JPS5861458A - Oxygen detector and oxygen concentration measuring device - Google Patents

Abstract

PURPOSE:To offer the oxygen concentration measuring apparatus, by correcting an output from an oxygen detector using no temperature compensation element by an electric signal given from a temperature measuring element and outputting the oxygen concentration calibrated by the temperature of the object to be measured. CONSTITUTION:A notch is made on a side edge of an electrode supporting body 3 of an oxygen detector having an oxygen permeable diaphragm 4 and the tip end of a temperature measuring element B penetrating the body 3 is exposed to the notch. Each amplifier 13 and 14 is connected to an oxygen electrode A and the element B and is switched to either side by a switching circuit 15. A sample holding circuit 16 an A/D converter 17 and a microprocessor 18 are connected next to the circuit 15 and the output of the electrode A of the output from the element B at each temperature is taken in the microprocessor 18 and saturated quantity of dissolved oxygen in a sample is operated and is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an oxygen detector and an oxygen concentration measuring device using a diaphragm electrode for oxygen measurement as a detection section. Conventionally, oxygen permeable diaphragms and oxygen permeable diaphragms were used as electrodes for measuring oxygen concentration.
an electrode body having a cathode and an anode arranged such that an electrolyte is interposed between the diaphragm and the cathode of the electrode body;
An electrode is used in which the electrode body is immersed in an electrolytic solution, and the electrode body and electrolytic solution are arranged in a housing including the diaphragm. Generally, an electrode with this structure is called a diaphragm electrode. As the use of diaphragm electrodes progresses, it has become clear that they have practical problems. The first problem is that the temperature change rate of the oxygen reduction current is large, which impairs the quantitative ability of oxygen in a measurement target subject to significant temperature changes. As shown by curve a in Figure 1, the oxygen permeability of the oxygen permeable diaphragm increases by approximately 5% as the temperature rises by 7°C. As shown, the change in the amount of saturated dissolved oxygen decreases by about 2% as the temperature rises to /'C.In order to overcome this weakness regarding temperature fluctuations, a method of temperature compensation using a thermistor has been proposed. is Br1gg5 (J.

Sci.
), improvements derived from this technical idea have also been proposed. This type of temperature compensation device uses a temperature measurement element for calibration, and a thermistor, which is a nonlinear temperature negative resistance element whose output characteristics are opposite to the temperature of the electrode, is used for temperature compensation. It is used as a feedback resistor in an amplifier to change the amplification degree. However, such a device has a drawback that it is difficult to miniaturize the detection section because the detection section uses a temperature measuring element, an oxygen electrode, and a thermistor.

Moreover, the effective temperature range that can be compensated by the thermistor is limited to 70°C (70°C at most), and in order to cope with wider temperature changes, there is the inconvenience of having to prepare several temperature compensation elements and resistors. Moreover, in order to use thermistors and resistors that are suitable for these temperature ranges, adjustment was required in advance, which required a lot of effort and time.Furthermore, even if the electrodes were adjusted once, if they were to be replaced due to failure, etc., they would have to be adjusted again. There were disadvantages such as poor compatibility, such as the fact that the temperature compensation element had to be removed, and failures often occurred due to deterioration of the temperature compensating element. It is proportional to the dissolved oxygen concentration, but the dissolved oxygen concentration decreases as the concentration of NaCl increases in the saline solution.In this case, the oxygen partial pressure of the tea liquor is assumed to be constant at θ2/atm, and the diaphragm, electrode The disadvantage was that the oxygen reduction currents obtained in both methods were the same.

The present invention was proposed in order to solve these problems. An object of the present invention is to provide an oxygen concentration measuring device that outputs the temperature-calibrated oxygen concentration of an object to be measured.

Its features include an oxygen-permeable diaphragm, an electrode body having a cathode and an anode arranged so that an electrolyte is interposed between the diaphragm and the cathode of the electrode body, and an electrolyte in which the electrode body is immersed. An oxygen detector characterized in that, in an oxygen electrode in which the electrode main body and the electrolytic solution are arranged in one housing (including the diaphragm), a temperature measuring element is provided in the housing or an extending portion thereof.

an amplifier that amplifies the signal from the detector, an A/D converter that converts the analog signal amplified by the amplifier into a digital signal, a microprocessor that processes the digital signal, and the microprocessor. A constant is stored in the memory of the microprocessor in advance, and based on the constant, the oxygen temperature of the object to be measured is calibrated according to the input digital signal. It is found in an oxygen concentration measuring device that calculates and outputs the concentration.

Embodiments of the present invention will be described below with reference to the drawings.

The oxygen electrode of the oxygen detector used in the present invention is a diaphragm electrode type,
It can be used in any of the polarographic type, the galvanic cell type that does not require an applied voltage, the Clark type with a detection section at the tip, and the MaCkereth type with a large detection surface on the side. Curve a in FIG. 1 shows the relative value of oxygen reduction current of the diaphragm electrode with respect to temperature, and curve a shows the value of saturated dissolved oxygen phase it with respect to temperature. Figure Ω is a sectional view showing one embodiment of the diaphragm electrode. q is an oxygen-permeable diaphragm, which is held between a diaphragm holder and an O ringeter.

One surface of the diaphragm is exposed to the outside so as to come into contact with the test liquid (not only liquid but also gas) as the object to be measured. Another side of the diaphragm! , an electrode body having a cathode 7 and an anode g with an electrolytic solution interposed therebetween. Electrode body/
The surrounding area including the anode Yg and the cathode 7 is filled with an electrolytic solution and heated to .degree.

Therefore, the electrolytic solution 9 is formed by inserting the diaphragm, the diaphragm holder/, and the electrode body// into the cylindrical electrolyte tank and the electrode body//.
/ is inserted into the housing, which consists of three electrode supports. The hot film holder / is screwed into one end of the electrolyte tank, and the electrode support It is fitted to the other end of the electrolyte tank.

The O-ring S is held between one end of the electrolyte tank and the diaphragm on the diaphragm support 3. There is a cutout on the side edge of the electrode support body, and the tip of the temperature measuring element B, which is inserted through the electrode support body 3, is exposed in the cutout. Electrode body //
The wiring of the temperature measuring element B and the temperature measuring element B are led to the outside by an electrode lead wire 10. As mentioned above, the oxygen detector consists of an oxygen electrode composed of a temperature measuring element and other members.

FIG. 3 shows an embodiment of an oxygen concentration measuring device for measuring the oxygen concentration of an object to be measured using the oxygen detector shown in FIG. The oxygen detector/2 inserted into the object to be measured is composed of an oxygen electrode A and a temperature measuring element B. Oxygen electrode A and temperature measuring element B each have an amplifier/3. /ll are connected and they are the switching circuit /ll.
S can be used to switch to either one. A sample and hold circuit /B is connected to the next stage of the switching circuit 15, and an analog-to-digital converter (hereinafter referred to as an A/D converter) /7 is connected to the next stage of the sample and hold circuit. A microprocessor 7g is connected to the next stage of the A/D converter /7, and controls the switching circuit /S, sample and hold circuit /B, and A/D converter /g. A display device/9 is connected after the microprocessor/g.

Next, the operation of the present invention will be explained with reference to FIGS. 1 to 3. First, place the oxygen detector/2 into an oxygen-free liquid (anhydrous sodium sulfate aqueous solution). The output of oxygen detector/2 should be almost zero, but some oxygen detectors output a small amount. This output is called the residual current, and this current is almost unaffected by the temperature of the oxygen-free liquid and has a nearly constant value.

The residual current is generated from the oxygen electrode amplifier/3 to the A/D converter/7.
After that, it is stored in the memory of the microprocessor/g. Next, air is blown into the water to create air-saturated water, and the oxygen detector/2 is placed in it. At this time, the temperature of the object to be measured is sufficiently controlled, and the output It of the oxygen electrode B for each temperature of the output destination of the temperature detection element B is taken into the microprocessor/g. The relationship between the output It of the electrode of saturated oxygen water at the temperature t is given by the following approximate expression.

rt2a, t" 10s, t2+C, 10d,
・・・・・・・・・・・・・・・ +11 Here,
It;, output of L'C elementary electrode, t: temperature of saturated oxygen water at the time of measurement) Apply the output to equation (1) and calculate dl
By obtaining the value of , the output It of the oxygen electrode of the saturated oxygen water at the temperature t can be calculated from equation (1).

Here, a4. bl, C, are constants (values fixed in advance) determined by the structure of the oxygen electrode, and d is, for example, the output value of the oxygen electrode at a temperature of 0 degrees (value calculated by back calculation from equation (1)). , these constants aI * bI t c,
The value of t dl is stored in the microprocessor memory. The relationship between the output It of the oxygen electrode and the temperature t is shown by curve a in FIG. Next, when measuring the oxygen concentration of the test liquid, put the oxygen detector 12 into the test liquid and calculate the output from the temperature measurement element (temperature of the test liquid) tm by (1)
Substitute it into the formula and calculate the value, that is, the oxygen electrode at the temperature tm
Its output when the temperature is in oxygen-saturated water at ℃ is output and stored in memory. The output Itm from the oxygen electrode A is also stored in the memory. Next, the saturated dissolved oxygen amount DO8 at the temperature tK given by the following equation is calculated using tm.

DO9-/lI/Otsu/-θ39'13t+〇, 0077
/1lt2-θρ0θ0 tt3... (2) where DO8; saturated dissolved oxygen amount t at temperature t; fl above the temperature of the test liquid), It and DO at temperature tm from equation (2)
The values rts and DO8m of 8 are calculated and stored in the memory, and the output Itm from the oxygen electrode A is also stored in the memory.

xts, DOsm, I stored in these memories
tm and Zo are each retrieved from the memory by specifying an address, and the dissolved oxygen amount DOm of the test liquid is calculated by the microprocessor/g by applying the following equation, and the result is displayed on the display device/q.

However, if the test solution contains salts, D in equation (2)
Using O8, the saturated dissolved oxygen amount DO8S is calculated as
yongπ'mv＞・・・・・・・・・ (4) Here, DO8S; saturated dissolved oxygen amount t when containing chlorine ions s (ppm); temperature of the test liquid; tm in equation (4). Assuming that the value obtained by substituting and calculating DO8S is DO8Sm, by substituting DO8Sm in place of DO8m in equation (3), the saturated dissolved oxygen amount DO8S of the test liquid containing salts will be calculated and output. In this embodiment, a detector in which the oxygen electrode A and the temperature measuring element are integrated as shown in FIG. 2 is used, but the detector is not limited to this and may be separated.

As described above, the present invention eliminates the need for temperature compensation with a narrow temperature compensation range using a temperature compensation element when measuring dissolved oxygen concentration. There is no need for labor, there is no need for readjustment due to deterioration of the temperature compensation element, and there is an effect of being able to perform a wide range of temperature calibration using the temperature measurement element without using a temperature compensation element. Moreover, since the oxygen detector is composed only of a temperature measuring element and an oxygen electrode, it has the advantage of being able to be made smaller and simpler.

[Brief explanation of the drawing]

Fig. 1 is a curve diagram of the relative oxygen reduction current value and saturated dissolved oxygen relative value of the diaphragm electrode with respect to temperature, Fig. 2 is a sectional view showing the oxygen detector of the present invention, and Fig. 3 is the oxygen concentration measuring device of the present invention. FIG. q; Oxygen permeable diaphragm B; Temperature measuring element 7; Cathode g; Anode 9; Electrolyte //; Electrode body 123, G; Housing/2; Oxygen detector/3. /'l;Amplifier/7; Converter 7g: Microprocessor A; Oxygen electrode B; Temperature measurement element Patent applicant: Oriental Yeast Industry Co., Ltd.
Rinto Wakabayashi Store, Thirst /Il (”C) Figure 1

Claims (1)

[Claims] il+ An electrode body having an oxygen permeable diaphragm, a cathode and an anode disposed such that an electrolyte is interposed between the diaphragm and the electrode body, an electrolyte in which the electrode body is immersed, and the electrode The main body and the electrolyte are arranged in a housing including the diaphragm (2); an oxygen detector consisting of a temperature measuring element and an oxygen electrode; an amplifier that amplifies the signal from the detector; and an analog sensor amplified by the amplifier. The microprocessor includes an A/D converter that converts a signal into a digital signal, a microprocessor that processes the digital signal, and a display device that displays the output of the microprocessor. stored,
An oxygen concentration measuring device characterized in that, based on the constant, the temperature-calibrated oxygen concentration of the object to be measured is calculated and output according to the input digital signal.