JP2015004645A - Oxygen concentration measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen concentration measurement device being compact in size and also capable of controlling the supply amount of a reference gas with high accuracy.SOLUTION: An oxygen concentration measurement device according to the present invention has a zirconia element connected to an external electrode on a side in contact with a measurement gas to be measured and an internal electrode on a side in contact with a reference gas, the zirconia element generating an electromotive force in accordance with a difference between the oxygen concentration of the measurement gas and the oxygen concentration of the reference gas, and measures an oxygen concentration in accordance with the magnitude of the generated electromotive force. The oxygen concentration measurement device is provided with a reference gas supply part having a vibrator vibrating in accordance with an electric signal, the reference gas supply part being connected to a supply port through which the reference gas is supplied and supplying the reference gas by a vibration corresponding to the electric signal of a vibrator, for example, a piezoelectric element.

Description

  The present invention relates to an oxygen concentration measuring apparatus for measuring oxygen concentrations in various furnace atmospheres. In particular, the present invention relates to an oxygen concentration measuring apparatus that is small and that can control the supply amount of a reference gas with high accuracy.

  In a furnace used for heat treatment, surface treatment, etc. of metal parts, oxygen is very small. In order to measure such a small amount of oxygen, an oxygen concentration measuring apparatus mainly using ceramics is employed.

  Patent Document 1 discloses a moisture measuring device that measures a water vapor concentration in a measurement gas using a solid electrolyte element. In the moisture measuring device disclosed in Patent Document 1, a reference gas (reference gas) is introduced into a gas reservoir chamber by operating a pump.

  Further, Patent Document 2 discloses an oxygen partial pressure measuring device in which a reference gas supply method to a direct insertion type oxygen sensor is different from that of Patent Document 1. In the oxygen partial pressure measuring device disclosed in Patent Document 2, a reference gas adjusted to a predetermined oxygen partial pressure is supplied to a hollow member using a cylinder.

JP 60-114765 A JP 07-159370 A

  In the oxygen concentration detector disclosed in Patent Document 1 and the oxygen partial pressure measuring device disclosed in Patent Document 2, both a sensor unit (electrode unit) that generates an electromotive force for measuring the oxygen concentration was generated. The data processing unit for detecting the oxygen concentration based on the electromotive force is separated by the outer wall portion into which the oxygen sensor main body is inserted, and a reference gas supply pump or cylinder is connected to the data processing unit that does not have a relatively large temperature change. Is arranged. Therefore, there is a problem that it is difficult to reduce the size of the data processing unit, and there is a possibility that the entire apparatus may be increased in size.

  Further, when the reference gas is supplied by the pump, it is difficult to reduce vibration, noise, and the like due to the pump drive, and it is also difficult to increase the accuracy of adjusting the supply amount of the reference gas. Similarly, when the reference gas is supplied from the cylinder, the cylinder needs to be replaced in accordance with the remaining amount of the reference gas in the cylinder, so that the operation becomes complicated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an oxygen concentration measuring apparatus that is small in size and capable of controlling the supply amount of a reference gas with high accuracy.

  In order to achieve the above object, an oxygen concentration measuring apparatus according to the present invention is connected to an external electrode on a side in contact with a measurement gas to be measured and an internal electrode on a side in contact with a reference gas, respectively. In an oxygen concentration measurement apparatus that has a zirconia element that generates an electromotive force according to the difference between the oxygen concentration of the reference gas and the oxygen concentration of the reference gas, and that measures the oxygen concentration according to the magnitude of the generated electromotive force, A reference gas supply unit having a vibrator that vibrates in accordance with the reference gas supply unit, which is connected to a supply port that supplies the reference gas to the inside of the apparatus. A reference gas is supplied.

  In the above configuration, the reference gas supply unit having the vibrator that vibrates according to the electric signal is connected to the supply port that supplies the reference gas to the inside of the apparatus, and the reference gas is supplied by the vibration according to the electric signal of the vibrator. Since the space for installing the pump, cylinder, piping, etc. for supplying the reference gas to the outside of the sensor unit is not required, the supply amount of the reference gas can be controlled by the vibration frequency of the vibrator. By controlling the current or voltage to be oscillated, it becomes possible to control the supply amount of the reference gas with high accuracy.

  In the oxygen concentration measuring apparatus according to the present invention, the reference gas supply unit preferably uses a piezoelectric element as the vibrator.

  In the above configuration, since the piezoelectric element is used as the vibrator, the reference gas can be supplied with less noise and less power consumption than a pump or the like.

  In the oxygen concentration measuring apparatus according to the present invention, it is preferable that the piezoelectric element is arranged orthogonal to a direction in which the reference gas is supplied and vibrates along the direction in which the reference gas is supplied.

  In the above configuration, the piezoelectric element is arranged orthogonal to the direction in which the reference gas is supplied and vibrates along the direction in which the reference gas is supplied. Therefore, the overall length of the apparatus can be shortened and the ejection pressure is reduced. The reference gas can be supplied at a constant ejection pressure so as to be uniform without pulsation.

  Moreover, it is preferable that the oxygen concentration measuring apparatus according to the present invention includes a filter in an opening for taking in the reference gas.

  In the above configuration, since the filter is provided in the opening for taking in the reference gas, dust such as dust contained in the outside air taken in as the reference gas can be eliminated by the filter, and deterioration in function due to the adhesion of dust to the piezoelectric element or the like can be prevented. Can be prevented.

  According to the above configuration, the reference gas supply unit having the vibrator that vibrates in accordance with the electric signal is connected to the supply port that supplies the reference gas, and the reference gas is supplied by the vibration in accordance with the electric signal of the vibrator. No need for a space to install a pump, cylinder, piping, etc. for supplying the reference gas to the outside of the sensor unit, and the reference gas supply amount can be controlled by the vibration frequency of the vibrator. By controlling the current or voltage to be supplied, the supply amount of the reference gas can be controlled with high accuracy.

It is sectional drawing which shows the structure of the oxygen concentration measuring apparatus which concerns on embodiment of this invention. It is a fragmentary sectional view which shows the structure of the front-end | tip part of the oxygen concentration measuring apparatus which concerns on embodiment of this invention. It is a graph which shows the relationship between the electromotive force which generate | occur | produces in a zirconia element, and the oxygen concentration of measurement gas. It is sectional drawing which shows the structure of the reference gas supply part of the oxygen concentration measuring apparatus which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows the structure of the reference | standard gas supply part of the oxygen concentration measuring apparatus which concerns on embodiment of this invention. It is an expanded sectional view near the reference gas jet outlet of the reference gas supply part of the oxygen concentration measuring device concerning an embodiment of the invention.

  Hereinafter, an oxygen concentration measuring apparatus according to an embodiment of the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of an oxygen concentration measuring apparatus according to an embodiment of the present invention. The oxygen concentration measuring apparatus 1 according to the present embodiment includes a zirconia element 12 at one end (tip) of a cylindrical alumina tube (reference gas inflow tube) 13 into which a reference gas serving as a reference for measuring the oxygen concentration flows. An oxygen sensor unit 10 is provided. The other end of the alumina tube 13 is provided with a reference gas inlet (supply port) 2 through which a reference gas flows. Further, an alumina pipe (reference gas outflow pipe) 20 for interposing the alumina pipe 13 is provided, and the space between the alumina pipe 13 and the alumina pipe 20 functions as a reference gas outflow path.

  FIG. 2 is a partial cross-sectional view showing the configuration of the distal end portion of the oxygen concentration measuring apparatus 1 according to the embodiment of the present invention. As shown in FIG. 2, in the oxygen concentration measuring apparatus 1 according to the present embodiment, an alumina tube 13 provided with an oxygen sensor unit 10 including a zirconia element 12 at one end is provided as a protective tube 19 into which an alumina tube 20 is inserted. It is stored. The zirconia element 12 is connected to the internal electrode 16 on the side in contact with the reference gas flowing inside the alumina tube 13 and the external electrode 17 on the side in contact with the measurement gas to be measured for oxygen concentration.

  The platinum electrode 15 is connected to the external electrode 17, and the platinum electrode 14 is connected to the internal electrode 16. The zirconia element 12 is formed integrally with the external electrode 17 and the internal electrode 16. The internal electrode 16 is formed, for example, by applying a platinum paste on the side of the zirconia element 12 that contacts the reference gas and baking the platinum electrode 14 while pressing it with a sensor holding member to be described later.

  The zirconia element 12 has a property that charges move from a higher oxygen concentration to a lower oxygen concentration under a constant high temperature environment. Therefore, the oxygen concentration of the measurement gas can be measured by measuring the electromotive force generated in the zirconia element 12 due to the movement of electric charge as the potential difference between the internal electrode 16 and the external electrode 17.

That is, when the oxygen concentration of the reference gas is P _R (%) and the oxygen concentration of the measurement gas is P _M (%), the Nernst equation of (Equation 1) holds.

  In the present embodiment, in the zirconia element 12, ion conduction occurs in which oxygen ions are generated on the high oxygen concentration side and oxygen is generated from the oxygen ions on the low oxygen concentration side. The chemical reaction formula of ion conduction can be expressed as (Formula 2).

  Therefore, “the number of electrons n included in the reaction” in (Formula 1) is “4”.

Since the oxygen concentration P _R of the reference gas is known, by measuring the electromotive force E generated by the zirconia element 12, it is possible to calculate the oxygen concentration P _M of the measuring gas (Equation 1). FIG. 3 is a graph showing the relationship between the electromotive force E generated in the zirconia element 12 and the oxygen concentration P _M of the measurement gas. As shown in FIG. 3, the oxygen concentration P _M is seen to vary as a logarithmic function value of the electromotive force E. Thus, by measuring the electromotive force E generated by the zirconia element 12, it is possible to determine the oxygen concentration P _M of the measuring gas.

As can be seen from the Nernst equation shown in (Equation 1), the electromotive force E varies depending on the temperature (absolute temperature) T of the surrounding atmosphere. Therefore, by measuring the temperature (absolute temperature) T of the reference gas by the thermocouple temperature measurement unit using the thermocouple 18, the correct electromotive force E can be obtained from the Nernst equation, and the measurement gas can be measured more accurately. it is possible to determine the oxygen concentration P _M.

  Returning to FIG. 2, the oxygen concentration measuring apparatus 1 according to the present embodiment can be fitted to the cylindrical first sensor holding member 31 and the first sensor holding member 31 at one end of the alumina tube 13. And a columnar second sensor holding member 32 that holds the zirconia element 12. The first sensor holding member 31 is hollow and allows the reference gas to flow by being connected to the alumina tube 13. The second sensor holding member 32 is solid, and the reference gas flows into a space formed between the first sensor holding member 31 and the second sensor holding member 32. The reference gas that flows into the space between the first sensor holding member 31 and the second sensor holding member 32 is generated when the first sensor holding member 31 and the second sensor holding member 32 are fitted together. From the gap, it flows out to the outside through the reference gas outflow path 61 between the alumina tube 13 and the alumina tube 20.

  The first sensor holding member 31 provided at the tip of the alumina tube 13 is made of an alumina-based material, and the second sensor holding member 32 fitted to the first sensor holding member 31 is also an alumina-based material. It is formed with. The thermocouple 18 is inserted through a hole that penetrates the alumina tube 13 and the first sensor holding member 31.

  Returning to FIG. 1, in the oxygen concentration measuring apparatus 1 according to the present embodiment, a reference gas inlet (supply port) 2 for supplying a reference gas is connected to a reference gas outlet 45 by a communication tube 42. The reference gas outlet 45 includes a reference gas supply unit 41 having a vibrator that vibrates in accordance with an electrical signal.

  The vibrator is not particularly limited as long as it can vibrate according to an electric signal to supply the reference gas. However, it goes without saying that it is preferable to make the entire apparatus as small as possible. Therefore, in this embodiment, a flat plate piezoelectric element is used as the vibrator, and the reference gas is supplied by vibrating the piezoelectric element in accordance with an electric signal. By using the piezoelectric element, it is possible to supply the reference gas with less noise and less power consumption than when using a pump or the like.

  FIG. 4 is a cross-sectional view showing the configuration of the reference gas supply unit 41 of the oxygen concentration measuring apparatus 1 according to the embodiment of the present invention, and FIG. 5 shows the configuration of the oxygen concentration measuring apparatus 1 according to the embodiment of the present invention. 4 is a longitudinal sectional view showing a configuration of a reference gas supply unit 41. FIG. As shown in FIG. 4, the reference gas supply unit 41 includes an inner case 50 and an outer case 51 that covers the inner case 50 in a non-contact manner with a predetermined gap.

  More specifically, the outer case 51 has a cylindrical cavity that opens downward, and the cylindrical inner case 50 is accommodated in the outer case 51 with a predetermined gap. The inner case 50 is elastically supported by the outer case 51 via a spring connecting portion 52. A plurality (four in FIG. 4) of spring connecting portions 52 are provided at regular intervals in the circumferential direction between the outer peripheral surface of the inner case 50 and the inner peripheral surface of the outer case 51.

  The spring connecting portion 52 is configured by a spring member such as a plate spring, and the spring elasticity in the vibration direction of the plate-like vibrator 53 shown in FIG. 5 is low, and the spring elasticity in the direction perpendicular to the vibration direction of the plate-like vibrator 53 is shown. Is installed to be high. Therefore, even when the inner case 50 vibrates in the vibration direction of the plate-like vibrator 53 with the resonance drive (vibration) of the plate-like vibrator 53, the vibration is prevented from reaching the outer case 51. can do. In addition, a reference gas (outside air) inflow passage 56 is formed between the inner case 50 and the outer case 51.

  The inner case 50 is open at the bottom, and a plate-like vibrator 53 is disposed so as to close the opening of the inner case 50, and the first blower chamber is disposed between the inner case 50 and the plate-like vibrator 53. 57 is formed.

  The plate-like vibrator 53 according to the present embodiment has a unimorph structure in which a piezoelectric element 53a formed of piezoelectric ceramics is attached to a central portion of a diaphragm 53b formed of a thin elastic metal plate. By applying a voltage of a predetermined frequency to the piezoelectric element 53a, the entire plate-like vibrator 53 is driven to resonate. In the present embodiment, the piezoelectric element 53a is attached to the surface of the diaphragm 53b opposite to the side where the first blower chamber 57 is formed.

  In this way, the plate-like vibrator 53 is arranged orthogonal to the direction in which the reference gas is supplied from the reference gas inlet (supply port) 2 to the inside of the apparatus as shown in FIG. Therefore, the overall length of the apparatus can be shortened. Further, since it is sufficient to apply a predetermined high-frequency voltage, the reference gas can be supplied at a constant ejection pressure so that the ejection pressure does not pulsate as in the case of using the pump, and becomes uniform.

  Of the wall surfaces forming the inner case 50, the first wall portion 50 a facing the plate-like vibrator 53 is also the upper wall portion of the first blower chamber 57. Therefore, when the first wall 50a is formed of a thin elastic metal plate like the diaphragm 53b, and the plate-like vibrator 53 is driven to resonate in a predetermined mode, the first wall 50a is excited accordingly. It is preferable to configure as described above. This is because by adopting such a configuration, the flow rate of the reference gas to be ejected can be dramatically increased. Moreover, you may form the 1st wall part 50a and the spring connection part 52 with the same member.

  A first opening 50b that connects the inside and the outside of the first blower chamber 57 is formed at the center of the first wall 50a. A second opening 51c is formed at the center of the second wall 51b of the outer case 51 facing the first wall 50a, that is, at a position facing the first opening 50b. The second opening 51 c serves as a jet outlet from which the reference gas is jetted by the vibration of the plate-like vibrator 53. A predetermined inflow space 56a is formed between the first wall 50a and the second wall 51b. The inflow space 56a guides the reference gas flowing in from the inflow passage 56 to the vicinity of the first opening 50b and the second opening 51c.

  A third wall portion 62 is disposed below the outer case 51 so as to close the opening of the outer case 51. A third opening 62 a that communicates the outside with the second blower chamber 60 is formed at the center of the third wall 62. The volume of the second blower chamber 60 and the opening area of the third opening 62 a are set so that a pseudo resonance space can be formed with the vibration of the plate-like vibrator 53. Since the second blower chamber 60 and the inflow passage 56 are in communication with each other, the reference gas that has flowed into the second blower chamber 60 from the third opening 62 a flows into the inflow space 56 a through the inflow passage 56.

  Here, the operation of the reference gas supply unit 41 configured as described above will be described. When an alternating voltage of a predetermined frequency is applied to the piezoelectric element 53a, the plate-like vibrator 53 is driven to resonate in the primary resonance mode or the tertiary resonance mode, and the volume of the first blower chamber 57 changes periodically. When the volume of the first blower chamber 57 increases, the reference gas in the inflow space 56a is sucked into the first blower chamber 57 from the first opening 50b, and conversely, the volume of the first blower chamber 57 decreases. The reference gas in the first blower chamber 57 is discharged from the first opening 50b to the inflow space 56a.

  Since the plate-like vibrator 53 is driven to resonate at a high frequency, the air flow of the reference gas discharged from the first opening 50b to the inflow space 56a is high speed and has high energy, and thus passes through the inflow space 56a. Then, it is ejected from the second opening 51c. At this time, since the reference gas in the inflow space 56a is ejected while being involved, a continuous air flow from the inflow passage 56 toward the inflow space 56a is generated, and the reference gas is continuously ejected from the second opening 51c. In particular, when the plate-like vibrator 53 is driven to resonate in a predetermined mode, the flow rate of the jetted reference gas can be dramatically increased by exciting the first wall portion 50a accordingly.

  FIG. 6 is an enlarged cross-sectional view of the vicinity of the reference gas outlet 45 of the reference gas supply unit 41 of the oxygen concentration measurement apparatus 1 according to the embodiment of the present invention. As shown in FIG. 6, the diameter of the first opening 50b is smaller than the diameter of the second opening 51c. Therefore, since the inflow speed of the reference gas flowing into the first blower chamber 57 side becomes faster than the inflow speed of the reference gas flowing out into the second opening 51c, a negative pressure is generated in the vicinity of the central space 56b. Thereby, since the reference gas in the inflow space 56a is sucked to the central space 56b side, the reference gas can be ejected from the second opening 51c (reference gas outlet 45) at a higher pressure.

  As described above, according to the present embodiment, the reference gas supply port 41 that supplies the reference gas to the reference gas supply unit 41 having the plate-like vibrator 53 that vibrates in accordance with the electrical signal (alternating current or alternating voltage) is used. 2 is directly connected to the sensor unit, so that a space for installing a pump, a cylinder, piping and the like for supplying the reference gas to the outside of the sensor unit is not required, and the reference gas supply amount of the plate-like vibrator 53 is reduced. Since it can be controlled by the frequency, the supply amount of the reference gas can be controlled with high accuracy by controlling the alternating current or the alternating voltage that vibrates the plate-like vibrator 53.

  The third opening 62a of the reference gas supply unit 41 may be directly exposed to the outside, but dust such as dust may be sucked into the reference gas supply unit 41. Therefore, in the present embodiment, as shown in FIG. 1, the reference wall gas supply unit 41 is provided on the inner wall 43a of the casing 43, and the outside air introduction opening (intake port) 43c is provided on the outer wall 43b, and the outside air introduction opening 43c. A filter 44 is provided.

  Since dust such as dust contained in the outside air taken in as the reference gas can be removed by the filter 44, it is possible to prevent deterioration of the function due to adhesion of dust to the piezoelectric element 53a and the like.

  In addition, it goes without saying that the embodiment described above can be changed without departing from the spirit of the present invention.

1 Oxygen concentration measuring device 2 Reference gas inlet (supply port)
10 Oxygen sensor section 12 Zirconia element 13 Alumina pipe (reference gas inflow pipe)
16 Internal electrode 17 External electrode 41 Reference gas supply part 43c Open air introduction opening (intake)
44 Filter 53 Vibrator 53a Piezoelectric Element 53b Diaphragm

Claims (4)

An external electrode is connected on the side in contact with the measurement gas to be measured, and an internal electrode is connected on the side in contact with the reference gas, and is generated according to the difference between the oxygen concentration of the measurement gas and the oxygen concentration of the reference gas. In an oxygen concentration measurement device that has a zirconia element that generates electric power and measures the oxygen concentration according to the magnitude of the generated electromotive force,
A reference gas supply unit having a vibrator that vibrates in response to an electrical signal,
The reference gas supply unit is connected to a supply port for supplying the reference gas to the inside of the apparatus, and supplies the reference gas by vibration according to an electric signal of the vibrator.   The oxygen concentration measuring apparatus according to claim 1, wherein the reference gas supply unit uses a piezoelectric element as the vibrator.   The oxygen concentration measuring apparatus according to claim 2, wherein the piezoelectric element is disposed orthogonal to a direction in which the reference gas is supplied, and vibrates along the direction in which the reference gas is supplied.   The oxygen concentration measuring device according to any one of claims 1 to 3, wherein a filter is provided in an opening for taking in the reference gas.

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