JPH0634008B2 - Component flow rate measuring device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a component flow rate measuring device for measuring a flow rate (component flow rate) of a specific component contained in a gas such as a respiratory gas.

[Technical Background of the Invention and Problems Thereof] When a fluid is composed of various components instead of a single component, it is often necessary to measure the flow rate of a specific component. For example, in the case of inhaling air or a gas in which oxygen is artificially added to air, such as breathing gas, and exhaling a gas containing carbon dioxide, the data obtained by measuring the carbon dioxide gas flow rate of exhaled gas (exhalation) is It is used to evaluate respiratory function as carbon dioxide production.

In general, the conventional measurement of carbon dioxide production is called the Douglas bag method, in which exhaled gas is collected in an airtight bag, the volume V and the carbon dioxide concentration Fco ₂ are measured, and the carbon dioxide production is calculated. Is a method of measuring as an average value over several breaths.

On the other hand, due to the progress of fluid flow rate measurement and component analysis methods, it is possible to measure the component flow rate in real time. For example, when measuring the carbon dioxide production amount, the instantaneous value v (t) of the flow rate of the exhaled gas (fluid) is measured. ) And the instantaneous value fco ₂ (t) of the concentration, which is the component analysis result for carbon dioxide, are simultaneously measured, and the product of them is obtained in the form of vco ₂ (t) = v (t) · fco ₂ (t) Carbon dioxide production is measured.

By the way, both the flow rate measurement and the concentration measurement are performed while flowing the fluid through the measurement tube, but in the past, the measurement tube for flow rate measurement and the measurement tube for concentration measurement were connected in series. Was being done. However, connecting two measuring tubes in series in this way is considerably large because the capacity of the measuring system for respiratory gas, the so-called dead space, is the sum of the values in the respective measuring tubes.
For this reason, there is a problem that the burden on the subject's respiratory ability becomes heavy and it is difficult to apply it to critically ill patients.

Further, providing the measuring tubes for the flow rate measurement and the concentration measurement in series in this way has a problem in terms of measurement accuracy. This is because there is a time lag in the timing of both measurements due to the distance between the two measuring tubes. That is, if the distance from the flow rate measuring tube to the concentration measuring tube is L and the flow velocity of the fluid is V, the time required for a certain mass of flow to reach the concentration measuring tube. The td (time lag) is td = L / V, which changes according to the flow velocity. In order to eliminate the effect of this time lag td, conventionally, the value of this td is stored and the carbon dioxide gas production amount is obtained in the form of vco ₂ (t) = v (t) · fco ₂ (t + td). However, particularly in a compressible fluid such as a breathing gas, the flow velocity changes variously during one breath and the flow velocity also changes due to the pressure change, so that the change of the time lag td is complicated, and is represented by the above equation. It was extremely difficult to make such a correction exactly.

Further, in the above-mentioned conventional component flow rate measuring device, particularly when the fluid is a gas, when the gas is liquefied and the liquid is accumulated in the measuring tube, the liquid has a problem that the flow rate and the concentration are adversely affected. .

[Object of the Invention] An object of the present invention is to accurately measure the flow rate of a specific component of a gas with a minimum dead space amount and with high accuracy without being affected by a change in the flow velocity of the gas in the measuring tube. It is an object of the present invention to provide a component flow rate measuring device that does not require treatment and can be performed without being affected by a liquid generated by gas liquefaction.

[Configuration of the Invention] The present invention is a component flow rate measuring device that performs flow rate measurement using ultrasonic waves and optically performs component concentration measurement, and is on a line that traverses the gas flow direction in a tubular body through which gas flows. And a pair of ultrasonic transducers are mounted to face each other, and a pair of light transmission windows are hermetically attached to the wall surface of the region between the pair of ultrasonic transducers of the tubular body. And the light transmission window, the intersection of the tube axis center line of the tube and the beam center line of the ultrasonic waves transmitted and received between the pair of ultrasonic transducers,
A plane intersecting with the light flux center line or a part of the light flux of the light transmitted through the pair of light transmission windows, and a plane passing through the tube axis center line, the beam and the center line, and the tube axis center line and the light flux center line or the light flux. Of the ultrasonic transducers, which are arranged so that the surface passing through a part of the ultrasonic transducers and one of the ultrasonic transducers are substantially aligned on one horizontal plane, and are transmitted by these ultrasonic transducers. A flow rate measuring unit that measures a flow rate of the gas from ultrasonic signals received by a sound wave transducer, and the tube is irradiated from one of the pair of light transmission windows, the gas in the tube is transmitted, and Component concentration measurement for measuring the concentration of the specific component of the gas by detecting the amount of light having a wavelength that is absorbed by at least the specific component of the gas among the lights guided to the outside from the other of the pair of light transmission windows. Means and
It is characterized in that it is provided with means for calculating the flow rate of the specific component of the gas from the flow rate and concentration measured by the flow rate measuring means and the component concentration measuring means.

[Effect of the Invention] According to the present invention, since the flow rate measurement and the concentration measurement can be performed in one tube, compared to the case where the measurement tubes for each measurement are individually prepared and arranged in series. The volume of the measurement system for the gas to be measured, that is, the dead space amount is reduced, and the burden on the subject can be significantly reduced.

Further, since the flow rate measurement and the concentration measurement are performed at substantially the same position, the time lag between these measurements is zero or an extremely small time. Therefore, in order to eliminate the influence of this time lag, the complicated correction conventionally required becomes unnecessary, or even when the correction is performed, the time lag is originally small, and the difference between the flow rate measurement position and the concentration measurement position is small. Is very small, there is substantially no change in the flow velocity during this period, and this time lag can be regarded as always constant, which is an advantage that a very simple process can be performed. As a result, it is possible to simplify the structure of the entire measuring device in combination with the downsizing of the measuring tube, and there is no measurement error due to the influence of the gas flow velocity change in the measuring tube, which is extremely high. It is possible to accurately measure the component flow rate.

Further, in the present invention, the plane passing through the tube axis center line of the tubular body and the ultrasonic beam center line and the plane passing through the tube axis center line and the light flux center line of the light are substantially coincident with each other on one horizontal plane. Since it is arranged in the tube, even if the gas is liquefied inside the tube and the liquid accumulates at the bottom of the tube, the front surface of the ultrasonic transducer and the light transmission window are not blocked by the liquid. Stable measurement is possible without deterioration of sound wave propagation or light transmission.

[Embodiment of the Invention] FIG. 1 is a configuration diagram of a component flow rate measuring apparatus according to an embodiment of the present invention.

In the figure, 1 is a measuring tube for simultaneous measurement of flow rate and concentration,
One tube body 2 through which a measured gas, for example, a respiratory gas flows
In addition, an ultrasonic transducer for flow rate measurement and an optical sensor for concentration measurement are attached. That is, a pair of ultrasonic transducers 4a and 4b are provided at positions separated by a predetermined distance in the length direction of the pipe body 2 so as to face each other on a line diagonally crossing the flow direction of the fluid flowing through the pipe body 2. Is installed. The ultrasonic transducers 4a and 4b are the tube 2
Although it may be provided so as to project inward, in this embodiment, the recesses 3a and 3b are formed inside the tube body 2 so as not to affect the flow of the fluid as much as possible, and the ultrasonic transducers 4a and 4b
Are arranged.

On the other hand, on the wall surface of the region between the ultrasonic transducers 4a and 4b of the tubular body 2, a pair of light transmission windows 5a and 5b are airtightly attached to face each other. These light transmission windows 5a and 5b are for transmitting the light for density measurement. Here, in this embodiment, the intersection point P between the tube axis center line of the tube body 2 and the beam center line of the ultrasonic waves transmitted and received between the ultrasonic vibrations 4a and 4b and the light flux of the light passing through the light transmission windows 5a and 5b. In such a manner that the center line intersects with each other and the plane passing through the tube axis center line and the beam center line and the plane passing through the tube axis center line and the light flux center line or a part of the light flux are substantially coincident with each other on one horizontal plane. Ultrasonic transducers 4a and 4b and light transmission windows 5a and 5b are arranged.

A component flow rate measuring device is configured by combining the elements described below with the measuring tube 1 configured as described above. That is, the flow rate measuring circuit 6 is connected to the pair of ultrasonic transducers 4a and 4b. As the flow rate measuring circuit 6, for example, a circuit based on the propagation time difference method is used.

FIG. 2 shows a basic configuration of a flow rate measuring circuit using the propagation time difference method. The ultrasonic transducers 4a and 4b are connected to the drive circuit 21.
a, 21b simultaneously drive the other ultrasonic transducers 4b, 4a, which are then received by the respective ultrasonic transducers 4a, 4b.
From the ultrasonic transducer 4a to the ultrasonic transducer 4b, and the ultrasonic signals from the ultrasonic transducer 4a to the ultrasonic transducer 4b are converted into electric signals by the receiving circuits 22a and 22b and guided to the time difference calculation circuit 24 through the waveform shaping circuits 23a and 23b. The flow rate signal v (t) is obtained by obtaining the difference from the ultrasonic wave propagation time from the ultrasonic wave oscillator 4b to the ultrasonic wave oscillator 4a and multiplying it by a predetermined constant. It should be noted that FIG. 2 shows only the principle configuration, and a more improved configuration such as that described in, for example, JP-A-57-77914 and JP-A-57-77915 is shown. It is also possible to take.

On the other hand, the concentration measurement is performed as follows, for example, according to the principle described in JP-A-57-23843.
That is, the light source 8 which is turned on by the power source 7 is provided outside one of the light transmitting windows 5a, and the light from the light source 8 is introduced into the tube body 2 through the light transmitting window 5a. The light introduced into the tube body 2 passes through the gas flowing through the tube body 2 and is then guided to the outside through the other light transmitting window 5b. The light guided to the outside reaches the chopper rotating plate 10 driven by the motor 9 at a constant rotation speed. This rotating plate 10
Includes a first filter 11 that passes only a specific component contained in the gas to be measured, for example, light having a wavelength absorbed by carbon dioxide gas, and a light having a wavelength not absorbed by any component contained in the gas to be measured. Second filter 12
And are arranged at different positions in the circumferential direction. The light transmitted through the filters 11 and 12 is guided to the photodetector 13, converted into an electric signal, and then supplied to the component concentration measuring circuit 14.

The concentration measuring circuit 14 is constructed, for example, as shown in FIG. This configuration is disclosed in Japanese Patent Application Laid-Open No. 57-23843. After the output of the photodetector 13 is amplified by the amplifier 31, the first filter 11 is activated in synchronization with the rotation of the rotation plate 10 for the chiyhopper. The component caused by the light of the transmitted wavelength and the component caused by the light of the wavelength transmitted by the second filter 12 are synchronously detected by the first and second detectors 32a and 32b, and the ratio of the respective detection outputs is detected. (First detector output / second
The detector output) is obtained by the division circuit 33, and this ratio is logarithmically converted by the logarithmic amplifier 34 to obtain a specific component,
For example, the concentration signal fco ₂ (t) for carbon dioxide is obtained. Note that the configuration of the component concentration measuring circuit 14 is merely an example, and basically any configuration may be used as long as it optically measures the concentration of the specific component. Here, the flow rate measuring circuit 6 and the component concentration measuring circuit 1
Reference numeral 4 denotes sampling of light by rotation of the chopper rotating plate 10 by means of a synchronization signal 16 and ultrasonic transducers 4a and 4b.
It operates so that the emission of ultrasonic waves from the equipment is synchronized. That is, for example, the detection of light transmitted through the first filter 11 and the emission of ultrasonic waves from the ultrasonic transducers 4a and 4b are performed simultaneously. As a result, the measurement of the flow rate and the measurement of the component concentration are performed for the same mass of the gas to be measured.

The flow rate signal v (t) and the component concentration signal fco ₂ (t) thus obtained from the flow rate measuring circuit 6 and the component concentration measuring circuit 14 respectively are supplied to the arithmetic processing circuit 15,
Here, for example, the calculation of ∫v (t) · fco ₂ (t) is performed, so that the component flow rate for the specific component, for example, the carbon dioxide gas production amount is obtained. That is, the flow rate signal v obtained as described above
Since (t) and the component concentration signal fco ₂ (t) correspond to the same flow mass of the gas to be measured and there is no time lag, the arithmetic processing circuit 15 can directly perform arithmetic processing on these.

As described above, according to the present invention, since the flow rate and the concentration of the specific component can be simultaneously measured using the same measuring tube, compared to the case where individual measuring tubes connected in series are used for these measurements, The volume of the entire measurement system for the measurement gas can be reduced, and the burden on the subject is greatly reduced. This is a great effect especially in the case of respiratory management of critically ill patients.

Further, the fact that the flow rate and the component concentration are measured in the same measuring tube means that these measurement positions are close to each other, so that there is very little time lag between these two measurements for the same stream. Therefore, there is an advantage that the signal processing for measurement becomes simple. In particular, in the above embodiment, the flow rate measurement point and the component concentration measurement point are the intersections of the center line of the tube axis of the tube body forming the measurement tube and the center line of the ultrasonic beam transmitted and received between the pair of ultrasonic transducers. Since they coincide with each other, this time shift becomes almost completely zero, so that the process for the correction is completely unnecessary. As a result, it becomes possible to measure the component flow rate with higher accuracy than in the past.

It should be noted that the flow rate measurement point and the component concentration measurement point do not necessarily have to match exactly, and the intersection point between the center line of the tube axis of the tubular body and the center line of the ultrasonic wave transmitted and received between the ultrasonic transducers ,
Even if it intersects with a part of the light flux passing through the light transmission window, substantially the same effect can be obtained.

Further, in the above-described embodiment, as shown in the drawing, a surface passing through the tube axis center line of the tube body 2 and the beam center line of the ultrasonic waves transmitted and received between the ultrasonic transducers 4a and 4b, and the light transmission window 5a, The optical axis center line of the light passing through 5b and the plane passing through the tube axis center line of the tube body 2 are substantially coincident with each other, in other words, the ultrasonic transducer 4a,
4b and the light transmission windows 5a and 5b are located on one surface passing through the tube axis center line of the tube body 2. Therefore, by disposing the measuring tube 1 so that this surface is horizontal,
Even if a gas such as a breathing gas flowing through the inside liquefies and the liquid accumulates at the bottom, the ultrasonic transducers 4a and 4b are provided and the recesses 3a and 3b and the light transmission windows 5a and 5b are formed. Since it is not blocked by the liquid, stable measurement is possible without deterioration of ultrasonic wave propagation or light transmission state.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a component flow rate measuring device according to an embodiment of the present invention, FIG. 2 is a diagram showing a concrete configuration example of a flow rate measuring circuit in the same embodiment, and FIG. It is a figure which shows a structural example. 1 ... Measuring tube, 2 ... Tube body, 3a, 3b ... Recess, 4
a, 4b ... Ultrasonic transducer, 5a, 5b ... Light transmission window,
6 ... Flow rate measuring circuit, 7 ... Power supply, 8 ... Light source, 9 ...
Motor, 10 ... Rotating plate for chopper, 11, 12 ... Filter, 13 ... Photodetector, 14 ... Component concentration measuring circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Machida Inventor 1385-1385 Shimoishigami, Otawara, Tochigi Prefecture Tokyo Shibaura Electric Co., Ltd. Nasu factory (72) Inventor Soju Kurahashi 1-31 Nishiochiai, Shinjuku-ku, Tokyo No. 4 in Nippon Koden Kogyo Co., Ltd. (56) Reference JP 57-119240 (JP, A) JP 57-16339 (JP, A) Actual development 55-148640 (JP, U) Actual development Sho 58 -65526 (JP, U)

Claims (1)

[Claims] 1. A pair of ultrasonic transducers are attached to a tubular body through which gas flows, facing each other on a line transverse to the flow direction of the gas, and relative to the wall surface of a region between the pair of ultrasonic transducers of the tubular body. The pair of light-transmitting windows facing each other are airtightly attached, and these ultrasonic transducers and light-transmitting windows are the center of the ultrasonic beam transmitted and received between the center line of the tube axis and the pair of ultrasonic transducers. A point of intersection with the line and a center line of the light beam or a part of the light beam that passes through the pair of light transmission windows intersects each other, and a surface that passes through the tube axis center line and the beam center line, and the tube axis center line. A measuring tube arranged so that the plane passing through the light flux center line or a part of the light flux is substantially aligned on one horizontal plane, and drives the pair of ultrasonic transducers. From the ultrasonic signals transmitted and received by other ultrasonic transducers, Flow rate measuring means for measuring the flow rate of gas, the tube is irradiated from one of the pair of light transmission windows,
Of the light led out from the other of the pair of light transmission windows through the gas in the tube, at least the light amount of the wavelength of the light absorbed by the specific component of the gas is detected to detect the gas. And a means for calculating the flow rate of the specific component of the gas from the flow rate and the concentration measured by the flow rate measuring means and the component concentration measuring means. Component flow rate measuring device.