JPH0313820A - Volume measuring apparatus - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by changing the frequency of a filter in response to the frequency of a noise. CONSTITUTION:A correcting tank 31 is provided at a part separated from a main tank 30 through a partitioning wall. The partitioning wall is vibrated with a speaker 33. The volumes of the main tank 30 and the correcting tank 31 are changed. The internal pressures are detected with microphones 34a and 34b and processed. Thus, the volume of liquid (c) is computed. Only the component of the central frequency omega0 in the outputs of the microphones 34a and 34b is taken out with bandpass filters 37a and 37b. The amplitudes are detected by amplitude detectors 39a and 39b. The results are divided in a divider 40. The volume of a cavity part in the main tank 30 is computed. The output of the microphone 34b is inputted into a bandpass filter 38a having the central frequency in the vicinity of the frequency omega0 and a bandpass filter 38b having the central frequency at a frequency omega1 which is lower than omega0. When the output of the bandpass filter 38b is larger than the output of 38a, the central frequency of the bandpass filters 37a and 37b is switched to omega1.

Description

[Detailed description of the invention] [Industrial application field]

This invention uses liquid and powder stored in a tank. The present invention relates to a volume measuring device that measures the volume of particles, irregularly shaped objects, etc.

[Conventional technology]

For example, as a conventional volume measuring device of this type, for example,
There is No.-27808. The above-mentioned application as the prior art shown in FIGS. 3 to 8 will be specifically described below. First, the principle will be explained with reference to Figures 3 to 6.
30 is an irregularly shaped main tank that stores, for example, liquid, powder, irregularly shaped objects, etc., and is connected to this main tank 30 via a connecting pipe 32, which has a smaller volume than the main tank 30. A correction tank 31 is connected. Further, a small diameter ventilation hole 35 is bored in the upper part of the irregularly shaped main tank 30 (note that the ventilation hole 35 does not need to be provided), and a piston, for example, is provided in the upper part of the correction tank 31. , a volume changing means (mechanism) 33 such as a speaker shape (hereinafter referred to as a speaker) is provided, and the operation of the volume changing mechanism 33 causes the correction tank 3 to
The principle of measurement using the above-described configuration will be explained below. Measurement principle (1) Consider a connected tank system as shown in Figure 3. This is a correction tank 31 with a small volume ■1 and a large volume ■z
It is constructed by connecting the main tank 30 of the main tank 30. The tanks 31.30 are connected by a pipe 32 of flow resistance r+, and the vent 35 of tank 30 has a flow resistance r2. Let γ be the specific heat ratio of the gases in both tanks 30 and 31, R be the gas constant, and τ be the thermal time constant of the tank 31. A volume change mechanism 33 using a piston, diaphragm, bellows, speaker shape, etc. is attached to the tank 31, and the amount of volume change actually generated by this volume change mechanism 33 is assumed to be V(t). When the tank 30.31 is a rigid body, when the internal pressure of the tank 30.31 is increased or decreased, the tank 30.31 is a rigid body. 31 is not distorted, the amount of volume change V @ (t) due to the piston, diaphragm, bellows, etc. and the amount of volume change that actually occurs v (t
) are equal. If the tank 30 is flexible, the tank 30 will be distorted when the internal pressure of the tank 30.31 is increased or decreased, and therefore v(t) will change by an amount corresponding to the volume change due to expansion or contraction. When v(t)-0, the absolute pressure and temperature of the gas in the tank 31 are Pa and T, respectively. , , n, if the measurement environment does not change significantly, the tank 31.30 is
Since gas flows inside and outside, the absolute pressure P0 inside the tank 31.30 is equal to the outside pressure, and its change is very slow and equal to the outside pressure. When v(t)≠0, the pressure and temperature also change according to the situation of the volume change mechanism 33, and in the tank 31, the pressure is P0+ΔP+(t). The temperature changes as T1+ΔT+(t) and the number of moles changes as nl−Δn+x(t). In the tank 30, the pressure is P0+ΔPg(t). The temperature is Tt+ΔTz(t). The number of moles is n8+Δn+g(t)−Δn! (t). Δn+z(t) is the number of moles of air flowing from the tank 31 to the tank 30, and Δnt(t) is the number of moles of air flowing from the tank 30 to the vent hole 35.
is the number of moles of air that leaks to the outside through the We now make the following assumptions about this system. 1) The gas in the tank 31.30 is an ideal gas. 2) V(t) ((V,,Vo) 3) The heat capacity of the tank 30 is large, and the pressure change ΔPg(1
) The temperature change inside the tank due to the change in volume is very slow compared to the speed of change in the volume change amount V(1) and can be ignored. 4) The rate of change of the volume change amount v(t) is such that the pressure that changes accordingly is the same throughout the tank 30, 31. 5) Even if an object to be measured is placed in the tank 30, the object does not create two or more closed gas spaces, that is, a hollow portion, in the tank 30. The above assumptions are not a major constraint. ΔP+(t), ΔPg(t
). ΔTt(t), ΔTt(t), Δn+z(t), Δ
The change in nt(t) is originally expressed by a nonlinear equation, but
From assumption 2), its size is Po * T1, T! ,
It is very small with respect to nI and nI, so it can be approximated by a linear equation. In a static state, the relationship between the pressure of the gas in the tank 30 and 31 and the temperature per mole is expressed by the following algebraic equation. P(IVI −n 1RT++ P oVz=nzRT
z (la) Also, assumptions 1), 3), 4),
5), in the dynamic state the pressure of the gas in the tank 30.31. The relationship between temperature and number of moles is expressed by the following linear ordinary differential equation. (1b) Δ↑+(0)=0 (1f) Flow resistance ``, that is, r++r! in the above equation can be obtained from the length 2 and diameter d of the pipe 32 as shown in the following experimental equation. Yes, Δv(t) is the volume change mechanism 33
This is the amount of change in volume due to expansion or contraction of the tank 30 due to a change in volume 1vo(t). Applying Laplace transform to equations (1a) to (li), input v(
The transfer function from t) to the output ΔP+(t) is as follows. "Mu" -r "Kg (3+r++r!+V
I+Vt)v(s) Vl+V! +ΔV(
2a) This formula is calculated when the length l is 50 to 650 mml and the diameter d is 2
．． It was experimentally determined using an aluminum pipe of 0 to 9.0 mml. Further, the volume change 1v(t) is expressed as follows. v (t) = v o (t) − Δv (t)
(lh)Δ■ is determined from the material, shape, volume, etc. of the tank, and is a coefficient rlVz/RTx +r+Vz/RTz,
r+V+/RT++r+lh/RT+ is the time constant of pressure change. For example, rzVz/RTI is a time constant of pressure attenuation when gas at absolute temperature T2 in the hollow portion of the tank 30 flows out of the tank 30 through the vent hole 35 with flow resistance r. Correction coefficient kg (Lr+, rg+V+
+Vt) varies depending on the volume 3 of the main tank 30, but ktC3+r++rz+V, V shown in FIG.
t) can be approximately regarded as a constant by selecting an appropriate frequency, for example, a frequency of 4X10-' to 10-Hz in section A. r, <<< rtcrt is the flow resistance of the air vent 35), and the thermal time constant τ and rt (V++ old n Vz) /
If RTt has a similar value, the following angular frequencies exist. (2c) Under this condition, the correction coefficient kg (3, r++rz+V+
+V*) is approximated as follows. nig(iω* r'++ r!+ Vll Vg)
−11, t(iω+ rt+ rt+ Vll Vri = O(2d) Therefore, if the condition of equation (2c) is satisfied, the transfer function from the input v(t) to the output Δp r (t) is TPo(vt+vt+ΔV). Become. Note that the volume change mechanism 33 has an angular frequency ω. When driven in a sinusoidal manner, . Δh(s) v (s)″7 P. v,t +Δvkt(s, rz* V!') (2
f) This is considered to be equivalent to the state where 32 is blocked. That is, it is sufficient if . (2) Next, consider a single tank system as shown in Figure 5. This corresponds to a case in which the cross-sectional area of the vibrator 32 connecting the tanks 31 and 30 in FIG. 3 is made very large, and the value of the flow resistance r of the pipe 32 is thereby made very small. From this, from v(t) in Figure 5 to 8Pg(
The transfer function up to t) is based on the formula % V z' -V r + V, and is expressed as follows: Max (4) <ω(2h) rz °vt For example, in the frequency characteristics shown in Figure 6, 104Hz shown in A
This is the frequency above. By setting such a frequency, the correction coefficient becomes (iωr r! r vs'
) is approximated as follows. lk+ Nω, rz, y3+ )l! :il. kl (iω, r, , V3') #0 (2i) At this time, the transfer function is TP, V, l+Δ■). Next, a specific example to which the above principle is applied will be explained based on FIG. 7. In FIG. 7, 33 is a speaker (volume changing means), and the main tank 30 and the correction tank 31 are partitioned by this volume changing means. Furthermore, a condenser microphone 34b serving as a first pressure fluctuation detector is provided on the main tank 3, 0 side, and a correction tank 3
On the first side, there is a dynamic microphone 34a which is a second pressure fluctuation detector having lower sensitivity than the first microphone.
is provided. Further, the speaker 33 has a predetermined angular frequency ω. Drive with. In this case, the single tank system theory shown in FIG. 5 applies. Here, the volume of the correction tank 31 is Vl, and the volume of the main tank 30 is
The volume of the gas in the main tank 30 is Vt, the volume of the fluid in the main tank 30 is vL, and the sum of the volumes of the correction tank 31 and the main tank 30 is vT. The pressure change ΔP+(t) in the correction tank 31 is calculated as follows using the angular frequency ω8 that satisfies equation (2h): ΔP+(t) −7−! -! l kl l vosin
(ωx t+φ,)vl+ΔV O =γ □vosin ωHt (3a)v
l+ΔV, and the main tank 30 is a rigid body, that is, Δ■
−〇, and when the angular frequency ω9 satisfies equation (2h), Δ
P+(t) becomes as follows. ΔP+(t) = r-! 1-Ll k, l vos
in(ω11 +φ2) Also, when the amplitude of ΔPI'(t) on the correction tank 31 side is measured when v(t) is driven at the angular frequency ω, ΔP+
'(t) = γ-'' l kl l v+5in(s, t+φ2
)V! +ΔV Here, when the volume change mechanism 33 is driven so that the pressure change becomes a sine wave, the amplitude value of the pressure change in the correction tank 31 is AI, and the amplitude value of the pressure change in the main tank 30 is A! Then, the ratio of these amplitude values is expressed as Equations (3a) and (3b
). From this, V,, 1-LI V,-Δ■, and the main k
. The volume of the liquid stored in the tank 30 is V, -V
, -V, =V, -(1I5-LI Vl -A'
/ )g. Make it a spider. Next, specific prior art based on the above principle will be explained. In FIG. 7, a constant angular frequency ω is set by a speaker drive circuit 36 between the correction tank 31 and the main tank 30. It is equipped with a speaker (volume change means) 33 driven by
In addition, in order to equalize the static pressure of the main tank 30 and the correction tank 31, an orifice 47a is provided between the two tanks 31 and 30.
connected by a thin vibrator 47 with a main tank 30
and the correction tank 31 so that they are not affected by atmospheric pressure.
Since it is an almost completely closed system, the speaker 33
The driving angular frequency ω. is very large compared to the slow change in atmospheric pressure, and the fluid resistance in the vent hole 35 is very large, so that the vent hole 35 acts as if it were blocked while the speaker 33 is being driven. 30.
The pressure inside the tank 31 is not affected by the difference in pressure between the inside and outside of the tank 30. Here, the time constant of the pressure transmission through the pipe 47 (is larger than the time constant of the internal pressure change in the correction tank 31 caused by the speaker 33). Large enough and tank 30.
This is based on the premise that the time constant of the pressure change of the atmospheric pressure outside 31, that is, the absolute pressure, is sufficiently smaller than the time constant of the pressure change of the speaker 33.
, and v, ) sin ω. If the correction tank 31 and the main tank 30 are given a volume change as a function of t, that is, the principle of a single tank system is applied to both the main tank 30 and the correction tank 31. Therefore, V(t)mv, sinω. t (4
a), the pressure change in the correction tank 31 ΔP+(t)
If, ΔP + (t) = r PgV6 sinω,, t
(4b) 'I, ΔPg(t) is as follows. (4c) Here, in the above equation, the main tank 30 is a rigid body and the angular frequency ω is the same as the correction tank 31. When satisfies formula (2h), it becomes. That is, the volume of each of the main tank 30 and the correction tank 31 is increased by V+stnωat at the angular frequency ω by the speaker 33. When the pressure inside the main tank 30 and the correction tank 31 are varied regularly, the pressure fluctuations inside the main tank 30 and the correction tank 31 are detected by the dynamic microphone 34a and the condenser microphone 34b attached to the respective tanks 30 and 31, and the pressure inside the main tank 30 is The output of the condenser microphone 34b that detected the fluctuation has a gain of 1 (dB)
, central angular frequency ω. The angular frequency ω is set by the bandpass filter 37b. The signal component of V: is extracted and then supplied to the second amplitude detector 39b, where TPovo- is detected and output. Furthermore, the output of the dynamic microphone 34a that detects the pressure fluctuation of the correction tank 31 has a gain Vl and a center angular frequency ω. The angular frequency ω is determined by the bandpass filter 37a. Only the signal component of
6V@ is detected and output. The output γP6v, from the first amplitude detector 39a is then divided by the divider 40 by the output γ5 from the second amplitude detector 39b, and V! The volume ■2 of the hollow part of the main tank 30 is calculated, and the calculation result is supplied to the subtractor 41 and subtracted from the set total volume ■t of the main tank 30. As a result, the volume inside the main tank 30 is The volume of liquid stored in , is calculated.

[Problem to be solved by the invention]

However, in such a conventional volume measuring device, when the main tank 30 is used as a fuel tank for a vehicle, for example, the vehicle carrying the main tank 39 runs on a paved road and an unpaved road. In this case, the noise contained in the detection signal detected by the condenser microphone 34b varies depending on the frequency, and there is a problem in that it is not always possible to accurately measure the amount of liquid remaining in the tank. This invention was made in view of the above-mentioned problems, and it is an object of the present invention to provide a volume measuring device that can accurately measure the amount of liquid remaining in a tank.

[Means to solve the problem]

The volume measuring device according to the present invention detects the change in the tank internal volume as a pressure fluctuation by changing the volume of the tank storing the object to be measured, and detects the change in the tank internal volume as a pressure fluctuation, and among the detection signals of the pressure fluctuation detector. Only a specific frequency is passed through a filter circuit, and the volume of the object to be measured is calculated based on the amplitude of the passed detection signal. A detector that detects the frequency of the noise component at at least two points, and a magnitude of the noise component detected by this detector is compared, and the passing frequency of the filter circuit and the volume changing means are determined based on the comparison result. A comparator that outputs a switching signal for changing the predetermined driving frequency. [Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail based on the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.
In the figure, the same or equivalent components as in FIG. 7 are denoted by the same reference numerals, and redundant explanation will be omitted. In the figure, 38
a is ω of the noise components superimposed on the detection signal detected by the condenser microphone 34b. A filter circuit that extracts an angular frequency component ω0+Δω that is somewhat larger than 3.
8b is ω of the noise components superimposed on the detection signal detected by the condenser microphone 34a. The angular frequency ω1+Δω(ω1+
Δω〈ω. ), and 42 is a comparator that compares the magnitude of the noise components extracted by the filter circuits 38a and 38b.This comparator 42 indicates that the noise component extracted by the filter circuit 38a is
The passing frequencies of the bandpass filters 37a and 37b and the driving frequency of the speaker driving circuit 43 are set to ω while the frequency is larger than the noise component extracted by ω. A switching signal for switching from ω1 to ω1 is output. Reference numeral 44 denotes a timer that closes a switch in order to output the switching signal from the comparator 42 to the bandpass filters 37a, 37b and the speaker drive circuit 43 at predetermined time intervals. Next, the operation will be explained. Now, when a vehicle is traveling on a paved road, a noise component shown by a solid line in FIG. 2 is superimposed on the detection signal detected by the condenser microphone 34b. 4
3 is the angular frequency ω. Since priority is given to ω, the center angular frequency of the bandpass filters 37a, 37b and the speaker drive circuit 43 is ω. is set to Next, when the vehicle is traveling on an unpaved road, the detection signal detected by the condenser microphone 34b is superimposed with a noise component shown by a dotted line in FIG. 38a and 38b extract, but the output of the filter circuit 38b is extracted by the filter circuit 38.
Since the output of the comparator 42 is larger than the output of
A switching signal is output when the switch of the timer 44 is closed. Furthermore, when the vehicle starts traveling on a paved road again, the output of the filter circuit 38a becomes larger than the output of the filter circuit 38b, so the comparator 42 is replaced by the bandpass filter 37a. 37b and the speaker drive circuit 43 with an angular frequency ω. A switching signal for selecting the timer 44 is output when the switch of the timer 44 is closed. (Effects of the Invention) As explained above, the present invention has a configuration including a volume changing means for varying the respective volumes of a main tank that stores an object to be measured and a correction tank whose volume is smaller than the volume of the main tank; A drive circuit that drives the volume change means at a predetermined frequency, a pressure fluctuation detector that detects pressure fluctuations in the main tank, a filter circuit that passes a specific frequency of the detection signal of the pressure fluctuation detector, and a remaining amount detection means for calculating the volume of the object to be measured based on the amplitude value of the detection signal passed through the filter circuit; The magnitude of the noise component detected by the detector is compared with that of the noise component detected by the detector, and based on the comparison result, the passing frequency of the filter circuit that passes the specific frequency and a predetermined predetermined value that drives the volume changing means are determined. Since the volume measuring device is equipped with a comparator that outputs a switching signal for changing the frequency, it has the effect of accurately measuring the volume of a non-measurable object no matter what road surface the vehicle travels on.

[Brief explanation of drawings]

FIG. 1 is a system explanatory diagram showing an embodiment of the volume measuring device according to the present invention, FIG. 2 is a frequency spectrum diagram of a detection signal of a condenser microphone when a vehicle runs on a paved road and an unpaved road, and FIG. The figure is an explanatory diagram of the principle of the prior art, and Figure 4 shows the coefficients of the transfer function when the drive frequency of the volume changing means and the volume of the contents in the tank are changed in Figure 3! FIG. 5 is a principle explanatory diagram for explaining the prior art, and FIG. 6 is a characteristic diagram showing the change state of the volume change means in FIG. FIG. 7 is a diagram illustrating a system according to the prior art. 30... Main tank, 31... Correction tank, 3
2... Connected vibrator, 33... Speaker (volume change means), 34a... Second microphone, 34b...
First microphone, 35...Vent hole, 37a, 37
b...Band pass filter, 38a, 38b...Filter circuit, 39a, 39b...Amplitude detector, 40.
...Divider, 41...Subtractor, 42...Comparator, 4
3... Speaker drive circuit, 44... Timer, 47.
... Pipe, 47a... Orifice.

Claims (1)

[Claims] a volume changing means for varying the respective volumes of a main tank for storing an object to be measured and a correction tank having a volume smaller than the volume of the main tank; a drive circuit for driving the volume changing means at a predetermined frequency; A pressure fluctuation detector that detects pressure fluctuations in the tank, a filter circuit that passes a specific frequency of the detection signal of this pressure fluctuation detector, and a filter circuit that detects the above-mentioned fluctuation based on the amplitude value of the detection signal that has passed through this filter circuit. a remaining amount detection means for calculating the volume of the object to be measured;
Comparing the magnitude of the noise component detected by a detector that detects the frequency of the noise component superimposed on the detection signal detected by the pressure fluctuation detector at at least two points with this detector,
A volume measuring device comprising: a comparator that outputs a switching signal that changes a passing frequency of the filter circuit that allows each of the specific frequencies to pass and a predetermined frequency that drives the volume changing means based on a comparison result.