JP2020091283A - Gas sensor and gas concentration measurement method - Google Patents

Abstract

To provide a gas sensor and gas concentration measurement method capable of preventing reduction of measurement accuracy due to delay of a measurement time.SOLUTION: In a gas sensor 10, a preliminary vacant chamber 21, an oxygen density adjustment chamber 18, and a measurement vacant chamber 20 are formed in a structure 14 made of a solid electrolyte while they are communicated with each other in the sequence from a gas introduction port 16 in this order. The gas sensor measures a measurement pump current Ip3 of the measurement vacant chamber 20 while switching a preliminary pump cell 80 of the preliminary vacant chamber 21 between ON and OFF in a constant cycle. By rapidly determining a stationary value of the measurement pump current Ip3 on the basis of the peak value of a time change rate dIp3/dt of the measurement pump current Ip3, the switching cycle of ON/OFF of the preliminary pump cell 80 is accelerated.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a gas sensor and a gas concentration measuring method using an oxygen ion conductive solid electrolyte.

Conventionally, gas sensors have been proposed that measure the concentrations of a plurality of components such as nitrogen oxides (NO) and ammonia (NH ₃ ) that coexist in the presence of oxygen such as exhaust gas.

For example, in Patent Document 1, a spare electrolyte chamber, a main chamber, a sub chamber, and a measurement chamber are provided in a solid electrolyte having oxygen ion conductivity with a diffusion resistance portion therebetween, and a pumping electrode is provided in each chamber. A gas sensor provided with is described. In this gas sensor, the drive (ON) or stop (OFF) of the spare pump cell in the spare chamber is switched to switch the progress or stop of the oxidation reaction from NH ₃ to NO in the spare chamber. Then, based on the change in the pump current (hereinafter, also referred to as the measured pump current Ip3) of the measurement electrode in the measurement chamber caused by the difference in the diffusion rate of NH ₃ and NO from the preliminary chamber to the main chamber, NH ₃ and The gas concentration of NO is measured.

International Publication No. 2017/222002

The gas sensor described in Patent Document 1 acquires the measured pump current Ip3 while switching the standby pump cell in the standby chamber on or off at regular intervals. When the spare pump cell is switched on or off, the measured pump current Ip3 transiently fluctuates and then settles to a steady value. Therefore, in order to obtain the measured pump current Ip3, it is necessary to wait a time until the measured pump current Ip3 settles to a steady value, and the switching cycle of the operation state of the auxiliary pump cell is set longer than the time until the measured pump current Ip3 settles to the steady value. is doing.

However, the state of the inflowing exhaust gas changes every moment. Therefore, if the concentration of the measurement target gas fluctuates during the switching cycle, the steady value of the measured pump current Ip3 may fluctuate. As a result, the concentration of the target component gas reflected by the measured pump current Ip3on when the spare pump cell is turned on differs from the concentration of the target component gas reflected by the measured pump current Ip3off when the spare pump cell is turned off. There are cases. As described above, if the concentration of the target component in the measurement chamber fluctuates greatly during the switching cycle of one cycle of the auxiliary pump cell, the preconditions for the measurement are not satisfied, and the measurement accuracy deteriorates. ..

It is an object of the present invention to provide a gas sensor and a gas concentration measuring method capable of preventing a decrease in measurement accuracy due to a delay in measurement time of the measurement pump current Ip3.

One aspect of the present invention is a gas sensor for measuring the concentration of a plurality of components in the presence of oxygen, a structure composed of an oxygen ion conductive solid electrolyte, formed in the structure, the gas to be measured is introduced. A gas introduction port having a spare pump electrode, a spare chamber communicating with the gas supply port, a pump electrode, an oxygen concentration adjusting chamber communicating with the spare chamber, and a measuring electrode, Under the operation of the measurement chamber that communicates with the oxygen concentration adjusting chamber, the preliminary oxygen concentration control unit that controls the oxygen concentration in the preliminary chamber based on the voltage of the preliminary pump electrode, and the operation of the preliminary oxygen concentration control unit. , A specific component measuring means for detecting a measured pump current (Ip3) flowing through the outer pump electrode and the measuring electrode, and a measured pump current (Ip3on from the specific component measuring means during the first operation of the preliminary oxygen concentration control means). ) And the measured pump current (Ip3off) from the specific component measuring means during the second operation of the preliminary oxygen concentration control means (ΔIp3), the measured pump current (Ip3on) and the measured pump current (Ip3off). ), the target component acquiring means for acquiring the concentration of the target component in the gas to be measured, wherein the specific component measuring means includes a first operation and a second operation of the preliminary oxygen concentration control means. In the gas sensor, the steady value of the measurement pump current (Ip3on) or the steady value of the measurement pump current (Ip3off) is obtained based on the peak value of the time rate of change of the measurement pump current (Ip3) when the operation is switched. ..

Further, another aspect of the present invention, a structure comprising an oxygen ion conductive solid electrolyte, a gas inlet formed in the structure, the gas to be measured is introduced, and a preliminary pump electrode, A spare chamber communicating with the gas inlet, having a pump electrode, an oxygen concentration adjusting chamber communicating with the spare chamber, a measuring electrode having a measuring chamber communicating with the oxygen concentration adjusting chamber, A preliminary oxygen concentration control unit that controls the oxygen concentration in the preliminary chamber based on the voltage of the preliminary pump electrode, and a measurement pump that flows between the outer pump electrode and the measurement electrode under the operation of the preliminary oxygen concentration control unit. A specific component measuring means for detecting a current (Ip3), and a measured pump current (Ip3on) from the specific component measuring means during the first operation of the preliminary oxygen concentration control means and a second operation of the preliminary oxygen concentration control means. In the measured gas based on the amount of change (ΔIp3) from the measured pump current (Ip3off) from the specific component measuring means, and one of the measured pump current (Ip3on) and the measured pump current (Ip3off). A gas concentration measuring method using a gas sensor having a target component acquisition means for acquiring the concentration of a component, the operation switching step of performing switching control between the first operation and the second operation of the preliminary oxygen concentration control means. A step for the specific component measuring means to obtain a peak value of a time change rate of the measured pump current (Ip3) accompanying the switching control between the first operation and the second operation of the preliminary oxygen concentration control means; The component measuring means calculates the steady-state value of the measurement pump current (Ip3) from the correlation between the peak value of the temporal change rate of the measurement pump current (Ip3) previously obtained and the steady-state value of the measurement pump current (Ip3). A gas concentration, the step of obtaining and the step of obtaining the concentration of the target component in the gas to be measured based on the steady value of the measured pump current (Ip3) from the specific component measuring unit by the target component acquisition unit. There is a measuring method.

According to the gas sensor and the gas concentration measuring method of the above aspect, the pump of the measurement electrode is pumped by paying attention to the time change rate of the pump current value (measurement pump current) of the measurement electrode due to the switching of the operating state of the auxiliary pump cell in the auxiliary chamber. Obtain the predicted steady-state value of the current value. This makes it possible to obtain the steady-state value of the pump current value before the pump current value of the measurement electrode settles down. Therefore, the operation state of the auxiliary pump cell can be switched before the pump current value of the measurement electrode settles to the steady value, and the operation cycle of the operation state of the auxiliary pump cell can be shortened. As a result, the delay in the measurement time of the measurement pump current Ip3 is reduced, and the measurement accuracy can be prevented from being degraded.

It is sectional drawing which shows one structural example of the gas sensor which concerns on 1st Embodiment. It is a block diagram of the gas sensor of FIG. It is explanatory drawing which shows typically the reaction at the time of turning off a preliminary|backup pump cell in the gas sensor of FIG. It is explanatory drawing which shows typically the reaction at the time of turning ON a spare pump cell in the gas sensor of FIG. It is a flow chart which shows acquisition processing of measurement pump current Ip3 in a gas sensor of Drawing 1. It is a figure which shows typically the change of the measured pump current Ip3 at the time of turning on a spare pump cell, and its time change rate. 7 is a graph showing a measurement result of a change in the measured pump current Ip3 accompanying the switching of the operating state of the auxiliary pump cell under the condition that the NO concentration of the measured gas is 0 ppm. 8 is a graph showing a time change rate of the measured pump current Ip3 of FIG. 7. 9 is a graph showing the correlation between the peak value of the rate of change over time of the measured pump current Ip3 in FIG. 8 and the NH ₃ concentration. 6 is a graph showing a measurement result of a change in the measured pump current Ip3 due to switching of the operating state of the auxiliary pump cell under the condition that the NO concentration of the gas to be measured is 500 ppm. It is a graph which shows the time change rate of the measured pump current Ip3 of FIG. It is a graph showing the correlation between the peak value and the NH ₃ concentration in the time rate of change of FIG. Simulation results of the measurement results of changes in the NH ₃ concentration in the measured gas by the FT-IR method and the detected values of the NH ₃ concentration by the gas sensor of FIG. 1 when the operation switching cycle of the auxiliary pump cell was 1 second (1 Hz) It is a graph which shows the obtained result (Experimental example 3). The measurement result of the change of the NH ₃ concentration in the measured gas by the FT-IR method and the detected value of the NH ₃ concentration by the gas sensor of FIG. 1 when the operation switching period of the auxiliary pump cell is 4 seconds (0.25 Hz) are shown. It is a graph which shows the result (comparative example) calculated|required by simulation. It is a flow chart which shows acquisition processing of measurement pump current Ip3 concerning a 2nd embodiment.

Hereinafter, embodiments of a gas sensor and a gas concentration measuring method according to the present invention will be described with reference to FIGS. 1 to 15. In addition, in this specification, "-" which shows a numerical range is used as the meaning which includes the numerical value described before and after that as a lower limit or an upper limit.

(First embodiment)
The gas sensor 10 according to the present embodiment has a sensor element 12 as shown in FIGS. 1 and 2. The sensor element 12 includes a structure 14 made of a solid electrolyte having oxygen ion conductivity, a gas inlet 16 formed in the structure 14 and into which a gas to be measured is introduced, and a gas introduction port formed in the structure 14. It has an oxygen concentration adjusting chamber 18 communicating with the port 16 and a measurement chamber 20 formed in the structure 14 and communicating with the oxygen concentration adjusting chamber 18.

The oxygen concentration adjusting chamber 18 has a main vacant chamber 18a provided on the gas introduction port 16 side and a sub vacant chamber 18b communicating with the main vacant chamber 18a. The measurement chamber 20 communicates with the sub chamber 18b. The oxygen concentration adjusting chamber 18 may be composed of only the main empty chamber 18a.

Further, the gas sensor 10 has a spare chamber 21 between the gas inlet 16 and the main chamber 18a in the structure 14. The main vacant chamber 18 a communicates with the gas introduction port 16 via the spare vacant chamber 21.

The structure 14 having such a plurality of vacant chambers 18a, 18b, 20, 21 is formed by laminating a plurality of layers of substrates made of ceramics, for example. Specifically, the structure 14 of the sensor element 12 includes a first substrate 22a, a second substrate 22b, a third substrate 22c, a first solid electrolyte layer 24, a spacer layer 26, and a second solid electrolyte layer 28. Six layers consisting of are laminated in order from the bottom. Each layer is composed of an oxygen ion conductive solid electrolyte such as zirconia (ZrO ₂ ).

A gas inlet 16 is provided at one end of the sensor element 12. The gas inlet 16 is formed between the lower surface 28b of the second solid electrolyte layer 28 and the upper surface 24a of the first solid electrolyte layer 24.

Between the lower surface 28b of the second solid electrolyte layer 28 and the upper surface 24a of the first solid electrolyte layer 24, there is further provided a first diffusion rate controlling part 30, a preliminary chamber 21, a second diffusion rate controlling part 32, and oxygen. A concentration adjusting chamber 18, a third diffusion controlling part 34, and a measurement chamber 20 are formed. A fourth diffusion rate controlling unit 36 is provided between the main chamber 18a and the sub chamber 18b that form the oxygen concentration adjusting chamber 18.

The gas inlet 16, the first diffusion control part 30, the auxiliary chamber 21, the second diffusion control part 32, the main chamber 18a, the fourth diffusion control part 36, the sub chamber 18b, and the third The diffusion-controlling part 34 and the measurement chamber 20 are formed adjacent to each other so as to communicate with each other in this order. The portion from the gas inlet 16 to the measurement chamber 20 is also referred to as a gas distribution unit.

The gas inlet 16, the spare chamber 21, the main chamber 18a, the sub chamber 18b, and the measurement chamber 20 are formed so as to penetrate the spacer layer 26 in the thickness direction. The lower surface 28b of the second solid electrolyte layer 28 is exposed at the upper part of the chambers 18a, 18b, 20, 21 and the upper surface 24a of the first solid electrolyte layer 24 is exposed at the lower part. The side portions of the vacant chambers 18a, 18b, 20 and 21 are partitioned by the spacer layer 26 or the diffusion rate controlling portions 30, 32, 34 and 36.

The first diffusion control part 30, the third diffusion control part 34, and the fourth diffusion control part 36 are each provided with two horizontally long slits. That is, the slit has slit-shaped openings extending in a direction perpendicular to the plane of the drawing in the upper and lower portions. Further, the second diffusion control part 32 is provided with one horizontally long slit.

A reference gas introduction space 38 is provided at the other end of the sensor element 12 (the end opposite to the end where the gas introduction port 16 is provided). The reference gas introduction space 38 is formed between the upper surface 22c1 of the third substrate 22c and the lower surface 26b of the spacer layer 26. The side portion of the reference gas introduction space 38 is partitioned by the side surface of the first solid electrolyte layer 24. For example, oxygen or the atmosphere is introduced into the reference gas introduction space 38 as a reference gas.

The gas introduction port 16 is a portion open to the external space, and the gas to be measured is taken into the sensor element 12 from the external space through the gas introduction port 16.

The first diffusion control part 30 is a part that imparts a predetermined diffusion resistance to the gas to be measured that is introduced from the gas inlet 16 into the spare chamber 21. The spare vacant chamber 21 will be described later.

The second diffusion control part 32 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the spare chamber 21 into the main chamber 18a.

The main chamber 18a is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced from the gas inlet 16. The oxygen partial pressure is adjusted by the operation of the main pump cell 40.

The main pump cell 40 is an electrochemical pump cell including a main pump electrode 42, an outer pump electrode 44, and an oxygen ion conductive solid electrolyte sandwiched therebetween, and is also called a main electrochemical pumping cell. The main pump electrode 42 is provided on each of the upper surface 24 a of the first solid electrolyte layer 24, the lower surface 28 b of the second solid electrolyte layer 28, and the side surface of the spacer layer 26, which partition the main empty space 18 a. The outer pump electrode 44 is formed on the upper surface of the second solid electrolyte layer 28. The position of the outer pump electrode 44 is preferably provided in a region corresponding to the main pump electrode 42 so as to be exposed to the external space. The main pump electrode 42 is preferably made of a material having a reduced reducing ability for nitrogen oxide (NO) components in the gas to be measured. For example, it can be configured as a rectangular porous cermet electrode in plan view.

The main pump cell 40 applies a first pump voltage Vp1 by a first variable power supply 46 provided outside the sensor element 12 to flow a first pump current Ip1 between the outer pump electrode 44 and the main pump electrode 42. This makes it possible to pump out oxygen in the main chamber 18a to the outside or pump oxygen in the external space into the main chamber 18a.

Further, the sensor element 12 has a first oxygen partial pressure detection sensor cell 50 which is an electrochemical sensor cell. The first oxygen partial pressure detection sensor cell 50 includes a main pump electrode 42, a reference electrode 48, and an oxygen ion conductive first solid electrolyte layer 24 sandwiched between these electrodes. The reference electrode 48 is an electrode formed between the first solid electrolyte layer 24 and the third substrate 22c, and is made of the same porous cermet as the outer pump electrode 44. The reference electrode 48 is formed in a rectangular shape in plan view. A reference gas introduction layer 52 made of porous alumina and connected to the reference gas introduction space 38 is provided around the reference electrode 48. The reference gas in the reference gas introduction space 38 is introduced into the surface of the reference electrode 48 via the reference gas introduction layer 52. The first oxygen partial pressure detection sensor cell 50 is disposed between the main pump electrode 42 and the reference electrode 48 due to the oxygen concentration difference between the atmosphere in the main chamber 18a and the reference gas in the reference gas introduction space 38. 1 Electromotive force V1 is generated.

The first electromotive force V1 generated in the first oxygen partial pressure detection sensor cell 50 changes according to the oxygen partial pressure of the atmosphere existing in the main chamber 18a. The sensor element 12 feedback-controls the first variable power supply 46 of the main pump cell 40 by the first electromotive force V1. As a result, the first pump voltage Vp1 applied to the main pump cell 40 by the first variable power supply 46 can be controlled according to the oxygen partial pressure of the atmosphere in the main chamber 18a.

The fourth diffusion rate controlling unit 36 imparts a predetermined diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 40 in the main empty chamber 18a, and subordinates the measured gas. This is a part that leads to the vacant chamber 18b.

In the sub-chamber 18b, after the oxygen concentration (oxygen partial pressure) in the main chamber 18a is adjusted in advance, the oxygen partial pressure by the auxiliary pump cell 54 is further added to the measured gas introduced through the fourth diffusion control section 36. It is provided as a space for making adjustments. As a result, the oxygen concentration in the sub-chamber 18b can be kept constant with high precision, and the NOx concentration can be measured with high precision.

The auxiliary pump cell 54 is an electrochemical pump cell, and is provided on the lower surface 28b of the second solid electrolyte layer 28 in a substantially entire area facing the sub-chamber 18b, the outer pump electrode 56, and the second solid electrode. And an electrolyte layer 28. The auxiliary pump electrode 56 is also formed of a material having a reduced ability to reduce NOx components in the gas to be measured, like the main pump electrode 42.

By applying a desired second pump voltage Vp2 between the auxiliary pump electrode 56 and the outer pump electrode 44, the auxiliary pump cell 54 pumps out oxygen in the atmosphere in the sub-chamber 18b to the external space or externally. It can be pumped into the sub-chamber 18b from the space.

Further, in order to control the oxygen partial pressure in the atmosphere in the sub-chamber 18b, the auxiliary pump electrode 56, the reference electrode 48, the second solid electrolyte layer 28, the spacer layer 26, and the first solid electrolyte layer 24. And form an electrochemical sensor cell. That is, the second oxygen partial pressure detection sensor cell 58 for controlling the auxiliary pump is configured.

The second oxygen partial pressure detection sensor cell 58 is provided between the auxiliary pump electrode 56 and the reference electrode 48 due to the oxygen concentration difference between the atmosphere in the sub-chamber 18b and the reference gas in the reference gas introduction space 38. The second electromotive force V2 is generated. The second electromotive force V2 generated in the second oxygen partial pressure detection sensor cell 58 changes according to the oxygen partial pressure of the atmosphere existing in the sub-chamber 18b.

The sensor element 12 controls the second variable power source 60 based on the second electromotive force V2 to pump the auxiliary pump cell 54. As a result, the oxygen partial pressure in the atmosphere inside the sub-chamber 18b is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

Along with this, the second pump current Ip2 of the auxiliary pump cell 54 is used to control the second electromotive force V2 of the second oxygen partial pressure detection sensor cell 58. Specifically, the second pump current Ip2 is input to the second oxygen partial pressure detection sensor cell 58 as a control signal. As a result, the second electromotive force V2 is controlled so that the gradient of the oxygen partial pressure in the measured gas introduced into the sub-chamber 18b through the fourth diffusion control section 36 is controlled to be always constant. When the gas sensor 10 is used as a NOx sensor, the oxygen concentration in the sub-chamber 18b is accurately maintained at a predetermined value under each condition by the functions of the main pump cell 40 and the auxiliary pump cell 54.

The third diffusion rate controlling unit 34 imparts a predetermined diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 54 in the sub-chamber 18b to measure the measured gas. This is a part that leads to the chamber 20.

The measurement of the NOx concentration is performed mainly by the operation of the measurement pump cell 61 provided in the measurement chamber 20. The measurement pump cell 61 is an electrochemical pump cell configured by the measurement electrode 62, the outer pump electrode 44, the second solid electrolyte layer 28, the spacer layer 26, and the first solid electrolyte layer 24. The measurement electrode 62 is provided, for example, on the upper surface 24a of the first solid electrolyte layer 24 in the measurement chamber 20, and is made of a material having a higher reducing ability for the NOx component in the measurement gas than the main pump electrode 42. The measurement electrode 62 can be, for example, a porous cermet electrode. Further, it is preferable that the measurement electrode 62 uses a material that also functions as a NOx reduction catalyst that reduces NOx existing in the atmosphere.

The measurement pump cell 61 decomposes nitrogen oxide around the measurement electrode 62 in the measurement chamber 20 to generate oxygen. Further, the measuring pump cell 61 can pump out oxygen generated at the measuring electrode 62 and detect the amount of generated oxygen as the measuring pump current Ip3, that is, the sensor output.

Further, in order to detect the oxygen partial pressure around the measurement electrode 62 in the measurement chamber 20, the first solid electrolyte layer 24, the measurement electrode 62, and the reference electrode 48 form an electrochemical sensor cell, that is, measurement. A third oxygen partial pressure detection sensor cell 66 for controlling the pump is configured. The third variable power supply 68 is controlled based on the third electromotive force V3 detected by the third oxygen partial pressure detection sensor cell 66.

The gas to be measured guided to the sub-chamber 18b reaches the measurement electrode 62 in the measurement chamber 20 through the third diffusion rate controlling unit 34 under the condition that the oxygen partial pressure is controlled. Nitrogen oxide in the measured gas around the measurement electrode 62 is reduced to generate oxygen. The oxygen generated here is pumped by the measuring pump cell 61. At that time, the third pump voltage Vp3 of the third variable power supply 68 is controlled so that the third electromotive force V3 detected by the third oxygen partial pressure detection sensor cell 66 becomes constant. The amount of oxygen generated around the measuring electrode 62 is proportional to the nitrogen oxide concentration in the gas to be measured. Therefore, the measurement pump current Ip3 of the measurement pump cell 61 can be used to calculate the nitrogen oxide concentration in the measured gas. That is, the measurement pump cell 61 constitutes the specific component measuring means 104 for measuring the concentration of the specific component (NO) in the measurement chamber 20.

Moreover, the gas sensor 10 has an electrochemical sensor cell 70. The sensor cell 70 includes a second solid electrolyte layer 28, a spacer layer 26, a first solid electrolyte layer 24, a third substrate 22c, an outer pump electrode 44, and a reference electrode 48. The electromotive force Vref obtained by the sensor cell 70 can detect the oxygen partial pressure in the gas to be measured outside the sensor.

Further, in the sensor element 12, the heater 72 is formed so as to be sandwiched between the second substrate 22b and the third substrate 22c from above and below. The heater 72 generates heat by being supplied with electric power from the outside via a heater electrode (not shown) provided on the lower surface 22a2 of the first substrate 22a. When the heater 72 generates heat, the oxygen ion conductivity of the solid electrolyte forming the sensor element 12 is enhanced. The heater 72 is buried over the entire area of the spare chamber 21, the oxygen concentration adjusting chamber 18, and the measurement chamber 20, so that a predetermined place of the sensor element 12 can be heated and kept at a predetermined temperature. Is becoming A heater insulating layer 74 made of alumina or the like is formed above and below the heater 72 for the purpose of obtaining electrical insulation from the second substrate 22b and the third substrate 22c. Hereinafter, the heater 72, the heater electrode, and the heater insulating layer 74 are collectively referred to as a heater section.

The spare chamber 21 is driven by the drive control unit 108 (see FIG. 2) described later, and is a space for adjusting the oxygen partial pressure in the measured gas introduced from the gas introduction port 16 during the driving. Function. The oxygen partial pressure is adjusted by operating the auxiliary pump cell 80.

The preliminary pump cell 80 is configured by a preliminary pump electrode 82 provided on the lower surface 28 b of the second solid electrolyte layer 28 substantially in the entire area facing the preliminary chamber 21, an outer pump electrode 44, and the second solid electrolyte layer 28. It is an electrochemical pump cell.

As with the main pump electrode 42, the auxiliary pump electrode 82 is also made of a material having a reduced ability to reduce NOx components in the gas to be measured.

The preliminary pump cell 80 pumps out oxygen in the atmosphere in the preliminary vacant chamber 21 to the external space or external space by applying a desired preliminary voltage Vp0 between the preliminary pump electrode 82 and the outer pump electrode 44. Therefore, it is possible to pump oxygen into the spare space 21.

Further, the gas sensor 10 has a preliminary oxygen partial pressure detection sensor cell 84 for controlling a preliminary pump in order to control the oxygen partial pressure in the atmosphere in the preliminary empty chamber 21. This preliminary oxygen partial pressure detection sensor cell 84 has a preliminary pump electrode 82, a reference electrode 48, a second solid electrolyte layer 28, a spacer layer 26, and a first solid electrolyte layer 24. The preliminary oxygen partial pressure detection sensor cell 84 preliminarily generates an electromotive force between the preliminary pump electrode 82 and the reference electrode 48, which is generated by the difference between the oxygen concentration in the atmosphere in the preliminary chamber 21 and the oxygen concentration in the reference gas. It is detected as electric power V0.

Note that the auxiliary pump cell 80 performs pumping by the auxiliary variable power supply 86 whose voltage is controlled based on the auxiliary electromotive force V0 detected by the auxiliary oxygen partial pressure detection sensor cell 84. As a result, the oxygen partial pressure in the atmosphere in the spare chamber 21 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

Along with this, the preliminary pump current Ip0 is used to control the preliminary electromotive force V0 of the preliminary oxygen partial pressure detection sensor cell 84. Specifically, the preliminary pump current Ip0 is input to the preliminary oxygen partial pressure detection sensor cell 84 as a control signal, and the preliminary electromotive force V0 thereof is controlled, so that the preliminary diffusion current Ip0 is transferred from the first diffusion rate controlling unit 30 into the preliminary chamber 21. The gradient of the oxygen partial pressure in the measured gas introduced is controlled so that it is always constant.

The spare vacant chamber 21 also functions as a buffer space. That is, it is possible to cancel the fluctuation in the concentration of the gas to be measured caused by the fluctuation in the pressure of the gas to be measured in the external space. Examples of such pressure fluctuations of the gas to be measured include pulsation of exhaust pressure of exhaust gas of an automobile.

Further, the gas sensor 10 controls the temperature of the oxygen concentration control means 100 (main oxygen concentration control means) for controlling the oxygen concentration in the oxygen concentration adjusting chamber 18 and the temperature of the sensor element 12, as schematically shown in FIG. Temperature control means 102, specific component measuring means 104 for measuring the concentration of a specific component (NO or NH ₃ ) in the measurement chamber 20, preliminary oxygen concentration control means 106, drive control means 108, target component acquisition means. 110 and.

The oxygen concentration control means 100, the temperature control means 102, the specific component measurement means 104, the preliminary oxygen concentration control means 106, the drive control means 108, and the target component acquisition means 110 are, for example, one or a plurality of CPUs (central processing units). And one or more electronic circuits having a storage device and the like. The electronic circuit is also a software function unit in which a predetermined function is realized by the CPU executing a program stored in a storage device, for example. Of course, an integrated circuit such as an FPGA (Field-Programmable Gate Array) in which a plurality of electronic circuits are connected according to their functions may be used.

The gas sensor 10 includes, in addition to the oxygen concentration adjusting chamber 18, the oxygen concentration controlling means 100, the temperature controlling means 102, and the specific component measuring means 104, the spare chamber 21, the spare oxygen concentration controlling means 106, the drive controlling means 108, and the purpose. By providing the component acquisition means 110, it is possible to acquire each concentration of NO (nitrogen oxide) and NH ₃ (ammonia).

The oxygen concentration control means 100 feedback-controls the first variable power supply 46 based on a preset oxygen concentration condition and the first electromotive force V1 generated in the first oxygen partial pressure detection sensor cell 50 (see FIG. 1). Then, the oxygen concentration in the oxygen concentration adjusting chamber 18 is adjusted to the concentration according to the above conditions.

The temperature control unit 102 feedback-controls the heater 72 based on a preset sensor temperature condition and a measurement value from a temperature sensor (not shown) that measures the temperature of the sensor element 12, thereby the sensor The temperature of the element 12 is adjusted to the temperature according to the above conditions.

The gas sensor 10 is controlled by the oxygen concentration control means 100 and the temperature control means 102 so that all NH ₃ is converted to NO without decomposing NO in the oxygen concentration control chamber 18. Control the state of.

The specific component measuring means 104 detects and outputs the measurement pump current Ip3 flowing between the measurement electrode 62 and the outer pump electrode 44. Further, the specific component measuring means 104 obtains the time change rate dIp3/dt of the measured pump current Ip3 after the switching of the auxiliary pump cell 80, and detects the peak value thereof. Furthermore, the specific component measuring means 104 refers to the second map 114 to obtain the change amount ΔIp3 from the peak value of the time change rate dIp3/dt of the measured pump current Ip3 to the steady value of the measured pump current Ip3, and the change thereof. The steady value (predicted value) of the measured pump current Ip3 is obtained by adding the amount ΔIp3 to the measured pump current Ip3 before switching. The second map 114 shows that the steady-state value of the measured pump current Ip3 is set at each point specified by the peak value of the time change rate dIp3/dt of the measured pump current Ip3 that accompanies the ON/OFF switching of the auxiliary pump cell 80. Up to the change amount ΔIp3 are included in the data group. Further, the second map 114 shows that NH _{3 in the} gas to be measured is specified for each point specified by the peak value of the time rate of change dIp3/dt of the measured pump current Ip3 due to the ON/OFF switching of the auxiliary pump cell 80. It may further include a data group in which the relationship with the density is registered. As the data group registered in the second map 114, the relationship obtained in advance by experiments or simulations is used.

The preliminary oxygen concentration control unit 106 feedback-controls the preliminary variable power supply 86 based on the preset oxygen concentration condition and the preliminary electromotive force V0 generated in the preliminary oxygen partial pressure detection sensor cell 84 (see FIG. 1). Thus, the oxygen concentration in the spare chamber 21 is adjusted to the concentration according to the conditions.

Then, the target component acquisition unit 110 outputs the sensor output from the specific component measuring unit 104 according to the first operation of the preliminary oxygen concentration control unit 106 and the sensor output from the specific component measuring unit 104 according to the second operation of the preliminary oxygen concentration control unit 106. Each concentration of NO and NH ₃ is acquired based on the difference from the output.

Here, by the preliminary voltage Vp0 applied to the preliminary pump electrode 82 by the preliminary oxygen concentration control means 106, NO and NH ₃ in the gas to be measured change as follows.

First, in the first voltage range, NH ₃ in the spare chamber 21 is kept as NH ₃ . NH ₃ in the spare chamber 21 remains in the NH _{3 state} and passes through the second diffusion rate controlling unit 32 to reach the oxygen concentration adjusting chamber 18. Further, NO in the spare chamber 21 passes through the second diffusion rate controlling unit 32 as it is, and reaches the oxygen concentration adjusting chamber 18.

In the second voltage range, NH ₃ in the spare chamber 21 is oxidized into NO, passes through the second diffusion control part 32, and reaches the oxygen concentration adjusting chamber 18. Further, NO passes through the second diffusion rate controlling unit 32 as it is, and reaches the oxygen concentration adjusting chamber 18.

The preliminary oxygen concentration control means 106 applies the first voltage Va as the preliminary voltage Vp0 during the first operation, and outputs the second voltage Vb as the preliminary voltage Vp0 during the second operation. In addition, depending on the oxygen concentration of the gas to be measured, oxygen may be pumped into the spare chamber 21, and in that case, the first voltage Va may take a negative value. When oxygen is not pumped out or pumped into the spare chamber 21, the first voltage Va may be Voff.

As described above, during the first operation, the NH ₃ component remains NH ₃ and passes through the second diffusion rate controlling unit 32, and is reflected in the measured pump current (sensor output) Ip3. Further, during the second operation, the NH ₃ component passes through the second diffusion rate controlling unit 32 as NO and is reflected in the measured pump current (sensor output) Ip3. Since NH ₃ can diffuse through the second diffusion rate controlling unit 32 faster than NO, the measured pump current (sensor output) Ip3 changes between the first operation and the second operation. The magnitude of the difference reflects the concentration of NH _{3 in} the measured gas. That is, the measured pump current (sensor output) Ip3 can be decomposed into the NO component and the NH ₃ component by utilizing the diffusion speed difference between NH ₃ and NO. Therefore, the gas sensor 10 obtains the concentrations of NO and NH ₃ based on the difference between the sensor output from the specific component measuring unit 104 according to the first operation and the second operation of the preliminary oxygen concentration control unit 106.

Next, the processing operation of the gas sensor 10 will be described with reference to FIGS. 3 and 4.

First, while the preliminary oxygen concentration control unit 106 is in the first operation by the drive control unit 108, as shown in FIG. 3, NH ₃ introduced through the gas introduction port 16 reaches the oxygen concentration adjustment chamber 18. In the oxygen concentration adjusting chamber 18, since the oxygen concentration controlling means 100 controls to convert all NH ₃ into NO, the NH ₃ flowing into the oxygen concentration adjusting chamber 18 from the reserve chamber 21 is oxygen concentration adjusting chamber. A reaction occurs in which NH ₃ is oxidized to NO in 18 and all NH ₃ in the oxygen concentration adjusting chamber 18 is converted to NO. Therefore, NH ₃ introduced through the gas inlet 16 passes through the first diffusion rate controlling unit 30 and the second diffusion rate controlling unit 32 with a diffusion coefficient of NH ₃ (for example, 2.2 cm ² /sec) to adjust the oxygen concentration. After being converted into NO in the chamber 18, it passes through the third diffusion control part 34 with a diffusion coefficient of NO (for example, 1.8 cm ² /sec) and moves into the adjacent measurement space 20.

On the other hand, during the period in which the preliminary oxygen concentration control unit 106 is in the second operation by the drive control unit 108, as shown in FIG. 4, an oxidation reaction of NH ₃ to NO occurs in the preliminary vacant chamber 21, and the gas introduction port 16 All NH ₃ introduced through is converted to NO. Therefore, NH ₃ passes through the first diffusion-controlling part 30 with the diffusion coefficient of NH ₃ , but after the second diffusion-controlling part 32 behind the spare space 21, it passes with the diffusion coefficient of NO, and the measurement space 20. Move to.

That is, when the preliminary oxygen concentration control unit 106 switches from the first operating state to the second operating state, the place where the NH ₃ oxidation reaction occurs moves from the oxygen concentration adjusting chamber 18 to the preliminary vacant chamber 21.

The fact that the location where the NH ₃ oxidation reaction occurs moves from the oxygen concentration adjusting chamber 18 to the preliminary vacant chamber 21 means that the state when NH ₃ in the measured gas passes through the second diffusion control part 32 is from NH ₃ to NO. Is equivalent to changing to. Since NO and NH ₃ have different diffusion coefficients, the difference between passing NO in the second diffusion control part 32 and passing in NH ₃ is the difference in the amount of NO flowing into the measurement chamber 20. The measured pump current Ip3 that appears and flows through the measuring pump cell 61 is changed.

In this case, the change amount ΔIp3 between the measured pump current Ip3 (Vb) during the second operation of the auxiliary pump cell 80 and the measured pump current Ip3 (Va) during the first operation of the auxiliary pump cell 80 is the measured gas. It is uniquely determined by the concentration of NH ₃ in the solution. Therefore, the concentrations of NO and NH ₃ can be calculated from the measured pump current Ip3 (Vb) or Ip3 (Va) and the change amount ΔIp3 of the measured pump current Ip3.

The target component acquisition means 110 uses the first map 112 of the measured pump current Ip3 (Va) during the first operation of the auxiliary pump cell 80 and the variation ΔIp3 of the measured pump current Ip3 during the first operation and the second operation. Based on this, the concentrations of NO and NH ₃ are obtained. The first map 112 is a data group showing a correlation between the change amount ΔIp3 and the NH ₃ concentration obtained in advance by an experiment or a simulation, and is composed of a plurality of data groups corresponding to a plurality of different NO concentrations. Based on the measured pump current Ip3off when the auxiliary pump cell 80 is OFF, the target component acquisition means 110 determines which NO concentration the change ΔIp3 corresponding to the correlation with the NH ₃ concentration should be used, and applies it. The NH ₃ concentration is identified based on the change amount ΔIp3.

Further, the target component acquisition means 110 obtains the relationship between the variation ΔIp3 and the NH ₃ concentration in advance by an experiment or a simulation, and obtains the NH ₃ concentration from the variation ΔIp3 when the auxiliary pump cell 80 is ON and OFF. Good. Then, the NO concentration obtained by subtracting the NH ₃ concentration obtained above is subtracted from the NO concentration obtained from the sensor output when the auxiliary pump cell 80 is OFF, that is, the total NO concentration obtained by converting all the concentrations of NO and NH ₃ into NO. May be asked.

Here, the acquisition process of the measured pump current Ip3 (sensor output) and the acquisition process of the target component by the target component acquisition unit 110 in the specific component measurement unit 104 of the gas sensor 10 as described above are illustrated in the flowchart of FIG. Description will be given with reference to the drawings.

First, in step S10 of FIG. 5, the gas sensor 10 switches the auxiliary pump cell 80 to ON (second operation). As a result, NH ₃ in the gas to be measured is converted into NO in the spare chamber 21 and passes through the second diffusion control part 32, and the difference in diffusion coefficient between NO and NH ₃ in the second diffusion control part 32 becomes. Based on this, the measured pump current Ip3 flowing through the measuring pump cell 61 changes.

Here, when the operating state of the auxiliary pump cell 80 is switched from OFF to ON, the measured pump current Ip3 is, as shown in FIG. 6, NO gas diffusion resistance, electrode reaction resistance on the measurement electrode surface, and each pump voltage control. After making a transient change due to the delay of, settles to a steady value. The time change rate dIp3/dt of the measured pump current Ip3 is large immediately after the switching, and changes so as to settle to a constant value over time. The time change rate dIp3/dt of the measured pump current Ip3 is substantially proportional to the amount of change ΔIp3 which is the difference between the measured pump current Ip3on when the auxiliary pump cell 80 is ON and the measured pump current Ip3off when the auxiliary pump cell 80 is OFF. To do. Therefore, in this embodiment, attention is paid to the time change rate dIp3/dt of the measured pump current Ip3.

That is, in step S20 of FIG. 5, the specific component measuring unit 104 acquires the peak value of the time change rate dIp3/dt of the measured pump current Ip3on. As shown in FIG. 6, the peak value of the time change rate dIp3/dt of the measured pump current Ip3on appears within 0.5 seconds after the switching of the operating state of the auxiliary pump cell 80 until the measured pump current Ip3on reaches a steady value. The result can be obtained faster than about 2 seconds.

After that, in step S30 of FIG. 5, the specific component measuring unit 104 determines the transient peak value of the time change rate dIp3/dt of the measured pump current Ip3on acquired in step S20 and the time change rate previously obtained by experiment or simulation. Based on the correlation between the peak value of dIp3/dt and the steady-state value of the measured pump current Ip3on, the predicted value of the steady-state value of the measured pump current Ip3on is obtained.

Then, in step S40, the gas sensor 10 switches off the auxiliary pump cell 80 (first operation). The time during which the standby pump cell 80 is continuously turned on from step S10 to step S30 can be shorter than the time until the measured pump current Ip3 settles to a steady value (for example, about 2 seconds), for example, about 0.5 seconds. Can be

When the operation state of the auxiliary pump cell 80 is switched from ON to OFF, NH ₃ in the measured gas in the auxiliary chamber 21 passes through the second diffusion rate controlling unit 32 as it is, and as shown in FIG. It is converted to NO in the concentration adjusting chamber 18. The measurement pump current Ip3 flowing in the measurement pump cell 61 changes based on the difference in the diffusion coefficient between NO and NH ₃ in the second diffusion control unit 32.

At this time, by switching the operating state of the auxiliary pump cell 80 from ON to OFF, the measured pump current Ip3 is transient due to the diffusion resistance of NO gas, the electrode reaction resistance on the surface of the measurement electrode, and the delay of each pump voltage control. After making a change, settles to a steady value. The time change rate dIp3/dt of the measured pump current Ip3 is approximately proportional to the amount of change ΔIp3 which is the difference between the measured pump current Ip3off when the backup pump cell 80 is OFF and the measured pump current Ip3on when the backup pump cell 80 is ON. To do. In step S50, the specific component measuring unit 104 measures the transient peak value of the time change rate dIp3/dt of the measured pump current Ip3off.

In the next step S60, the specific component measuring means 104, the transient peak value of the time change rate dIp3/dt of the measured pump current Ip3 obtained in step S50, and the time change rate dIp3/dt previously obtained by experiment or simulation. The predicted value of the steady-state value of the measured pump current Ip3off is obtained based on the correlation between the peak value of 1 and the steady-state value of the measured pump current Ip3.

In the next step S70, the target component acquisition means 110 determines the target component NH based on the measured pump current Ip3on obtained in step S30, the measured pump current Ip3off obtained in step S60, and their variation ΔIp3. ₃ concentration and NO concentration are acquired.

That is, if the target component acquisition means 110 uses the correlation between the change amount ΔIp3 and the NH ₃ concentration corresponding to any NO concentration in the first map 112, based on the measured pump current Ip3off when the preliminary pump cell 80 is OFF. Whether it is good or not is determined, and the NH ₃ concentration is identified based on the corresponding change amount ΔIp3. Then, NH ₃ target component acquiring unit 110, the NO concentration obtained from the sensor output at the time of OFF of the pre-pump cell 80, namely that all the concentrations of NO and NH ₃ from the total NO concentration converted to NO, obtained by the above-described The NO concentration is obtained by subtracting the concentration.

After that, in step S80, the gas sensor 10 checks whether or not there is an input for ending the measurement. If there is no input of measurement end, the process proceeds to step S10. In this case, the time taken to switch from step S40 to step S10 may be shorter than the time taken for the measured pump current Ip3 to reach a steady value, and can be set to, for example, about 0.5 seconds.

On the other hand, if it is determined in step S80 that there is an input to end the measurement, the gas sensor 10 ends the measurement.

As described above, according to the gas sensor 10 of the present embodiment, the switching cycle of the operation of the auxiliary pump cell 80 can be shortened, so that the measurement accuracy can be prevented from lowering due to the delay of the measurement time of the measurement pump current Ip3.

(Experimental example 1)
Hereinafter, an experimental example using the gas sensor 10 of the present embodiment will be described. In Experimental Example 1, six kinds of measured gases having NO concentration of 0 ppm and NH ₃ concentration of 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm and 500 ppm were supplied to the gas sensor 10, and the operation state of the auxiliary pump cell 80 was changed. The time rate of change of the measured pump current Ip3 when switching from OFF to ON was obtained.

As shown in FIG. 7, in Experimental Example 1, the operation state of the auxiliary pump cell 80 was switched at time 15 seconds. It was confirmed that the measured pump current Ip3on converges to a steady value in about 2 seconds regardless of the NH ₃ concentration in the measured gas. Further, it was confirmed that the slope of the measured pump current Ip3 tends to increase as the NH ₃ concentration increases.

When the rate of change of the measured pump current Ip3 with respect to each gas to be measured is obtained, as shown in FIG. 8, a peak value of the rate of time change appears about 0.5 seconds after the switching time of the standby pump cell 80 of 15 seconds, and the peak value thereof appears. The larger the change in the measured pump current Ip3on after switching, the larger the value. Further, it was confirmed that there is a certain correlation between the rate of change of the measured pump current Ip3 with time and the amount of change ΔIp3 of the measured pump current Ip3 after switching. Therefore, by obtaining the time change rate of the measured pump current Ip3, the steady value can be obtained before the measured pump current Ip3 converges to the steady value.

As shown in FIG. 9, the time change rate dIp3/dt of the measured pump current Ip3 changes substantially in proportion to the NH ₃ concentration in the measured gas. Therefore, the NH ₃ concentration in the measured gas can be directly obtained from the time change rate dIp3/dt of the measured pump current Ip3.

(Experimental example 2)
Next, in Experimental Example 2, six types of measured gases having NO concentration of 500 ppm and NH ₃ concentration of 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm were supplied to the gas sensor 10, and the preliminary pump cell 80 The time rate of change of the measured pump current Ip3 when the operating state was switched from OFF to ON was obtained.

As shown in FIG. 10, even when the NO concentration was 500 ppm, it was confirmed that the slope of the measured pump current Ip3 tended to increase as the NH ₃ concentration increased. Further, as shown in FIG. 11, it was confirmed that the peak value of the time change rate dIp3/dt of the measured pump current Ip3 takes a larger value as the changed change of the measured pump current Ip3on becomes larger. Therefore, it was confirmed from Experimental Example 2 that the measured pump current Ip3on (steady value) can be obtained from the peak value of the time change rate dIp3/dt of the measured pump current Ip3 even in the measured gas in which NO is mixed. Further, the peak value of the time change rate dIp3/dt of the measured pump current Ip3 can be obtained in about 0.5 seconds, and the measured pump current Ip3on is obtained without waiting until the measured pump current Ip3 converges to a steady value. Be done.

Further, as shown in FIG. 12, even in the measured gas in which NO is mixed, there is a correlation between the peak value of the time change rate dIp3/dt of the measured pump current Ip3 and the NH ₃ concentration in the measured gas. I was able to confirm that there is. Therefore, the NH ₃ concentration when NO is 500 ppm can also be directly obtained from the time change rate dIp3/dt of the measured pump current Ip3 based on the correlation of FIG.

(Experimental Example 3 and Comparative Example)
In order to confirm the effect of the gas sensor 10 and the gas concentration measuring method of the present embodiment, the case where the switching cycle of the operation state of the auxiliary pump cell 80 is set to 4 seconds (0.25 Hz) (comparative example) and 1 second (1 Hz). The difference in the measurement results in the case (Experimental Example 3) was confirmed by simulation calculation. The NO concentration and NH ₃ concentration of the measured gas are the results measured by the FT-IR method, and are shown by solid lines in FIGS. 13 and 14, respectively.

Here, the measured pump current Ip3on and the measured pump current Ip3off are approximately obtained by multiplying the NO concentration and the NH ₃ concentration by the FT-IR method by the respective unique coefficients and adding them. That is, the measurement pump current Ip3off, respectively were obtained by adding by multiplying a predetermined coefficient NO concentration by FT-IR method at time t1 to be measured (t1) and NH ₃ concentration (t1). The measured pump current Ip3on is obtained by multiplying the NO concentration (t2) and the NH ₃ concentration (t2) by the FT-IR method at time t2, which is a half cycle before the time t1, before the time t1 by multiplying them by a predetermined coefficient. I asked. Note that here, since attention is paid to variations in the measured pump current Ip3on and the measured pump current Ip3off, the values themselves of the coefficients by which the NO concentration and the NH ₃ concentration are multiplied may be appropriate. The NO concentration and the NH ₃ concentration obtained based on the first map 112 are plotted in FIGS. 13 and 14 with respect to the measured pump current Ip3off and the measured pump current Ip3on obtained by the above method.

When the switching cycle is 1 second (1 Hz) as in Experimental Example 3 in FIG. 13, the delay of the measurement time of the NO concentration and the NH ₃ concentration is suppressed to 0.5 seconds, and the deterioration of the measurement accuracy is suppressed. I understand.

On the other hand, as in the comparative example of FIG. 14, when the switching cycle is 4 seconds (0.25 Hz), the delay of the measurement time of the NO concentration and the NH ₃ concentration is about 2 seconds, which is obtained by the FT-IR method. It can be seen that a large error occurs in the measurement result.

The gas sensor 10 and the gas concentration measuring method of the present embodiment described above have the following effects.

In the gas sensor 10 and the gas concentration measuring method of the present embodiment, the preliminary oxygen concentration control means 106 (preliminary pump cell 80) performs the first operation (OFF) in a cycle shorter than the standby time until the measured pump current Ip3 converges to the steady value. ) And the second operation (ON). As a result, the measurement cycle is shortened, so that it is possible to suppress a decrease in measurement accuracy due to a delay in measurement time.

(Second embodiment)
Another example of the acquisition processing of the measured pump current Ip3 (sensor output) in the specific component measuring means 104 of the gas sensor 10 and the acquisition processing of the target component by the target component acquiring means 110 will be described.

As shown in FIGS. 9 and 12, the peak value of the time change rate dIp3/dt of the measured pump current Ip3 has a correlation with the NH ₃ concentration in the measured gas. Therefore, in this embodiment, the specific component measurement unit 104, the correlation between the NH ₃ concentration of the peak value and the measurement gas time rate of change DIP3 / dt of the measuring pumping current Ip3, directly obtained NH ₃ concentration.

As shown in the flowchart of FIG. 15, in step S110, the gas sensor 10 switches the operation state of the auxiliary pump cell 80 to ON. Then, in step S120, the specific component measuring unit 104 obtains the peak value of the time change rate dIp3/dt of the measured pump current Ip3on.

After that, in step S130, the specific component measuring unit 104 refers to the second map 114 to obtain the NH ₃ concentration in the measured gas from the peak value of the time change rate dIp3/dt of the measured pump current Ip3.

Next, in step S140, the gas sensor 10 switches the operation state of the auxiliary pump cell 80 to OFF. Then, in step S150, the specific component measuring unit 104 acquires the peak value of the time change rate dIp3/dt of the measured pump current Ip3off.

Next, in step S160, the specific component measuring unit 104 obtains a steady-state measured pump current Ip3off (predicted value) from the peak value of the time change rate dIp3/dt of the measured pump current Ip3 acquired in step S150.

Then, in step S170, the target component acquisition unit 110 obtains the total NO concentration from the measured pump current Ip3off (predicted value), and subtracts the NH ₃ concentration obtained in step S130 from this total NO concentration, thereby measuring The NO concentration that is the target component in the gas is acquired.

Next, in step S180, the gas sensor 10 detects the presence/absence of a measurement end input, and if there is no measurement end input, the flow returns to step S110 to continue the measurement, and the measurement end input is performed. In that case, the measurement is terminated.

As described above, in the gas sensor 10 and the gas concentration measuring method of the present embodiment, the specific component measuring means 104 is experimentally measured in advance, and the preliminary oxygen concentration control means 106 (preliminary pump cell 80) is in the first operation and in the first operation. The second map 114 in which the relationship with the concentration of the specific component in the measured gas is registered at each point specified by the peak value of the time change rate dIp3/dt of the measured pump current Ip3 due to the switching of the operation between the two operations. , The peak value of the time change rate dIp3/dt of the measured pump current Ip3 from the specific component measuring means 104 in the operation switching of the preliminary oxygen concentration control means 106 (preliminary pump cell 80) in actual use, and the second map 114. The concentration of the specific component (NH ₃ ) in the measurement gas may be acquired by comparing with.

Although the present invention has been described above with reference to the preferred embodiments, the present invention is not limited to the above embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. Yes.

10... Gas sensor 12... Sensor element 14... Structure 16... Gas inlet 18... Oxygen concentration adjusting chamber 20... Measurement chamber 21... Spare chamber 42... Main pump electrode 44... Outer pump electrode 48... Reference electrode 62... Measurement electrode 100... Oxygen concentration control means 104... Specific component measuring means 106... Preliminary oxygen concentration control means 108... Drive control means 110... Target component acquisition means 112... First map 114... Second map

Claims (10)

A gas sensor for measuring the concentration of multiple components in the presence of oxygen,
A structure composed of a solid electrolyte having oxygen ion conductivity,
A gas inlet formed in the structure, the gas to be measured is introduced,
A spare chamber having a spare pump electrode and communicating with the gas inlet,
An oxygen concentration adjusting chamber having a pump electrode and communicating with the spare chamber,
Having a measurement electrode, and a measurement chamber communicating with the oxygen concentration adjustment chamber,
Preliminary oxygen concentration control means for controlling the oxygen concentration in the preliminary chamber based on the voltage of the preliminary pump electrode,
Specific component measuring means for detecting a measured pump current (Ip3) flowing through the outer pump electrode and the measuring electrode under the operation of the preliminary oxygen concentration control means;
The measured pump current (Ip3on) from the specific component measuring unit during the first operation of the preliminary oxygen concentration control unit and the measured pump current (Ip3off) from the specific component measuring unit during the second operation of the preliminary oxygen concentration control unit. ) With the change amount (ΔIp3), and one of the measured pump current (Ip3on) and the measured pump current (Ip3off), the target component acquisition means for acquiring the concentration of the target component in the measured gas. Prepare,
The specific component measuring means determines the measured pump current (Ip3) based on the peak value of the time change rate of the measured pump current (Ip3) at the time of switching the operation between the first operation and the second operation of the preliminary oxygen concentration control means. A gas sensor for obtaining a steady value of Ip3on) or a steady value of the measured pump current (Ip3off). The gas sensor according to claim 1, wherein the preliminary oxygen concentration control means switches the operation between the first operation and the second operation in a cycle shorter than a standby time until the measured pump current converges to a steady value. , Gas sensor. The gas sensor according to claim 1 or 2, wherein
The specific component measuring means,
A point specified by the peak value of the time change rate of the measured pump current (Ip3) accompanying the operation switching between the first operation and the second operation of the preliminary oxygen concentration control means, which is experimentally measured in advance, and the gas to be measured. Use the map that registered the relationship with the concentration of specific components in
In the gas under measurement, the peak value of the time change rate of the measured pump current (Ip3) from the specific component measuring means in the operation switching of the preliminary oxygen concentration control means during actual use is compared with the map. A gas sensor that obtains the concentration of a specific component of. The gas sensor according to claim 3, wherein the specific component is NH ₃ . The gas sensor according to any one of claims 1 to 4, wherein:
The gas sensor, wherein the oxygen concentration adjusting chamber includes a main vacant chamber and a sub vacant chamber, the main vacant chamber communicating with the preliminary vacant chamber, and the sub vacant chamber communicating with the measurement vacant chamber. A structure made of an oxygen ion conductive solid electrolyte, a gas inlet formed in the structure, into which a gas to be measured is introduced, and a spare pump electrode, and a spare chamber communicating with the gas inlet. An oxygen concentration adjusting chamber having a pump electrode and communicating with the spare chamber, a measuring chamber having a measuring electrode and communicating with the oxygen concentration adjusting chamber, and the spare unit based on the voltage of the spare pump electrode. Preliminary oxygen concentration control means for controlling the oxygen concentration in the chamber, and specific component measuring means for detecting the measured pump current (Ip3) flowing through the outer pump electrode and the measurement electrode under the operation of the preliminary oxygen concentration control means. And a measured pump current (Ip3on) from the specific component measuring means during the first operation of the preliminary oxygen concentration control means and a measured pump current from the specific component measuring means during the second operation of the preliminary oxygen concentration control means. And a target component acquisition means for acquiring the concentration of the target component in the gas to be measured, based on the amount of change (ΔIp3) from (Ip3off) and one of the measured pump current (Ip3on) and the measured pump current (Ip3off). A method for measuring gas concentration using a gas sensor having,
An operation switching step of performing switching control between the first operation and the second operation of the preliminary oxygen concentration control means;
A step in which the specific component measuring means obtains a peak value of a time change rate of the measured pump current (Ip3) accompanying switching control between the first operation and the second operation of the preliminary oxygen concentration control means;
From the correlation between the peak value of the temporal change rate of the measured pump current (Ip3) and the steady value of the measured pump current (Ip3), the specific component measuring means determines the steady state of the measured pump current (Ip3). The step of finding the value,
The target component acquiring unit acquires the concentration of the target component in the gas to be measured based on a steady value of the measurement pump current (Ip3) from the specific component measuring unit,
And a gas concentration measuring method. The gas concentration measuring method according to claim 6, wherein switching control between the first operation and the second operation of the preliminary oxygen concentration control means is performed until the measured pump current (Ip3) converges to a steady value. A gas concentration measurement method that is repeatedly performed in a cycle shorter than time. 7. The gas concentration measuring method according to claim 6, wherein the specific component measuring means is experimentally measured in advance, and the measuring pump is accompanied by switching between the first operation and the second operation of the preliminary oxygen concentration control means. Using the second map in which the relationship between the point specified by the peak value of the time change rate of the current (Ip3) and the concentration of the specific component in the measured gas is registered, the preliminary oxygen concentration control means in actual use is used. The peak value of the rate of change over time of the measured pump current (Ip3) from the specific component measuring means in the operation switching of step 2 is compared with the second map to obtain the concentration of the specific component in the measured gas. A gas concentration measuring method having a specific component acquisition step. The gas concentration measuring method according to claim 8, wherein the specific component is NH ₃ . The gas concentration measuring method according to any one of claims 6 to 9,
The gas concentration measuring method, wherein the oxygen concentration adjusting chamber includes a main vacant chamber and a sub vacant chamber, the main vacant chamber communicating with the preliminary vacant chamber, and the sub vacant chamber communicating with the measurement vacant chamber.