JPH03215737A - Method for measuring oxygen concentration - Google Patents

Abstract

PURPOSE:To use an oxygen electrode for a long time over a wide range of concns. by controlling the overcurrent of the electrode and changing the thickness of the gas permeation membrane in accordance with the concn. CONSTITUTION:A voltage is supplied to the oxygen electrode 1 from the power source part 3 of an oxygen electrode control part 2, and a current is outputted from the electrode 1. Since the output current is feeble, the output current of the electrode 1 is converted into a voltage by a current-voltage converter part 4 at a magnification of 10<6>-10<7>V/A and outputted. The output at the converter part 4 is monitored by an output current comparator part 5, and the voltage of the power source part 3 is lowered when the output exceeds a set value to keep the output current constant. Furthermore, an oxygen electrode having a thin gas permeation membrane is prepared to measure the oxygen concn. in the low-concn. region, and the oxygen electrode having a thick oxygen permeation membrane is prepared to measure the oxygen concn. in the high- concn. region. Consequently, the maximum output current of the oxygen electrode is limited, the consumption of the anode and electrolyte is controlled, the measuring range is widened, and the service life of the electrode is prolonged.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method for measuring oxygen concentration using a Clark-type oxygen electrode, and the present invention relates to a method for measuring oxygen concentration using a Clark-type oxygen electrode. The purpose is to: ■ change the thickness of the gas permeable membrane so that when the output current of the oxygen electrode exceeds a set value, the power supply voltage supplied to the oxygen electrode is reduced to limit the output current to a constant level. By this, the sensitivity characteristics to oxygen concentration can be controlled. ■ By using two or more oxygen electrodes with different sensitivity characteristics to oxygen concentration, it is possible to measure a wider concentration range. It consists of an electrode control section. Furthermore, the oxygen electrode control section includes a power supply section that supplies voltage to the oxygen electrode, a current-to-voltage conversion section that converts the output current of the oxygen electrode into voltage, and a preset setting for the output current of the oxygen electrode that has been converted into voltage. and an output current comparison section that compares the output current with the maximum output current.

[Industrial Application Field] The present invention relates to an oxygen concentration measuring method using a Clark type oxygen electrode.

Oxygen electrodes are used to measure dissolved oxygen concentration in various fields. For example, biochemical oxygen demand (BOD) in water is measured from the viewpoint of water quality conservation, and an oxygen electrode is used as a measuring device for this dissolved oxygen concentration.

In addition, in the fermentation industry, in order to efficiently ferment alcohol, etc., it is necessary to adjust the dissolved oxygen concentration in the fermenter. An oxygen electrode is used as this measuring device.

Furthermore, the oxygen electrode can be combined with an enzyme to form an enzyme electrode, which can be used to measure the concentration of sugars, vitamins, etc. For example, glucose is catalyzed by an enzyme called glucose oxidase. It reacts with dissolved oxygen and is oxidized to gluconolactone, which reduces the amount of dissolved oxygen that diffuses into the oxygen electrode, which can be used to measure glucose concentration. In this way, oxygen electrodes can be used in various fields such as environmental measurement, fermentation industry, and clinical medicine.

[Conventional technology] FIG. 5 is a schematic diagram of the oxygen electrode.

In the figure, 6 is an electrode container, 7 is a cathode, 8 is an anode, 9 is an electrolytic solution, 10 is a gas permeable membrane, and 11 is an electrode terminal.

Is the oxygen electrode conventionally known as the Clark type? It has become mainstream. As shown in the schematic diagram in FIG. /AgCl ) and an anode 8 consisting of a reference electrode of potassium chloride (KCff
i) Consists of an electrolytic solution 9 made of an aqueous solution, a gas permeable membrane IO made of silicone rubber or fluororesin, and an electrode terminal 11 that is supplied with voltage from a power supply section and sends an output current to a current-to-voltage conversion section. .

-0.5 to 2 between the cathode 7 and the anode 8.
When a voltage of 0 ■ is applied, it passes through the gas permeable membrane 10 and
Oxygen (0■) diffused into the electrolyte 9 inside the oxygen electrode is reduced on the cathode 7 by the following reaction, and a current value proportional to the oxygen concentration is obtained.

Oz +2Hz O+4 e--+40H On the other hand, the following reaction occurs on Anoto '8.

Ag+Cf! --→AgCf+e In this way, the anode 8 and electrolyte 9 are consumed by using the oxygen electrode. As shown in the above equation, this consumption is
It progresses according to the output current of the oxygen electrode.

[Problem to be Solved by the Invention] Therefore, oxygen electrodes inevitably suffer from consumption of the anode and electrolyte, and should they be maintained and managed by replacing the electrolyte after each use for a certain period of time? It was necessary to replace it with a new oxygen electrode.

However, maintenance and management of oxygen electrodes is complicated. Skill was required to maintain its performance. Also,
Oxygen electrodes themselves were not cheap and could not be disposable.

An object of the present invention is to extend the interval at which maintenance is required by increasing the continuous use time of the oxygen electrode.

[Means to solve the problem]

Figure 1 is a principle diagram of the oxygen concentration measuring method according to the present invention, Figure 2
The figure shows the sensitivity characteristics of the oxygen electrode according to the present invention.

In the figure, 1 is an oxygen electrode, 2 is an oxygen electrode control section 3 is a power supply section, 4 is a current-to-voltage conversion section, and 5 is an output current comparison section.

The oxygen concentration measuring device used in the present invention is comprised of an oxygen electrode 1 and an oxygen electrode control section 2, as shown in FIG.

Furthermore, the oxygen electrode control unit 2 includes a power supply unit that supplies voltage to the oxygen electrode 1, a current-voltage conversion unit 4 that converts the output current of the oxygen electrode 1 into voltage, and an output of the oxygen electrode 1 that is converted into voltage. It is comprised of an output current comparison section 5 that compares the current with a preset maximum output current.

Since the output current of the oxygen electrode 1 is extremely weak and it is inconvenient to record the oxygen concentration with a recorder or the like if the current is kept as it is, the output current is converted into voltage by the current-to-voltage converter 4. is the output of the oxygen electrode 1.

This output is monitored by the output current comparator 5, and if the output current exceeds the set value, the output current is reduced by lowering the voltage of the power supply 3 that supplies the oxygen electrode 1, as shown in FIG. Keep it constant.

In addition, the sensitivity characteristics of the oxygen electrode are expressed by the following equation.

1 = A - C/d where ■ is the output current and A is a constant. C is the oxygen concentration, and d is the thickness of the gas permeable membrane.

Therefore, by controlling the thickness d of the gas permeable membrane, it is possible to obtain an oxygen electrode having characteristics that do not exceed the above set value at various oxygen concentrations.

That is, if the gas permeable membrane is made thinner, a higher output current can be obtained, which is advantageous for measuring oxygen concentration in a low concentration region, but in a high concentration region, the value exceeds the above-mentioned set value and measurement cannot be performed. Therefore, an oxygen electrode with a thick gas permeable membrane is prepared for use in a high concentration region.

(Function) According to the present invention, in order to limit the maximum output current of the oxygen electrode, consumption of the anode and electrolyte in the oxygen electrode can be suppressed.

Although this makes it possible to extend the life of the oxygen electrode, it limits the output current value, making measurement at high oxygen concentrations impossible.

Therefore. By changing the thickness of the gas permeable membrane, we can prepare oxygen electrodes that can handle various oxygen concentration ranges, and by switching the oxygen electrode to be used depending on the oxygen concentration to be measured. It becomes possible to measure oxygen concentration over a wide range over a long period of time.

[Example] Figure 3 is a circuit diagram of an example of the oxygen concentration measuring method of the present invention.
FIG. 4 shows the sensitivity characteristics of the oxygen electrode according to the embodiment of the present invention.

In the figure. 1 is an oxygen electrode, 2 is an oxygen electrode control section, 3 is a power supply section, 4 is a current-voltage conversion section, and 5 is an output current comparison section.

As shown in Figure 3, the voltage supplied to the oxygen electrode l is .
It is produced by the power supply section 3. The output current of the oxygen electrode 1 is converted into voltage by a current-to-voltage converter 4 at a multiplication factor of 106 to 10' V/A. This converted output is compared by the output current comparator 5 with the maximum output current set in advance by a resistor. If the output current exceeds this set value, adjust the voltage input to the power supply section 3.
The output current of the oxygen electrode 1 is kept constant.

Using three sets of oxygen electrodes 1 with different thicknesses of the oxygen electrode control unit 2 and the gas permeable membrane 10 of the oxygen electrodes 1 used in FIG.
When configuring the oxygen concentration measuring device. FIG. 4 shows the sensitivity characteristics expressed by the relationship between the output current of the oxygen electrode 1 and the dissolved oxygen concentration.

Three oxygen electrodes 1 are used for low concentration, medium concentration, and high concentration, and the thickness ratio of each gas permeable membrane 10 is set to 1:
The time was set at 4:10. For example, this permeable membrane 10 may be made of fluororesin. Membranes with a thickness of 40 and 100 μm were used, respectively.

Since this device is intended to measure dissolved oxygen concentration in water, it is capable of measuring oxygen concentrations up to 10 ppm. Of course, when measuring a sample whose oxygen concentration is within a limited range, or when using it as a measuring device to control the oxygen concentration at a constant level, it is sufficient to prepare only one set of corresponding measuring devices. For example, if the oxygen concentration in the fermenter is to be maintained at 3 ppm, one set of equipment for medium concentrations may be used.

[Effects of the Invention] As explained above, according to the method of the present invention, in order to suppress excessive current from flowing to one oxygen electrode, consumption of the anode and electrolyte in the oxygen electrode can be suppressed. It can be used for a long time.

Furthermore, by controlling the thickness of the gas permeable membrane, it is possible to obtain oxygen electrodes that can accommodate three different concentration ranges. This prevents the output current from becoming too large when measuring a high concentration of oxygen, or from becoming extremely weak when measuring a low concentration, and makes it possible to obtain a level of output that is easy to handle.

The use of the above two techniques is particularly useful when the range of oxygen concentration that can be handled is limited, such as with a measuring device for controlling oxygen concentration at a constant level.

[Brief explanation of drawings]

Figure 1 is a principle diagram of the oxygen concentration measuring method according to the present invention, Figure 2 is the sensitivity characteristics of the oxygen electrode according to the present invention, Figure 3 is a circuit diagram of an embodiment of the oxygen concentration measuring method according to the present invention, and Figure 4 is Sensitivity characteristics of an oxygen electrode according to an embodiment of the present invention. FIG. 5 is a schematic configuration diagram of an oxygen electrode. In the figure. 1 is an oxygen electrode. 2 is an oxygen electrode control unit, 3 is a power supply unit, 4 is a current-voltage conversion unit, 5 is an output current comparison unit, 6 is an electrode container, 3 is an anode, number is a cathode, 9 is an electrolyte,
10 is the gas permeable membrane 11 is the electrode terminal according to the present invention.
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Claims (1)

[Claims] 1) An oxygen concentration measuring method characterized in that when the output current of the oxygen electrode exceeds a set value, the power supply voltage supplied to the oxygen electrode is reduced to limit the output current to a constant value. . 2) The method for measuring oxygen concentration according to claim 1, characterized in that sensitivity characteristics to oxygen concentration are controlled by changing the thickness of the gas permeable membrane. 3) The oxygen concentration measuring method according to claim 1 or 2, wherein a wider concentration range can be measured by using two or more oxygen electrodes having different sensitivity characteristics to oxygen concentration. 4) The circuit device that limits the output current to a constant level is composed of an oxygen electrode and an oxygen electrode control section, and the oxygen electrode control section further includes a power supply section that supplies voltage to the oxygen electrode and a circuit that controls the output current of the oxygen electrode. 2. The oxygen electrode according to claim 1, further comprising: a current-to-voltage converter that converts into a voltage; and an output current comparator that compares the output current of the oxygen electrode converted into a voltage with a preset maximum output current. How to measure oxygen concentration.