JPH04340457A - Limit current type oxygen sensor - Google Patents

Abstract

PURPOSE:To impart self-diagnostic function for preventing erroneous measurement to a limit current type oxygen sensor for measuring the concn. of oxygen in an atmosphere. CONSTITUTION:The current generated in a main electrode film 2a in such a case that oxygen flows in (or flows out of) an oxygen diffusion passage 5 through an oxygen ion conductive solid electrolyte plate 1 by the operation of an auxiliary electrode film 7b is compared with the current generated in the main electrode film 2a when the auxiliary electrode film 7b is not operated. When a sensor is deteriorated, the ratio of both currents becomes a value different from a use initial value and, therefore, the deterioration of the sensor can be detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor for measuring oxygen concentration in an atmosphere, and particularly to a sensor equipped with a self-diagnosis function to prevent erroneous measurements.

0002

2. Description of the Related Art FIG. 5 shows a partially cutaway oblique view of a conventional limiting current type oxygen sensor. 1 is a solid electrolyte plate exhibiting oxygen ion conductivity, and electrode films 2a are formed on both surfaces thereof. A spiral spacer 3 is arranged on one side of the solid electrolyte plate 1 to surround the electrode film 2a and form an oxygen diffusion passage 5 such that the starting end and the ending end thereof are spaced apart from each other. It is located. Oxygen diffusion passage 5
is formed by a spiral space surrounded by the opposing partition walls of the spiral spacer 3, the solid electrolyte plate 1, and the seal plate 4, and oxygen diffuses into the electrode film 2a via the oxygen diffusion passage 5. A heating section 6 is formed on the seal plate 4 to heat 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, a predetermined voltage is similarly applied to the electrode films 2a formed on both surfaces via lead wires (not shown). Then, oxygen in the air flows through the oxygen diffusion passage 5 to the electrode film 2a, and further flows into the electrode film 2a on the cathode side.
From there, it moves as oxygen ions toward the electrode film on the anode side, and is released again as oxygen at the electrode film on the anode side. Oxygen moves through the solid electrolyte plate 1 due to this oxygen pumping action, and a current is generated accordingly, but since the oxygen diffusion path restricts the inflow of oxygen molecules,
A saturation current (referred to as a limiting current) occurs depending on the oxygen concentration. Since this limiting current value is approximately proportional to the oxygen concentration, the oxygen concentration can be determined by measuring the limiting current value.

0004

[Problem to be Solved by the Invention] When actually using a sensor, for example, if the heater in the heating section deteriorates and the temperature of the solid electrolyte plate drops, the characteristics may deviate from the normal state, causing an error. Measurement occurs. However, since the conventional structure cannot verify this erroneous measurement, it is unclear whether the oxygen concentration display value of the sensor is correct or whether an erroneous measurement has occurred, and the only option is to trust the oxygen concentration display value. Particularly in ordinary homes where it is difficult to verify the oxygen concentration display, sensor reliability is a top priority because a lack of indoor oxygen concentration can lead to death. Therefore,
A conventional structure in which self-diagnosis of sensor deterioration cannot be performed is inconvenient because even if sensor deterioration occurs and an erroneous measurement occurs, this erroneous measurement value is displayed as a correct value.

The present invention solves such conventional problems by self-diagnosing the presence or absence of sensor abnormality, and in case of an abnormality,
This is to prevent erroneous measurements by determining it as abnormal.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the limiting current type oxygen sensor of the present invention has a main electrode film formed on one side of an oxygen ion conductive solid electrolyte plate having main electrode films formed on both sides. A spiral spacer whose encircling start end and end end are spaced apart from each other is disposed, and a seal plate is disposed above the helical spacer, so that the opposite partition walls of the helical spacer, the solid electrolyte plate, and the seal plate are arranged. Oxygen diffusion holes are formed in a spiral space surrounded by , and auxiliary electrode films are formed and arranged on both sides of the solid electrolyte plate in the oxygen diffusion holes.

[0007]

[Operation] Generally, the relationship between the oxygen concentration and the limiting current value of a limiting current type oxygen sensor is determined by the opening area and length of the oxygen diffusion hole and the sensor temperature. Therefore, when these values change due to sensor deterioration, the oxygen diffusion behavior also changes, and the relationship between the oxygen concentration and the limiting current value changes accordingly.

[0008] Therefore, the present invention aims to calculate the current (II) generated in the main electrode membrane when oxygen is further flowed into the oxygen diffusion hole through the solid electrolyte plate due to the operation of the auxiliary electrode membrane, and the current generated in the main electrode membrane (II) when the auxiliary electrode is not activated. The current (I) generated by the electrode film is compared, and if the ratio differs from the initial value of use, deterioration of the sensor is detected. In this configuration, if the opening area and length of the oxygen diffusion hole and the sensor temperature are constant, the current ratio of the main electrode film shows the same value whether the auxiliary electrode is activated or not. Therefore, if the sensor is normal, the current ratio will be the same value as the initial value.

However, when the opening area and length of the oxygen diffusion hole and the sensor temperature change due to sensor deterioration, the oxygen diffusion behavior in the oxygen diffusion hole changes. This change in oxygen diffusion behavior changes the current in the main electrode membrane (I) when the auxiliary electrode is not activated. On the other hand, when oxygen further flows into the oxygen diffusion hole through the solid electrolyte plate due to the operation of the auxiliary electrode, the diffusion behavior of this inflow oxygen changes, and the total amount of oxygen added to the oxygen from the original oxygen diffusion hole is Since the diffusion behavior of oxygen changes, the current (II) of the main electrode film changes. Since the rate of change in the oxygen diffusion behavior is not the same as the rate of change in the oxygen diffusion behavior when the auxiliary electrode is not activated, the current ratio of the main electrode membrane when the auxiliary electrode is activated or not is different from the initial value of use. Therefore, sensor deterioration can be detected.

0010

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

FIG. 1 is a partially cutaway perspective view 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 main electrode membranes 2a and 2
b (not shown) is formed on both sides. A spiral spacer 3 surrounding the main 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 4 is arranged above the spiral spacer 3. The oxygen diffusion passage 5 is formed in a spiral space surrounded by the opposing partition walls of the spiral spacer 3, the solid electrolyte plate 1, and the seal plate 4, and oxygen passes through the oxygen diffusion passage 5 to the main electrode film 2a. Spread. A heating section 6 is formed on the seal plate 4 to heat the solid electrolyte plate 1 to improve conduction of oxygen ions. On the other hand, in the oxygen diffusion passage 5, auxiliary electrode films 7a (not shown) and 7b are formed and arranged on both sides of the solid electrolyte plate 1, and oxygen flows into the oxygen diffusion passage 5 through the solid electrolyte plate 1. There is.

Next, a description will be given based on a specific experimental example. In the limiting current type oxygen sensor having the structure shown in Fig. 1, ZrO2 ・Y2 O3 (Y2 O3 8
mol% addition), main electrode films 2a and 2b (not shown), auxiliary electrode films 7a (not shown) and 7b are platinum, and spiral spacer 3 is glass (thermal expansion coefficient is ZrO2 ・Y2
(approximately the same as O3 and containing a trace amount of heat-resistant particles of a predetermined particle size) was used. The manufacturing method will be explained. First, the main electrode films 2a and 2b (not shown) and the auxiliary electrode films 7a and 7b (not shown) are placed on the solid electrolyte plate 1, and then the spiral spacer 3
was formed on the solid electrolyte plate 1 using thick film printing technology and baking technology. On the other hand, a heating portion 9 was formed on the seal plate 8 using thick film printing technology and baking technology. and,
A sealing plate 4 was laminated on the spiral spacer 3 on the solid electrolyte plate 1 and heated and melted to form an oxygen diffusion passage 5. Finally, attach the lead wires (not shown) and it is complete. The dimensions of the finished product are 10 x 10 x 0.9 mm. This completed product was then wrapped with a heat insulating material, and the heat insulating material was further wrapped with a stainless steel wire mesh casing to form a packaged product. Hereinafter, the effect was tested using this implementation.

FIG. 2 is a characteristic diagram showing the characteristics of a limiting current type oxygen sensor which is an embodiment of the present invention. Main electrode films 2a and 2b when applying a voltage of 1.4V (not shown)
The generated current (I) and the main electrode films 2a and 2b (not shown)
and the current (II) generated from the main electrode films 2a and 2b (not shown) with voltage applied to the auxiliary electrode films 7a and 7b,
Measurements are made by changing the heater power. Note that the generated current (II) is 1.4 in the main electrode films 2a and 2b (not shown).
A voltage of V is applied, and an auxiliary electrode film 7a (not shown) is applied.
- This is the current of the main electrode membranes 2a and 2b (not shown) in a state in which a voltage is applied to 7b to flow a constant current of 25 μA, and oxygen further flows into the oxygen diffusion path via the solid electrolyte plate 1.

The generated current (I) changes approximately in proportion to the oxygen concentration, and its value has a characteristic that it decreases as the sensor temperature decreases. On the other hand, the generated current (II) also changes almost in proportion to the oxygen concentration, but has a characteristic that is obtained by moving the generated current (I) almost in parallel.

[0015] This characteristic was such that the closer the auxiliary electrode film was placed to the main electrode film, or the larger the constant current value from the auxiliary electrode film, the more the parallel movement occurred.

FIG. 3 is an effect diagram showing the effect of a limiting current type oxygen sensor which is an embodiment of the present invention. The characteristics in FIG. 2 are organized in terms of the relationship between the generated current (I), the generated current (II), and the current ratio (II/I) of the generated current (I).

It can be seen that there is a correlation between the current ratio (II/I) and the generated current (I), and that the correlation characteristic changes as the sensor temperature (heater power in this case) changes. Therefore,
Calculate the current ratio (II/I) of the generated current (I) in an atmosphere with a constant oxygen concentration, compare the value with the initial value (heater power 3.30W), and if the value is different, the sensor is abnormal (this It can be seen that heater deterioration) can be detected.

On the other hand, in the case of clogging or seal deterioration in the oxygen diffusion passage of the sensor, the current ratio in the generated current (I) changes when clogging or seal deterioration occurs. .30W), it can be seen that if the value is different, a sensor abnormality (in this case, clogging or seal deterioration) can be detected.

According to the present invention, deterioration of the sensor can be detected, and this effect is similar even under conditions where oxygen flows out from the oxygen diffusion passage. A similar effect was also obtained by applying a constant potential to the auxiliary electrode film.

[0020]

As described above, the limiting current type oxygen sensor of the present invention has a configuration in which an auxiliary electrode film is arranged in the oxygen diffusion passage, and the auxiliary electrode film allows oxygen to flow into the oxygen diffusion passage through the solid electrolyte plate. The current generated in the main electrode film (II) when the auxiliary electrode film is not activated (or flows out) is compared with the current generated in the main electrode film (I) when the auxiliary electrode film is not activated. In this configuration, if the opening area and length of the oxygen diffusion passage and the sensor temperature are in a constant normal state, the current ratio of the main electrode membrane with or without operation of the auxiliary electrode membrane exhibits the same value as in the initial stage of use. However, if the opening area and length of the oxygen diffusion passage and the sensor temperature change due to sensor deterioration, the current ratio becomes a value different from the initial value of use, so that it is possible to detect the deterioration of the sensor.

[Brief explanation of drawings]

[Fig. 1] A partially cutaway perspective view of a limiting current type oxygen sensor that is an embodiment of the present invention.

[Fig. 2] Characteristic diagram showing the characteristics of a limiting current type oxygen sensor that is an embodiment of the present invention

[Fig. 3] Effect diagram showing the effect of the limiting current type oxygen sensor which is an embodiment of the present invention.

[Figure 4] Partially cutaway perspective view of a conventional limiting current type oxygen sensor

[Explanation of symbols]

1 Oxygen ion conductive solid electrolyte plate 2a Main electrode film 3 Spiral spacer 4 Seal plate 5 Oxygen diffusion passage 6 Heating part 7b Auxiliary electrode film

Claims (1)

[Claims] 1. A spiral spacer surrounding the main electrode film and having a starting end and a terminal end spaced apart from each other is disposed on one side of an oxygen ion conductive solid electrolyte plate having main electrode films formed on both sides, and the spiral spacer A sealing plate is disposed on the top of the spiral spacer, and an oxygen diffusion passage is formed in a spiral space surrounded by the opposite partition walls of the spiral spacer, the solid electrolyte plate, and the sealing plate, and an oxygen diffusion passage is auxiliary to the oxygen diffusion passage. A limiting current type oxygen sensor in which electrode films are formed and arranged on both sides of the solid electrolyte plate.