JP2013196812A - Discharge tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge tube capable of preventing deterioration in performance.SOLUTION: At least parts of an electrode pin 4 and an anode electrode 51 at an inside of a discharge tube 1 are covered with a coating film 4a and a coating film 5a, respectively, the coating films comprising a material having a work function larger than energy corresponding to a wavelength of an ultraviolet ray. Thus, discharge at the covered parts can be prevented, and accordingly, deterioration in performance can be prevented.

Description

  The present invention relates to a discharge tube that discharges when irradiated with an electromagnetic wave having a predetermined wavelength.

  2. Description of the Related Art Conventionally, a discharge tube used for detecting the presence or absence of a flame based on ultraviolet rays emitted from a flame in a combustion furnace or the like is known (for example, see Patent Document 1). The discharge tube includes a sealing device filled and sealed with a predetermined gas, an electrode support pin penetrating the sealed container, and two electrodes supported in parallel in the sealing device by the electrode support pin. It is to be prepared. In such a discharge tube, when a voltage is applied between the electrodes via the electrode support pin, when one of the electrodes arranged opposite to the flame is irradiated with ultraviolet rays, electrons are emitted from the electrode by the photoelectric effect. The electrons are excited one after another to form an avalanche with the other electrode. Therefore, the presence or absence of a flame can be detected by measuring a change in impedance between electrodes, a change in voltage between electrodes, a current flowing between electrodes, and the like.

JP-A-10-115548

  In the above-described discharge tube, an aging operation of the electrode surface is generally performed so that the discharge is performed for a predetermined time and reacts only in a predetermined wavelength region. At this time, if the discharge is started from the peripheral edge where the electric field strength of one electrode is strong or the electrode support pin, the discharge is performed around these places, and the entire electrode cannot be uniformly modified. End up. As a result, defects such as discharge or self-discharge appear even outside the predetermined wavelength range, greatly reducing productivity. Even after shipment as a product, the discharge is performed not from between the electrodes but from the peripheral portion of the electrode or the electrode support pin, and the performance as a product is low.

  Then, an object of this invention is to provide the discharge tube which can prevent the fall of performance.

  In order to solve the above-described problems, a discharge tube according to the present invention is provided with a pedestal, a plurality of pins that pass through the pedestal, and supported by these pins and spaced apart from each other by a predetermined distance. A tube that includes a pair of electrodes, a tube that accommodates a part of the pin and the electrode, and that forms the envelope together with the pedestal; At least a part of the body is made of a material that transmits an electromagnetic wave having a predetermined wavelength, and the covering member is made of a material having a work function larger than that of the material of the pin and the electrode.

  In the above discharge tube, the electrode may be made of a material having a work function smaller than the energy corresponding to the wavelength of the electromagnetic wave.

  According to the present invention, at least a part of the pin and the electrode inside the envelope is covered with the covering member made of a material having a work function larger than that of the material of the pin and the electrode. As a result, it is possible to prevent discharge from being started, and as a result, it is possible to prevent a decrease in performance.

FIG. 1 is a perspective view schematically showing a configuration of a discharge tube according to an embodiment of the present invention. FIG. 2 is a diagram showing a method of manufacturing a discharge tube according to the embodiment of the present invention. FIG. 3 is a diagram showing a method of manufacturing a discharge tube according to the embodiment of the present invention.

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

<Configuration of discharge tube>
As shown in FIG. 1, a discharge tube 1 according to the present embodiment includes a glass tube 2, a pedestal 3 joined to the glass tube 2, and six electrode support pins (electrode pins) penetrating the pedestal 3. 4, two electrodes 5 supported in parallel through six electrode pins 4, and an exhaust pipe 6 projecting from the pedestal 3 to the opposite side of the glass tube 2.

  The glass tube 2 includes a cylindrical side glass 21 and a top plate 22 that closes one end of the side glass 21. The side glass 21 is made of ordinary borosilicate glass, and it is difficult for ultraviolet rays to enter the discharge tube 1 from this portion. On the other hand, the top plate 22 is made of UV transmissive glass, and ultraviolet rays are incident on the discharge tube 1 from this portion. In the present embodiment, the top plate 22 is set to transmit only light having a wavelength of 185 nm or more. Thus, when the discharge tube 1 is installed with the top plate 22 facing, for example, a boiler flame, ultraviolet light having a wavelength of 185 to 245 nm emitted from the flame enters the glass tube 2.

  The pedestal 3 is made of borosilicate glass like the side glass 21 and is formed in a substantially disc shape. In the vicinity of the periphery of the pedestal 3, six electrode pins 4 are penetrated at equal intervals in the circumferential direction. At this time, the axis of the electrode pin 4 is in a state parallel to the central axis of the pedestal 3. A through hole 31 is formed in the central portion of the base 3, and an exhaust pipe 6 is joined to the opposite side of the through hole 31 from the glass tube 2.

  The electrode pin 4 is composed of six electrode support pins that are equally spaced in the circumferential direction in the vicinity of the periphery of the pedestal 3, and is provided in a state of penetrating the pedestal 3 as described above. These electrode pins 4 are made of a conductive material, and for example, a metal such as Kovar (having the same thermal expansion coefficient as glass) can be used. The electrode 5 is fixed to the end (hereinafter referred to as “fixed end”) of the electrode pin 4 on the top plate 22 side, and the end on the opposite side (hereinafter referred to as “terminal end”) is illustrated. Control circuit not connected. Among such electrode pins 4, three electrode pins 41 are provided on the pedestal 3 at equal intervals in the circumferential direction, and an anode electrode 51 to be described later is fixed, thereby serving as a support and a terminal for the anode electrode 51. Function. Further, the remaining three electrode pins 42 are provided on the pedestal 3 at equal intervals in positions that are different from each other in the circumferential direction of the electrode pins 41, and the cathode electrode 52 described later is fixed, whereby the cathode electrode 52 Functions as a support and terminal. The fixed end of the electrode pin 41 that supports the anode electrode 51 protrudes closer to the top plate 22 of the glass tube 2 than the fixed end of the electrode pin 42 that supports the cathode electrode 52. As a result, the anode electrode 51 and the cathode electrode 52 are arranged to face each other with a predetermined distance therebetween.

Here, the surface of the part which protrudes from the base 3 of the electrode pin 4 to the top plate 22 side of the glass tube 2 is coat | covered with the coating film 4a.
The constituent material of the coating film 4a is made of a material having a work function larger than energy corresponding to ultraviolet rays, and nickel (Ni, work function: 5.15) is used in the present embodiment. .
Further, the constituent material of the coating film 4 a has a work function larger than that of the constituent material from the electrode pins 4 and the electrodes 5. In the present embodiment, the electrode pin 4 is made of iron (Fe, work function: 4.5) and the electrode 5 is made of tungsten (W, work function: 4.55), and nickel constituting the coating film 4a. Has a larger work function than those.

  The electrode 5 is composed of two metal electrodes formed in a circular shape, and is composed of an anode electrode 51 disposed opposite to the top plate 22 of the glass tube 2 and a cathode electrode 52 disposed opposite to the base 3. Yes. Here, the anode electrode 51 is formed in a net shape, and the cathode electrode 52 is formed in a flat plate shape. In addition, the anode electrode 51 and the cathode electrode 52 are supported by the electrode pins 4 as described above, and are arranged in parallel with each other with a predetermined distance therebetween. A notch 521 is provided at the periphery of the cathode electrode 52 so as not to interfere with the electrode pin 4 connected to the anode electrode 51.

Here, the coating film 5 a is provided on the peripheral edge of the cathode electrode 52, in other words, on the end of the cathode electrode 52 and in the vicinity of this end.
The constituent material of the coating film 5a is made of a material having a work function larger than energy corresponding to ultraviolet rays, and nickel (Ni, work function: 5.15) is used in the present embodiment. .
The constituent material of the coating film 5 a has a work function larger than that of the electrode pins 4 and the electrodes 5. In the present embodiment, the electrode pin 4 is made of iron (Fe, work function: 4.5) and the electrode 5 is made of tungsten (W, work function: 4.55), and nickel constituting the coating film 5a. Has a larger work function than those.

  The exhaust pipe 6 is an elongated cylindrical body, one end of which is joined to the pedestal 3 and the other end is closed. Similar to the glass tube 2 and the pedestal 3, the exhaust tube 6 is made of borosilicate glass. When the other end of the exhaust pipe 6 is closed, a space is formed in the interior by the glass tube 2, the pedestal 3 and the exhaust pipe 6, and a gas having a predetermined composition is sealed in this space.

<Discharge tube manufacturing method>
Next, a method for manufacturing the discharge tube 1 according to the present embodiment will be described.

  First, the base 3, the electrode pin 4, and the exhaust pipe 6 are integrally formed. Specifically, the tubular borosilicate glass is heated and press-molded together with the electrode pins 4 arranged at predetermined positions, thereby integrating the base 3, the electrode pins 4 and the exhaust pipe 6 as shown in FIG. Let

  When the pedestal 3, the electrode pin 4 and the exhaust pipe 6 are integrally formed, the electrode pin 4 is washed with an acid. As described above, when the base 3, the electrode pin 4, and the exhaust pipe 6 are fired to integrate, the surface of the electrode pin 4 is oxidized and a film is formed. This coating interferes with the formation of the coating film 4a on the electrode pins 4 and affects the discharge characteristics. Therefore, the film is removed by washing the electrode pins 4 with an acid.

  When the oxide film is removed, the terminal end side of the electrode pin 4 is masked, and the surface of the electrode pin 4 is coated with nickel by a plating method. As a result, a coating film 4 a made of nickel is formed on the surface of the electrode pin 4 on the fixed end side.

  When the coating film 4a is formed, the electrode pin 41 is positioned inside the notch 521 so that the cathode electrode 52 does not interfere with the electrode pin 41, and then the cathode electrode 52 is attached to the fixed end of the electrode pin 42, and the laser Fix by welding.

  When the cathode electrode 52 is fixed, the anode electrode 51 is attached to the fixed end of the electrode pin 41 and fixed by laser welding or the like. Here, a coating film 5 a is formed on the cathode electrode 52 in advance. Similar to the coating film 4a, the coating film 5a is formed by masking the central portion of the cathode electrode 52 and coating the surface of the cathode electrode 52 with nickel by a plating method.

  When the anode electrode 51 is fixed, the glass tube 2 is joined to the side of the pedestal 3 where the exhaust pipe 6 is not joined.

  When the glass tube 2 is joined, after a gas having a predetermined composition is sealed, the exhaust tube 6 is closed by blowing a predetermined position of the exhaust tube 6 with a flame of a burner. When the exhaust pipe 6 is closed, an aging process is performed in which a predetermined voltage is applied to the electrode 5 via the electrode pin 4 and discharge is continuously generated.

  Here, in the aging step, the entire electrode 5 can be aged efficiently and stably by causing a discharge from the central portion of the electrode 5 (cathode electrode 51). Therefore, it is desirable that the discharge in the aging process is performed uniformly on the entire surface of the electrode 5 by causing the discharge to start from the central portion of the electrode 5.

  However, for example, when discharge is performed starting from a place other than the central portion of the electrode 5, such as between the peripheral edge of the cathode electrode 52 and the anode electrode 51, between the electrode pin 4 and the cathode electrode 52, or between the electrode pins 4. The entire electrode 5 cannot be efficiently and stably modified. Then, since defects such as insufficient sensitivity and self-discharge appear, productivity is pressed and reliability as a product is low.

  Therefore, in the present embodiment, the coating film 4 a is provided on the electrode pin 4 inside the discharge tube 1, and the coating film 5 a is provided on the periphery of the anode electrode 52. The material of the coating film 4a and the coating film 5a has a work function larger than that of the material of the electrode pin 4, the anode electrode 51, and the anode electrode 52. Then, discharge is performed in a portion that is not covered with the coating film 4a and the coating film 5a, that is, a portion excluding the peripheral portion of the electrode pin 4 and the anode electrode 52. Thereby, since the surface of the electrode 5 is uniformly modified, it is possible to prevent a decrease in performance as a discharge tube.

  When the aging process is completed, the manufacturing process of the discharge tube 1 is completed and shipped.

  As described above, according to the present embodiment, the inside of the discharge tube 1 is formed by the coating film 4a and the coating film 5a made of a material having a work function larger than the material of the electrode pins 4 and the anode electrode 51. Since at least a part of the electrode pin 4 and the cathode electrode 52 is covered, discharge at the covered part can be prevented, and as a result, a decrease in performance can be prevented.

  In this embodiment, the case where the coating film is provided on both the electrode pins 4 and the peripheral edge of the cathode electrode 52 has been described as an example. However, the coating film may be provided on only one of them.

  In the present embodiment, the case where the coating film 4a and the coating film 5a are formed by plating a metal has been described as an example. However, for example, a material other than a metal such as an organic material may be plated. Good.

  In the present embodiment, the case where the coating film 4a and the coating film 5a are formed by plating has been described as an example. However, the method of forming the coating member is not limited to plating, and can be freely set as appropriate. it can. For example, it may be covered with plastic or glass.

  In this embodiment, the case where nickel is used as the material of the coating film 4a and the coating film 5a has been described as an example. However, if the work function is larger than the material of the member to be coated, the coating film The material of 4a and the coating film 5a is not limited to nickel, and can be set freely as appropriate. Further, the material of the coating film 4a and the coating film 5a is more preferably composed of a material having a work function larger than the energy corresponding to the wavelength of the irradiated electromagnetic wave. Thereby, even if the electromagnetic wave is irradiated, the emission of electrons due to the photoelectric effect can be more effectively prevented.

  In this embodiment, the case of a discharge tube that discharges when irradiated with ultraviolet rays such as a flame sensor has been described as an example. However, the irradiated electromagnetic waves can be freely set as appropriate, not only ultraviolet rays. . In this case, it is realizable by changing suitably the material of the top plate 22 and the electrode 5 based on the wavelength of the electromagnetic waves which discharge. At this time, the covering member is made of a material having a work function larger than that of the electrode pin and the electrode 4.

  The present invention can be applied to various devices that generate discharge, such as a flame sensor.

DESCRIPTION OF SYMBOLS 1 ... Discharge tube, 2 ... Glass tube, 3 ... Base, 4, 41, 42 ... Electrode pin, 4a, 5a ... Coating film, 5 ... Electrode, 6 ... Exhaust tube, 21 ... Side glass, 22 ... Top plate, 31 ... through hole, 51 ... anode electrode, 52 ... cathode electrode, 521 ... notch.

Claims (2)

A pedestal,
A plurality of pins penetrating this pedestal;
A pair of electrodes supported by these pins and arranged parallel to each other at a predetermined interval;
A tube that houses a part of the pin and the electrode, and forms an envelope together with the pedestal;
A covering member that covers at least a part of the pin and the electrode inside the envelope; and
At least a part of the tubular body is made of a material that transmits electromagnetic waves having a predetermined wavelength,
The said covering member is comprised from the material which has a larger work function than the material of the said pin and the said electrode. The discharge tube characterized by the above-mentioned. The discharge tube according to claim 1, wherein the electrode is made of a material having a work function smaller than energy corresponding to the wavelength of the electromagnetic wave.

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