JPH04264250A - Limiting-current-type oxygen sensor - Google Patents

Abstract

PURPOSE:To specifically self-diagnose existence of sensor deterioration and determine the deterioration in case deterioration occurs to prevent erroneous measurement as long as a limiting-current-type oxygen sensor for measuring oxygen concentration in an atmosphere is concerned. CONSTITUTION:A limiting-current-type oxygen sensor comprises a plurality of pairs of electrode films 2a, 2b, 3a, 3b placed on both surfaces of an oxygen ion conductive solid electrolytic body 1 and a plurality of diffusion rate determining elements surrounding one side of the electrode film (which comprise a plurality of spiral spacers 4', 4'' and a seal plate 5). Further the sensor comprises sensor elements where the areas of the electrode films 2a, 2b, 3a, 3b or lengths and cross-sectional areas of oxygen diffusion paths of the diffusion rate determining elements are made different respectively and a comparison circuit which compares ratios of respective current values obtained from the plural pairs of the electrode films 2a, 2b, 3a, 3b, so that when the current value ratio is largely different from an initial value when the sensor elements were used, the sensor can determine that the elements are defective.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a limiting current type oxygen sensor for measuring oxygen concentration in the atmosphere, and in particular, it self-determines whether the sensor has deteriorated or not, and if it does, it is judged as deterioration to prevent erroneous measurements. It is something to do.

0002

2. Description of the Related Art FIG. 10 shows a partially broken structure of a conventional limiting current type oxygen sensor. 1 is a solid electrolyte plate exhibiting oxygen ion conductivity, and electrode films 2a and 2b (not shown) are provided on both sides.
is formed. A spiral spacer 4 surrounding the electrode film 2a and having a starting end and a terminal end spaced apart from each other is arranged on one surface of the solid electrolyte plate 1, and a sealing plate 5 is arranged above the spiral spacer 4. The oxygen diffusion path is formed in a spiral space surrounded by opposing partition walls of the spiral spacer 4, the solid electrolyte plate 1, and the seal plate 5, and oxygen diffuses into the electrode film 2a via the diffusion path. A heating section 6 is formed on the seal plate 5, and heats the solid electrolyte plate 1 to improve conduction of oxygen ions.

[0003] The operation will be explained. In the above configuration, a predetermined power is applied to the heating section 6 via a lead wire (not shown), and the solid electrolyte plate 1 is heated to a predetermined temperature via the heating section 6. On the other hand, similarly, a lead wire (not shown) is connected to the solid electrolyte plate 1 (in this case, the electrode films 2 formed on both sides).
A, 2b (not shown)) are also applied with a predetermined voltage. Then, oxygen in the air flows through the oxygen diffusion path to the electrode film 2a, further moves from the cathode side electrode film 2a toward the anode electrode film 2b (not shown) as oxygen ions, and Anode electrode film 2b (not shown)
It is released again as oxygen. Oxygen moves through the solid electrolyte plate 1 due to this oxygen pumping action, and a current is generated accordingly. However, since the inflow of oxygen molecules is restricted by the oxygen diffusion path, a saturation current (referred to as a limiting current) depending on the oxygen concentration is generated. arise. By measuring this limiting current value, the oxygen concentration can be determined.

0004

[Problems to be Solved by the Invention] However, with the structure of the conventional limiting current type oxygen sensor, even if an abnormality (for example, clogging of the diffusion hole or leakage) occurs after long-term use of the sensor, the abnormality will not be resolved. Undetectable. Therefore, the true oxygen concentration cannot be measured, resulting in erroneous measurements.

The present invention solves such conventional problems by self-diagnosing whether or not there is an abnormality in the sensor, and if an abnormality is detected, it is determined to be abnormal and erroneous measurements are prevented.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the limiting current type oxygen sensor of the present invention comprises: a plurality of diffusion-limiting bodies located on one side of the solid electrolyte body, arranged so as to individually surround the electrode membranes, and each having an oxygen diffusion passage for restricting the movement of incoming oxygen molecules, a sensor element having different lengths and cross-sectional areas of oxygen diffusion paths and different critical voltage values at which the limiting current begins; applied voltage generating means for applying a predetermined voltage to the plurality of pairs of electrode films; a plurality of detection means for detecting each current obtained from the plurality of pairs of electrode films by the voltage generation means; a comparison means for comparing a ratio of each current value obtained from the detection means; and a ratio of each current value. The device is equipped with a determining means that determines that there is an abnormality when the value is significantly different from the initial value when the sensor element is used.

[0007]

[Operation] According to the present invention, when an abnormality such as clogging or leakage of the diffusion hole occurs due to the above structure, the ratio of each current value obtained from multiple pairs of electrode films will be a value that is significantly different from the initial value at the beginning of sensor use. By comparing the initial value when the sensor is first used and the value during use of the sensor, it is possible to self-diagnose whether there is an abnormality in the sensor, and if an abnormality occurs, it can be determined as abnormal and erroneous measurements can be prevented. This will be explained in detail as follows. (1) In the case of clogging of the diffusion passages, if clogging occurs on one oxygen diffusion passage side, the current value thereof decreases, but the current values on the other oxygen diffusion passage sides do not change. Therefore, each current value ratio differs greatly from the initial value, and a sensor abnormality can be detected. (2) Regarding the deterioration of the seal of the diffusion barrier due to the occurrence of cracks, when a crack occurs on the side of one diffusion barrier, the current value increases, but the current value on the side of the other diffusion barrier does not change. Therefore, the ratio of each current value differs greatly from the initial value, and an abnormality in the sensor can be detected. (3) Regarding deterioration of the electrode film and solid electrolyte plate, when insulation resistance is generated in the element due to deterioration, the oxygen ion conductivity of the solid electrolyte plate decreases. Therefore, on the side that begins to show a limiting current at a high critical voltage value, the ratio of the amount of oxygen that can be discharged from the solid electrolyte plate to the amount of oxygen that passes through the oxygen diffusion passage is smaller than the initial value, and the current value does not show the limiting current value and is initially used. becomes smaller than the value. On the other hand, on the side where the limiting current begins to show at low critical voltage, even if insulation resistance is generated in the element, the amount of oxygen that can be discharged from the solid electrolyte plate is overwhelmingly larger than the amount of oxygen that passes through the oxygen diffusion path, and the current value is The limit current value remains constant and does not change. Therefore, when the electrode film or the solid electrolyte plate deteriorates, the ratio of each current value differs greatly from the initial value, and an abnormality in the sensor can be detected. In other words, taking advantage of the fact that it is rare for the characteristics of multiple diffusion-limiting bodies to change at the same time and at the same rate, we can form multiple oxygen receptors in one element and compare their ratios. This means that self-diagnosis can be realized.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an assembly diagram of an element of a limiting current type oxygen sensor which is an embodiment of the present invention. 1 is an oxygen ion conductive solid electrolyte plate, and a pair of electrode films 2a and 2
b, 3a and 3b are formed in pairs on both sides. Two cathode side electrode films 2 are placed on one side upper part of this solid electrolyte plate 1.
Two spiral spacers 4' and 4 surround a and 3a and are arranged such that their starting and ending ends are spaced apart from each other.
A seal plate 5 is disposed on top of the spiral spacers 4' and 4'', and a seal plate 5 is disposed on top of the spiral spacers 4' and 4''.
A heating section 6 is arranged on the upper part of the sensor element to constitute a sensor element. In addition, the diffusion-limiting body is the spiral spacer 4' and 4''
and a sealing plate 5, and the oxygen diffusion passage is formed by a spiral spacer 4' or 4'' facing partition walls and a solid electrolyte plate 1.
Oxygen diffuses into the cathode electrode film 2a or 3a via the spiral space. On the other hand, either a method in which the areas of the electrode films 2a and 3a (or areas of the electrode films 2b and 3b) are made different from each other, or a method in which the ratio of the length and cross-sectional area of the spiral spacers 4' and 4'' are respectively changed. Using this method, the critical voltage value at which the limiting current begins to be shown is varied for each.

FIG. 2 is a schematic circuit diagram of a limiting current type oxygen sensor which is an embodiment of the present invention. A pair of electrode films 2a and 2b formed on the element and a pair of electrode films 3a,
Applied voltage generating means 7 applies a predetermined voltage to electrode films 2a, 2b and 3a, 3.
Current detection means 8' for detecting each current obtained from b.
and a current detection means 8'', a current ratio comparison means 9 for comparing the ratio of each current value obtained from the two current detection means, and a current ratio for determining an abnormality if the ratio is significantly different from the initial value when the sensor element is used. It consists of a determining means 10.

On the other hand, a predetermined power is applied to the heating section 6 by a power generating means 11, and the power generating means 11 is further provided with a voltage detecting means 12 for detecting the generated voltage or a current detecting means 13 for detecting the generated current. A determining means 14 is provided which determines that there is an abnormality if the voltage or generated current is significantly different from the initial value when the sensor element is used.

Next, a description will be given based on a specific example. In the limiting current type oxygen sensor shown in Fig. 1, Z is used as the solid electrolyte plate 1.
rO2 ・Y2 O3 (Y2 O3 8 mol % added), platinum for the electrode films 2a, 2b and 3a, 3b, glass for the spiral spacers 4' and 4'' (the coefficient of thermal expansion is approximately the same as ZrO2 ・Y2 O3, and the predetermined grain size is Forsterite was used as the seal plate 5, and a platinum heater was used as the heating part 6.The manufacturing method will be explained.First, the electrode films 2a, 2b and 3a, 3b are placed on the solid electrolyte plate 1. Further, spiral spacers 4' and 4'' were formed on the solid electrolyte plate 1 using thick film printing technology and baking technology. On the other hand, a heating section 6 was formed on the sealing plate 5 using a thick film printing technique and a baking technique. Next, the spiral spacers 4', 4'' on the solid electrolyte plate 1 and the seal plate 5 were laminated and heated and melted to form an oxygen diffusion passage.Then, lead wires (not shown) were attached to complete the process. Yes.The dimensions of the finished device are 10 x 10 x 0.9 mm.
It is. In addition, in this finished device, the lead wires are electrically connected to the lead terminals of the plastic bottom body that constitutes the evaluation device, and then the outside is wrapped with a heat insulating filler, and the heat insulating filler is then wrapped in a stainless steel wire mesh. The device was packaged with a plastic bag and used as an evaluation device. Below, this oxygen sensor evaluation device (φ24×17
mm) was used to test its characteristics.

(Experiment 1-1) The oxygen diffusion passage formed by the spiral spacer 4' has a cross-sectional area of 0.4 x 0.03 mm2.
Sensor I with a length of 10 mm (electrode area 11 mm2)
) and a spiral spacer 4'' with a cross-sectional area of 0.6 x 0.03 mm2 and a length of 8 mm. Sensor II (electrode area 11 mm2) is placed between the solid electrolyte plate 1 and the seal plate 5. We prototyped an element with a different dimension of the oxygen diffusion path.We included this element in an oxygen sensor evaluation device and measured the correlation between the applied voltage and the generated current.The results are shown in Figure 3.The limiting current The critical voltage value at which sensor II begins to exhibit is 0.8 V for sensor I, while
are 1.4V and are different from each other.

[0014] The reason why the critical voltage value at which the limiting current starts to show changes by changing the dimensions of this oxygen diffusion path is as follows.
When the cross-sectional area/length ratio is large, the amount of oxygen passing through the oxygen diffusion passage becomes large, and the ratio of the amount of oxygen passing through the oxygen diffusion passage to the amount of oxygen that can be discharged from the solid electrolyte plate becomes large, resulting in a large limiting current value. and begins to show a limiting current at a high critical voltage value. On the other hand, if the cross-sectional area/length ratio is small, the amount of oxygen passing through the oxygen diffusion passage will be small, and the ratio of the amount of oxygen passing through the oxygen diffusion passage to the amount of oxygen that can be discharged from the solid electrolyte plate will be small, and the limiting current value becomes small and begins to show a limiting current at a low critical voltage value.

(Experiment 1-2) FIG. 4 shows the results of measuring the correlation between oxygen concentration and generated current for Sensor I and Sensor II described above. It can be seen that the generated current has a linear relationship with the oxygen concentration.

On the other hand, the ratio of the generated currents for sensor I and sensor II (sensor II current/sensor I current)
Figure 5 shows the results of calculating the correlation with oxygen concentration. It can be seen that the ratio of generated current is almost constant regardless of the oxygen concentration.

(Experiment 1-3) In the aforementioned Sensor I and Sensor II, the oxygen diffusion passage of Sensor I was clogged by blocking about half of the inlet portion of the oxygen diffusion passage of Sensor I. The results of measuring the current generated by this sensor (
Table 1) shows the results.

Due to clogging of the oxygen diffusion passage of sensor I, the ratio of generated current changes from the initial value of use, and a sensor abnormality can be detected.

[0019]

[Table 1]

(Experiment 1-4) A heat shock was applied to the aforementioned sensor I and sensor II to deteriorate the degree of sealing of the oxygen diffusion passages of sensor I and sensor II. The results of measuring the generated current for this sensor (Table 2)
Shown below.

[0021]

[Table 2]

Due to the deterioration of the sealing degree of the oxygen diffusion passage of the sensor, the ratio of the generated current changes from before the deterioration, and an abnormality in the sensor can be detected.

(Experiment 1-5) A 2000 hour durability test was conducted on the aforementioned Sensor I and Sensor II. The results of measuring the generated current for this sensor are shown in (Table 3).

[0024]

[Table 3]

The current generated by the sensor subjected to the durability test is:
Sensor I is the same before and after the test, whereas sensor II
is smaller after the durability test than before the durability test.

The reason for this is that before the durability test, the critical voltage value at which Sensor I starts to show a limiting current is 0.8V, so even if the durability test is carried out, the test applied voltage of 1.40V is not enough to show the limiting current. It remains as shown and the generated current does not change. However, before the durability test, Sensor II had a critical voltage value of 1.4V at which it began to show a limiting current, and when the durability test was conducted, the generated current changed to an ionic current at the test applied voltage of 1.40V. Therefore, the current generated by sensor II deviates from the limit current region of a constant value, resulting in an ionic current having a small value.

From this, the ratio of generated current decreases after the durability test compared to before the durability test, and sensor abnormality can be detected.

(Experiment 2) Sensor III in which the oxygen diffusion passage formed by the spiral spacer 4' had a cross-sectional area of 0.6 x 0.03 mm2 and a length of 12 mm (electrode area 9 mm2)
) and a spiral spacer 4" with a cross-sectional area of 0.6 x 0.03 mm2 and a length of 12 mm. Sensor IV (electrode area: 13 mm2) is attached to the solid electrolyte plate 1.
A prototype element was fabricated between the seal plate 5 and the seal plate 5. The device with the electrode area varied was included in an oxygen sensor evaluation device, and the correlation between the applied voltage and the generated current was measured. The results are shown in FIG.

The critical voltage value at which the limiting current begins to show is 1.4 V for sensor III, whereas it is 1.4 V for sensor IV.
．． 2V, and each is different.

The ratio of current generated by this element (sensor IV current/sensor III current) is almost constant at 0.784 regardless of the oxygen concentration, and as in the previous case, the clogging test, oxygen diffusion passage seal deterioration test, When a further 2000 hour durability test was conducted, the ratio of generated current deteriorated before and after the test, and a sensor abnormality was detected. In particular, the fact that the critical voltage value at which a limiting current begins to be shown by changing the electrode area is different between Sensor III and Sensor IV means that even if an endurance test is conducted, the critical current will still be sufficiently shown. Sensor IV, whose current does not change, and Sensor III, whose generated current changes to ionic current after the durability test is performed, and therefore the generated current becomes ionic current with a small value.
There is an advantage in being able to distinguish between

[0031] The reason why the critical voltage value at which the limiting current starts to change by changing the electrode area is that when the electrode area is small, the amount of oxygen that can be discharged from the solid electrolyte plate decreases, and the amount of oxygen that passes through the oxygen diffusion path decreases. This is because the ratio of the amount of oxygen to the amount of oxygen that can be discharged by the solid electrolyte plate increases, and the critical current value increases and begins to show a critical current at a high critical voltage value. On the other hand, if the electrode area is large, the amount of oxygen that can be discharged from the solid electrolyte plate will be large, and the ratio of the amount of oxygen passing through the oxygen diffusion passage to the amount of oxygen that can be discharged from the solid electrolyte plate will be small, and the limiting current value will be small. It begins to show a limiting current at a critical voltage value.

(Experiment 3) In the sensor, when the electric power applied to the heating element decreases, the generated current decreases, resulting in erroneous measurements. In order to prevent this, a determining means is provided which determines that an abnormality occurs when the applied voltage or generated current differs greatly from the initial value when the sensor element is used. Table 4 shows the results of measuring the current generated when the electric power applied to the heating body was changed for the above-mentioned Sensor I and Sensor II.

[0033]

[Table 4]

The current generated by the sensor element changes in proportion to the power applied to the heating element to the 0.75th power, but by providing a judgment means that determines that there is an abnormality if the applied voltage or the generated current differs greatly from the value used by the sensor element. It can be seen that erroneous measurements due to changes in the generated current can be prevented.

FIG. 7 is an assembly diagram of an element of a limiting current type oxygen sensor which is another embodiment of the present invention. The difference in FIG. 7 from the device embodiment of FIG. This is a configuration in which reference electrode films 15a and 15b are arranged.

FIG. 8 is a schematic circuit diagram of the limiting current type oxygen sensor shown in FIG. 7, which is another embodiment of the present invention. 8 is different from the circuit embodiment of FIG. 2 in that a voltage generating means 16 applies a predetermined voltage to the pair of reference electrode films 15a and 15b, and a current detection means 16 detects the current generated in the applied voltage generating means 16. This configuration includes a means 17 and a reference electrode current determining means 18 that determines an abnormality when the value of the generated current is significantly different from the initial value when the sensor element is used.

(Experiment 4) Electrode area of reference electrode film: 9 mm2
FIG. 9 shows the results of measuring the generated current when the power applied to the heating body was varied.

Since the generated current is a function of the temperature of the heating element, it is approximately constant regardless of the oxygen concentration when the power applied to the heating element is constant; however, if the value of the generated current differs greatly from the initial value when using the sensor element. It can be seen that the power applied to the heating element can be determined to be abnormal.

[0039] In the present invention, the configuration of a spiral spacer and a seal plate is used as the diffusion barrier in the examples, but other configurations (for example, pinhole type diffusion barrier, porous diffusion barrier) may also be used. It was equally effective.

[0040]

[Effects of the Invention] As described above, according to the limiting current type oxygen sensor of the present invention, the following effects can be obtained. (1) Arrange multiple pairs of electrode membranes and multiple diffusion control bodies surrounding one side of the electrode membranes in an oxygen ion conductive solid electrolyte body, and compare the ratio of each current value obtained from the multiple pairs of electrode membranes. Since the current value ratio is significantly different from the initial value when the sensor element is used, it can be determined that the element is abnormal (clogging or diffusion barrier seal deterioration). (2) Since the sensor element is configured so that the electrode film area or the length and cross-sectional area of the oxygen diffusion path of the diffusion barrier are different, the critical voltage value at which the limiting current starts to be shown is different. (decrease in the generated current related to the temperature) can be detected when the ratio of the current values is significantly different from the initial value when the sensor element is used. (3) With the above configuration, the sensor can make a self-judgment, and in the unlikely event that something is wrong, it can be determined as an abnormality and erroneous measurements can be prevented.

[Brief explanation of the drawing]

[Fig. 1] A perspective view of an element assembly of a limiting current type oxygen sensor which is an embodiment of the present invention.

[Figure 2] Schematic circuit diagram of the limiting current type oxygen sensor

[Figure 3] Diagram showing the correlation between applied voltage and generated current of the same limiting current type oxygen sensor

[Figure 4] Diagram showing the correlation between oxygen concentration and generated current of the same limiting current type oxygen sensor

[Figure 5] Diagram showing the correlation between oxygen concentration and generated current ratio of the same limiting current type oxygen sensor

FIG. 6 is a diagram showing the correlation between applied voltage and generated current of a limiting current type oxygen sensor which is another embodiment of the present invention.

[Figure 7] A perspective view of the element assembly of the same limiting current type oxygen sensor

[Figure 8] Schematic circuit diagram of the limiting current type oxygen sensor

[Figure 9] Diagram showing the correlation between the oxygen concentration voltage of the reference electrode and the generated current of the same limiting current type oxygen sensor

[Figure 10] Element configuration diagram of a conventional limiting current type oxygen sensor

[Explanation of symbols]

1 Oxygen ion conductive solid electrolyte body 2a, 2b, 3a, 3b electrode film 4’, 4” spiral spacer 5 Seal plate 6 Heating body 7a, 7b Reference electrode film

Claims (4)

[Claims] 1. An oxygen ion conductive solid electrolyte body in which a plurality of paired electrode films are formed on both surfaces, and the solid electrolyte body is located on one side of the solid electrolyte body and is arranged so as to surround each of the electrode films, and flows into the solid electrolyte body. It consists of a plurality of diffusion rate limiting bodies each having an oxygen diffusion path that restricts the movement of oxygen molecules, and the electrode film area or the length and cross-sectional area of the oxygen diffusion path are made different so that the critical voltage value at which the limiting current begins to be determined is determined. A plurality of sensor elements each having different sensor elements, an applied voltage generating means for applying a predetermined voltage to the plurality of pairs of electrode films, and a plurality of applied voltage generating means for detecting each current obtained from the plurality of pairs of electrode films by the applied voltage generating means. A limit comprising a detection means, a comparison means for comparing the ratio of each current value obtained from the detection means, and a judgment means for determining that there is an abnormality when the ratio value of each of the current values is significantly different from the initial value when using the sensor element. Current type oxygen sensor. 2. The diffusion barrier comprises a spiral spacer whose starting end and terminal end are spaced apart from each other, and a seal plate located above the spiral spacer. Limiting current type oxygen sensor. 3. A heating element disposed close to the sensor element to heat the oxygen ion conductive solid electrolyte body, power generation means for applying a predetermined power to the heating element, and a voltage applied or generated by the power generation means. 2. The limiting current type oxygen sensor according to claim 1, further comprising a detection means for detecting a current, and a judgment means for determining an abnormality when the value of the applied voltage or the generated voltage is significantly different from an initial value when the sensor element is used. 4. A pair of reference electrode membranes located on both sides of the oxygen ion conductive solid electrolyte body and arranged in a portion not surrounded by the diffusion barrier, and a voltage for applying a predetermined voltage to the pair of reference electrode membranes. 2. The sensor according to claim 1, further comprising a generating means, a detecting means for detecting the generated current in the applied voltage generating means, and a determining means for determining that there is an abnormality when the value of the generated current is significantly different from an initial value when the sensor element is used. Limiting current type oxygen sensor.