RU173565U1 - CUVETS FOR CONTACTLESS MEASUREMENT OF THE ELEMENT COMPOSITION OF GAS MIXTURES - Google Patents

Abstract

The utility model relates to the field of measurement technology and relates to a cell for non-contact measurement of the elemental composition of gas mixtures. The cuvette is a chamber with a metal target placed inside it, designed to create a laser-induced plasma on it due to the effect of optical breakdown. The target is fixed in the chamber with the possibility of rotational-translational movement to ensure the absence of degradation caused by ablation of the target material. The camera is equipped with an input and output for pumping the test gas mixture and two connectors with optical fibers connected to them. One of the connectors contains elements for focusing the laser radiation used to create optical breakdown, and the other contains elements for focusing the radiation generated during optical breakdown on a metal target. The technical result consists in lowering the threshold value of the radiation power density required for optical breakdown. 4 s.p. f-ly, 3 ill.

Description

Technical field

The utility model relates to measuring technique, namely, devices for analyzing the elemental composition of a substance, including in a gaseous state, and can be used to perform analysis in hard-to-reach areas, at power facilities, radiation monitoring objects, etc., for example, inside an inert chambers, thus providing an analysis of the composition of gas mixtures, which is valuable for a number of industries, such as nuclear energy and metallurgy.

State of the art

There are various analyzers of the composition of condensed matter, which use the method of laser-induced breakdown for analysis, followed by registration of the atomic emission of the resulting plasma, identification of the lines of atomic emission and determination of the concentration of substances that make up the sample by the intensity of the detected lines (patent RU No. 95844, US No. 5751416, US No. 5715053, US No. 6762835). In these solutions, the test sample should be in close proximity to the analyzer, the measurement results of which should be monitored by a person, which is not suitable for inert chambers that do not imply the presence of a person in them, as well as any other hard-to-reach measurement zones where it is impossible to place all components of the measuring system .

The prior art recording cuvette for a photothermal acoustic analyzer (RU No. 2460990, published September 10, 2012, class G01N 21/03). The cuvette consists of a sealed chamber filled with a gas that absorbs optical radiation. At the opposite ends of the camera, the input and output windows are located on the same optical axis, which are inclined to the optical axis at an angle of 45 °. On the side of the camera are located acoustically matched to each other emitter and receiver of ultrasonic vibrations so that along the optical axis there is a combination of optical and acoustic radiation. The cuvette provides an increase in sensitivity by increasing the length of the optical path and the interaction region of the acoustic and optical rays.

This solution requires the placement and adjustment of numerous optical elements and analyzing equipment in the immediate vicinity of the cell, which may not be feasible in the case of gas analysis in a hard-to-reach area. In addition, an increase in sensitivity in the above solution is achieved by increasing the optical path, that is, the dimensions of the device, which may not be suitable for analysis in a small closed volume.

Also known from the prior art is a cuvette for analyzing gases or liquids (DE 19729936 A1 published 01/14/1999, CL G01N 21/03; G01N 21/05; G01N 21/11), adopted as the closest analogue. The cuvette contains at least two optical windows, at least two seals. The principle on which the analysis method implemented in this cuvette is based is to create a gas discharge and subsequent spectral analysis of the plasma emission lines. The main disadvantage of the presented cell is the need to place measuring equipment near it, which makes it difficult (or impossible) to analyze in an inaccessible volume. In addition, gas discharge spectroscopy in some practically important cases is inferior in sensitivity to the method of laser-induced plasma spectroscopy due to the impossibility of using the analysis of the time response of the signal, which requires pulse excitation, as well as to incomplete dissociation of molecules in a gas discharge, while Laser-induced plasma dissociation is complete and plasma temperature is high.

Utility Model Disclosure

The objective of the proposed technical solution is to create a device for providing remote non-contact determination of the chemical composition of the gas mixture in hard-to-reach areas, such as an inert chamber or a burning chamber at power plants.

The technical result achieved by using the claimed utility model is to reduce the threshold value of the radiation power density required for optical breakdown by laser pulses of nanosecond duration due to the fact that the breakdown is carried out not directly in the gas, but on the surface of a metal target, while avoiding degradation the target has the ability to move. As a result, it becomes possible to use pulses of reduced intensity to create a breakdown, and the introduction of laser radiation to create an optical breakdown on a metal target can be carried out using a multimode optical fiber.

In such a configuration, it is possible to arrange the main parts of the device in which the inventive device is used, such as a laser source, spectrometer and a personal computer necessary for processing spectral data, outside the atmosphere of the inaccessible area in which the inventive cell is placed.

The problem is solved in that the claimed cell for non-contact measurement of the elemental composition of gas mixtures is a chamber with a metal target placed inside it, designed to create a laser-induced plasma on it due to the effect of optical breakdown, and fixed to one side of the chamber with the possibility of translational -rotational movement inside it to ensure that there is no degradation of the target surface associated with the laser ablation effect, while the camera is equipped with an entrance to an outlet for pumping the test gas mixture and two connectors with optical fibers connected to them, while one of the connectors contains elements for focusing laser radiation used to create optical breakdown, and the other contains elements for focusing radiation generated during optical breakdown on a metal target . The target may be a cylindrical rod rotatably placed around its axis during translational movement, or a plate placed at an acute angle to the plane of laser radiation propagation (i.e., the normal plane of the metal plate should lie in the plane of the optical system and make an angle of about 45 ° with the optical axis (shown by a dashed line in FIG. 1) of the focusing system used to create the optical breakdown). The metal rod can be made of tungsten, or alloy steel, or titanium and has a diameter of at least 10 mm, and the camera is made of metal to ensure rigid fastening of all composite elements.

The main principle of the claimed device is the use of laser-induced breakdown with subsequent registration of atomic emission of the components of the mixture. The measured ratio of emission intensities and calibration data obtained for mixtures with a known content of components determine the concentration of substances. In this case, a laser breakdown is created on the surface of the condensed medium — the rod — and has a low threshold for the power density of laser radiation. The seed electrons formed at the phase boundary lead to the development of the process of ionization of the gas sample in the nearby region.

Brief Description of the Drawings

The inventive utility model is illustrated by the following figures, where

in FIG. 1 schematically depicts the claimed cell;

in FIG. 2 which shows a diagram of a gas analyzer in which the inventive device is used;

in FIG. Figure 3 shows graphs characterizing the spectra of lines of various atoms obtained during gas accumulation after an inert chamber atmosphere is fed into the cuvette.

The positions in the drawings indicate:

1 - camera

2 - connector for optical fiber, through which laser radiation enters the cuvette,

3 - a device designed to focus laser radiation on a metal target

4 - target for creating optical breakdown,

5 - collecting lens designed for light collection of laser-induced plasma radiation

6 - connector for optical fiber, which collects the radiation of laser-induced plasma,

7 - input for supplying the gas mixture to the cell,

8 - exit for pumping gas from the cell,

9 - laser radiation source,

10 - focusing lens

11 - optical fiber for introducing laser radiation into the cell,

12 - optical fiber for collecting radiation from laser-induced plasma,

13 - spectrometer

14 is a computer.

Utility Model Implementation

The inventive device is a metal chamber 1, for example, duralumin, equipped with two connectors for attaching an optical fiber 2 and for connecting a light-collecting optical fiber 6, as well as input 7 and output 8 for supplying / pumping a gas mixture to / from a cell. The relative position of the entrance and exit is not critical. Connectors 2 and 6 are arranged so that the axes of the optical systems (indicated by dashed lines in FIG. 1) installed in these connectors converge on the surface of the optical system.

In the connector 2, there is a focusing optical system 3, consisting, for example, of two short-focus lenses made of K8 glass, arranged so that the laser radiation coming out of the optical fiber fixed in the connector 2 is focused on the metal target 4. Inside the cuvette there is a metal target 4, which is fixed to one side of the cell chamber. As the target, a metal cylindrical rod made, for example, of tungsten, titanium or alloy steel can be used. The rod is fixed with the possibility of rotation around its axis (namely, the axis perpendicular to the plane formed by the optical axes of the focusing systems) and translational movement along its axis. The target can also be made in the form of a metal plate located at an acute angle to the direction of propagation of laser radiation (the normal plane of the metal plate should lie in the plane of the optical axes of the focusing system 3 and lens 5 and should be at an angle of about 45 ° to the axis of the optical system 3).

A lens 5, made, for example, of KU-1 glass, is placed so that the radiation of the laser-induced plasma is focused on the end of the connector 6. In the connector 6 is a multimode optical fiber designed for light collection of the radiation of the laser-induced plasma.

The fastening of the optical fibers to connectors 2 and 6 can be carried out by means of, for example, SMA connectors.

The inventive device operates as follows. The use of the claimed device is possible as part of a gas analyzer system that provides non-contact measurement of the elemental composition of gas mixtures. The cuvette is placed in an inaccessible area, for example, in an inert chamber.

Gas can be supplied either by forced pumping of gas through connectors 7 and 8, or gas can flow arbitrarily from the inert atmosphere through open connectors 7 and 8. Note, however, that in this case the error in determining the elemental composition of the inert chamber is worsened, compared with the case of forced pumping of gas from the atmosphere of an inert chamber. Gas from the test volume penetrates into the cuvette through connectors 7 and 8. Through a focusing device 3, pulsed laser radiation generated through an optical fiber is directed to target 4 (target 4 can be fixed or translationally rotate to reduce degradation of the target surface as a result of laser ablation ) in this case, in the chamber volume of the cell 1 in the region of the focus of lenses 3 and 5 as a result of optical breakdown on the target surface 4 and in the gas, a laser-induced plasma is generated, the radiation of which is transferred from power lens 5 on the connector 6, to which is attached a light guide (optical fiber 12) for light collection. The optical signal from the optical fiber 12 connected to the connector 6 is then transmitted to a spectrometer 13, which implements the emission spectrum of the laser-induced plasma. The spectrometer 13 is connected to a computer 14, through which the spectral pattern is analyzed in order to determine the elemental composition.

The technical result is achieved by focusing laser radiation on the surface of a metal target, the optical breakdown threshold of which is several orders of magnitude lower than the optical breakdown threshold in gases. As a result, it becomes possible to use low-intensity pulses to create a breakdown, and the introduction of laser radiation to create an optical breakdown on a metal target can be carried out using a multimode optical fiber.

Concrete example

In the example below, the inventive device was used to control the atmosphere in an inert chamber with an argon atmosphere, namely, in this example, the concentrations of oxygen and hydrogen were measured.

The radiation of a laser 9 with an active element from AIG: Nd ³⁺ (wavelength 1064 nm, energy 80 mJ, repetition frequency 10 Hz, pulse duration at the level of 0.5-13 ns, divergence at the level of 0.83-3 mrad) was initiated using a 10 v lens a quartz optical fiber 11 with a diameter of 1 mm, the other end of which was connected via a SMA connector to the device connector 2, the housing 1 of which was made of aluminum and had dimensions 5 × 5 × 5 cm ³ , and was focused on a tungsten target by a system of two lenses 3, enlightened under a wavelength of 1064 nm. Target 4 was a plate 1 × 2 cm in size and 3 mm thick, while the target was fixed inside the cuvette. When the source of the laser source 9 was turned on, an optical breakdown occurred on the target 4, and a laser-induced plasma was formed, the radiation of which was collected using a quartz lens 5 with a focal length of 3 cm and made of KO-1 glass onto a quartz optical fiber 12 with a diameter of 600 μm, one from the ends of which it was connected to the output optical connector 6 of the device through an SMA type connector. The second end of the optical fiber was connected via an SMA connector to a 13 Maua 2000 Pro spectrometer (Ocean Optics, USA), which made it possible to record the plasma emission spectrum from each laser pulse. Obtained using a spectrometer 13, the data were analyzed on a computer 14.

The gas used is the argon atmosphere of an inert chamber. Argon enters the cuvette through the gas inlet, and the spectrum of the radiation of laser-induced plasma arising from optical breakdown on the target is recorded (Fig. 2).

The repetition rate of laser pulses (and plasma flashes in the cell) was 10 Hz, each spectrum was measured for one second, every second throughout the experiment. To assess the content of impurities in the atmosphere of the cell, 10 spectra were used.

To estimate the concentrations from the spectra, a range corresponding to the atomic line was selected, after which the ratio of the maximum of the line (not the average value that was used previously) to the maximum of the argon line was calculated, after which the concentration was calculated from the ratio of the maximums from the calibration curves obtained earlier.

In FIG. Figure 3 shows the selected spectra minus the approximation of the background obtained for one of the 10 selected pulses.

The oxygen content in the inert chamber was 4 ± 2 ppm (ppm is the millionth fraction in terms of the main gas, in this case argon), as the average value over 10 pulses. The error estimate corresponds to the spread in the ratio of the maxima of the oxygen and argon lines in the emission spectra of laser-induced plasma. Comparison with the data of independent sensors showed that a certain oxygen concentration coincided with the exact value (3.8 ± 0.2 ppm) within the error.

Claims (5)

1. A cuvette for non-contact measurement of the elemental composition of gas mixtures, characterized in that it is a chamber with a metal target placed inside it, designed to create a laser-induced plasma on it, due to the effect of optical breakdown, and fixed to one side of the chamber with the possibility of rotational-translational movement inside it to ensure the absence of degradation caused by ablation of the target material, while the camera is equipped with an input and output for pumping the gas mixture, and two connectors with optical fibers connected to them, while one of the connectors contains elements for focusing the laser radiation used to create optical breakdown, and the other contains elements for focusing the radiation generated during optical breakdown on a metal target. 2. The cuvette according to claim 1, characterized in that the target is a cylindrical rod placed with the possibility of rotation around its axis during translational movement. 3. The cuvette according to claim 2, characterized in that the metal rod is made of tungsten or alloy steel or titanium and has a diameter of at least 10 mm. 4. The cuvette according to claim 1, characterized in that the target is a plate placed at an acute angle, i.e. the normal plane of the metal plate should lie in the plane of the optical axes of the focusing systems 3 and lens 5 and should be at an angle of 45 ° to the axis of the optical system 3. 5. The cuvette according to claim 1, characterized in that the chamber is made of metal.

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