JPH03140843A - Concentration measuring device for gaseous mixture - Google Patents

Abstract

PURPOSE: To improve the measurement accuracy by providing an air calibration circuit where a gaseous calibration mixture flows to an air measurement circuit and measuring and calibrating concentration using the same measurement cell at different times. CONSTITUTION: The device has a suction pump 40, an air sampling circuit where the entrance and exit are connected to a main duct 10, a measurement cell 56, a suction pump 59, and an air measurement circuit where one terminal is connected to the air sampling circuit and the other is connected to the main duct 10. Also, it is connected to the air sampling circuit by a bypass for separating the air sampling circuit from the duct 10 and has an air calibration circuit where a gaseous calibration mixture flows to an air measurement circuit. Then, a light intensity measurement means 80 measures the light intensity of fluorescence induced inside a measurement cell and outputs an electrical signal corresponding to the light intensity of fluorescence. Then, the concentration of a constituent in a mixture that flows in the duct 10 is measured from calibration measurement to be performed when a gaseous calibration mixture flows in an air measurement circuit by a processing means 82.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention relates to a device for measuring the concentration of a gaseous mixture, and in particular,
The present invention relates to a device for measuring the concentration of gaseous mixtures, which is applied to testing the presence of toxic components in gaseous mixtures released into the atmosphere.

BACKGROUND OF THE INVENTION Gaseous mixtures, for example those resulting from the reprocessing of materials, are released into the atmosphere. For this reason, it is necessary to ensure that no toxic components are present in the gaseous mixture, even at very low concentrations. Extremely sensitive concentration measurement devices are capable of detecting anything above a certain concentration threshold, which is set at a very low level for safety reasons. must be done.

FIG. 1 is a schematic diagram showing an example of the configuration of a conventional gaseous mixture concentration measuring device, and in this figure, the gaseous mixture is
It flows inside the main tact 10 in the direction shown by the arrow in the figure. A portion of the gaseous mixture is sucked into a bypass air circuit with a measuring cell 14 under the action of a suction pump 12.
I can get two. The flow rate and pressure of the gaseous mixture are determined by a flow meter 22 and a pressure gauge 24 provided at the inlet of the measuring cell 14.
Measured by

The light beam emitted by a given laser 16 passes completely through the measuring cell 14 . The wavelength of the light beam is preferably selected in such a way that it excites the component to be examined.

This light beam is modulated by a light modulator or chopper 26, which allows synchronous detection.

The fluorescence emitted outside the measurement cell 14 through the side shielding window 18 is filtered by a filter 20 for removing diffused light from the excitation beam.

A photomultiplier 28 powered by 31m [30] collects the fluorescence and outputs an electrical signal proportional to the detected light intensity.

A second measuring cell 34 filled with a gaseous mixture of known concentration and containing the components to be examined is arranged in the path of the excitation light beam arriving from the measuring cell 14 . System 35 is subordinate to pressure gauge 24 and has a second
makes it possible to equalize the pressure in the measuring cell 34 with the pressure in the measuring cell 14.

The excitation beam is absorbed into the second measurement cell 34 and causes a fluorescence emission in a portion of the same component as the component to be examined. The fluorescence emitted outside the second measurement cell 34 via the side shielding window 33 is powered by a power supply 30 after being filtered by a filter 36 for removing parasitic light from the excitation beam spread. are collected by a photomultiplier 38. Photomultiplier 38 outputs an electrical signal proportional to the detected light intensity.

The electrical signals output from the two photomultipliers 28 and 38 are fed to two inputs of the processing means 32. Measuring the fluorescence intensity of a component with a known concentration makes it possible to infer the concentration of the component to be tested based on the light intensity emitted by the component to be tested. The measurements carried out on the basis of the second measuring cell 34 constitute a calibration of the measuring device.

[Problems to be Solved by the Invention] By the way, the conventional gaseous mixture concentration measuring device described above has a number of drawbacks as shown below.

First, its sensitivity is 1012 molecules/cm' in an industrial medium.
It does not make it possible to measure concentrations of:

And this sensitivity is not suitable when it is necessary to test multiple components that are highly toxic, and yet
These multiple components are subject to extremely low release standards.

Inadequate sensitivity leads to long reaction times. If the detected signal is very weak, a concentration measurement can be obtained by averaging successive measurements. The number of these measurements increases as the signal becomes weaker and increases as the signal gets lost in noise. During the measurement, the concentration of the components changes significantly.

And that distorts the measurement results.

In order to perform calibration effectively, the two photomultipliers 28 and 38 must have identical characteristics. That leads to control complexity and calibration difficulties.

This conventional concentration measuring device does not make it possible to distinguish between parasitic fluorescence emitted from other components that likely constitute the gaseous mixture.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a concentration measuring device for a gaseous mixture that can eliminate the above-mentioned drawbacks.

``Means for Solving the Problems'' The invention according to claim 1 includes an air sampling circuit having a suction pump, the inlet and outlet of which are connected to a main duct, and a gaseous mixture at a known flow rate and pressure. a measuring cell suitable for circulating the water and a suction pump,
One end is connected to the air sampling circuit, the other end is connected to the main tact, and the gaseous mixture is
an air measuring circuit which is sucked up by an air sampling circuit and discharged into said main duct; and gaseous calibration mixture supply means for supplying a gaseous calibration mixture containing the components to be tested in a known and randomly variable concentration. , an air calibration circuit connected to the air sampling circuit by a bypass capable of separating the air sampling circuit from the main duct, through which the gaseous calibration mixture flows to the air measurement circuit, and inducing fluorescence of the components inside the measurement cell; a fluorescence inducing means for measuring the light intensity of the fluorescent light and outputting an electrical signal corresponding to the light intensity of the fluorescent light; processing means for processing the electrical signal, the input of which is connected to the output of the light intensity measuring means, in order to determine the concentration of the components contained in the mixture flowing in the main duct on the basis of a calibration measurement; It is characterized by having the following.

Moreover, the invention according to claim 2 is characterized in that in the invention according to claim 1, the air sampling circuit includes a pyrolyzer.

Furthermore, the invention according to claim 3 is characterized in that in the invention according to claim 1, the gaseous calibration mixture supply means includes a cryogenic exchanger.

In addition, the invention according to claim 4 is characterized in that, in the invention according to claim 1, an optical trap is provided to prevent a light beam that has already passed vertically through the air measurement cell from returning to the measurement cell. .

"Action" According to the invention as claimed in claim 1, the above-mentioned calibration measurement is based on the fluorescence emitted by a component that is the same as the component to be tested, but contained in a known concentration in the gaseous calibration mixture. will be carried out.

Also, the calibration measurements and the concentration measurements of the component to be tested are performed at different times but using the same measurement system.

Furthermore, calibration and measurement are performed using the same tool.

This proves the validity of the measurement and improves the accuracy of the measurement.
It makes it possible to do two things.

In addition, in order to transition from normal operation to the "calibration" mode, it is possible to prevent the arrival of the gaseous mixture emitted from the main duct and to send a calibration mixture of known composition into the air measuring circuit. is necessary.

Furthermore, according to the invention as claimed in claim 2, in the invention as claimed in claim 1, it is possible, if desired, to separate each component present in the gaseous mixture and including the component to be examined. be. Without a pyrolyzer, the amount of the component to be tested present in the mixture would not be covered by the measurements.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic diagram showing the configuration of an apparatus for measuring the concentration of a gaseous mixture according to an embodiment of the present invention. As shown in the figure, it is flowing inside the main duct 10. The air sampling circuit is connected to the main duct 10.
connected in parallel. The suction pump 40 flows a portion of the gaseous mixture into the air sampling circuit at a volumetric flow rate of ill/mm at atmospheric pressure.

A valve 42 blown at the inlet of the air sampling circuit provides isolation of the air sampling circuit or regulation of the pressure of the gaseous mixture flowing into the air sampling circuit. Pressure and flow rate are controlled with the help of pressure gauge 46 and flow meter 44.

The air sampling circuit also includes a pyrolyzer 48 of, for example, quartz. If desired, it is possible to separate the compounds of the gaseous mixture that contain the components to be examined.

The piping and various components of the air sampling circuit are
Made from materials that have no chemical affinity with the toxic component being tested. This prevents the above-mentioned components from accumulating within the air sampling circuit. The suction pump 40 and the separation valve 42 as well as the piping are made of, for example, Teflon (
Made from (product name). The pyrolyzer 48 is, for example,
Made from quartz. The flow meter 44 is made of, for example, glass and Teflon (trade name).

The air measuring circuit is connected at one end to the air sampling circuit and at the other end to the main duct IO downstream of the outlet of the air sampling circuit. This air measurement circuit includes a flowmeter 50, a valve 52, a pressure gauge 54, and a measurement cell 5.
6 and a suction pump 59. Desirably, the pressure within the measurement cell 56 is 100 Pa or less. The pressure must be adjusted so that excitation of fluorescence occurs under the most possible conditions.

The power of the suction pump 59 is 100 cc/m
It is preferably suitable for obtaining a pressure in the measuring cell 56 of approximately Q, 1 mbar at a volumetric flow rate of m.

A portion of the gaseous mixture circulating in the air sampling circuit is sucked up into the air measuring circuit under the action of a suction pump 59 .

1 2 Flow meter 50 and pressure gauge 54 are used to control the flow rate and pressure within measurement cell 56 .

The pressure in the measuring cell 56 is regulated with the help of the valve 52.

The measuring cell 56 has two windows 58 inclined, for example, by a Brewster angle with respect to the longitudinal axis of the measuring cell 56, in order to prevent parasitic reflections into the measuring cell 56 when the light beam passes through the measuring cell 56. and 60. A side obscuring window is provided on the side of the measuring cell 56 for observing the fluorescence emitted from the component to be examined within the measuring cell 56 .

As in the case described above, the materials making up the air measurement circuit have no chemical affinity with the component to be tested. Flow meter 50 and pressure gauge 54 are identical to flow meter 44 and pressure gauge 46 of the air sampling circuit. The valve 52 is made of, for example, Teflon (trade name). Windows 58 and 60 and shielding window 62 are made of quartz, for example.

Laser 16, for example a dye laser, emits a light beam that has a narrow spectral width and can selectively excite the component to be examined. Chopper 26 modulates the light beam. This chopper allows synchronous detection of fluorescence.

Lens 64 focuses the light beam onto an optical fiber 66 that guides the light beam toward measurement cell 56 . After propagation within optical fiber 66, the light beam enters measurement cell 56.
Focused inward by lens 68, window 58
to excite the component to be examined.

There is no overall absorption of the light beam. In other words, the absorption of the light beam is in most cases trivial, since the component to be examined is the only component that absorbs the light beam, but only in very small concentrations. Because it doesn't exist. The light beam therefore passes through the second window 60 after passing through the measurement cell 56 .

A light trap 70 is provided in the measurement cell 5 to prevent the light beam from returning into the measurement cell 56 causing parasitic light reflections.
Completely absorbs the light beam that passes through 6.

After excitation by the light beam, the components to be examined contained in the gaseous mixture circulating in the measuring cell 56 generate fluorescence. A portion of the fluorescence is emitted to the outside through the shielding window 62.

A lens 72 placed in the vicinity of the shielding window 62 collimates the fluorescent light into a collimated beam which passes through an interference filter 74 which makes it possible to remove most of the light scattered by the excited light beam.

Lens 76 focuses the filtered light beam into an optical fiber. The optical fiber guides the filtered light beam towards a light intensity measuring means 80 for measuring the light intensity of the fluorescence, preferably constituted by a multi-channel spectrometer.

Multichannel spectrometers have dispersive elements that spread the light beam as a function of wavelength. The expanded light beam is detected by a photodiode array, each photodiode corresponding to a narrow wavelength range.

Thereby, the multi-channel spectrometer simultaneously outputs electrical signals proportional to the light intensity corresponding to each wavelength range.

Since the wavelength of the fluorescence of the component to be examined is known, parasitic light of other wavelengths, light partially left from the dispersion of the excited light beam and other components present in the gaseous mixture can be detected. It is consequently possible to filter out the stimulated parasitic fluorescence (electrically by simply tapping out the signal of interest).

The electrical signal corresponding to the light intensity of the fluorescence of the component to be tested is
It is supplied to the input of a processing means 82 such as a micro-on-computer. Processing means 8? ! determines the concentration of the component to be tested based on the measured light intensity and a calibration curve stored in memory.

As described below, calibration is performed via the air measurement circuit described above. This calibration is carried out at the beginning of the introduction of the gaseous mixture into the concentration measuring device and is then repeated from time to time. Further, this concentration measuring device 5 6 is automatically initialized by the processing means 82 when the concentration of the component to be tested exceeds a preset threshold. To obtain this case and time, it is possible to control just one special operating point without repeating the complete calibration.

In this way, the reliability of the measurements is controlled virtually instantly, since the transition from the "measurement" mode to the "calibration" mode is simple and fast, as will be seen later.

Calibration consists in measuring the light intensity of the fluorescence emitted by a component contained in a gaseous calibration mixture with a known concentration and measured actual pressure and identical to the component to be tested. Various measurements are performed by changing these different parameters and a calibration curve (
′! , stored in memory within the microcomputer.

The intermediate value between the two curves is estimated.

To perform calibration measurements, the air sampling circuit
It is separated from the main duct 10 and connected to the air calibration circuit by a bypass. The air calibration circuit comprises three valves 42, 86 and 88 made of, for example, Teflon (trade name), and is controlled manually or automatically by the processing means β2 connected to this air calibration circuit. An isolation valve 42 makes it possible to separate the intake of the air sampling circuit from the main duct 10.

The air calibration circuit has means for supplying a gaseous calibration mixture containing the above-mentioned components of known concentration and whose concentration can be varied randomly.

As specifically shown in FIG. 2, the means described above consist of a cryogenic exchanger 90.

A valve 42 connects the air sampling circuit to the main duct 10.
When separated from the gaseous mixture, valve 86 is opened and the gaseous mixture,
For example, a selection of air, argon or nitrogen compressed into the reservoir is released. The released gas circulates within a duct 94 immersed in a cryogenic fluid 96 contained within a sealed container. Inside the sealed container, the temperature of the cryogenic fluid 96 is controlled by the power supply 1 immersed in the cryogenic fluid 96 and controlled by the processing means 82.
The temperature of the thermistor 98 connected to 00 is measured. The temperature of cryogenic fluid 96 varies by an amount of -100 to +10 degrees Celsius.

Inside the container, duct 94 has a helical section containing crystals 102 of the same composition as the component to be tested. The vapor tension of the crystal is known, and therefore simply changing the temperature of the cryogenic fluid 96 randomly and in a known manner changes the concentration of the gaseous components in the gaseous mixture flowing within the duct 96. It is possible.

Duct 94 is connected to the air sampling circuit and when valve 42 is closed and valves 86 and 88 are opened, a gaseous calibration mixture having known components and concentrations is introduced into the air sampling circuit and the air measuring circuit. be swept away by

Thereby, a calibration curve is obtained at different concentrations with the aid of the same measuring device used as the device for measuring the concentration. This eliminates any setting difficulties and inaccuracies.

Returning to the "measure" mode is accomplished by closing valves 86 and 88 and opening valve 42.

The concentration measuring device according to the invention has high sensitivity and makes it possible to measure extremely low concentrations.

A measurement that automatically confirms that a certain threshold has been exceeded is
Reliable and allows to trigger alarm devices. The pyrolyzer also makes it possible to measure the concentration of components that are normally present in one compound and that are to be tested. The measurements described above are not normally performed.

Note that it is clear that the present invention is not limited to the above-mentioned specific examples and does not cover all variations thereof.

[Effects of the Invention j As explained above, according to the present invention, there is an effect that concentration measurement and calibration can be performed at different times using the same measurement cell.

Also, calibration can be performed at regular intervals.

However, in addition, as a result of the quick and easy transition from the "measurement" mode to the "calibration" mode, the threshold value may be exceeded at certain concentrations.

90 For this reason, the operation of the measuring device is controlled and reliable measurements are allowed to issue alarms at will.

The sensitivity of the concentration measuring device according to the invention makes it possible to examine components released in very low concentrations.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of a conventional gaseous mixture concentration measuring device, and FIG. 2 is a schematic diagram showing the configuration of a gaseous mixture concentration measuring device according to an embodiment of the present invention. degree measuring means, 82...processing means, 90...
Container, 92... Storage vessel, 94... Duct, 96 Low temperature Xt body, 98... Thermistor, 100
・・Power source, 102...Crystal.

Claims (4)

[Claims] (1) an air sampling circuit comprising a suction pump (40), the inlet and the outlet of which are connected to the main duct (10) and measurements suitable for circulating a gaseous mixture at a known flow rate and pressure; a cell (56) and a suction pump (59), one end of which is connected to the air sampling circuit;
an air measuring circuit connected at the other end to said main duct (10) and in which said gaseous mixture is sucked up by said air sampling circuit and discharged into said main duct (10) and tested at a known and randomly variable concentration; gaseous calibration mixture supply means (90) for supplying a gaseous calibration mixture containing the desired components;
) an air calibration circuit connected to the air sampling circuit by a bypass capable of isolating the air sampling circuit from the air sampling circuit, through which the gaseous calibration mixture flows to the air measurement circuit; and inducing fluorescence of the components within the measurement cell (56). a light intensity measuring means (80) for measuring the light intensity of the fluorescent light and outputting an electrical signal corresponding to the light intensity of the fluorescent light; and the gaseous calibration mixture flows through the air measuring circuit. The main duct (10
), the input of which is connected to the output of the light intensity measuring means (80) for measuring the concentration of the components contained in the mixture flowing through the said light intensity measuring means (80); An apparatus for measuring the concentration of a gaseous mixture, comprising: (2) The air sampling circuit includes a pyrolyzer (48)
2. The device for measuring the concentration of a gaseous mixture according to claim 1, comprising: (3) The device for measuring the concentration of a gaseous mixture according to claim 1, characterized in that the gaseous calibration mixture supply means (90) comprises a cryogenic exchanger. 4. Gaseous gas according to claim 1, characterized in that it comprises an optical trap (70) which prevents a light beam that has already passed vertically through the air measuring cell (56) from returning to the measuring cell (56). A device for measuring the concentration of mixtures.