JP2007078433A - Sheathed thermocouple coated with polyimide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem, wherein a function of a measured device is lost or a handling person receives an electrical shock, by a flow of a current which is not meant to be caused between a potential generated portion and a grounded portion, through a metal sheath of a lead-in sheathed thermocouple, when measuring a temperature of the potential generated portion with respect to grounding in an inside of a fuel cell, by the sheathed thermocouple; also to solve a problem wherein an induction noise is generated in a measured signal of the sheathed thermocouple, when the current is fluctuated, not allowing accurate temperature measurement, or the like. <P>SOLUTION: This sheathed thermocouple is coated with a polyimide having 1-10 μm of thickness, on the whole surface ranging over from a temperature measuring side tip to 10-150 mm of length therefrom, in the sheathed thermocouple with ϕ 0.1-ϕ 0.2 mm of outside diameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheathed thermocouple for a fuel cell that is installed in a narrow place at a high temperature with a potential to be measured.

  A sheathed thermocouple is a metal sheath containing an inorganic insulating material such as magnesia and containing a thermocouple wire. It can withstand use in a reducing or corrosive atmosphere, and it can be electrically conductive in the surroundings. It has features such as contact with the body does not affect the measurement, and is widely used as a temperature sensor.

There are two types of sheathed thermocouples: non-grounded type and grounded type, and these structures are shown in FIGS. FIG. 1 is a longitudinal sectional view of a non-grounded sheath thermocouple. FIG. 2 is a longitudinal sectional view of a grounding type sheathed thermocouple, and FIG. 3 is a diagram showing a II section in FIG. 1 and a II-II section in FIG. In both the non-grounding type and the grounding type, an inorganic insulating material 2 such as magnesia (MgO) is interposed in the metal sheath 1, and the + side thermocouple element 3 and the-side thermocouple element 4 are accommodated. . On the distal end side, the two strands are joined (non-grounding type in FIG. 1) or the strand and the sheath tip are joined (grounding type in FIG. 2), and the distal end portion is used as a temperature measuring section. Further, the base end opening is sealed with an epoxy resin or the like in order to prevent moisture from entering the inorganic insulating material 2 to deteriorate the insulation. The base end may be provided with a sleeve that accommodates a connection portion between the thermocouple element and the compensation conductor, and a terminal box that accommodates a terminal block for connection with the compensation conductor.
Japanese Patent Application No. 2004-252580

  When the temperature of a portion where a potential is generated between the fuel cell and the ground is measured by the sheath thermocouple, the portion where the potential is generated is grounded through the metal sheath of the sheathed thermocouple. A current that should not flow between the two parts flows, resulting in loss of function of the device under test and electric shock of the operator, and if this current fluctuates, inductive noise appears in the measurement signal of the sheath thermocouple. Occurs and accurate temperature measurement cannot be performed.

  Since the inside of the fuel cell is in a reducing atmosphere, a sensor that is deteriorated by the reducing atmosphere and causes a measurement error cannot be used. If the temperature to be measured is not high, cover the thermocouple wire with PFA resin (one of fluororesins, commonly called “Tetra fluoroethylene-perfluoroalkylvinyl ether copolymer”), As a result, a material that is insulated from the potential and shielded from the reducing atmosphere of the thermocouple wire is used. However, since the PFA resin softens when the temperature exceeds 260 ° C. and carbonizes at a higher temperature, it cannot be used at a temperature higher than 260 ° C. In addition, it is desirable that the gap leading from the cell having a potential difference from the ground of the fuel cell to the grounded place is as narrow as possible. However, the PFA-coated thermocouple has a minimum minor axis of a flat cross-sectional dimension of 0.22 mm ( 4), the gap needs to have a width larger than this, and a thermocouple with a small diameter is required.

  The innovation requirement items required for the thermocouples used in the above fuel cells are summarized as follows.

  a. Can be used in a reducing atmosphere for a long time.

  b. Can be used at the highest possible temperature of 260 ° C or higher.

  c. The outer surface of at least the part installed in the potential cell must be covered with an insulating material so that the temperature of the potential fuel cell can be measured.

  d. The portion covered with the insulating material can pass through the narrowest possible gap of 0.22 mm or less.

  In response to such a demand, the sheath thermocouple shown in FIGS. 5 and 6 was invented.

  FIG. 5 shows a thickness of 1 μm to 10 μm over the entire surface 10 mm to 150 mm (length B in the figure) from the temperature measuring side tip of the sheath thermocouple having an outer diameter A of φ0.1 mm to φ0.2 mm in the figure. (Length of H in the figure) is coated with polyimide. The sheath thermocouple has a minimum diameter that can be manufactured or a diameter close thereto, and can be used in a reducing atmosphere for a long time by using the sheath thermocouple.

  The coating polyimide is an insulating material that can withstand temperatures up to 350 ° C, and the sheath thermocouple body has a heat resistance of 1000 ° C or higher if Inconel 600 is used as the sheath material, so it can be used in the temperature range up to 350 ° C. The use high temperature region is increased by about 90 ° C. compared to the conventional case.

  The coating length of 10 mm to 150 mm is based on the size of the fuel cell having an electric potential with respect to the earth. By selecting from this length range, the portion having an electric potential from a small cell to a large cell is selected. The thermocouple can be routed at the polyimide coated part. That is, the uncoated portion can be routed only to the portion of the ground potential. The coating thickness of 1 μm to 10 μm is determined by the magnitude of the potential of the measurement site with respect to the ground (size on the + side and − side). If the potential is about ± several volts, the thickness may be several μm, and if the potential is increased, the thickness needs to be increased. However, if the thickness is 10 μm, it is possible to cope with a potential of ± 500 volts or more.

  Furthermore, when a sheath thermocouple with a diameter of 0.1 mm is used, if there is a gap of 0.1 mm + coating thickness, it can be routed, and the required gap is ½ or less of the conventional gap. Even when using a sheathed thermocouple with a diameter of 0.2 mm, the required gap is narrower than the conventional one.

  As described above, the fuel cell thermocouple sensor of FIG. ~ D. It satisfies.

  FIG. 6 shows a radial force applied to a portion 10 mm to 150 mm (length of E in the figure) from the temperature measuring side tip of the sheath thermocouple having an outer diameter C of φ0.15 mm to φ0.2 mm in the figure, The cross section was deformed into a flat shape with a vertical width (F in the figure) of 1/2 to 3/4 and a horizontal width (G in the figure) of 4/3 to 2 times the original diameter. The surface is coated with polyimide having a thickness of 1 μm to 10 μm (thickness H in the figure) so as to cover the entire surface of the part (part of FIG. D).

  The difference between FIG. 6 and FIG. 5 is that the tip section is flattened. The values 1/2 to 3/4, 4/3 to 2 times related to the flattening rate are as follows. This is a result of increasing the flatness as much as possible within the range where no disconnection, contact between the metal sheath and the thermocouple element, and contact between the + and − thermocouple elements occur. In addition, when a sheathed thermocouple with an outer diameter of less than φ0.15 mm is processed into a flat shape, wire breakage, contact between the metal sheath and the thermocouple wire, and contact between the + and – thermocouple wires are also generated. In order to facilitate, the sheath thermocouple processed into a flat shape has an outer diameter of 0.15 mm or more. The sensor of FIG. 6 is similar to that of FIG. ~ D. However, the required gap is further reduced by adopting a flat cross section.

  Embodiments of the shape of FIG. 5 are shown below.

  The dimensions are as follows:

    A: φ0.1 mm, B: 100 mm, H: 5 μm, length from the tip to the seal 5: 150 mm, of course, the length of B varies depending on the size of the fuel cell used.

  The thermocouple wires 3 and 4 use K thermocouple wires shown in JIS C 1602, the sheath 1 is Inconel 600, the inorganic insulating material 2 charged inside is magnesia (MgO), and the seal 5 material is epoxy. is there. The type of the sheath thermocouple is a non-grounding type shown in FIG.

  Polyimide coating is done by dipping a sheath thermocouple in a solution in which polyimide is dissolved in a solvent, attaching the solution to a 100 mm portion from the tip, lifting it, and baking it until the polyimide thickness reaches 5 μm. Formed. Of course, it may be created by other methods.

  It was confirmed that the insulation by this polyimide coating can withstand a voltage of 500 V DC or more and is a thermocouple that can sufficiently withstand use in a normal fuel cell.

  Next, an embodiment is shown for the shape of FIG.

  The dimensions are as follows.

C: φ0.15 mm, E: 30 mm, D: 35 mm, H: 5 μm, length from tip to seal 5: 150 mm, F: 0.1 mm (2/3 of the original diameter), G: about 0. 2mm (about 4/3 of the original diameter)
Of course, the length of E varies depending on the size of the fuel cell used. Also, after leaving the gap between the cells of the fuel cell, it is the place of ground potential, so the length of D to be coated may be basically the same as the length of E, but the displacement of the thermocouple position In consideration of such margins, it is 5 mm longer than E.

  As for the material, as in FIG. 5, the couple wires 3 and 4 are K thermocouple wires shown in JIS C 1602, the sheath 1 is Inconel 600, and the inorganic insulating material 2 filled therein is magnesia (MgO). The material of the seal 5 is epoxy. The type of the sheath thermocouple is also a non-grounding type as shown in FIG. Further, the coating method of the polyimide coating is the same as in the case of FIG.

  The insulation of the coating shown in FIG. 6 can withstand a voltage of 500 V DC or more and can sufficiently withstand use in a normal fuel cell.

  Although the present invention has been described with respect to a thermocouple for measuring the temperature of a fuel cell, it can be used to measure the temperature of an object having a potential with respect to ground.

It is a longitudinal direction sectional view of a non-grounding type sheathed thermocouple. It is a longitudinal direction sectional view of a grounding type sheathed thermocouple. It is sectional drawing of the radial direction of FIG. 1 and FIG. FIG. 3 is a cross-sectional view of a PFA resin-coated thermocouple having a flat cross-sectional dimension with a minimum minor axis. It is a front view explaining the state of the sheath thermocouple which coated polyimide on the surface of the present invention. It is a two-view figure of the front view and bottom view explaining the state which flattened the temperature measurement front end side of this invention, and coated the polyimide on the surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal sheath 2 ... Inorganic insulating material 3 ... + side thermocouple strand 4 ...-side thermocouple strand 5 ... Seal 6 ... PFA resin coating

Claims (2)

  A sheathed thermocouple in which polyimide having a thickness of 1 μm to 10 μm is coated on the entire surface of 10 mm to 150 mm from the temperature measuring side tip of the sheath thermocouple having an outer diameter of φ0.1 mm to φ0.2 mm.   A radial force is applied to a portion 10 mm to 150 mm from the temperature measuring tip of the sheath thermocouple having an outer diameter of φ0.15 mm to φ0.2 mm, and the vertical width of the section is 1/2 to the original diameter. A sheathed thermocouple that is deformed into a flat shape with a width of 3/4 and a horizontal width of 4/3 to 2 times, and is coated with polyimide having a thickness of 1 μm to 10 μm so as to cover the entire surface of the flattened portion.

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