JP2820448B2 - Volume measurement method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a volume measuring method for measuring a volume (volume) of a liquid or the like, which is an object to be measured, stored in a tank and an apparatus therefor.

[Prior art]

Conventional volume measurement methods and devices of this type include:
As a prior art, for example, there is one disclosed in Japanese Patent Application No. 1-28088, which will be described with reference to FIGS. First, referring to FIG. 3, the principle will be described. Reference numeral 30 denotes an irregularly shaped main tank for storing an object to be measured such as a liquid, powder, or an irregularly shaped object. A correction tank 31 having a smaller volume than the main tank 30 is connected via the main tank 30. Further, a small-diameter vent hole 35 is formed in the upper part of the irregularly shaped main tank 30 (the vent hole 35 may not be provided). A volume changing means (mechanism) 33 such as a piston and a speaker (hereinafter referred to as a speaker) is provided on the upper part of the correction tank 31, and the volume in the correction tank 31 is controlled by the operation of the volume changing means 33. Can be changed. The above is the configuration of the present embodiment. Next, the principle of measurement by the configuration will be described. Measurement principle (1) First, consider a correction tank 31 of small volume V _1, the connection tank system as shown in FIG. 3 that the main tank 30 of the large volume V ₂ is connected. This is what the correct tank 31 main tank 30 is connected by a pipe 32 of the flow resistance r _1, the vent hole 35 of the tank 30 is a flow resistance r _2. The specific heat ratio of the gas in both tanks 30 and 31 is γ, the gas constant is R, and the thermal time constant of the tank 31 is τ. A volume changing means 33 using a piston, a diaphragm, a bellows, a speaker shape or the like is attached to the tank 31, and the volume change actually generated by the volume changing means 33 is defined as v (t). When the tanks 30 and 31 are rigid bodies, the tanks 30 and 31 are not distorted when the internal pressure of the tanks 30 and 31 is increased or decreased.
The volume change amount V ₀ (t) due to the diaphragm, the bellows and the like is equal to the volume change amount v (t) actually generated. If the tank 30 is flexible, the tank 30 is distorted when the internal pressure of the tanks 30 and 31 is increased or decreased, so that the actual volume change amount v corresponds to the volume change amount due to expansion or contraction.
(T) changes. When v (t) = 0, the absolute pressure, temperature, and mole number of the gas in the tank 31 are P ₀ , T ₁ , n ₁ , and the absolute pressure, temperature, and mole number of the gas in the tank 30 are, respectively. P ₀ , T ₂ , n ₂ respectively
And If the measurement environment does not change significantly,
Gas flows into and out of tanks 30 and 31 via
The absolute pressure P ₀ within 1,30 is equal to the outside pressure, its change is very slow and changes equal to the outside pressure. When v (t) ≠ 0, the pressure, temperature, and number of moles also change according to the state of the volume changing means 33. In the tank 31, the pressure is P ₀ + ΔP ₁ (t), and the temperature is T ₁ + ΔT ₁ (t The number of moles changes as n ₁ −Δn ₁₂ (t). In the tank 30, the pressure changes as P ₀ + ΔP ₂ (t), the temperature changes as T ₂ + ΔT ₂ (t), and the number of moles changes as n ₂ + Δn ₁₂ (t) −Δn ₂ (t). Δn
₁₂ (t) is the number of moles of air flowing from the tank 31 to the tank 30, and Δn ₂ (t) is the number of moles of air leaking from the tank 30 to the outside through the vent hole 35. Here, the following assumptions are made for this system. 1) The gas in the tanks 30, 31 is an ideal gas. 2) v (t) ≪ ｛V ₁ , V ₂ ｝ 3) The heat capacity of the tank 30 is large, and the temperature change in the tank due to the pressure change ΔP ₂ (t) depends on the speed of change of the volume change amount v (t). Very slow to ignore. 4) The rate of change of the volume change amount v (t) is such that the pressure that changes accordingly is equal throughout the tanks 30 and 31. 5) Even if an object to be measured is placed in the tank 30, this object does not form two or more closed gas spaces, that is, hollow portions in the tank 30. The above assumption is not a major constraint. ΔP ₁ (t), ΔP ₂ (t), ΔT _{1 with} respect to the volume change amount v (t)
The changes in (t), ΔT ₂ (t), Δn ₁₂ (t), and Δn ₂ (t) are originally represented by nonlinear equations, but from Assumption 2), the magnitudes are P ₀ , T ₁ , T ₂ , n ₁ , n ₂ are very small and can therefore be approximated by linear equations. Tank 3 in static state
The relationship between the pressure, temperature, and number of moles of the gas in 0,31 is expressed by the following algebraic equation. P ₀ V ₁ = n ₁ RT ₁ , P ₀ V ₂ = n ₂ RT ₂ (1a) Assumptions 1), 3), 4) and 5) indicate that the gas in tanks 30 and 31 in the dynamic state The relationship between pressure, temperature and number of moles is
It is expressed by the following linear ordinary differential equation. The flow resistance r, in the above equation, r ₁ and r ₂ are determined from the length l and the diameter d of the pipe 32 as in the following experimental equation. In this formula, the length 1 is 50 to 650 [mm], and the diameter d is 2.0 to 9.0.
It was obtained experimentally using an aluminum pipe of [mm]. The volume change amount v (t) is expressed as follows. v (t) = v ₀ (t) −Δv (t) (1h) ΔV is a constant peculiar to the tank determined by the material, shape, volume, etc. of the tank, and Δv (t) is a volume change due to expansion or contraction of the tank 30 due to a change in the volume change amount v ₀ (t) of the volume changing means 33. Quantity. Expressions (1a) to (1i) are subjected to Laplace transform, and input v
The transfer function from (t) to the output ΔP ₁ (t) is obtained as follows. here The coefficients r ₂ V ₂ / RT ₂ , r ₁ V ₂ / RT ₂ , r ₁ V ₁ / RT ₁ and r ₁ V ₂ / RT ₁ are time constants of the pressure change. For example, r ₂ V ₂ / RT ₂ is a gas having an absolute temperature T ₂ in a hollow portion of the tank 30 and a gas flow hole 35 having a flow resistance r _2.
Is the time constant of the pressure decay when flowing out of the tank 30 via. The correction coefficient k ₂ (s, r ₁ , r ₂ , V ₁ , V ₂ ) is
Although it changes with the volume V ₂ of 0, k ₂ (s, r
_1, the frequency characteristics of the _{r 2, V 1, V 2} ), the appropriate frequency, approximately constant and considered to by selecting the 4 × 10 ^-4 ~10 ^-3 Hz frequency, for example sections A. If the thermal time constant τ and r ₂流量 V ₁ + Min V ₂ ｝ / RT _{2 in} r ₁ << r ₂ (r ₂ is the flow resistance of the air hole 35 such as air) are approximately the same, the following angle There is a frequency ω. Under this condition, the correction coefficient k ₂ (s, r ₁ , r ₂ , V ₁ , V ₂ ) is approximated as follows. | K ₂ (iω, r ₁ , r ₂ , V ₁ , V ₂ ) | ≒ 1∠K ₂ (iω, r ₁ , r ₂ , V ₁ , V ₂ ) = 0 (2d) Therefore, equation (2c) If the condition is satisfied, the input v (t)
From the output ΔP ₁ (t) is γP ₀ / (V ₁ + V ₂
+ ΔV). Incidentally, if the volume change unit 33 is driven at an angular frequency omega ₀ sinusoidally, Is satisfied, it is considered equivalent to a state where the pipe 32 is closed. That is, Should be fine. (2) Next, consider a single tank system as shown in FIG. This is the pipe 3 connecting the tanks 31 and 30 in FIG.
2 of cross-sectional area which was very large, thereby corresponds to the case where the value of the flow rate resistance r ₁ of the pipe 32 becomes very small. Thus, the transfer function from v (t) to ΔP ₂ (t) in FIG. 5 is r ₁ → 0, T ₂ = T ₁ , ΔP ₂ = ΔP ₁ , in equation (2a).
V ₂ ′ = V ₁ + V ₂ and is as follows. here, Becomes Consider the following angular frequency ω. For example, the frequency is 10 ^-3 Hz or more indicated by A in the frequency characteristic of FIG. By setting such a frequency, the correction coefficient K ₁ (iω, r ₂ , V ₃ ′) is approximated as follows. | k ₁ (iω, r ₂ , V ₃ ′) | ≒ 1, k ₁ (iω, r ₂ , V ₃ ′) ≒ 0 (2i) At this time, the transfer function is γP ₀ / (V ₂ ′ + ΔV). Become. Next, the above principle will be described with reference to FIG. In FIG. 7, reference numeral 33 denotes a speaker (volume changing means), which is configured so that the main tank 30 and the correction tank 31 are separated by the volume changing means 33. Further, a condenser microphone (first pressure detecting means) 34b is provided on the main tank 30 side, and a dynamic microphone (second pressure detecting means) having lower sensitivity 34b than the first microphone is provided on the correction tank 31 side. 34a is provided. Further, the loudspeaker 33 is driven at a predetermined angular frequency omega _0. In this case, the theory of the single tank system shown in FIG. 5 applies. Here, the volume of the correction tank 31 is V ₁ , the volume of the gas in the main tank 30 is V ₂ , the volume of the liquid in the main tank 30 is V _L ,
The sum of the volume of the compensation tank 31 and the main tank 30 and V _T. Pressure change [Delta] P ₁ of the correction tank 31 (t) is the use of the angular frequency omega _H satisfying the equation (2h), Becomes Further, the main tank 30 is made rigid, that is, ΔV =
0 and the angular frequency ω _H satisfies the equation (2h), ΔP
₁ (t) is as follows. Also when measuring the amplitude of [Delta] P ₁ of the correction tank 31 side '(t) when driven v a (t) at an angular frequency omega _H, Here, the amplitude value of the pressure change in the correction tank 31 when the volume changing means 33 is driven so that the pressure change becomes a sine wave is
A ₁ , if the amplitude value of the pressure change of the main tank 30 is A ₂ ,
The ratio of these amplitude values is obtained from equations (3a) and (3b). Becomes Than this And the volume V of the liquid stored in the main tank 30
_L is Becomes Note that | k ₁ / k ₂ |, ΔV is determined in advance by an experiment. Next, a specific prior art based on the above principle will be described. FIG. 7 shows a speaker (volume changing means) 33 placed between the correction tank 31 and the main tank 30. In order to equalize the static pressures of the main tank 30 and the correction tank 31, both tanks 30, 31 is connected by a thin pipe 47 having an orifice 47a, and the main tank 30 and the correction tank 31 are almost completely closed so as not to be affected by the atmospheric pressure. Since the angular frequency ω ₀ is very large compared to the slowly changing atmospheric pressure, and the fluid resistance r ₂ in the vent hole 35 is very large, the speaker
During the operation of 33, the air holes 35 act as if they are closed, so that the air pressure in the tanks 30, 31 is not affected at all by the pressure difference between the inside and outside of the tanks 30, 31. Here, the time constant of the pressure transmission of the pipe 47 is sufficiently larger than the time constant of the pressure change in the correction tank 31 by the speaker 33 and the time constant of the atmospheric pressure outside the tanks 30 and 31, ie, the pressure change of the absolute pressure. Assuming that it is much smaller, drive speaker 33,
When a volume change as shown by a function of v ₀ sin ω ₀ t is given to the correction tank 31 and the main tank 30, that is, the principle of the single tank system is applied to both the main tank 30 and the correction tank 31. Then, assuming that V (t) = v ₀ sin ω ₀ t (4a), the pressure change ΔP ₁ (t) of the correction tank 31 becomes And when the angular frequency ω ₀ satisfies (2h) in the above equation, Becomes ΔP ₂ (t) is as follows. Here, in the above equation, when the main tank 30 is a rigid body and the angular frequency ω ₀ satisfies the equation (2h) as in the case of the correction tank 31, Becomes That is, the speaker 33, the respective volumes of the main tank 30 correction tank 31 is regularly varied in angular frequency omega ₀ only V ₀ sinω ₀ t, respectively pressure within the correction tank 31 main tank 30 Fluctuations are caused by the dynamic microphones 34a,
Is detected by the capacitor microphone 34b, the output of the condenser microphone 34b that detects the pressure fluctuations in the main tank 30, a gain 1, the signal component of the center angular frequency omega angular frequency omega ₀ by a band-pass filter 37b of ₀ is extracted, then , Supplied to the second amplitude detector 39b,
P ₀ v ₀ / V ₂ is output is detected. The output of the dynamic microphone 34a detects a pressure variation of the correction tank 31, only the signal component of the gain V _1, the angular frequency omega ₀ by a band-pass filter 37a of the center angular frequency omega ₀ is extracted is ₁ × V, then Supplied to the first amplitude detector 39a,
γP ₀ v ₀ is detected and output. After that, the output γP ₀ v ₀ from the first amplitude detector 39a is divided by the output γ P ₀ v ₀ / V ₂ from the second amplitude detector 39b by the divider 40, and the cavity moiety is the volume V ₂ of the calculation, the calculation result is supplied to the subtractor 41 is subtracted from the total volume V _T of the main tank 30 that is set, as a result, the liquid stored in the main tank 30 volume V _L is calculated for.

[Problems to be solved by the invention]

However, in such a conventional volume measurement method and its device, the amplitude detector 39a, which detects the output amplitude value of the band-pass filters 37a, 37b for removing noise from the electric signal from the speaker 33, Since the signal detected by the microphones 34a and 34b by 39b or the like is processed in an analog manner, and a large noise is superimposed on the signal in a low frequency range, there is a problem that a measurement error is likely to occur. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a volume measuring method and an apparatus therefor which greatly reduce superimposed noise and improve measurement accuracy.

[Means for Solving the Problems]

The volume measurement method according to the first aspect is a detection output and a volume change obtained by changing respective internal pressures of a main tank and a correction tank provided in communication by a signal of a predetermined frequency whose phase is inverted every fixed section. An autocorrelation is obtained with a signal for driving the means, and the volume of the object to be measured stored in the main tank is measured based on the correlation value. A volume measuring device according to a second aspect includes a first oscillator that oscillates at a predetermined frequency, and 1/1 of an oscillation frequency of the first oscillator.
a second oscillator that oscillates in synchronization with n, a multiplier that multiplies the oscillation outputs of the first and second oscillators, a main tank that stores the device under test, and a communication unit that is provided in communication with the main tank. Correction tank, volume change means for changing the internal pressure of each of these tanks by a multiplication signal of the multiplier, a detection output of detecting a pressure change by the volume change means, and a multiplication signal for driving the volume change means. And an object-to-be-measured calculating means for measuring the volume of the object to be measured housed in the main tank based on the correlation value obtained by the auto-correlation means. It is a thing.

[Action]

In the volume measuring method according to the first aspect, the internal pressures of the main tank and the correction tank provided in communication with each other are changed by the volume changing means, and a detection output detecting the pressure change accompanying the driving and the volume changing means are driven. The correlation is calculated with a drive signal of a predetermined frequency whose phase is inverted every fixed section. The volume measuring device according to the second aspect changes the internal pressure of each of the main tank and the correction tank provided in communication with each other to detect a change in the pressure of both tanks, and outputs the detected output and a drive signal for driving the volume changing means. Are obtained by autocorrelation means.

【Example】

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, the same or equivalent components as those in FIG. In the figure, 50 is a signal
A first oscillator that outputs V ₀ sinωt, 51 is a signal sin n ω
The second oscillator 51 outputs t and oscillates in synchronization with the oscillation frequency of the second oscillator 51 at 1 / n of the oscillation frequency of the first oscillator 50 (where n is an even number). 52 is a first multiplier for multiplying the oscillation signals of the first and second oscillators 50 and 51,
The speaker 33 which is a volume changing means is driven by the multiplied signal. Reference numeral 53 denotes a phase difference detection circuit, which outputs an output signal V ₀ sinωt · sin n ωt from the first multiplier 52 and the first microphone 3
4a, the detection signal A ₁ sin (ωt + φ) · sin (n
ωt + φ) is detected. Reference numeral 54 denotes a first phase matching circuit, which is an output signal V ₀ sinωt + s of the first multiplier 52.
in n ωt is matched with the phase of the output of the first microphone 34a by the phase difference φ of the detection output from the phase difference detection circuit 53. 55 is a second multiplier, which is the detection output A ₁ sin (ωt + φ) · sin n ωt of the first microphone 34a and the output V ₀ sin (ωt + φ) · sin (nωt + φ) of the first phase matching circuit 54.
Multiply with Reference numeral 56 denotes a second phase matching circuit having the same function as the first phase matching circuit 54, and outputs the output signal sin n ωt of the second oscillator 51 as a signal sin (nωtφ). 57 is a zero cross detection circuit, and a second phase matching circuit 56
Outputs an integration start signal at a zero crossing at a certain point in time of the output sin (nωtφ), and then performs an m-th predetermined time (t)
An integration end signal is output at the later zero cross. 58 is a first integrator that integrates the output from the second multiplier 55 based on the integration start signal and the integration end signal from the zero cross detection circuit 57 and outputs γP ₀ v ₀ . The integrator 58 does not output its integration until the integration end signal comes. 59 is an inverting circuit for inverting the output from the first phase matching circuit 54, and 60 is a third multiplier having the same function as the second multiplier 55. 61
Is a second integrator having the same function as the first integrator 58,
When the integration end signal is supplied from the zero cross detection circuit 57, the integration is stopped and γ P ₀ v ₀ / V ₂ is output. Next, the operation will be described. The first oscillator 50 has V ₀ sinωt shown in FIG.
And the second oscillator 51 outputs the output signal of sinωt shown in FIG. 2 (b) to the first multiplier 52, and the multiplied signal V ₀ shown in FIG. 2 (c). sinωt ・ s
in nωt is supplied to the speaker 33 to drive the speaker 33. Based on the output V ₀ sinωt · sin nωt of the first multiplier 52, the detection output A ₁ sin (ω
t + φ) (for example, FIG. 2 (d)) is detected by the phase difference detection circuit 53, and the detected phase difference φ
Output V ₀ sinωt · sin n from the first multiplier 51 based on
By correcting the phase of ωt, V ₀ sin (ωt + φ) · sin (nωt
+ Φ) (FIG. 2 (e)). The corrected signal V ₀ sin (ωt + φ) · sin (nωt + φ) is converted by a second multiplier 55 into a detection signal A ₁ sin (ω) from the first microphone 34a.
t + φ). On the other hand, the output signal sin nωt of the second oscillator 51 is converted by the second phase matching circuit 56 into sin (nωt + φ) as shown in FIG. Then, the multiplication signal supplied from the second multiplier 55 to the first integrator 58 is integrated based on the integration start signal from the zero cross detection circuit 57, and
Then, the integration is terminated based on the integration termination signal from the zero-cross detection circuit 57 after a predetermined time (t). Let S be a signal component that should be obtained in the section from the start of integration to the end of integration, and when a steady noise N is superimposed on this, in the positive section shown in FIG. Is calculated, and the total integration result is , The noise N is cut off, and only the signal component S is calculated. That is, γP ₀ v ₀ is obtained. On the other hand, the output V ₀ sin of the first phase matching circuit 54 (ωt +
φ) · sin (nωt + φ) is inverted by the inverting circuit 59, and the output −V ₀ sin · (ωt + φ) · sin (nωt + φ) is the detection signal −A ₂ sin (ωt +) from the second microphone 34b.
θ) · sin (nωt + φ) is multiplied by the third multiplier 60, and based on the integration signal from the zero-crossing detection circuit 57, the second integrator 61 performs the same operation as the first integrator 58 γ
Obtain P ₀ v ₀ / V _2. After that, the divider 40 integrates the integrated value γP ₀ v ₀ of the first integrator 58 with the integrated value γ P ₀ v ₀ /
Divided by V _2, obtains the results V ₂ of the gas in the main tank 30, and then the measurement of the main tank 30 by subtracting the volume V ₂ of gas from the total volume V _T of the main tank 30 by the subtractor 41 The volume _VL of the object can be determined.

As described above, according to the first aspect, the internal pressure of each of the main tank and the correction tank provided in communication with the configuration is a signal of a predetermined frequency in which the phase is inverted every fixed section. The pressure change is detected by a pressure sensor, and the detected output of the pressure sensor is correlated with the signal for driving the volume changing means, and then based on the correlation value. Since the volume measurement method is used to measure the volume of the object stored in the main tank, effects such as greatly reducing superimposed noise and increasing measurement accuracy can be obtained. Further, according to the second aspect, a first oscillator oscillating the configuration at a predetermined frequency, and an oscillation frequency of the first oscillator.
A second oscillator that oscillates in synchronism with 1 / n, a multiplier that multiplies the oscillation outputs of the first and second oscillators, a main tank that stores the device under test, and communicates with the main tank. The correction tank provided, volume changing means for changing the internal pressure of each of these tanks with the multiplication signal of the multiplier, a detection output obtained by detecting a pressure change by the volume changing means, and the volume changing means. Autocorrelation means for calculating a correlation between the multiplication signal to be driven, and a measured object for measuring a volume of the object to be measured housed in the main tank based on the correlation value obtained by the autocorrelation means. The volume measurement device was equipped with an object volume calculation means, so the S / N for stationary noise was maintained without reducing the S / N for random noise.
Since / N can be improved, effects such as improvement in measurement accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of a volume measuring method and apparatus according to the present invention, FIG. 2 is a time chart for explaining FIG. 1, and FIG. 3 is a principle of the prior art. illustration, Figure 4 is a characteristic diagram showing a change in state of the coefficient K ₂ of the transfer function when changing the object to be measured volume of the driving frequency and the tank of volume change means in Figure 3, Figure 5 is principle explanatory diagram for explaining a prior art, FIG. 6 is changing state of the coefficients K ₁ of the transfer function when changing the object to be measured volume of the driving frequency and the main tank volume change means in Figure 5 FIG. 7 is an explanatory diagram of a specific system according to the prior art. 30: Main tank, 31: Correction tank 33: Speaker (volume changing means) 50, 51: Oscillator, 52: First multiplier 53: Phase difference detection circuit 54, 56: Phase matching circuit, 55: Second multiplication 57: Zero cross detection circuit, 58: First integrator 60: Third multiplier, 61: Second integrator

Claims (2)

(57) [Claims] An internal pressure of each of a main tank and a correction tank provided in communication with each other is changed using volume changing means driven by a signal of a predetermined frequency whose phase is inverted every predetermined section, and the pressure change is performed. Is detected by a pressure sensor, and the detected output of the pressure sensor is correlated with the signal for driving the volume changing means, and then the volume of the measured object stored in the main tank is measured based on the correlation value. Volume measurement method. 2. A first oscillator that oscillates at a predetermined frequency, a second oscillator that oscillates in synchronization with 1 / n of an oscillation frequency of the first oscillator, and oscillations of the first and second oscillators. A multiplier for multiplying the output, a main tank for storing the device under test, a correction tank provided in communication with the main tank, and a volume for changing the internal pressure of each of these tanks by a multiplication signal of the multiplier Changing means, autocorrelation means for calculating a correlation between a detection output obtained by detecting a pressure change by the volume changing means and a multiplication signal for driving the volume changing means, and autocorrelation means. A volume measuring device comprising: a measuring object volume calculating means for measuring a volume of the measuring object stored in the main tank based on a correlation value.