JPH05172743A - Ozone concentration measuring method and light absorption type gas phase ozone concentration meter - Google Patents

Abstract

PURPOSE:To measure ozone concentration over a wide concentration range by a concentration meter with a wide measuring range by executing operation by means of a conversion equation for utilizing a growth curve in the function block of a CPU and correcting measured data. CONSTITUTION:Ozone is separated from a gas phase fluid by means of a catalyst within an ozone analyzer 1. Separated ozone is led into a measuring cell 6 and exhausted through a suction route. Ultraviolet light from a lamp 2 is separated into two beams by a half mirror, one is led to the cell 6 and the other to a detector 5. Within the cell 6 the photoelectric conversion of transmitted light is performed and its detection result is input to a CPU 11. The measurement is shown on a display 12. The influence of the variation of light intensity is corrected according to the output signal of the detector 5. Within the CPU 11 various conditions 14 are set and various information 15 is output. The CPU 11 is equipped with a linear operation means 13 as a function block and correction operation is executed on the basis of a conversion equation by means of a growth curve and the linear area is enlarged to display.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ozone concentration measuring method and a light absorption type gas phase ozone concentration meter, and more particularly to a technique for expanding the measurement range of an ultraviolet absorption type ozone concentration meter.

[0002]

2. Description of the Related Art An ultraviolet absorption type gas phase ozone concentration meter is a measuring instrument for measuring the ozone concentration in a dynamic fluid by utilizing the change in the amount of absorption of ultraviolet rays. The ozone concentration in the absorption cell is determined by the amount of absorption of 254 nm light by the sample gas. The following characteristics are related to this numerical determination.

(A) Absorption coefficient (μ) of ozone at a wavelength of 254 nm (b) Optical path length of absorption cell passing through the sample gas (L) (c) Transmittance of sample gas at a wavelength of 254 nm (I / I ₀ ) Here, I of the transmittance (I / I ₀ ) is the intensity of transmitted light when there is a sample gas containing ozone in the absorption cell, and I
₀ is a measured value of the intensity of transmitted light when ozone is not included. This transmittance value is defined by the following equation according to Beer-Lambert's law of absorption.

Transmittance = I / I ₀ = exp (−μyL) (1) where μ = 304 ± 4 atm ⁻¹ cm ⁻¹ (0 ° C., 760 tor
r), y = ozone concentration in the atmosphere, L = optical path length of the above-mentioned absorption cell.

Therefore, the ozone concentration y (ppm) is calculated by the following equation. y (ppm) =-(10 ⁶ / μL) · ln (I / I ₀ ) = (10 ⁶ / μL) · ln (I ₀ / I) (2)

[0006]

When the relationship between the concentration value measured by the above equation (2) and the actual ozone concentration is graphed, it becomes as shown in FIG. 6, and the ozone concentration increases and the transmittance increases. When it decreases (that is, when the amount absorbed by ozone increases), the measured value saturates and the rate of change decreases, causing a deviation between the measured value and the actual concentration value. That is, even if the ozone concentration value actually increases linearly, the measured value does not change linearly following this, and an error occurs in the measured value. According to the experimental results, the transmittance is in the linear range up to about 40%, but when the transmittance becomes 30%, an error of about 3% occurs, and when the transmittance is 20%, the error becomes about 6%.

As described above, since the area (linearity area) in which the measured value proportional to the actual ozone concentration is obtained is limited, one device can operate over a wide ozone concentration range (for example, the environmental level ( It is not possible to measure from 0 to 2 ppm) to high concentration levels (0 to 9999 ppm).

Therefore, in practice, a device having a limited measurement range (that is, the measurement cell length L is adjusted according to each range, and the measurement range in charge is set to be within the above-mentioned linearity range). A plurality of devices are prepared, and the user responds by selectively using these devices according to the concentration level of the measurement target.

The present invention has been made on the basis of such a consideration, and its purpose is to expand the linear region in ozone concentration measurement to a transmittance of 1%, and to measure the measurement range (correct Expand the measurement range)
It is to be able to measure the ozone concentration over a wide concentration range with one unit.

[0010]

The invention according to claim 1 is
Using a growth curve, where the information on the light transmittance is a variable t, and the ozone concentration to be obtained is a variable x, x = K
₀ · ln {(D + t) / (D−t)}, (K ₀ , D is
The linear region is enlarged by executing the calculation by the conversion formula of arbitrary coefficient) and calibrating the measurement data.

According to the second aspect of the invention, in order to realize the calibration function, the calibration calculation means is added to the ozone concentration meter. The calibration calculation means is realized, for example, as a functional block (means for executing a predetermined function, which is constructed as a result of the hardware operating according to the software) in the CPU.

[0012]

The conversion method for calibrating the measured values is required to linearize the data in the non-linear region according to the actual density value and not distort the original data in the linear region. However, the relationship between the actual concentration value and the output of the ozone concentration meter differs depending on the measurement cell length and the delicate characteristics of each device, so the optimum conversion formula should be directly determined by focusing only on the characteristics of the measurement data itself. I can't ask.

Therefore, in the present invention, a growth curve (logistic curve) having a shape very similar to the curve of the actual concentration value-output of the ozone concentration meter is selected, and the calibration curve is utilized by utilizing the characteristics of this growth curve. To get.

That is, the growth curve is a hyperbolic function and has a convergence point (convergence point) at −∞ and + ∞, and the actual concentration value−the output of the ozone concentration meter converges like a curve. There is no factor of destabilization, and when its logarithm is taken, it has a characteristic that it becomes a linear function (straight line) having a predetermined slope.

Therefore, by selecting the coefficient of the equation for obtaining the logarithmic value of the growth curve so that the slope of the straight line obtained by taking the logarithm of the growth curve matches the desired calibration line as much as possible. The value obtained by the conversion equation gives almost no error to the data in the linear region, and only the data in the non-linear region that needs calibration is lifted to obtain the effect of restoring the linearity.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of the ultraviolet absorption type ozone concentration meter of the present invention.

The ozone decomposer 1 uses a catalyst to separate ozone from the gas phase fluid. The measurement cell 6 has a predetermined amount of gas suctioned by a suction pump 10 via a flow meter 8 and a needle valve 9, and the ozone separated by the ozone decomposer 1 is measured via a three-way solenoid valve 4. 6 and is discharged through the gas suction route.

The ultraviolet light from the ultraviolet lamp 2 is separated into two directions by the half mirror 3, one of which is guided to the measuring cell 6 and the other of which is guided to the detector 5 for detecting the light intensity. When a low-pressure mercury lamp is used for the lamp and a phototube having a sensitivity of 300 nm or less is used for the detector, it becomes a monochromator for the emission line spectrum of wavelength 254 nm, and the peak value of the ultraviolet absorption of ozone can be matched.

The light transmitted through the measuring cell 6 is photoelectrically converted by the detector 7, and the detection signal is input to the CPU 11.
The measurement result is displayed on the display 12. The output of the detector 5 is also input to the CPU 11,
Based on this signal, correction is performed so as to eliminate the influence of fluctuations in light intensity during signal processing. Various conditions 14 can be set in the CPU 11 and various information 15 can be output.

The CPU 11 is provided with a linearization calculation means 13 as a functional block, and instead of directly reflecting the output of the detector 7 on the display, it performs a calibration calculation,
Enlarge and display the linear area.

Next, the calibration conversion operation of the linearization calculation means 13 by the conversion equation using the growth curve will be described. FIG. 4 shows the shape of the growth curve 40 to be applied, which is represented by the following equation (3). ln {y / (ay)} = bx + c (3) In this growth curve, the convergence points are "0" and "a", which has a linear region in the central part and a saturated region in the peripheral part. The characteristics are very similar to the output curve of an ozone concentration meter.

However, since the output of the ozone concentration meter has a shape on the right side of x = Q1 in FIG. 4, the origin of the coordinates is moved to the point P of y = a / 2 in order to match this. Then, the measured value is applied to the variable y, the actual concentration value is applied to the variable x, and the value at which the measured value converges is A (= a /
If the equation (2) is adopted, the equation (3) can be transformed into the following equation (4). ln {(A + y) / (A-y)} = Bx ...
(4), where B is a constant derived by experiment.

This equation (4) means that the logarithm of the equation for y is converted into a straight line for x having a slope of B, and Bx is a calibrated measurement. If the line representing the value-actual density relationship is made to match as much as possible, the linearity is guaranteed in the range of the match. When the formula (4) is transformed into a formula for the ozone concentration x, x = (1 / B) ln {(A + y) / (A−y)} ... (5), and (1 / B) is If B ₀ is set again, then x = B ₀ ln {(A + y) / (A−y)} ... (6)

Letting t be the changing part of the right side of the above-mentioned equation (2), that is, the logarithm of the reciprocal of the transmittance, then y
Since there is a proportional relationship between t and t, y is replaced by t in the equation (6), coefficient adjustment is performed, and x = K ₀ · ln {(D + t) / (D−t)} ··· (7 ) Is obtained. In this equation, by appropriately selecting K ₀ and D, highly reliable calibration conversion can be performed.

Actually, the conversion from the measured value to the ozone concentration (calibration conversion) is performed by the procedure as shown in FIG. That is, the transmittance I / I ₀ is calculated (step 2
0), the calibrated concentration C (ppm) is obtained by using the conversion formula as shown (step 21), and output such as display is performed (step 22).

In the conversion formula of step 22, L is the measurement cell length of the ozone concentration meter, and K and D are arbitrary coefficients selected by experiments. By performing this conversion, the linearity of up to about 1% was guaranteed, while the conventional range of up to 40% was guaranteed, and the measurement range of one device could be expanded several times. it can. FIG. 5 is a diagram showing the effect of the present embodiment, and shows the results before and after correction (calibration) when the present embodiment is applied to a device having a cell length of 3 mm and applied to a conventional maximum measured concentration of about 10000 ppm. A comparison is shown (A before correction, B after correction). It can be seen that the correction hardly affects the linearity in the low density region, while improving the linearity in the high density region.

The procedure of the processing which characterizes the present embodiment described above is summarized in FIG. That is, first, a growth curve approximate to the measured value-concentration curve is selected, and the measured value is assigned to the variable y and the ozone concentration to be obtained is assigned to the variable x (step 30). Next, the logarithm of the growth curve is taken to obtain the basic form of the calibration line (step 31). Next, the coefficient of the calibration straight line is adjusted so that the slope of the straight line is matched with the straight line that accurately displays the actual measured value-ozone concentration relationship (step 3).
2). As a result, an optimum conversion formula is obtained, and calibration is performed using this formula to expand the linear range from the conventional transmittance of 40% to 1% and expand the measurement range (step 33).

[0028]

As described above, according to the present invention, the conversion equation for linearization is obtained by paying attention to the characteristic of the growth curve, and the calibration conversion is performed by this, so that the conventional linear region is not affected. The range of the linear region can be expanded to about 5 times that of the conventional case without giving. As a result, the linear region in ozone concentration measurement is expanded to a transmittance of 1%, the measurement range of the measuring device (range in which accurate measurement can be performed) is expanded, and the ozone concentration of the ozone concentration over a wide concentration range can be increased by one unit. Measurement becomes possible, and high performance of the measuring device can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an ultraviolet absorption type ozone concentration meter of the present invention.

FIG. 2 is a diagram showing an actual procedure of conversion (calibration conversion) from a measured value to ozone concentration.

FIG. 3 is a diagram summarizing a procedure of processing that characterizes the embodiment of FIG.

FIG. 4 is a growth curve 4 applied to the conversion formula in the present invention.
It is a figure which shows the shape of 0.

5 is a diagram showing the effect of the embodiment of FIG. 1 with a cell length of 3
Approximately 10,000 ppm, which is the conventional maximum measurement concentration of mm
It is a figure which shows the comparison before and after correction (calibration) at the time of applying this Example to the apparatus applied to.

FIG. 6 is a diagram showing a relationship between a measured value and an actual concentration in an ozone densitometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ozone decomposer 2 Ultraviolet lamp 3 Half mirror (semi-transparent mirror) 4 Three-way solenoid valve 5 Light intensity correction detector 6 Measuring cell 7 Photoelectric converter (detector) 8 Flow meter 9 Needle valve 10 Suction pump 11 CPU 12 Indicator 13 Linearization calculation means 14 Setting items 15 Output items

Claims (4)

[Claims] 1. An ozone concentration measuring method for measuring the intensity of light passing through a gas-phase fluid in a measuring cell and obtaining an ozone concentration value of the gas-phase fluid in the measuring cell based on the measurement data. The information regarding the light transmittance obtained from the measurement data is set as a variable t, and the ozone concentration to be obtained is set as a variable x, and the calculation is performed by the following conversion formula to convert the measurement data to the ozone concentration to obtain the ozone concentration. A method for measuring ozone concentration, which comprises obtaining a value. (Conversion formula) x = K ₀ · ln {(D + t) / (D−t)} where K ₀ and D are arbitrary coefficients. 2. The information on the light transmittance obtained from the measurement data is the light transmittance (I / I ₀ ; I is measured,
Is the intensity of the transmitted light that has been absorbed by ozone,
₀ is the logarithm (ln (I ₀ / I)) of the reciprocal of the intensity of the transmitted light in the case where there is no absorption due to ozone, which is obtained in advance
The ozone concentration measuring method according to claim 1. 3. A detector (7) measures the intensity of light passing through the gas-phase fluid in the measurement cell (6), and based on this measurement data, the gas-phase fluid in the measurement cell (6) is measured. A light absorption type gas phase ozone concentration meter for obtaining an ozone concentration value, wherein information on the light transmittance obtained based on the measurement data by the detector (7) is a variable t, and the ozone concentration to be obtained is a variable. A light absorption type vapor phase ozone concentration meter characterized in that it has a calculation means (13) for executing a calculation by the following conversion formula as x. (Conversion formula) x = K ₀ · ln {(D + t) / (D−t)} where K ₀ and D are arbitrary coefficients. 4. The information on the light transmittance obtained based on the measurement data is the light transmittance (I / I ₀ ; I is the measured intensity of transmitted light absorbed by ozone,
I ₀ is a logarithm (ln (I ₀ / I ₀ / I ₀ / intensity of transmitted light in the case where there is no absorption by ozone) obtained in advance.
I)) is a light absorption type vapor phase ozone concentration meter according to claim 3.