JPS62175657A - Method of measuring gas concentration - Google Patents

Abstract

PURPOSE:To measure concentration of moisture and concentration of a carbon dioxide in gas to be measured simply and quickly, by using a level difference between a flat part, and the bottom part of a trough part of respective voltage-current characteristic curve in a threshold current type oxygen sensor. CONSTITUTION:When measuring the concentration moisture and the concentration of carbon dioxide in a gas to be measured containing water and carbon dioxide, a low voltage V1 is applied to a threshold current type oxygen sensor using a solid electrolyte to obtain a threshold current value 1L1 at a first flat part 12 by oxygen, a high voltage V2 is applied to obtain a threshold current value 1L2 dye to the existence of carbon dioxide and water at a second flat part 13 and further, a higher voltage V3 is applied to obtain a threshold current value 1L3 at the bottom part 14a of the through 14. A differential current value DELTA1L* is determined from the difference (1L3-1L2) between the current values 1L2 and 1L3 and differential current value DELTA1L** is calculated from the difference (1L2-1L3) between the current values 1L2 and 1L3. Thus, when the concentration of water and the concentration of carbon dioxide are previously determined corresponding to the current values DELTA1L* and DELTA1L** respectively, the density of moisture and concentration of carbon dioxide can be determined immediately from the current values DELTA1L* and DELTA1L**.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for simultaneously measuring the concentrations of different gases contained in a gas to be measured.

<Prior art> In the case of the gas to be measured, such as the atmosphere, oxygen (0□), nitrogen (NZ), and other oxygen-containing substances such as moisture (H, O), carbon dioxide gas (Co□), and sulfurous acid are used. gas(
SOt ), -carbon oxide (CO), nitrogen oxide (NO
2, N01N20), and even rare gases (He, Ar, Ne
etc.) and various other gases are included.

The gas concentrations of these substances have been measured by various methods, but in recent years, sensors as electronic components have become popular because they can be easily and quickly measured, and the detected information can be easily controlled and handled. Commonly used.

Currently, for oxygen concentration, a limiting current type sensor using an oxygen ion conductive plate of a solid electrolyte, a so-called oxygen sensor, is used.

Here, the limiting current type oxygen sensor is a general term for sensors that are equipped with a means to limit the supply of oxygen molecules (ions) (or limit the rate of diffusion) to a solid electrolyte that has oxygen ion conductivity. A solid electrolyte with electrodes formed on both sides is covered with a hollow capsule in which a minute gas communication port is opened between the outside air, and the limiting current characteristic caused by the gas diffusion resistance of the gas communication port is utilized. or porous materials (materials with many fine through-holes, e.g. ceramics) instead of gas flow ports that cause diffusion resistance.
A porous body is formed to surround one or both surfaces of the solid electrolyte, or the entire solid electrolyte, and a diffusion control layer is provided on the electrode on the solid electrolyte surface. A layer on which a layer to prevent diffusion is formed, or a solid electrolyte plate with electrodes formed on both sides of at least one side with a small gap is arranged, and the gap makes use of the gas diffusion resistance effect. , a type in which electrodes are provided on the inner and outer surfaces of a cylindrical solid electrolyte with one end closed, and a diffusion control body as described above is provided on one of the electrodes, which limits the oxygen ion transport phenomenon of the solid electrolyte (rate limiting). ) includes all sensors that measure concentration by

The present inventors have also continued to develop such oxygen sensors, and have proposed various types to date.

In particular, it has recently been discovered that when the applied voltage is increased using the same type of oxygen sensor as above for a gas to be measured that contains two or more different types of gases, a unique voltage-current characteristic curve can be obtained. We have been conducting research with a focus on

For example, if the measured gas contains moisture (H2o) in addition to oxygen as shown in Figure 7, the voltage-current characteristic curve 1 of the sensor will have two flat regions, and the first flat region will be Region 2 (first flat part) is formed due to oxygen in the gas, and the next flat region 3 (second flat part) is the presence of oxygen atoms (oxygen ions) due to the decomposition of water at the same time as oxygen in the gas. The oxygen concentration was determined from the limiting current value ILt' of the first flat part, and the limiting current value IL,' of the second flat part and the limiting current value of the first flat part IL,
We have already proposed a method for determining the water concentration from the difference between ILz' and ΔIL'(IL+') = ΔIL' (Patent Application No. 1983).
-291569).

Also, as shown in Figure 8, if the gas to be measured contains oxygen, nitrogen, and carbon dioxide gas (C:Og) (in this case, the gas to be measured must be dehydrated to avoid the influence of moisture). )
In the voltage-current characteristic curve 1'' of the sensor, two stages of a first flat portion 2'' and a second flat portion 3'' appear, and at the same time, a valley portion 4'' appears after the second flat portion 3°. It was also found that the bottom 4a' of this valley 4' is at approximately the same level as the first flat part 2'.In this case, the first flat part 2' is also caused by oxygen in the gas. It has been confirmed that the next second flat part 3'' is formed due to the presence of oxygen atoms (oxygen ions) due to the decomposition of carbon dioxide gas at the same time as oxygen in the gas, and this first flat part The oxygen concentration is determined from the limiting current value IL,', and the limiting current value rt, z of the second flat part
” and the limiting current value ILI of the first flat portion (IL
,'-IL.

He has already proposed a method for determining the carbon dioxide concentration from ")=ΔIL" (Japanese Patent Application No. 60-291571).

The present inventors paid attention to the appearance of the valley 4° in FIG. 8 and conducted various studies, and discovered the following new fact.

In other words, in the case of a gas to be measured that is a mixed gas of oxygen, nitrogen, and carbon dioxide plus moisture, a level difference occurs between the first flat part and the bottom of the valley, and this difference directly increases the water concentration. I discovered that it appears.

Furthermore, it has been found that the carbon dioxide concentration can be obtained from the level difference between the second flat part and the bottom of the valley in the gas to be measured.

The present invention was made based on this result.

One aspect of the present invention is a limiting current method using a solid electrolyte in measuring the water concentration in a gas to be measured containing at least water and carbon dioxide. A voltage is applied to the oxygen sensor to determine the limiting current value at the first flat part and the limiting current value at the bottom of the valley that appears after the second flat part, and from the difference between these two limiting current values, the There is a gas concentration measurement method that obtains the moisture concentration. Another aspect of the present invention is to apply a voltage to a limiting current type oxygen sensor using a solid electrolyte in measuring the carbon dioxide concentration in a gas to be measured containing at least water and carbon dioxide. , the limiting current value of the second flat part and the limiting current value of the bottom of the valley that appears after the second flat part are determined, and the carbon dioxide concentration in the gas to be measured is obtained from the difference between these two limiting current values. Gas concentration measurement. It's in the method.

Hereinafter, the method of the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows a voltage-current characteristic curve of a limiting current type oxygen sensor using a solid electrolyte. still,
The sensor used here consists of a solid electrolyte with electrodes formed on both sides, covered with a hollow capsule in which a minute gas flow port is opened between the outside air, and the limiting current characteristic caused by the gas diffusion resistance of the gas flow port. It has a structure that utilizes.

In Fig. 1, the voltage-current characteristic curve 1) is a mixed gas (Oz, Nz, Cot, Hz).
, containing HE O), as the applied voltage to the sensor is increased, first a first flat part 12 appears due to the presence of oxygen, and then a flat part due to the presence of carbon dioxide and moisture appears. A second flat portion 13 appears, and after that it once descends to form a valley portion 14, and then rises again. The level of the bottom portion 14a of this valley portion 14 is higher than the first flat portion 12, as described above.

Here, the gas to be measured (02, N2, COt
This mixed gas (0□, Nz,
Cot, Hz O), only the bone where HE O is present,
Since the oxygen partial pressure becomes relatively small, the level in the first flat part 12 becomes low, and the level in the second flat part 13 becomes high due to the presence of both CO2 and 820 components. The second flat part 13 appears because of Co2 and HE 0
It is inferred that this is due to the decomposition of oxygen and the production of oxygen.

Further, it is inferred that the level of the valley portion 14 after the second flat portion 13 is higher than that of the first flat portion 12 due to the presence of oxygenated bone due to the decomposition of water.

Therefore, if a low voltage V1 is applied, the limiting current value IL of the first flat part 12 due to oxygen is obtained, and if a high voltage v2 is applied, the limiting current value IL of the second flat part 13 due to the presence of carbon dioxide and moisture is obtained. , is obtained, and if a higher voltage V is applied, the limit current value IL3 at the bottom 14a of the valley 14 is obtained.

The difference between the above limit current value IL+ and limit current value IL (
The difference current value ΔIL" is obtained from IL3-IL, ), and the difference between the limit current value IL and the limit current value IL (ILz
The difference current value ΔIL1 is determined from IL, ).

When the present inventors determined the correlation between the difference current value ΔIL'' and the water concentration in the mixed gas, it was found that there is a proportional relationship between the two, as shown in FIG. When the correlation between the difference current value ΔIL'' and the carbon dioxide concentration in the mixed gas was determined, it was found that there was a proportional relationship between the two as shown in FIG.

From this, if the water concentration corresponding to the difference current value ΔIL" is found in advance, the water concentration can be immediately found from the difference current value ΔIL". Similarly, if the carbon dioxide concentration corresponding to the difference current value ΔIL- is determined in advance, the carbon dioxide concentration can be immediately determined from the difference current value ΔIL1.

In addition, the oxygen concentration is determined by the oxygen limiting current value I as shown in Figure 4.
Since it is already known that it is proportional to L, it can be immediately determined from the limit current value IL+.

<Example> Using a capsule-type oxygen sensor with a diffusion hole, various moisture concentrations (set concentration set by adding known moisture in advance, and other 02, N2, CO□) were measured at a measurement temperature of 25°C. When we actually measured a mixed gas with a constant concentration of
It was as shown in the table.

Table 1 The values determined from Table 1 were plotted and graphed as shown in Figure 5.

From this graph, it can be seen that ΔIL'' and the actual measured values correspond well.

In addition, using a capsule-type oxygen sensor with a diffusion hole, various carbon dioxide concentrations (set concentrations set by adding known carbon dioxide gas in advance, etc.) were measured at a measurement temperature of 25°C.
, NZ , H, O concentration is constant),
The actual measurements were as shown in Table 2.

Table 2 The values determined from Table 2 were plotted and graphed as shown in Figure 6.

It can be seen from this graph that ΔIL- and the actual measured values correspond well.

In carrying out the present invention, patent application 1986-20
As shown in No. 2169, different voltages may be applied to the internal electrodes of multiple fields, or two sensors may be used in parallel, and furthermore, by sweeping the applied voltage, two-step A flat area may be realized and measured.

<Effects of the Invention> As is clear from the above description, according to the present invention, at least the moisture concentration, carbon dioxide concentration, and, if necessary, oxygen concentration in the gas to be measured can be easily and quickly measured.

In particular, in the case of carbon dioxide concentration, relatively high concentrations on the order of percent can be measured with high precision.

[Brief explanation of drawings]

Fig. 1 is a graph showing each voltage-current characteristic curve in a limiting current type oxygen sensor to explain the method of the present invention, and Fig. 2 is a graph showing the relationship between the difference current value ΔIL'' between the limiting current values and the water concentration. 3 is a graph showing the relationship between the difference current value ΔIL- between the limiting current values and the carbon dioxide concentration. FIG. 4 is a graph showing the relationship between the limiting current value and the oxygen concentration. Figure 5 is a graph showing the difference current value ΔIL between the limiting current values and the actual measured value, and Figure 6 is the graph showing the difference current value ΔI between the limiting current values.
Graphs showing L- and actual measured values, and FIGS. 7 and 8 are graphs showing other voltage-current characteristic curves in the limiting current type oxygen sensor. In the figure, 1)... Voltage-current characteristic curve of gas containing moisture and carbon dioxide, 12... First flat part, 13... Second flat part, 14... Valley part, 14a... Bottom, Patent applicant: Fujikura Electric Cable Co., Ltd. Figure 1 V+ V2 V3 E9 Power 0 Denta Figure 5 Mekurote Ito j (om) Figure 2 Figure 4 Rut! =5Lth (01・) Figure 3 Greeting j Washiki・Sunoshi ('/.) -12 Figure 7 E mouth Ka0 Den ami Figure 8 Ep Power O Den Mr.

Claims (2)

[Claims] (1) In measuring the moisture concentration in a gas to be measured containing at least moisture and carbon dioxide, a voltage is applied to a limiting current type oxygen sensor using a solid electrolyte,
The method is characterized in that the limiting current value at the first flat portion and the limiting current value at the bottom of the valley appearing after the second flat portion are determined, and the water concentration in the gas to be measured is obtained from the difference between these two limiting current values. Gas concentration measurement method. (2) In measuring the carbon dioxide concentration in a gas to be measured containing at least water and carbon dioxide, a voltage is applied to a limiting current type oxygen sensor using a solid electrolyte, and the limit of the second flat part is measured. A gas concentration measuring method characterized in that a current value and a limiting current value at the bottom of a valley appearing after the second flat portion are determined, and the carbon dioxide concentration in the gas to be measured is obtained from the difference between these two limiting current values.