JP7379243B2 - Gas sensor inspection device, gas sensor inspection method, and reference sensor - Google Patents

Description

The present invention relates to a gas sensor testing device, a gas sensor testing method, and a reference sensor.

The sensor element testing device described in Patent Document 1 aims to provide a testing device that has excellent testing efficiency and can perform highly reliable testing.

In order to solve this problem, the inspection device and inspection method described in Patent Document 1 prepares a chamber including an element insertion/removal section, a tapered section, and a gas introduction section. The element insertion/removal section is a substantially cylindrical body whose one end is an opening opened to the outside and whose other end is a bottomed end, and is a substantially cylindrical space continuing from the opening. The tapered portion is a space that is connected to the element insertion/removal portion, and has a tapered cross-sectional view in which the cross section perpendicular to the longitudinal direction becomes larger toward the inside. The gas introduction section is a substantially cylindrical space that is continuous from the tapered section to the bottom.

Then, with the sensor element inserted into the chamber so that the tip reaches the tapered part while leaving a gap between the sensor element and the chamber, the chamber is inspected from a predetermined gas supply means through the supply port provided in the gas introduction section. Electrical measurements of the sensor element are performed while supplying test gas and allowing the test gas to flow out from the gap.

The gas sensor described in Patent Document 2 aims to further suppress a decrease in sensitivity of a measurement electrode in a sensor element.

In order to solve this problem, the gas sensor described in Patent Document 2 is provided with a diffusion-limiting section, and the diffusion-limiting section is located on the upper side, which is one or more and three or less of the upper, lower, left, and right inner circumferential surfaces of the gas distribution section to be measured. It is formed between the surface and the partition wall. The measurement electrode is formed on a lower surface of the upper, lower, left, and right inner circumferential surfaces of the third internal cavity, which is a surface in a different direction from the surface on which the diffusion-limiting portion is formed.

Patent No. 4944972 Japanese Patent Application Publication No. 2015-200642

By the way, a model gas generation device is required to evaluate the characteristics of a gas sensor such as a _NOx sensor. The model gas generation device can create a mixed gas of any concentration by adjusting the balance of multiple gases with flow rate regulators (for example, mass flow controllers) connected to respective pipes. Variations in the gas concentration of the mixed gas depend on the accuracy of the flow regulator. Since the flow rate regulator varies the flow rate, it also introduces control errors. When there are many types of gases to be mixed, multiple flow rate adjustment devices are used, which increases the error and does not improve the gas concentration accuracy in principle.

Further, in the manufacturing process of the gas sensor, an inspection process is performed after manufacturing to test the performance of the gas sensor in detecting a specific gas concentration. It is conceivable to use, for example, the gas sensor described in Patent Document 1 as a measuring device for measuring the specific gas concentration in the test gas before the inspection process. However, measurement accuracy may be low, and as a result, a span gas whose specific gas concentration deviates from a desired value may be prepared.

The present invention has been made in consideration of such problems, and an object of the present invention is to provide a gas sensor testing device, a gas sensor testing method, and a reference sensor that can reduce the concentration error of mixed gas.

A first aspect of the present invention includes a chamber in which at least one sensor element is mounted, and a gas supply means for supplying a predetermined test gas to the chamber, and the gas supply means includes a plurality of gas a supply source, a plurality of switches connected correspondingly to each of the gas supply sources, a plurality of fixed flow rate nozzles each having a different flow rate and connected to each of the gas supply sources, and a plurality of the gas supplies. and a mixer for mixing multiple gases from the source.

A second aspect of the present invention is a gas sensor testing method for testing a gas sensor by supplying a predetermined testing gas to a chamber in which at least one sensor element is installed, in which each gas is output from a plurality of gas supply sources. sending the plurality of gases from the plurality of switches to a plurality of switches connected correspondingly to each of the gas supply sources; , a step of sending the gases to a plurality of fixed flow rate nozzles each having a different flow rate, a step of mixing a plurality of gases from the plurality of fixed flow rate nozzles in a mixer, and a step of supplying the mixed gas from the mixer to the chamber. , has.

A third aspect of the present invention is a test device that is used in the gas sensor inspection device according to the first aspect, in which either oxygen or NOx is used as a specific gas, and the specific gas and base gas are used without the other. A reference sensor for detecting a specific gas concentration, which is the concentration of the specific gas in the gas to be measured, using a gas to be measured, the sensor element having a structure made of an oxygen ion conductive solid electrolyte; a diffusion rate-limiting part for rate-limiting diffusion in the gas introduction part to the sensor element; a gas introduction port formed in the structure and into which the gas to be measured is introduced; and a main cavity communicating with the gas introduction port. , a first outer electrode disposed outside the structure so as to be in contact with the gas to be measured and containing a noble metal having catalytic activity; and a first outer electrode disposed outside the structure so as to be in contact with the gas to be measured. a second outer electrode containing a catalytically active noble metal; a measurement electrode disposed inside the main cavity and containing a catalytically active noble metal; formed on the structure, into which a reference gas is introduced; By applying a constant voltage between the reference gas introduction space, the reference electrode formed in the reference gas introduction space, the first outer electrode, and the measurement electrode, the limit of the flow between the first outer electrode and the measurement electrode is established. a first concentration detection section that detects the concentration of a specific gas based on current; and a second concentration detection section that detects the concentration of the specific gas based on a Nernst electromotive force due to a concentration difference between the second outer electrode and the reference electrode. It has a detection part.

According to the first aspect, second aspect, or third aspect of the present invention, it is possible to reduce the concentration error of the mixed gas.

FIG. 2 is a cross-sectional view showing an example of a sensor element used in the testing device and testing method according to the present embodiment. FIG. 1 is a block diagram showing an example of the configuration of an inspection device according to the present embodiment. FIG. 2 is a block diagram showing an inspection device according to a comparative example. It is a graph showing the difference in accuracy depending on the flow rate of a flow rate regulator (mass flow controller). Table 1 shows the concentration accuracy errors of each gas and the accuracy errors of mixed gas with respect to the set concentration when using the inspection device according to the comparative example. 2 is Table 2 showing concentration accuracy errors of each gas and accuracy errors of mixed gas with respect to set concentrations when the inspection apparatus according to Example 1 is used. FIG. 2 is a cross-sectional view showing an example of a reference sensor used in the testing device and testing method according to the present embodiment. FIG. 3 is an explanatory diagram showing the electrical connection relationship of the heater section of the reference sensor. FIG. 2 is a block diagram showing a connection relationship between a control device and a sensor element. FIG. 10A is a plan view showing a first example of the arrangement relationship between the first outer electrode and the second outer electrode, and FIG. 10B is a plan view showing a second example of the arrangement relationship between the first outer electrode and the second outer electrode. 10C is a plan view showing a third example of the arrangement relationship between the first outer electrode and the second outer electrode. FIG. 11A is a cross-sectional view showing an example of the diffusion-limiting section of the gas flow section to be measured, and FIG. 11B is a cross-sectional view showing another example of the diffusion-limiting section. It is a graph showing the relationship between control voltage and pump current. Graph showing the relationship between the actual concentration of the test gas (NO concentration: 500 ppm) for each number of measurements detected by the gas sensor of Example 2, and the NO concentration for each number of measurements detected by the gas sensor of Comparative Example 2. It is. 14 is a graph showing the relationship between the measurement variations of Example 2 and the measurement variations of Comparative Example 2, based on the results of FIG. 13.

Embodiments of a gas sensor testing device, a gas sensor testing method, and a reference sensor according to the present invention will be described below with reference to FIGS. 1 to 14.

First, as shown in FIG. 1, the sensor element 14 of the gas sensor 12 to which the gas sensor inspection device (hereinafter referred to as inspection device 10) according to the present embodiment is applied is mainly made of zirconia, which is an oxygen ion conductive solid electrolyte. This is a NOx sensor constructed using ceramics as a structural material.

In the sensor element 14, a first internal cavity 16 communicates with a gas inlet 22 opened to the external space through a first diffusion-limiting part 18 and a second diffusion-limiting part 20, and a second internal cavity 24 communicates with a third diffusion-limiting part 22. This is a so-called serial two-chamber structure type NOx sensor element, which is configured to communicate with the first internal cavity 16 through the rate-limiting section 26 . Using this sensor element 14, the following process is executed to calculate the NOx gas concentration in the gas to be measured.

First, the gas to be measured introduced into the first internal cavity 16 passes through the outer pump electrode 30 provided on the outer surface of the sensor element 14 and the inner pump electrode 32 provided in the first internal cavity 16, and both of them. The oxygen concentration is adjusted to a substantially constant level by the pumping action (pumping in or pumping out oxygen) of the main pump cell, which is an electrochemical pump cell constituted by the ceramic layer 34 between the electrodes, and then the second internal cavity is heated. It will be introduced on 24th. In the second internal cavity 24, it is composed of an outer pump electrode 30, which is also an electrochemical pump cell, an auxiliary pump electrode 36 provided in the second internal cavity 24, and a ceramic layer 38 between both electrodes. Due to the pumping action of the auxiliary pump cell, the oxygen in the gas to be measured is pumped out, and the gas to be measured is brought into a sufficiently low oxygen partial pressure state.

NOx in the gas to be measured in a low oxygen partial pressure state is reduced or decomposed at the measurement electrode 42 provided in the second internal cavity 24 so as to be covered with the protective layer 40 . Oxygen ions generated by this reduction or decomposition are formed by a measuring electrode 42, a reference electrode 48 provided in a porous alumina layer 46 communicating with a reference gas inlet 44, and a ceramic layer 50 between the two. It is pumped by a measuring pump cell, which is an electrochemical pump cell. Then, based on the fact that there is a linear relationship between the current value of the current (NOx current) generated at that time and the NOx concentration, the NOx concentration in the gas to be measured is determined.

Note that the sensor element 14 is provided with a heater section (not shown), and the above-described operation is performed while heating the sensor element 14 to a temperature of about 600° C. to 800° C. by supplying electricity to the heater section. Therefore, the inspection in the inspection apparatus 10 is also performed after heating the sensor element 14 to the above-mentioned temperature.

As shown in FIG. 2, the inspection apparatus 10 includes a chamber 100 (also referred to as an attachment chamber) in which at least one sensor element 14 is mounted, and a gas supply means 102 that supplies a predetermined inspection gas to the chamber 100. (also referred to as model gas generation device 102).

The gas supply means 102 includes a plurality of gas supply sources, namely a first gas supply source 104A of NO (1%), a second gas supply source 104B of O ₂ (100%), and a third gas supply source 104B of N ₂ (100%). It has a gas supply source 104C. The gas supply means 102 includes four first switches 106a to 106d connected to the first gas supply source 104A, and four second switches 108a connected to the second gas supply source 104B. 108d, and four third switches 110a to 110d connected correspondingly to the third gas supply source 104C.

Further, the gas supply means 102 is connected to the four first switches 106a to 106d, and is connected to the first fixed flow rate nozzles 112a to 112d, each having a different flow rate, and to the four second switches 108b to 108d. It has second fixed flow rate nozzles 114a to 114d which are connected to each other and have different flow rates, and third fixed flow rate nozzles 116a to 116d which are connected to four third switches 110b to 110d and have different flow rates, respectively.

It is preferable that the first fixed flow rate nozzles 112a to 112d are configured as critical nozzles in which a constricted portion in the pipe is machined so that each has an individual flow rate (gas concentration). High flow rate accuracy can be obtained. The same applies to the second fixed flow rate nozzles 114a to 114d and the third fixed flow rate nozzles 116a to 116d.

The gas supply means 102 is a single mixing device that mixes multiple types of gases from four first fixed flow rate nozzles 112a to 112d, four second fixed flow rate nozzles 114a to 114d, and four third fixed flow rate nozzles 116a to 116d. It has a container 120.

As the first switches 106a to 106d, the second switches 108a to 108d, and the third switches 110a to 110d, for example, cock-type switching valves can be used.

Furthermore, the gas supply means 102 has one fixed flow rate nozzle 122 connected between the mixer 120 and the chamber 100. It is preferable that this fixed flow rate nozzle 122 is also configured as a critical nozzle.

Here, the operation of the inspection device 10 will be explained. First, the gas output from the first gas supply source 104A flows to the fixed flow rate nozzle through the closed (ON) switch among the first switches 106a to 106d. In the example of FIG. 2, only the first switch 106a is closed (ON), so the gas output from the first gas supply source 104A is passed through the first switch 106a to the corresponding first flow rate fixed nozzle. 112a. The gas whose flow rate (concentration) has been adjusted by the first fixed flow rate nozzle 112a is supplied to the mixer 120 at the subsequent stage.

The gas output from the second gas supply source 104B flows to the corresponding fixed flow rate nozzle through the closed (ON) switch among the second switches 108a to 108d. In the example of FIG. 2, only the second switch 108a is closed (ON), so the gas output from the second gas supply source 104B is passed through the second switch 108a to the corresponding second fixed flow rate nozzle. 114a. The gas whose flow rate (concentration) has been adjusted by the second fixed flow rate nozzle 114a is supplied to the mixer 120 at the subsequent stage.

Similarly, the gas output from the third gas supply source 104C is transmitted through the closed (ON) switch (the third switch 110a in the example of FIG. 2) among the third switches 110a to 110d. The flow rate fixed nozzle (in the example of FIG. 2, the third flow rate fixed nozzle 116a) is supplied with the flow rate fixed nozzle. Also in this case, the gas whose flow rate (concentration) has been adjusted by the third fixed flow rate nozzle 116a is supplied to the mixer 120 at the subsequent stage.

That is, in the mixer 120, the gas from the first fixed flow rate nozzle 112a, the gas from the second fixed flow rate nozzle 114a, and the gas from the third fixed flow rate nozzle 116a are mixed and output as a mixed gas. .

The mixed gas from the mixer 120 has its flow rate fixed by the flow rate fixing nozzle 122, and is then supplied to the downstream chamber 100, where it is used as a test gas for the plurality of sensor elements 14.

Although three types of gas supply sources are shown in the above example, one, two, four, or five or more gas supply sources may be used depending on the type of gas used. In addition, four switches and four fixed flow rate nozzles were used for each gas supply source, but depending on the concentration used, one, two, three, or five or more switches were used. A switch or a fixed flow rate nozzle may also be used.

Although an example is shown in which the fixed flow rate nozzle 122 is connected between the mixer 120 and the chamber 100, the fixed flow rate nozzle 122 does not necessarily need to be connected as long as a constant flow rate is output from the mixer 120. .

[First example]
Next, the advantages of the inspection device 10 will be described while comparing it with an inspection device 200 according to a comparative example (hereinafter referred to as a comparative example 200).

[Comparative example 200]
First, as shown in FIG. 3, the comparative example 200 includes one first flow regulator 206a (High Range) connected to the NO (1%) gas supply source 202A via the first switch 204a; One second flow regulator 206b (Low Range) is connected to the NO (3000 ppm) gas supply source 202B via the second switch 204b, and the second flow rate regulator 206b (Low Range) is directly connected to the O ₂ (1%) gas supply source 202C. one third flow regulator 206c, and one fourth flow regulator 206d directly connected to the N ₂ (100%) gas supply source 202D.

Further, the comparative example 200 includes one mixer 208 that mixes multiple types of gases from the first flow rate regulator 206a to the fourth flow rate regulator 206d. The chamber 100 is connected to the rear stage of the mixer 208 .

Generally, a model gas generation device is required to evaluate the characteristics of a gas sensor such as a NOx sensor. The model gas generation device can create a mixed gas of any concentration by adjusting the balance of a flow rate regulator (for example, a mass flow controller) connected to each pipe of a plurality of gases. The variation in gas concentration depends on the accuracy of the flow regulator. Since the flow rate regulator varies the flow rate, a control error occurs. When there are many types of gases to be mixed, multiple flow rate adjustment devices are used, which increases the error and does not improve the gas concentration accuracy in principle.

Furthermore, as shown in FIG. 4, mass flow controllers serving as flow rate regulators often have different accuracy between high flow rate and low flow rate. If it is 30% or more with respect to the full scale, there is an accuracy error of 1% with respect to the set point, but if it is less than 30%, it is an accuracy error of 1% of the full scale. In other words, if the flow rate is less than 30% of the full scale, the accuracy error will be 1% or more of the set point.

In order to confirm the above-mentioned matters, for the above-mentioned comparative example 200 using a mass flow controller as a flow rate regulator, NO concentration was determined using source gases of NO: 1%, O ₂ : 20%, and N ₂ : 100%. The maximum accuracy error and the root-square were confirmed when creating a mixed gas with O 2 concentration of 0 ppm to 3000 ppm and O ₂ concentration of 0 to 20%, and are shown in Table 1 of FIG.

As can be seen from Table 1 in FIG. 5, when the NO concentration was 500 ppm or more, the accuracy error was 6.0 or less, and when it was 1000 ppm or more, the accuracy error was 3.0 or less. Further, when the O ₂ concentration was 1%, the accuracy error was 6.0, when the O 2 concentration was 5%, the accuracy error was 1.2, and when the O 2 concentration was 20%, the accuracy error was 0.3. Note that since the N ₂ concentrations were all around 100%, the accuracy error was 1.0.

As a result, the maximum accuracy error of the mixed gas output from the mixer 208 (see FIG. 3) varied, not only in the single digit range but also in 31.0% and 13.0%. As for the root-square value, the example in which the set concentrations were 100 ppm for NO, 0% for O ₂ concentration, and 99.99 for N ₂ concentration stood out at 30.0, and there was a large variation.

[Example 1]
Regarding the inspection device 10 according to the present embodiment, the maximum accuracy error and the root-square were confirmed under the same conditions as the comparative example 200 described above, and are shown in Table 2 of FIG.

As can be seen from Table 2 in FIG. 6, since a critical nozzle was used in place of the flow rate regulator of Comparative Example 200, the accuracy error when passing through the critical nozzle is as shown in the column of concentration accuracy error for each gas. Both values were 0.4, and there was no variation in accuracy.

As a result, the maximum precision errors of the mixed gas output from the mixer 208 are 0.4, 0.8, and 1.2, and the root mean squares are also 0.4, 0.6, and 0.7. , it can be seen that the concentration accuracy is high.

Next, the reference sensor 500 used to adjust the concentration of the model gas output from the model gas generation device 102 described above will be described with reference to FIGS. 7 to 11B.

First, as shown in FIG. 7, the reference sensor 500 uses one of oxygen and NOx as a specific gas, and a test gas that does not contain the other but includes the specific gas and a base gas. Detects the concentration of a specific gas inside. The reference sensor 500 includes a long rectangular parallelepiped sensor element 502 shown in FIG. 7, a pump power source 504, a pump current acquisition section 510, an electromotive force acquisition section 512, a heater power source 514 shown in FIG. It includes a current acquisition section 516, a heater voltage acquisition section 518, a control device 520 shown in FIG. 9, and a display operation section 522.

As shown in FIG. 7, the sensor element 502 includes a first substrate layer 530, a second substrate layer 532, a third substrate layer 534, a first solid electrolyte layer 536, a spacer layer 538, and a second solid electrolyte layer. It has a structure 542 (an example of an element body) in which six layers including layer 540 are laminated in this order from the bottom. These six layers each consist of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). Further, the solid electrolyte forming these six layers is a dense and airtight electrolyte.

In the sensor element 502, between the lower surface of the second solid electrolyte layer 540 on the front end side and the upper surface of the first solid electrolyte layer 536, there is a gas inlet 550, a diffusion-limiting section 552, and an internal space 554 ( The main vacancies) are formed adjacent to each other in such a manner that they communicate with each other in this order. The region from the gas inlet 550 to the internal space 554 is also referred to as a gas flow section to be measured. In this measured gas flow section, the gas introduction port 550 opens to the external space at the front end surface of the sensor element 502. A gas to be measured is introduced into the sensor element 502 from the external space through the gas inlet 550 . The diffusion rate controlling section 552 applies a predetermined diffusion resistance to the gas to be measured taken in from the gas introduction port 550. The diffusion rate controlling section 552 is provided as two slits, upper and lower. The longitudinal direction of the opening of each slit is along the left-right direction. The gas to be measured that has passed through the diffusion control section 552 flows into the internal space 554 and reaches the measurement electrode 556.

In the sensor element 502, a reference gas introduction space 558 is provided on the opposite side (here, the rear end side) of the gas flow section to be measured. The reference gas introduction space 558 is provided at a position between the upper surface of the second substrate layer 532 and the lower surface of the first solid electrolyte layer 536, and whose side portions are defined by the side surfaces of the third substrate layer 534. There is. The reference gas introduction space 558 has an opening provided on the rear end surface of the sensor element 502. For example, atmospheric air is introduced into the reference gas introduction space 558 as a reference gas when measuring the specific gas concentration.

Further, the sensor element 502 includes a pump cell 560, a sensor cell 562, and a heater section 564.

Pump cell 560 is an electrochemical pump cell for pumping oxygen from interior cavity 554. The pump cell 560 includes a first outer electrode 570, a measurement electrode 556, and a second solid electrolyte layer 540 that serves as a flow path for oxygen ions between the first outer electrode 570 and the measurement electrode 556. The first outer electrode 570 is disposed outside the sensor element 502 so as to be in contact with the gas to be measured. More specifically, the first outer electrode 570 is disposed on the front side of the upper surface of the second solid electrolyte layer 540.

On the other hand, the measurement electrode 556 is disposed on the lower surface of the second solid electrolyte layer 540 in the internal space 554. However, the measurement electrode 556 only needs to be disposed at a position in the gas to be measured distribution section where the gas to be measured after being provided with diffusion resistance reaches, for example, on the upper surface of the first solid electrolyte layer 536. may be set.

The sensor cell 562 is an example of an oxygen concentration battery cell. The sensor cell 562 includes a second outer electrode 572, a reference electrode 574, a first solid electrolyte layer 536, a spacer layer 538, and a second solid electrolyte layer 540 provided between the second outer electrode 572 and the reference electrode 574. It is equipped with The second outer electrode 572 is disposed outside the sensor element 502 so as to be in contact with the gas to be measured. More specifically, the second outer electrode 572 is disposed on the front side of the upper surface of the second solid electrolyte layer 540. The second outer electrode 572 is arranged behind the first outer electrode 570. The reference electrode 574 is disposed within the reference gas introduction space 558 so as to be in contact with the reference gas. In this embodiment, the reference electrode 574 is provided on the lower surface of the first solid electrolyte layer 536. In this sensor cell 562, an electromotive force Ve based on the Nernst electromotive force is generated between the second outer electrode 572 and the reference electrode 574 depending on the oxygen concentration difference between the surroundings of the second outer electrode 572 and the reference electrode 574. . This electromotive force Ve allows the oxygen concentration (oxygen partial pressure) around the second outer electrode 572 to be determined.

It is preferable that the second outer electrode 572 has a smaller area than the first outer electrode 570. The second outer electrode 572 is used to measure the electromotive force Ve, and almost no current flows therethrough, so that even if the area is reduced, the catalytic activity is unlikely to change due to oxidation of the noble metal. Furthermore, by reducing the area, temperature distribution within the second outer electrode 572 when heated by the heater 580 is less likely to occur. That is, the temperature inside the second outer electrode 572 tends to be uniform. Therefore, the smaller the area of the second outer electrode 572, the less likely the correspondence relationship between the electromotive force Ve and the specific gas concentration will change. Therefore, since the area of the second outer electrode 572 is smaller than that of the first outer electrode 570, the detection accuracy of the specific gas concentration is less likely to decrease, and the accuracy of abnormality determination of the detected specific gas concentration is increased. At least one effect can be obtained. Here, the area of the first outer electrode 570 and the second outer electrode 572 is the surface of the element main body (here, the laminate) on which the first outer electrode 570 and the second outer electrode 572 are disposed (here, the surface of the sensor element 502 (top surface) when viewed from a direction perpendicular to the top surface of 502 (in this case, the area when viewed from the top). In this embodiment, as shown in FIGS. 7 and 10A, the second outer electrode 572 has a shorter longitudinal length than the first outer electrode 570, so that the second outer electrode 572 is shorter than the first outer electrode. The area is smaller than that of the electrode 570. Of course, as shown in FIG. 10B, the first outer electrode 570 and the second outer electrode 572 may be arranged side by side. Further, as shown in FIG. 10C, the first outer electrode 570 may have a recess 576, and the second outer electrode 572 may be disposed within the recess 576.

Furthermore, in the above-described embodiment, as shown in FIGS. 7 and 11A, the measured gas flow section of the sensor element 502 was equipped with the gas inlet 550, the diffusion-limiting section 552, and the internal space 554; Not limited. The gas to be measured flow section may be disposed inside the element body of the sensor element 502, introduce the gas to be measured, and allow it to flow to the measurement electrode 556 while imparting diffusion resistance. For example, as shown in FIG. 11B, the gas flow section to be measured may include a diffusion-limiting section 552a made of a porous material. In this case, the front surface of the diffusion-limiting portion 552a becomes the gas introduction port 550. Further, the diffusion rate controlling portion 552a may be a porous body that covers the measurement electrode 556. Furthermore, the gas to be measured portion may not include the internal space 554, and the entire portion to be measured may be filled with a porous material. Furthermore, in this embodiment, there is one diffusion-limiting section 552 and one internal cavity 554, but the gas distribution section to be measured may include a plurality of diffusion-limiting sections or a plurality of internal cavities.

The first outer electrode 570, the second outer electrode 572, the reference electrode 574, and the measurement electrode 556 are electrodes each containing a noble metal having catalytic activity (for example, at least one of Pt, Rh, Pd, Ru, and Ir). It is. The first outer electrode 570, the second outer electrode 572, the reference electrode 574 (see FIG. 7), and the measurement electrode 556 are each made of a cermet containing a noble metal and an oxide having oxygen ion conductivity (here, ZrO ₂ ). It is preferable to use an electrode as follows.

Further, it is preferable that each of the first outer electrode 570, the second outer electrode 572, the reference electrode 574, and the measurement electrode 556 is a porous body. In this embodiment, the first outer electrode 570, the second outer electrode 572, the reference electrode 574, and the measurement electrode 556 are all porous cermet electrodes made of Pt and _ZrO2 .

As shown in FIG. 7, the heater section 564 plays the role of temperature adjustment to heat and keep the sensor element 502 warm in order to increase the oxygen ion conductivity of the solid electrolyte. The heater section 564 includes a heater 580, a lead section 582, a through hole 584, a heater connector electrode 590, and a heater insulating layer 592.

The heater 580 is disposed inside the sensor element 502 so as to be sandwiched between the first substrate layer 530 and the second substrate layer 532. The heater 580 is an electric resistor and generates heat when supplied with power from the outside.

The heater 580 is routed so as to be turned back a plurality of times, and is embedded in the sensor element 502 over the entire area below the first outer electrode 570, the second outer electrode 572, the reference electrode 574, and the measurement electrode 556. . The heater 580 is capable of adjusting the temperature of the sensor element 502 to a temperature at which the solid electrolyte is activated (for example, 800 to 900° C.).

As shown in FIG. 8, the lead portion 582 includes a pair of current-carrying leads 582a, 582b connected to both ends of the heater 580, and a pair of current-carrying leads 582a, 582b connected to both ends of the heater 580 in parallel. Voltage measurement leads 582c and 582d are provided. The heater connector electrode 590 is an electrode disposed at the rear end of the lower surface of the first substrate layer 530 (see FIG. 7).

Although only one heater connector electrode 590 is shown in FIG. 7, as shown in FIG. There are four heater connector electrodes, a pair of heater connector electrodes 590c and 590d electrically connected to a pair of voltage measurement leads 582c and 582d.

As shown in FIG. 8, the energizing leads 582a, 582b and the heater connector electrodes 590a, 590b are connected through through holes 584 (only one is shown in FIG. 7), respectively. The voltage measurement leads 582c, 582d and the heater connector electrodes 590c, 590d are connected via leads (not shown) disposed on the side and bottom surfaces of the sensor element 502. As shown in FIG. 7, the heater section 564 can be electrically connected to the outside of the sensor element 502 via a heater connector electrode 590.

The heater insulating layer 592 is disposed on the upper and lower surfaces of the heater 580 and the lead portion 582, and insulates the heater 580 and the lead portion 582 from the first substrate layer 530 and the second substrate layer 532. The heater insulating layer 592 is, for example, an insulator such as alumina.

As shown in FIGS. 7 and 9, the pump power supply 504 applies a control voltage Vp between the first outer electrode 570 of the pump cell 560 and the measurement electrode 556. When the pump current Ip flows through the pump cell 560 due to the control voltage Vp, the pump cell 560 pumps oxygen in the internal cavity 554 to the surroundings of the first outer electrode 570, that is, to the external space.

The pump current acquisition unit 510 is configured as a current detection circuit that acquires the pump current Ip. The pump current acquisition unit 510 is connected between the first outer electrode 570 and the pump power source 504, as shown in FIG. Pump current acquisition section 510 outputs the acquired pump current Ip to control device 520.

The electromotive force acquisition unit 512 is configured as a voltage detection circuit that acquires the electromotive force Ve. The electromotive force acquisition unit 512 is connected between the second outer electrode 572 and the reference electrode 574, as shown in FIG. The electromotive force acquisition unit 512 outputs the acquired electromotive force Ve to the control device 520.

As shown in FIG. 8, the heater power source 514 is connected to the heater 580 via heater connector electrodes 590a, 590b and energizing leads 582a, 582b. The heater power supply 514 supplies power to the heater 580 to cause the heater 580 to generate heat. Heater current Ih flows through heater 580 by heater power supply 514 .

The heater current acquisition section 516 is configured as a current detection circuit that acquires the heater current Ih. Heater current acquisition section 516 is connected between heater connector electrode 590a and heater power source 514. The heater current acquisition unit 516 outputs the acquired heater current Ih to the control device 520 (see FIG. 9).

As shown in FIG. 8, the heater voltage acquisition unit 518 is configured as a voltage detection circuit that acquires the heater voltage Vh, which is the voltage (potential difference) across the heater 580. Heater voltage acquisition section 518 is connected between heater connector electrodes 590c and 590d. The heater voltage acquisition unit 518 outputs the acquired heater voltage Vh to the control device 520 (see FIG. 9).

The display/operation unit 522 in FIG. 9 includes an operation unit such as a touch panel or buttons, and a display unit such as an LED or display, and is used to input instructions from the worker and output information to the worker. do.

As shown in FIG. 9, the control device 520 includes a calculation section 600, a storage section 602, an input/output section 604, and the like. The calculation unit 600 has a processor including a CPU and the like, and realizes various functions by executing a program stored in the storage unit 602 by the processor.

In this embodiment, the calculation unit 600 functions as at least a gas sensor control unit 610, a first specific concentration detection unit 612A, a second specific concentration detection unit 612B, a specific concentration determination unit 614, and an abnormality determination unit 616. . The storage unit 602 includes storage devices such as ROM and RAM. Note that output of various control signals from the control device 520 and input of various signals from the outside are performed through the input/output unit 604.

The storage unit 602 stores a first correspondence relationship 620A, a second correspondence relationship 620B, and the like, in addition to a processing program executed by the calculation unit 600 when detecting a specific gas concentration, which will be described later, for example.

The first correspondence 620A stored in the storage unit 602 is information representing the correspondence between the pump current Ip and the specific gas concentration in the gas to be measured under a constant control voltage Vp. The second correspondence relationship 620B is information representing the correspondence relationship between the electromotive force Ve (EMF) and the specific gas concentration in the gas to be measured. The first correspondence relationship 620A and the second correspondence relationship 620B each include information such as a relational expression (for example, a linear function expression) and a map. The first correspondence relationship 620A and the second correspondence relationship 620B can be determined in advance through experiments, simulations, or the like.

The gas sensor control unit 610 receives the pump current Ip from the pump current acquisition unit 510, the electromotive force Ve from the electromotive force acquisition unit 512, the heater current Ih from the heater current acquisition unit 516, the heater voltage Vh from the heater voltage acquisition unit 518, and Operation signals and the like from the display operation section 522 are input. Gas sensor control section 610 outputs control signals to pump power source 504 and heater power source 514 to control pump cell 560 and heater section 564, and outputs a display signal to display operation section 522.

An example of how the reference sensor 500 configured in this manner is used will be described below. First, an operator attaches the sensor element 502 of the reference sensor 500 to a pipe (not shown). At this time, the operator can, for example, seal and fix the sensor element 502 with an element sealing body (not shown) so that the gas in the pipe can reach the front end side of the sensor element 502, and the rear end side is connected to the reference gas. (in this case, the atmosphere). In addition, the operator mixes the specific gas and the base gas (for example, nitrogen) at a predetermined ratio, and mixes the test gas to the model gas generation device 102 according to the present embodiment ( (see Figure 2).

Thereafter, this test gas is flowed into the pipe as a gas to be measured. As a result, the gas to be measured reaches the front end side of the sensor element 502, and the first outer electrode 570 and the second outer electrode 572 come into contact with the gas to be measured. Furthermore, when the gas to be measured is introduced into the gas-to-be-measured flow section from the gas introduction port 550, the gas to be measured passes through the first diffusion-limiting section 552 and reaches the internal cavity 554.

In this case, the model gas generation device 102 adjusts to the desired concentration by opening and closing the nozzles with different flow rates and their systems, as described above. That is, the concentration of the model gas changes stepwise by adjustment. Therefore, the reference sensor 500 can be used not only for adjusting the concentration of the model gas but also for self-diagnosis. That is, it can be used for daily inspection of the model gas generation device 102, for checking leakage of outside air from the mounting chamber 100 of the gas sensor 12, and the like. By providing the reference sensor 500 with a self-diagnosis function, it is possible to provide an inspection device that can ensure gas concentration more reliably.

The operation of the reference sensor 500 when detecting the specific gas concentration will be described below.
First, the temperature of the heater 580 is proportional to the resistance value of the heater 580. Therefore, gas sensor control unit 610 derives a resistance value based on heater current Ih and heater voltage Vh, converts the derived resistance value into temperature, and performs feedback control of heater power supply 514 described above. Note that the gas sensor control unit 610 may perform feedback control so that the derived resistance value becomes the target resistance value without converting the resistance value into temperature. Even in this case, the gas sensor control unit 610 essentially performs feedback control so that the temperature of the heater 580 reaches the target temperature.

Here, as shown in FIG. 8, the lead portion 582 includes energizing leads 582a and 582b, and voltage measuring leads 582c and 582d connected in parallel to the energizing leads 582a and 582b. Then, the heater voltage acquisition unit 518 measures the voltage between the voltage measurement leads 582c and 582d as the heater voltage Vh. Therefore, the gas sensor control unit 610 derives the resistance value of the heater 580 using the so-called four-terminal method. This is one of the features of the reference sensor 500, and is implemented in order to accurately perform constant temperature control.

As shown in FIG. 9, the gas sensor control unit 610 outputs a control signal to the pump power supply 504 so that the pump power supply 504 applies a constant control voltage Vp between the first outer electrode 570 and the measurement electrode 556. . Due to this control voltage Vp and the catalytic activity of the measurement electrode 556, oxygen ions are generated around the measurement electrode 556, and the oxygen ions become carriers of electrons to move inside the solid electrolyte layer (here, the second solid electrolyte layer 540). A pump current Ip flows by passing through and heading toward the first outer electrode 570. When the specific gas is NOx, the oxygen ions generated around the measurement electrode 556 are oxygen ions derived from oxygen generated by reduction of NOx in the gas to be measured that has flowed to the internal space 554.

In this way, by flowing the pump current Ip using the control voltage Vp, oxygen derived from the specific gas is pumped from around the measurement electrode 556 to around the first outer electrode 570. Therefore, this pump current Ip has a value that corresponds to the specific gas concentration in the gas to be measured.

Further, the control voltage Vp is determined in advance through experiments so that the oxygen concentration around the measurement electrode 556 becomes substantially zero. More specifically, the control voltage Vp is determined as a value such that the pump current Ip becomes a limiting current. The value of the control voltage Vp for the pump current Ip to reach the limit current is determined by the diffusion resistance of the gas flow part to be measured from the outside to the measurement electrode 556 (here, mainly the diffusion resistance of the diffusion-limiting part 552), It changes depending on the specific gas concentration in the gas. Therefore, an appropriate control voltage Vp can be determined in advance according to this diffusion resistance and the desired specific gas concentration that is desired to be adjusted this time. Since the pump current Ip is a limiting current, the pump current Ip has a value that accurately corresponds to the specific gas concentration in the gas to be measured. The first specific concentration detection unit 612A detects the specific gas concentration in the gas to be measured based on the pump current Ip of the pump cell 560.

Here, the pump current Ip has a value corresponding to the specific gas concentration in the gas to be measured, as described above. Therefore, the first specific concentration detection unit 612A can detect the first specific gas concentration based on the pump current Ip acquired from the pump current acquisition unit 510 and the first correspondence relationship 620A. The detected first specific gas concentration is stored in the storage unit 602 via the input/output unit 604, for example.

On the other hand, as described above, since the second outer electrode 572 contains a noble metal having catalytic activity, when the specific gas is NOx, the sensor cell 562 detects NOx in the gas to be measured around the second outer electrode 572. An electromotive force Ve is generated based on the oxygen concentration generated by the reduction of . Therefore, the electromotive force Ve also has a value corresponding to the specific gas concentration in the gas to be measured.

Therefore, the second specific concentration detection unit 612B detects the specific gas concentration based on the electromotive force Ve acquired from the electromotive force acquisition unit 512 and the second correspondence relationship 620B. The detected second specific gas concentration is stored in the storage unit 602 via the input/output unit 604, for example.

The specific concentration determination unit 614 determines the specific gas concentration from the first specific gas concentration and the second specific gas concentration stored in the storage unit 602 according to a preset algorithm. The specific concentration determination unit 614 sets the first specific gas concentration to the specific gas concentration, or sets the second specific gas concentration to the specific gas concentration, for example.

The abnormality determination unit 616 determines whether there is an abnormality in the first specific gas concentration and the second specific gas concentration detected by the first specific concentration detection unit 612A and the second specific concentration detection unit 612B. The abnormality determination unit 616 performs abnormality determination processing, for example, each time the first specific concentration detection unit 612A and the second specific concentration detection unit 612B execute the processing once. The abnormality determination unit 616 first obtains a specific gas concentration based on the pump current Ip and a specific gas concentration based on the electromotive force Ve stored in the storage unit 602, respectively.

The abnormality determination unit 616 determines whether or not there is an abnormality in at least one of these values, based on the difference between the acquired first specific gas concentration and second specific gas concentration. The abnormality determination unit 616 determines that there is an abnormality, for example, when the difference or ratio between the two acquired specific gas concentrations is greater than a predetermined threshold. When determining that there is an abnormality, the abnormality determination unit 616 notifies the operator that there is an abnormality in the specific gas concentration value. For example, a display signal is output to the display operation unit 522 to notify the operator of the abnormality. This allows the operator to know the possibility that the currently detected specific gas concentration value in the test gas is incorrect. Thereafter, the operator checks the detection accuracy of the specific gas concentration of the reference sensor 500 and calibrates the reference sensor 500 as necessary. When the control device 520 notifies the operator of the abnormality, it ends the specific gas concentration detection process.

When the control device 520 detects the specific gas concentration, it outputs the value of the detected specific gas concentration. For example, the control device 520 outputs the value to the storage unit 602 for storage, or outputs the value to the display operation unit 522 to display the value to the operator. The control device 520 may output the detected specific gas concentration value when there is no abnormality, and may not output the specific gas concentration value when there is an abnormality. If there is no abnormality and the control device 520 outputs the value of the detected specific gas concentration, the control device 520 ends the specific gas concentration detection process.

Here, unlike, for example, exhaust gas from an internal combustion engine, the test gas has a stable specific gas concentration. Therefore, the control device 520 only needs to perform the specific gas concentration detection process at least once. Further, the control device 520 may perform a predetermined abnormality determination every time the specific gas concentration detection process is executed a predetermined number of times or every time a predetermined time elapses. However, it is preferable that the control device 520 performs abnormality determination at least once in one specific gas concentration detection process, and more preferably performs abnormality determination every time specific gas concentration detection is performed.

Since the reference sensor 500 assumes that the test gas containing only one of oxygen and NOx is the gas to be measured, there is no need to separate oxygen and NOx. Taking advantage of this fact, the reference sensor 500 does not perform multiple feedback controls and simply applies a constant control voltage Vp to the pump cell 560 to cause the pump current Ip to flow. Therefore, in the reference sensor 500, a decrease in detection accuracy due to instability of feedback control does not occur. Further, in the reference sensor 500, the control voltage Vp is determined as a value such that the pump current Ip becomes a limit current.

Here, FIG. 12 is an explanatory diagram showing the relationship between the control voltage Vp and the pump current Ip. For example, if the value of the control voltage Vp (value a in FIG. 12) is appropriately determined so that the pump current Ip becomes the limit current (value b in FIG. The value is based on the diffusion resistance and specific gas concentration.

Also, consider a case where the noble metals of the first outer electrode 570 and the measurement electrode 556 of the reference sensor 500 are oxidized and the catalytic activity changes with use. In this case, the relationship between the control voltage Vp and the pump current Ip is such that, as shown by the dashed line in FIG. ) itself is difficult to change.

Therefore, if the control voltage Vp is determined within a range (for example, region R in FIG. 12) in which the pump current Ip stably reaches the limit current, the pump current Ip will increase as the reference sensor 500 is used. Hard to deviate from the correct value corresponding to a specific gas concentration.

As described above, in the reference sensor 500, by not using feedback control to control the pump cell 560 and by determining the control voltage Vp so that the pump current Ip becomes the limit current, the reference sensor 500 can accurately control the specific gas concentration. A corresponding pump current Ip can be obtained.

[Second example]
An example in which a gas sensor was specifically manufactured will be described below as an example. Note that the present invention is not limited to the following examples.

First, as shown in FIG. 2, a model gas generation device 102 according to the present embodiment was used as a model gas generation means.

[Example 2]
As Example 2, one reference sensor 500 was installed in the chamber 100 (see FIG. 2). The reference sensor 500 was manufactured as follows. That is, the sensor element 502 shown in FIGS. 7 to 10A and FIG. 11A is manufactured, and as shown in FIG. The reference sensor 500 was manufactured by connecting the electromotive force acquisition section 512, the heater current acquisition section 516, the heater voltage acquisition section 518, and the display operation section 522.

The sensor element 502 was manufactured as follows. First, six ceramic green sheets were prepared by tape-molding a mixture of zirconia particles to which 4 mol % of yttria as a stabilizer had been added, an organic binder, a dispersant, a plasticizer, and an organic solvent. A plurality of sheet holes used for positioning during printing and lamination, holes corresponding to the internal space 554 and reference gas introduction space 558, through holes 584, etc. were formed in advance in this green sheet. Furthermore, a paste pattern for forming each electrode and heater section 564 was printed on each green sheet. Then, six green sheets were stacked in a predetermined order and pressed together under predetermined temperature and pressure conditions. An unfired laminate having the size of the sensor element 502 was cut from the crimped body thus obtained. Then, the cut out unfired laminate was fired to obtain a sensor element 502. A conductive paste for forming the first outer electrode 570, the second outer electrode 572, the measurement electrode 556, and the reference electrode 574 was prepared by mixing Pt, zirconia powder, and a binder.

[Comparative example 2]
As Comparative Example 2, a gas analyzer (Bex-1003NH, manufactured by Best Sokki Co., Ltd.) was used.

[Evaluation test]
The detection accuracy of Example 2 and Comparative Example 2 was compared. First, a gas with a base gas of nitrogen, a known NO concentration, and no oxygen was prepared and used as a test gas. The NO concentration of this test gas was measured 100 times in each of Example 2 and Comparative Example 2. The NO concentration in Example 2 was a value based on the pump current Ip. The timing of each measurement was immediately before the calibration timing (every 4 hours) determined by the gas analyzer of Comparative Example 2. That is, in Comparative Example 2, the specific gas concentration was measured 100 times at the timing when the detection accuracy is most likely to decrease immediately before the calibration, while performing calibration at appropriate calibration timings as time passes. The time required for one measurement (the time for flowing the test gas) is about 15 minutes in both Example 2 and Comparative Example 2. Further, the elapsed time from the first measurement to the 100th measurement was about 850 hours. Of these 850 hours, the time during which the reference sensor 500 of Example 2 was driven and exposed to the test gas was approximately 15 minutes x 100 times = approximately 25 hours. The same applies to Comparative Example 2.

Figure 13 shows the actual concentration of the test gas (NO concentration: 500 ppm), the NO concentration for each number of measurements detected by the gas sensor of Example 2 (see "x"), and the number of measurements detected by the gas sensor of Comparative Example 2. 12 is a graph showing the relationship between NO concentration (see "---") at FIG. 14 is a graph showing the relationship between the measurement variation of Example 2 (see "x") and the measurement variation of Comparative Example 2 (see "---") based on the results of FIG. 13.

As shown in FIGS. 13 and 14, Comparative Example 2 has larger measurement variations overall than Example 2, with a maximum value of 506.9, a minimum value of 494.1, and a root mean square value of approximately It was 2.32. On the other hand, in Example 2, the measurement variation was generally small, with a maximum value of 501.3, a minimum value of 498.7, and a root mean square of approximately 0.71. Ta.

From FIGS. 13 and 14 and the above-mentioned matters, in Example 2, compared to Comparative Example 2, the deviation ratio from the actual concentration (500 ppm) was smaller in any measurement period from 1 to 100 measurements. That is, in Example 2, the maximum value, minimum value, and root mean square were all close to 0% compared to Comparative Example 2. The reference sensor 500 of Example 2 always tended to have higher detection accuracy than the gas analyzer of Comparative Example 2. In addition, as mentioned above, the deviation ratio from the actual concentration in Comparative Example 2 is the value before calibration when regular calibration is performed, and even if regular calibration is performed, this level of detection It can be seen that a decrease in accuracy is possible. On the other hand, the reference sensor 500 of Example 2 has higher detection accuracy than Comparative Example 2 (state before calibration of the gas analyzer) despite not being calibrated during the 100 measurement period. It was a trend. Further, in the reference sensor 500 of Example 2, no decrease in detection accuracy due to an increase in the number of measurements was observed, and the measurement accuracy was maintained over a long period of time.

[Invention obtained from embodiment]
The invention that can be understood from the above embodiments will be described below.

[1] The gas sensor inspection device 10 according to the present embodiment includes a chamber 100 in which at least one sensor element 14 is mounted, and a gas supply means 102 that supplies a predetermined inspection gas to the chamber 100. The gas supply means 102 includes a plurality of gas supply sources (104A, 104B, 104C) and a plurality of switches (first switches 106a to 106d) connected correspondingly to each gas supply source (104A, 104B, 104C). , second switches 108a to 108d, third switches 110a to 110d) and a plurality of fixed flow rate nozzles (first flow rate fixed nozzles 112a to 112d, second fixed flow rate nozzles 114a to 114d, and third fixed flow rate nozzles 116a to 116d), and a mixer 120 that mixes a plurality of types of gas from the plurality of fixed flow rate nozzles.

Conventionally, a model gas generation device has been designed to create a mixed gas of an arbitrary concentration by adjusting the balance of a flow rate regulator (for example, a mass flow controller) that connects a plurality of gases to respective pipes. However, variations in the gas concentration of the mixed gas depend on the accuracy of the flow rate regulator, and since the flow rate regulator varies the flow rate, there is a problem in that control errors also occur.

In contrast, the inspection device 10 according to the present embodiment uses a plurality of fixed flow rate nozzles each having a different flow rate instead of a flow rate regulator that causes an error during flow rate control, and further uses a plurality of fixed flow rate nozzles with different flow rates. A switch is connected to selectively supply gas. As a result, the accuracy error when passing through the fixed flow rate nozzle is small, and there is almost no variation in accuracy. Further, since a plurality of fixed flow rate nozzles each having a different flow rate are used, by appropriately combining them, it is possible to mix the gases to an arbitrary concentration.

[2] In the present embodiment, a plurality of switches (first switches 106a to 106d, second switches 108a to 108d, and third switch 110a) correspond to each gas supply source (104A, 104B, 104C). - 110d), a plurality of fixed flow rate nozzles (first fixed flow rate nozzles 112a to 112d, second fixed flow rate nozzles 114a to 114d, and third fixed flow rate nozzles 116a to 116d) are connected.

Thereby, the gas from the gas supply source can be supplied only to the necessary fixed flow rate nozzles, so it is possible to improve the efficiency of gas supply. For example, if an on-off valve is installed after each fixed-flow nozzle, after gas has been supplied to all the fixed-flow nozzles, it will flow to the next stage only through the closed on-off valve, so there is no need to flow extra gas. , and it is not efficient.

[3] This embodiment includes a fixed flow rate nozzle 122 connected between the mixer 120 and the chamber 100. As a result, the flow rate of the gas output from the mixer 120 can be temporarily fixed at the flow rate fixing nozzle 122, so that the concentration of the test gas supplied to the chamber 100 can be quickly stabilized. .

[4] In this embodiment, the fixed flow rate nozzle is a critical nozzle. By using a critical nozzle as a fixed flow rate nozzle, high flow rate accuracy can be obtained.

[5] The gas sensor testing method according to the present embodiment is a gas sensor testing method in which the gas sensor 12 is tested by supplying a predetermined testing gas to the chamber 100 in which at least one sensor element 14 is installed. A plurality of gases outputted from the respective gas supply sources (104A, 104B, 104C) are connected to a plurality of switches (first switches 106a to 104C) corresponding to each gas supply source (104A, 104B, 104C). 106d, second switches 108a to 108d, third switches 110a to 110d), and connecting a plurality of gases from the plurality of switches in correspondence to each gas supply source (104A, 104B, 104C). and sending it to a plurality of fixed flow rate nozzles (first fixed flow rate nozzles 112a to 112d, second fixed flow rate nozzles 114a to 114d, and third fixed flow rate nozzles 116a to 116d), each having a different flow rate, and from the plurality of fixed flow rate nozzles. The method includes a step of mixing a plurality of gases in a mixer 120, and a step of supplying the mixed gas from the mixer 120 to the chamber 100.

[6] This embodiment includes a step of sending the mixed gas from the mixer 120 to one fixed flow rate nozzle 122, and a step of sending the mixed gas from one fixed flow rate nozzle 122 to the chamber 100.

[7] In this embodiment, each of the above-described fixed flow rate nozzles 122 is a critical nozzle. In the critical nozzle, the constricted portion inside the pipe is machined so that each flow rate (gas concentration) is individual, so that high flow rate accuracy can be obtained.

By the way, in the manufacturing process of NOx sensors and O ₂ sensors, there is a process for inspecting the sensitivity performance of the products, and standards are required to ensure the gas concentration for inspection. A gas analyzer or standard NOx sensor is used as a reference. As for the principle, there are devices using infrared absorption method (NDIR/FTIR) and chemiluminescence method (CLD).

Generally, in order to maintain measurement accuracy, it is necessary to perform calibration every few hours using a span gas (reference gas). Additionally, measuring instruments using NOx sensors and O ₂ sensors may be used as standards. The electrodes of these sensors use platinum or a catalytic metal made by adding a small amount of a substance to platinum. For example, in the case of a NOx sensor, a catalytic electrode decomposes O ₂ and N ₂ using a catalytic reaction, and the NO concentration is measured from the O ₂ concentration. When Pt and Rh, which are used as electrode materials for catalytic electrodes, are exposed to O ₂ , PtO, PtO ₂ and RhO are produced, which evaporate at lower temperatures than Pt and Rh. Furthermore, when Pt or Rh is oxidized, the catalytic reactivity deteriorates, the gas decomposition power decreases, and as a result, the sensor sensitivity decreases, so periodic calibration is required.

Temperature control is important for sensors, and the heater section of the sensor uses either two terminals for driving the heater, or three terminals with an additional terminal for monitoring the voltage drop in the heater lead section. It is being said. However, due to the influence of the contact resistance of the connector section between the sensor detection section and the sensor controller section, temperature control may be disrupted and the temperature of the sensor element may change, resulting in variations in the output of the sensor.

Furthermore, in order to measure the concentration of several hundred to about 10 ppm, the conventional NOx sensor has three empty chambers ^. It is necessary to keep the concentration as low as below. Therefore, it is necessary to simultaneously and constantly control three parameters: the voltages V1 and V2 corresponding to the vacancy concentration of the second and third chambers, and the current Ip1 pumped from the second chamber. However, if the control is deviated, the magnitude of the current Ip2, which is the final output, changes, and as a result, the NO output of the sensor may vary.

In order to solve these problems, it is preferable to adopt the configuration from [8] below.

[8] That is, in the present embodiment, a test gas that is used in the gas sensor inspection device 10 described above, uses either oxygen or NOx as a specific gas, and contains the specific gas and the base gas without containing the other. A sensor element 502 that is a reference sensor 500 that detects a specific gas concentration, which is the concentration of the specific gas in the measured gas, as a measured gas, and has a structure 542 made of an oxygen ion conductive solid electrolyte; A diffusion rate-limiting part 552 for rate-limiting diffusion at the gas introduction part to the sensor element 502, a gas introduction port 550 formed in the structure 542 and into which the gas to be measured is introduced, and a main gas introduction port 550 communicating with the gas introduction port 550. a cavity (internal cavity 554), a first outer electrode 570 that is disposed on the outside of the structure 542 so as to be in contact with the gas to be measured and includes a noble metal having catalytic activity, and a first outer electrode 570 that is in contact with the gas to be measured. a second outer electrode 572 disposed outside the structure 542 and containing a catalytically active noble metal; a measurement electrode 556 disposed inside the main cavity 554 and containing a catalytically active noble metal; By applying a constant voltage Vp between the reference gas introduction space 558 formed in the reference gas introduction space 558 into which the reference gas is introduced, the reference electrode 574 formed in the reference gas introduction space 558, the first outer electrode 570, and the measurement electrode 556, Based on the concentration difference between the first specific concentration detection section 612A that detects the concentration of the specific gas based on the limiting current Ip flowing between the first outer electrode 570 and the measurement electrode 556, and the second outer electrode 572 and the reference electrode 574. It has a second specific concentration detection section 612B that detects the concentration of the specific gas based on the Nernst electromotive force.

That is, the following (1) to (3) are adopted.
(1) Use a measurement principle that is not affected by changes in catalyst reactivity.
(2) To accurately control the heater, use a connection method that is not affected by contact resistance, such as a connector.
(3) Avoid using complicated controls.

In (1) above, a diffusion layer is provided in the gas introduction part of the sensor element 502 to control the rate of diffusion, and the current Ip is measured using the limiting current characteristic when a fixed voltage Vp is applied to the detection part. Since the current Ip is related only to the diffusion resistance, it is not easily affected by reaction resistance due to catalyst deterioration.

In (2) above, in order to accurately control the heater, four terminals with separate current and voltage terminals are used (see FIG. 8). Since no current flows through the voltage terminals, measurements can be made without being affected by the contact resistance of the connector, making it possible to accurately determine the voltage at the heater. This allows accurate temperature control to be performed.

In the case of (3) above, output variations due to unstable control can be eliminated by performing the minimum control of only applying a constant voltage Vp.

[9] The present embodiment includes a self-diagnosis unit (abnormality determination unit 616) that monitors the output of the first specific concentration detection unit 612A and the output of the second specific concentration detection unit 612B to monitor the presence or absence of an abnormality. . For example, if the difference between the output of the first specific concentration detection section 612A and the output of the second specific concentration detection section 612B exceeds a preset normal range, it can be reported that an abnormality has occurred.

[10] In this embodiment, the structure 542 has a heater section 564, and the heater section 564 has two current supply leads 582a and 582b and two voltage measurement leads 582c and 582d. That is, four terminals are used, with the current terminal and voltage terminal separated. Since no current flows through the voltage terminals, measurements can be made without being affected by the contact resistance of the connector, making it possible to accurately determine the voltage at the heater and perform accurate temperature control.

[11] In this embodiment, the second outer electrode 572 has a smaller area than the first outer electrode 570. Here, the second outer electrode 572 is used to measure the electromotive force Ve, and since almost no current flows therethrough, even if the area is reduced, changes in catalyst activity due to oxidation or volatilization of the noble metal are unlikely to occur. By reducing the area, temperature distribution within the second outer electrode 572 is less likely to occur, that is, the temperature is more likely to be uniform within the second outer electrode 572, so the correspondence relationship between the electromotive force Ve and the specific gas concentration changes. It's hard to do. Therefore, it is possible to obtain at least one of the following effects: the detection accuracy of the specific gas concentration is less likely to deteriorate, and the accuracy of abnormality determination of the detected specific gas concentration is increased. Here, the area of the first outer electrode 570 is the area of the structure 542 when viewed from a direction perpendicular to the surface on which the first outer electrode 570 is disposed. The area of the second outer electrode 572 is the area of the structure 542 when viewed from a direction perpendicular to the surface on which the second outer electrode 572 is disposed.

[12] In this embodiment, the first outer electrode 570 and the second outer electrode 572 may be arranged in this order in the depth direction of the structure 542.

[13] In this embodiment, the first outer electrode 570 has a recess 576 in a portion facing the second outer electrode 572, and the second outer electrode 572 is formed within the recess 576. The first outer electrode 570 and the second outer electrode 572 are disposed close to each other, so that a temperature difference between them is unlikely to occur. Therefore, the accuracy of abnormality determination of the detected specific gas concentration increases.

[14] In this embodiment, the first outer electrode 570 and the second outer electrode 572 are arranged in the width direction of the structure 542. Also in this case, a temperature difference is unlikely to occur between the first outer electrode 570 and the second outer electrode 572. Therefore, the accuracy of abnormality determination of the detected specific gas concentration increases.

[15] In the present embodiment, the diffusion rate controlling section 552 has slits in a portion facing the upper portion and a portion facing the lower portion of the gas inlet 550, respectively. That is, the slit formed at the upper part of the gas introduction port 550 and the slit formed at the lower part of the gas introduction port 550 can constitute the diffusion rate controlling part 552.

[16] In this embodiment, the diffusion-limiting section 552a is formed of a porous layer. In this case, the front surface of the diffusion-limiting portion 552a constitutes the gas inlet 550.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

In carrying out the present invention, various means for improving reliability as an automobile part may be added to the extent that the idea of the present invention is not impaired.

10... Inspection device 12... Gas sensor 14... Sensor element 100... Chamber 102... Gas supply means (model gas generation device)
104A...first gas supply source 104B...second gas supply source 104C...third gas supply source 106a-106d...first switch 108a-108d...second switch 110a-110d...third switch 112a-112d...th 1 Fixed flow rate nozzles 114a to 114d...Second flow rate fixed nozzles 116a to 116d...Third flow rate fixed nozzles 120...Mixer 122...Fixed flow rate nozzles 500...Reference sensor 502...Sensor element 504...Pump power supply 510...Pump current acquisition section 512 ...Electromotive force acquisition section 514...Heater power supply 516...Heater current acquisition section 518...Heater voltage acquisition section 520...Control device 522...Display operation section 530...First substrate layer 532...Second substrate layer 534...Third substrate layer 536... First solid electrolyte layer 538...Spacer layer 540...Second solid electrolyte layer 542...Structure 550...Gas inlet 552...Diffusion controlling part 552a...Diffusion controlling part 554...Internal cavity (main cavity) 556...Measuring electrode 558 ...Reference gas introduction space 560...Pump cell 562...Sensor cell 564...Heater part 570...First outer electrode 572...Second outer electrode 574...Reference electrode 576...Recessed part 580...Heater 582...Lead part 582a, 582b...Electrification lead 582c, 582d...Voltage measurement lead 584...Through hole 590, 590a to 590d...Heater connector electrode 592...Heater insulating layer 600...Calculating section 602...Storage section 604...Input/output section 610...Gas sensor control section 612A...First specific concentration detection section 612B...Second specific concentration detection section 614...Specific concentration determination section 616...Abnormality determination section 620A...First correspondence relationship 620B...Second correspondence relationship Ih...Heater current Ip...Pump current Ve...Electromotive force Vh...Heater voltage Vp...Control Voltage

Claims (16)

a chamber in which at least one sensor element is mounted;
a gas supply means for supplying a predetermined test gas to the chamber;
The gas supply means includes:
multiple gas sources;
a plurality of switches connected correspondingly to each of the gas supply sources;
A plurality of fixed flow rate nozzles each having a different flow rate and each connected to the front stage or the rear stage of the plurality of switches corresponding to each of the gas supply sources;
A gas sensor inspection device comprising: a plurality of the fixed flow rate nozzles connected in parallel to each other and a mixer for mixing a plurality of types of gases from the plurality of the fixed flow rate nozzles. The gas sensor inspection device according to claim 1,
A gas sensor inspection device, wherein the plurality of fixed flow rate nozzles are connected to a rear stage of the plurality of switches in correspondence with each of the gas supply sources. The gas sensor inspection device according to claim 1 or 2,
A gas sensor inspection device comprising a fixed flow rate nozzle connected between the mixer and the chamber. In the gas sensor inspection device according to any one of claims 1 to 3,
A gas sensor inspection device, wherein the fixed flow rate nozzle is a critical nozzle. In a gas sensor testing method, the gas sensor is tested by supplying a predetermined testing gas to a chamber in which at least one sensor element is installed,
sending a plurality of gases respectively output from a plurality of gas supply sources to a plurality of switches connected correspondingly to each of the gas supply sources;
Sending a plurality of gases from the plurality of switches to a plurality of fixed flow rate nozzles connected correspondingly to each of the gas supply sources and each having a different flow rate;
mixing the plurality of gases from the plurality of fixed flow rate nozzles in a mixer in which the plurality of fixed flow rate nozzles are connected in parallel to each other;
A method for testing a gas sensor, comprising the step of supplying a mixed gas from the mixer to the chamber. The gas sensor testing method according to claim 5,
directing the mixed gas from the mixer to one fixed flow rate nozzle;
A method for testing a gas sensor, comprising the step of sending a mixed gas from the one fixed flow rate nozzle to the chamber. In the gas sensor testing method according to claim 5 or 6,
A method for testing a gas sensor, wherein the fixed flow rate nozzle is a critical nozzle. It is used in a gas sensor inspection device, and uses either oxygen or NOx as a specific gas, and a test gas containing the specific gas and a base gas without the other as the gas to be measured. A reference sensor that detects a specific gas concentration, which is a gas concentration,
The gas sensor inspection device includes:
a chamber in which at least one sensor element is mounted;
a gas supply means for supplying a predetermined test gas to the chamber;
The gas supply means includes:
multiple gas sources;
a plurality of switches connected correspondingly to each of the gas supply sources;
A plurality of fixed flow rate nozzles each having a different flow rate and each connected to the front stage or the rear stage of the plurality of switches corresponding to each of the gas supply sources;
a mixer that mixes a plurality of types of gas from the plurality of fixed flow rate nozzles;
The reference sensor is
a sensor element having a structure made of an oxygen ion conductive solid electrolyte;
a diffusion rate-limiting part for rate-limiting diffusion in a gas introduction part to the sensor element having the structure;
a gas introduction port formed in the structure and into which a gas to be measured is introduced;
a main chamber communicating with the gas inlet;
a first outer electrode disposed outside the structure so as to be in contact with the gas to be measured, and containing a noble metal having catalytic activity;
a second outer electrode disposed outside the structure so as to be in contact with the gas to be measured, and containing a noble metal having catalytic activity;
a measurement electrode disposed inside the main cavity and containing a noble metal having catalytic activity;
a reference gas introduction space formed in the structure and into which a reference gas is introduced;
a reference electrode formed in the reference gas introduction space;
a first concentration detection unit that detects the concentration of a specific gas based on a limiting current flowing between the first outer electrode and the measurement electrode by applying a constant voltage between the first outer electrode and the measurement electrode;
A reference sensor, comprising: a second concentration detection section that detects a concentration of a specific gas based on a Nernst electromotive force due to a concentration difference between the second outer electrode and the reference electrode. The reference sensor according to claim 8,
A reference sensor comprising a self-diagnosis section that monitors the output of the first concentration detection section and the output of the second concentration detection section to determine whether there is an abnormality. The reference sensor according to claim 8 or 9,
a heater portion formed in the structure;
The heater section is a reference sensor having two current supply leads and two voltage measurement leads. The reference sensor according to any one of claims 8 to 10,
A reference sensor, wherein the second outer electrode has a smaller area than the first outer electrode. The reference sensor according to any one of claims 8 to 11,
In the reference sensor, the first outer electrode and the second outer electrode are arranged in this order in the depth direction of the structure. The reference sensor according to claim 12,
The first outer electrode has a recess in a portion facing the second outer electrode,
The reference sensor, wherein the second outer electrode is formed within the recess. The reference sensor according to any one of claims 8 to 11,
The reference sensor, wherein the first outer electrode and the second outer electrode are arranged in the width direction of the structure. The reference sensor according to any one of claims 8 to 14,
The diffusion control section is a reference sensor, and has slits in a portion facing an upper portion and a portion facing a lower portion of the gas inlet. The reference sensor according to any one of claims 8 to 15,
In the reference sensor, the diffusion-limiting section is constituted by a porous layer.

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