JP2010249667A - Temperature sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature sensor for preventing lead wires of a sensor element from becoming thin and stably maintaining the accuracy of detected temperatures. <P>SOLUTION: The temperature sensor includes a sensor element unit 10 having a temperature sensing body 2 whose electric resistance varies with the temperature, a pair of lead wires 4 electrically connected to the temperature sensing body 2, and a covering material 5 sealing the temperature sensing body 2 and a predetermined area of the lead wires 4, the lead wires 4 extracted from a sealing end 6 of the covering material 5; a metal protective tube 20 housing the sensor element unit 10 except a part of the lead wires 4; and a ceramic shielding body 7 located between the sensor element unit 10 and the metal protective tube 20 and surrounding the sealing end 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a temperature sensor provided with a temperature sensing element whose electrical resistance varies with temperature.

  In order to measure the temperature of automobile exhaust gas, water heaters, boilers, microwave ovens, stoves, and the like, temperature sensors using a temperature sensing element whose resistance value changes with temperature are widely used. As shown in FIG. 4, a temperature sensor element (hereinafter simply referred to as a sensor element) used in such a temperature sensor includes a temperature sensing body 2 provided with a pair of electrodes 3, and lead wires 4 connected to the pair of electrodes 3. And a covering material 5 made of heat-resistant crystalline glass, amorphous glass, or the like for sealing the temperature sensitive body 2. When the sensor element is installed in an electric oven (electricity sensor), radiant heater, combustion appliance, exhaust gas purification device, etc., the sensor element is hermetically sealed to protect the sensor element from vibration, external force, combustion gas, etc. It is used in a state of being housed in a high metal protective tube.

  According to Patent Document 1, when the use environment temperature becomes 750 ° C. or higher, the oxygen partial pressure around the temperature sensing element 2 may fluctuate due to oxidation of the metal protective tube constituting the temperature sensor. Since the temperature-resistance value characteristic becomes unstable due to fluctuation of the composition of No. 2, it is disclosed that a seismic filler having a porosity of 30 to 70% is filled in the metal protective tube.

  However, according to the study by the present inventors, when used at a high temperature of 600 ° C. to 1000 ° C., the metal protective tube that protects the sensor element is oxidized, and a pair drawn from the covering material 5. It has been found that the anode side of the lead wire 4 is gradually narrowed, and a gap is formed in the close contact portion between the covering material 5 and the thin lead wire 4. If a gap is generated between the covering material 5 and the lead wire 4, the sealed state from the atmosphere around the temperature sensing element 2 cannot be maintained, and there is a concern about the influence on the characteristics of the sensor element. However, Patent Document 1 does not disclose or suggest any gap generated between the covering material 5 and the lead wire 4.

JP 2008-215919 A Japanese Patent No. 3806434

  The present invention has been made based on such a technical problem, and provides a temperature sensor that can prevent the lead wire of the sensor element from being thinned and can maintain the accuracy of the detected temperature stably. With the goal.

  As the metal protective tube, a stainless alloy and a Ni-base superalloy excellent in high temperature heat resistance are mainly used. These heat-resistant alloys contain nickel and chromium as main components, but constituent atoms such as nickel, chromium and iron are evaporated and released under a high temperature environment. Further, platinum, platinum alloy, nickel, and oxides thereof constituting the lead wire 4 also start to evaporate at a temperature exceeding 500 ° C. The present inventors presume that these may be a factor for thinning the lead wire, and the composition adhered to the surface of the sensor element used at a high temperature of 600 to 1000 ° C., particularly the covering material 5. The constituent elements of were analyzed. As a result, as shown in FIG. 5, this composition contains a large amount of chromium (Cr) and oxygen (O), and it was found that this composition is chromium oxide having conductivity. Chromium is contained in a metal protective tube that protects the sensor element. It is considered that the metal protective tube is oxidized by exposure to a high temperature and is released as an oxide inside the metal protective tube. Although the released oxide containing chromium oxide adheres to the surface of the covering material 5, a part of the oxide fills between the pair of lead wires 4.

Between the lead wires 4, since a covering material 5 made of crystalline glass, amorphous glass or the like having high insulation performance is interposed, even if the sensor element is energized, as shown in FIG. There is no leakage current between the lead wires 4. In FIG. 6, arrows indicate current. However, as described above, when a conductive material, for example, chromium oxide described above adheres so as to fill the space between the lead wires 4, the insulation performance between the lead wires 4 is impaired, and as shown in FIG. Leakage current is generated between the lead wires 4 by energization. Therefore, electrolytic corrosion (high temperature migration) occurs in the lead wire 4 on the anode side, and metal electrons constituting the lead wire 4 are emitted. As a result, the anode-side lead wire 4 from which the metal electrons have been emitted becomes gradually thinner, and a gap is formed between the covering material 5 and the anode-side lead wire 4 as shown in FIG. 6C. Found out.
In the above, the adhesion of chromium oxide was specifically shown. However, depending on the composition of the metal protective tube, other metal elements may cause high-temperature migration, and the elements constituting the lead wire 4 are high-temperature migration. It may be a cause.

  As described above, it is necessary to prevent the conductive composition due to the metal protective tube or the lead wire 4 from adhering between the lead wires 4 in order to prevent the occurrence of high temperature migration. The temperature sensor of the present invention made there is premised on including a sensor element and a metal protective tube that accommodates the temperature sensing element except for a part of the lead wire. The sensor element seals a temperature sensing element whose electrical resistance varies with temperature, a pair of lead wires electrically connected to the temperature sensing element, and a lead wire within a predetermined range from the temperature sensing element and the connection portion. And a covering material to be stopped. Further, in this sensor element, the lead wire is pulled out from the sealing end of the covering material. The temperature sensor of the present invention having the above configuration is characterized in that a ceramic shield is provided between the sensor element and the protective tube and surrounds the sealing end, and this shield is arranged on the temperature sensing element side. A shielding part having a mortar-shaped recess and a lead wire protection part that is connected to the shielding part and accommodates through the lead wire are disposed, and the shielding part is disposed so as to surround at least the sealing end. By arranging the shielding portion so as to surround at least the sealing end in this way, it is possible to prevent the conductive composition mainly due to the metal protective tube from adhering between the lead wires, It becomes possible to prevent migration.

  In the temperature sensor of the present invention, a filler for regulating the displacement between the covering material and the shield may be interposed in the concave portion of the shielding portion. Thereby, while adhering of the composition which has electroconductivity is prevented more reliably, positioning of the shield with respect to a sensor element can be performed appropriately, and the stability of the shape and performance of a temperature sensor can be ensured.

  In the temperature sensor of the present invention, it is preferable that the outer diameter of the shield is not more than the outer diameter of the sensor element. The outer diameter of the metal protective tube that houses the shield and the sensor element can be kept the same as the outer diameter when only the sensor element is housed. The occurrence of migration can be prevented. The outer diameter of the shield is specified by the maximum outer diameter of the shield, and the outer diameter of the sensor element is specified by the maximum outer diameter of the sensor element.

  According to the temperature sensor of the present invention, it is possible to prevent high-temperature migration due to adhesion of a conductive substance between the lead wires, and to maintain the sealed state of the temperature sensing element by the covering material. Therefore, it is possible to stably ensure the temperature detection accuracy of the temperature sensor.

(A) is a longitudinal cross-sectional view of the temperature sensor of this embodiment, (b) is a plan view of the shield, and (c) is a bottom view of the shield. (A) is a longitudinal cross-sectional view which shows the modification of this embodiment, (b) is a longitudinal cross-sectional view which shows the other modification of this embodiment, (c) is a longitudinal cross-sectional view of the temperature sensor of a comparative example. It is a graph which shows the result of the high temperature electricity supply test done using the temperature sensor of this embodiment shown in FIG. 1, and the temperature sensor of the comparative example shown in FIG.2 (c). It is a figure which shows the conventional sensor element. It is a graph which shows the elemental analysis result of the deposit | attachment between lead wires. (A) A state of detection current application in a conventional sensor element is shown, (b) shows a state of leakage current generation, and (c) shows a thin lead wire.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Fig.1 (a) shows the temperature sensor 1 of this embodiment.
The temperature sensor 1 includes a sensor element unit 10 and a metal protective tube 20 that houses the sensor element unit 10 except for a part on the rear side of the lead wire 4.
The sensor element unit 10 includes a temperature sensing element 2 whose electrical resistance varies with temperature, a pair of lead wires 4 electrically connected to the temperature sensing element 2 via an electrode 3, and the temperature sensing element 2 and the electrode 3. And a covering material 5 for sealing the lead wires 4 within a predetermined range. The lead wire 4 is drawn out from the sealing end 6 of the covering material 5.

  Although it is preferable to use a thermistor as the temperature sensing element 2, those whose electric resistance varies with temperature can be widely applied. When used in a high temperature range of 500 to 1000 ° C., the thermistor includes, for example, Y, Cr, Mn, Ca and O previously disclosed in Patent Document 2 by the present inventor, and Y: Cr: Mn: Ca It is preferable to use a metal oxide having a molar ratio of 75 to 85: 7 to 10: 7 to 10: 1 to 5. The temperature sensing element 2 composed of this metal oxide can measure the temperature up to a high temperature of 1000 ° C. or higher. However, this is only an example, and it goes without saying that other thermistors can be used.

  As the lead wire 4, platinum or a platinum alloy can be used. As the platinum alloy, one containing 1 to 20 wt% of iridium is preferable from the viewpoint of high temperature durability.

The covering material 5 is made of amorphous glass or crystalline glass. Each can be used alone, but it is also possible to use a mixture of amorphous glass and crystalline glass so as to have a desired thermal expansion coefficient. The crystalline glass, for example, silicon oxide, calcium oxide, manganese oxide, preferably those composed of aluminum oxide, more specifically _{SiO 2: 30~60wt%, CaO:} 10~30wt%, MgO: 5 Those having a composition of ˜25 wt% and Al ₂ O ₃ : 0 to 15 wt% can be used in the present invention. Moreover, you may comprise using what added inorganic material powder to glass. Examples of the inorganic material powder added to the glass include aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ), and zirconium oxide (ZrO ₂ ). An oxide etc. are mentioned.

The sensor element unit 10 includes a shield 7 made of ceramic.
The shield 7 provided between the sensor element unit 10 and the metal protective tube 20 has a truncated cone shape and surrounds the rear end side of the covering material 5 to seal the sealing end 6. Therefore, the conductive composition does not adhere between the lead wires 4. The shield 7 is made of a ceramic such as alumina (Al ₂ O ₃ ) or silicon nitride (Si ₃ N ₄ ).

  The temperature sensor 1 includes a metal protective tube 20 that houses the sensor element unit 10 except for a part on the rear side of the lead wire 4. The metal protective tube 20 is made of a stainless alloy, a Ni-base superalloy, or other heat resistant alloy. These alloys contain a large amount of Ni and Cr in order to ensure heat resistance. For example, JIS NCF600, which is an example of a Ni-base superalloy, contains about 75 wt% Ni and about 16 wt% Cr.

The cylindrical shield 7 is formed with a mortar-shaped recess 7c on the front side. The recess 7c is surrounded by a shielding wall 7w provided along the outer periphery of the recess 7c. A shielding part 71 is constituted by the recess 7c and the shielding wall 7w. The shield body 7 is integrally formed with a lead wire protection portion 72 that is continuous with the shield portion 71 and penetrates from the bottom of the recess 7 c toward the rear to form two holding holes 7 h through which the lead wires 4 are inserted. The
The shield 7 is disposed such that the rear side of the covering material 5 is accommodated in the recess 7c. Therefore, the shielding wall 7w surrounds the sealing end 6 and can prevent the conductive composition from adhering between the lead wires 4. In addition, although there is a gap between the covering material 5 and the shielding wall 7w, the conductive composition adheres between the lead wires 4 even if there is such a gap from the result of a high-temperature energization test described later. It was confirmed that this can be prevented.
In the temperature sensor 1, the outer diameter of the shield 7 is set to be equal to the maximum outer diameter of the covering material 5 (which may of course be the following), and therefore the outer dimensions of the temperature sensor 60 and the case where the shield 7 is not provided. Can be made equivalent.

Further, in order to position and fix the shielding body 7 at a fixed position with respect to the covering material 5 and the lead wire 4, as shown in FIG. The temperature sensor 30 filled with the material 8 may be used. Thereby, while being able to prevent more effectively that an electroconductive composition adheres, the displacement with the coating | covering material 5 and the shielding body 7 can be controlled. This function can be obtained not only with the ceramic adhesive 8 but also with a filler obtained by sintering ceramic powder supplied as a slurry.
Further, as shown in FIG. 2 (b), a temperature at which the lead wire protection part 72 of the shield 7 is extended long and a caulking part 20 c is provided on the metal protection pipe 20 to fix the shield 7 to the protection pipe 20. The sensor 40 can also be used.

Using the temperature sensor 1 according to the embodiment, a current of 10 mA was passed in the atmosphere at 800 ° C. and held continuously for 1000 hours, and the electrical resistance during that time was measured. For comparison, the same measurement was performed using a comparative temperature sensor 50 shown in FIG. The results are shown in FIG. FIG. 3 shows the rate of change of electrical resistance with respect to electrical resistance at 25 ° C.
The electric resistance of the comparative temperature sensor (comparative example) greatly increases at the 100th hour, whereas the temperature sensor 1 (embodiment) according to the present embodiment varies in electric resistance even after 1000 hours. Did not occur.
As described above, it was proved that the conductive composition can be prevented from adhering between the lead wires 4 only by surrounding the sealing end 6 with the shielding wall 7w. As shown in FIG. 2A, even when the heat-resistant ceramic adhesive 8 was filled in the recess 7c of the shield 7, the same result as that of the temperature sensor 1 was obtained.

  The temperature sensor according to the present invention can be used for various applications. As an example, it can be used for temperature control of an electric heater and can be used for temperature control of a flame burner. In any case, the detected temperature from the temperature sensor S and the set temperature are compared in a control circuit including an energization circuit. Based on the comparison result, the electric power is controlled in the case of an electric heater, and the flame burner is controlled. In some cases, the fuel and air to be input are controlled. Specific examples of the electric heater include an oven, a radiant heater, a filter regeneration heater of an exhaust gas purification device (DPF: Diesel particulate filter), and the like. As the flame burner, a gas burner and an oil burner are listed. However, this is only an example and does not limit the present invention.

  Although the embodiment of the present invention has been described in detail with reference to the drawings, the configuration described in the above embodiment is selected or changed to another configuration as long as it does not depart from the gist of the present invention. Is possible.

DESCRIPTION OF SYMBOLS 1,30,40,50 ... Temperature sensor 10 ... Sensor element unit 2 ... Temperature sensing body, 3 ... Electrode, 4 ... Lead wire, 5 ... Covering material, 6 ... Sealing end 7 ... Shielding body 7c ... Recessed part, 7h ... Holding hole, 7w ... shielding wall, 71 ... shielding part, 72 ... lead wire protection part 8 ... ceramic adhesive 20 ... metal protection tube

Claims (3)

Seals a temperature sensing element whose electrical resistance varies with temperature, a pair of lead wires electrically connected to the temperature sensing element, the temperature sensing element, and the lead wires within a predetermined range from the connecting portion. A sensor element with which the lead wire is drawn out from a sealing end of the covering material,
A metal protective tube that accommodates the sensor element except for a part of the lead wire;
A ceramic shield between the sensor element and the protective tube and surrounding the sealing end;
With
The shield is
A shielding part provided with a mortar-shaped recess disposed on the temperature-sensitive body side;
A lead wire protection part that is connected to the shielding part and is accommodated through the lead wire;
The temperature sensor, wherein the shielding part is disposed so as to surround at least the sealing end.   The temperature sensor according to claim 1, wherein a filler that regulates displacement between the covering material and the shielding body is interposed in the concave portion of the shielding portion.   The temperature sensor according to claim 1 or 2, wherein an outer diameter of the shield is equal to or smaller than an outer diameter of the sensor element.

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