JPS60117149A - Apparatus for measuring flow rate of component - Google Patents

Abstract

PURPOSE:To reduce the load imparted to a person to be examined by reducing a dead space amount, by making it possible to perform the measurements, of a flow rate and a concn. by one tubular body. CONSTITUTION:A flow rate/concn. simultaneous measuring tube is constituted by attaching a flow rate measuring ultrasonic transducer and a concn. measuring optical sensor to one tubular body 2 through which a fluid to be measured, for example, breathing air. That is, a pair of ultrasonic vibrators 4a, 4b are attached and a pair of light transmittable windows 5a, 5b for measuring a concn. are attached between the vibrators 4a, 4b so as to be opposed to each other in an air-tight state. Further, a flow rate measuring circuit 6 is connected to a pair of the ultrasonic vibrators 4a, 4b and a component concn. measuring circuit 14 is connected through the light transmittable windows 5a, 5b.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a component flow rate measuring device that measures the flow rate of a specific component (component flow rate) contained in a fluid such as respiratory gas.

[Technical Background of the Invention and Problems Therewith] When a fluid is composed of various components rather than a single component, a need often arises to measure the flow rate of a specific component.

For example, when breathing gas, such as air or a gas in which oxygen is artificially added to the air, is inhaled and a gas containing carbon dioxide is exhaled, the data obtained by measuring the carbon dioxide flow rate of the exhaled gas (exhalation) is It is used to evaluate respiratory function as the amount of carbon dioxide produced.

Generally, the conventional method for measuring the amount of carbon dioxide gas produced is called the Douglas bag method, in which exhaled gas is collected in an airtight bag, and the product of its volume ■ and the carbon dioxide concentration Fco2 is calculated to calculate the amount of carbon dioxide gas produced. Count.

On the other hand, advances in fluid pumping measurement and component analysis methods have made it possible to measure component flow rates in real time.For example, when measuring the amount of carbon dioxide gas produced, the instantaneous value v( t) and the instantaneous value fco2(t) of the concentration, which is the result of the component analysis of carbon dioxide gas, are simultaneously measured, and the product of these is vco2 (t) = v (t) −fco
The amount of carbon dioxide produced has been measured in the form of 2 (t).

Incidentally, both flow mouth measurement and m degree measurement are performed while flowing the fluid through the measurement tube, but in the past, the measurement tube for pumping measurement and the measurement tube for concentration measurement were connected in series. I was conducting measurements. However, when two measuring tubes are connected in series in this way, the capacity of the measuring system for respiratory gas, so-called dead space amount, becomes the sum of the values in the respective measuring tubes, and becomes quite large.

This poses a problem in that it places a heavy burden on the breathing capacity of the subject, making it difficult to apply it to critically ill patients.

Moreover, providing measurement tubes for flow rate measurement and 11 degree measurement in series in this way also poses a problem in terms of measurement accuracy.

This is because a time lag occurs in the timing of quantity measurement due to the distance between the two measuring tubes. In other words, if the distance from the flow rate measurement pipe to the concentration measurement pipe is L and the flow velocity of the fluid is V, then the time td required for a certain flow rate to reach the concentration measurement pipe is
(time lag) is t(1=L/V) and changes according to the flow velocity.In order to remove the influence of this time lag td, conventionally the value of td is memorized and VCO2(t) =v(t)−fco2(t+td)
The amount of carbon dioxide produced was measured in the form of -. However, especially in compressible fluids such as breathing gas, the flow velocity changes variously during one breath, and the flow velocity also changes due to pressure changes, so the change in time lag td is complicated, and as shown in the above equation. It has been extremely difficult to make such a correction strictly.

[Purpose of the Invention] The purpose of the invention is to measure the flow rate of a specific component of a fluid with as little dead space as possible and with high precision without being influenced by changes in flow velocity in the measurement pipe of the fluid. It is an object of the present invention to provide a component flow rate measuring device which can perform the above-mentioned flow rate measurement without requiring complicated correction processing.

[Summary of the Invention] This invention is a component flow rate measuring device in which flow port measurement is performed using ultrasonic waves and component concentration measurement is performed optically. A pair of ultrasonic transducers are mounted so as to face each other on a line intersecting with the oscillator, and a pair of light transmitting windows are airtightly mounted so as to face each other on a wall surface of an open area of the pair of ultrasonic transducers of the tube body. a measurement tube, and a flow rate measurement circuit that drives the pair of ultrasonic transducers and measures the flow rate of the fluid from ultrasonic signals transmitted by each of the ultrasonic transducers and mutually received by the other ultrasonic transducers. and identifying at least the fluid among the light that is completely irradiated into the tube body from one of the pair of light transmission windows, passes through the fluid in the tube body, and is led out from the other of the pair of light irradiation windows. a component a degree measurement circuit that measures the concentration of the specific component of the fluid by detecting light D having a wavelength that is absorbed by the component, and the flow rate and component concentration measured by the flow rate measurement circuit and the component concentration measurement circuit. The present invention is characterized by comprising means for calculating the flow rate of the specific component of the flow rate from the flow rate.

[Effects of the Invention] According to the present invention, flow m measurement and concentration measurement can be performed in one tube. Each time of the measurement system for the fluid to be compared and measured, that is, the dead space is reduced, and the burden on the subject can be significantly reduced.

Further, since the flow m measurement and the concentration measurement are performed at almost the same position, the time lag between these measurements is zero or extremely small. Therefore, in order to eliminate the influence of this time lag, the complicated correction that was required in the past is not necessary, or even if correction is made, the time lag is small to begin with, and the difference between the flow rate measurement position and the concentration measurement position. Since the distance is minute, there is virtually no change in flow velocity during this time, and this time lag can always be considered constant, it has the advantage of requiring very simple processing. As a result, along with the downsizing of the measuring tube, it is possible to simplify the overall configuration of the measuring device, and there is no measurement error due to changes in fluid flow velocity within the measuring tube, resulting in extremely high performance. Accurate measurement of component flow becomes possible.

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

In the figure, 1 is a measurement tube for simultaneous flow rate and concentration measurement;
The structure is such that an ultrasonic transducer for measuring flow rate and an optical sensor for measuring concentration are attached to one tube 2 through which a fluid to be measured, such as breathing gas, flows. That is,
This tube body 2 is placed at a predetermined distance apart in the length direction of the tube body 2.
A pair of ultrasonic transducers 4 a and ' 4 b are arranged opposite to each other on a line that diagonally crosses the flow direction of the fluid flowing through them.
is installed. Note that the ultrasonic transducers 4a and 4b may be provided to protrude into the tube body 2, but in this embodiment, recesses 3a, 3b, and an ultrasonic transducer 4a is placed here.
, 4b are arranged.

On the other hand, a pair of light transmission windows 5a and 5+b are airtightly attached to the wall surface of the region between the ultrasonic transducers 4a and 4b of the tube body 2, facing each other. These light transmission windows 5a and 5b are for transmitting light for concentration measurement. Here, in this embodiment, the tube axis center line of the tube body 2 and the ultrasonic transducers 4a, 4
The intersection point P with the beam center line of the ultrasound transmitted and received between b,
The ultrasonic transducers 4a, 4b and the light transmitting window 5a are arranged so that the center lines of the light beams passing through the light transmitting windows 5a, 5b intersect.

5b is placed.

A component flow rate measuring device is constructed by combining the measuring tube 1 thus constructed with the elements described below. That is, a flow rate measurement circuit 6 is connected to the pair of ultrasonic transducers 4a and 4b. This flow rate measuring circuit 6 uses, for example, one based on the propagation time difference method.

FIG. 2 shows the basic configuration of a flow rate measuring circuit using the propagation time difference method.
．． 21b simultaneously, and at that time each ultrasonic transducer 4a, 4. Other ultrasonic transducers 4b and 4a received by b
The receiving circuits 22a and 22b convert the ultrasonic signals from the ultrasonic waves into electric signals, which are guided to the time difference calculation circuit 24 through the waveform shaping circuits 23a and 23b, thereby calculating the ultrasonic propagation time from the ultrasonic transducer 4a to the ultrasonic transducer 4b. The flow rate signal v(t) is obtained by calculating the difference between the ultrasonic propagation time from the ultrasonic transducer 4b to the ultrasonic transducer 4a and multiplying this by a predetermined constant. Note that FIG. 2 only shows the basic configuration, and it is possible to use a more improved configuration as described in, for example, Japanese Patent Laid-Open No. 57-77914, Japanese Patent Laid-Open No. 57-77915, etc. It is also possible to take

On the other hand, concentration measurement is carried out as follows, for example, according to the principle described in Japanese Patent Application Laid-open No. 57723843.

That is, a light source 8 turned on by a power source 7 is provided outside one light transmitting window 5a, and light from this 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 fluid flowing through the tube body 2, and then is guided to the outside through the other light transmission window 5b. The light led to the outside reaches a chopper rotary plate 10 driven by a motor 9 at a constant rotation speed. This rotating plate 10
includes a first filter 11 that passes only light with a wavelength that is absorbed by a specific component contained in the fluid to be measured, such as carbon dioxide gas, and a first filter that passes light with a wavelength that is not absorbed by any component contained in the fluid to be measured. second filter 12
and are arranged at different positions in the circumferential direction. The light transmitted through these filters 11 and 12 is guided to a photodetector 13, converted into an electrical signal, and then supplied to a component concentration measuring circuit 14.

The concentration measuring circuit 14 is configured as shown in FIG. 3, for example. This configuration is described in Japanese Patent Application Laid-Open No. 57-23843, and after the output of the photodetector 13 is amplified by the amplifier 31, the first
A component caused by the light of the wavelength transmitted through the filter 11 of
The component resulting from the light having the wavelength transmitted through the second filter 12 and the component resulting from the light having the wavelength transmitted through the second filter 12. Synchronous detection is performed by the second detectors 32a and 32b, the ratio of the respective detection outputs (first detector output/second detector output) is determined by the divider circuit 33, and this ratio is further determined by the logarithmic amplifier 34. The configuration is such that a concentration signal fcO2('j) for a specific component, for example, carbon dioxide gas, is obtained by logarithmic conversion. 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 a specific component.

Here, the flow rate measurement circuit 6 and the component concentration measurement circuit 14 are as follows.
The synchronization signal 16 operates so that the sampling of light caused by the rotation of the chopper rotating plate 10 and the emission of ultrasonic waves from the ultrasonic transducers 4a and 4b are performed in synchronization. That is, for example, detection of the light transmitted through the first filter 11 and 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 on the same flow mass of the fluid to be measured.

The flow rate signal (1) and the component concentration signal fco2 (t) obtained from the flow rate measurement circuit 6 and the component concentration measurement circuit 14 in this way are supplied to the arithmetic processing circuit 15, where, for example, fV(t) By performing the calculation fco2(t), the component flow rate of a specific component, for example, the amount of carbon dioxide gas produced, can be determined. That is, the flow rate signal v(t
) and component concentration signal fc.

2 (i>) corresponds to the same flow mass of the fluid to be measured and there is no time lag, so the arithmetic processing circuit 15 can directly perform arithmetic processing on these.

As explained above, according to the present invention, the flow rate and the concentration of a specific component can be measured simultaneously using the same measuring tube. The capacity of the entire measurement system for the measurement fluid can be reduced, and the burden on the subject is greatly reduced. This is particularly effective when managing the breathing of critically ill patients.

In addition, the fact that flow rate and component 11 degrees are measured in the same measurement tube means that these measurement positions are close to each other, and therefore the time lag in measuring these quantities for the same flow mass is very large. This has the advantage of simplifying signal processing for measurement. In particular, in the above embodiment, the flow rate measurement point and the component concentration measurement point are the intersections of the tube axis center line of the tube body constituting the measurement tube and the beam center line of the ultrasonic waves transmitted and received between the pair of ultrasonic transducers. Since they match, this time lag becomes almost completely zero, so there is no need for any processing to correct it.

This makes it possible to measure component flow ports with higher precision than in the past.

Note that the flow rate measurement point and the component concentration measurement point do not necessarily have to match exactly, but should be ,
Almost the same effect can be obtained even if only a portion of the light flux passing through the light transmission window intersects.

Further, in the above embodiment, as shown in the figure, a plane 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 plane passing through the optical axis center line of the light transmitted through 5b and the tube axis center line of the tube body 2 almost coincides, in other words, the ultrasonic transducer 4a,
4b and the light transmission windows 5a, 5b are located on one surface passing through the tube axis center line of the tube body 2. Therefore, if the measuring tube 1 is arranged so that this surface is horizontal, when the fluid flowing through the tube body 2 is a gas such as breathing gas, liquefaction will occur within the tube body 2, and the liquid will flow to the bottom. Even if the liquid accumulates in the liquid, the recesses 3a, 3b where the ultrasonic transducers 4a, 4b are installed and the light transmission windows 5a, 5b will not be blocked by the liquid, preventing ultrasonic propagation and light. Stable measurement is possible without deterioration of the transmission state.

This invention can be implemented in various other ways. For example, a pair of It is not necessary that the beams of light passing through the light transmission windows 5a and 5b intersect, and in short, the light transmission windows 5a and 5b are the ultrasonic transducers 4a.

It suffices if it is attached to the wall surface of the tube body 2 in the area between 4b. In particular, when the length in the tube axis direction in the region between the ultrasonic transducers 4a and 4b of the tube body 2 is as short as several inches, the time lag between flow rate measurement and concentration measurement is virtually no problem. However, even if this time lag is corrected, changes in the time lag due to changes in flow velocity can be ignored, so there is an advantage that signal processing for correction is very simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a component concentration measuring circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific configuration example of the flow measuring circuit in the same embodiment, and FIG. It is a figure showing a concrete example of composition. DESCRIPTION OF SYMBOLS 1... Measuring tube, 2... Tube body, 3a, 3b... Recess, 4a, 4b... Ultrasonic vibrator, 5a, 5b... Light transmission window, 6... Flow rate measurement Circuit, 7... Power supply, 8...
・Light source, 9...Motor, 10...Chopper rotating plate, 11.12...Filter, 13...Photodetector, 1
4...Component concentration measurement circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 31!1

Claims (4)

[Claims] (1) A pair of ultrasonic transducers are installed in a pipe body through which fluid flows so as to face each other on a line diagonally crossing the fluid flow direction, and the open area of the pair of ultrasonic transducers of the pipe body is A measuring tube consisting of a pair of light transmitting windows airtightly mounted opposite to each other on a wall surface and the pair of ultrasonic transducers are driven, and the waves transmitted by each ultrasonic transducer are transmitted to each other by the other ultrasonic transducers. a flow rate measurement circuit that measures the flow rate of the fluid from a received ultrasonic signal; and a light irradiation window that is irradiated into the tube body from one of the pair of light transmission windows and transmitted through the fluid in the tube body. a component concentration measuring circuit that measures the concentration of the specific component of the fluid by detecting the amount of light of a wavelength that is absorbed by at least a specific component of the fluid, out of the light guided to the outside from the other side of the fluid; A component flow rate measuring device comprising: a measuring circuit; and means for calculating the flow m of the specific component of the flow rate from the flow rate and component concentration measured by the component +1 degree measuring circuit. (2) A pair of ultrasonic transducers and a pair of light transmission windows are located at the intersection of the tube axis center line of the tube body and the beam center line of the ultrasonic waves transmitted and received between the pair of ultrasonic transducers, and the pair of light beams. 2. The component flow rate measuring device according to claim 1, wherein the component flow rate measuring device is arranged so that the center line of the light flux of the light transmitted through the transmission window or a part of the light flux intersects with each other. (3) The pair of ultrasonic transducers and the pair of light transmission windows are connected to a plane passing through the tube axis center line of the tube body and the beam center line of the ultrasonic waves transmitted and received between the pair of ultrasonic vibrators, and the tube body. Claim 1 or 2, characterized in that the tube axis center line of the tube is arranged so that a plane passing through the center line of the light flux of light transmitted through the pair of light transmission windows substantially coincides with each other. The component flow rate measuring device described. (4) According to claim 1, the flow rate measurement by the flow rate measurement circuit and the concentration measurement of a specific component by the component concentration measurement circuit are performed simultaneously for the same flow rate flowing through the tube. component flow measuring device.