JPH0716997Y2 - Oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a limiting current type oxygen sensor, in which an electrode for controlling a limiting current value is provided in a cap portion (inside and outside) in addition to a sensing electrode. The present invention relates to an oxygen sensor that can be used for high concentration, low concentration, etc. by controlling a limiting current value.

<Prior Art> As a conventional oxygen sensor, for example, one having a structure as shown in FIG. 3 has been proposed.

In the case of this oxygen sensor, a pair of sensing electrodes is provided on both sides of a sensing substrate 1 made of a solid electrolyte such as zirconia.
2 and 3 are provided, a cap 4 having a small hole 5 for diffusion is capped on one side surface (upper surface in the drawing) of the sensing substrate 1, and a heater 6 for heating is provided on the upper surface of the cap 4 and the like. The sensing electrodes 2 and 3 are connected to the sensing power source 7, a necessary ammeter 8 and a voltmeter 9 respectively.
Etc. are connected. On the other hand, a heating power source 10 is connected to the heating heater 6.

In such an oxygen sensor, in order to measure the oxygen concentration, first, the sensor itself is heated to a desired driving temperature (for example, about 400 ° C.) by the heater 6, and when the driving temperature is reached, the sensing electrodes 2, 3 The current value (limit current value) due to the energization of is read by the ammeter 8 and the oxygen concentration may be obtained from this current value.

<Problems to be Solved by the Invention> However, in the above-described conventional oxygen sensor, the cap 4
The critical current value greatly depends on the small hole size (inner diameter) of.

However, the size of the small hole 5 is uniquely determined at the stage when the sensor is manufactured, and therefore its use is fixed.
Conversely, it is necessary to determine the small hole size according to the application and manufacture a corresponding oxygen sensor.

Even if the size of this small hole is determined, it is extremely difficult from the viewpoint of manufacturing technology if it is too small, and it cannot be set freely and freely.

The present invention has been made in view of such a conventional situation.

<Means for Solving the Problems> The feature of the present invention is that a pair of sensing electrodes are provided on both sides of a sensing substrate made of a solid electrolyte, and a small diffusion surface is provided on one side of the sensing substrate. In an oxygen sensor in which a cap having a hole is capped and a heater for heating is provided on the upper surface of the cap or the like, the cap is formed of a solid electrolyte and a counter electrode is formed inside the cap with a heater electrode of the heater. An oxygen sensor for controlling a limiting current value by providing an internal electrode for controlling a limiting current value and connecting a control power supply between the internal electrode and the heater electrode.

<Operation> By applying a constant current or applying a constant voltage between the internal electrode for controlling the limiting current value and the heater electrode (by changing the magnitude of polarity, current, voltage, etc.), the solid electrolyte of the cap itself is used. Since the pumping action on oxygen is adjusted, it is possible to freely set the limiting current value.

<Embodiment> FIG. 1 shows an embodiment of the oxygen sensor according to the present invention.

The oxygen sensor of the present invention has substantially the same basic structure as the oxygen sensor of FIG. 3 except for the internal electrode 11 for controlling the limiting current value and the controlling electrode 12, and therefore, the same portion Are given the same reference numerals.

However, in the case of this oxygen sensor, the cap 4 is also formed of a solid electrolyte such as zirconia, and the internal electrode 11 for controlling the limiting current value serves as a counter electrode to the heater electrode 6a of the heater 6 for heating. 4 is provided on the top (inner upper surface) inside.

A power source 12 for controlling the limiting current value is connected between the internal electrode 11 and the heater electrode 6a. Also, this power supply 12
The polarity of can be freely changed by replacing the power supply 12 itself, attaching a changeover switch, or the like.

Next, a method of using the oxygen sensor of the present invention will be described.

(1) In the case of high concentration measurement (for example, when the oxygen concentration is 21% or more) In this high concentration measurement, the sensor life becomes a problem. This is because the limiting current is large in the high-concentration region, the load on the sensing electrodes 2 and 3 is large, and the electrode performance deteriorates quickly. Therefore, conventionally, in high-concentration measurement, a sensor with a small limiting current value (a sensor with a small cap small hole 5) was created and used.

However, conventionally, in order to minimize the small hole 5, in terms of manufacturing,
There were some limits.

With the oxygen sensor of the present invention, in the case of this high concentration measurement, the second
As shown in the figure (A), internal electrodes for controlling the limiting current value
A constant current source is connected as a control power supply 12 with the 11 side as a negative pole and the heater electrode 6a side as a positive pole.

Owing to the connection of the constant current source, oxygen in the cap 4 is pumped by the electrodes 2 and 3 on the sensing substrate 1 side as shown by the arrow in the figure, and the cap 4 itself is solidified by the internal electrode 11 and the heater electrode 6a. It is also discharged by the pumping action of the electrolyte.

In this case, the size of the control power supply 12 is set so that the pumping action on the cap side is smaller than the pumping action on the sensing substrate side.

In any case, according to the method of using the oxygen sensor, a part of the oxygen in the cap 4 which has been pumped on the sensing substrate 1 side in the past is discharged by the pumping action on the cap 4 side. Apparently,
A sensor having a small cap small hole 5, that is, a sensor having a small limiting current value can be obtained.

Therefore, even if the actual size of the small hole 5 is not so small as to be difficult to manufacture, a sensor having a small predetermined limiting current value can be obtained, and the load on the sensing electrodes 2 and 3 is reduced. Therefore, the sensor life can be improved.

(2) When measuring low concentration (for example, when the oxygen concentration is 1% or less) In this low concentration measurement, resolution becomes a problem. Conventionally, for low-concentration measurement, a sensor having a large limiting current value (a sensor having a large cap small hole 5) was created to improve the resolution.

However, if the cap small hole 5 is made too large, there are problems such as a decrease in yield in the drilling process (increased breakage rate) and a decrease in gap strength.

With the oxygen sensor of the present invention, in the case of this constant concentration measurement, the second
As shown in the figure (B), internal electrodes for controlling the limiting current value
A constant current source or a constant voltage source is connected as the control power source 12 by using the 11 side as a positive pole and the heater electrode 6a side as a negative pole.

By connecting the constant current source and the constant voltage source, oxygen from the outside air is introduced into the cap 4 through the small holes 5 as shown by an arrow in the figure, and the cap 4 is formed by the internal electrode 11 and the heater electrode 6a. It is also introduced by the pumping action of its own solid electrolyte.

In this case, the size of the control power supply 12 is set so that the pumping action on the cap side is smaller than the pumping action on the sensing substrate side.

In any case, according to the method of using this oxygen sensor, a part of oxygen in the cap 4, which has been conventionally entirely introduced from the cap small hole 5 side, is also introduced by pumping from the cap 4 side. As a result, it is possible to obtain a sensor having a large cap small hole 5, that is, a sensor having a large limiting current value.

Since the amount of oxygen introduced by pumping on the side of the cap 4 depends on the oxygen concentration in the low concentration region, not only the limit current value is simply increased but also the resolution is improved.

In each of the above-described usage methods, the case of measuring high concentration and low concentration has been described, but the oxygen sensor of the present invention can of course be applied to ordinary concentration measurement such as oxygen concentration in the atmosphere.

<Effect of Device> As is clear from the above description, the oxygen sensor of the present invention can be expected to have the following excellent effects.

(1) In high-concentration measurement, even if the cap small hole is defined to have a certain size and a certain size, the limit current value can be controlled to a small value by the electrode for limiting current control provided in this cap portion. It is possible to measure concentration,
Further, the life of the sensor can be improved by reducing the load on the sensing electrode.

(2) In low concentration measurement, even if the cap small hole is fixed to a certain size, the limit current value can be greatly controlled by the electrode for limiting current control provided in this cap part, so low concentration measurement is possible. Further, since the amount of oxygen introduced at this time depends on the oxygen concentration in the low concentration range, a predetermined resolution can be obtained.

(3) Also in the sensor structure, since the existing heater electrode is used as the electrode for controlling the limiting current and the internal electrode is only provided in the cap, the manufacturing is simple.

(4) Of course, it is necessary to change the control power supply or changeover switches,
Since it is possible to easily change the polarity of the limit current control electrode and change the current value and voltage value with other parts,
With one sensor, it is possible to obtain an excellent sensor that can handle a wide range from high concentration to low concentration.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of an oxygen sensor according to the present invention, FIGS. 2 (A) and 2 (B) are explanatory views showing respective usages of the oxygen sensor of FIG. 1, and FIG. FIG. 6 is an explanatory diagram showing an example of a conventional oxygen sensor. In the figure, 1 ... Sensing substrate, 2, 3 ... Sensing electrode, 4
...... Cap, 5 ... Small hole, 6 ... Heater, 6a ... Heater electrode, 11 ... Internal electrode, 12 ... Control power supply,

Claims (3)

[Scope of utility model registration request] 1. A pair of sensing electrodes are provided on both sides of a sensing substrate made of a solid electrolyte, a cap having a small hole for diffusion is capped on one side surface of the sensing substrate, and the upper surface of the cap is heated. In the oxygen sensor provided with a heater for use, the cap is formed of a solid electrolyte, and an internal electrode for controlling a limiting current value that forms a counter electrode with the heater electrode of the heater is provided inside the cap, and the internal electrode and the An oxygen sensor characterized by connecting a control power supply to a heater electrode to control a limiting current value. 2. The oxygen sensor according to claim 1, wherein the internal electrode is a negative electrode for high concentration measurement. 3. The oxygen sensor according to claim 1, wherein the internal electrode is a positive electrode for low concentration measurement.