair of thermocouple wires pass through the seal at the base end, in the processing of the base end portion. In this manner, this embodiment is economically advantageous in that an existing method for producing a commonly commercially-available double-element sheathed thermocouple can be applied to the production of the wire-breakage-prevention sheathed thermocouple 1 merely by excluding some of the processing steps.

[0055] However, in the case where it is difficult to exclude those steps for the reason that the production process is automated, for example, or in the case where the exclusion of those steps actually increases the production costs, those steps need not be excluded, and a wire-breakage-prevention sheathed thermocouple in which each pair of thermocouple wires of the two pairs of thermocouple wires are joined to each other at the leading ends, and both of the two pairs of thermocouple wires pass through the seal at the base end may be produced. In this case, the shape of the wire-breakage-prevention sheathed thermocouple 1 is exactly the same as that of a double-element sheathed thermocouple, and thus, a double-element sheathed thermocouple can be applied to the wire-breakage-prevention sheathed thermocouple of the present invention as-is. The temperature measurement is performed using either pair of the two pairs of thermocouple wires.

[0056] In addition to the above-described economic advantages, this embodiment is convenient in that, since the wire-breakage-prevention sheathed thermocouple 1 has the same outer diameter as the replaced single-element sheathed thermocouple, it is unnecessary to change the shape of a mount portion.

[0057] Note that, as described above, in a double-element sheathed thermocouple, a pair of thermocouple wires that are added to a single-element sheathed thermocouple are disposed in free spaces of the single-element sheathed thermocouple. Thus, as shown in Table 1, there is no significant difference in the diameter of the thermocouple wires between a commercially available single-element sheathed thermocouple and a commercially available double-element sheathed thermocouple. However, with regard to a triple-element sheathed thermocouple, since no free space in which a pair of thermocouple wires can be added is left in a double-element sheathed thermocouple, as can be understood from a comparison between FIGS. 3A and 3C, three pairs of thermocouple wires with a reduced diameter are equidistantly arranged in a commercially available triple-element sheathed thermocouple.

[0058] Even if the wire-breakage-prevention sheathed thermocouple has three pairs of thermocouple wires, the wire-breakage preventing effect is small, because the diameter of the thermocouple wires is reduced if the MI cable and the production method of a commercially available triple-element sheathed thermocouple are applied. In addition, generally, a triple-element sheathed thermocouple is rarely used, and therefore, does not offer benefits in terms of mass production and is expensive. Thus, a wire-breakage-prevention sheathed thermocouple having three pairs of thermocouple wires is inferior to a wire-breakage-prevention sheathed thermocouple having two pairs of thermocouple wires in terms of economic effects.

[0059] If a single-element sheathed thermocouple is used to monitor the temperature of a device, such as a reciprocating engine or a turbine engine, in which a change in temperature is repeatedly caused by the device starting and stopping, a problem may arise in that the thermocouple wires will break. In that case, the present invention exhibits its effects to address this problem. As an actual example, there was an instance in which the thermocouple wires of a single-element sheathed thermocouple that was attached to monitor the temperature of a reciprocating engine for testing frequently broke, but breakage ceased to occur as a result of applying the present invention.