JP2005030954A - Oxygen enriching apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen enriching apparatus provided with an ultrasonic oxygen concentration flow rate measuring means capable of minimizing the lowering of an ultrasonic reception signal voltage, and capable of restraining variation factors in the distance between ultrasonic oscillators to one factor, even when the inside radius of a pipe connecting between the ultrasonic oscillators gets smaller than the outside diameter of the ultrasonic oscillator. <P>SOLUTION: In this oxygen enriching apparatus provided with the ultrasonic oxygen concentration flow rate measuring means, is characterised in that an end face in each of the ultrasonic oscillators is installed to get parallel to an end face of the pipe opposed thereto, a distance d is set in the range of 0<d<D<SP>2</SP>/(4λ), and the ultrasonic oscillators, housings for covering the ultrasonic oscillators and the pipe for connecting a space between the housings are fixed to form one chamber unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an oxygen concentrator that separates and concentrates oxygen from the air. More particularly, the present invention relates to a medical oxygen concentrating device having means for measuring the oxygen concentration and / or flow rate of an oxygen concentrating gas delivered from an oxygen concentrating device used for medical purposes.

Various proposals have been made regarding methods and apparatus for measuring the concentration or flow rate of sample gas using the propagation time or propagation speed of ultrasonic waves obtained by transmitting and receiving ultrasonic waves in the sample gas. Has been done. For example, Japanese Patent Laid-Open No. 6-213877 discloses that two ultrasonic transducers are arranged facing each other in a pipe through which a sample gas passes, and the propagation time of ultrasonic waves propagating between the ultrasonic transducers is measured. Describes an apparatus for measuring the concentration and flow rate of a sample gas. U.S. Pat. No. 5,060,506 describes an apparatus for measuring the concentration of a sample gas composed of two types of molecules by measuring changes in the speed of ultrasonic waves.
Japanese Patent Laid-Open No. 6-213877 U.S. Pat.No. 5,060,506 JP 2002-214012 JP

  In the method of measuring the concentration and flow rate of the sample gas based on such signals obtained by transmission / reception of ultrasonic waves, it is necessary to specify the ultrasonic propagation time and sound speed based on the ultrasonic reception signals. When measuring the concentration, ultrasonic wave transmission / reception is performed in both forward and reverse directions with respect to the flow of the sample gas, the speed of sound in the sample gas with the flow rate component canceled is measured, and the temperature of the sample gas is measured. Thus, various methods for calculating the concentration of the sample gas from the relationship between the speed of sound and temperature have been proposed. Also, when measuring the flow rate, the sound speed obtained when performing ultrasonic transmission / reception in the forward direction with respect to the flow of the sample gas, the sound speed obtained when performing ultrasonic transmission / reception in the reverse direction, Various methods have been proposed in which the flow rate of the sample gas is obtained by measuring each difference, and the flow rate is obtained by multiplying the inner area of the pipe through which the sample gas flows.

  The value obtained directly by transmission / reception of ultrasonic waves is the propagation time of ultrasonic waves, not the speed of sound. In order to calculate the speed of sound, it is necessary to calculate “distance between ultrasonic transducers / ultrasonic propagation time” using the distance between ultrasonic transducers. However, for example, when the piping connecting the transducers is easily deformed by an external force, the distance between the transducers is easily changed, which hinders accurate sound speed measurement. There is a problem of end. In addition, it is also known that the distance between ultrasonic transducers changes due to temperature changes due to the characteristics of the material itself connecting the ultrasonic transducers, and a single ultrasonic transducer distance is used as a constant. For example, in Japanese Patent Application Laid-Open No. 2002-214012, etc., using the linear expansion coefficient of the piping material, the distance between the ultrasonic transducers is corrected according to the temperature measurement value of the sample gas. A method for improving the temperature characteristics has been proposed. However, this method can be applied if the only factor that changes the distance between the ultrasonic transducers is a change in distance due to a temperature change in accordance with the linear expansion coefficient of the piping material. If the structure changes the distance between the transducers, there is a problem that it is difficult to accurately predict the distance between the ultrasonic transducers.

  Furthermore, when measuring the flow rate, it is necessary to obtain the difference in the sound velocity of the ultrasonic waves obtained in both forward and reverse directions with respect to the flow of the sample gas. In order to improve the measurement accuracy, it is desirable that the difference between the sound speeds obtained in the forward and reverse directions is large, because the time measurement resolution can be improved. In order to increase the difference in sound speed obtained in both the forward and reverse directions, the distance between the ultrasonic transducers is increased, or the inner diameter of the piping connecting the ultrasonic transducers is reduced, and even in the same flow rate, the inside of the piping is reduced. A method of increasing the flow rate of the flowing sample gas can be considered. However, in the former method, there is a problem that the apparatus becomes large, and in the latter method, when the inner diameter of the pipe becomes smaller than the outer diameter of the ultrasonic transducer, a part of the transmitted ultrasonic wave Only propagates through the inside of the pipe, resulting in a problem that the voltage value of the received ultrasonic signal becomes very small and the S / N ratio deteriorates.

As a result of intensive studies to achieve the above object, the present inventors have found the following oxygen concentrator. That is, the present invention relates to an oxygen concentrator provided with an oxygen concentration means for separating oxygen from the air, and an ultrasonic measurement means for measuring the concentration and / or flow rate of the oxygen-enriched gas by ultrasonic waves downstream of the oxygen concentration means. The ultrasonic measurement means is a means including two ultrasonic vibrators, a housing portion that surrounds each of the ultrasonic vibrators and includes an inlet / outlet of oxygen-enriched gas, and a pipe that connects the housings, A distance d between the end face of the ultrasonic transducer and the end face of the pipe is set in a range of 0 <d <D ² / (4λ).
However,
d: Distance [m] between the end face of the ultrasonic transducer and the end face of the pipe
D: Diameter of effective ultrasonic irradiation surface of ultrasonic transducer [m]
λ: Maximum wavelength of ultrasonic wave [m]

  The present invention also provides an oxygen concentrator characterized in that the inner diameter of the pipe is smaller than the outer diameter of the ultrasonic transducer.

  Further, the present invention is characterized in that the ultrasonic measurement means is fixed to the oxygen concentrator by a fixing means that allows expansion and contraction of the ultrasonic measurement means in the major axis direction. Means for fixing one of the housings located at both ends of the means and the fixing substrate in the oxygen concentrator, or the fixing means is provided at one place of the piping of the ultrasonic measuring means and the fixing substrate in the oxygen concentrator. The oxygen concentrator is characterized in that it is a means for fixing the above.

The oxygen concentrator of the present invention minimizes the decrease in the ultrasonic reception voltage by setting the distance d between the end face of the ultrasonic transducer and the end face of the pipe within the range of 0 <d <D ² / (4λ). In other words, the deterioration of the S / N ratio can be minimized. Furthermore, in order to increase the difference in sound speed between the forward and reverse directions with respect to the flow of the sample gas while realizing a reduction in the size of the oxygen concentrator, a method for reducing the inner diameter of the pipe connecting the ultrasonic transducers was selected and the pipe When the inner radius becomes smaller than the outer diameter of the ultrasonic transducer, the distance between the transducer and the pipe end face becomes important.

  Furthermore, the temperature can be controlled by limiting the factor that determines the distance between the ultrasonic transducers in the ultrasonic oxygen concentration flow measurement means mounted in the oxygen concentrator to only the length change according to the linear expansion coefficient due to temperature. It is possible to predict a precise distance between ultrasonic transducers only by measuring, and an accurate sound speed measurement can be realized.

  The configuration of the oxygen concentrator in the present embodiment is as shown in FIG. The oxygen concentrator 10 sucks air as a raw material gas, and feeds the air to the oxygen concentrating means 13 through the filter 11, the oxygen concentrating means 13 for separating oxygen from the air, and downstream of the oxygen concentrating means 13. The ultrasonic oxygen concentration flow rate measuring means 15 described below is provided.

  A schematic cross-sectional view of the structure of the ultrasonic oxygen concentration flow rate measuring means 15 is as shown in FIG. The ultrasonic oxygen concentration flow rate measuring means 15 in this embodiment includes two ultrasonic transducers 20 and 21 having a center frequency of 40 kHz, and housings 25 and 26 that enclose each of the ultrasonic transducers. Are provided with holes 28 and 29 which serve as inlets and outlets for the oxygen-enriched gas, and a pipe 27 connecting the two housings. The outer diameter of the ultrasonic transducers 20 and 21 is 10 mm, and the inner diameter of the pipe 27 is 5 mm so that a flow rate suitable for this embodiment can be obtained. The central axis of the pipe 27 and the central axis of the ultrasonic vibrators 20 and 21 are arranged so as to be aligned on a straight line, and the end face of the ultrasonic vibrator 20, 21 faces the end face of the pipe 27. It is installed so that the end faces are parallel. The ultrasonic transducers 20 and 21 are installed on the substrates 23 and 24, respectively, and the substrates 23 and 24 are also provided with temperature sensors 37 and 38 for measuring the temperature of the oxygen-enriched gas. The substrates 23 and 24 and the housings 25 and 26 are fixed by screws 43 and 44 through O-rings 39 and 40 to seal the oxygen-enriched gas. The housings 25 and 26 and the pipe 27 are fixed 41 and 42 by welding. That is, the ultrasonic transducers 20 and 21, the housings 25 and 26, and the pipe 27 are fixed so as to form one chamber unit through which oxygen-enriched gas can flow.

  The distance between the ultrasonic transducers 20 and 21 was designed to be 150 mm at a temperature of 20 ° C. The connection method of the housings 25 and 26 and the pipe 27 is not limited to the welding shown in the present embodiment, and may be fixed by other fixing means such as a cap nut, The outer side of the end may be processed into a male screw and the inner side of the ends of the housings 25 and 26 may be processed into a female screw, and the sealing material may be injected while being connected. Further, the housings 25 and 26 and the pipe 27 may be integrally formed without being separate parts.

  Further, the substrates 23 and 24 at both ends of the chamber unit are provided with connectors 31 and 34, and components such as a microcomputer for performing transmission / reception of ultrasonic waves, temperature detection of oxygen-enriched gas, signal processing, etc. Are electrically connected to the connectors 32 and 35 provided on the substrate 30 for fixing the chamber unit and the cables 33 and 36.

  The pipe 27 and the housings 25 and 26 are made of the same aluminum alloy so that they are not easily deformed by an external force. In this embodiment, one side 25 of the housing and the substrate 30 are fixed by screws 45, and the chamber unit is fixed to the substrate 30 so as to have a cantilever structure (the opposite housing 26). Is not fixed to the substrate 30). By creating the ultrasonic oxygen concentration flow rate measuring means 15 with this structure, the factors that change the distance between the ultrasonic transducers 20 and 21 are the pipe 27 and the housings 25 and 26 that accompany the temperature change. This is only expansion / contraction due to thermal expansion / contraction, and when the expansion / contraction actually occurs, the housing 26 side is not fixed to the substrate 30, so that the change can be released. Yes.

  Further, since the pipe 27 and the housings 25 and 26 are made of the same aluminum alloy, if the current temperature is measured by using the linear expansion coefficient of the aluminum alloy, the ultrasonic transducers at the temperature The distance can be easily corrected from the relationship between the temperature and the linear expansion coefficient, for example, by the method disclosed in Japanese Patent Application Laid-Open No. 2002-214012. The method of fixing the chamber unit to the substrate 30 is not limited to the method shown in the present embodiment as long as it does not limit the expansion and contraction of the chamber unit in the major axis direction due to the temperature change. For example, the structure may be such that only the central portion of the pipe 27 is fixed to the substrate 30 with screws, and the change in expansion and contraction can be released toward the left and right with the fixed portion of the pipe 27 as the center.

  The distance d between the end faces of the ultrasonic transducers 20 and 21 and the end face of the pipe 27 shown in FIG. 2 is a very important design item. In general, ultrasonic waves radiated from an ultrasonic transducer have a property of going straight in a section called a near field, and in a region beyond the near field (far field) It is known that the emitted ultrasonic wave has a property of diffusing in a spherical wave shape (FIG. 3). That is, if the distance d between the ultrasonic transducers 20 and 21 and the end face of the pipe 27 is always within the short-distance sound field section, the irradiated ultrasonic waves are efficiently input into the pipe 27. On the contrary, if the distance is far to the far field, the irradiated ultrasonic wave is diffused in a spherical wave shape, so the ultrasonic wave injected into the pipe 27 decreases. As a result, the amplitude value of the ultrasonic reception waveform obtained as a result becomes small, and the SN ratio becomes worse.

The distance Z ₀ [m] separating the near field and the far field is D [m] as the effective irradiation surface diameter of the ultrasonic transducer, and λ [m] as the wavelength in the atmosphere in which the ultrasonic wave propagates. Then, it is known that it is represented by the following formula (1).
Z ₀ = D ² / (4λ) ---------- Formula (1)
Further, it is known that there is a relationship of the following equation (2) between the wavelength λ [m] in the atmosphere, the sound velocity C [m / sec], and the ultrasonic center frequency f [Hz].
C = fλ ---------- Formula (2)
Therefore, equation (1) can be rewritten as equation (3) below using equation (2).
Z ₀ = fD ² / (4C) ---------- Formula (3)

The center frequency f of the ultrasonic transducers 20 and 21 in this embodiment is 40 kHz, and the diameter D of the effective irradiation surface is 7 mm. Also, the sound velocity C of the ultrasonic wave propagating in the atmosphere is a value that varies depending on the concentration of the atmospheric gas and the temperature. In order to always keep the distance d between the end faces of the ultrasonic transducers 20 and 21 and the end face of the pipe 27 within the section of the short-distance sound field, the state where Z ₀ in Equation (3) is minimized It is necessary to consider. That is, a condition for maximizing the sound speed C is required. It is known that the sound velocity C in a gas is expressed by the following equation (4) using the gas temperature T, the gas average molecular weight M, the gas specific heat ratio k, and the gas constant R.

したがって、音速Cは、温度が高いほど、また、平均分子量が小さいほど大きい値となる。

Therefore, the sound velocity C becomes larger as the temperature is higher and the average molecular weight is smaller.

It has been found that the temperature of the oxygen-enriched gas transmitted through the oxygen concentrator in this example is a maximum of 40 ° C., and the oxygen concentration range measured by the ultrasonic oxygen concentration flow rate measuring means is from atmospheric to 100% oxygen. Therefore, the condition for minimizing the average molecular weight is when measuring the atmosphere. That is, the sound speed of the ultrasonic wave propagating in the atmosphere at 40 ° C. is the maximum sound speed value in the present embodiment, and the value is about 355 [m / sec], and Z ₀ in Expression (3) is as follows: Can be calculated.
Z ₀ ≒ (40000 × 0.007 ² ) / (4 × 355) ≒ 0.0014 [m] ---- Formula (5)

  Therefore, it is desirable that the distance d between the end faces of the ultrasonic transducers 20 and 21 and the end face of the pipe 27 is designed to be less than 1.4 mm. Here, the distance d between the end faces of the ultrasonic transducers 20 and 21 of the ultrasonic oxygen concentration flow rate measuring means and the end face of the pipe 27 in this embodiment is changed to 0.3 mm, 1.0 mm, and 1.8 mm. Examples of ultrasonic reception waveforms obtained in this case are shown in FIGS. 4, 5, and 6, respectively. As is apparent from FIGS. 5 and 6, when the distance between the end face of the ultrasonic transducer and the end face of the pipe exceeds 1.5 mm, the amplitude value of the ultrasonic reception waveform rapidly decreases. Yes. In this example, by adopting 0.7 mm as the distance d, it was possible to obtain an ultrasonic wave reception waveform having a necessary S / N ratio.

Schematic which shows the structure of the oxygen concentration apparatus of this invention. The schematic sectional drawing which shows the structure of the ultrasonic type oxygen concentration flow measurement means of this invention. The relationship between the near field and the far field. An example of an ultrasonic reception waveform when the distance between the end face of the ultrasonic transducer and the end face of the pipe is 0.3 mm. An example of an ultrasonic reception waveform when the distance between the end face of the ultrasonic transducer and the end face of the pipe is 1.0 mm. An example of an ultrasonic reception waveform when the distance between the end face of the ultrasonic transducer and the end face of the pipe is 1.8 mm.

Explanation of symbols

10 Oxygen concentrator
11 Filter
12 Compressor
13 Oxygen enrichment means
14 Flow rate setting method
15 Ultrasonic oxygen concentration flow measurement means
16 Product filters
20 Ultrasonic transducer
21 Ultrasonic transducer
23 Board
24 substrates
25 Housing
26 Housing
27 Piping
28 Oxygen enriched gas inlet
29 Oxygen enriched gas outlet
30 substrates
31 Connector
32 connectors
33 Cable
34 Connector
35 connector
36 cable
37 Temperature sensor
38 Temperature sensor
39 O-ring
40 O-ring
41 Welding points
42 Welding points
43 screws
44 screws
45 screws

Claims (5)

In the oxygen concentrating device comprising oxygen concentrating means for separating oxygen from the air, and ultrasonic measuring means for measuring the concentration and / or flow rate of the oxygen-enriched gas by ultrasonic wave downstream of the oxygen concentrating means, the ultrasonic measuring means comprises The ultrasonic transducer includes: two ultrasonic transducers; a housing portion that surrounds each of the ultrasonic transducers and includes an inlet / outlet of an oxygen-enriched gas; and a pipe that connects the housings. An oxygen concentrator characterized in that a distance d between the end face of the pipe and the end face of the pipe is set in a range of 0 <d <D ² / (4λ).
However,
d: Distance [m] between the end face of the ultrasonic transducer and the end face of the pipe
D: Diameter of effective ultrasonic irradiation surface of ultrasonic transducer [m]
λ: Maximum wavelength of ultrasonic wave [m]   The oxygen concentrator according to claim 1, wherein an inner diameter of the pipe is smaller than an outer diameter of the ultrasonic transducer.   The oxygen concentrator according to claim 1 or 2, wherein the ultrasonic measuring means is fixed to the oxygen concentrator by a fixing means that allows expansion and contraction of the ultrasonic measuring means in the major axis direction.   4. The oxygen concentrator according to claim 3, wherein the fixing means is means for fixing one of the housings located at both ends of the ultrasonic measuring means and a fixing substrate in the oxygen concentrator.   4. The oxygen concentrating apparatus according to claim 3, wherein the fixing means is means for fixing one portion of a pipe of the ultrasonic measuring means and a fixing substrate in the oxygen concentrating apparatus.

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