JPH06194335A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain a high sensitivity oxygen sensor having a simple structure by inserting a cathode into a cathode insertion hole made through a support and supporting the cathode while covering the outer peripheral surface expect the surface opposing to a diaphragm. CONSTITUTION:A columnar cathode support 16 having one end inserted into a cathode support insertion hole 8 has one end face on which a cathode burying hole 18 is formed, and in which a cathode is contained. The cathode 20 and the support 16 abut, on one end faces thereof, on a diaphragm 12 and thereby the cathode 20 is covered by the support 16 airtightly except the surface opposing to the diaphragm 12. Such quantity of oxygen as proportional to the oxygen concentration of outer atmosphere to be measured passes through the diaphragm 12 to reach the cathode 20 where electrochemical reaction takes place to cause a current flow proportional to the quantity of transmitted oxygen between an anode 28 and the cathode 20, thus allowing measurement of oxygen concentration to be carried out. Since the cathode 20 is buried in the support 16, the oxygen couldn't but flow through the diaphragm 12 and, thereby, the dark current decrease to enhance SN ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor capable of measuring a minute amount of oxygen concentration in liquid or gas.

[0002]

2. Description of the Related Art Conventionally, there are a polarographic type and a galvanyl cell type oxygen sensor.

FIG. 5 shows an example of a conventional polarographic oxygen sensor, and 52 in the figure is a cylindrical casing having a bottom. An electrolytic solution supply hole 54 and a support insertion hole 56 are formed through the bottom of the casing 52. Further, the oxygen permeable diaphragm 5 is provided on the outer surface of the bottom of the casing.
8 are stretched. The cathode 60 is fitted in the cathode embedding hole 64 of the support 62 and is in contact with the diaphragm 58. Therefore, the electrolytic solution 66 is supplied to the cathode 60 through the supply hole 54. 68 is an anode, 7
Reference numeral 0 is a temperature sensor, and 72 is a membrane fixing ring for tensioning and fixing the diaphragm 58 on the bottom of the casing 52. The principle of oxygen concentration measurement by such a sensor is to measure an electric current generated by an amount of oxygen corresponding to the oxygen concentration of the atmosphere outside the sensor, passing through the diaphragm 58, reaching the cathode, and being reduced at the cathode. . Various studies have been added to the above-mentioned sensor in order to enhance the detection sensitivity. For example, in order to reduce the amount of dissolved oxygen in the electrolytic solution inside the sensor, an oxygen consuming electrode is provided in the electrolytic solution (JP-A-53-50892), and the cathode electrode is an oxygen permeable diaphragm. In addition to being in close contact, the cathode electrode is surrounded by a guard electrode so as to eliminate the influence of dissolved oxygen in the electrolytic solution, and the structure is devised (Japanese Patent Publication No. 61-428).
No. 21). However, these sensors have problems such as insufficient sensitivity, and complicated structure, which makes them difficult to handle.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxygen sensor having high sensitivity and a simple structure.

[0005]

[Means for Solving the Problems] To achieve the above object
In addition, the present invention is based on an oxygen sensor case filled with an electrolyte solution.
And a casing attached to the sensor casing.
An oxygen-permeable diaphragm that separates the inside and the outside of the ring,
A cover placed in contact with the diaphragm while being immersed in the electrolyte.
Oxygen with sword and anode immersed in electrolyte
In the sensor, the cathode is a support and the cathode is inserted.
The outer peripheral surface other than the surface inserted into the hole and facing the diaphragm is covered.
And is supported by the inner surface of the casing.
An electrolyte flow control member is placed near the diaphragm at regular intervals.
The oxygen sensor is configured so that
The diaphragm faces the cathode inside the casing
An oxygen consuming electrode made of a metal film is formed in the area other than the area
Including that

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, 2 is a cylindrical first casing 4 having a bottom.
It is a connecting member that connects a and the second casing 4b by screwing. A cathode support insertion hole 8 is provided at the center of the bottom portion 6 of the first casing 4a, and a predetermined number (8 in this embodiment) of electrolyte solution supply holes 10 are provided along a circumference concentric with the insertion hole 8.
Has been drilled.

Reference numeral 12 denotes an oxygen-permeable diaphragm which is stretched in close contact with the outer surface of the bottom 6 and is liquid-tightly fixed to the bottom 6 by a diaphragm fixing ring 14, whereby oxygen permeates the inside and outside of the casing 4a. It is isolated in a state where it does.

Reference numeral 16 denotes a columnar cathode support having one end inserted into the cathode support insertion hole 8. A cathode embedding hole 18 is formed in one end surface of the cathode support insertion hole 8 and a cathode 20 is accommodated therein. ing. The cathode and one end surface of the support member 16 are in contact with the diaphragm 12, so that the cathode 20 is hermetically covered by the support member 16 except for the surface facing the diaphragm 12.

Reference numeral 22 denotes a cylindrical electrolyte flow control member, which is fitted to the support 16 and is provided on the bottom 6 of the casing 4a.
The small chamber 24 is formed between the member 22 and the inner surface of the bottom portion 6 by being fixed to the inner surface with a predetermined gap.

The control member 22 is a casing 4a.
Since the inner diameter of the casing 4a is smaller than the inner diameter of the casing 4, a thin layer passage 26 having a predetermined width is formed between the inner peripheral surface of the casing 4a and the outer peripheral surface of the member 22.

Reference numeral 28 is a cylindrical anode arranged along the outer peripheral surface of the support 16, and reference numeral 30 is a lead wire of the anode 28.

The casing 4a is filled with an electrolytic solution 32, and the cathode 20 and the anode 28 are electrically connected through this electrolytic solution. Incidentally, 33 is a temperature sensor, and 34a and 34b are lead wires of the temperature sensor. Reference numeral 36 is a cathode lead wire.

The operation of the oxygen sensor having the above structure will be described below.

Oxygen in an amount proportional to the oxygen concentration in the external atmosphere to be measured permeates the diaphragm 12 and reaches the cathode, and the electrochemical reaction generated here causes the amount of oxygen permeated between the anode and the cathode. A proportional current flows so that the oxygen concentration can be measured. In this case, since the cathode 20 is embedded in the support body 16, there is nothing but oxygen passing through the diaphragm, so that the dark current is reduced and the S / N ratio of the sensor is improved. Further, since the electrolyte flow control member 22 is provided in the casing and the electrolyte is supplied to the cathode 20 through the narrow thin layer passage 26, noise due to the vibration of the electrolyte is prevented, and the flow is further prevented. The electrolytic solution is supplied to the small chamber 24 by the control member 22.
By separating the above into other components, the movement of the dissolved oxygen in the electrolytic solution to the cathode 20 due to vibration or diffusion can be suppressed, and the effect of reducing the dark current of the sensor can be obtained.

Furthermore, when the electrolytic solution is separated into the small chamber 24 and other parts by the flow control member 22, when the external environment becomes zero oxygen concentration, the thin layer passage 26 is narrow, so that an oxygen concentration gradient occurs in this portion. The oxygen concentration is lower in the electrolyte layer closer to the diaphragm. Therefore, even if the oxygen concentration in other parts is high, the oxygen concentration of the electrolytic solution in the small chamber 24 should be close to zero in a relatively short time after the oxygen concentration in the external environment becomes zero. Therefore, the response speed of the electrode can be increased, and highly sensitive analysis can be performed.

FIG. 2 shows another embodiment of the present invention. In this configuration, in addition to the configuration shown in FIG. 1, an oxygen consuming electrode made of a metal film is further provided on the surface of the diaphragm inside the casing.

That is, FIG. 2A is a partially enlarged view of the oxygen sensor, and an oxygen consuming electrode 38 made of a metal film is formed on the inside of the casing 4a of the diaphragm 12 stretched over the casing 4a. This consumption electrode 38 is shown in FIG.
As shown in (4), it is formed in a region 42 other than the region 40 facing the cathode 20.

Reference numeral 44 denotes a contact formed on the outer surface of the bottom of the casing 4a. The oxygen consuming electrode 38 is in contact with the contact 44 and is electrically connected thereto. 46
Is a lead wire connected to the contact 44, and a voltage is applied to the oxygen consuming electrode 38 via this lead wire. The applied voltage is preferably the same as that of the cathode 20 or within ± 0.2 V from the potential of the cathode 20.

As the metal material of the oxygen consuming electrode 38,
What can be used as an oxygen reduction electrode such as gold, platinum, or tungsten is used. As a method for forming the oxygen consuming electrode, a vacuum vapor deposition method, a sputtering method, or the like can be used, and the electrode film thickness is preferably 100 to 1000 Å.

A known material can be used for the oxygen permeable diaphragm, and for example, Teflon or the like is preferable. The thickness of the diaphragm is 1
It is preferably about 0 to 30 μm.

The present invention will be further described below with reference to test examples. (Test Example 1) Oxygen sensor (comparative product 1) shown in FIG. 5 and FIG.
FIG. 3 shows the result of comparison of the response speeds of the oxygen sensor shown in FIG. The product of the present invention provided with the flow control member had a faster response speed than the comparative product not provided with the flow control member. Test Example 2 The results of comparing the response speeds of the oxygen sensor shown in FIG. 2 (invention product 2) and the oxygen sensor shown in FIG. 5 (comparative product 1) are shown in FIG. 4 and Table 1. The product 2 of the present invention provided with the flow control member and the oxygen consuming electrode exhibited even better response characteristics.

[0023]

[Table 1] The oxygen sensor can be used as a known sensor for measuring hydrogen peroxide, ozone, etc., and in this case, it falls within the technical scope of the present invention.

[0024]

In the oxygen sensor of the present invention, since the electrolytic solution flow control member is provided near the cathode, the electrolytic solution is supplied to the cathode through the thin layer passage, and the S / N based on the flow of the electrolytic solution is provided. Ratio deterioration is effectively prevented.

Furthermore, since the oxygen consuming electrode is formed on the surface of the diaphragm inside the sensor, the effect of dissolved oxygen can be effectively prevented. Further, the oxygen consuming electrode is structurally simple and advantageous in manufacturing.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view showing an embodiment of the present invention.

FIG. 2A is a partially enlarged side sectional view showing another embodiment of the present invention. (B) is a plan view showing the structure of the diaphragm.

FIG. 3 is a graph showing responsiveness of electrodes.

FIG. 4 is a graph showing responsiveness of electrodes.

FIG. 5 is a partially enlarged sectional view showing the configuration of a conventional oxygen sensor.

[Explanation of symbols]

 2 connecting member 4a 1st casing 4b 2nd casing 6 bottom 8 cathode support insertion hole 10 electrolyte solution supply hole 12 diaphragm 14 diaphragm fixing ring 16 cathode support 18 cathode embedding hole 20 cathode 22 flow control member 24 small chamber 26 thin layer Passage 28 Anode 30 Lead wire 32 Electrolyte 33 Temperature sensor 34a, 34b Lead wire 36 Lead wire 38 Oxygen consuming electrode 40 Area facing the cathode 42 Area other than the area facing the cathode 44 Contact 46 Lead wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Yokoyama 2-29-7 Chikawa, Toshima-ku, Tokyo (72) Inventor Toshio Kaizuka 2-14-2 Hanasaki, Narashino City, Chiba Prefecture (72) Inventor Hideo Abe Saitama Prefecture 2046-9 Yamada, Kawagoe City (72) Inventor Toshio Yamamoto 642-192 Rokumi Goka, Matsudo City, Chiba Prefecture 642-192 (72) Yutaka Arakawa 3-18-2 Minatomachi, Funabashi City, Chiba Prefecture

Claims (2)

[Claims] 1. An oxygen sensor casing filled with an electrolytic solution, an oxygen permeable diaphragm attached to the sensor casing to separate the inside and the outside of the casing, and the oxygen sensor casing immersed in the electrolytic solution and contacting the diaphragm. In an oxygen sensor having a cathode disposed in contact with the anode and an anode immersed in an electrolytic solution, the cathode is inserted into a cathode insertion hole of a support, and an outer peripheral surface other than the surface facing the diaphragm is covered. An oxygen sensor which is supported and is provided with an electrolyte flow control member in the vicinity of the diaphragm with a predetermined distance from the inner surface of the casing. 2. The oxygen sensor according to claim 1, wherein the diaphragm has an oxygen consuming electrode formed of a metal film in a region other than a region facing the cathode inside the casing.