JPS60114764A - Measurement of oxygen concentration - Google Patents

Abstract

PURPOSE:To lower the operation temp. of a solid electrolyte sensor and to also reduce a limit current value, by diluting gas to be detected with reference gas to lower the oxygen concn. of the gas to be detected while guiding the diluted gas to the solid electrolyte sensor. CONSTITUTION:Gas G1 to be detected and diluting reference gas G2 are respectively guided from a first flow valve 6 and a second flow valve 7 both of which are controlled in cooperated relation to each other by a controller 5 and mixed to dilute the gas G1 to be detected with the reference gas G2 at definite magnification while the diluted gaseous mixture G3 is guided to a solid electrolyte oxygen sensor 9 by a pump 8 to calculate the oxygen concn. in the diluted gaseous mixture G3. As the reference gas G2, for example, 100% nitrogen gas or a gaseous mixture of nitrogen gas and oxygen, of which the oxygen concn. is known, is used. By this constitution, a sensor retains limit current characteristics even at a relatively low heating temp. (about 300 deg.C) and the limit current value thereof comes to a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for measuring oxygen concentration using a solid electrolyte oxygen sensor.

<Prior art and its problems> Conventionally, an oxygen senna using a solid electrolyte such as zirconia has a structure as shown in FIG. As mentioned above, this senna is a cubic crystal system (Z
An oxygen ion conductive plate 1 is prepared using a solid electrolyte of RO20.9-Y20!10.1), and electrode plates 2.2' made of a porous metal film such as platinum are provided on both sides of the conductive plate 10. One side of the plate 10 is covered with a cover 3 having a minute-diameter diffusion hole 4 on the top plate part to form an isolation plate -C.

According to this oxygen sensor, during measurement, a voltage for measurement is generally applied between the electrodes 2 and 2 at a considerably high temperature (approximately 700° C. or higher) (heating the test gas and the senna itself). This applied voltage is gradually increased, and the gap between the electrodes 2 and 2 is
．． For example, as shown in Figure 2, the current flowing between 2 is measured, and the current special value IL of the sensor is read, and from this limit current value processing, the current selling point (sensor's applied voltage) is calculated as shown in Figure 3. The oxygen concentration in the test gas can be adjusted depending on the voltage (voltage, etc.). Here, the limit current value is determined by determining the flat part b where the current hardly increases even if the applied voltage increases as described above. : The current value when
The amount of oxygen molecules in the electrode R being released to the outside through the oxygen ion conductive plate 1 is larger than the amount of diffusion introduced into the isolation chamber R through the diffusion hole 4, and the isolation is achieved. Seal R
This is a phenomenon that occurs when the oxygen concentration in the 2nd electrode becomes almost 0, and the current flowing between the electric currents m2 and 2' is limited.

However, in the case of an oxygen sensor that adjusts the oxygen concentration by modifying the limit current value, due to its characteristics, the above-mentioned flat part may appear clearly enough to be discernible in the current characteristic curve a. is necessary.

However, the appearance of this flat area in the same oxygen sensor is largely dependent on differences in measurement temperature, oxygen concentration in the sample gas, etc. That is, in the case of the test gas having the same oxygen concentration, as shown in FIG. 4, a flat part clearly appears on the current characteristic surface 14aIPc when the measurement temperature is high (approximately 500°C), and its limit The current value processing can also be read as a fairly large value, but when the measurement temperature is low (approximately 300°C), the current characteristic curve a2 is υ.
In extreme cases, the flat portion of the curve does not clearly appear, making it impossible to determine the limit current value IL. In addition, even if the measurement temperature is the same, in the case of test gases with different oxygen concentrations, as shown in Figure 5, when the oxygen concentration is low (approximately 5 inches), the current characteristic curve a5 has a clear flat part. However, in the current characteristic curve al1%a5 when the oxygen concentration is high (Tsuri 15-man, 21-chi), The flat area becomes very narrow, making it difficult to adjust the limiting current value. In other words, it loses its limiting current characteristics and ends up dead.

Therefore, in the conventional solid electrolyte e-element sensor, as mentioned above, it is used while being heated to a suitable high temperature so that the flat part in the current characteristic curve a clearly and widely appears. This makes it possible to handle test gases with a certain oxygen concentration. As a result, the naturally obtained limiting current value I also takes a large value, which is preferable in terms of accuracy.

However, the use of heating the oxygen sensor 9 to a high temperature to make the flat portion of the limiting current value as wide and clear as possible has the following various problems.

(a) A large-sized means is required as a heating source for senna, and power consumption for heating is extremely large.

(b) In addition, when a heating means is provided, the temperature becomes high44, a large amount of heat is diverted to the outside, and power consumption due to heat loss cannot be ignored.

(c) When using senna in a high temperature state, there is a large temperature difference with the outside world (room temperature), so it is easy to be affected by the outside world, and it is necessary to maintain a constant temperature. , this will lead to a decrease in foot measurement accuracy.

(d) Furthermore, when the senna is operated at a high temperature with a limit current equivalent to 1 pulse IL, a large value of the limit current t
The current causes self-heating, which places a heavy burden on the zirconia solid solution of the oxygen ion conductive plate7.
As a result, problems such as damage to the senna properties and separation of the electrodes occur, resulting in a significantly shortened senna life.

<Object of the Invention> The present invention has been made in view of the problems of the prior art, and its purpose is to minimize power consumption when using a solid electrolyte oxygen sensor. [0009]The present invention also provides a method for measuring oxygen concentration that does not impose an undue burden on senna itself.

<Configuration of the Invention> In order to achieve all of the above-mentioned objects, the present invention uses a relatively low heating temperature (approximately 30
This method focuses on the fact that the limiting current characteristics can be obtained at 0℃) and the limiting current value obtained at that time is small.The oxygen concentration in the gas is measured with a solid-state electric oxygen sensor In this step, the test gas is diluted with a reference gas, guided to the solid electrolyte sensor, measured as a low oxygen concentration, and after 7ζ, multiplied by the dilution factor described above to find the true oxygen concentration. It is something to do.

Here, the reference gas is a gas whose oxygen concentration is known,
Examples include 100% nitrogen gas, a mixed gas of nitrogen gas and oxygen, and the like.

<Embodiment> An embodiment of the present invention is shown in FIG. 6 or 7.

In the case of the oxygen concentration measurement method shown in Fig. 6, the controller 5
The test gas G1 is supplied from the first flow valve 6 which is interlocked controlled by the flow valve 6, and the reference gas 02 for dilution is supplied from the second flow volume T, and mixed. Dilute this diluted mixed gas G5 with pump 8 to solid electrolyte oxygen sensor? 9, the oxygen concentration in the diluted mixed gas G5 is first multiplied by the above dilution factor,
This method calculates the true oxygen concentration and is suitable for continuous measurement.

In the case of the oxygen concentration measurement method shown in FIG. 7, the controller 5 performs interlocking control to control the gas G!
02″ft of reference gas for dilution is introduced from the second flow valve T, and once mixed, KYfJ# in the tank 10,
L, the diluted mixed gas G5 is guided from this tank 10 to the solid electrolyte oxygen sensor 9 by the pump 8 controlled by the controller 5, and the diluted mixed gas G is produced in the same manner as in the case of FIG. 6 above.

First, calculate the oxygen concentration in the water, and then multiply this value by the above dilution factor to determine the true oxygen concentration.This method is a patch method that is particularly useful for measuring 61 degrees when desired. be.

In each of the above methods, the reference gas G2 is not particularly limited, and may be a gas that is not subjected to the bombin pink effect by the acid-base ion conductive plate of the sensor, such as the aforementioned nitrogen gas or inert gas. can be used alone or as a mixed gas, and in the case of oxygen-containing gases or gases containing molecules that, like oxygen, are pumped by the oxygen ion conductive plate, the oxygen concentration and the content of the contained molecules can be adjusted. It is preferable to use a gas whose concentration is known. Furthermore, the dilution ratio of the test gas is preferably such that the oxygen concentration in the diluted mixed gas after dilution is about 5%.

In this way, when the oxygen concentration is about 5%, solid electrolyte oxygen senna maintains its limiting current characteristics even at relatively low heating temperatures, and its limiting current value also remains small. Take.

Note that the present invention is not limited to the above-mentioned embodiments, and any method that can dilute the oxygen concentration in the test gas,
Other methods are also possible.

<Effects of the Invention> As is clear from the above description, the present invention dilutes the test gas with a reference gas when measuring the oxygen concentration in a test gas, resulting in a low oxygen concentration state. Since the oxygen senna is operated by the oxygen sensor, the operating temperature of the senna may be relatively low (approximately 300° C.), and the limiting current value at this time can also be obtained as a small value. Ninthly, you can expect various excellent effects such as:

(a) The heating source for the senna may be of the ljX type, and power consumption for heating can be greatly reduced.

(b) Since the heating temperature is not so high, heat loss due to heat leakage to the outside is small, and from this point of view as well, it is possible to reduce power consumption.

(c) Furthermore, since the temperature difference with the outside world is greatly reduced compared to conventional ones, it is resistant to influences from the outside world and always enables highly accurate measurements.

(d) Furthermore, since Senna operates at a relatively low temperature and its limiting current value is small, no large current flows through the oxygen ion conductive plate, which places an unreasonable burden on the solid electrolyte and causes self-heating phenomenon. I can't help but feel inspired,-
t71: There is no peeling of the electrode, and the sensor life can be greatly improved.

Furthermore, although the explanation so far has focused on the limiting current type oxygen sensor, the method of diluting the detected gas with the reference gas is to pass a constant current between both electrodes, and from the time-voltage characteristics at that time, the oxygen sensor is It can also be applied to a method of detecting concentration, and similarly excellent effects can be achieved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an example of a solid electrolyte oxygen sensor, Figure 2 is a graph showing the voltage-current characteristics of the sensor, and Figure 3 is a graph showing the voltage-current characteristics of the sensor.
The figure is a graph showing the oxygen concentration vs. limiting current value of the above senna,
Figure 83 is a graph showing the voltage-current characteristics when the measurement temperature is changed using the above-mentioned sensor, and Figure 5 is a graph showing the voltage-current characteristics due to differences in the oxygen concentration in the test gas in the above-mentioned sensor. , FIG. 6, and FIG. 7 are schematic explanatory diagrams illustrating an embodiment of the method for measuring oxygen concentration according to the present invention. Gl...-Test dregs, G2...Reference gas, 9...
・Solid electrolyte oxygen sensor. Patent applicant: Fujikura Electric Cable Co., Ltd. Procedural Sleeve (Method) March 17, 1980 Director-General of the Patent Office Kazuo Wakasugi1, Indication of the case 1981 Patent Application No. 2239042, Name of the invention #Steel fIk Measurement of degree 3, relationship with the case of the person making the amendment

Claims (1)

[Claims] When measuring the oxygen concentration in a test gas with a solid electrolyte oxygen sensor, the test gas is diluted with a reference gas and then guided to the solid electrolyte sensor, and after measurement as a low m elementary concentration, the above dilution magnification is applied. A method for measuring 6 degrees of oxygen, characterized in that the true oxygen concentration is determined by multiplying by .