JPS6217172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to the field of flow meters and more particularly to sonic flow meters for measuring the flow rate or velocity of fluid flowing along a defined flow path.

A typical sonic flow meter is disclosed in US Pat. No. 3,109,112. The flow meter has a pair of transducers for generating and receiving compression waves in the audio or ultrasonic frequency range, the transducers being disposed within an enclosure through which fluid flows. The transducers are arranged to be switched alternately into a transmitting mode and a receiving mode, so that compression waves are generated in the gas by the transmitting transducer and received by the other transducers. By measuring the phase difference between the transmitted and received waves in both directions, the velocity of the gas flowing through the transducer is determined.

As a variation on the technique disclosed in the above-mentioned U.S. patents, the transducer has transmitting and receiving portions configured to substantially avoid problems due to compositional or temperature fluctuations in the gas. It can be designed as follows.

In known constructions such as those described above, it is required that the transducer be placed in the flow path of the gas whose velocity is to be measured, or alternatively in a recess formed in the conduit wall. In either arrangement, the normal flow of fluid is altered considerably as it passes through the transducer, thereby degrading the accuracy of the flow meter. Additionally, precipitated particles within the fluid can collect around the transducer and impair the transmit and receive characteristics of the transducer.

The following flowmeters have been developed to solve the above-mentioned problems of known sonic flowmeters, as well as other problems. i.e. Edward James
DeWath, US Pat. No. 4,003,252, discloses an improved flow meter that is designed to have no obstructions along the flow path. In this flowmeter, the transducer is of approximately cylindrical construction and is located within the wall of the fluid conduit, so that all obstructions in the flow path are removed and cavities in which sediment can collect are removed from the conduit wall. is not formed.

Although it is true that the flowmeter described in the above-mentioned U.S. patent does remove obstructions in the flow path and eliminates depressions in the conduit wall, this flowmeter does not allow the composition of the gas flowing through it to be The disadvantage is that if the composition differs from the one for which it is calibrated, it may become completely inaccurate or even cease to function. In fact, this is a common problem with most sonic flow meters. This is because the velocity of acoustic compression waves in a gas is a function of the chemical composition of the gas, and the accuracy of a typical sonic flowmeter depends on the meter's calibration for the particular gas whose flow rate or velocity is being measured. This is because that. And it is inconvenient to correct the calibration each time the flow meter is used for a different gas. For example, in cases where the composition of the gas in which the flowmeter is used fluctuates, such as in a pulmonary function analyzer, a sonic flowmeter cannot be used unless corrective feedback is performed from the gas analyzer to compensate for changes in gas composition. It becomes completely inaccurate.

It is therefore an object of the present invention to provide an accurate flow meter that is not affected by variations in the composition or temperature of the gas in use.

Yet another object of the invention is to provide means for automatically adjusting the operation of the flow meter as a function of dynamic changes in gas composition and temperature and generating sound velocity measurements that are correlated to the average molecular weight of the gas. Our purpose is to provide flowmeters.

A preferred embodiment of a sonic flowmeter according to the invention has two transducers mounted within the walls of the conduit, with no obstructions to the flow of gas and no recesses where particulate matter can collect. are not formed on the conduit wall. The transducer is connected to an electronic circuit that alternately switches one side into transmit mode and the other side into receive mode. The purpose is that the energy of the acoustic compression wave generated by the transmitting transducer is maximized at the receiving transducer, thereby compensating for velocity variations of the acoustic compression wave in the gas caused by changes in gas composition or temperature. Automatic circuit adjustment means are provided for adjusting the transmission frequency at.

The electronic circuit determines the phase difference between the acoustic compression wave signal generated by the transmitting transducer and the signal generated by the receiving transducer in response to the acoustic compression wave during each of two successive transmit and receive cycles. It is equipped with circuitry for measuring and storing. Circuit means are also provided for determining the difference between two successive phase differences, at least one of which is previously stored, in which case the symbol of said difference signal corresponds to the direction of gas flow. and the magnitude of the difference signal corresponds to the gas flow rate through the flow meter. Furthermore, a circuit is provided for generating a sum signal of two successive phase differences that is proportional to the speed of sound in the gas flowing through the flow meter.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring first to FIG. 1, a flow meter according to the present invention includes a transducer assembly 10 shown in longitudinal section with a central opening through which gas flows in the direction indicated by arrow 12. It includes a substantially cylindrical body having a cylindrical shape. Note that arrows 12 represent gas flow through transducer assembly 10 from left to right as viewed in FIG. However, gas can flow through assembly 10 in the opposite direction if desired.

Transducer assembly 10 is constructed generally according to the description found in Edward James Dowers, U.S. Pat. No. 4,003,252, entitled Acoustical Wave Flow Meter. The transducer assembly 10 of the present invention may additionally include a cylindrical casing (not shown in FIG. 1) made of metal or other suitable material surrounding the support member 14. The support member 14 itself is preferably made of polyurethane foam rubber or other material with good acoustic damping properties. Two annular notches 16 and 18 are formed in the inner wall of support member 14 and spaced apart from each other along a fluid flow path indicated by arrow 12. Two additional annular cutouts 20 and 2 are provided at opposite ends of the support member 14.
2 is provided.

A cylindrical transducer 24 and 26, respectively, is disposed within each annular cutout 16 and 18 and in contact with the surface thereof, and each of the transducers 24 and 26 has a cylindrical shape extending therethrough. The cylindrical bore is substantially coextensive with a cylindrical bore 28 extending between the annular notches in the support member 14.

It should be noted that suitable modifications may be made to the remainder of the transducer assembly 10 to ensure that the centrally located through-hole is not obstructed and that the hole walls are free of indentations in which particulate matter may collect, e.g. It is also possible to use other forms of transducers, such as transducers.

A terminal ring 30 and 32 is disposed within each annular cutout 20 and 22, respectively. These terminal rings are preferably constructed from a sound absorbing material such as a polyurethane sound damping foam such as "Y-370 Vibration Damping Tape" manufactured by 3M Corp. However, similar sound-absorbing materials could be used for the terminal rings 30 and 32. Terminal rings 30 and 32 each have a cylindrical bore in substantially coextensive relationship with an adjacent cylindrical bore 28 of support member 14 . Therefore arrow 12
As shown, the fluid flow path through the transducer assembly 10 has substantially continuous walls so that fluid flowing therethrough does not encounter bumps or depressions.

Transducers 24 and 26 may be comprised of any of a number of conventional devices capable of operating to generate acoustic compression waves in the gas flowing through assembly 10 in a radial or hoop mode. I can do it. Examples of suitable materials for transducers 24 and 26 include cylindrical bodies made of polyvinyldene fluoride or other highly polymeric organic piezoelectric materials, barium titanate, zircon lead titanate, or other materials. Mention may be made of ceramic type transducers made from extremely polycrystalline ferroelectric magnetic materials, as well as quartz tourmaline and other equivalent electromechanical devices known to those skilled in the art.

The inner and outer surfaces of transducers 24 and 26 have conductive coatings that constitute electrical drive electrodes. The conductive coatings on the inner surfaces of transducers 24 and 26 are connected via wires 34 and 36, respectively, to externally located crystal drive/receive circuits 38 and 40. The conductive coatings on the outer surfaces of transducers 24 and 26 are connected to crystal drive/receive circuits 38 and 40 via wires 42 and 44, respectively. Electrical connection wire pairs 34, 42 and 36, 44 for transducers 24 and 26, respectively, are routed through openings 46 and 48 that communicate from outside of assembly 10 into annular cutouts 16 and 18 of the transducers. There is.

The operation of the above-described transducer assembly 10 and its associated electronic circuitry is essentially the same as that disclosed in the above-mentioned U.S. patent, the contents of which are hereby incorporated by reference. be used for. Basically, the transducer assembly is connected to an external source of fluid whose flow rate is to be measured using a flexible hose or the like. Although the fluid itself may be a gas or a liquid, the presently described embodiments of the invention flow through transducer assembly 10 in the axial direction indicated by arrow 12 or in the opposite direction. It is designed for gas flow measurements. A control circuit 50 is coupled to transducer drive/receive circuits 38 and 40 via lines 52 and 54, respectively. The control circuit 50 causes one of the transducer drive/receiver circuits 38 or 40 to transmit electrical signals to the coupled cylindrical transducers 24 and 26, respectively, and the other drive/receiver circuit 40.
or 38 is operative to condition the signal from the coupled transducer 26 or 24 to be received. Transducer 24 or 26, which receives an electrical signal from one of the drive/receive circuits as previously described, generates an acoustic compression wave in the fluid in response. generating an electrical signal in response to an acoustic compression wave generated in the other transducer or fluid simultaneously coupled to the other drive/receiver circuit 38 or 40; detected by the circuit.

The acoustic compression wave generated by one of the transducers 24 or 26 takes a finite amount of time to propagate from the transmitting transducer to the receiving transducer. This propagation time depends on the direction and velocity of the fluid flowing through the transducer as well as the speed of sound within the fluid flowing within the transducer 10. These relationships are discussed in detail in the above-mentioned US patent specifications.

Each transducer 24 and 26 described above may be replaced by a pair of transducers attached to assembly 10 in a similar manner. One transducer of this pair of transducers is specifically used for transmitting or generating an acoustic compression wave, and the other is a receiving transducer, generating a receive signal in response to an acoustic compression wave in the gas stream. Used as a converter.

Transducer assembly 10 and circuitry coupled thereto operate in the following manner. Control circuit 50 initially controls one transducer, either transducer 24 or 26.
to generate an acoustic compression wave in the fluid and simultaneously adjust the other transducer, either 26 or 24, to receive the acoustic compression wave from the first transducer. This operating mode is the first transmission/reception cycle. The transmission signal is simultaneously transmitted from the control circuit 50 to the line 52.
or one drive/receiver circuit 38 via 54
or 40 and via line 56 to phase detector 58 . Receiving converter 24 or 26
The received signal from is provided by either transducer drive/receive circuit 38 or 40 via lines 60 or 62, respectively, to phase detector 58. Phase detector 58 responds to the transmitted and received signals to generate a signal on line 64 indicating the phase difference between the transmitted and received signals. This signal or information is coupled via line 64 to a phase adder/subtractor 66. The phase adder/subtractor 66 includes storage means for temporarily storing the phase difference received from the phase detector 58.

Control circuit 50 then switches the roles of transducers 24 and 26. That is, the other transducer 24 or 26 is switched to transmit mode to generate an acoustic compression wave in the fluid and the first transducer 24 or 26 is switched to receive mode. This mode of operation is the second transmit/receive cycle. Phase detector 5
8 detects the phase difference between the transmitted signal and the received signal during a second transmission/reception cycle, and this second phase difference is transmitted via line 64 to a phase adder/subtractor 66, the latter of which Temporarily stores the phase difference.

Once the two phase differences are stored as described above, the phase adder/subtractor 66 calculates the sum and difference between these two stored phase differences. The difference between the two stored phase differences as well as one correction amount as described in connection with FIG. 6 is applied to output line 68. This output line 68 provides a signal representative of the flow rate or flow rate through the transducer assembly 10 by calibrating the flow meter of the present invention accordingly. Additionally, the algebraic sign of the difference between the two phase differences calculated by phase detector 58 indicates the direction of gas flow through transducer assembly 10, where a positive sign indicates the direction of gas flow through assembly 10. Represents any one direction of fluid flow; a negative symbol represents the opposite direction.

The sum of the two phase differences calculated by phase adder/subtractor 66 is provided to output line 70. The magnitude of this output line 70 signal is the magnitude of the assembly 10 compared to the sound velocity in the reference gas used for calibration.
is proportional to the speed of sound in the gas. The sum signal is also sent via line 72 to control circuit 50 for use as will be explained in more detail below. This sum signal is further used to modify the flow value signal on line 68. The value provided on output line 70 is a relative value and therefore the flowmeter according to the invention must be calibrated so that the magnitude of the signal on line 70 can be interpreted or evaluated.

As outlined above, a disadvantage of the flowmeter disclosed in the above-referenced U.S. patent is that it does not operate in an environment where the speed of sound in the gas passing through the transducer changes dynamically during its use. At the point. The inventors have discovered that cylindrical transducers operate by generating strong resonant echoes diametrically across the tube at one or more natural frequencies. For example, this relationship can be approximately expressed as 2.3λ=D. Here, λ is the sound wavelength in the fluid (cm), and D is the internal diameter of the tube (cm). The frequency at which a resonant echo occurs at diameter D is called the unique cavity resonant frequency of the 02 mode. Other useful frequencies at which resonant echoes occur are substantially 0.73λ,
Equal to 1.4λ, 3.2λ or 3.9λ. The drawbacks described above are therefore due to the fact that the velocity of the acoustic compression wave in the gas passing through the flow sensing transducer varies as a function of gas composition. This causes the amplitude of the acoustic compression wave detected by the transducer of the assembly in receive mode to vary. This is because the inner diameter of the transducer is no longer equal to the characteristic wavelength, so that the amplitude or magnitude of the signal generated by the receiving transducer is significantly reduced. Therefore, it becomes more difficult to detect the received signal, and detection errors may occur in the detection of acoustic compression waves.
Alternatively, there is a possibility that detection may not be possible at all. Such drawbacks can be overcome by changing the internal diameter dimensions of the transducers within the assembly or alternatively by changing the frequency of the acoustic compression wave generated by the transmitting transducer. Since the transducer assembly itself is not suitable for adjusting the internal diameter of the transducer, it is clear that in an attempt to solve the above problem it is better to adjust the frequency of the acoustic compression wave generated by the transmitting transducer. . Therefore, the sum signal of the phase differences calculated by the phase adder/subtractor 66 is transmitted to the line 72.
is transmitted to the control circuit 50 via. As mentioned above, the signal on line 72 is related to the speed of sound in the gas through assembly 10. This signal is used in control circuit 50 to vary the frequency of the acoustic compression wave generated by the transmitting transducer during each transmitting and receiving cycle to maintain a constant wavelength, thereby maximizing the signal received by the receiving transducer. used for a purpose.

The inventors also discovered that after correcting the frequency to hold the wavelength constant, the apparent flow velocity must be multiplied by the speed of sound to obtain accurate velocity measurements that are not affected by variations in gas composition. discovered.

Experience has shown that flowmeters of the type described in the above-cited U.S. patent sometimes suffer from errors due to reflections of acoustic compression waves from other parts of the system to which the transducer is connected. receive. Such reflections are often due to acoustic compression waves reflecting from other fluid transfer devices coupled to the transducer assembly. Problems also arise when the transducer itself is used in a breath analyzer placed in close proximity to the mouth of the person whose breath is being analyzed.

The present invention solves the above-described reflection problem by providing terminal rings 30 and 32 located at opposite ends of assembly 10. These rings 30 and 32 are made of an acoustically attenuating material as previously described which acts to substantially reduce the amplitude of acoustic compression waves passing therethrough. actual ring 3
0 and 32, the amount of attenuation provided thereby is sufficient to allow one end of the assembly 10 to be placed in close proximity to the mouth of the individual whose breathing is being analyzed. Even if inserted, the above-mentioned problems caused by acoustic reflection are essentially solved.
The damping provided by rings 30 and 32 also satisfactorily solves the problems associated with reflections, such as those described above, that occur when assembly 10 is coupled to a fluid transport system.

The above discussion in connection with FIG. 1 generally describes the circuit of the present invention and its operation. The circuits of FIGS. 2 and 4 to 6 show actual embodiments of the present invention for use in a pulmonary function testing device. However, as will be apparent to those skilled in the art, various modifications and changes may be made to this specific example, and circuit elements may be modified to optimize the circuit for the purpose of applying the invention to other applications. It goes without saying that it could be done.

The circuit of FIG. 2 includes a pulse generator for generating control pulses for operating the circuits shown in FIGS. 4-6. In contrast, FIG. 3 is a pulse diaphragm showing the pulse trains generated from the various outputs of the circuit of FIG. In summary, the circuit of Figure 2 comprises an oscillator circuit, which may be a "CD4047" type integrated circuit, and which includes a 121kHz resistor to control the output frequency, which may be, for example, 400Hz. and a 4700pF capacitor connected. Because two series-connected JK flip-flops, each forming one half of the CD4027 integrated circuit, generate timing pulses at a slower rate than those generated by the CD4047 oscillator integrated circuit. It is used in The signals produced by the oscillator and flip-flop are combined by the AND gate and NAND gate of FIG. 2, thereby producing a pulse train as shown in FIG. The pulse diagram of output Q ₀ is not shown in FIG. This output pulse Q ₀
is a rectangular wave having a frequency twice that of Q ₁ and the positive leading edge of the pulse Q ₀ occurs at the same time as the positive leading edge of the output pulse Q ₁ of "CD4047".

Referring next to Figure 5, the integrated circuit "CD4046" has a voltage controlled oscillator (VCO) that generates a square wave signal at output pin 4, the frequency of which is connected in series between pin 11 and ground. and a voltage applied to pin 9. The voltage at pin 9 is approximately +7.5V
For the particular resistor shown in FIG. 5, the frequency of the square wave output at pin 4 of the voltage controlled oscillator is nominally 51 kHz. When the voltage present at input pin 9 changes, it causes the frequency of the voltage controlled oscillator to transition. The circuit of FIG. 5 causes the frequency of the VCO, or voltage controlled oscillator, to respond dynamically to variations in the acoustic velocity within the gas, as will be explained in more detail below.

The square wave signal from the voltage controlled oscillator available on pin 4 is passed through line 100 to pin 3 of circuit CD4046.
connected to. This circuit internally uses a phase detector (φ
DET). The square wave signal is also connected via line 102 to a NAND gate whose output is connected to an operational amplifier.
Connected to LM318 and arithmetic multiplier XR2208. The function of these circuits is to generate at circuit point 104 a sinusoidal signal having the same frequency as the square wave signal appearing on line 102. However, as will be appreciated by those skilled in the art, the circuit between line 102 and circuit point 104 may be comprised of any of a number of circuits known for converting square wave signals to sinusoidal signals. It goes without saying that equivalent circuits other than those described above may be used.

There is a circuit between circuit point 104 and output terminal AC.
Three operational amplifiers consisting of LM318 and 8043C are arranged. Operational amplifier LM318 is at circuit point 1
This is for amplifying the sine wave at 04. The two operational amplifiers 8043C are for adjusting the phase of the signal appearing at the output terminal AC, and the phase of the signal at the output terminal AC is adjusted by the adjustment resistor 10.
6 and 108, it can be adjusted approximately 360 degrees. These resistors are adjusted during flow meter calibration and are preferably adjusted so that the signal at pin 9 of circuit CD4046 is +7.5V when there is no air flow through transducer assembly 10 (FIG. 1). It is preferable to do so. Next, a mechanism for varying the voltage at pin 9 by adjusting the phase of the signal at the output terminal AC will be explained.

The circuit of FIG. 4 consists of converter drive/receiver circuits, and these circuits are shown in
and 26 are explained.
The circuit of FIG. 4 is divided into a drive portion, seen to the left of dashed line 110, and a receiver portion, excluding transducers 24 and 26, seen to the right of dashed line 110.

The sinusoidal signal from the circuit of FIG. 5 is connected to input terminal AC of FIG. 4 and from there to two converter drive circuits. The first drive circuit consists of Q5 and the second drive circuit has Q6. These transistors Q5 and Q6 pass the sinusoidal signal from the input terminal AC to the converter 24 or 26 coupled thereto, thereby placing the converter in a transmit mode. The gate signal is generated by a circuit including transistor pairs Q1, Q3 and Q2, Q4 and the circuit of FIG. 2, with the gate signal appearing at terminals X and Y. The gating signals at terminals X and Y appear at different times and alternate as shown in FIG. 3, so that transducers 24 and 26 are alternately switched to the transmit mode.

Directly connected to the converters 24 and 26 are receiver circuits 116 and 118, respectively, which are connected directly to the converters 24 and 26 depending on whether their respective input shorting transistors Q7 or Q8 are in the OFF or ON state. Depends on converter 2
4 or 26 or not. For example, transistor Q
7 is controlled by gate pulse signal Q ₃ to ground line 112 when signal Q ₃ is positive. Similarly, transistor Q8 receives the gate signal
Whenever ₃ is positive, line 114 is grounded. As is clear from the pulse waveform diagram in Figure 3,
When X is positive, Q ₃ is positive, so receiver 116 is inactive when converter 24 is in transmit mode and receiving a signal from input terminal AC. Similarly, receiver 118 does not operate when converter 26 is in transmit mode since ₃ is positive. In this way a given transducer 24 or 26
Whenever the is in transmit mode, the receiver circuitry 116 or 118 coupled thereto is inoperative. However, when one transducer is in transmit mode, the receive circuit 116 or 118 coupled to the other transducer 24 or 26 is enabled. This is because the corresponding gate signal Q ₃ or ₃ is at ground potential. For example, during a first transmit-receive cycle, converter 24 is in transmit mode and the input terminal
Receiving the signal from AC, transistor Q7
Switched on by Q ₃ to isolate receiver 116 through ground 112 , receiver circuit 118 is operatively coupled to transducer 26 . This is because transistor Q8, whose gate signal ₃ was at ground potential, has been turned off. At the same time, the gate signal Y is at ground potential, i.e., earth potential, so that the signal appearing at the input terminal AC is transmitted to the transistor Q6.
is prevented from being coupled to transducer 26 via. A second transmit-receive cycle occurs when the converter 26 receives a signal from the input terminal AC _, transistor Q7 is switched off by the signal _Q3 , transistor Q8 is switched on by the gate signal Y becomes positive and gate signal X
becomes the ground potential. Transducer 26 is thus in transmit mode, receive circuit 116 is active, and receive circuit 118 is inactive.

A receiver circuit 116 coupled to converter 24 includes two operational amplifiers 120 and 12 connected in series.
2, which operates when transistor Q7 is not turned on, amplifies the signal appearing on input line 112. The amplified signal appears at pin 6 of operational amplifier 122. This pin 6 is connected to the inverting input of the comparison circuit 124. Comparator circuit 124 is enabled whenever gate signal A is a logic "0", thereby causing an output signal to appear at pin 7.

The output signal at pin 7 is at a positive potential (approximately +
15V) and 0 volts when the input signal at pin 3 is at a positive potential. In this manner, comparator 124 converts a sine wave input to a square wave output.
Note that the comparison circuit 126 does not operate when the comparison circuit 124 operates, and operates when the comparison circuit 124 does not operate.

Receiver 118 has two series connected operational amplifiers 130 and 132 which amplify the signal appearing on input line 114;
The amplified signal is sent to output pin 6 of operational amplifier 132.
supply to. The output signal at this pin of amplifier 132 is applied to the inverting input of comparator circuit 126, and circuit 126 is enabled whenever gate signal B is logic "0". The output at pin 7 of comparator circuit 126 is a square wave of approximately +15V voltage whenever the input signal at pin 3 is at a negative potential, and is at approximately zero potential when the input at pin 3 is at a positive potential.
Since gate signals A and B occur at different times, the operation of one comparison circuit 124 or 126 does not affect the operation of another comparison circuit 126 or 124.

Thus, comparator circuits 124 and 126 operate independently and the combined converter 24 or 26 operates independently whenever the converter is in receive mode and the required gating signal is applied to activate the receive circuit 116 or 118. A rectangular wave signal is generated at each output terminal from a sine wave signal generated at the output terminal. The output pin of the comparator circuit is coupled to terminal SIG, so
The signal appearing on SIG is output to comparators 124 and 126.
represents the logical product of the signals generated at the output terminal of .

The outputs from receiving circuits 116 and 118 are the fourth
The input terminal of the response in Figure 5 via the terminal SIG in Figure
SIG and is transmitted to pin 14 of the integrated circuit CD4046 which is internally connected to the phase detection circuit. The phase detector itself operates functionally like an exclusive-OR circuit, with its output internally connected to pin 2 of the integrated circuit CD4046, with only one input of the phase detector being a logic "1". always generates a logic "1" output level. The signal appearing at pin 2 of the integrated circuit CD4046 is therefore a pulse width modulated square wave signal, the width of each pulse being equal to the transmitted signal, i.e. line 1.
00 signal and the received signal, ie the signal appearing at pin 14 of the integrated circuit CD4046.

During normal operation of a flow meter according to the invention, if the composition of the gas passing through the transducer assembly 10 (FIG. 1) has changed since the time of meter calibration, the phase of the signal appearing at input terminal SIG, FIG. will be different from the phase that appears at the input terminals when the circuit is calibrated.
Therefore, the output of the phase detector is also different, so that the voltage across the low-pass filter capacitor consisting of a 1 MΩ resistor and a 1 μF capacitor connected to the output of operational amplifier 156 is the same as the voltage at which the flowmeter was calibrated. On the other hand, it varies in the manner described below. The variation in the voltage present on this 1 μF capacitor causes the voltage at pin 9 of the integrated circuit CD4046 to vary, which in turn causes the frequency of the signal generated by the voltage controlled oscillator to vary. The device is designed so that the phase difference between the transmitted and received signals is 1
Continue adjusting the frequency of the voltage controlled oscillator until it no longer causes voltage fluctuations on the μF capacitor.

A very important feature of the present invention over the prior art is that the operating frequency can be varied in response to changes in gas composition. It has been found that the transducer of the present invention provides maximum energy transfer from the transmitting transducer to the receiving transducer when operated at a natural frequency that depends on the internal diameter of the transducer. Therefore, if the gas in the transducer assembly when calibrating the flow meter is air, the frequency of the voltage controlled oscillator will generate an acoustic compression wave in the direction of the transducer diameter with a fractional value of a half wavelength corresponding to the natural frequency. Corresponds to frequencies occurring in the air. If the density of the gas subsequently changes, the velocity of the acoustic compression wave will also change, and therefore a different phase difference will be detected by the phase detector. This causes the frequency of the acoustic compression wave generated by the voltage controlled oscillator to be varied in a manner to be detailed below, such that the new frequency is such that the diameter of each transducer is now at the new frequency within the gas within the transducer assembly. This corresponds to the frequency which is the number of eigenvalues of a half wavelength. In this way maximum energy transfer is maintained between the transmitting and receiving converters.

The pulse width modulated signal appearing at the output of the phase detector is connected to one of the two inputs of AND gate 140.
applied to. The output signal of the AND gate 140 is coupled to an integrator circuit indicated generally by the reference numeral 142. The second input to AND gate 140 is gate signal A or gate signal B.
The integrability enable signal IE is always a logic "1" when either one of the IE is a logic "0". This logical condition states that the output of the phase detector corresponds to the phase difference between the transmitted and received signals. Accordingly, a pulse width modulated signal is provided through AND gate 140 when AND gate 140 is enabled by integration enable signal IE. The output signal of the integrator circuit 142 appears at pin 6 of the operational amplifier LM318 and represents the integrated level during the integrable period, the final level value of which is the signal transmitted by one converter and the other. is related to the phase difference between the signal received at the transducer of 1 and is coupled via line 144 to input pin 5 of two different sample-and-hold circuits 146 and 148.
Sample and hold circuit 146 or 1
48 samples the voltage appearing at pin 5 when a gate signal is applied to gate pin 6 as a respective control input. The sampled voltage appears at pin 11 and has the same level as the voltage that appeared at pin 5 when the gate signal was present. Sample and hold circuit 146
The voltage at pin 11 of and 148 remains unchanged between pin 6 gate pulses. The sample-and-hold circuit 146 is switched to the sampling mode whenever the signal appearing at the input terminal u becomes a logic "1". Similarly, sample-and-hold circuit 148 is switched to sampling mode whenever input terminal D is a logic "1".

During a sampling operation in both sample-and-hold circuits 146 and 148, an integrator reset signal appears at input terminal IR, switching on transistor Q12 and connecting it between pins 6 and 2 of the operational amplifier in the integrator circuit. short-circuit the capacitor. As a result, the integrator is reset and its output voltage becomes zero.

In operation, sample and hold circuits 146 and 148 operate to store or accumulate a DC voltage representing the phase difference between the transmitted signal at one converter and the received signal at the other converter. In the case of a sample-and-hold circuit 146 switched by a gate signal at input terminal u, the signal sent by the downstream converter 26 and in response the signal sent by the upstream converter 2
A voltage (which can be arbitrarily defined) is accumulated that corresponds to the phase difference between the signal generated at 4 and the so-called upstream phase difference. Sample-and-hold circuit 148, on the other hand, determines the phase difference between the signal transmitted by upstream transducer 24 in response to gate signal D and the signal generated by downstream transducer 26 in response; That is, a signal representing a so-called downstream phase difference is stored.

The output signals of sample and hold circuits 146 and 148 are respectively connected to the inverting and non-inverting inputs of operational amplifier 150, respectively. The operational amplifier 150 is configured to generate a voltage at its output pin 14 equal to the difference (φ _D −φ _U ) between the voltage applied to the non-inverting input terminal and the voltage applied to the inverting input terminal. . As previously stated, this difference represents the unmodified gas flow rate or flow rate through the transducer assembly 10 (FIG. 1). To properly calibrate the flowmeter, the non-inverting input terminal of the operational amplifier has an offset adjustment circuit. This circuit, indicated generally by the reference numeral 152, adjusts the voltage at the non-inverting input terminal such that when the flow rate through the transducer assembly 10 is zero, the voltage appearing at the output pin 14 is zero. do the work. This off-set amount adjustment circuit 152
is the amount of off-set of the various circuits, especially the off-set of sample-and-hold circuits 146 and 148.
It works to compensate for the set amount.

The outputs of sample and hold circuits 146 and 148 are each connected to input pin 5 of another sample and hold circuit 154 via a 20 kHz resistor. The outputs of sample-and-hold circuits 146 and 148 are connected in the manner shown, so that the voltage at pin 5 of sample-and-hold circuit 154 is between two sample-and-hold circuits 146.
and 1/2 of the sum of the two phase differences stored in 148. This sum is stored or accumulated within sample and hold circuit 154 in response to the summation signal received at input terminal 5. The output of the sample and hold circuit 154 is connected to another operational amplifier 156 which generates a DC voltage at the output pin 8. This DC voltage is the voltage related to the sum of the phase differences stored in sample and hold circuits 146 and 148 when the gate signal appears. This voltage (φ _D +φ _U ) at output pin 8 of amplifier 156 as previously described provides a relative indication of the speed of sound within the gas within transducer assembly 10.

The voltage appearing at pin 8 of amplifier 156 (φ _D +
φ _U ) is fed back to a low pass filter with a 1 MΩ resistor and a 1 μF capacitor. This 1μF
The voltage across the capacitor is supplied to pin 9 of circuit CD4046. Note that the circuit CD4046 has an internal VCO.
That is, it is connected to a voltage controlled oscillator and adjusts its operating frequency. Therefore, the frequency of the voltage controlled oscillator varies as the speed of sound within the gas within transducer 10 changes.

The circuitry of FIGS. 4 and 5 cooperates with the circuitry shown in FIG. generates an output signal relating to the speed of sound within the gas within transducer assembly 10. As mentioned above, it is assumed that converter 24 is an upstream converter and converter 26 is a downstream converter, so when the voltage appearing at pin 14 of amplifier 150 is negative, this negative voltage is an upstream converter. It is shown that fluid is actually flowing through the transducer assembly in the direction from the vessel 24 to the downstream transducer 26. Additionally, the magnitude of the voltage appearing at pin 14 of amplifier 150, which is related to the flow rate or flow rate of fluid through assembly 10, can be modified or corrected by the circuit of FIG. On the other hand, if the voltage at pin 14 of amplifier 150 is positive, this indicates that fluid is flowing through assembly 10 in a direction from downstream transducer 26 to upstream transducer 24. Also, the magnitude of the voltage appearing at pin 14 of amplifier 150 corresponds to the unmodified flow rate in converter assembly 10.

However, in the case of the circuit shown in FIG. 5, the output signal of amplifier 156 is merely an indication of the speed of sound in the gas. To determine whether the speed is greater or less than the speed calibrated to the instrument, the amplitude must be recorded at the time the calibration is made and the current reading compared to the previously recorded value. . However, this circuit can be easily modified so that the output voltage is equal to zero whenever calibration fluid is present in the transducer assembly. Therefore, as the speed of sound in the fluid changes, the output voltage becomes positive or negative, and the sign of the voltage indicates whether the actual velocity has increased or decreased relative to the velocity of the fluid at which the instrument was calibrated. handle. The magnitude of the output voltage also corresponds to the relative difference between the speed of sound in the gas currently flowing through the transducer and the speed of sound in the gas of the transducer assembly at the time of calibration. Further circuitry is required to utilize this output voltage to indicate relative sound speed. This is because the output signal of amplifier 156 is the voltage controlled oscillator VCO.
This is because it is used as an error voltage for frequency adjustment and as an input signal to the circuit of FIG.

Alternative configurations may be used to adjust the output voltage to be equal to "1", for example, when air is present within the transducer assembly. Therefore, whenever the speed of sound in the gas flowing through the transducer assembly changes, the magnitude of the output voltage will also change to correspond to the speed of sound in the gas relative to the speed of sound in air.

The circuit of FIG. 6 includes circuitry for receiving an unmodified flow rate signal from the output signal of amplifier 150 of FIG. 5 and generating a modified flow rate output indication signal. It has been found that the output signal of amplifier 150 has an error proportional to f ₁ /f ₂ . Here f ₁ is the fifth
is the initial calibration frequency of the VCO shown in the figure and f ₂
is the frequency of the VCO when gases with different sound velocities are in the transducer. In the circuit of FIG. 6, the uncorrected flow rate output signal of amplifier 150 is multiplied by f ₂ /f ₁ to generate a modified flow rate signal at pin 7 of amplifier LM324B of FIG.

Appears at the output side of amplifier 156 in FIG.
The VCO error voltage is proportional to frequency and is used to set a correction factor to modify the flow rate or flow rate. Operational amplifier LM308 in Figure 6
acts as a signal conditioning circuit and receives the VCO error voltage (φ _D +φ _U ). By adjusting the zero adjustment resistor connected to amplifier LM308, pin 6 is set to a 0 volt output when the error voltage is at the nominal level (+7.5V). The signal conditioning circuit generates an output voltage of 1.0V for every ±5kHz deviation.

The output signal at pin 6 of LM304 is sent to amplifier LM3.
24A and a duty cycle modulator consisting of LM311 and the circuitry connected thereto. When the VCO is operating at the calibrated frequency, the LM308 output signal is zero and the LM324
The duty cycle adjustment resistor connected to A is adjusted to a value of 50%, where FET switch Q
14 and Q15 will be off for 1/2 period,
It is on for 1/2 period. As a result amplifier LM3
24B has a gain of 1, and amplifier 150 of FIG.
The uncorrected flow rate from the LM324B pin 7 represents the flow rate or rate of gas through the transducer without any correction or modification.

When the operating frequency of the VCO changes, the LM in Figure 6
The voltage appearing at pin 6 of 308 becomes positive for decreasing frequency and negative for increasing frequency. This voltage controls the duty cycle generator to vary the duty cycle. Amplifier LM324B with duty cycle variation
The gain of LM varies as the VCO frequency varies, so that the unmodified flow rate signal from the circuit of Figure 5 is LM
324B, the output signal of which will be proportional to the flow rate or flow rate through the transducer.

In the above discussion of acoustic wave flowmeters, particular emphasis is placed on the preferred electronic circuitry that cooperates with the transducer assembly to determine not only the flow rate and its direction, but also the relative speed of sound within the flowing gas. I explained. It will be understood from this description that the invention is particularly suitable for measuring flow direction, flow rate and sound velocity in gases, however the device of the invention is also suitable for measuring flow direction, flow direction and sound velocity in liquids. It can be used to measure the speed of sound as well, and variations in the values of certain circuit elements may also be required to optimize the performance of the flowmeter; Needless to say, it can also be used to measure the flow direction, flow rate, and sound velocity of other objects. Additionally, other modifications may be made to the flowmeter by those skilled in the art without departing from the spirit and scope of the invention. For example, instead of a phase detector and a phase sum and phase difference calculator, other equivalent means may be used to calculate a quantity proportional to or equal to the velocity of the acoustic compression wave traveling from the transmitting transducer to the receiving transducer. It is possible. Each calculated velocity has two components. One is the velocity of the fluid flow and the other component is the velocity of the acoustic compression wave in the absence of flow in the fluid. Such an equivalent speed calculator has means for determining the time difference between the onset of generation of the acoustic compression wave in the transmitting transducer and the time at which the receiving transducer generates the received signal in response to the acoustic compression wave. I could do that. Each time difference thus calculated is also proportional to the speed of the acoustic compression wave traveling from the transmitting transducer to the receiving transducer.

Further advantages of the flow meters described above can be obtained by combining or even rearranging the signals representing different parameters. For example, changes in gas composition that cause changes in the molecular weight of the gas mixture also cause changes in the speed of sound. It is thus possible to measure the transition from a gas mixture with an average molecular weight M _A to a gas mixture with an average molecular weight M _B as well as the part of the gas mixture A mixed with the gas mixture B. Such a method can be carried out, for example, using a gas flow meter to proportionally measure the amount of carbon dioxide in the exhaled mixture compared to the carbon dioxide in the inspired mixture.

The speed of sound is given by the following equation.

In the above formula, γ = ratio of specific heat at constant pressure to specific heat at constant volume K = Boltzmann constant, 1.38 x 10 ^-23 /℃ T = absolute temperature M = molecular mass in gas (Kg) Therefore, it is clear to those skilled in the art As such, molecular weight is proportional to c ^-2 and, assuming other variables are constant, an electrical output can be generated that is proportional to the change in molecular weight. Obviously, this simple case can be extended to combine changes in specific heat and temperature with variations in molecular weight to identify gas mixture A by one set of conditions and gas mixture B by another set of conditions. can be identified.

Furthermore, if the pressure or density fluctuates very significantly, the flow rate may be corrected to approximately standard conditions or true mass by combining the pressure measurements with the parameters obtained from the flow meter described above. I can do it. In this case, the flow rate is given by the following equation.

M〓=V〓mp/RT (Kg/sec) In the above formula, p=pressure (Newtons/m ² ) Therefore, from the above equation regarding the speed of sound c, M〓=V〓pr/c ^2As is clear to those skilled in the art A pressure transducer can be connected to measure the absolute pressure within the flowmeter, and also the output signal from the pressure transducer is multiplied by the flow rate from the flowmeter and the signal obtained from the flowmeter is also the sonic velocity. An approximation to the true flow rate can be obtained by dividing by the square of c and a suitable constant.

For a fixed value of γ, certain changes in the gas mixture will lead to errors in the measurement; however, in many cases such variations in γ are not significant. It will be obvious to those skilled in the art to use the parameters described above to generate a flow signal reduced to standard temperature and pressure.

Although a flowmeter device has been described which is capable of accurately measuring flow rate or flow rate independent of composition, the method according to the invention can also be advantageously applied to other acoustic flowmeters, for example when the transducer is cylindrical or arc-shaped. Needless to say, the present invention can also be applied to flowmeters in which there are some kind of obstructions or depressions in the flow path. That is, the idea of the present invention can be advantageously applied to acoustic flowmeters in which errors occur due to variations in the speed of sound in a fluid.

Furthermore, as will be apparent to those skilled in the art, the sonic flowmeter described above achieves the primary objective of the present invention, namely to make the accuracy of the flowmeter relatively insensitive to variations in gas composition. . Furthermore, it will be apparent to those skilled in the art that various modifications can be made to the circuits described above to achieve similar operation without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

1 is a diagram schematically illustrating a flowmeter having a transducer assembly and the electronic circuitry used in connection therewith; FIG. 2 is a diagram for controlling the operation of the circuitry of FIGS. 4 and 5 provided in accordance with the present invention; FIG. 3 is a diagram of the timing pulses of the circuit of FIG. 2, and FIGS. 4 to 6 are detailed circuit diagrams of the timing pulse generator of the circuit of FIG. 1 is a detailed circuit diagram illustrating an embodiment of a flow meter circuit according to the present invention using pulses; FIG. 2, 3, 5, 6, 7, 9, 11, 14...pin,
10...Transducer assembly, 14...Support member, 16,1
8, 20, 22... Notch, 24, 26... Converter,
30, 32...Terminal ring, 34, 36, 42, 4
4... Wire, 46, 48... Aperture, 38, 40... Converter drive/reception circuit, 50... Control circuit, 58... Phase detector, 66... Phase adder/subtractor, 116, 1
18...Receiver, 124, 126...Comparison circuit, 14
0...AND gate, 142...Integrator circuit, 12
0, 122, 130, 132... operational amplifier, 14
6,148...Sample and hold circuit.

Claims (1)

[Scope of Claims] 1. A flow meter for measuring the flow of a fluid along a flow path, comprising means for forming a substantially cylindrical flow path defining a fluid flow; first and second substantially cylindrical transducers disposed and each having an inner diameter substantially equal to the diameter of said flow path; and a signal representative of a first transmit/receive cycle and a signal representative of a second transmit/receive cycle. means for alternately generating a first acoustic compression wave in the fluid during the first transmit/receive cycle, and means for generating a first acoustic compression wave in the fluid during the first transmit/receive cycle; and driving the first transducer to receive a first receive signal generated from the second transducer and generating a second acoustic compression wave in the fluid during the second transmit/receive cycle. means for providing a signal to the second transducer to generate a second acoustic compression wave and receive a second receive signal generated from the first transducer in response to the second acoustic compression wave; a first proportional indicator signal representative of the speed of an acoustic compression wave traveling from the first transducer to a second transducer in response to each of the first transducer drive signals and each of the first received signals; (first measurement means)
and a second signal representing the velocity of an acoustic compression wave traveling from the second transducer to the first transducer in response to each of the second transducer drive signals and each of the second receive signals. means for generating a proportional display signal (second measuring means) as the first and second measuring means, respectively, and the first proportional display signal generated by the first measuring means is transmitted and received by each of the first transmitting and receiving means. a first generated by said first converter during a cycle;
a first phase difference signal which is a phase difference between an acoustic compression wave of and said first received signal generated by said second transducer and generated by said second measuring means; A second proportionality indicating signal includes a second acoustic compression wave generated by the second transducer and a second acoustic compression wave generated by the first transducer during each of the second transmit/receive cycles. a second phase difference signal that is a phase difference between a received signal of the flow path and a second phase difference signal that is a phase difference between a received signal of is a function of flow direction and velocity, and the first
difference generating means responsive to the first and second measuring means to generate a difference having a magnitude equal to the difference between the phase difference of and the second phase difference;
The magnitude of the difference signal is directly related to the instantaneous fluid flow rate and the sign of the difference signal is representative of the direction of fluid flow along the flow path;
and means for generating a signal indicative of the instantaneous speed of sound in the fluid flowing along the flow path corresponding to the sum of the second proportional display signal; controlling the frequency of acoustic compression waves generated by both transducers in response to a signal indicating a preselected fixed wave length in the fluid diametrically of said transducers; 1. A flowmeter comprising means for maintaining an operating state at the time of acoustic resonance and maximizing the magnitude of a received signal. 2. The flow meter according to claim 1, comprising means for indicating the speed of sound in the fluid. 3 Each converter is made of polyvinylidene fluoride, barium titanate, zircon/lead titanate, crystal, tourmaline,
2. A flowmeter as claimed in claim 1 made from a material selected from the group consisting of high polymeric organic piezoelectric materials and polarized polycrystalline ferroelectric ceramic materials. 4 means coupled to each transducer are connected to the first and second
Claim 1 comprising a voltage controlled oscillator coupled to the first and second transducers respectively for generating an acoustic compression wave during a transmitting and receiving cycle of the
Flowmeter described in section.