Measuring cell for optical measurement of gases

Abstract

To provide a recoverable measurement cell for optical measurement of gas.SOLUTION: A measurement cell is demarcated by a gas conduction pipe having an input side end adapted so as to be connected to gas flow input for allowing as to enter the measurement cell and an output side end adapted so as to be connected to gas flow output. A pipe end is also adapted so as to be coupled to an optical element. The optical element includes an optical transmitter for transmitting light into the measurement cell and an optical receiver adapted so as to receive light through the measurement cell. Optical beams in the measurement cell have a predetermined shape. The optical element includes a light source, at least two mirrors, and an optical receiver mounted to a predetermined position on an external frame covered with the pipe end. The measurement cell has a slender shape corresponding to the shape of optical beams.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a recoverable measurement cell using an optical measurement method for gases, and a measuring device using such a cell.

Background Art

[0002] More specifically, the present invention relates to a multiple reflection type sample cell used in a gas analyzer such as an infrared gas analyzer, and more specifically, to a multiple reflection type sample cell capable of obtaining a long optical path with a limited volume. Such systems are well known as shown in U.S. Patent No. 5,726,752 and U.S. Patent Application No. 2017 / 168275A1, and as confirmed in U.S. Patent No. 5,726,752, where it is desirable that the sample cell is not larger than the envelope representing the light beam propagating through the cell so that the exchange of gas in the cavity is accelerated. However, as described in U.S. Patent No. 5,726,752, these solutions use specific samples of gas that slow down the measurement process. International Publication No. 2015 / 069934 describes an example of a solution having a plurality of optical paths, where the volume outside the optical path is reduced to a minimum.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In addition, process gases such as exhaust gas from an engine may contain contaminants that foul the optical system. An example of this is exhaust gas from a combustion process. Particles and contaminants in the exhaust gas adhere to the inside of the measurement cell and the optical system. After being used for a while, the transmittance inside the cell decreases, and it is necessary to clean the optical system and the cell. Such maintenance is often difficult and time-consuming. Therefore, an object of the present invention is also to provide a solution that can replace the gas cell unit in a quick and reliable manner.

[0004] Disassembling optical instruments is time-consuming, and adjusting their optics is virtually impossible outside of a laboratory. This problem can be solved by mounting and adjusting all optical elements in a frame and inserting a gas guide device within the frame. The gas guide device can be easily removed, providing access to all optical elements that need cleaning. Furthermore, the gas guide device can be easily replaced with a new one, or cleaned and reinstalled. Such a replaceable cell is described in U.S. Patent Application No. 2010 / 0110437.

[0005] One of the main problems with conventional gas cells is that, when continuous flow is applied, gas exchange within the measurement cell takes time. When the gas inlet and outlet are located close to each other, the new gas flowing into the cell usually mixes with the old gas, and the gas exchange follows a typical dilution flow, such as 50% for the first gas cell volume injected and 75% for the second. If the gas cell is very long relative to its diameter, laminar flow can be obtained, and most of the gas can be exchanged by filling just one gas volume. In more common gas cells, laminar flow occurs between the gas inlet and outlet, but this leaves some of the gas in the cell unexchanged. And generally, it takes time to exchange all the gas in the cell. One of the objectives of the present invention is to provide a solution that allows for continuous measurement in order to achieve a short response time when a change in gas composition occurs. [Means for solving the problem]

[0006] The above-mentioned objectives can be achieved using a replaceable gas cell having the features described in the independent claims of the attached patent claims, and a measuring instrument including said cell.

[0007] Therefore, to allow the gas volume to be replaced as quickly as possible at a given flow rate, the walls of the gas cell according to the present invention have a combined inlet for the optical measurement beam and the gas flow so as to track the ray path. In this way, the volume within the gas cell can be minimized. Furthermore, the volume used can be minimized by making the gas cell thin and elongated, preferably by having the optical paths intersect themselves. To avoid the phenomenon where laminar flow occurs in part of the cell and no flow occurs in other parts of the cell, forced turbulence or vortices are generated in the flow motion. The inlet flow preferably initiates a rotational flow, and the flow pattern forms a vortex within the gas cell. This vortex flow ensures that all the old gas flows in front of the new gas, leaving no pockets of old gas. Preferably, a similar structure is provided at the outlet to force the outlet gas into turbulence. [Brief explanation of the drawing]

[0008] The present invention will be described below with reference to the attached drawings showing embodiments of the present invention. [Figure 1] This is a cross-sectional view of a gas cell according to a preferred embodiment of the present invention. [Figure 2] This diagram shows the optical path of an optical measurement beam. [Figure 3] This figure shows the movement of gas flow within a cell according to a preferred embodiment of the present invention. [Figure 4a] This figure shows the shape of the end of a gas cell according to a preferred embodiment of the present invention. [Figure 4b] This figure shows the shape of the end of a gas cell according to a preferred embodiment of the present invention. [Figure 5] This figure shows an assembly including a measuring instrument and a gas cell according to a preferred embodiment of the present invention. [Figure 6] Figure 5 shows a top view of the assembly and a cross-sectional view of the connection between the cell and the measuring instrument. [Figure 7] This figure shows an alternative measuring instrument suitable for receiving the gas cell according to the present invention. [Figure 8] This figure shows alternative measuring instruments, including a gas cell, as shown in Figure 7. [Modes for carrying out the invention]

[0009] Figure 1 shows a gas cell according to a preferred embodiment of the present invention. The gas cell consists of a pipe 1 having a cell 2 through which a measurement gas flows. The pipe has a gas inlet 3 and a gas outlet 4. In addition, mounting portions 1a and 1b, including, for example, screws and seals 1c (Figure 8), are provided at each end of the pipe for attaching the cell to a measuring instrument 12 (Figure 5) including optical elements.

[0010] As described above and as shown in Figure 2, the cell volume can be minimized by calculating the shape of the trajectory of the light beam 2a used to measure the gas. In a preferred embodiment shown in Figure 2, the optical system 5a included in the measurement system includes a light source 6 that emits light in a wavelength range selected according to the characteristics of the gas being measured, as is well known to those skilled in the art. The light source 6 may include a lens that shapes or parallelizes the beam propagating from the first portion 5a toward the second portion 5b of the other end 1b of the pipe 1. At the second end 1b of the pipe, the corresponding portion 5b of the measuring instrument includes a mirror 8b that reflects the beam back into the cell toward the mirror 8a at the first end 5a of the optical system. The mirror 8a at the first end 5a reflects the beam again through the cell toward the receiver 7 at the second portion 5b of the optical system, where the receiver 7 and transmitter 6 are connected to a known measurement system that analyzes the absorption spectrum of the gas. The envelope containing the propagating and intersecting light beams 2a is calculated, and the shape of the cell 2 is determined according to the shape of the light beams 2a.

[0011] Thus, in a preferred embodiment, the light beam propagates through the gas three times, thus achieving the same effect as if the length of the measurement cell were three times longer. Furthermore, as shown in Figure 2, the light beam may be configured to cross the same volume at least twice. This can increase the sensitivity of the system.

[0012] Furthermore, other configurations may be considered in which a mirror is added to each end 5a, 5b opposite the transmitter and receiver, respectively, so that the optical signal passes through the cell five times. Also, different mirror shapes and lenses may be selected to shape the beam. However, as mentioned above, in order to reduce the volume of the cell, it is important that the shape of cell 2, i.e., the internal shape of the pipe volume, corresponds to the shape of the beam.

[0013] Figure 3 shows the gas flow 9 propagating along cell 2 defined by pipe 1. By generating a swirling flow, even if the gas composition is non-uniform, the swirling gas flow passes through the beam multiple times, providing a realistic measurement of the gas content while simultaneously forcing out old gas from the cell without leaving gas pockets.

[0014] A means for achieving mixing is shown in Figure 4a, which shows the input end of the measuring cell. In the figure, the gas enters the cell on the optical element side of the asymmetric feature 10a, thereby guiding the gas to one side of the cell. In the embodiment shown in the figure, this guides the introduced gas to the upper wall of the cell, and the pressure pushes the gas around the shape of the cell and into the gas conductor, thereby producing a vortex.

[0015] Figure 4b shows a similar feature 10b at the output end of the gas conductor or cell. This ensures that the vortex flow continues until it exits the cell. Trivial features along the cell pipe that maintain the vortex flow may also be considered, as long as they do not obstruct the movement of gas through the optical path or cell.

[0016] Other solutions for mixing the gases may also be considered, provided that the light beam is not obstructed by any features within the pipe. The embodiment shown in the figure relates to a preferred embodiment that includes asymmetric features, but other features may be used, such as inserts or similar components positioned before the gas enters the optical path.

[0017] Figure 5 shows an assembly according to a preferred embodiment of the present invention, in which an exchangeable measurement cell is mounted within the measurement unit 12. As described above, the measurement unit comprises optical elements 7, 8 for transmitting, reflecting and receiving the measurement light beam that has passed through the cell. When the cell is removed, the optical elements can be easily cleaned, and the cell itself can also be easily replaced.

[0018] Furthermore, the measuring device 12 includes an inlet 13 and an outlet 14 for the gas. As described above, these are connected to the input in the vicinity of the optical element so that the flow preferably enters the same aperture as the measurement cell for the measurement light beam. Thus, measurements can be made along the excess of the gas flow or against its vortices.

[0019] The cell is fixed and sealed to the measuring device using suitable means 11 available to those skilled in the art.

[0020] Figure 6 is a view showing the measuring device 12 as seen from above, and cross-sections A-A and B-B show the connection regions of the cell ends 1a, 1b. As shown in the figure, the cell ends cover the region surrounding the optical elements 7, 8, as well as the gas input 13a or the gas output 14a respectively connected to the inlet 13 and the outlet 14. As shown in the figure, due to the shape of the cell on the input side 1a, the gas is guided to the vortex channels 9 at the input side end and the output side end.

[0021] Thus, the present invention provides a multiple reflection type measurement cell in which incident light is reflected a plurality of times in order to analyze a sample within the sample cell. This is · An external frame 12 in which all optical components such as the light source 6, the detector 7, the mirror 8, and the window or lens are mounted, adjusted and fixed in the correct position of the measuring device so that the measuring device functions properly, and · A gas guide device 1 that can be easily attached or replaced, functions as a wall within the gas cell and as a fluid conductor from the input side to the output side, and can reduce the amount of gas required for analysis, comprising.

[0022] As shown in the figures, the present invention is primarily intended for measuring gases such as exhaust gases, but it may be modified to also measure liquids within the scope of the present invention.

[0023] Preferably, the gas guide volume occupies the space just beyond the envelope region through which the incident light passes within the sample cell and has means to generate the forced turbulence or mixing described above so as to not leave pockets of old gas when new gas enters the cell under continuous flow. Preferably, this flow pattern forms a vortex through the gas cell. To ensure efficient gas exchange, the length of the cell is at least four times the diameter of the apparatus. This prevents pockets of old gas from remaining and mixing of old and new gas.

[0024] Figures 7 and 8 show the housing of an alternative device 15. In device 15, an eccentric bolt 16 is used to secure the cell within the device. As is well known to those skilled in the art, the cell is locked in place by inserting the bolt into the appropriate opening 1e in the device and the cell and rotating the bolt (180 degrees in the embodiment shown in the figures).

[0025] As shown in Figure 8, a preferred embodiment of the cell is provided with sealing means at both ends, represented here by a seal ring 1c and a pressure plate 1d. Therefore, when installed in the cavity of the equipment, the cell is sealed against the cavity ends. This prevents gas leakage from the system.

[0026] Preferably, the fluid measuring cell is made of a rigid material, and each end of the device has means by which the user can operate a gasket to seal the fluid between the fluid guide device and the frame. This allows for airtightness to the fluid. Preferably, the cell material is a polymer such as POM (polyoxymethylene), Teflon, PE (polyethylene), or PP (polypropylene).

[0027] In summary, the present invention relates to a recoverable measuring cell for optical measurements in a gas. The cell is defined by a gas conduction pipe having an input end adapted to connect to a gas flow input that allows gas to enter the cell, and an output end adapted to connect to a gas flow output.

[0028] Furthermore, the pipe end of the gas cell is adapted to be coupled to an optical element which includes an optical transmitter that transmits light into the cell and an optical receiver adapted to receive the light that has passed through the cell. The optical element includes a light source, at least two mirrors, and an optical receiver, which are mounted in place on an external frame covered by the pipe end. This defines a known beam shape.

[0029] One end of the pipe is fitted to connect to a transmitter and at least one mirror, and the other end of the pipe is fitted to connect to a receiver and the same number of mirrors as the other end. The light beam travels through the cell at least three times, depending on the number of mirrors. Here, the cell has an elongated shape corresponding to the shape of the light beam. The shape of the beam may be defined using beam-shaping mirrors or lenses, etc.

[0030] Preferably, the cell at the input end of the pipe has an asymmetrical shape adapted to allow a rotating or turbulent gas flow through the pipe. This mixes the gas as it passes through the cell. Alternatively, the above features of the flow path may be used as long as they do not impede the gas processing capacity.

[0031] The pipe may include sealing means for connecting to measuring instruments connected to gas flow input and output, optical transmitters and receivers, and optical elements including mirrors.

[0032] The present invention also relates to a measuring device for receiving a recoverable measuring cell in a predetermined space. The device comprises a gas inlet section adapted to provide a sealed connection to the gas inlet pipe end in a frame at a first end of the space, and a gas outlet section adapted to provide a sealed connection to the gas outlet end of the pipe. The measuring device also comprises the optical elements in the sealed connection section that transmit and receive light from within the cell.

[0033] All optical elements are covered and mounted in place on the pipe ends, and are adjusted and fixed in place on an external frame composed of measuring instruments so that the optics function fully, with or without cells.

Claims

1. A measuring cell for optical measurement of gases, The measuring cell is defined by a gas conduction pipe having an input end adapted to be connected to a gas inlet for introducing gas into the measuring cell, and an output end adapted to be connected to a gas outlet. The input end and the output end are adapted to be coupled to an optical element which includes an optical transmitter that transmits light into the measurement cell and an optical receiver adapted to receive the light that has passed through the measurement cell. The light beam in the measurement cell has a predetermined shape, The optical element includes the optical transmitter, at least two mirrors, and the optical receiver. Each of the optical elements is covered by the end of the gas conduction pipe and mounted at different predetermined positions on the outer frame. The input end and the output end are adapted to be connected to the optical transmitter and at least one of the mirrors. The other of the input end and the output end is adapted to be connected to the optical receiver and the same number of mirrors as the input end and the output end, The light beam moves through the measurement cell at least three times. The measurement cell has an elongated shape corresponding to the shape of the light beam, The measuring cell at the input end of the gas conduction pipe is adapted to allow a rotating gas flow or turbulent gas flow to pass through the gas conduction pipe. Measurement cell.

2. The measuring cell according to claim 1, wherein the measuring cell at the input end of the gas conduction pipe has an asymmetrical shape to provide the rotating gas flow into the gas conduction pipe.

3. The measuring cell according to claim 1, wherein the gas conduction pipe includes sealing means for connecting to a measuring instrument comprising the gas inlet and gas outlet, the optical transmitter and the optical receiver, and the mirror.

4. The measuring cell according to claim 3, wherein the sealing means is comprised of a sealing ring.

5. The measuring cell according to claim 1, wherein the measuring cell is a hollow gas conduction pipe configured to receive a gas flow.

6. The measuring cell according to claim 1, wherein the shape of the measuring cell is defined by the shape of a parallelized beam that is reflected at least once at each end of the measuring cell.

7. The measuring cell according to claim 1, wherein the measuring cell is made of a rigid material which is a polymer material containing POM (polyoxymethylene), Teflon (registered trademark), PE (polyethylene), or PP (polypropylene).

8. The measuring cell according to claim 1, wherein the measuring cell is composed of a pipe having one opening at each end.

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