Gas sensor and method of measuring quantity of specific compounds in measuring gas

Abstract: A gas sensor for measuring a quantity of specific component in a measuring gas includes a main pump means (1) which has an electrochemical pump cell. The electrochemical pump cell includes a solid electrolyte partition (2) exposed to external space, an inner pump electrode (3) and an outer pump electrode (4) formed on the inner surface and outer surface of the solid electrolyte partition, respectively. The main pump means treats oxygen contained in the measuring gas introduced from the outer space by pumping processing on the basis of a control voltage applied between the inner pump electrode and the outer pump electrode. An RLC element (8) which has a specific electric characteristic value corresponding to a characteristic value of the electrochemical pump cell is connected in parallel with the electrochemical pump cell.

Description: 1. Field of the Invention The present invention relates to a gas sensor for measuring a quantity of specific component in a measuring gas and a method of measuring thereof. More specifically, the present invention is directed to a gas sensor and a method for accurately and readily correcting a dispersion in output characteristics among sensors. 2. Description of Related Art Hitherto, there is known a method of measuring a quantity of specific component such as oxygen gas, in which an electrochemical pump cell including a partition made of solid electrolyte such as a zirconia ceramic and provided with a pair of electrodes thereon is used, and the diffusion limiting current is measured when applying current between these electrodes. In the method, the diffusion limiting current varies with the difference in structure of sensor element, particularly with the dispersion of micro-structure of electrode and of porosity in gas diffusion resistance layer. Accordingly, accurate measurement needs to apply correction responding to the sensitivity of individual sensor elements. Different from sensors used in analyzers, there is a problem on correcting the dispersion among sensors used as automobile parts. That is, dispersion among individual sensors in terms of sensor characteristic is not able to be adjusted from the interface side. Consequently, sensors mounted on an automobile require means to correct the dispersion among individual sensors. For correcting that type of dispersion among individual sensors, there are known methods such as: 1) a method, as shown in Fig. 8, in which a diffusion limiting current is divided into two routes using two resistors, 32 and 33, to adjust the diffusion limiting current to a predetermined value; and 2) a method in which after measuring the respective sensor characteristics, the measured characteristics are ranked, then as shown in Fig. 7, the fixed resistor 12 having a resistance value corresponding to each rank is built in the connector casing. The method illustrated in Fig. 8 is configured by a circuit which comprises: an electrochemical pump cell 60 including a solid electrolyte partition 2, a pair of electrodes 3 and 4 formed on the inner surface and outer surface thereof, and a gas diffusion resistance layer 5 formed on the electrode 3; a power source 9; and a current detection means 10 both of which are arranged between output terminals 6 and 7 of the electrochemical pump cell 60, wherein a diffusion limiting current to flow to the electrochemical pump cell 60 is divided by the resistors 32 and 33, thereby the current proportional to the concentration of specific component in the measuring gas flows through the current detection means 10. Further, according to a method shown in Fig. 7, a sensor is configured by a circuit which comprises: an electrochemical pump cell 60 including a solid electrolyte partition 2, a pair of electrodes 3 and 4 formed on the inner surface and outer surface thereof, and a gas diffusion resistance layer 5 formed on the electrode 3; a power source 9; and a current detection means 10 both of which are arranged between output terminals 6 and 7 of the electrochemical pump cell 60, wherein after measuring the characteristic thereof, the measured characteristic is ranked. Subsequently, as shown in Fig. 7, a connector casing in which a fixed resistor 12 corresponding to each rank is built is combined with the electrochemical pump cell 60 to detect current by a separate current detection means 15 which is connected to the fixed resistor 12 in series. However, for a sensor having shunt resistors or a sensor having a fixed resistor responding to each rank, both of which are described above, there are disadvantages that the number of terminals on a connector increases, the reliability decreases and the production cost increases. EP-A-0678740 discloses a gas sensor formed of an ion-conductive solid electrolyte body having a reference gas space, a measurement space and a pumping space. An electrode located in the reference gas channel is connected via a power source and a current detection means to an electrode in the measurement space; and the electrode located in the reference gas channel is connected to an electrode on the pumping space via a potentiometer. A separate pair of electrodes are also provided on a wall of the body such that one electrode is located in the pumping space and one is located on an external surface of the body. These two electrodes are connected by a power supply which itself is controlled by the output of the potentiometer. SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a correction method that can solve the problems of the conventional correction methods. According to the present invention, there is provided a gas sensor as set out in claim 1 and a method as in claim 4. Further, according to the present invention, there is provided a method of measuring a quantity of specific target component in a measuring gas as set out in claim 4. As described above, the present invention relates to an improvement of the above-described conventional method 2). According to the present invention, the interface mounted on an automobile stores the correction value corresponding to each rank, thus reading the label on sensor side before actuating the sensor, and selecting an adequate correction value to correct the sensor output. It should be noted that according to the present invention, the RLC element is preferably a resistor (R), also the RLC element is preferably either of capacitor (C), a series circuit of a capacitor (C) and a resistor (R), or a series circuit of a capacitor (C) and an inductor (L). Furthermore, other than the combination of these resistor, capacitor, and inductor as an RLC element, an oscillator or a filter which has maximum or minimum value at a specific frequency may be used. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view of a main part of a sensor element and a circuit showing an example of a comparative gas sensor structure Fig. 2 is a cross sectional view of a main part of the sensor element and the circuit showing an example of a basic gas sensor structure according to the present invention; Fig. 3 is a cross sectional view of a main part of the sensor element and the circuit showing an example of a gas sensor according to the present invention; Fig. 4 is a cross sectional view of a main part of the sensor element and the circuit showing another example of a gas sensor according to the present invention; Fig. 5 is a cross sectional view of a main part of the sensor element and the circuit showing another example of a gas sensor according to the present invention; Fig. 6 is a cross sectional view of a main part of the sensor element and the circuit of another example of a gas sensor according to the present invention; Fig. 7 is a cross sectional view showing the structure and circuit of a conventional gas sensor; and Fig. 8 is a cross sectional view of another example of a sensor element and circuit of a conventional gas sensor. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 is a diagram showing a circuit illustrating an example of a comparative gas sensor structure. An electrochemical pump cell 1 is made up of a solid electrolyte partition 2 comprising a zirconia ceramic which shows substantially no ion conductivity at room temperature but shows ion conductivity at an elevated temperature, a pair of electrodes 3 and 4 formed on the inner surface and outer surface of the solid electrolyte partition 2, respectively, and a gas diffusion resistance layer 5 formed on the electrode 3. A resistor 8 having a resistance corresponding to the sensitivity of the cell is connected to output terminals 6 and 7 of the electrochemical pump cell 1 in parallel therewith. In the above-described configuration of the sensor circuit, when a predetermined voltage (control voltage) is applied by a power source 9 to the output terminals 6 and 7 of the electrochemical pump cell 1, almost no current flows through the cell 1 because the impedance of the cell 1 is very high at room temperature, the current flows substantially only through a fixed resistor 8. Accordingly, if the measurement of the current is conducted by a current detection means 10, the resistance value of the fixed resistor 8 can be read. Since the resistance value is set to correspond to the sensitivity of each cell, information relating to the resistance value of the cell is stored in the current detection means 10 that measures the current flowing across the cell, thereby being capable of correcting the value of current in the case of cell actuation at an elevated temperature based on the equation given below: I 0 = K n (I n - V/R n ) where, l 0 is the diffusion limiting current after correcting sensitivity, K n is the correction factor corresponding to the sensitivity of each cell, I n is the value of current flowing across the current detection means 10, R n is the resistance of the fixed resistor 8, and V is the voltage at the power source 9. It should be noted that the internal resistance of the current detection means 10 is assumed as negligible small. Sensitivity of ceil (sensor output) and offset value are examples of the characteristic values of electrochemical pump cell (electric signal characteristic of sensor in the case of including an electric signal conversion means as shown in Fig. 3 through Fig. 5, described later) represented by the characteristic value of an RLC element as a resistor in Fig. 1. Examples of sensitivity of cell (sensor output) are: (1) rate of increase of pump current relative to the concentration of a specific target component in the measuring gas; (2) rate of reduction of electromotive force relative to the concentration of a specific target component in the measuring gas: and (3) rate of change of resistance relative to the concentration of a specific target component in the measuring gas. Examples of offset value of a cell (sensor output) are: (1) a pump current value at zero concentration of a specific target component in the measuring gas; (2) an electromotive force generated at zero concentration of a specific target component in the measuring gas; and (3) a resistance at zero concentration of a specific target component in the measuring gas. As a result, I 0 in Fig. 1 becomes a value after correcting the dispersion of sensitivity in each cell, thus I 0 and the composition of a measuring gas have a very close correlation with each other. The fixed resistor 8 may be configured with thermet as the resistor sintered onto the sensor element, or may be contained in the connector casing of the sensor. Fig. 2 is a circuit diagram illustrating an example of a basic structure of a gas sensor according to the present invention. Similar to the basic structure of Fig. 1, an electrochemical pump cell 1 is made up of a solid electrolyte partition 2, a pair of electrodes 3 and 4 formed on the inner surface and outer surface thereof, respectively, and a gas diffusion resistance layer 5 formed on the electrode 3. A power source 9 and a current detection means 10 are arranged between output terminals '6 and 7 of the electrochemical pump cell 1. On the inner surface and outer surface of the solid electrolyte partition 2 made of a zirconia ceramic or the like, a further pair of electrodes 23 and 24 are provided, respectively, to form an electrochemical pump cell 21 combined with the gas diffusion layer 5 formed on the electrode 23. A fixed resistor 28 having a resistance corresponding to the sensitivity of the electrochemical pump cell 1 adjacent to the electrochemical pump cell21 is connected to the output terminals 26 and 27 of the electrochemical pump cell21 via a capacitor 29 in parallel with the cell. In a sensor circuit having a configuration described above, when a specific voltage is applied from an alternating current power source 30 to the output terminals 26 and 27 of the cell 21 via a capacitor 31, almost no current flows through the cell 21 because the impedance of the cell 21 is very high at room temperature, the current flows substantially only through the fixed resistor 28. Accordingly, if the measurement of the current is conducted by a second current detection means 11, the resistance value of the fixed resistor 28 may be read. Since the resistance value is set to correspond to the sensitivity of the electrochemical pump cell 1, the information relating the resistance value of the cell is stored in the second current detection means 11, thereby being capable of correcting the value of current in the case of actuation of the cell21 at an elevated temperature based on the equation given below: I 0 = K n x I n where, I 0 is a diffusion limiting current value after correcting sensitivity, K n is a correction factor corresponding to the sensitivity of each cell, and I n is a value of current flowing to the current detection means 10. With the method described above, correction is capable of being effected without influencing the current detection circuit of the electrochemical pump cell 1 and, even in the case of the electrochemical pump cell 21 for measuring an electromotive force, without influencing the electromotive force. For instance, in Fig. 2, a potential difference (voltage) detection means 35 conducts the measurement of electromotive force corresponding to the difference of oxygen concentration between the electrodes 23 and 24. The voltage applied to the electrochemical pump cell 1 is adjusted to control the electromotive force to a specific value. The present invention is described in more detail in the examples given below referring to the drawings. Fig. 3 shows a cross sectional view of a major part of a NOx sensor provided with a heater section, and an electric circuit thereof. In Fig. 3, the NOx sensor includes a first internal space 42 and a second internal space 44 which are arranged separately with each other while positioning the first internal space 42 at the front end of the sensor element. A reference gas introduction space 47 as a reference gas existing space extends in the longitudinal direction of the sensor element independently from the first internal space 42 and from the second internal space 44. A first diffusion controled section 41 wh i ch connects' the fiiit internal space 42 with an external measuring gas exiting space is arrange at the tip of the sensor element. The first internal space 42 and the second internal space 44 are connected with each other by a second diffusion controlled section 43. The portion on a solid electrolyte partition 2 exposed to the first internal space 42 is provided with an inner pump electrode 13. An outer pump electrode 14 is formed on the outer surface of the solid electrolyte partition 2 at an opposite side of the inner pump electrode 13. A main pump means (electrochemical pump cell) 1 is made up of these electrodes 13 and 14, and the solid electrolyte partition 2. Between output terminals 6 and 7 of the main pump means 1, power source 9 and current detection means 10 are arranged in the circuit, a fixed resistor 8 having a resistance value corresponding to the sensitivity of the main pump means 1 is connected between the output terminals 6 and 7 in parallel. The measuring electrode 45 is formed on a portion of the solid electrolyte partition 2 exposed to the second internal space 44, and a reference electrode 46 is formed on a portion of the solid electrolyte partition 2 exposed to the reference gas introduction space 47. A measuring pump means 20 is made up of a measuring electrode 45, the reference electrode 46, and the solid electrolyte partition 2. The circuit is structured to have a power source 17 and a current detection means 18 between the output terminals of the measuring pump means 20. It should be noted that a heater section 40 is provided in the NOx sensor in such a manner that a heater 16 is buried while being surrounded by the solid electrolyte of the sensor. The heater generates heat by receiving power from a heater power source 48. According to the NOx sensor thus configured, the measuring gas passes through the first diffusion controlled section 41 to enter the first internal space 42. By applying power from the power source 9 with a specific voltage to the pair of pump electrodes 13 and 14 formed on the inner surface and outer surface of the solid electrolyte partition 2 made of a zirconia ceramic, the diffusion limiting current value of oxygen is determined by the current detection means 10. The NO which is not decomposed in the internal space 42 passes through the second diffusion controlled section 43 to enter the second internal space 44. By applying a voltage from the power source 17 between the measuring electrode 45 and the reference electrode 46, NO is decomposed. The quantity of oxygen generated by the decomposition of NO is measured by a current detection means 18 to determine the quantity of NOx. When the value of resistance of resistor 8 is set to a value corresponding to the sensitivity to oxygen in the first internal space 42, or to the sensitivity to NOx gas in the second internal space 44 , the value of the pump current flowing through the main pump means 1, or the value of the current flowing through the measuring pump means 3 is able to be corrected using the correction factor derived from, or based on, the measured value of the resistance of the resistor 8 using the current detection means 10 at room temperature. Particularly when the NOx concentration is corrected, the main pump means 1 does not decompose N0, so that the current flowing into the resistor 8 is independent of NOx measurement. As a result, the correction of NOx sensitivity or of offset may be effected with high accuracy. Fig. 4 shows a cross sectional view of a main part of another NOx sensor and the electric circuit thereof. According to the example, the NOx sensor has only the first internal space 42 and does not have the second internal space 44. Instead of the second internal space 44, the second diffusion controlled section 43, made of gas diffusion resistance layer, is formed. Further, the measuring electrode 45 exhibits catalytic activity suitable to decompose NOx. At a portion of the solid electrolyte partition 2 exposed to the first internal space 42, the inner pump electrode 13 is formed, whereas, at a portion of the solid electrolyte partition 2 exposed to the reference gas introduction space 47, the outer pump electrode 14 which is common with the reference electrode is formed. The main pump means 1 is structured by these electrodes 13 and 14, and the solid electrolyte partition 2. A circuit having the power source 9 is formed between the output terminals of the main pump means 1. A different portion exposed to the first internal space 42, a measuring electrode 45 which has a catalytic activity to decompose NOx gas is formed. The second diffusion controlled section 43 comprising a gas diffusion resistance layer is formed covering the measuring electrode 45. At a portion of the solid electrolyte partition 2 exposed to the reference gas introduction space 47, the reference electrode 14 which is common with the outer pump electrode is formed. The measuring pump means 1 is structured by the measuring electrode 45, the reference electrode 14, and the solid electrolyte partition 2. A circuit having the power source 17 and the current detection means 10 is formed between the output terminals of the measuring pump means, while the fixed resistor 8 is connected between the output terminals of the electrochemical sensor cell in parallel with the cell. According to the NOx sensor thus configured, the measuring gas passes through the first diffusion controlled section 41 to enter the first internal space 42. By applying power from the power source 9 a specific voltage to the pair of pump electrodes 13 and 14 formed on the inner surface and outer surface of the solid electrolyte partition 2 made of a zirconia ceramic, a quantity of oxygen within the first internal space 42 is brought to near a zero level. The NOx gas which passes through the second diffusion controlled section 43 and arrives at the measuring electrode 45 having a catalytic activity is decomposed to generate oxygen. The quantity of oxygen is measured by the current detection means 10 to determine the quantity of NOx. When the value of resistance of resistor 8 is set to a value corresponding to the sensitivity to NOx, the NOx sensitivity is capable of being corrected at a high accuracy by measuring the value of resistance of resistor 8 using the current detection means 10 at room temperature and by applying the correction factor derived from the measured value of the resistance of resistor 8. Fig. 5 shows a cross sectional view of a main part of a diffusion limiting current type oxygen sensor and the electric circuit thereof. According to the example, the inner pump electrode 13 is formed on a portion of the solid electrolyte partition 2 exposed to the internal space 52, and the outer pump electrode 14 is formed on the outer surface of the solid electrolyte partition 2 at a side opposite to the inner pump electrode 13. The main pump means 1 is structured by these electrodes 13 and 14, and the solid electrolyte partition 2. At a different exposed portion in the internal space 52 of the solid electrolyte partition 2, the measuring electrode 53 is formed. At a portion of the solid electrolyte partition 2 exposed to the reference gas introduction space 47, the reference electrode 54 is formed. The oxygen concentration cell is structured by the measuring electrode 53, the reference electrode 54, and the solid electrolyte partition 2. A circuit having the power source 9 and the current detection means 10 is formed between the output terminals of the main pump means 1, while connecting a series circuit of an alternate current power source 70, a resistor 56, and a capacitor 71 between the output terminals of the oxygen concentration cell, and also connecting a series circuit of a resistor 68 and a capacitor 69 between the output terminals of the oxygen concentration cell in parallel therewith. According to the oxygen sensor thus configured, the measuring gas passes through the diffusion controlled section 51 to enter the internal space 52. By applying power from the power source 9 with a specific voltage to the pair of electrodes 13 and 14 formed on the inner surface and outer surface of the solid electrolyte partition 2 made of a zirconia ceramic, a quantity of oxygen within the internal space 52 is brought to a near zero level. The oxygen partial pressure in the internal space 52 is measured by a potential difference detection means 55, as the electromotive force which is determined by the ratio to the oxygen partial pressure in the reference gas introduction space 47 using the oxygen concentration cell structured by the electrodes 53 and 54 and by the solid electrolyte partition 2. Then, the voltage of the power source 9 is controlled to match the determined electromotive force with the predetermined value. During the course of measurement, the current flowing across the current detection means 10 corresponds to the oxygen concentration in the measuring gas. If the value of the resistance of a resistor 68 is set to a value corresponding to the sensitivity to oxygen gas, then it is possible that the value of the resistance of resistor 68 is measured by the potential difference (voltage) detection means 55 as a divided voltage of the alternate current power source 70 using the resistors 56 and 68, and that the sensitivity of measurement is matched to the sensitivity of individual sensors. The impedance of capacitors 69 and 71 is assumed as sufficiently small. Fig. 6 shows a cross sectional view of a main part of a sensor element provided with an auxiliary pump for further adjusting fine variation of oxygen partial pressure in the measuring gas which has been subjected to the adjustment of oxygen partial pressure in the main pump cell 1, and conducting measurement of NOx concentration by means of electromotive force. Fig. 6 also shows the electric circuit of the sensor element. Compared with an example of Fig. 3, the example of Fig. 6 has basically the same configuration of the main pump 1 and the heater section 40, and differs in that an auxiliary pump 80 is added, that the NOx concentration is measured by means of electromotive force generated in a concentration detection means 90 which comprises a detection electrode 82 and the reference electrode 46. According to this example, a circuit is structured by locating the power source 9 between the output terminals 6 and 7 of the main pump means 1, while connecting the fixed resistor 8 having a resistance corresponding to the sensitivity of the concentration detection means 90 between the output terminals 6 and 7 in parallel with the power source. A portion of the solid electrolyte partition 2 exposed to the second internal space 44 is provided with the detection electrode 82. A portion of the solid electrolyte partition 2 exposed to the reference gas introduction space 47 is provided with the reference electrode 46. The concentration detection means 90 is structured by the detection electrode 82, the reference electrode 46, and the solid electrolyte partition 2. Also, a different portion in the second internal space 44 is provided with the auxiliary pump electrode 80. The auxiliary pump means 84 is structured by the auxiliary pump electrode 80, the reference electrode 46 formed in the reference gas introduction space 47, and the solid electrolyte partition 2. A potential difference detection means 83 is arranged between the output terminals of the concentration detection means 90. A circuit having the power source 85 is formed between the output terminals of the auxiliary pump means 84, while connecting a fixed resistor 88 having a resistance corresponding to the offset value of the concentration detection means 90 in parallel therewith. According to the NOx sensor thus configured, the measuring gas passes through the first diffusion controlled section 41 to enter the first internal space 42. By applying a predetermined voltage from the power source 9 to the pair of electrodes 13 and 14 located on the inner surface and outer surface of the solid electrolyte partition 2, the oxygen pumping action is induced, which pumping action controls the oxygen partial pressure to a predetermined level at which NO does not decompose. The measuring gas in which the oxygen partial pressure is controlled to a predetermined level passes through the second diffusion controlled section 43 to enter the second internal space 44. By applying voltage from the power source 85 between the auxiliary pump electrode 80 and the reference electrode 46, the measuring gas is adjusted to a lower level of oxygen partial pressure. The NO is decomposed on the detection electrode 82 which has an ability of NO decomposition and which is formed in the second internal space 44. Thus, the NOx concentration is determined by determining the oxygen generated along with the decomposition of NO by means of the potential difference detection means 83. When the resistance of the resistor 8 is set to a value corresponding to the sensitivity (reduction rate of electromotive force relative to the NOx concentration) of the concentration detection means 90, and when the resistance of the resistor 88 is set to a value corresponding to the offset value of the concentration detection means 90, the measurement of resistance of the resistor 8 and of the resistor 88 by the current detection means 10 and by the current detection means 81, respectively, allows the setting of the correction factor to an optimum value for the sensor before actuating thereof. As a result, the NOx concentration is determined at higher accuracy. The description given above employed a configuration that an element has two electrochemical pump cells with two resistors. Nevertheless, the resistor may be other RLC element. In addition, the number of RLC elements is arbitrarily chosen responding to the number of pump cells.

Claims: A gas sensor for measuring the quantity of a specific target component in a measuring gas comprising: main pump means including an electrochemical pump cell (1) comprising a solid electrolyte partition (2) exposed to an external space, an inner pump electrode (3) and an outer pump electrode (4) formed on the inner surface and the outer surface of the solid electrolyte partition (2), respectively, and said main pump means treating oxygen contained in an internal space (42, 52) in the measuring gas introduced from said external space by pumping processing on the basis of a control voltage applied between said inner pump electrode (3) and said outer pump electrode (4); electric signal conversion means for generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of the target component contained in the measuring gas after having been treated by the pumping processing by said main pumping means, the electric signal conversion means having a pair of detection electrodes formed on said solid electrolyte partition, with one (23, 45, 53) of said pair of the detection electrodes exposed to the atmosphere of the internal space (42, 52) whose oxygen concentration is controlled by the main pump means and the other (24, 46, 14, 54) of the detection electrodes exposed to an external atmosphere; a resistor (8, 68, 88) capable of being used in calculating or estimating a corrected value for outputs of said sensor from a value of its resistance at room temperature; and detection means comprising a power source (9, 17, 30, 70) and resistor current detector means (10, 11, 58); wherein: the resistor and the detection means are both connected in parallel with output terminals of said electrochemical pump cell, or the resistor and the detection means are both connected in parallel with output terminals of said electric signal conversion means. A gas sensor as claimed in claim 1, wherein said electric signal conversion means comprises: measuring pump means (20) for conducting pumping processing of oxygen generated by decomposition or reduction of the target component contained in the measuring gas, after the measuring gas has been treated by the pumping processing by said main pumping means, on the basis of measuring voltage applied between said pair of detection electrodes (45, 46); and pump current detection means (18) for detecting pump current generated in the measuring pump means, wherein: the quantity of the target component in the measuring gas is determined on the basis of pump current detected by the current detection means (18). A gas sensor as claimed in claim 1, wherein said electric signal conversion means comprises: concentration detection means for generating an electromotive force corresponding to the difference between a quantity of oxygen generated by decomposition or reduction of the target component contained in the measuring gas after having been treated by the pumping processing by said main pumping means and a quantity of oxygen contained in a reference gas on the side of a said detection electrode formed on the side of reference gas; and voltage detection means (55) for detecting the electromotive force generated in the concentration detection means, wherein: the quantity of the specific component in the measuring gas is determined on the basis of electromotive force detected by the voltage detection means. A method of measuring the quantity of a specific target component in a measuring gas comprising: using main pump means of a sensor including an electrochemical pump cell (1) comprising a solid electrolyte partition (2) exposed to an external space, an inner pump electrode (3) and an outer pump electrode (4) formed on the inner surface and the outer surface of the solid electrolyte partition (2), respectively, to control oxygen gas partial pressure in the measuring gas in an internal space (42, 52) to a predetermined value by conducting pumping processing of the oxygen contained in the measuring gas introduced into said internal space (42, 52) from the external space on the basis of a control voltage applied between said inner pump electrode (3) and said outer pump electrode (4); converting a target component contained in the measuring gas after having been treated by pumping processing by said main pump means using electric signal conversion means having a pair of detection electrodes formed with one (23, 45, 53) of said pair of the detection electrodes exposed to the atmosphere of the internal space (42, 52) whose oxygen concentration is controlled by the main pump means and the other (24, 46, 14, 54) of the detection electrodes exposed to an external atmosphere, said detecting electrodes producing an electric signal corresponding to a quantity of oxygen generated either by decomposition or reduction; and measuring a quantity of a specific component in the measuring gas on the basis of an electric signal coming from said electric signal conversions means; wherein: (a) detection means, which comprises a power source (9, 17, 30, 70) and resistor current detector (10, 11, 55) and (b) a resistor (8, 68, 88), which has a predetermined electric characteristic value corresponding to a characteristic value of said electric signal, are both connected in parallel with the output terminals of said electrochemical pump cell or are both connected in parallel with the output terminals of said electric signal conversion means; and the setting of an output correction of said electric signal conversion means at an elevated temperature is carried out at room temperature by using said detection means in determining the electric characteristic value of said resistor (8, 68, 88) in a state that ion conductivity of the solid electrolyte is removed; and the output of said electric signal conversion means is corrected on the basis of the determined electric characteristic value of said resistor (8, 68, 88).

Inventors: INA NORIYUKI, KATO NOBUHIDE, INA, NORIYUKI, KATO, NOBUHIDE
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1997
Main classification: G01N27
IPC codes: G01N27