JP5060429B2 - Oxygen concentration measuring unit and oxygen concentration measuring method - Google Patents

Description

  The present invention relates to an oxygen concentration measurement unit and an oxygen concentration measurement method.

  Conventionally, a limit current type oxygen sensor in which a limit current flows between a cathode layer and an anode layer in accordance with the oxygen concentration in an inert gas has been proposed (see, for example, Patent Document 1). This limiting current type oxygen sensor sandwiches a solid electrolyte layer between a cathode layer and an anode layer, and on the opposite side of the cathode layer to the side in contact with the solid electrolyte layer, a porous gas diffusion rate-controlling device that functions as a rate-limiting material for oxygen gas. It is the structure which provided the use diffusion layer.

  In such a limiting current type oxygen sensor, oxygen gas is supplied to the cathode layer through the diffusion layer for gas diffusion control. A predetermined voltage is applied between the cathode layer and the anode layer, and the oxygen gas supplied to the cathode layer receives electrons and is ionized. The oxygen ions move in the solid electrolyte layer toward the anode layer, emit electrons in the anode layer, and become oxygen gas again.

As described above, a current flows between the cathode layer and the anode layer using oxygen ions as carriers. This current is saturated at a certain value according to the oxygen concentration. This current value at the time of saturation is called a limit current. The oxygen concentration measurement unit can measure the oxygen concentration by detecting the limit current of the limit current type oxygen sensor.
JP 2004-93273 A

  However, the value of the limit current of the limit current type oxygen sensor is affected by the gas type of the inert gas serving as the balance gas. For example, when the balance gas is nitrogen and when helium or argon is used, the value of the limit current obtained is different even at the same oxygen concentration. Therefore, when it is attempted to measure the oxygen concentration based on the limit current value, there is a possibility that the oxygen concentration cannot be measured accurately depending on the type of the balance gas. This problem is not limited to the limiting current type oxygen sensor using the diffusion layer for gas diffusion control, but is a problem common to the limiting current type oxygen sensor using the pinhole.

  The present invention has been made to solve such conventional problems, and an object of the present invention is to provide an oxygen concentration measurement unit and an oxygen concentration measurement method capable of improving the measurement accuracy of the oxygen concentration. There is to do.

  The oxygen concentration measuring unit of the present invention includes a limiting current type oxygen sensor in which a limiting current flows between a cathode layer and an anode layer in accordance with the oxygen concentration in an inert gas, and a current detection means for detecting the value of the limiting current. A setting means for setting the gas type of the inert gas, a correction means for correcting the current value detected by the current detection means in accordance with the gas type set by the setting means, and a current value corrected by the correction means And oxygen concentration calculating means for calculating the oxygen concentration based on the above.

  The oxygen concentration measurement unit of the present invention further includes a storage unit that stores a correction coefficient corresponding to the gas type of the inert gas, and the correction unit stores the current value detected by the current detection unit in the storage unit. The correction is preferably performed by multiplying the corrected correction coefficient.

  Further, the oxygen concentration measurement method of the present invention is a method for measuring oxygen concentration of an oxygen concentration measurement unit including a limiting current type oxygen sensor in which a limiting current flows between a cathode layer and an anode layer according to the oxygen concentration in an inert gas. A current detection step for detecting a limit current value; a setting step for setting a gas type of an inert gas; and a current detected in the current detection step according to the gas type set in the setting step. A correction step of correcting the value; and an oxygen concentration calculation step of calculating an oxygen concentration based on the current value corrected in the correction step.

  In the oxygen concentration measurement method of the present invention, it is preferable that the correction step performs correction by multiplying the current value detected in the current detection step by a correction coefficient stored in advance.

  According to the present invention, the detected limit current value is corrected according to the gas type of the inert gas, and the oxygen concentration is calculated based on the corrected current value. For this reason, even if the limit current value varies depending on the gas type of the inert gas, the limit current value is corrected according to the specified gas type of the inert gas, and the oxygen concentration is reduced. Accordingly, information on the value of the limit current is obtained. Therefore, the measurement accuracy of the oxygen concentration can be improved.

  In addition, since the correction is performed by multiplying the detected limit current value by the correction coefficient, the measurement accuracy of the oxygen concentration can be improved by a simple calculation.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an oxygen concentration measurement unit according to an embodiment of the present invention. The oxygen concentration measurement unit 1 shown in the figure includes a limiting current type oxygen sensor 10, a heating unit 20, and an oxygen concentration measurement unit 30.

  The limiting current type oxygen sensor 10 has a limiting current that flows in accordance with the oxygen concentration in the balance gas made of an inert gas. The limiting current type oxygen sensor 10 is used for the cathode layer 11, the anode layer 12, the solid electrolyte layer 13, and the gas diffusion rate limiting. A diffusion layer 14 is provided. The cathode layer 11 and the anode layer 12 are porous electrodes made of platinum or the like. The solid electrolyte layer 13 is a member such as stabilized zirconia disposed between the cathode layer 11 and the anode layer 12 and has oxygen ion conductivity. The diffusion layer for gas diffusion control 14 is a porous substrate such as alumina that functions as an oxygen gas control material for supplying diffusion-controlled oxygen gas to the cathode layer 11.

  In this limiting current type oxygen sensor 10, oxygen gas reaches the cathode layer 11 through the rate-determining diffusion layer 14 for gas diffusion, and receives and ionizes electrons in the cathode layer 11. Then, oxygen ions reach the anode layer 12 through the solid electrolyte layer 13, emit electrons in the anode layer 12, and become oxygen gas again. Thus, the limiting current type oxygen sensor 10 has a structure in which a limiting current flows between the cathode layer 11 and the anode layer 12 using oxygen ions as carriers.

  The heating unit 20 heats the solid electrolyte layer 13 of the limiting current oxygen sensor 10 to increase the ionic conductivity, and includes a heater resistor 21, a power source 22, and a constant resistance circuit 23. The heater resistor 21 is a resistor provided on the surface opposite to the surface on which the cathode layer 11 is provided in the gas diffusion rate limiting diffusion layer 14, and heats the limiting current type oxygen sensor 10. The power source 22 applies a voltage to the heater resistor 21. The constant resistance circuit 23 functions to keep the temperature of the limiting current oxygen sensor 10 heated by the heater resistor 21 substantially constant.

  Here, the operation of the constant resistance circuit 23 will be described. First, it is assumed that the temperature of the heater resistor 21 changes due to the influence of wind or the like. As a result, the resistance value of the heater resistor 21 changes. In response to this change, the constant resistance circuit 23 operates to change the voltage applied to the heater resistor 21 to keep the temperature of the limiting current oxygen sensor 10 substantially constant. As described above, the constant resistance circuit 23 changes the voltage applied to the heater resistor 21 to keep the temperature of the limit current oxygen sensor 10 constant when the temperature of the limit current oxygen sensor 10 is about to change. .

  The oxygen concentration measurement unit 30 measures the limit current value to calculate the oxygen concentration, and includes a power source 31, a calculation unit 32, and an operation unit (setting means) 33. The power supply 31 applies a voltage to the cathode layer 11 and the anode layer 12. The calculation unit 32 includes a current detection unit (current detection unit) 32a, a correction unit (correction unit) 32b, a concentration calculation unit (oxygen concentration calculation unit) 32c, and a storage unit (storage unit) 32d. . The current detector 32 a detects the value of the limit current flowing through the cathode layer 11 and the anode layer 12.

The operation unit 33 receives a setting operation for setting the gas type of the balance gas from the user. The correction unit 32 b corrects the value of the limit current detected by the current detection unit 32 a according to the gas type set via the operation unit 33. Here, the value of the limit current has a characteristic that varies depending on the gas type of the balance gas. Specifically, the value I of the limit current can be expressed by the formula (1).
I = 4F · D _{(O2-B) kn} · Sc / L · C _O2 (1)
Note that F is a Faraday constant, and D _{(O2-B) kn} is a diffusion coefficient of oxygen under a balance gas. Sc is the area of the anode layer 12, L is the thickness of the gas diffusion rate-limiting diffusion layer 14, and CO ₂ is the oxygen partial pressure.

Further, D _{(O2-B) kn} can be represented by the formula (2).
D _{(O2-B) kn} = _DO2kn (1-C _B · D _Bkn ) (2)
_{Here, D O2kn} is the diffusion coefficient of oxygen, _{C B} is the partial pressure of the balance _{gas, D Bkn} is the diffusion coefficient of the balance gas.

As is clear from the equations (1) and (2), the oxygen diffusion coefficient (D _{(O2-B) kn} ) under the balance gas is a value that varies depending on the gas type of the balance gas. Therefore, it can be said that the value I of the limit current has a characteristic that varies depending on the type of the balance gas. The correction unit 32b corrects the value of the limit current detected by the current detection unit 32a based on such characteristics.

More specifically correcting unit 32b, based on the correction formula relative to the case where the balance gas is nitrogen (3), to correct the value I _B of the detected limit current by the current detecting section 32a into a current value I _Bco .
I _Bco = α · I _B (3)
Here, α is a correction coefficient corresponding to the gas type of the balance gas. Since the formula (3) is based on the case where the balance gas is nitrogen, the value of α is “1” when the balance gas is nitrogen.

The value of α can be expressed by I _N2ca / I _Bca . Here, I _N2ca is the value of the limiting current obtained when the balance gas of the formulas (1) and (2) is nitrogen, and I _Bca is the balance gas of the formulas (1) and (2). It is the value of the limiting current obtained when an inert gas other than is used. Note that the value of _IBca is a value that varies depending on the gas type of the balance gas. For example, the value of _IBca differs depending on _whether the balance gas is argon or helium.

  The concentration calculation unit 32c calculates the oxygen concentration according to the limit current value corrected by the correction unit 32b. The storage unit 32d stores arithmetic expressions necessary for oxygen concentration calculation. In addition to the above, the storage unit 32d stores a correction coefficient α corresponding to the gas type of the balance gas for each gas type.

  As described above, the oxygen concentration measurement unit 1 according to the present embodiment corrects the limit current value according to the gas type of the balance gas, and calculates the oxygen concentration based on the corrected current value. For this reason, the measurement precision of oxygen concentration can be improved.

  Next, an oxygen concentration measurement method according to this embodiment will be described. FIG. 2 is a flowchart showing an oxygen concentration measurement method according to this embodiment. First, the user applies a predetermined voltage to the heater resistor 21 of the heating unit 20 to heat the solid electrolyte layer 13 to a predetermined temperature, and applies a predetermined voltage to the cathode layer 11 and the anode layer 12.

  Then, the flowchart shown in FIG. 2 is executed. First, the calculation unit 32 determines whether or not the balance gas type is set through the operation unit 33 (S1). When it is determined that the gas type is not set (S1: NO), this process is repeated until it is determined that the gas type is set.

  On the other hand, when it is determined that the gas type is set (S1: YES), the current detection unit 32a detects the value of the limit current (S2). Thereafter, the correction unit 32b reads a correction coefficient corresponding to the set gas type from the storage unit 32c (S3). Then, the correction unit 32b corrects the current value detected in step S2 by multiplying it by the correction coefficient read in step S3 (S4).

  Next, the concentration calculation unit 32c calculates the oxygen concentration based on the current value corrected in step S4 (S5). Thereafter, the process shown in FIG. 2 ends. The process shown in FIG. 2 is repeatedly executed until the power of the oxygen concentration measurement unit 1 is turned off.

  FIG. 3 is a graph showing a correction result by the oxygen concentration measurement unit 1 according to the present embodiment. In FIG. 3, the horizontal axis indicates the oxygen concentration, and the vertical axis indicates the limiting current.

  For example, when the oxygen concentration is 20% and the balance gas is nitrogen, the measured value of the limit current indicates about “90” (arbitrary unit). On the other hand, when the balance gas is helium, the measured value of the limit current shows about “70” (arbitrary unit), and when the balance gas is argon, the measured value of the limit current is about “95” (arbitrary unit). ). Thus, even with the same oxygen concentration, the limit current value is different for each of the balance gases nitrogen, helium and argon. Therefore, even if the oxygen concentration is accurately calculated as 20% when the balance gas is nitrogen, the oxygen concentration is not calculated as 20% when the balance gas is helium or argon.

  However, in the present embodiment, the correction coefficient for each balance gas is stored in the storage unit 32d, and correction is performed by the correction unit 32b. Therefore, when the oxygen concentration is 20%, the limit current is corrected to about “70” regardless of whether the balance gas is helium or argon. Thereby, even if the balance gas is helium or argon, the oxygen concentration is calculated to be 20%. Therefore, in this embodiment, the measurement accuracy of the oxygen concentration is improved regardless of the gas type of the balance gas.

  In the present embodiment, the measurement accuracy is improved not only when the oxygen concentration is 20%, but also with other oxygen concentrations. For example, when the oxygen concentration is 10% and the balance gas is nitrogen, the measured value of the limit current indicates about “45” (arbitrary unit). On the other hand, when the balance gas is helium, the measured value of the limit current shows about “35” (arbitrary unit), and when the balance gas is argon, the measured value of the limit current is about “47” (arbitrary unit). ). However, in this embodiment, the limit current is corrected to about “45” regardless of whether the balance gas is helium or argon. Thereby, the measurement accuracy of the oxygen concentration is improved.

  Thus, according to the oxygen concentration measurement unit 1 and the oxygen concentration measurement method according to the present embodiment, the detected limit current value is corrected according to the gas type of the inert gas, and the corrected current value is corrected. Based on this, the oxygen concentration is calculated. For this reason, even if the limit current value varies depending on the gas type of the inert gas, the limit current value is corrected according to the specified gas type of the inert gas, and the oxygen concentration is reduced. Accordingly, information on the value of the limit current is obtained. Therefore, the measurement accuracy of the oxygen concentration can be improved.

  In addition, since the correction is performed by multiplying the detected limit current value by the correction coefficient, the measurement accuracy of the oxygen concentration can be improved by a simple calculation.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention. For example, in the present embodiment, the limiting current type oxygen sensor 10 having the gas diffusion rate limiting diffusion layer 14 has been described as an example. However, the present invention is not limited to this, and the limiting current type oxygen sensor 10 is a type using a pinhole. May be.

  In the present embodiment, the storage unit 32d may store only one correction coefficient for each balance gas, or may store a plurality of correction coefficients for each balance gas. Here, when a plurality of correction coefficients are stored, there are the following advantages. As shown in FIG. 3, in the region where the oxygen concentration is 50% or less, the difference between the actually measured value and the correction value decreases as the oxygen concentration increases, whereas in the region where the oxygen concentration exceeds 50%, the oxygen concentration As the value increases, the difference between the actual measurement value and the correction value decreases. For this reason, if there is only one correction coefficient, accurate correction cannot be performed. However, by storing a plurality of correction coefficients, accurate correction can be performed from the low concentration region to the high concentration region, and the measurement accuracy of the oxygen concentration can be improved. When a plurality of correction coefficients are stored, the correction unit 32b reads one correction coefficient suitable for correction from the storage unit 32d based on the limit current value detected by the current detection unit 32a. Will be corrected.

  In addition, in the case of having only one correction coefficient, there are the following advantages. In general, the limiting current type oxygen sensor is often used for detecting an oxygen concentration at a low concentration (for example, 1000 ppm). For this reason, it is not necessary to detect the oxygen concentration from a low concentration to a high concentration, and in the case of detecting the oxygen concentration in a limited concentration region, even if a plurality of correction coefficients are not stored. The accuracy of measuring the oxygen concentration can be improved. Therefore, by storing only one correction coefficient, it is possible to improve the measurement accuracy of the oxygen concentration while reducing the storage amount of the storage unit 32d and simplifying the program.

It is a block diagram which shows the oxygen concentration measurement unit which concerns on embodiment of this invention. It is a flowchart which shows the oxygen concentration measuring method which concerns on this embodiment. It is a graph which shows the correction result by the oxygen concentration measurement unit which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Oxygen concentration measurement unit 10 ... Limit current type oxygen sensor 11 ... Cathode layer 12 ... Anode layer 13 ... Solid electrolyte layer 14 ... Gas diffusion rate-controlling diffusion layer 20 ... Heating part 21 ... Heater resistance 22 ... Power source 23 ... Constant resistance circuit 30 ... Oxygen concentration measurement unit 31 ... Power source 32 ... Calculation unit 32a ... Current detection unit (current detection means)
32b ... Correction unit (correction means)
32c ... Concentration calculation unit (oxygen concentration calculation means)
32d ... Storage section (storage means)
33 ... operation unit (setting means)

Claims (4)

A limiting current type oxygen sensor in which a limiting current flows between the cathode layer and the anode layer according to the oxygen concentration in the inert gas;
Current detection means for detecting the value of the limiting current;
Setting means for setting the gas type of the inert gas;
Correction means for correcting the current value detected by the current detection means in accordance with the gas type set by the setting means;
Oxygen concentration calculating means for calculating an oxygen concentration based on the current value corrected by the correcting means;
An oxygen concentration measurement unit comprising: A storage means for storing a correction coefficient corresponding to the gas type of the inert gas;
2. The oxygen concentration measurement unit according to claim 1, wherein the correction unit corrects the current value detected by the current detection unit by multiplying by a correction coefficient stored in the storage unit. An oxygen concentration measuring method of an oxygen concentration measuring unit including a limiting current type oxygen sensor in which a limiting current flows between a cathode layer and an anode layer according to the oxygen concentration in an inert gas,
A current detection step of detecting a value of the limiting current;
A setting step for setting a gas type of the inert gas;
A correction step of correcting the current value detected in the current detection step according to the gas type set in the setting step;
An oxygen concentration calculation step of calculating an oxygen concentration based on the current value corrected in the correction step;
A method for measuring oxygen concentration, comprising: The oxygen concentration measurement method according to claim 3, wherein the correction step performs correction by multiplying the current value detected in the current detection step by a correction coefficient stored in advance.

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