JP2000266579A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which enables ideal use of an oxygen consumption meter. SOLUTION: A transmitter 4 and receivers 5a, 5b and 5c are arranged at an open hole of a wall part of a passage. When inhaled or exhaled air flows through the passage, an ultrasonic wave as burst wave is transmitted from the transmitter 4 to detect first phase differences Δϕ and Δϕ' as such between received signals of the receivers 5a and 5c and second phase differences ΔϕC1 and ΔϕC2 as such between the received signal of the receiver 5b and a reference wave. Phase comparators 32 and 36 for detecting the first and second phase differences are provided to determine the flow rate of the inhaled or exhaled air based on the first phase differences and the second phase differences. Sample holding circuits 34 and 38 are provided to sample an output alone corresponding to a signal received by the receivers 5a-5c at a time zone when the burst wave propagating the exhaled or inhaled air is expected to be received out of outputs of the phase comparators 32 and 36.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter having an ultrasonic transmitter and a receiver for measuring the flow of respiratory gas.

[0002]

2. Description of the Related Art Oxygen consumption meters are used to measure the amount of oxygen consumed in the body during exercise and the amount of carbon dioxide emitted from the body, and are used to evaluate lung function, measure metabolic rate, and measure basic physical fitness. It has been established as a medical evaluation device that provides powerful data for analysis of human body and selection of optimal exercise load.
Previous oxygen consumption meter, for exercise load of a certain time,
Oxygen consumption relative to the average amount of exercise during that time was measured, but in recent years, more detailed analysis has been required, and data per breath, called the breath-by-breath method, has been required. It has come to be. The oxygen consumption meter is mainly composed of a respiratory air flow meter, a carbon dioxide concentration meter, and an oximeter, and when data for each breath is required as described above, these components are also considered. More sophisticated functions are being demanded.

[0003] As a flow meter of an oxygen consumption meter,
Practical ones include a hot wire flow meter, a laminar flow meter, and a turbine flow meter.

[0004]

However, the above-mentioned various flow meters have the following problems. In the hot wire method, it is difficult to take a mechanically strong structure in order to improve heat transfer characteristics. In the laminar flow method, a pressure loss is large because the flow of the respiratory air is forcibly changed to a laminar flow by a restricting mechanism in which minute thin tubes are bundled. For this reason, the amount of respiratory air may be significantly lower than actual. In addition, there is a concern that the saturated vapor contained in the exhaled gas will condense on the thin tube and block it. Furthermore, in the turbine type, the deterioration of the rotating movable part over time is inevitable, and the responsiveness is low due to the inertia of the mechanical operation. In particular, there is a concern that the flow rate cannot be measured accurately when exhalation and inspiration are switched. . In addition, these flowmeters have a structure that is not suitable for sterilization work after use because a structure that obstructs the flow of respiratory air must be arranged in the flow path.

On the other hand, there is an ultrasonic flow meter as a generally used flow meter, which is widely used for industrial and experimental purposes. In this ultrasonic flowmeter, one or more sets of ultrasonic transceivers are provided in a conduit through which the fluid passes, and the flow rate of the fluid is determined based on the propagation time until the ultrasonic waves emitted from the transmitter are received by the receiver. It is to be measured. Specifically, two types are known as follows. One is to use two sets of transceivers,
Provided at different points in the pipeline, from one set of transmitters to the other set of receivers, and then from the other set of transmitters to the one set of receivers, pulsed The flow rate is determined based on the difference between the times at which the pulse wave is emitted and propagated to each set of receivers. The other type emits a continuous wave ultrasonic wave from a transmitter and detects the ultrasonic wave based on the phase difference between the received waves received by a plurality of receivers. However, the former of these ultrasonic flow meters has a very small difference in the measured time, so various measures are required for the measurement, a complicated circuit configuration is required, and the cost is high. Difficult to apply to meter. Further, since the latter is a continuous wave, a reflected wave or a leaked wave in the tube poses a problem, and only ultrasonic waves directly transmitted from a target transmitter are used.
It was difficult to detect with good / N ratio. For this reason, the fluid to be measured is limited to a liquid having a large acoustic impedance and a large amplitude at the time of receiving the propagating ultrasonic wave,
It is difficult to apply to an oxygen consumption meter that uses respiratory gas as a fluid.

The present invention has been made in view of the above circumstances, and has as its object to provide an ultrasonic flowmeter which can solve the above-mentioned various problems and can be suitably used for an oxygen consumption meter.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides an ultrasonic transmitter and an ultrasonic transmitter in a hole of a wall of a flow path through which breathing air flows. Three ultrasonic receivers are provided so as to face the ultrasonic transmitter, and a first ultrasonic receiver among the three ultrasonic receivers includes the ultrasonic receiver and the ultrasonic receiver. A straight line connecting the transmitter and the transmitter is installed so that the straight line connecting the transmitter and the ultrasonic transmitter has an angle of + θ with respect to the direction of the breathing air. -For the direction
θ, the third ultrasonic receiver is installed such that a straight line connecting the ultrasonic receiver and the ultrasonic transmitter is substantially orthogonal to the direction, Transmits ultrasonic waves as a burst wave from the ultrasonic transmitter when flowing through the flow path, and calculates a phase difference between reception signals of the first ultrasonic receiver and the second ultrasonic receiver. Detecting a certain first phase difference and a second phase difference that is a phase difference between a received signal of the third ultrasonic receiver and a reference wave;
An ultrasonic flowmeter, wherein the flow rate of the respiratory gas is obtained based on the first phase difference and the second phase difference.

According to the first aspect of the present invention, an ultrasonic flowmeter in which one ultrasonic transmitter and three ultrasonic receivers are installed in an opening in a wall of a flow path through which breathing air flows. Therefore, it is possible to solve various problems of a hot wire type, a laminar flow type, and a turbine type flow meter conventionally used for an oxygen consumption meter. That is, since the receiver and transmitter are embedded in the opening in the wall of the flow path, the structure is simple and there are no obstacles on the flow path. The measurement can be performed with the normal momentum of the respiratory gas as it is, and it is unlikely to be blocked by saturated vapor or the like. Also, the sterilization operation is easy. Furthermore, since there is almost no mechanical operation like a turbine type,
There is almost no deterioration over time, and the responsiveness is improved.

The first aspect of the present invention is a system for detecting two types of phase differences using three receivers, and therefore has a simple circuit configuration as compared with a conventional time difference type ultrasonic flow meter. And cost can be reduced. Furthermore, since a burst wave is used as a transmission wave, compared with a conventional phase difference type ultrasonic flowmeter using a continuous wave, it is possible to efficiently detect only a target reception wave,
Even if the fluid is a gas, it is sufficiently applicable.

Here, the burst wave is a continuous wave that is continuous for a limited period of time and has a certain interval between the continuous waves. The angle θ is 9
It is a value other than 0 degrees. Further, the reference wave is a burst wave transmitted from the transmitter when there is no flow of respiratory gas. In this case, the phase data of the reference wave may be obtained from the received signal actually received by the receiver or may be obtained by calculation, and thus may be obtained from a signal generation circuit or the like. .

According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, the phases of the reception signals of the first ultrasonic receiver and the second ultrasonic receiver are compared to each other. A first phase comparator that outputs a result, a second phase comparator that compares a phase of a reference signal corresponding to the reference wave with a reception signal of the third ultrasonic receiver, and outputs a result of the comparison. , When the burst wave transmitted from the ultrasonic transmitter and propagating through the respiratory gas is expected to be received, the first and second ultrasonic signals are output from the first phase comparator. A first sample and hold circuit for sampling only an output corresponding to a signal received by the sound wave receiver;
And a second sample-and-hold circuit that samples only the output corresponding to the signal received by the third ultrasonic receiver in the time period among the outputs of the phase comparator.

According to the second aspect of the present invention, it is expected that the sample hold circuit receives, from the output of the phase comparator, a burst wave transmitted from the ultrasonic transmitter and transmitted through the respiratory gas. Since only the output corresponding to the signal received during a certain time period is sampled, various noises such as a signal propagating through the wall of the flow path and a reflected signal are removed from the received signal, and only the intended signal is extracted. Thus, the subsequent arithmetic processing can be performed accurately.

According to a third aspect of the present invention, in the ultrasonic flowmeter according to the second aspect, the first phase comparator is used during a time period when the burst waves are not received by the three ultrasonic receivers. , Two simulation signals having a phase difference of 90 degrees are input to the second phase comparator, and the reference signal and a simulation signal having a phase difference of 90 degrees from the reference signal are input to the second phase comparator. Is input.

According to the third aspect of the present invention, even when the burst wave is not received, two signals having a phase difference of 90 degrees are input to the first and second phase comparators. Therefore, this makes it possible to stabilize the operations of the first and second phase comparators.

According to a fourth aspect of the present invention, there is provided the ultrasonic flowmeter according to the second or third aspect, further comprising a filter for cutting a direct current component from the output of the first phase comparator. I do.

According to the fourth aspect of the present invention, since the DC component is cut out of the output of the first phase comparator by the filter, the offset voltage generated inside the circuit provided in the ultrasonic flowmeter can be reduced. The influence of the calculation error due to the influence of the signal and the temporal instability of the signal is removed, and a stable output can be obtained for the first phase difference.

Since the ultrasonic flowmeter according to any one of claims 1 to 4 has the above-mentioned excellent functions and effects, it is suitable for an oxygen consumption meter as in the invention according to claim 5. Can be used.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. FIG.
FIG. 1 is a diagram showing a basic configuration of an ultrasonic flowmeter of the present invention. The ultrasonic flow meter 1 shown in FIG. 1 is provided in an oxygen consumption meter and mainly includes a mask 3 and a plastic flow path 2, and has a plurality of openings formed in a wall of the flow path 2. (Only one is shown in FIG. 2), one transmitter (ultrasonic transmitter)
4 and three receivers (ultrasonic receivers) 5a, 5b, 5c
Are provided so as to face each other. The receiver (third ultrasonic receiver) 5b is provided so as to be located in front of the transmitter 4, and the receivers 5a and 5c (first and second ultrasonic receivers) are The receivers 5a and 5c are provided on the left and right sides of the receiver 5b such that a straight line connecting the receivers 5a and 5c has an angle of ± θ with respect to the direction of the flow of the respiratory gas in the flow path 2. Transmitter 4
Emits ultrasonic waves at regular intervals and outputs the ultrasonic waves to the receiver 5
a, 5b, and 5c receive. Transmitter 4
Is a continuous wave that is continuous for a limited period of time, there is a certain interval between the continuous wave,
Here, it is called a burst wave.

The transmitter 4 and the receivers 5a to 5c have substantially the same structure, and FIG. 2 schematically shows the structure.
The transmitter 4 (receivers 5a to 5c) has an opening 2a in the flow path 2.
A piezoelectric element 14 that emits ultrasonic waves is fixed via an adhesive 13 inside a metal holder 12 inserted therein, and has a drip-proof structure. Metal holder 12 and opening 2
The space between a is sealed by O-rings 11 made of a material such as rubber. The upper part of the opening 2a, that is, the upper part of the metal holder 12 is covered with an elastic plate 10 made of rubber or the like, and the elastic plate 10 is covered with a fixing plate 18. The metal holder 12 includes the fixing plate 18 and the elastic plate 1.
0, and is fixed in the opening 2a by fastening screws 17, 17 screwed into the wall portion 2b of the flow channel 2. The lead wires 18 connected to the piezoelectric element 14 are the elastic plates 1.
0, penetrating through the fixing plate 18 and extending to the outside of the transceiver. The elastic plate 10 is provided to reduce an ultrasonic component propagating between the transmitter and the receiver via the flow path 2.

Here, the transmitter 4 to the receiver 5 shown in FIG.
The propagation of the ultrasonic waves transmitted to a to 5c is analyzed as follows. In the ultrasonic flow meter 1, when generating an ultrasonic wave, a drive voltage is applied to the piezoelectric element 13 (FIG. 4A), and upon receiving the drive voltage, the transmitter 4 transmits a (transmitted wave). As shown in FIG. 4 (b), an ultrasonic wave is emitted as a continuous burst wave for a certain period of time.

When a burst wave is generated from the transmitter 4 at a certain time, a fluid (here, suction) is propagated and the receivers 5a to 5a.
The time until the ultrasonic wave reaches 5c is determined by the receivers 5a and 5c.
Ta, Tb, and Tc are the times of arrival at b, 5c, respectively.
Then, Ta = L / (C1 + V1cosθ) (1) Tc = L / (C1−V1cosθ) (2) Tb = D / C1 (3) Here, L is the distance between the transmitter 4 and the receivers 5a and 5c, D is the diameter of the flow path 2, C1 is the sound speed at the time of intake, and V1 is the flow rate of the intake. Furthermore, when the Ta-Tc and ΔT, ΔT = -2Dcotθ · V1 / (C1 2 -V1 2 cos 2 θ) (4) where, because a ^{C1 2 »V1 2 cos 2 θ,} ΔT = -2Dcotθ · V1 / C1 ² (5)

At the time of exhalation, the receivers 5a, 5b, 5c
The time reaching the respective, Ta ', Tb', 'When, expressed in the same manner as described above, Tb' Tc is = D / C2 (6) ΔT '= 2Dcotθ · V2 / C2 2 (7). Here, C2 is the sound speed at the time of expiration, V2 is the flow speed of expiration, and ΔT ′ = Ta−Tc.

As is apparent from equations (5) and (7),
The flow rates V1 and V2 of the respiratory gas are ΔT, ΔT ′, C1, C
2 and the values of D and θ shown in FIG.

As described above, since the transmission waves are continuous for a limited period of time, the ultrasonic waves (received waves) received by the receivers 5a to 5c are also continuous for some time. The phase difference (first phase difference) Δφ (during inspiration) and Δφ ′ (during expiration) of the reception waves received by the receivers 5a and 5c within the time period in which the reception waves are continuous are the same as those of the reception waves. Assuming that the angular frequency is ω, the angular frequency can be expressed as in equations (8) and (9). Δφ = ωΔT (8) Δφ ′ = ωΔT ′ (9) In the present embodiment, the time differences ΔT and ΔT ′ are represented by ω
Detected as the first phase differences Δφ and Δφ 'which are multiplied, and can be detected with high sensitivity.

The phase difference between the received wave received by the receiver 5b when there is an inspiratory flow and the reference wave is Δφ _C1 , and the position of the received wave and the reference wave received when there is an expiratory flow is Assuming that the phase difference is Δφ _C2 , Δφ _C1 = ωΔTb (10) Δφ _C2 = ωΔTb '(11)

In the signal processing circuit 80 described later, the reference wave is set so as to have a phase difference of 90 degrees with respect to the received signal at the time of calibration. Therefore, for Δφ _C1 which is actually the output of the phase comparator 36 (FIG. 3), taking the case of intake as an example, Δφ _C1 = ωΔTb∽ω (D / C0−D / C1) = ωD (1 / C0−) a 1 / C1) = ωDΔC1 / C0 2. Here, C0 is the sound speed (known) at the time of the flow rate calibration of the device, and C1 = C0 + ΔC1. ΔC1 is C
It represents the width of change of the sound speed with respect to 0, and C0≫ΔC1.
That is, the output of the phase comparator 36 indicates a change in the speed of sound (ΔC
This corresponds to 1). Since C0 is known, C1 is thereby calculated. Δφ _{C2 for} exhalation
Is similarly required. Naturally, it is desirable that the sound speed of the reference wave be selected near the center of the expected sound speed change width of the respiratory gas.

Then, the sound velocities C1 and C2 are obtained from the second phase differences Δφ _C1 and Δφ _C2 , and ΔT and ΔT are obtained from the first phase differences Δφ and Δφ '.
When T 'is determined, as described above, the flow velocities V1 and V2 are determined from Expression (5) or Expression (7).

FIG. 3 shows a signal processing circuit 8 of the ultrasonic flow meter 1.
FIG. 3 is a block diagram showing a configuration of a 0. This signal processing circuit 8
0 transmits and receives ultrasonic waves, and thereby detects Δφ, Δφ ′, Δφ _C1 , and Δφ _C2 described above.
The signal processing circuit 80 mainly includes the blocks 50, 60, 70
It is composed of The block 50 has a function of transmitting ultrasonic waves to the transmitter 4 and generating various operation signals and control signals. The block 60 mainly has a function of shaping the waveform of the received waves received by the receivers 5a, 5b, and 5c. The block 70 mainly has a function of extracting only signals corresponding to the phase differences Δφ, Δφ ′, Δφ _C1 and Δφ _C2 .

Next, the function of each section in FIG. 3 will be described in relation to the operation of the signal processing circuit 80. First, Δ
The detection of φ and Δφ 'will be described. First, based on the instruction signal from the signal generation circuit 23, the drive circuit 22
A drive voltage having a large amplitude and continuing for a certain period of time as shown in FIG.
Applied to Here, the period in which the drive voltage is applied is such that the reflected waves in the flow path 2 are sufficiently attenuated and the receivers 5a to 5c
Interval that is no longer received by
0 to 20 msec. When the driving voltage is applied, the transmitter 4
Then, a burst wave having a continuous waveform as shown in FIG. 4B is emitted, and is received by the receivers 5a to 5c. When received by the receivers 5a, 5c, the received signal is amplified by the amplifiers 24, 30 of the block 60, and the output of the amplifier 24 is passed through the phase shifter 25 to the waveform shaping circuit 26.
And the output from the amplifier 30 is sent to the waveform shaping circuit 31. The waveform shaping circuits 26 and 31 shape the input waveform and convert it into a rectangular wave. Here, the rise time of the rectangular wave corresponds to Ta and Tc in the case of inhalation, and corresponds to Ta ′ and Tc ′ in the case of exhalation.

The rectangular waves output from the waveform shaping circuits 26 and 31 are input to a phase comparator (first phase comparator) 32 of a block 70. In this phase comparator 32, “ωΔ
T ”or“ ωΔT ′ ”, that is, Δφ or Δ
Calculation processing for obtaining φ ′ is performed. In this arithmetic processing, in the case of a continuous input wave, the input phase difference at which a linear output is obtained is limited to a range of 180 °. Therefore, if the operation reference point when the flow rate (breathing air) is zero is 90 °, the largest input range can be ensured. Since the receiver 5a and the receiver 5c are located at the same distance from the transmitter 4, when the flow rate is zero, the reception waves of the receivers 5a and 5c are in phase. Therefore, the phase shifter 25 is provided in the block 60, and the phase shifter 25 shifts the phase of the reception wave of the receiver 5c so that the input phase difference becomes 90 ° when the flow rate is zero in the phase comparator 32. It has become.

Since the ultrasonic wave emitted from the transmitter 4 is a burst wave, only the received signal is compared with the phase comparator 3
When inputting to 2 is performed, the input signal becomes discrete, and there is no input signal at most times. Therefore, in order to stabilize the operation of the phase comparator 32, when there is no input signal, the signal generation circuit 23 sends a signal to the waveform shaping circuits 26 and 31.
As shown by signal lines P1 and P2, a simulation signal having a phase difference of 90 ° is input. By inputting such a simulation signal, a signal is always input to the phase comparator 32 as shown in FIG. 5, and when the receivers 5a and 5c do not receive the reception wave, the signals in FIG. As shown by the dotted line, if a signal having a phase shift of 90 ° is input and the receivers 5a and 5c receive the received wave, the signals have the phase difference Δφ or Δφ ′ as shown by the solid line in FIG. A signal is input.

Δφ obtained by the phase comparator 32,
The signal corresponding to Δφ ′ is sent to the low-pass filter 33. The low-pass filter 33 converts the rectangular waveform output from the phase comparator 32 into an analog voltage and outputs the analog voltage to the sample-and-hold circuit 34.

The sample-and-hold circuit 34 samples and holds only the target signal, which is proportional to the phase difference of the signal transmitted through the respiratory gas, from the signals input from the low-pass filter 33. FIG. 4 (c) shows the received signal.
As shown in the figure, in addition to the target signal component (part B),
Induction noise, noise propagating through the pipes constituting the flow path 2 (part A), and noise reflected from the wall of the flow path 2 (part C)
And so on. However, as is clear from FIG. 4, the noise of the portion A is received at substantially the same time as the drive voltage (FIG. 4A), and the noise of the portion C is more than three times in the flow path 2 in the radial direction. Because it is received after being propagated,
The signal is received at a different time from the signal of the target B portion. Therefore, the sample and hold circuit 34 outputs the output corresponding to the signal received by the receivers 5a and 5c in the time zone in which the signal of the target B portion is expected to be received among the outputs of the phase comparator 32. Only sample.

The timing and time at which the sample and hold circuit 34 performs the sample and hold is in accordance with the sample and hold signal (signal line P5) from the signal generation circuit 23. This sample hold signal is output at the timing and time shown in FIG. In the calculation, t1 and t2 shown in FIG. 4D are t1 = L / C1 or t1 = L / C2, t2 = 3D / C1 or t2 = 3D
/ C2, the generation of the ultrasonic wave from the piezoelectric element 14 is slightly delayed from the generation of the drive voltage due to the effect of inertia as shown in FIG. In consideration of the influence of the agent 13 and the metal holder 12, the value is set to a value slightly larger than the above calculation result.

The signal output from the sample and hold circuit 34 is sent to a DC cut circuit 35. The DC cut circuit 35 plays a role as a filter that cuts low frequency components (cut frequency is fc or less), which are DC components, and passes only AC components. In the case of expiration and inspiration, the flow directions are opposite, and only the AC component is required to obtain the flow velocity (flow rate). Therefore, such processing can be performed. Due to the processing in the DC cut circuit 35, the influence of the offset voltage generated inside the circuit and the block 7
The influence of the calculation error due to the instability on the time (1 / fc or more) of various signals generated at 0 is eliminated. here,
As the fc value, a value sufficiently smaller than the assumed lowest respiratory frequency at rest is set.

The signal output from the DC cut circuit 35 is input to an A / D (analog / digital) converter 39 and is converted into a digital value.

Next, detection of Δφ _C1 and Δφ _C2 will be described. This is because, as already mentioned, the reference wave and the receiver 5b
Are compared to determine the phase difference between the two. The specific processing performed in each section of the signal processing circuit 80 is substantially the same as the case where Δφ and Δφ ′ are obtained. The following description focuses on differences from the case where Δφ and Δφ ′ are obtained. The signal received by the receiver 5b is
The signal is amplified by the amplifier 27 and converted into a signal having a phase shifted by 90 ° from the reference wave by the phase shifter 28. Next, the waveform shaping circuit 29
When there is no received signal from the receiver 5b, a simulation signal having a phase difference of 90 ° with respect to the reference wave is input to the waveform shaping circuit 29 as shown by a signal line P3. Is done.

Next, a phase comparator (second phase comparator) 3
6, the signal generation circuit 2 as shown by the signal line P4.
3 outputs a reference wave signal corresponding to the reference wave. As a result, the signal output from the waveform shaping circuit 29 is compared with the reference wave, and a calculation process for obtaining ωΔTb (ωΔTb ′) is performed. Note that, even when the received signal is not input to the phase comparator 36, a simulation signal having a 90 ° phase shift with respect to the reference wave is input via the waveform shaping circuit 29. Is the reference signal and the simulation signal.
Input two signals. The comparison result in the phase comparator 36 is output to the low-pass filter 37, and is output to the A / D converter 40 via the sample-and-hold circuit 38.
Is converted into a digital value by the / D converter 40 and the sound speed C
1, used for calculation of C2. Sample hold circuit 3
The function of No. 8 is the same as that of the sample and hold circuit 34, and only the reception signal other than noise is sampled based on the sample and hold signal (signal line P6) from the signal generation circuit 23.

In the ultrasonic flow meter according to the present embodiment, the flow velocities V1 and V2 are obtained based on the digital data from the A / D converters 39 and 40.
The flow rate is obtained by multiplying the cross-sectional area of the flow path 2.

The number of samples of the signal obtained every second by the ultrasonic flow meter 1 is 50 to 100, which is a sufficient number to reproduce the change in the respiratory air flow.

According to the above ultrasonic flow meter 1, the transmitter 4 and the receivers 5a, 5b, 5c are provided in the openings 2a in the wall of the flow path 2.
With the simple structure embedded with the flowmeter, it is possible to solve various problems of the hot wire type, laminar flow type, and turbine type flow meters used in the conventional oxygen consumption meter. In other words, since the structure is simple and there are no obstacles on the flow path, it is easy to make it mechanically strong, pressure loss does not occur, it can be measured with the normal momentum of breathing air, and it may be blocked by saturated steam etc. Hateful. Further, the sterilization operation is easy. Furthermore, since there is no mechanical operation part, there is almost no deterioration over time, and the responsiveness is improved.

Since the phase difference is detected using the three receivers 5a to 5c, a simple circuit configuration is required and the cost can be reduced as compared with a conventional time difference type ultrasonic flow meter. Furthermore, since a burst wave is used as a transmission wave, compared to a conventional phase difference type ultrasonic flow meter using a continuous wave, it is possible to efficiently detect only a target reception wave, and the fluid Is sufficiently applicable even if is a gas.

Further, according to the sample and hold signal from the signal generation circuit 23, the sample and hold circuit 3
4, 38, the outputs of the phase comparators 32, 36
Only the signals received in the time zones in which the burst waves propagated in the respiratory air are expected to be received by the three ultrasonic receivers 5a to 5c are sampled, and the arithmetic processing can be performed accurately.

In addition, according to the simulation signal from the signal generation circuit 23, two signals having a phase difference of 90 degrees are input to the phase comparators 32 and 36 even when no reception signal is received. Thus, the operation of the phase comparators 32 and 36 is stabilized.

Since the DC component of the output of the phase comparator 32 is cut by the DC cut circuit 35, the influence of the offset voltage generated in the signal processing circuit 80 and the signal output from the signal generation circuit 23 are removed. The effect of the calculation error due to the temporal instability of is removed.

As described above, the ultrasonic flow meter 1 has remarkable functions and effects not found in the conventional flow meter, and thus can be suitably used for an oxygen consumption meter.

The ultrasonic flow meter of the present invention can be suitably used especially for an oxygen consumption meter. Examples of the oxygen consumption meter include an oxygen concentration meter, a carbon dioxide concentration meter, and a respiratory gas. A sampling device or the like for sampling is required. Further, the ultrasonic flow meter of the present invention can be applied as a fluid flow meter in various devices and apparatuses other than the oxygen consumption meter.

[0048]

According to the first aspect of the present invention, one ultrasonic transmitter and three ultrasonic transmitters are provided in the opening of the wall of the flow path through which the respiratory air flows.
Since it is an ultrasonic flowmeter equipped with two ultrasonic receivers, it can solve various problems of the hot wire type, laminar flow type, and turbine type flowmeters conventionally used for oxygen consumption meters. it can. That is, since the receiver and transmitter are embedded in the opening in the wall of the flow path, the structure is simple and there are no obstacles on the flow path. The measurement can be performed with the normal momentum of the respiratory gas as it is, and it is unlikely to be blocked by saturated vapor or the like. Also, the sterilization operation is easy. Furthermore, since there is almost no mechanical operation like a turbine type,
There is almost no deterioration over time, and the responsiveness is improved.

Further, according to the first aspect of the invention, 3
Since two types of phase differences are detected using two receivers, a simple circuit configuration is required and costs can be reduced as compared with a conventional time difference type ultrasonic flow meter. Furthermore, since a burst wave is used as a transmission wave, compared to a conventional phase difference type ultrasonic flow meter using a continuous wave, it is possible to efficiently detect only a target reception wave, and the fluid Is sufficiently applicable even if is a gas.

According to the second aspect of the present invention, the first aspect is provided.
In addition to the effects of the invention described in the above, by the sample and hold circuit, of the output of the phase comparator, during the time zone when it is expected that the burst wave transmitted from the ultrasonic transmitter and propagated in the respiratory air is expected to be received Since only the output corresponding to the received signal is sampled, various noises such as a signal propagating through the wall of the flow path and a reflected signal among the received signals are removed, and only the target signal is taken out. Arithmetic processing can be performed accurately.

According to the invention set forth in claim 3, according to claim 2
In addition to the effects of the invention described in (1), even when the burst wave is not received, the first and second phase comparators have 90
Since two signals having a phase difference of degrees are input,
Thus, the operations of the first and second phase comparators can be stabilized.

According to the invention described in claim 4, according to claim 2
Or, in addition to the effect of the invention described in 3 above, since the DC component is cut out of the output of the first phase comparator by the filter, the influence of the offset voltage generated inside the circuit provided in the ultrasonic flowmeter and In addition, the influence of the calculation error due to the temporal instability of the signal is removed, and a stable output can be obtained for the first phase difference.

As in the fifth aspect of the present invention, the first aspect
The ultrasonic flowmeter according to any one of the above-described items 4 to 4, can be suitably used for an oxygen consumption meter.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an ultrasonic flowmeter as an example of the present invention.

FIG. 2 is a diagram showing a schematic structure of a transceiver.

FIG. 3 is a block diagram showing a configuration of a signal processing circuit of the ultrasonic flowmeter of FIG.

FIGS. 4A and 4B are diagrams for explaining timings of various signals in the ultrasonic flowmeter of FIG. 1, wherein FIG.
(B) shows a transmission wave, (c) shows a reception wave, and (d) shows a sample hold signal.

FIG. 5 is a diagram illustrating signals input to the phase comparator of FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ultrasonic flow meter 2 Flow path 2a Opening 4 Transmitter (ultrasonic transmitter) 5a Receiver (first ultrasonic receiver) 5b Receiver (third ultrasonic receiver) 5c Receiver (second ultrasonic wave) Receiver) 22 Drive circuit 23 Signal generation circuit 24, 27, 30 Amplifier 25, 28 Phase shifter 26, 29, 31 Waveform shaping circuit 32 Phase comparator (first phase comparator) 36 Phase comparator (second Phase comparator) 33, 37 low-pass filter 34 sample-hold circuit (first sample-hold circuit) 38 sample-hold circuit (second sample-hold circuit) 35 DC cut circuit (filter) 39, 40 A / D converter

Claims (5)

[Claims] 1. An opening in a wall of a flow path through which breathing air flows
Three ultrasonic transmitters and three ultrasonic receivers are provided so as to face the ultrasonic transmitter, and a first ultrasonic receiver among the three ultrasonic receivers is:
A straight line connecting the ultrasonic receiver and the ultrasonic transmitter is installed so as to have an angle of + θ with respect to a direction in which the respiratory gas flows, and a second ultrasonic receiver includes the ultrasonic receiver and the ultrasonic transmitter. The straight line connecting the ultrasonic transmitter is installed so as to have an angle of -θ with respect to the direction, the third ultrasonic receiver,
A straight line connecting the ultrasonic receiver and the ultrasonic transmitter is installed so as to be substantially orthogonal to the direction. When the respiratory gas is flowing through the flow path, the ultrasonic transmitter transmits ultrasonic waves. A first phase difference that is transmitted as a burst wave and is a phase difference between reception signals of the first ultrasonic receiver and the second ultrasonic receiver, and a reception signal of the third ultrasonic receiver And detecting a second phase difference that is a phase difference between the first and second reference waves, and determining a flow rate of the respiratory air based on the first and second phase differences. Flowmeter. 2. A first phase comparator for comparing phases of reception signals of the first ultrasonic receiver and the second ultrasonic receiver and outputting the result, and a third ultrasonic reception. And comparing the phase of the received signal of the detector with the phase of the reference wave signal corresponding to the reference wave and outputting the result.
A phase comparator of the output of the first phase comparator, during the time zone in which it is expected that the burst wave transmitted from the ultrasonic transmitter and propagating the respiratory gas is expected to be received, A first sample-and-hold circuit that samples only an output corresponding to a signal received by the second ultrasonic receiver; and, among the outputs of the second phase comparator, the third ultrasonic wave during the time period. The ultrasonic flowmeter according to claim 1, further comprising: a second sample and hold circuit that samples only an output corresponding to a signal received by the receiver. 3. During a time period when the burst waves are not received by the three ultrasonic receivers, two simulation signals having a phase difference of 90 degrees are input to the first phase comparator, The ultrasonic flowmeter according to claim 2, wherein the reference wave signal and a simulation signal having a phase difference of 90 degrees from the reference wave signal are input to the second phase comparator. 4. The ultrasonic flowmeter according to claim 2, further comprising a filter that cuts a direct-current component of the output of the first phase comparator. 5. The ultrasonic flowmeter according to claim 1, which is provided in an oxygen consumption meter.