JPH062212U - Galvanic battery type dissolved oxygen sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a galvanic cell type dissolved oxygen sensor that facilitates diaphragm replacement, is stable for a long period of time, and is highly reliable [Constitution] A positive electrode 5 attached to an outer surface of a container body 1,
An O-ring mounting portion 1a recessed on the outer periphery of the positive electrode 5 of the container body 1 and an O-ring 6 mounted on the O-ring mounting portion 1a.
A diaphragm 4 for covering the positive electrode 5 and the O-ring 6, a holding lid 2 for pressing the diaphragm 4 and the O-ring 5, and a diaphragm-protecting metal mesh 7 arranged on the outer surface of the diaphragm 4. By pressing the O-ring 5 and the diaphragm 4 with the annular pressing lid 2 and the O-ring mounting portion, the diaphragm 4 and the positive electrode 3 are brought into close contact with each other, the diaphragm 4 is fixed, and the electrolytic solution 9 is sealed. The diaphragm protecting metal mesh 7 is configured to prevent expansion and damage of the diaphragm 4 due to an increase in sensor internal pressure.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a galvanic cell type dissolved oxygen sensor for measuring the amount of dissolved oxygen in an aqueous solution. More specifically, the present invention relates to a galvanic cell type dissolved oxygen sensor intended to withstand repeated sterilization treatment by high-temperature steam and maintain its characteristics, which is particularly found in use in a culture tank.

[0002]

[Prior art]

 An electrochemical oxygen sensor is generally composed of a catalyst electrode as a positive electrode, a lead electrode as a negative electrode, an electrolytic solution, and a diaphragm made of a fluororesin that allows oxygen to permeate but prevents water vapor from permeating. is there.

Regarding the disposition of the diaphragm, in the case of an aerial oxygen sensor, since the concentration diffusion of oxygen is fast, even if a cap for protection is provided on the outside of the diaphragm covering the positive electrode, I should have secured a flow passage. However, in the case of an underwater type dissolved oxygen sensor, it was necessary to expose this thin and weak diaphragm to the outside, and it was necessary to handle it carefully so as to prevent stretching and damage.

The reason for exposing the diaphragm to the outside is that the diffusion rate of dissolved oxygen in water is very slow. In other words, unlike in air, in water, oxygen consumed in the positive electrode cannot be supplemented only by concentration diffusion, and in order to accurately measure the amount of dissolved oxygen, a special electrode such as a positive electrode having a very small electrode area can be used. Unless otherwise, the test water must be flowing at all times, and in order not to obstruct the flow, the diaphragm, which is the detector, is located on the outermost side, and the surrounding area should be as free of protrusions as possible. Was designed to.

By the way, although biotechnology has been remarkably developed in recent years, the object to be cultivated is changed from plant cells to animal cells more recently, and long-term culturing has been performed in addition to short-term culturing. There has been a demand for adding DO values to the conventional parameters such as temperature and pH for controlling the operating conditions.

Here, when considering the use of the dissolved oxygen sensor in the culture tank, it becomes the minimum necessary condition that the performance of the sensor is maintained even after sterilization treatment with high-temperature steam. Not to mention the heat resistance of the components that make up the sensor, the most important consideration is the protection of the diaphragm. As mentioned above, know-how is necessary to prevent damage to the diaphragm while exposing it to the outside. That is, when a pressure difference occurs between the inside of the sensor and the measurement environment due to the sterilization process, if no measures are taken, the diaphragm is stretched due to an increase in the internal pressure due to boiling of the electrolytic solution, and it does not return to its original state. Etc. This makes the sensor output unstable.

Of course, some dissolved oxygen sensors have been developed and marketed for culture tanks. They include a method of compensating for the pressure difference between the inside and outside of the sensor by providing a pressure equalizing hole in the body of the sensor, as disclosed in, for example, Kaishin Sho-58-69274, and in Japanese Patent Laid-Open No. 62-27657. In order to eliminate the effect on the output when the internal pressure of the diaphragm rises, a cushion is put on the outside of the diaphragm and then covered with a metal wire mesh from the outside to stabilize the diaphragm.

[0008]

[Problems to be solved by the device]

 In order to use the dissolved oxygen sensor in the culture tank, it is important to prevent the extension or damage of the diaphragm due to the increase of the internal pressure of the sensor during the sterilization treatment with high temperature steam. In the method of providing the pressure equalization hole in the body of the, the steam enters through the pressure equalization hole, and the internal electrolytic solution is ejected, resulting in the electrolytic solution being diluted, and the sensor output decreases each time the sterilization process is repeated. In the end, there was a problem that the output would stop. In addition, recently, in order to completely eliminate the influence of various bacteria, the sterilization condition used to be 20 to 30 minutes at 121 ° C in the past, but there are cases where sterilization is performed at 130 ° C for 1 hour. The gushes of the liquid are considered to be more intense. Further, since the ejection of the electrolytic solution means that impurities are mixed into the medium, the method having the pressure equalizing holes is also inconvenient in that respect.

The above problem can be solved by adopting a completely closed structure having no pressure equalizing hole, but it is necessary to consider how to protect the thin and low-strength diaphragm. In view of this, there is a sensor in which the diaphragm is covered with a metal wire mesh so that the diaphragm does not change even when the internal pressure rises. This is shown in JP-A-62-27657, but it cannot be used as it is for a culture tank. According to this method, the diaphragm must be fixed by heat seal or adhesive as a method of fixing the diaphragm, the material of the diaphragm is limited, and since the main body material is a thermoplastic resin, it is heat resistant. Is insufficient.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a long-term structure that can endure steam sterilization while having a closed structure without pressure equalizing holes. It is intended to provide a galvanic battery type dissolved gas sensor sensor which has a stable life.

[0011]

[Means for Solving the Problems]

 Therefore, in the present invention, a positive electrode composed of a catalytic electrode effective for the electrochemical reduction reaction of oxygen, a negative electrode composed of lead, an electrolytic solution, a container accommodating them, and a diaphragm arranged outside the positive electrode. In a membrane-dissolved gas sensor basically composed of, a positive electrode attached to the outer surface of the container body, an O-ring mounting portion recessed in the outer periphery of the positive electrode of the container body, and an O-ring mounting portion. An O-ring, a diaphragm covering the positive electrode and the O-ring, a holding lid for pressing the diaphragm and the O-ring, and a metal membrane for protecting the diaphragm arranged on the outer surface of the diaphragm, and an annular holding lid. By pressing the O-ring and the diaphragm with the O-ring mounting part, the diaphragm and the positive electrode are brought into close contact with each other, the diaphragm is fixed and the electrolytic solution is sealed, and the diaphragm for protecting the diaphragm increases the pressure inside the sensor due to the metal mesh for protecting the diaphragm. To prevent swelling and damage With diaphragm type dissolved gas sensor, characterized in that it is configured to allow, solves St. the problems.

[0012]

[Function] By adopting the above-mentioned structure in which the O-ring is used for fixing the diaphragm and sealing the electrolytic solution, it becomes possible to use a heat-resistant fluororesin film, and even if sterilization treatment with high temperature steam is performed. It maintains the same output characteristics, output level, and response speed before and after that. Furthermore, the metal mesh on the outer surface of the diaphragm can prevent the diaphragm from expanding or being damaged due to an increase in the sensor internal pressure. Moreover, the present invention devises the formation of the O-ring groove formed by the diaphragm pressing lid and the container in the diaphragm fixing and the electrolytic solution sealing using the O-ring, so that the diaphragm can be collapsed when the O-ring is crushed. Can be made to extend in a convex shape, and as a result, the cathode part, which is the detection part, can be positioned at the outermost part, and the detection part can be formed in a shape without protrusions. In addition, by eliminating the projections on the detection part, the output decrease due to the obstruction of the flow of water is minimized, and the accumulation of air bubbles in the detection part is prevented. Prevents measurement errors caused by air bubbles even in internal measurements.

[0013]

【Example】

 Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a sectional structure of a galvanic cell type dissolved oxygen sensor according to an embodiment of the present invention. In the figure, 1 is a container body, 5 is a positive electrode attached to the outer surface of the container body, 1a is an O-ring mounting portion recessed in the outer periphery of the positive electrode 5 of the container body 1, and 6 is an O-ring mounting portion 1a. O-ring attached to the diaphragm, 4 a diaphragm covering the positive electrode 5 and the O-ring 6, 2 a cap for pressing the diaphragm and the O-ring, and 7 a diaphragm protecting the outer surface of the diaphragm. Is a metal mesh.

A stainless cover lid 2 is screwed to a container body 1 made of heat-resistant fluororesin with a tightening ring 3. At this time, the diaphragm 4 made of a tetrafluoroethylene-6-fluoropropylene copolymer film having a thickness of 25 μm is made of silicon so as to be in close contact with the positive electrode 5 as a catalyst electrode obtained by vapor deposition of gold on porous carbon. It is fixed by the O-ring 6 of. Here, the O-ring 6 is sandwiched between the container body 1 and the pressing lid 2, and thereby not only fixes the diaphragm 4, but also serves to seal the inside of the container body 1 from the outside. Carry. Further, the diaphragm 4 is stretched to a convex shape as the O-ring 6 is deformed, but since the crushing margin of the O-ring 6 is always constant, the diaphragm 4 is always adhered to the positive electrode 5 with a constant tension, For example, it contributes to minimizing variations in sensor output even when the diaphragm 4 is replaced. Further, the pressing lid 2 has a donut shape in which a hole is formed in the positive electrode portion, and after the O-ring 6 is pressed and fixed, its outer surface is flush with the positive electrode 5. Is designed. Further, a metal mesh 7 for protecting the diaphragm is provided outside the pressing lid 2. In this embodiment, a stainless steel net having a thickness of 0.1 mm in which only the portion corresponding to the positive electrode is meshed by etching is fixed to the pressing lid 2 by spot welding. In addition, an electrolytic solution (pH = 6) 8 containing acetic acid as a main component is placed inside the main body 1, and a sensor is composed of a negative electrode 9 made of lead, a positive electrode lead 10 made of titanium wire, and a detection resistor 11. Has been done.

FIG. 2 shows changes in the sensor output of the galvanic cell type dissolved oxygen sensor obtained in the above-described embodiment, each time the sterilization process is repeated. In the figure, the horizontal axis indicates the number of sterilization treatment repetitions [times], and the vertical axis indicates the sensor output voltage as a relative value when the initial value is 100. In the test, the sensor was sterilized using an electric autoclave at 128 ° C for 1 hour, then taken out from the autoclave, immersed in a constant temperature water bath at 37 ° C and cooled. The output was recorded at (atmospheric saturated water output). FIG. 2 shows the result of repeating this operation, but the sensor output is stable over 50 times or more. Although not shown in the figure, the sensor output in anhydrous sodium sulfite aqueous solution (0 ppm in-liquid output) was also measured together with the measurement of the atmospheric saturated water output, and it was stabilized at 0.2 μA or less after being converted to the current value. Have confirmed that. It has also been confirmed that the linearity of the sensor output is maintained. In addition, in the examples of the present invention, in addition to the structure described so far, the special electrolytic solution (mixed aqueous solution of acetic acid-potassium acetate-lead acetate) according to Japanese Patent Publication No. 3-2259 by the applicant of the present application is used. Therefore, it is not affected by carbon dioxide and has a long life. Since this electrolyte has a pH of 6 and is on the acidic side, it is not affected by carbon dioxide gas, which has been a problem with conventional type sensors that use alkaline electrolyte. In addition, this electrolyte has a solubility of PbO generated in the negative electrode as a result of the electrode reaction that is 10 times or more that of the alkaline electrolyte (conventional type), and the sensor has a long life. Therefore, by using the present invention, it is possible to provide a galvanic cell type dissolved oxygen sensor for a culture tank, which is particularly suitable for long-term cultivation.

[0016]

[Effect of device]

 As described above, according to the present invention, the culture medium is not contaminated by the ejection of the electrolytic solution from the pressure equalizing hole, the expansion and damage of the diaphragm due to the increase of the internal pressure of the sensor can be prevented, and the repeated sterilization is stable and the diaphragm can be replaced. It is possible to provide a galvanic cell type dissolved oxygen sensor that can be easily performed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing a change in output level due to repeated sterilization of a sensor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Container Body 2 Holding Cap 3 Tightening Ring 4 Diaphragm 5 Positive Electrode 6 O-ring 7 Metal Mesh 8 Electrolyte 9 Negative Electrode

Claims (1)

[Scope of utility model registration request] 1. A positive electrode composed of a catalytic electrode effective for an electrochemical reduction reaction of oxygen, a negative electrode composed of lead, an electrolytic solution, a container accommodating them, and a diaphragm arranged outside the positive electrode. In the basically constituted galvanic cell type dissolved oxygen sensor, a positive electrode (5) attached to the outer surface of the container body (1) and an O recessed in the outer periphery of the positive electrode (5) of the container body (1). Ring mounting part (1a) and O ring (6) mounted on the O ring mounting part (1a)
A diaphragm (4) covering the positive electrode (5) and the O-ring (6), a holding lid (2) for pressing the diaphragm (4) and the O-ring (5), and an outer surface of the diaphragm (4). And a metal mesh (7) for protecting the diaphragm disposed in the O-ring (5) with the annular pressing lid (2) and the O-ring mounting portion.
And the diaphragm (4) are pressed to adhere the diaphragm (4) to the positive electrode (3), fix the diaphragm (4), and hold the electrolytic solution (9).
The membrane-dissolved gas sensor is characterized in that it is configured so as to prevent expansion and breakage of the diaphragm (4) due to an increase in sensor internal pressure, while being sealed by the above.