JP2897630B2 - Volumetric meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic volume meter utilizing a change in resonance frequency of an acoustic resonator.

[0002]

2. Description of the Related Art A conventional volume meter is disclosed in
No. 4127. In such a volume meter, an acoustic tube is connected to a container to be measured and an auxiliary acoustic resonator is acoustically coupled to a Helmholtz resonator, or the acoustic tube is also used as an auxiliary acoustic resonator. In the acoustic system, the effect of the change in the resonance frequency caused by the change in temperature is corrected based on the ratio between the resonance frequency of the Helmholtz resonator and the resonance frequency of the auxiliary acoustic resonator to determine the volume of the container to be measured.

Here, the resonance frequency is measured using a PLL (phase synchronization) circuit, the PLL circuit is synchronized with the phase at the resonance point, and the resonance frequency is obtained from the oscillation frequency.

[0004]

However, in the conventional volume meter, two resonance frequencies are set independently of the frequency characteristics of the sound source. By the way, FIG.
Is a graph showing the frequency characteristics of the sound source, that is, FIG.
Is a graph showing the amplitude characteristics of the sound source, and FIG. 12B is a graph showing the phase characteristics of the sound source. Here, in the case of an ideal sound source, both the amplitude characteristic and the phase characteristic are flat in all frequency bands. However, in actuality, the sound source is affected by the presence of a mechanical resonance point of the sound source, and as shown in FIG. Amplitude for frequency f
H | and the phase ΔH are not constant. Therefore, P
When a resonance frequency is obtained using an LL circuit or the like, each resonance frequency does not change as theoretically, and as a result, a measurement error occurs.

This will be described in detail with reference to FIG. The ideal frequency characteristic at the resonance point of the Helmholtz resonator is
In the amplitude characteristic, a peak of the amplitude | H | appears as shown in FIG. 13A, and in the phase characteristic, the phase ΔH is inverted as shown in FIG. 13B. Therefore, temperature changes (eg, 10, 20, 30)
C.), the phase ΔH at the resonance point (●) is always φ ₁ even if the resonance frequency f ₁ changes.
When the phase characteristic of the circuit is the characteristic shown by the phase characteristic line 20,
Since the phase ΔH of the lock point R ₁ is always φ ₁ , an accurate resonance frequency f ₁ is always obtained. However, the frequency characteristic of the sound source actually used is not flat as shown in FIG.
The phase ΔH changes with respect to the frequency f, and especially near the resonance point of the sound source, the phase ΔH greatly changes. Since a sound source having such characteristics is input to the resonator, the phase characteristic of the transfer function (frequency characteristic) of the resonator (between the sound source and the microphone) is
As shown in FIG. 13 (c), becomes tilted characteristics not have characteristics or flat along the phase characteristic of the sound source, the phase ∠H always φ not _one resonance point (●), thus locking points of the PLL circuit R ₁ is the point marked with a circle in the figure. In other words, since the PLL circuit locks at a phase shifted from the original resonance point (●),
Becomes frequency oscillation frequency is deviated from the original resonance frequency f ₁ of the PLL circuit, the difference Delta] f ₁ and a difference Delta] f ₁ 'are different. The same is true for all other resonance points. Therefore, also for another resonance frequency f ₂ detected for temperature compensation, the oscillation frequency of the PLL circuit is shifted from the original resonance frequency f ₂ , and Δf ₂ , Δf
_{If 2} ′ is the same as the difference Δf ₁ , Δf ₁ ′ when the resonance frequency is f ₁ , the difference Δf ₂ is different from the difference Δf ₂ ′. Therefore, if the phase characteristics of the sound source near the _two resonance frequencies f ₁ and f ₂ change differently (slope), the rate of frequency change at each resonance point differs. That is, (Δf ₁ ′ / Δf ₁ ) ≠ (Δf ₂ ′ / Δ
f ₂ ). For this reason, the temperature compensation according to the theory is not performed, and a measurement error occurs.

The present invention has been made to solve the above-mentioned problem, and has as its object to provide a volume meter capable of accurately measuring the volume of a container to be measured.

[0007]

In order to achieve this object, according to the present invention, a transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube is detected. Calculating the resonance frequency of the Helmholtz resonator and the resonance frequency of the acoustic tube,
In a volume meter for calculating the volume of the container under measurement based on both resonance frequencies, a resonance point locus on a transfer function phase characteristic of the Helmholtz resonator with respect to temperature and a resonance point locus on a transfer function phase characteristic of the acoustic tube with respect to temperature Is stored in advance, and the two resonance frequencies are calculated from the intersection of the detected transfer function phase characteristic and the stored two resonance point trajectories.

A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube is detected, and a resonance frequency of the Helmholtz resonator and a resonance frequency of the acoustic tube are determined from the transfer function phase characteristic. And a second constant corresponding to a resonance point trajectory on the transfer function phase characteristic of the acoustic tube with respect to temperature and a first constant corresponding to a resonance point trajectory on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature. Is stored in advance, and the volume of the container to be measured is calculated based on the calculated resonance frequency of the Helmholtz resonator, the resonance frequency of the acoustic tube, the first constant, and the second constant.

A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube is detected, and a resonance frequency of the Helmholtz resonator and a resonance frequency of the acoustic tube are determined from the transfer function phase characteristic. Calculating a volume of the container to be measured based on both resonance frequencies, wherein a locus of resonance point on a transfer function phase characteristic of the Helmholtz resonator with respect to temperature, and a transfer function phase characteristic of the acoustic tube with respect to temperature. The shape of the acoustic tube is set so that the inclination with the resonance point locus above matches.

In addition, a transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container is detected, and the Helmholtz resonance is determined from the transfer function phase characteristic. The resonance frequency of the
Calculating the resonance frequency of the acoustic tube and the auxiliary container,
In the volume meter for calculating the volume of the container under measurement based on both resonance frequencies, the resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature and the transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to temperature Are stored in advance, and the two resonance frequencies are calculated from the intersection between the detected transfer function phase characteristic and the stored two resonance point trajectories.

Further, a transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container is detected, and the Helmholtz resonance is detected from the transfer function phase characteristic. The resonance frequency of the
Calculating the resonance frequency of the acoustic tube and the auxiliary container,
A first constant corresponding to a resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature and a second constant corresponding to a resonance point locus on the transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to temperature Is stored in advance,
The volume of the container under measurement is calculated based on the calculated resonance frequency of the Helmholtz resonator, the resonance frequencies of the acoustic tube and the auxiliary container, the first constant and the second constant.

A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container is detected, and the Helmholtz resonance is determined from the transfer function phase characteristic. The resonance frequency of the
Calculating the resonance frequency of the acoustic tube and the auxiliary container,
In a volume meter for calculating the volume of the container under measurement based on both resonance frequencies, a resonance point locus on a transfer function phase characteristic of the Helmholtz resonator with respect to temperature, and a transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to temperature are provided. The shape of the acoustic tube or the auxiliary container is set so that the inclination with the upper resonance point locus coincides.

[0013]

In the volume meter according to the present invention, the trajectory of the resonance point on the transfer function phase characteristic of the Helmholtz resonator with respect to the temperature and the resonance point trajectory of the transfer function phase characteristic of the acoustic tube with respect to the temperature are stored in advance and detected. Since the two resonance frequencies are calculated from the intersection of the transfer function phase characteristic and the stored two resonance point trajectories, even when the amount of phase change at both resonance frequencies is different from each other, the resonance point is always accurate. The frequency can be determined.

The first constant corresponding to the resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to the temperature and the second constant corresponding to the resonance point locus on the transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to the temperature. Is stored in advance, and the volume of the container to be measured is calculated based on the calculated resonance frequency of the Helmholtz resonator, the resonance frequency of the acoustic tube and the auxiliary container, and the first and second constants. Temperature compensation can be performed according to the frequency.

The shape of the acoustic tube is set so that the slope of the resonance point trajectory on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature matches the resonance point trajectory of the transfer function phase characteristic of the acoustic tube with respect to temperature. Therefore, the rate of change of the phase with respect to both resonance frequencies becomes equal.

Further, when the surroundings of the acoustic tube are covered with the auxiliary container, intrusion of disturbance can be prevented.

[0017]

FIG. 1 is a view showing a volume meter according to the present invention. As shown in the figure, a lid 3 is provided on a container 2 to be measured whose volume when empty is V, one end of an acoustic tube 1a having a length L and an internal sectional area S is connected to the lid 3, and a Helmholtz resonator is provided. It is configured. A sound source 4 is provided on the lid 3, and the sound source 4 acoustically drives air inside the Helmholtz resonator. The length of the acoustic tube 1 a is set so that the resonance frequency f ₁ of the Helmholtz resonator and the minimum resonance frequency f ₂ of the acoustic tube 1 a do not coincide with the resonance point of the sound source 4. Further, a microphone 5a is provided on the lid 3, a microphone 5b is provided on the acoustic tube 1a, and the microphones 5a and 5b detect a sound pressure inside the Helmholtz resonator. Further, microphone amplifiers 6a and 6b are connected to the microphones 5a and 5b, filters 7a and 7b having respective resonance frequency components as pass bands are connected to the microphone amplifiers 6a and 6b, and a phase comparator 8a is connected to the filters 7a and 7b. , 8b, loop filters 9a, 9b, voltage controlled oscillators (VCO) 10a, 10b
b, PLL circuits 15a and 15b are connected, and the adder / sound source amplifier 11 is connected to the PLL circuits 15a and 15b.
Drive. Then, the microphone amplifiers 6a, 6
b, filters 7a and 7b, PLL circuits 15a and 15b,
Frequency measuring means 19 by adder / sound source amplifier 11
Is configured. Further, an arithmetic unit 16 including a CPU 12, a setting switch 13, and an output device 14 is connected to the PLL circuits 15a and 15b.

In this volume meter, the microphone 5
Output signals a and 5b are amplified to appropriate levels by amplifiers 6a and 6b, respectively. Since the microphone 5a mainly detects the resonance frequency component of the Helmholtz resonator,
The filter 7a is set so that a frequency near this component is set as a pass band. Here, assuming that the sound speed is c, the resonance frequency f ₁ of the Helmholtz resonator is expressed by the following equation.

F ₁ = (c / 2π) √ (S / LV) (1) Similarly, since the microphone 5b mainly detects the resonance frequency of the acoustic tube 1a, the filter 7b is set accordingly. . The sound tube 1a is so open ends, the minimum resonance frequency f ₂ of the acoustic pipe 1a is expressed by the following equation.

F ₂ = c / 2L (2) Filters 7a and 7 having components of respective resonance frequencies f ₁ and f ₂
The output of b is input to the PLL circuits 15a and 15b, respectively. Here, PLL circuit 15a, 15b is set to lock (synchronization) with the phase phi ₁ at the resonance point of the Helmholtz resonator shown in Fig. That is, the PLL circuit 1
5a, since 15b locks (sync) at the intersection R ₁ and phase characteristic line 17a of the curves and the PLL circuit 15a representing a change of the transfer function phase ∠H, continuous PLL circuit 15a resonance frequency f ₁ of the Helmholtz resonator Oscillation. Similarly, the PLL circuit 15b locks at the phase φ ₂ (intersection R ₂ ) at the resonance point of the acoustic tube 1a shown in FIG. 3 and continuously oscillates at the resonance frequency f ₂ of the acoustic tube 1a. 2 and 3, the ranges 18a and 18b correspond to the PLL circuits 15a and 15b.
Is the lock range (synchronous holding range) of the PLL circuit 1
The lock range of 5a, 15b is the voltage controlled oscillator 10a,
It is set by adjusting 10b. The outputs of the voltage controlled oscillators 10a and 10b are input to the sound source 4 via the adder / sound source amplifier 11, and output from the sound source 4 at each of the resonance frequencies f ₁ and f _2.
And at the same time, the outputs of the voltage controlled oscillators 10a and 10b are input to the CPU 12, and when the resonance frequencies f ₁ and f ₂ are obtained by the CPU 12, the volume V can be obtained by the following equation.

V = (LS / π ² ) · (f ₂ / f ₁ ) ² (3) However, Equation (3) is a theoretical equation under ideal conditions, and is actually obtained experimentally. Using the constants a and b, the volume V is obtained by the following equation.

V = a (f ₂ / f ₁ ) ² + b (4) These constants a and b may be obtained experimentally by calibration using a container whose volume and dimensions are known. And CP
U12 is constants a and b preset by the setting switch 13.
Is used to calculate the volume V from equation (4), and the calculation result is output to the output device 14. The equation for calculating the volume V is
It is not limited to (4), and other approximate expressions may be used.

Next, a method of setting the length of the acoustic tube 1a so that the resonance frequency f ₁ of the Helmholtz resonator and the minimum resonance frequency f ₂ of the acoustic tube 1a do not coincide with the resonance point of the sound source 4 will be described. First, the resonance frequencies f ₁ and f ₂ are
It is obtained in advance from equations (1) and (2). Next, a temperature change experiment was performed in advance using a thermostatic chamber or the like, and the transfer function phase characteristics of the Helmholtz resonator as shown in FIG. 4 were measured.
A frequency band in which the inclination of the resonance point locus lines 21a and 21b indicating the locus of the resonance point (●) near the resonance frequencies f ₁ and f ₂ is found. Next, if a frequency band as described above is found, the value of that frequency is used (1),
The approximate length L of the acoustic tube 1a is determined by back calculation from the equation (2). At this time, the structure of the acoustic tube 1a is, for example, a structure in which the adjusting tube 30 is attached to the acoustic tube 1 as shown in FIG. 5, and several kinds of adjusting tubes 30 having different lengths are prepared. Changing and adjusting the length L of the acoustic tube 1a becomes easy.

In the volume meter shown in FIG.
Since the length of a is set so that the resonance frequency f ₁ of the Helmholtz resonator, the minimum resonance frequency f ₂ of the acoustic pipe 1a does not coincide with the resonance point of the sound source 4, the resonance frequency f _1,
The rate of change of the phase ΔH with respect to f ₂ is equal ((Δf ₁ ′
/ Δf ₁ ) = (Δf ₂ ′ / Δf ₂ )), so that the volume V of the container 2 to be measured can be accurately measured.

In the volume meter shown in FIG. 1, since the temperature compensation is performed using the resonance of the acoustic tube 1a, the resonance frequencies f ₁ and f ₂ are adjusted to the optimum frequencies by changing the length L of the acoustic tube 1a. Although the band is set, for example, the PLL circuits 15a and 15b
By changing the phase characteristics of the filters 7a and 7b, or by changing the cutoff frequencies of the filters 7a and 7b, the phase characteristics of the filters are electrically changed, and the resonance frequencies f ₁ and f ₂ are changed by the sound source. 4 may be set so as not to coincide with the resonance point.

FIG. 6 is a diagram showing another volume meter according to the present invention. As shown, for example, a sine wave synthesis wave, oscillator 24 for oscillating a flat signal E _s of the frequency characteristics, such as white noise is connected to the sound source 4, FFT analyzer 23 via the sound source amplifier 25. In addition, microphone 5
a and 5b are connected to a microphone amplifier 22 for amplifying the microphone output signals _Em1 and _Em2 to an appropriate level,
The microphone amplifier 22 is connected to the FFT analyzer 23. The CPU 12 controls operations of the FFT analyzer 23, the oscillator 24, and the memory 27, and performs a predetermined operation using the measured value and a constant set by the setting switch 13. That is, the CPU 12 fetches the data of the transfer function phase characteristic from the FFT analyzer 23 and further stores the resonance point locus line 21 shown in FIG.
a, performs calculation for obtaining the intersection of the transfer function phase characteristic at 21b and the container to be measured 2, and the frequency at the intersection with the resonance frequencies f _1, f _2, using the resonance frequency f _1, f ₂ (4 The volume V of the container 2 to be measured is obtained by the formula). The volume V calculated by the CPU 12 is output to an output device 14 (for example, a display device, a printer, or the like). And the oscillator 24, FFT
The arithmetic means 26 is constituted by the analyzer 23, the CPU 12, and the like.

The operation of the volume meter will be described. First, a temperature change experiment is performed using a container and a thermostat having a known volume in advance, and the transfer function phase characteristics of the Helmholtz resonator as shown in FIG. 4 are measured, and the resonance frequency f ₁ ,
A straight line indicating the trajectory of the resonance point (●) near f _2, that is, resonance point trajectory lines 21 a and 21 b is obtained, and the resonance point trajectory line 2
1a and 21b are stored in the memory 27 as straight lines on the ∠Hf (phase-frequency) plane. Then, the oscillator 24 by a command CPU12 oscillates the signal E _s, drives the sound source 4 via a sound source amplifier 25. This is an input to the Helmholtz resonator composed of the acoustic tube 1 and the container 2 to be measured, resonates at the frequency represented by the equation (1), is mainly detected by the microphone 5a, and is mainly detected by the microphone 5b. )
Resonance of the acoustic tube 1 of the formula is detected, the microphone 5a, an output signal E _m1, E _{m @ 2} of 5b is input to the FFT analyzer 23 via the microphone amplifier 22. Next, FFT analyzer 23 according to a command of CPU12 calculates the two to output an output signal E _m1, E _m2 as input signal E _s transfer function H ₁ (f), H ₂ (f) is at the same time. Here, _assuming that the results of Fourier transform of the signal E _s and the output signals E _m1 and E _m2 are E _s (f), E _m1 (f) and E _m2 (f), the transfer functions H ₁ (f) and H ₂ (f) It is expressed by the following equation.

H ₁ (f) = E _m1 (f) / E _s (f) (5) H ₂ (f) = E _m2 (f) / E _s (f) (6) Next, the CPU 12 Is completed, the oscillator 24
Stop oscillation. FFT analyzer 2 so far
3. All operations of the oscillator 24 are performed by the CPU 12 in synchronization. At this time, the transfer functions H ₁ (f) and H ₂ (f) obtained by the FFT analyzer 23 have characteristics such that the phase is inverted at each resonance point as shown in FIG. CPU 12
Is an operation for taking in the data of the measured transfer function phase characteristic from the FFT analyzer 23 and further calculating an intersection point between the resonance point trajectory lines 21 a and 21 b stored in the memory 27 and the transfer function phase characteristic in the container 2 to be measured. And the frequencies at the intersections are defined as resonance frequencies f ₁ and f ₂ . Next,
The volume V of the container 2 to be measured is obtained by the equation (4).

In this volume meter, the resonance point trajectory lines 21a and 21b obtained in advance are used. Therefore, even when the phase change amounts at the _two resonance frequencies f ₁ and f ₂ are respectively different, the resonance point (FIG. 13 ( Since the accurate frequency (peak frequency of the amplitude characteristic as shown in a) can be obtained, the volume V of the container 2 to be measured can be accurately measured.

It should be noted that the resonance point locus line does not necessarily have to be a straight line, and the resonance point locus line may be a curve when the measurement range is wide or the temperature changes greatly.

FIG. 7 is a diagram showing another volume meter according to the present invention. As shown, the acoustic tube 1, the sound source 4, an auxiliary container 28 lid 3 and volume microphone 5a is attached is V ₀ are together, it is placed on the container to be measured 2, An acoustic resonator having a closed space from the outside is formed. That is, the auxiliary container 28 is connected to the acoustic tube 1 of the Helmholtz resonator in which the container 2 to be measured is connected to one end of the acoustic tube 1. The signal lines of the sound source 4 and the microphones 5a and 5b are taken out to the outside by the connector 29, and are connected to the frequency measuring means 19 and the calculating means 16a for calculating the volume V by the expression (8) described later or its approximate expression. .

In this volume meter, frequency measuring means 1
The procedure for measuring the resonance frequency of the acoustic resonator and calculating the volume V of the container 2 is the same as that of the volume meter shown in FIG. Only different. That is, one acoustic tube 1
Are connected in parallel with each other (the container 2 to be measured and the auxiliary container 28), and the acoustic resonator is composed of three acoustic elements. Therefore, the resonance frequency f ₁ ′ is represented by the following equation.

F ₁ ′ = (c / 2π) √ {S (V + V ₀ )} / LVV ₀ (7) When performing temperature compensation using the resonance of the acoustic tube 1, k
= Π ² / SL, the volume V is represented by the following equation.

V = 1 / [{1 / k (f ₂ / f ₁ ′) ² } − (1 / V ₀ )] (8) However, the equation (8) is a theoretical equation under ideal conditions. And
The actual calculation formula may be an approximation formula using a constant obtained experimentally.

In such a volume meter, since the auxiliary container 28 is connected to the Helmholtz resonator and is an acoustic resonator having a space closed to the outside, the penetration of disturbance (such as external noise) is prevented. Therefore, the volume V of the container 2 to be measured can be accurately and stably measured.

FIG. 8 is a diagram showing another volume meter according to the present invention. As shown in the figure, an auxiliary container 28 is provided similarly to the volume meter shown in FIG.
The signal lines a and 5b are taken out to the outside by the connector 29, and are connected to the calculating means 26a for calculating the volume V by the equation (8) or its approximate equation.

In this volume meter, the procedure of measuring the resonance frequencies f ₁ and f ₂ and calculating the volume V of the container 2 to be measured by the calculating means 26 is the same as that of the volume meter shown in FIG.
The volume V of the container 2 to be measured is determined by equation (8) or an approximate equation thereof.

In such a volume meter as well, since the auxiliary container 28 is connected to the Helmholtz resonator, the intrusion of disturbance can be prevented, so that the volume V of the container 2 to be measured can be accurately and stably measured. can do.

FIG. 9 is a diagram showing another volume meter according to the present invention. As shown in the drawing, a formula (FIG. 10 described later) using the ratio α / β of the gradients α and β of the straight line indicating the relationship between the temperature and the sound speed c at the resonance frequencies f ₁ and f ₂ as shown in FIG. The calculation means 16b for obtaining the volume V by the expression (1) is provided.

By the way, the sound velocity at 0 ° C. is c ₀ ,
Assuming that the temperature in degrees Celsius is t, the sound speed c in air at 1 atm is generally represented by the following equation.

C = c ₀ + 0.6t (9) However, due to the phase characteristics of the sound source, the frequency change with respect to the temperature change becomes smaller than the theoretical value (Δf ₁ > Δt)
f ₁ ′) and the rate of phase change at the _two resonance frequencies f ₁ and f ₂ is different ((Δf ₁ ′ / Δf ₁ ) ≠ (Δf ₂ ′ / Δ
f ₂ )) means that the change of the formulas (1) and (2) is smaller than the theory with respect to the temperature change. Therefore, the change of the sound speed c in the numerator of the formulas (1) and (2) is This is considered to be equivalent to being smaller than theory. Furthermore, the fact that the ratio of the phase change at the _two resonance frequencies f ₁ and f ₂ is different means that
This is considered to be equivalent to the fact that the gradients α and β of the sound speed c in the equations (1) and (2) are different from each other. This is illustrated in FIG. 10, and the following relationship is established between the gradients α and β.

Α <0.6 and β <0.6 and α ≠ β (10) In particular, α ≠ β causes an error. Therefore, if α = β, the theoretical temperature compensation is performed, and in the volume meter shown in FIG. 1, this is realized by adjusting the length L of the acoustic tube 1. Therefore, the theoretical formula of the two measured resonance frequencies f ₁ and f ₂ can be expressed as the following formula.

F ₁ = {(c ₀ + αt) / 2π} · √ (S / LV) (11) f ₂ = (c ₀ + βt) / 2L (12) The temperature t is calculated by the _equations (11) and (12). If the term is eliminated in the calculation, temperature compensation will be performed. Therefore, (11), (1
The following equation is obtained from the equation (2).

V = [{A + (α / β) (Bf ₂ −A)} / f ₁ ] ² (13) Then, if a temperature change experiment is performed in a thermostat using a container having a known volume, the difference Δf ₁ ′ and Δf ₂ ′ can be obtained, and the differences Δf ₁ and Δf ₂ can be obtained from the equations (1) and (2). The ratio α / β can be obtained from the following equation.

Α / β = (Δf ₁ ′ / Δf ₁ ) / (Δf ₂ ′ / Δf ₂ ) (14) The value of the ratio α / β and the resonance frequency f ₁ ,
substituting f ₂ in equation (13), determining the constants A, B. Here, since equation (13) is a theoretical equation under ideal conditions,
Actually, the volume V may be obtained using the following equation using the constants a and b.

V = a [{A + (α / β) (Bf ₂ −A)} / f ₁ ] ² + b (15) The constants a and b change the volume of the container or other constants having different volumes. It is determined experimentally by calibration using a container.

Accordingly, in the volume meter shown in FIG. 9, the resonance frequencies f ₁ and f ₂ are obtained by the frequency measuring means 19, and the volume V is obtained by the equation (15) by the calculating means 16b.

In the volume meter as shown in FIG. 9, since the volume V is obtained using the ratio α / β, the resonance frequency f ₁ ,
Since temperature compensation can be performed according to f ₂ , the volume V of the container 2 to be measured can be accurately measured.

The equation for obtaining the volume V is not limited to the equation (15), but may be another approximate equation.

FIG. 11 is a view showing another volume meter according to the present invention. As shown in the figure, a calculating means 26b for obtaining the volume V by the equation (15) using the ratio α / β is provided.

In this volume meter, the calculating means 26b calculates the transfer functions H ₁ (f) and H ₂ (f), and calculates the transfer functions H ₁ (f) and H ₁ (f).
The resonance frequencies f ₁ and f ₂ are calculated from H ₂ (f) without using the resonance point trajectory lines 21a and 21b, and the volume V is obtained by the equation (15).

Also in such a volume meter, since the volume V is obtained using the ratio α / β, temperature compensation can be performed according to the resonance frequencies f ₁ and f _2. It can be measured accurately.

In the embodiment shown in FIG. 1, the length of the acoustic tube 1a is adjusted in order to equalize the rate of phase change with respect to the resonance frequencies f ₁ and f ₂ . Other shapes may be adjusted. The auxiliary container 28 shown in FIGS. 7 and 8 may be provided in the volume meter shown in FIG. Further, the present invention may be applied not only to the Helmholtz resonator and the acoustic tube but also to the Helmholtz resonator, the acoustic tube and the auxiliary container. Further, the shape of the auxiliary container may be changed without changing the shape of the acoustic tube.

[0054]

As described above, in the volume meter according to the present invention, the resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to the temperature and the resonance point locus on the transfer function phase characteristic of the acoustic tube with respect to the temperature. Is stored in advance, and the two resonance frequencies are calculated from the intersection of the detected transfer function phase characteristic and the stored two resonance point trajectories. However, since the accurate frequency of the resonance point can always be obtained, the volume of the container to be measured can be accurately measured.

A first constant corresponding to the resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to the temperature, and a second constant corresponding to the resonance point locus on the transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to the temperature. Is stored in advance, and the volume of the container to be measured is calculated based on the calculated resonance frequency of the Helmholtz resonator, the resonance frequency of the acoustic tube and the auxiliary container, and the first and second constants. Since the temperature can be compensated according to the frequency, the volume of the container to be measured can be accurately measured.

The shape of the acoustic tube is set so that the slope of the resonance point trajectory on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature and the resonance point trajectory of the transfer function phase characteristic of the acoustic tube with respect to temperature match. Therefore, the rate of change of the phase with respect to both resonance frequencies becomes equal, so that the volume of the container to be measured can be accurately measured.

Further, since the surroundings of the acoustic tube are covered with the auxiliary container, the intrusion of disturbance can be prevented, so that the volume of the container to be measured can be accurately and stably measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a volume meter according to the present invention.

FIG. 2 is a graph for explaining the operation of the volume meter shown in FIG.

FIG. 3 is a graph for explaining the operation of the volume meter shown in FIG. 1;

FIG. 4 is a graph illustrating phase characteristics of a Helmholtz resonator.

FIG. 5 is an explanatory diagram of a method for setting the length of an acoustic tube of the volume meter shown in FIG. 1;

FIG. 6 is a diagram showing another volume meter according to the present invention.

FIG. 7 is a diagram showing another volume meter according to the present invention.

FIG. 8 is a diagram showing another volume meter according to the present invention.

FIG. 9 is a diagram showing another volume meter according to the present invention.

FIG. 10 is a graph showing the relationship between temperature and sound speed.

FIG. 11 is a diagram showing another volume meter according to the present invention.

FIG. 12 is a graph showing frequency characteristics of a sound source.

FIG. 13 is a diagram for explaining a problem of a conventional volume meter.

[Explanation of symbols]

 1, 1a ... Acoustic tube 2 ... Container to be measured 4 ... Sound source 5a, 5b ... Microphone 15a, 15b ... PLL circuit 23 ... FFT analyzer 28 ... Auxiliary container

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01F 17/00 G01F 22/02

Claims (6)

(57) [Claims] A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube is detected, and a resonance frequency of the Helmholtz resonator and a resonance frequency of the acoustic tube are determined from the transfer function phase characteristic. And a volume meter for calculating the volume of the container to be measured based on the two resonance frequencies, wherein a resonance point locus on a transfer function phase characteristic of the Helmholtz resonator with respect to a temperature and a transfer function phase characteristic of the acoustic tube with respect to a temperature are provided. Wherein the two resonance frequencies are calculated in advance from the intersection between the detected transfer function phase characteristic and the stored two resonance point trajectories. 2. A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube is detected, and a resonance frequency of the Helmholtz resonator and a resonance frequency of the acoustic tube are determined from the transfer function phase characteristic. And a second constant corresponding to a resonance point trajectory on the transfer function phase characteristic of the acoustic tube with respect to temperature and a first constant corresponding to a resonance point trajectory on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature. Is stored in advance, and the volume of the container to be measured is calculated based on the calculated resonance frequency of the Helmholtz resonator, the resonance frequency of the acoustic tube, the first constant, and the second constant. Volumetric meter. 3. A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube, and a resonance frequency of the Helmholtz resonator and a resonance frequency of the acoustic tube are determined from the transfer function phase characteristic. And a volumetric meter for calculating the volume of the container under measurement based on the two resonance frequencies, comprising: a resonance point locus on a transfer function phase characteristic of the Helmholtz resonator with respect to temperature; and a transfer function phase characteristic of the acoustic tube with respect to temperature. A volume meter wherein the shape of the acoustic tube is set so that the inclination of the acoustic tube coincides with the locus of the resonance point. 4. A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container, and the Helmholtz resonance is detected from the transfer function phase characteristic. Calculating the resonance frequency of the measuring device and the resonance frequency of the acoustic tube and the auxiliary container, and calculating the volume of the container to be measured based on the two resonance frequencies, wherein the transfer function phase characteristic of the Helmholtz resonator with respect to temperature The resonance point trajectory on the transfer function phase characteristic of the acoustic tube and the auxiliary container with respect to the resonance point trajectory and the temperature above is stored in advance, and the detected transfer function phase characteristic and the stored resonance point trajectory are compared. A volume meter, wherein the two resonance frequencies are calculated from an intersection. 5. A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container, and the Helmholtz resonance is detected from the transfer function phase characteristic. Calculating the resonance frequency of the acoustic tube and the resonance frequency of the acoustic tube and the auxiliary container, and calculating the first constant corresponding to the resonance point locus on the transfer function phase characteristic of the Helmholtz resonator with respect to temperature and the acoustic tube with respect to temperature. And a second constant corresponding to a resonance point locus on a transfer function phase characteristic of the auxiliary container is stored in advance, and the calculated resonance frequency of the Helmholtz resonator, the resonance frequency of the acoustic tube and the resonance frequency of the auxiliary container, A volume meter for calculating a volume of the container to be measured based on a first constant and the second constant. 6. A transfer function phase characteristic of a Helmholtz resonator in which a container to be measured is connected to one end of an acoustic tube and the periphery of the acoustic tube is covered with an auxiliary container, and the Helmholtz resonance is detected from the transfer function phase characteristic. Calculating the resonance frequency of the measuring device and the resonance frequency of the acoustic tube and the auxiliary container, and calculating the volume of the container to be measured based on the two resonance frequencies, wherein the transfer function phase characteristic of the Helmholtz resonator with respect to temperature The shape of the acoustic tube or the auxiliary container is set so that the inclination of the resonance point trajectory above and the resonance point trajectory on the transfer function phase characteristics of the acoustic tube and the auxiliary container with respect to temperature match. Volumetric meter.