JPH0829385A - Oxygen concentration detection meter - Google Patents

Abstract

PURPOSE:To accurately detect oxygen concentration by introducing a plurality of standard gases containing known oxygen concentrations, calibrating reference gas detector part temperature and detector part temperature for gas to be detected, and detecting concentration of a gas to be detected. CONSTITUTION:The detector part is previously heated to about 600-800 deg.C, then a standard gas is introduced to the oxygen concentration detection meter, and an electromotive force E is read. After this operation is executed to at least two or more types of standard gases, reference gas detector part temperature T1 and detector part temperature T2 for gas to be detected are calculated (calibrated). The electromotive force E obtained by introducing the gas to be detected, oxygen concentrations P1 of the reference gas and calibreted temperatures T1, T2 are substituted into a formula E=(R)/(4F)[T1 ln (P1)-T2 ln (P2)] (where R is gas constant, and F is Faraday constant), and oxygen concentration P2 of the gas to be detected is calculated. Thus, since the standard gases are previously introduced thereby to accurately estimate the temperatures T1, T2, the oxygen concentration P2 can be accurately detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration detector excellent in measurement accuracy.

[0002]

2. Description of the Related Art An oxygen concentration detecting element having a structure in which electrodes such as platinum are provided on both surfaces of an oxygen ion solid electrolyte typified by zirconia, and one electrode contacts a reference gas and the other electrode contacts a test gas It is widely used as a gas analyzer. The measurement principle is that if the oxygen partial pressures in contact with both electrodes are different, a so-called concentration cell is formed and Nern shown in the following formula (3) is used.
This is because the difference in chemical potential between both electrodes is generated as an electromotive force according to the st formula. E = (RT) / (4F) ln (P1 / P2) (3) where E is electromotive force, R is gas constant, T is absolute temperature, F
Is the Faraday constant, P1 is the oxygen concentration of the reference gas, and P2 is the oxygen concentration of the test gas.

In general, the atmosphere (oxygen concentration is constant at 20.6%) is used as a reference gas, which is in contact with one electrode and introduces the test gas onto the other electrode to detect the oxygen concentration of the test gas. . Currently, the oxygen concentration detector using this method is
Widely used as a simple type.

The oxygen ion solid electrolyte of the above oxygen concentration detector reaches the oxygen ion conductivity which can be used as a sensor element, only when it is heated to a high temperature. When the most typical zirconia is used, the measurement is performed in a state where the detection part of the zirconia sensor element of the oxygen concentration detector is heated to 600 to 800 ° C. in an electric furnace.

However, in the conventional oxygen concentration detector,
When the test gas is introduced, since the temperature of the test gas is lower than the temperature of the element detection unit, the element detection unit is cooled and the oxygen concentration of the test gas cannot be accurately measured. This is because the absolute temperature T in the equation (3) is actually lower than the set value due to the above cooling effect, and the temperature is different between the reference gas side and the test gas side of the detection unit.

In order to solve such a drawback, there has been proposed an oxygen concentration measuring device in which a temperature detecting element is arranged in the test gas detecting portion and the oxygen concentration is detected according to the equation (1). (For example, Japanese Patent Laid-Open No. 53-52194) However, in this proposal as well, a measurement error proportional to the temperature difference between the set temperature of the electric furnace and the reference gas detection unit occurs, and further, the heat capacity and the heat conduction between the temperature detection element and the electrode serving as the detection unit. Since the rates are different, it cannot be said that the chemical potential on the test gas side is accurately estimated.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have completed the present invention as a result of continuing diligent research in order to solve the above-mentioned problems of the existing oxygen concentration detector. What is done is to provide an oxygen concentration detector capable of accurately detecting the oxygen concentration.

[0008]

The first invention for achieving the above object is to provide at least two or more kinds of standard gases whose oxygen concentration is known in an oxygen ion solid electrolyte concentration cell type oxygen concentration detector. Introduced, calibrate T1 and T2 in the following formula (1), and use the calibrated values of T1 and T2,
It is an oxygen concentration detector characterized by detecting the concentration of a test gas from equation (1). E = (R) / (4F) (T1ln (P1) -T2ln (P2)) ... (1)

A second aspect of the present invention is an oxygen ion solid electrolyte concentration cell type oxygen concentration detector, in which at least two or more standard gases having known oxygen concentrations are introduced, and ΔT and An oxygen concentration detector characterized by calibrating T2 and using the calibrated values of ΔT and T2 to detect the concentration of the test gas from the equation (2). E = (R) / (4F) (ΔTlnP1 + T2ln (P1 / P2)) ・ ・ (2)

Here, E is an electromotive force, T1 is a reference gas detection part temperature, T2 is a test gas detection part temperature, ΔT is a difference between the reference gas detection part temperature and the test gas detection part temperature (= T1-T2), P
1 is the reference gas concentration, P2 is the test gas concentration, R is the gas constant, and F is the Faraday constant.

The important point in the present invention is Nernst.
The formula is corrected to the form of the formula (1) or (2), and at the time of measurement, at least two kinds of standard gases having a known oxygen concentration are introduced for the cooling effect of the detection unit accompanying the introduction of the test gas. It is in the point estimated by doing. Furthermore, T1, T
Since 2 or ΔT and T2 are not estimated by the temperature detecting element but are calibrated from the difference in chemical potential, they are estimated as more thermodynamically accurate values. Hereinafter, a standard gas having a known oxygen concentration is simply referred to as a standard gas.

Equation (1) is an equation showing the difference in chemical potential when the temperatures of the reference gas detecting portion and the test gas detecting portion are different. The formula (2) is a correction formula in which the formula (1) is further corrected and arranged by the temperature difference of the gas detection unit and the temperature of the test gas detection unit.

In the oxygen concentration meter of the present invention, the detecting portion is heated at 600 to 800 ° C. before the measurement. Next, two or more standard gases are prepared and introduced into the oxygen concentration detector. Next, the electromotive force value for each gas is detected, and the electromotive force value E, the oxygen concentration P2 of the standard gas, and the oxygen concentration P1 of the reference gas are substituted into the equation (1) or (2) to obtain the reference gas detection part temperature. T1 and the temperature T2 of the detected gas detection portion, or ΔT (= T1−T2) and the temperature T2 of the detected gas detection portion.
Is calculated (calibrated). Then, the test gas is introduced, and the electromotive force value detected at that time and the T1, T2 or Δ
Substituting T and T2 into the equation (1) or (2), the oxygen concentration in the test gas is measured.

The flow rates of the introduced gas are T1, T2 and ΔT.
Therefore, when calibrating T1, T2, and ΔT, it is preferable that the flow rate of the standard gas be the same as that when introducing the test gas. Further, it is preferable to set the flow rate so as to be kept constant. When the flow rate is different or the fluctuation is large, the temperature of the detection unit also changes or fluctuates. In that case, T1, T2 and Δ
T cannot be accurately estimated. When measuring a test gas with a large flow rate fluctuation, it is preferable to keep the pressure of the test gas constant with a regulator or the like, or to keep the flow rate constant using a constant flow pump or the like. When detecting the oxygen concentration of the test gas at different flow rates, it is preferable to calibrate T1, T2 and ΔT for each flow rate to detect the oxygen concentration.

In the present invention, the standard gas used is 2
More than type. With one type of standard gas, T1, T2 and ΔT cannot be calibrated. If there are two or more standard gases, T
Although 1, T2 and ΔT can be calibrated, it is preferable to use as much standard gas as possible for a more accurate determination. Further, it is preferable to select the standard gas to be prepared with a concentration range as wide as possible, from those having a high oxygen concentration to those having a low oxygen concentration. T1, T2, and ΔT can be accurately calibrated by preparing as many standard gases as possible from a high oxygen concentration to a low oxygen concentration. The calibration method of T1, T2 and ΔT is preferably accurately determined by the least square method.

In the present invention, the reference gas is air (P1 =
Preference is given to using 0.206). When a gas other than air is used as the reference gas, the shape of the element and maintenance of the reference gas become complicated, which is not preferable.

An example of a flow chart for measuring the oxygen concentration in the case of the oxygen concentration meter of the first invention is shown in FIG. 1 and will be described below based on it. First, the standard gas is introduced into the oxygen concentration meter.
Then, the oxygen concentration of the standard gas is input, and the electromotive force value corresponding thereto is read. This operation is carried out for several standard gases. After finishing these operations, T1 and T2
Is calculated (calibrated). Then, the test gas is introduced. From the obtained electromotive force value E, the oxygen concentration P1 of the reference gas, and the calibrated T1 and T2, the oxygen concentration P2 is calculated according to the equation (1) and displayed. The oxygen concentration meter of this system is preferably of a type in which a microcomputer is installed for calculation or a type of calculation by a personal computer.

On the other hand, an example of a flow chart for measuring the oxygen concentration in the case of the oxygen concentration meter of the second invention is shown in FIG. 2 and will be described below based on it. Two kinds of variable resistors for ΔT adjustment and T2 adjustment are installed in the electric circuit of the oximeter. First,
A standard gas having the same oxygen concentration as the standard gas is introduced. As the reference gas shows the same oxygen concentration as the reference gas, Δ
Adjust the variable resistor for T adjustment. Then another standard gas is introduced. The T2 adjusting variable resistor is adjusted so as to indicate the oxygen concentration of the standard gas. With the above operation, ΔT and T
2 is calibrated. Then, the test gas is introduced. The oxygen concentration P2 is displayed according to the equation (2) from the obtained electromotive force value E, the oxygen concentration P1 of the reference gas, and the adjusted ΔT and T2. The oximeter of this system can also be manufactured as a simple type that is controlled by using an arithmetic circuit that uses the amplification of an operational amplifier.

No temperature measuring element is arranged in the element portion of the oximeter of the present invention. The temperature obtained by the temperature detecting element and the temperature obtained from the chemical potential of the detecting portion necessarily differ from each other due to the difference in their heat capacity and thermal conductivity. Therefore, the arrangement of the temperature detecting element is not preferable because it has no merit and the element structure is complicated.

The temperature of the oxygen concentration meter of the present invention is preferably set in consideration of the temperature decrease of the test gas detection section T2. In general, platinum used as an electrode has a minimum operating temperature of about 500 ° C, so T2 is 50
It is preferable to set the temperature to be 0 ° C or higher. However, in the oxygen concentration meter of the present invention, the temperature of the electrode portion is thermodynamically calibrated in a perfect form, so that the temperature difference ΔT between the detection electrodes may be large, and the oxygen concentration can be accurately detected. it can.

For the heating of the detector of the oximeter according to the present invention, it is preferable to keep the temperature of the detector constant by P control or PID control using an electric furnace. However, if there is enough time for measurement, constant current control, constant voltage control,
It can also be heated by constant output control.

Examples of the oxygen ion solid electrolyte used in the present invention include zirconia doped with one or more of calcium, magnesium or yttrium, or ceria or titania. Among them, the oxygen ion conductivity is A zirconia-based ceramic having a high oxygen ion transport number of 1 even under a low oxygen partial pressure is preferable.

As the electrodes installed in the detecting portion of the present invention, any electrodes may be used as long as they are used in the conventional oxygen concentration detector. Examples thereof include noble metals such as platinum, silver and gold, and perovskite type or spinel type oxides.

[0024]

Example 1 Cylindrical zirconia doped with 8 mol% yttria as an oxygen ion solid electrolyte (shape: outer diameter 1
0 mm, inner diameter 7 mm, length 200 mm), and an oxygen concentration detection element using porous platinum baked at 1000 ° C. as an electrode in the detection part was installed in an electric furnace to 700 ° C.
It heated using the temperature controller (PID control) so that it might become. A platinum lead wire is installed from the detection part electrode, and the electromotive force from the element is measured by a digital electrometer (TR865).
2, made by Advantest, and detected through a personal computer (PC98) via the GP-IB interface.
01, manufactured by NEC). In the computer, first input the oxygen concentration of the standard gas, then read the electromotive force from the digital electrometer, repeat this operation for several standard gases, and perform T1 and T2.
Is calculated by the method of least squares in equation (1), then T1, T2,
A program for calculating the oxygen concentration of the test gas from the oxygen concentration P1 of the reference gas and the electromotive force value E obtained when the test gas is introduced is set, and the oxygen concentration is displayed on the display. The reference gas was the atmosphere (oxygen concentration 20.6%), and the flow rate was 300 cc / min.

Standard gases (nitrogen balance) having oxygen concentrations of 10 ppm, 1000 ppm and 20.6% were prepared.
The electromotive force value for the standard gas having an oxygen concentration of 10 ppm was 0.202 V, the electromotive force value for the standard gas of 1000 ppm was 0.108 V, and the electromotive force value for the standard gas of 20.6% was -0.0008 V. T1 and T2 are 69 by the computer by the method of least squares.
The calculated values were 7.9 ° C and 674.6 ° C.

Next, for the purpose of confirming that the oxygen concentration meter of the present invention is operating correctly, the oxygen concentration is 100 ppm.
And a standard gas known to be 1% was introduced as a test gas. Electromotive force for oxygen concentration of 100ppm is 0.15
At 5V, oxygen concentration shows 100.2ppm, and 1%
The electromotive force for the oxygen concentration was 0.061 V and the oxygen concentration was 1.00%, confirming that the oxygen concentration meter of the present invention is operating normally.

[0027]

[Comparative Example 1] Using the same oxygen concentration meter as in Example 1, the oxygen concentration was calculated by the commonly used Nernst equation of the equation (3) where T1 and T2 were not calibrated and the detection portion temperature T was 700 ° C. . 127 ppm was displayed for the standard gas having an oxygen concentration of 100 ppm, and 1.12% was displayed for the standard gas having an oxygen concentration of 1%.

[0028]

Example 2 Tamman tube type zirconia (shape: outer diameter 10 mm, inner diameter 7 mm, length 50 mm) doped with 8 mol% yttria was used as an oxygen ion solid electrolyte, and baked at 1000 ° C. as an electrode on the detection part. Installed oxygen concentration detection element using porous platinum in the electric furnace,
It heated using the temperature controller (P control) so that it might become 700 degreeC. A platinum lead wire was installed from the detection part electrode, the electromotive force from the element was amplified using an operational amplifier with a high input impedance, and an analog circuit was produced to instruct and output the oxygen concentration according to the equation (2). In addition, ΔT
(= T1−T2) and T2 are calibrated by first introducing a standard gas having the same oxygen concentration as the reference gas, adjusting ΔT with a variable resistance, then introducing another standard gas, and T2 with a variable resistance. I made it so that I could adjust it. The reference gas was the atmosphere (oxygen concentration 20.6%), and the flow rate was 200 cc / min.

A standard gas having an oxygen concentration of 20.6% (nitrogen balance) was introduced. The electromotive force was -0.0019V. Then, the variable resistor for adjusting ΔT is used to adjust the oxygen concentration of the indicator to 2
It was adjusted to show 0.6%. Then oxygen concentration 100
A standard gas of ppm (nitrogen balance) was introduced. The electromotive force was 0.148V. Then, the T2 adjusting variable resistor was adjusted so that the oxygen concentration of the indicator would indicate 100 ppm.

Next, the oxygen concentration is 10 ppm and 100.
A standard gas known to be 0 ppm was introduced as a test gas, and it was confirmed that the oxygen concentration meter of the present invention was operating properly. As a result, the electromotive force for the oxygen concentration of 10 ppm was 0.1935 V and the oxygen concentration was 9.97 ppm, and the electromotive force for the oxygen concentration of 1000 ppm was 0.1030 V and the oxygen concentration was 1002 ppm. It was confirmed that the oximeter of the invention is operating normally.

[0031]

[Third Embodiment] Using the element used in the second embodiment, an oximeter equipped with a digital circuit for processing and calculating data according to the formula (1) by a Z80 microcomputer was manufactured. Flow rate 20
When T1 and T2 are calibrated at 0 cc / min and then a test gas whose flow rate fluctuates from 300 cc / min to 100 cc / min is introduced, the oximeter indicates 130
It varied from ppm to 160 ppm. Next, install a constant flow pump at the test gas inlet and set the test gas introduction amount to 2
When stabilized at 00 cc / min ± 5 cc / min, the oximeter indicated 144 ppm to 145 ppm.

[0032]

[Comparative Example 2] K was added to the test gas side of the device used in Example 2.
A thermocouple was placed and an attempt was made to measure the temperature by the temperature sensing element on the side of the test gas. The electric furnace control and the flow rate of the gas to be detected are the same as those in the second embodiment.
The same conditions were used. As a result, the temperature obtained by the temperature measuring element was 673 ° C. With this value as T2 and the electric furnace control temperature as T1 (= 700 ° C.), the oxygen concentration was calculated from the equation (1). As a result, the oxygen concentration displayed for the oxygen concentration of 10 ppm is 14.9 ppm,
Also, the oxygen concentration is 12 for the oxygen concentration of 1000 ppm.
It was 50 ppm.

[0033]

As described above, according to the oxygen concentration meter of the present invention, the temperature T1 of the test gas detection unit and the temperature T2 of the reference gas detection unit in the formula (1) or the formula (2) The temperature difference (= T1-T2) between the test gas detection unit and the reference gas detection unit and the temperature T2 of the reference gas detection unit can be accurately estimated by previously introducing the standard gas, and as a result, the oxygen concentration can be accurately measured. It is possible to provide an oximeter capable of detecting

[Brief description of drawings]

FIG. 1 is a flow sheet diagram of the flow of oxygen concentration measurement in the case of the oximeter of the first invention.

FIG. 2 is a flow sheet diagram of a flow of oxygen concentration measurement in the case of the oxygen concentration meter of the second invention.

Claims (2)

[Claims] 1. In an oxygen ion solid electrolyte concentration cell type oxygen concentration detector, at least two or more kinds of standard gas having a known oxygen concentration are introduced, and T1 and T2 in the following formula (1) are calibrated and calibrated. An oxygen concentration detector characterized in that the concentration of the test gas is detected from the formula (1) using the values of T1 and T2 thus obtained. E = (R) / (4F) (T1ln (P1) -T2ln (P2)) ... (1) 2. In an oxygen ion solid electrolyte concentration cell type oxygen concentration detector, at least two or more kinds of standard gases having known oxygen concentrations are introduced, and ΔT and T2 in the following formula (2) are calibrated and calibrated. An oxygen concentration detector characterized in that the concentration of the test gas is detected from the equation (2) by using the obtained values of ΔT and T2. E = (R) / (4F) (ΔTlnP1 + T2ln (P1 / P2)) (2) where E is the electromotive force, T1 is the reference gas detection part temperature, T2 is the test gas detection part temperature, and ΔT is the reference gas. The difference between the detection part temperature and the test gas detection part temperature (= T1-T2), P1 is the reference gas concentration, P2 is the test gas concentration, R is the gas constant, and F is the Faraday constant.