JP5362687B2 - Oxygen partial pressure detection method - Google Patents
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Abstract
Description
本発明は、固体電解質を用いて酸素分圧を検知する酸素分圧検知方法に関する。 The present invention relates to an oxygen partial pressure detection method for detecting an oxygen partial pressure using a solid electrolyte.
固体電解質を含む電気化学的な酸素ポンプ及び酸素センサを有する酸素分圧制御装置により、酸素分圧を制御した雰囲気ガスを用いて、単結晶試料等を作成する方法が知られている（例えば、特許文献１，２）。 A method for producing a single crystal sample or the like using an atmospheric gas whose oxygen partial pressure is controlled by an oxygen partial pressure control apparatus having an electrochemical oxygen pump and an oxygen sensor containing a solid electrolyte is known (for example, Patent Documents 1 and 2).
特許文献２に示された図４の酸素分圧制御装置は、バルブ１０２を通った不活性ガスの流量を設定値に制御するマスフローコントローラ（ＭＦＣ）１０３と、このマスフローコントローラ１０３を通った不活性ガスを目的の酸素分圧に制御可能な電気化学的な酸素ポンプ１０４と、酸素ポンプ１０４で制御された不活性ガスの酸素分圧を検出して試料育成装置などの次工程（装置）に供給する供給ガス用の酸素センサ１０５を有する。 The oxygen partial pressure control device of FIG. 4 shown in Patent Document 2 includes a mass flow controller (MFC) 103 that controls the flow rate of the inert gas that has passed through the valve 102 to a set value, and an inert gas that has passed through the mass flow controller 103. Electrochemical oxygen pump 104 capable of controlling the gas to the target oxygen partial pressure, and detecting the oxygen partial pressure of the inert gas controlled by the oxygen pump 104 and supplying it to the next process (device) such as a sample growing apparatus And an oxygen sensor 105 for supply gas.
さらにこの装置は、所望の酸素分圧値を設定する酸素分圧設定部１０６と、酸素センサ１０５による検出値を酸素分圧設定部１０６による設定値と比較して酸素ポンプ１０４から送り出される不活性ガスの酸素分圧を所定値に制御する制御部１０７と、酸素センサ１０５による検出値を表示する酸素分圧表示部１０８を備える。 Further, this apparatus includes an oxygen partial pressure setting unit 106 that sets a desired oxygen partial pressure value, and an inertness that is sent from the oxygen pump 104 by comparing the detected value by the oxygen sensor 105 with the set value by the oxygen partial pressure setting unit 106. A control unit 107 that controls the oxygen partial pressure of the gas to a predetermined value and an oxygen partial pressure display unit 108 that displays a value detected by the oxygen sensor 105 are provided.
酸素センサ１０５は、図５に示すように、酸素イオン伝導性を有する筒状の固体電解質１０５ａの内外両面に電極１０５ｂ、１０５ｃを形成している。固体電解質１０５ａは、例えばジルコニア系の固体電解質であり、図示しないヒーターで加熱される。筒状固体電解質１０５ａには、その内面側及び外面側の一方に既知の酸素分圧を有する基準ガス、他方に未知の酸素分圧を有する検知対象ガスが供給される。固体電解質の内外に異なる酸素分圧が存在することにより、濃淡電池が形成され、酸素イオンの移動に伴って電極１０５ｂ、１０５ｃ間に、次のネルンストの式（式１）で表される起電力が発生する。
Ｅ＝（ＲＴ／４Ｆ）ｌｎ（Ｐｏ2'／Ｐｏ2''） （式１）
ここで、各記号は以下のものを示す。
Ｅ：起電力
Ｆ：ファラデー定数
Ｒ：気体常数
Ｔ：絶対温度
Ｐｏ2'：標準極側の酸素分圧
Ｐｏ2''：測定極側の酸素分圧
上記式１は、イオン輸率が１であることを前提としている。したがって、実際の起電力は、式１の「Ｅ」にイオン輸率を乗じた値となる。
As shown in FIG. 5, the oxygen sensor 105 has electrodes 105b and 105c formed on both inner and outer surfaces of a cylindrical solid electrolyte 105a having oxygen ion conductivity. The solid electrolyte 105a is, for example, a zirconia-based solid electrolyte and is heated by a heater (not shown). The cylindrical solid electrolyte 105a is supplied with a reference gas having a known oxygen partial pressure on one of the inner surface side and the outer surface side, and a detection target gas having an unknown oxygen partial pressure on the other side. Due to the presence of different oxygen partial pressures inside and outside the solid electrolyte, a concentration cell is formed, and the electromotive force expressed by the following Nernst equation (Equation 1) between the electrodes 105b and 105c as the oxygen ions move. Will occur.
E = (RT / 4F) ln (Po 2 '/ Po 2 ″) (Formula 1)
Here, each symbol indicates the following.
E: Electromotive force F: Faraday constant R: Gas constant T: Absolute temperature Po 2 ′: Oxygen partial pressure Po 2 ″ on the standard electrode side Oxygen partial pressure on the measurement electrode side It is assumed that there is. Therefore, the actual electromotive force is a value obtained by multiplying “E” in Equation 1 by the ion transport number.
この起電力Ｅは、検知対象ガスの酸素分圧Ｐｏ2''に対応したものとなる。したがって、起電力Ｅを測定することにより、検知対象ガスの酸素分圧を検知することができる。固体電解質を用いたこの種の酸素センサは、例えば特許文献１〜３に記載されている。 This electromotive force E corresponds to the oxygen partial pressure Po 2 ″ of the detection target gas. Therefore, by measuring the electromotive force E, the oxygen partial pressure of the detection target gas can be detected. This type of oxygen sensor using a solid electrolyte is described in Patent Documents 1 to 3, for example.
なお、酸素ポンプ１０４も筒状の固体電解質の内外両面に電極を形成している点で同様の構造を有するが、酸素ポンプ１０４においては、筒状の固体電解質内に供給される精製対象ガスから酸素を固体電解質外へ排出するために、固体電解質の内外電極間に電圧が印加される。 The oxygen pump 104 also has a similar structure in that electrodes are formed on both the inside and outside of the cylindrical solid electrolyte. However, the oxygen pump 104 uses a purification target gas supplied into the cylindrical solid electrolyte. In order to discharge oxygen out of the solid electrolyte, a voltage is applied between the inner and outer electrodes of the solid electrolyte.
図６は、酸素センサに用いられる固体電解質の温度及びガスの酸素分圧によって特定されるイオン輸率を示す図である。固体電解質には、例えば図６のグラフに示すように、イオン輸率≧０．９９と定義される電解伝導領域がある。酸素センサをこの領域内で作動させれば、高いイオン輸率に基づき効率的な起電力の発生（センサ出力）が得られるが、この領域外の作動ではイオン輸率が小さく、これに伴って実際の起電力（式１の起電力Ｅにイオン輸率を乗じた値）が低くなり、正確なセンサ出力が得られ難かった。 FIG. 6 is a diagram showing the ion transport number specified by the temperature of the solid electrolyte used in the oxygen sensor and the oxygen partial pressure of the gas. For example, as shown in the graph of FIG. 6, the solid electrolyte has an electrolytic conduction region defined as an ion transport number ≧ 0.99. If the oxygen sensor is operated in this region, efficient electromotive force generation (sensor output) can be obtained based on a high ion transport number. However, if the oxygen sensor is operated outside this region, the ion transport number is small. The actual electromotive force (the value obtained by multiplying the electromotive force E of Equation 1 by the ion transport number) was low, and it was difficult to obtain an accurate sensor output.
従来は、酸素センサに単一種の固体電解質を用いていたため、電解伝導領域がその固体電解質固有の範囲に限られていた。その結果、正確なセンサ出力が得られる酸素分圧の上下限が、用いる固体電解質の電解伝導領域により制限されていた。 Conventionally, since a single type of solid electrolyte is used for the oxygen sensor, the electrolytic conduction region is limited to a range unique to the solid electrolyte. As a result, the upper and lower limits of the oxygen partial pressure at which accurate sensor output can be obtained are limited by the electrolytic conduction region of the solid electrolyte used.
そこで、本発明は、このような従来技術の問題点を解決し、広い酸素分圧範囲で正確なセンサ出力を得ることができる酸素分圧検知方法を提供することを目的とする。 Accordingly, an object of the present invention is to solve such problems of the prior art and provide an oxygen partial pressure detection method capable of obtaining an accurate sensor output in a wide oxygen partial pressure range.
本発明は、前記目的を達成するため、固体電解質を用いた酸素センサによりガス中の酸素分圧を検知するための酸素分圧検知方法であって、固体電解質の酸素イオン輸率が１に近い温度−酸素分圧域である電解伝導領域が異なる複数種の酸素センサを構成し、検知対象ガスの酸素分圧が高いときは、酸素分圧域の高い電解伝導領域を有する酸素センサの出力を採用し、検知対象ガスの酸素分圧が低いときは、酸素分圧域の低い電解伝導領域を有する酸素センサの出力を採用することを特徴とする酸素分圧検知方法を提供するものである。 In order to achieve the above object, the present invention provides an oxygen partial pressure detection method for detecting an oxygen partial pressure in a gas by an oxygen sensor using a solid electrolyte, wherein the oxygen ion transport number of the solid electrolyte is close to 1. When multiple oxygen sensors with different electrolytic conduction regions in the temperature-oxygen partial pressure region are configured and the oxygen partial pressure of the detection target gas is high, the output of the oxygen sensor having an electrolytic conduction region with a high oxygen partial pressure region is output. When the oxygen partial pressure of the gas to be detected is low, an oxygen partial pressure detection method is provided that employs the output of an oxygen sensor having an electrolytic conduction region with a low oxygen partial pressure region.
上記検知方法においては、電解伝導領域が異なる複数種の酸素センサを構成し、検知対象ガスの酸素分圧が高いときは、電解伝導領域の酸素分圧域が高い酸素センサの出力を採用し、検知対象ガスの酸素分圧が低いときは、電解伝導領域の酸素分圧域が低い酸素センサの出力を採用する。また、正確なセンサ出力を確実に得るには、検知対象ガスの酸素分圧を、電解伝導領域の酸素分圧域に含む酸素センサを用いるのが望ましい。本発明では、これらの観点から、検知対象ガスの酸素分圧が高いときは、電解伝導領域の酸素分圧域が高い酸素センサの出力を採用し、検知対象ガスの酸素分圧が低いときは、電解伝導領域の酸素分圧域が低い酸素センサの出力を採用する。こうして出力を採用される酸素センサは、図３と共に後述するように、電解伝導領域内での作動に基づき、検知対象ガスの酸素分圧（対数）に対して直線性に優れた起電力を発生し、正確なセンサ出力の発生を可能とする。上記した電解伝導領域の酸素分圧域が高い酸素センサの作動は、検知対象ガスの酸素分圧低下と共に、電解伝導領域の下限を下回ると、センサ出力の上記直線性が低下する。これに対し、検知対象ガスの酸素分圧が低くなったときに、電解伝導領域の酸素分圧域が低い酸素センサの出力を採用することにより、その酸素センサを電解伝導領域内で作動させることができ、この段階においても酸素センサは、検知対象ガスの酸素分圧との対応が直線性に優れた起電力を発生し、正確なセンサ出力の発生を可能とする。このようにして、本発明によれば、酸素分圧が高いときにも低いときにも、正確なセンサ出力を得ることができる。 In the above detection method, a plurality of types of oxygen sensors with different electrolytic conduction regions are configured, and when the oxygen partial pressure of the detection target gas is high, the output of the oxygen sensor having a high oxygen partial pressure region of the electrolytic conduction region is adopted, When the oxygen partial pressure of the gas to be detected is low, the output of the oxygen sensor having a low oxygen partial pressure region in the electrolytic conduction region is employed. In order to reliably obtain an accurate sensor output, it is desirable to use an oxygen sensor that includes the oxygen partial pressure of the detection target gas in the oxygen partial pressure region of the electrolytic conduction region. In the present invention, from these viewpoints, when the oxygen partial pressure of the detection target gas is high, the output of the oxygen sensor having a high oxygen partial pressure region of the electrolytic conduction region is adopted, and when the oxygen partial pressure of the detection target gas is low The output of the oxygen sensor having a low oxygen partial pressure region in the electrolytic conduction region is employed. As described later with reference to FIG. 3, the oxygen sensor that employs the output generates an electromotive force that is excellent in linearity with respect to the oxygen partial pressure (logarithm) of the gas to be detected based on the operation in the electrolytic conduction region. Thus, accurate sensor output can be generated. When the operation of the oxygen sensor having a high oxygen partial pressure region in the electrolytic conduction region described above falls below the lower limit of the electrolytic conduction region as the oxygen partial pressure of the detection target gas decreases, the linearity of the sensor output decreases. On the other hand, when the oxygen partial pressure of the gas to be detected becomes low, the oxygen sensor is operated in the electrolytic conduction region by adopting the output of the oxygen sensor having a low oxygen partial pressure region in the electrolytic conduction region. Even at this stage, the oxygen sensor generates an electromotive force having excellent linearity in correspondence with the oxygen partial pressure of the detection target gas, and enables accurate sensor output. Thus, according to the present invention, accurate sensor output can be obtained both when the oxygen partial pressure is high and when it is low.
以上のように、本発明に係る酸素分圧検知方法によれば、広い酸素分圧範囲で正確なセンサ出力を得ることができる。 As described above, according to the oxygen partial pressure detection method of the present invention, an accurate sensor output can be obtained in a wide oxygen partial pressure range.
以下、本発明の実施形態について添付図面を参照しつつ説明する。図１は、本発明の一実施形態に係る酸素分圧検知方法を実施するための装置を示すブロック図である。この酸素分圧検知装置１は、検知対象ガスの酸素分圧を検知する検知部１０と、ガスの流路４とを備えている。流路４は、検知部１０の上流側に接続された第一流路４１と、検知部１０の下流側に接続された第二流路４２とを備えている。第一流路４１には、制御弁１１、レギュレータ（ＲＥＧ）１２及びマスフローコントローラ（ＭＦＣ）１３が設けられている。 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an apparatus for carrying out an oxygen partial pressure detection method according to an embodiment of the present invention. The oxygen partial pressure detection device 1 includes a detection unit 10 that detects an oxygen partial pressure of a detection target gas, and a gas flow path 4. The flow path 4 includes a first flow path 41 connected to the upstream side of the detection unit 10 and a second flow path 42 connected to the downstream side of the detection unit 10. In the first flow path 41, a control valve 11, a regulator (REG) 12, and a mass flow controller (MFC) 13 are provided.
流路４の始端４１０は、装置外のガス供給源に接続されるようになっており、該供給源から検知対象ガスが供給される。 The starting end 410 of the flow path 4 is connected to a gas supply source outside the apparatus, and the detection target gas is supplied from the supply source.
制御弁１１は検知対象ガス流の供給及び遮断を制御し、レギュレータ１２は、一流路４１の圧力を一定に保持し、マスフローコントローラ１３は検知対象ガスの流量を設定値に制御する。 The control valve 11 controls the supply and shutoff of the detection target gas flow, the regulator 12 keeps the pressure of the one flow path 41 constant, and the mass flow controller 13 controls the flow rate of the detection target gas to a set value.
この酸素分圧検知装置１は、２個の酸素センサ２１ａ，２１ｂを備えている。各酸素センサは、図５に示したのと同様に固体電解質、起電力測定機構等を備えて構成され、各々筒状の固体電解質２１１ａ，２１１ｂの内外面に白金等の電極層が設けられている。検知部１０はさらに、酸素センサ２１ａ，２１ｂを収容する検知室２７を備えている。検知室２７内の第一流路４１は、酸素センサ２１ａ，２１ｂに接続されている。 The oxygen partial pressure detection device 1 includes two oxygen sensors 21a and 21b. Each oxygen sensor is configured to include a solid electrolyte, an electromotive force measuring mechanism, and the like, as shown in FIG. 5, and electrode layers such as platinum are provided on the inner and outer surfaces of the cylindrical solid electrolytes 211a and 211b, respectively. Yes. The detection unit 10 further includes a detection chamber 27 that houses the oxygen sensors 21a and 21b. The first flow path 41 in the detection chamber 27 is connected to the oxygen sensors 21a and 21b.
検知室２７内には、加熱部２８ａ，２８ｂが設けられている。これらの加熱部は、各々酸素センサ２１ａ，２１ｂに対して作用し、固体電解質２１１ａ，２１１ｂを各々温度制御下に加熱するように構成されている。この加熱部は、例えば、固体電解質２１１の外周にシースヒータを装着し、その外側を断熱材で覆ったもの等とすることができる。加熱部の温度制御は、酸素センサに接続された制御部２３により行われる。制御部２３は、設定部２４に接続されており、該設定部により設定された条件等に応じて加熱部２８ａ，２８ｂの温度等を制御する。 In the detection chamber 27, heating units 28a and 28b are provided. These heating units act on the oxygen sensors 21a and 21b, respectively, and are configured to heat the solid electrolytes 211a and 211b under temperature control. The heating unit can be, for example, one in which a sheath heater is attached to the outer periphery of the solid electrolyte 211 and the outside is covered with a heat insulating material. The temperature control of the heating unit is performed by the control unit 23 connected to the oxygen sensor. The control unit 23 is connected to the setting unit 24, and controls the temperature and the like of the heating units 28a and 28b according to the conditions set by the setting unit.
酸素センサ２１ａ，２１ｂには、測定部２６が接続されている。測定部２６は、各酸素センサの固体電解質２１１ａ，２１１ｂの内外電極間の起電力を測定する機能を備えており、酸素分圧表示部２５に接続されている。酸素分圧表示部２５は、測定部２６が出力する測定値に基づいて、該測定値に対応する酸素分圧を表示する。 A measuring unit 26 is connected to the oxygen sensors 21a and 21b. The measuring unit 26 has a function of measuring an electromotive force between the inner and outer electrodes of the solid electrolytes 211 a and 211 b of each oxygen sensor, and is connected to the oxygen partial pressure display unit 25. The oxygen partial pressure display unit 25 displays the oxygen partial pressure corresponding to the measurement value based on the measurement value output from the measurement unit 26.
図１に示した酸素分圧検知装置１は、次のようにして使用される。設定部２４及び制御部２３による設定及び制御により酸素センサ２１ａ，２１ｂは、加熱部２８ａ，２８ｂにより所定温度に加熱される。この実施形態では、固体電解質２１１ａ，２１１ｂに対し、酸素分圧が既知の大気、不活性ガス等のガスが外面側に供給され、内面側に検知対象ガスが第一流路４１を通じて供給される。固体電解質２１１ａ，２１１ｂを経た検知対象ガスは、第二流路４２を通じて装置外へ排出される。 The oxygen partial pressure detecting device 1 shown in FIG. 1 is used as follows. The oxygen sensors 21a and 21b are heated to a predetermined temperature by the heating units 28a and 28b by setting and control by the setting unit 24 and the control unit 23. In this embodiment, a gas such as an atmosphere or an inert gas having a known oxygen partial pressure is supplied to the outer surface side of the solid electrolytes 211a and 211b, and a detection target gas is supplied to the inner surface side through the first flow path 41. The detection target gas that has passed through the solid electrolytes 211a and 211b is discharged out of the apparatus through the second flow path 42.
酸素センサ２１ａ，２１ｂの固体電解質２１１ａ，２１１ｂは、固体電解質の酸素イオン輸率が１に近い温度−酸素分圧域、すなわち電解伝導領域が相互に異なるものとされている。電解伝導領域は、固体電解質の材質を異なるものとすることにより相互に異なったものとすることができる。材質の異なる固体電解質は、ジルコニア、ランタンガレート、トリア等、異なる種類のものを用いる他、同じ種類であっても添加剤等の種類や量を異ならせることにより得ることができる。この実施形態では、酸素センサ２１ａの電解伝導領域の酸素分圧域が高く、酸素センサ２１ｂの電解伝導領域の酸素分圧域が低く設定されている。 The solid electrolytes 211a and 211b of the oxygen sensors 21a and 21b are different from each other in the temperature-oxygen partial pressure region where the oxygen ion transport number of the solid electrolyte is close to 1, that is, the electrolytic conduction region. Electrolytic conduction regions can be made different from each other by making the materials of the solid electrolyte different. Solid electrolytes of different materials can be obtained by using different types of materials such as zirconia, lanthanum gallate, and tria, and by using different types and amounts of additives, even if they are the same type. In this embodiment, the oxygen partial pressure region of the electrolytic conduction region of the oxygen sensor 21a is set high, and the oxygen partial pressure region of the electrolytic conduction region of the oxygen sensor 21b is set low.
この酸素分圧検知装置１は、以下のようにして使用される。酸素センサ２１ａ，２１ｂは、制御部２３により必要な制御状態の下に作動され、検知対象ガスが第一流路４１から各酸素センサ２１ａ，２１ｂに供給される。酸素センサ２１ａ，２１ｂは、検知対象ガスの酸素分圧に応じた検出値を各々出力する。前述のように、酸素センサ２１ａ，２１ｂは、電解伝導領域が相互に異なるように構成されている。この構成により、以下の作用効果が得られる。 This oxygen partial pressure detector 1 is used as follows. The oxygen sensors 21a and 21b are operated under a necessary control state by the control unit 23, and the detection target gas is supplied from the first flow path 41 to the oxygen sensors 21a and 21b. The oxygen sensors 21a and 21b each output a detection value corresponding to the oxygen partial pressure of the detection target gas. As described above, the oxygen sensors 21a and 21b are configured so that the electrolytic conduction regions are different from each other. With this configuration, the following operational effects can be obtained.
酸素センサの作動工程を、固体電解質の温度（逆数）と到達酸素分圧（対数）との関係を示すグラフ上で見れば、図２のようになる。図２は、酸素分圧域が高い電解伝導領域Ｄａ（酸素センサ２１ａ）と、酸素分圧域が低い電解伝導領域Ｄｂ（酸素センサ２１ｂ）の２つの電解伝導領域を示している。電解伝導領域は、図６にも示したように、横軸に温度の逆数、縦軸に酸素分圧の対数をとったときに、縦軸に近い側を頂点とするようにＶ字を横向きにした横Ｖ字形（またはその一部分）の境界線を有し、その境界線内の領域が電解伝導領域に相当する。電解伝導領域Ｄａは、酸素分圧の上限ラインＵａ及び下限ラインＬａで囲まれた領域であり、電解伝導領域Ｄｂは、酸素分圧の上限ラインＵｂ及び下限ラインＬｂで囲まれた領域である。電解伝導領域Ｄａにおける低酸素分圧部分と、電解伝導領域Ｄｂにおける高酸素分圧部分とは、図示のように一部を重複させている。 If the operation process of the oxygen sensor is viewed on a graph showing the relationship between the temperature (reciprocal) of the solid electrolyte and the ultimate oxygen partial pressure (logarithm), it is as shown in FIG. FIG. 2 shows two electrolytic conduction regions, an electrolytic conduction region Da (oxygen sensor 21a) having a high oxygen partial pressure region and an electrolytic conduction region Db (oxygen sensor 21b) having a low oxygen partial pressure region. As shown in FIG. 6, when the horizontal axis represents the reciprocal of temperature and the vertical axis represents the logarithm of oxygen partial pressure, the electrolytic conduction region has a V-shaped sideways so that the side close to the vertical axis is the apex. The horizontal V-shaped boundary line (or a part thereof) has a boundary line, and a region within the boundary line corresponds to an electrolytic conduction region. The electrolytic conduction region Da is a region surrounded by the oxygen partial pressure upper limit line Ua and the lower limit line La, and the electrolytic conduction region Db is a region surrounded by the oxygen partial pressure upper limit line Ub and the lower limit line Lb. The low oxygen partial pressure portion in the electrolytic conduction region Da and the high oxygen partial pressure portion in the electrolytic conduction region Db are partially overlapped as illustrated.
従来は、酸素センサに単一種の固体電解質を用いていたため、電解伝導領域がその固体電解質固有の範囲に限られていた。特に、低い酸素分圧の検知対象ガスの酸素分圧を検知する場合は、酸素分圧域が低い電解伝導領域Ｄｂを有する固体電解質を用いて検知を行う。その結果、矢印(b) で示す範囲の酸素分圧が実質的な検知の限界となっていた。また、酸素分圧が下限ラインＬｂを下回ると、固体電解質の起電力が低下し、正確な酸素分圧を得るのが困難となるという問題があった。なお、検知対象ガスの酸素分圧が高い場合は、電解伝導領域Ｄａを有する固体電解質を用いて検知を行うが、この場合も、矢印(a) で示す範囲の酸素分圧が実質的な検知限界となり、また、酸素分圧が下限ラインＬａを下回ると、固体電解質の起電力が低下し、正確な酸素分圧を得るのが困難となるという問題があった。 Conventionally, since a single type of solid electrolyte is used for the oxygen sensor, the electrolytic conduction region is limited to a range unique to the solid electrolyte. In particular, when detecting the oxygen partial pressure of the detection target gas having a low oxygen partial pressure, detection is performed using a solid electrolyte having an electrolytic conduction region Db having a low oxygen partial pressure region. As a result, the oxygen partial pressure in the range indicated by the arrow (b) was a practical limit of detection. Further, when the oxygen partial pressure is lower than the lower limit line Lb, there is a problem that the electromotive force of the solid electrolyte is lowered and it is difficult to obtain an accurate oxygen partial pressure. In addition, when the oxygen partial pressure of the gas to be detected is high, detection is performed using a solid electrolyte having the electrolytic conduction region Da. In this case as well, the oxygen partial pressure in the range indicated by the arrow (a) is substantially detected. When the oxygen partial pressure is lower than the lower limit line La, there is a problem that the electromotive force of the solid electrolyte is lowered and it is difficult to obtain an accurate oxygen partial pressure.
これに対し、酸素分圧検知装置１の測定部２６は、検知対象ガスの酸素分圧が高いときは、酸素分圧域の高い電解伝導領域Ｄａを有する酸素センサ２１ａの出力を採用し、検知対象ガスの酸素分圧が低いときは、酸素分圧域の低い電解伝導領域Ｄｂを有する酸素センサ２１ｂの出力を採用する。これにより、図２の矢印(c) で示すように、上限ラインＵａから下限ラインＬｂに至る広い範囲に亘って酸素分圧の検知を行なうことができる。また、２つの酸素センサ２１ａ，２１ｂの出力について上記選択による採用を行うので、検知対象ガスの酸素分圧が、高い電解伝導領域Ｄａの下限ラインＬａを下回り、その固体電解質２１１ａの起電力が低下しても、低い電解伝導領域Ｄｂの固体電解質２１１ｂにより高い起電力が得られる。したがって、上記選択による出力を採用することにより、高い起電力に基づく正確な酸素分圧の検知を行なうことができる。なお、図２において、矢印(a), (b), (c) を水平軸方向にずらせて表示しているのは、矢印の重なりによる不明瞭を避けるための便宜的なものであり、実質的には同じ絶対温度での作動を示すものである。また、検知範囲は、各矢印において上限ラインから下限ラインまでとして表示しているが、これらのラインの間の範囲とすることもできる。 On the other hand, when the oxygen partial pressure of the detection target gas is high, the measurement unit 26 of the oxygen partial pressure detection device 1 employs the output of the oxygen sensor 21a having the electrolytic conduction region Da having a high oxygen partial pressure region to detect the oxygen partial pressure. When the oxygen partial pressure of the target gas is low, the output of the oxygen sensor 21b having the electrolytic conduction region Db having a low oxygen partial pressure region is employed. Thereby, as shown by the arrow (c) in FIG. 2, the oxygen partial pressure can be detected over a wide range from the upper limit line Ua to the lower limit line Lb. Further, since the above selection is adopted for the outputs of the two oxygen sensors 21a and 21b, the oxygen partial pressure of the gas to be detected falls below the lower limit line La of the high electrolytic conduction region Da, and the electromotive force of the solid electrolyte 211a decreases. Even so, a high electromotive force can be obtained by the solid electrolyte 211b in the low electrolytic conduction region Db. Therefore, by adopting the output by the above selection, it is possible to accurately detect the oxygen partial pressure based on a high electromotive force. In FIG. 2, the arrows (a), (b), and (c) are shifted in the horizontal axis direction for convenience in order to avoid ambiguity due to overlapping of the arrows. In particular, it shows the operation at the same absolute temperature. Moreover, although the detection range is displayed as an upper limit line to a lower limit line in each arrow, it can also be a range between these lines.
測定部２６による上記出力の選択は、具体的には、次のようにして行なうことができる。第１の方法は、複数の酸素センサが出力する酸素分圧の内、最も低い酸素分圧を採用するという方法である。すなわち、酸素センサが２個の場合は、測定部２６は、酸素センサ２１ａ，２１ｂの出力を比較して低い酸素分圧を示す方の出力を選択する。これに関し、検知対象ガスの酸素分圧と酸素センサの起電力は、図３に示すグラフのような特性曲線を描く。図３において、酸素センサ２１ａの特性曲線を実線、酸素センサ２１ｂの特性曲線を破線で示す。特性曲線Ｓｃは、酸素センサ２１ａ及び２１ｂに基づく合成センサ特性である。グラフに示すように、酸素センサ２１ａは、特性曲線Ｓａが示すように、検知対象ガスの酸素分圧が高い場合に酸素分圧（対数）と起電力との関係において良好な直線性を示し、酸素センサ２１ｂは、特性曲線Ｓｂが示すように、検知対象ガスの酸素分圧が低い場合に酸素分圧（対数）と起電力との関係において良好な直線性を示す。特性曲線Ｓｃは、両センサの特性曲線Ｓａ，Ｓｂから抽出した直線部分を合成したものである。 Specifically, the selection of the output by the measurement unit 26 can be performed as follows. The first method is a method of adopting the lowest oxygen partial pressure among the oxygen partial pressures output from a plurality of oxygen sensors. That is, when there are two oxygen sensors, the measurement unit 26 compares the outputs of the oxygen sensors 21a and 21b and selects the output indicating the lower oxygen partial pressure. In this regard, the oxygen partial pressure of the detection target gas and the electromotive force of the oxygen sensor draw a characteristic curve such as the graph shown in FIG. In FIG. 3, the characteristic curve of the oxygen sensor 21a is indicated by a solid line, and the characteristic curve of the oxygen sensor 21b is indicated by a broken line. The characteristic curve Sc is a combined sensor characteristic based on the oxygen sensors 21a and 21b. As shown in the graph, as shown by the characteristic curve Sa, the oxygen sensor 21a exhibits good linearity in the relationship between the oxygen partial pressure (logarithm) and the electromotive force when the oxygen partial pressure of the detection target gas is high, As shown by the characteristic curve Sb, the oxygen sensor 21b exhibits good linearity in the relationship between the oxygen partial pressure (logarithm) and the electromotive force when the oxygen partial pressure of the detection target gas is low. The characteristic curve Sc is a combination of the linear portions extracted from the characteristic curves Sa and Sb of both sensors.
測定部２６は、酸素センサ２１ａ，２１ｂの出力を比較して低い酸素分圧を示す方の出力を選択する。すなわち、検知対象ガスが高い酸素分圧Pg1であるとき、酸素センサ２１ａ，２１ｂの出力を比較すると、酸素センサ２１ａは出力Ｖ１、酸素センサ２１ｂは出力Ｖ１’を出力する。各酸素センサの起電力と酸素分圧の対数値(log) とが直線的関係にあるものとして酸素分圧を推定すると、酸素センサ２１ａはｐ１、酸素センサ２１ｂはｐ１’の酸素分圧を示すことになる。なお、実際には酸素センサ２１ｂは、酸素分圧Pg1により特性曲線Ｓｂ上の点ｐ１”に基づき起電力Ｖ１’を出力しているが、検知操作を簡単にするために酸素センサ２１ｂの特性曲線を直線とみなすと（すなわち、合成センサ特性Ｓｃのようにみなすと）、起電力Ｖ１’は酸素分圧ｐ１’を示すことになる。ここで、低い方の酸素分圧を示す酸素センサ２１ａの出力を採用し、酸素分圧ｐ１を得る。こうして得られる酸素分圧ｐ１は、実際の酸素分圧Pg1 またはこれに近い値となる。 The measuring unit 26 compares the outputs of the oxygen sensors 21a and 21b and selects the output that shows the lower oxygen partial pressure. That is, when the detection target gas has a high oxygen partial pressure Pg1, when the outputs of the oxygen sensors 21a and 21b are compared, the oxygen sensor 21a outputs the output V1, and the oxygen sensor 21b outputs the output V1 '. When the oxygen partial pressure is estimated on the assumption that the electromotive force of each oxygen sensor and the logarithmic value (log) of the oxygen partial pressure are linear, the oxygen sensor 21a indicates the oxygen partial pressure of p1, and the oxygen sensor 21b indicates the oxygen partial pressure of p1 ′. It will be. Actually, the oxygen sensor 21b outputs the electromotive force V1 ′ based on the point p1 ″ on the characteristic curve Sb based on the oxygen partial pressure Pg1, but the characteristic curve of the oxygen sensor 21b is used to simplify the detection operation. Is regarded as a straight line (that is, regarded as the combined sensor characteristic Sc), the electromotive force V1 ′ indicates the oxygen partial pressure p1 ′, where the oxygen sensor 21a indicating the lower oxygen partial pressure The output is used to obtain the oxygen partial pressure p1, and the oxygen partial pressure p1 obtained in this way is the actual oxygen partial pressure Pg1 or a value close thereto.
検知対象ガスが低い酸素分圧Pg2であるときは、酸素センサ２１ａが出力Ｖ２、酸素センサ２１ｂは出力Ｖ２’を出力する。これらから、起電力と酸素分圧の対数値(log) とが直線的関係にあることを前提として酸素分圧を推定すると、酸素センサ２１ａはｐ２、酸素センサ２１ｂはｐ２’の酸素分圧を示すことになる。ここで、低い方の酸素分圧を示す酸素センサ２１ａの出力を採用し、酸素分圧ｐ２を得る。こうして得られる酸素分圧ｐ２は、実際の酸素分圧Pg2 またはこれに近い値となる。 When the detection target gas has a low oxygen partial pressure Pg2, the oxygen sensor 21a outputs an output V2, and the oxygen sensor 21b outputs an output V2 '. From these, when the oxygen partial pressure is estimated on the assumption that the electromotive force and the logarithmic value (log) of the oxygen partial pressure are in a linear relationship, the oxygen sensor 21a has the oxygen partial pressure of p2 and the oxygen sensor 21b has the oxygen partial pressure of p2 ′. Will show. Here, the output of the oxygen sensor 21a indicating the lower oxygen partial pressure is employed to obtain the oxygen partial pressure p2. The oxygen partial pressure p2 thus obtained is the actual oxygen partial pressure Pg2 or a value close thereto.
このように、第１の方法は、２個の酸素センサ２１ａ，２１ｂにより、合成センサ特性Ｓｃを得て、検知範囲を広げていると言うことができる。同様にして、複数の酸素センサを用いる場合は、酸素センサの出力から推定される酸素分圧の内、最も低い酸素分圧を採用することにより、複数の酸素センサによる合成センサ特性を得て、広い範囲の酸素分圧を検知することができる。 As described above, it can be said that the first method obtains the combined sensor characteristic Sc by the two oxygen sensors 21a and 21b and widens the detection range. Similarly, in the case of using a plurality of oxygen sensors, by adopting the lowest oxygen partial pressure among the oxygen partial pressures estimated from the output of the oxygen sensor, a combined sensor characteristic by a plurality of oxygen sensors is obtained, A wide range of oxygen partial pressures can be detected.
測定部２６の出力を選択する第２の方法は、図２に示した酸素センサ２１ａ，２１ｂ電解伝導領域について、以下の点を予め知得することに基づく。すなわち、電解伝導領域の酸素分圧の高い酸素センサ２１ａが検知時の作動温度において示す電解伝導領域の下限値、並びに、電解伝導領域の酸素分圧の低い酸素センサ２１ｂが検知時の作動温度において示す電解伝導領域の上限値の内の、少なくとも一つの限界値を出力選択の基準とする。そして、検知対象ガスの酸素分圧が高いときは電解伝導領域の酸素分圧域が高い酸素センサ酸素センサ２１ａの出力を採用し、酸素センサ２１ａ、２１ｂの出力のいずれかが基準の限界値のいずれかに到達または接近する前に、出力を採用する酸素センサを酸素センサ２１ｂに変更する。 The second method of selecting the output of the measurement unit 26 is based on knowing the following points in advance regarding the oxygen sensor 21a, 21b electrolytic conduction region shown in FIG. That is, the lower limit value of the electrolytic conduction region indicated by the operating temperature at the time of detection by the oxygen sensor 21a having a high oxygen partial pressure in the electrolytic conduction region and the oxygen sensor 21b having the low oxygen partial pressure of the electrolytic conduction region at the operating temperature at the time of detection. At least one limit value among the upper limit values of the electrolytic conduction region shown is set as a criterion for output selection. When the oxygen partial pressure of the detection target gas is high, the output of the oxygen sensor oxygen sensor 21a having a high oxygen partial pressure region in the electrolytic conduction region is adopted, and either of the outputs of the oxygen sensors 21a and 21b is a reference limit value. Before reaching or approaching either, the oxygen sensor that employs the output is changed to the oxygen sensor 21b.
こうすることにより、酸素センサの出力となる起電力を高く維持し、酸素分圧の正確な検知を行なうことができる。すなわち、検知する酸素分圧が電解伝導領域の下限ラインを下回ると、固体電解質の起電力が低下し、正確な酸素分圧を得るのが困難となるが、上記方法により下限ラインへの到達または接近の前に酸素センサを変更すれば、固体電解質の高い起電力を維持し、上記問題の発生を回避することができる。また、酸素センサは、図２に示したように、酸素分圧域の高い電解伝導領域Ｄａにおける低酸素分圧部分と、酸素分圧域の低い電解伝導領域Ｄｂにおける高酸素分圧部分とが、一部を重複させて用いられる。したがって、上記方法において、検知する酸素分圧が電解伝導領域Ｄｂの上限ラインＵｂに到達または接近する前に酸素センサを変更すると、電解伝導領域Ｄａの下限ラインＬａに到達または接近する前に、酸素センサ２１ｂに変更することになるので、下限ラインＬａを下回った酸素分圧で出力する酸素センサ２１ａへの依存を回避することができ、固体電解質が出力する起電力を高く維持し、正確な検知を行なうことができる。 By doing so, the electromotive force that is the output of the oxygen sensor can be maintained high, and the oxygen partial pressure can be accurately detected. That is, if the oxygen partial pressure to be detected is lower than the lower limit line of the electrolytic conduction region, the electromotive force of the solid electrolyte is lowered and it is difficult to obtain an accurate oxygen partial pressure. If the oxygen sensor is changed before approaching, the high electromotive force of the solid electrolyte can be maintained and the occurrence of the above problem can be avoided. Further, as shown in FIG. 2, the oxygen sensor has a low oxygen partial pressure portion in the electrolytic conduction region Da having a high oxygen partial pressure region and a high oxygen partial pressure portion in the electrolytic conduction region Db having a low oxygen partial pressure region. , Partly overlapped. Therefore, in the above method, if the oxygen sensor is changed before the oxygen partial pressure to be detected reaches or approaches the upper limit line Ub of the electrolytic conduction region Db, the oxygen oxygen pressure is reached before reaching or approaching the lower limit line La of the electrolytic conduction region Da. Since the sensor 21b is changed, it is possible to avoid dependence on the oxygen sensor 21a that outputs with the partial pressure of oxygen below the lower limit line La, and to maintain high electromotive force output from the solid electrolyte and to perform accurate detection. Can be performed.
酸素センサの変更は、制御部２３の作動によって行われる。制御部２３は、酸素センサにより得られる酸素分圧が電解伝導領域における酸素分圧の下限値に到達または接近する手前でこれを検知する。この検知は、例えば、予め準備した電解伝導領域の分布データと、酸素センサの作動温度及び酸素分圧の測定値とを比較することにより行うことができる。すなわち、電解伝導領域の分布データは、図６に例示したように、固体電解質の材質等にしたがって定まるので、酸素センサの作動温度及び酸素分圧の測定値と分布データとの比較により、電解伝導領域に対する現在の制御位置を判別することができる。これをモニタ等することにより、酸素センサにより得られる酸素分圧が電解伝導領域における酸素分圧の下限値に到達または接近する手前でこれを検知することができる。 The oxygen sensor is changed by the operation of the control unit 23. The control unit 23 detects this before the oxygen partial pressure obtained by the oxygen sensor reaches or approaches the lower limit value of the oxygen partial pressure in the electrolytic conduction region. This detection can be performed, for example, by comparing the distribution data of the electrolytic conduction region prepared in advance with the measured values of the operating temperature and oxygen partial pressure of the oxygen sensor. That is, as illustrated in FIG. 6, the distribution data of the electrolytic conduction region is determined according to the material of the solid electrolyte and the like. Therefore, by comparing the measured values of the operating temperature and oxygen partial pressure of the oxygen sensor with the distribution data, The current control position for the region can be determined. By monitoring this, the oxygen partial pressure obtained by the oxygen sensor can be detected before reaching or approaching the lower limit value of the oxygen partial pressure in the electrolytic conduction region.
以上、本発明の実施形態について説明したが、本発明はこれに限定されるものではなく、その趣旨を逸脱しない限りにおいて種々の変更が可能である。例えば、酸素分圧検知装置は、電解伝導領域が異なる３種類以上の酸素センサを備え、検知対象ガスの酸素分圧の高低に応じて、出力を採用する酸素センサを切り換えるようにしてもよい。 As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible unless it deviates from the meaning. For example, the oxygen partial pressure detection device may include three or more types of oxygen sensors having different electrolytic conduction regions, and the oxygen sensor that employs the output may be switched according to the level of the oxygen partial pressure of the detection target gas.
上記実施形態では、筒状をなす固体電解質の内側を、精製すべきガスの供給側とし、固体電解質の外側を酸素の排出側としたが、これを逆にして、固体電解質の外側を、精製すべきガスの供給側、内側を酸素の排出側とすることもできる。また、固体電解質を平面または曲面の板状とすることもできる。この場合は、固体電解質の一方の側及び他方の側のいずれかを、精製すべきガスの供給側、反対の側を酸素の排出側とすることができる。そして、固体電解質の供給側及び排出側のガスが相互に混合しないように、固体電解質に隣接する仕切り部材をガス精製部に設けるのが望ましい。 In the above embodiment, the inside of the solid electrolyte in the form of a cylinder is the gas supply side to be purified, and the outside of the solid electrolyte is the oxygen discharge side, but this is reversed and the outside of the solid electrolyte is purified. The gas supply side and the inside of the gas to be supplied can be the oxygen discharge side. Further, the solid electrolyte may be a flat or curved plate. In this case, either the one side or the other side of the solid electrolyte can be the supply side of the gas to be purified, and the opposite side can be the oxygen discharge side. It is desirable to provide a partition member adjacent to the solid electrolyte in the gas purification unit so that the gas on the supply side and the discharge side of the solid electrolyte are not mixed with each other.
１： 酸素分圧検知装置
１０： 検知部
２１ａ，２１ｂ：酸素センサ
２３： 制御部
２８ａ，２８ｂ：加熱部
２１１ａ，２１１ｂ：固体電解質
Ｄａ，Ｄｂ：電解伝導領域
Ｕａ，Ｕｂ：上限ライン
Ｌａ，Ｌｂ：下限ライン
1: Oxygen partial pressure detection device 10: Detection unit 21a, 21b: Oxygen sensor 23: Control unit 28a, 28b: Heating unit 211a, 211b: Solid electrolyte Da, Db: Electrolytic conduction region Ua, Ub: Upper limit lines La, Lb: Lower limit line
Claims (4)
固体電解質の酸素イオン輸率が１に近い温度−酸素分圧域である電解伝導領域が異なる複数種の酸素センサを構成し、
検知対象ガスの酸素分圧が高いときは、電解伝導領域の酸素分圧域が高い酸素センサの出力を採用し、検知対象ガスの酸素分圧が低いときは、電解伝導領域の酸素分圧域が低い酸素センサの出力を採用することを特徴とする酸素分圧検知方法。 An oxygen partial pressure detection method for detecting an oxygen partial pressure in a gas by an oxygen sensor using a solid electrolyte,
The oxygen ion transport number of the solid electrolyte is a temperature-oxygen partial pressure region close to 1, and a plurality of types of oxygen sensors having different electrolytic conduction regions are configured.
When the oxygen partial pressure of the gas to be detected is high, use the output of the oxygen sensor with a high oxygen partial pressure region in the electrolytic conduction region. When the oxygen partial pressure of the gas to be detected is low, the oxygen partial pressure region in the electrolytic conduction region An oxygen partial pressure detection method characterized by adopting the output of an oxygen sensor with low pressure.
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