JPH0233084B2 - YOSEKIKEI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the volume of a space filled with gas by utilizing the relationship between the change in volume of the gas and the change in pressure.

As one method for measuring the volume of a container having a complicated shape, a measurement method based on the so-called Boyle-Schard law has been known. This method calculates the volume from the pressure increase that occurs when a known volume of gas is injected into the container to be measured using a piston, etc., but in this case, it is necessary to separately know the static pressure of the gas inside the container. . Furthermore, since it is based on isothermal change, it is necessary to wait until the inside of the container is in a thermal equilibrium state to measure the pressure increase after pressurizing the gas, which also has the disadvantage that it takes time to measure. Furthermore, it cannot be applied if the container has a leakage from a vent hole etc. that leads to the outside.

Although the present invention also measures volume using the Boyle-Schard law, it uses a new method in which a reference container with a known volume is prepared in addition to the container to be measured, and alternating volume changes are applied to these containers. This eliminates the drawbacks and limitations of conventional methods. That is, the first object of the present invention is to provide a volume measurement method that is not affected by the type of gas in the container, its static pressure, temperature, etc. The second is to speed up the measurement by utilizing adiabatic changes due to alternating volume changes. Thirdly, the volume of the container to be measured can be measured even in a state where the container to be measured has a vent hole or the like that communicates with the outside and is not completely sealed.

In the embodiment of the invention shown in FIG. 1, 2 is a container to be measured, 1 is a reference container with a known reference volume V ₁ and 4 is a partition between the two. A liquid 3 such as fuel is collected at the bottom of the liquid 3, and the volume V ₂ of the space above the liquid 3 is the volume to be measured in this case.
When the volume V ₃ of liquid 3 changes, V ₂ changes, but
V ₂ + V ₃ is the total volume of container 2, which is constant, so if you know the volume of space V ₂ , you can calculate the volume of liquid.
You can also learn about V ₃ .

5 and 6 are small vent holes provided in containers 1 and 2, respectively, so that the static pressure inside containers 1 and 2 is equal to P, which in this case is equal to atmospheric pressure. . 7 and 8 are bellows attached to containers 1 and 2, respectively. Reference numeral 18 denotes a drive device consisting of a motor and a cam mechanism, which applies vibrational displacement to the bellows 7 and 8 via a lever 19, thereby creating alternating +ΔV ₁ and -ΔV ₂ with respect to volumes V ₁ and V ₂ . Gives minute volume changes.
As a result, the pressure inside containers 1 and 2 is -
Alternating pressure changes of ΔP ₁ and +ΔP ₂ are generated. Here, the volume change ratio ΔV ₂ /ΔV ₁ is determined only by the lever ratio l ₂ /l ₁ of the lever 19 and the effective cross-sectional area ratio S ₂ /S ₁ of the bellows 8, 7, and is a known constant value. be.

Now, assuming the above volume changes ΔV ₁ and ΔV ₂ , we can create sinusoidal waves with frequency and amplitude v ₁ and v ₂ , respectively: ΔV ₁ = v ₁ sin2πt (1) ΔV ₂ = v ₂ sin2πt (2) (t is time) When given, the pressure changes ΔP ₁ and ΔP ₂ in the container also become sinusoidal waves of the same frequency, and they are expressed as ΔP ₁ = p ₁ sin2πt (3) ΔP ₂ = p ₂ sin2πt (4). In the above equation, P ₁ and P ₂ are the amplitudes of pressure changes.

Here, it is assumed that the frequency of the volume change is sufficiently large and the gas inside the container undergoes an adiabatic change. It is also assumed that the vent holes 5 and 6 are sufficiently small so that there is almost no gas entering or exiting at the frequency. Under the above conditions, if the ratio of the constant pressure specific heat and constant volume specific heat of the gas is γ (gamma), then ΔP ₁ /P=γΔV ₁ /V ₁ (5) ΔP ₂ /P=γΔV ₂ /V ₂ (6) Therefore, p ₁ = γv ₁ P/V ₁ (7) p ₂ = γv ₂ P/V ₂ (8). Therefore, p ₁ /p ₂ = (v ₁ /v ₂ )(V ₂ /V ₁ ) (9) or V ₂ =V ₁ (v ₂ /v ₁ )(p ₁ /p ₂ ) (10). However, the amplitude ratio of the reference volume V ₁ and the volume change v ₂ /
Since v ₁ is known, the volume to be measured V ₂ can be found by measuring the amplitude ratio p ₁ /p ₂ of the pressure change.

In the actual device, the pressure changes ΔP ₁ and ΔP ₂ are guided through conduits 9 and 10 to pressure transducers 11 and 12, such as acoustic microphones, where they are detected and converted into electrical signals (conduits 9 and 10). 10
are included in the volumes V ₁ and V ₂ respectively). These electrical signals are amplified by amplifiers 13 and 14, rectified and smoothed by rectifiers 15 and 16, and become DC signals E ₁ and E ₂ . Since E ₁ and E ₂ are proportional to the amplitudes p ₁ and p ₂ of the pressure change, respectively, when these DC voltages are input to the divider 17 and the ratio of both is taken, the output E ₁ /E ₂ is The size is proportional to p ₁ /p ₂ , and from this the volume to be measured V ₂ can be determined.

Although the volume changes ΔV ₁ and ΔV ₂ have been described here as sinusoidal waves, the relationship between equations (5) and (6) is ΔV ₁ ,
Since ΔV ₂ holds true regardless of the minute volume change of any waveform, ΔV ₁ and ΔV ₂ can generally be arbitrary periodic signals such as rectangular waves, or even irregular signals that do not include a DC component. It may be. In these cases, the rectifier outputs E ₁ and E ₂ are proportional to the average absolute value of the pressure change | ₁ |, | ₂ |, respectively, and the amplitudes p ₁ and p ₂ are also proportional to the above | ₁ |, | ₂
Since | are both parameters representing the magnitude of the pressure change, it can be said that the present invention determines the volume to be measured V ₂ from the ratio of the magnitudes of the pressure changes ΔP ₁ and ΔP ₂ .

In the above description, the frequency of volume change was simply assumed to be such that there is almost no gas entering or exiting through the vent holes 5 and 6, but this point can be explained quantitatively as follows.

The volume V ₁ of the reference container 1 is combined with the resistance of the vent hole 5 to form a first-order lag system, and its time constant
T ₁ becomes T ₁ =R ₁ V ₁ /γP (11). Here, R ₁ is the flow resistance (volume flow rate/differential pressure) of the vent hole 5. For example, if the vent hole can be regarded as a capillary tube with radius r and length L, the flow resistance R is calculated by Poiseuil's formula as R =8μL/πr ⁴ (12) However, μ is the viscosity coefficient of the gas, and π is the constant of pi. Similarly, the time constant T ₂ of the first-order lag system constituted by the volume to be measured V ₂ and the resistance R ₂ of the vent hole 6 is T ₂ =R ₂ V ₂ /γP (13). The period of said volume change must be determined by comparison with these time constants. In other words, the frequency of volume change is the cutoff frequency 1/
Both 2πT ₁ and 1/2πT ₂ must be sufficiently large, and this determines the lower limit. For example, if there is air at 1 atm in a container with a volume of 20 liters, and this container is equipped with a capillary vent hole of L = 1 cm and r = 1 mm, the cutoff frequency of this container is approximately 2.5 Hz. . Therefore,
In this case, it is sufficient to set the frequency to about 10Hz or higher.

One upper limit is determined from the fact that the pressure of the gas within the container must vary spatially uniformly. In other words, the wavelength of the sound frequency in the gas must be sufficiently long compared to the sizes of containers 1 and 2. Ultimately, the frequency of volume change must be set to be sufficiently large compared to the cut-off frequency of the container, and so that the pressure change within the container can be considered spatially uniform. Note that there is also a lower limit for the frequency at which the gas in the container can be considered to undergo an adiabatic change, but this value is usually smaller than the cut-off frequency of the container. However, as will be described later, if the container is completely sealed and its time constant can be regarded as infinite, the condition for this adiabatic change becomes the lower limit of the frequency of the volume change.

As is clear from the above description, in the present invention, it is not necessary to know the static pressure P in the container or the amplitudes v ₁ and v ₂ of the volume change. There is also no need to know the temperature of the gas. Furthermore, the temperatures of the gases inside the containers 1 and 2 may be different. The specific heat ratio γ is
It is approximately 1.4 for many gases including air,
Slight differences in the composition of the gases in containers 1 and 2 do not normally pose a significant problem. Also,
Even if the difference in gas composition in containers 1 and 2 manifests as a difference in specific heat ratio γ, if the gas composition is constant for each container, γ
The difference in is also constant, and is calculated based on equation (10).
The true volume value can be found simply by multiplying the value of V ₂ by a certain coefficient. However, if there is a difference in gas composition between containers 1 and 2, it is more advantageous to take measures to actively equalize these differences in gas composition, as in the second embodiment described below. It is.

One drawback of the device shown in FIG. 1 is that if the gain of the signal path from pressure transducer 11 to rectifier 15 and the gain of the signal path from pressure transducer 12 to rectifier 16 change relative to each other, the This appears as an error, and the device shown in FIG. 2 is an improvement on this point.

In FIG. 2, 33 and 34 are driving devices such as speakers provided on the partition wall 4. When the coil section 33 is driven by the oscillator 31 and the amplifier 32, the cone section 34 makes a piston movement and the volume increases.
Differentially give equal volume changes +ΔV and −ΔV to V ₁ and V ₂ . That is, in this case, ΔV ₁ =ΔV ₂ , and v ₂ /v ₁ in equation (10) is 1. Further, there are no vent holes 5, 6, and the containers 1 and 2 are completely sealed. Therefore, the static pressure inside the container is different from atmospheric pressure, but between containers 1 and 2, the pressure is balanced by the method described later, and the static pressure is P in both containers.

Reference numeral 20 denotes an oscillator which generates rectangular pulses u ₁ (t) and u ₂ (t) as shown in FIG. 3, and controls the opening and closing of electromagnetic valves 21 and 22 according to their on/off states. The pressure change ΔP ₁ in the reference container 1 and the pressure change ΔP ₂ in the measured container 2 reach the solenoid valves 21 and 22 through conduits 23 and 24, respectively.
With 1 open and 22 closed, ΔP ₁ is introduced into conduit 25 and converted into an electrical signal by pressure transducer 26. It is amplified by an amplifier 27, and only the frequency components are extracted by a bandpass filter 28 to increase the signal-to-noise ratio.
The rectifier 29 converts the voltage into a DC voltage _E1 . This DC voltage is taken into an arithmetic unit 30 such as a microcomputer and stored. Next, solenoid valve 2
2 is opened and 21 is closed, ΔP ₂ is now introduced into the conduit 25 and the same pressure transducer 26
is converted into an electrical signal by Thereafter, a DC voltage E ₂ is generated at the output of the rectifier 29 in the same manner.
This DC voltage is taken into the arithmetic unit 30, and the _ratio E ₁ /
E ₂ is calculated, and the volume to be measured V ₂ is calculated from this. These series of operations of the arithmetic unit 30 are controlled by the aforementioned rectangular pulses u ₁ (t) and u ₂ (t).

The above-mentioned operation of alternately switching the pressure by the solenoid valve is performed at a longer cycle than the cycle 1/ of the volume change applied to the volumes V ₁ and V ₂ .
Even so, it is normally possible to switch at a cycle of a few seconds at most. The gain of the signal path from the pressure transducer 26 to the rectifier 29 only needs to be constant during that time, and gradual gain fluctuations do not affect the final measurement results. It goes without saying that this pressure switching can also be performed by, for example, a rotary valve driven by a motor.

In the waveform of Fig. 3, there is a period of length Δt ₀ in which u ₁ (t) and u ₂ (t) are both on and overlap, but this is due to the static pressure in containers 1 and 2. This is necessary to balance P. That is, during this period, both solenoid valves 21 and 22 are open, containers 1 and 2 are connected by the passages of conduits 23, 25, and 24, and the pressures therebetween are balanced. At the same time, gas enters and exits the container through this passage due to the alternating volume changes imparted in the meantime.
The composition of the gas inside 2 is made uniform. This pressure equilibrium and composition uniformity can also be achieved by providing a vent hole in the partition wall 4, but these are more facilitated by connecting through a conduit that is thicker than the vent hole as described above.

The pressure changes ΔP ₁ and ΔP ₂ are detected during a period of length Δt ₁ and Δt ₂ as shown in FIG.
During this time, containers 1 and 2 are each in a sealed state, and the time constant becomes infinite. Therefore, in this case, the lower limit of the frequency of volume change is determined by the conditions of adiabatic change.

FIG. 4 shows an embodiment in which the drive device for changing the volume is taken out of the container for explosion-proof reasons, and the parts not explained are the same as in FIG. 2. The coil section 33 and the cone section 34 of the drive device are attached to a small-volume container 35 which is further connected to the conduit 25, and the conduits 25 and 23 and the solenoid valve 21 or the conduits 25 and 24 and the solenoid valve 22.
A volume change of +ΔV ₁ and +ΔV ₂ is applied alternately through the channels. In this case, unlike the previous two cases,
Since the volume change is not applied differentially to containers 1 and 2, but is applied alternately over time, the two containers do not need to be placed back to back, but can be applied independently as shown in the figure. It can be placed anywhere. In this embodiment, vent holes 5 and 6 communicating with the outside are provided in each container to make the static pressure P inside the container equal to atmospheric pressure.

Considering the load seen from the driving device, the volume to which the volume should be changed changes by being alternately switched between V ₁ and V ₂ as the solenoid valves 21 and 22 operate. Therefore, the reaction (reaction force due to ΔP ₁ or ΔP ₂ ) due to the compression and expansion of the gas acting on the cone portion 34 also changes, and even if a sinusoidal voltage of a constant amplitude is applied to the coil portion 33, the volume changes ΔV ₁ and ΔV. _{The two} amplitudes are not necessarily equal. Therefore, in this embodiment, a velocity pickup 36 is attached behind the coil section 33 to detect the vibration speed of the cone section 34, and the signal is fed back to the amplifier 32, thereby controlling the amplitude of the vibration speed of the cone section 34. It is kept constant. If the vibration frequency is constant, the amplitude of vibration displacement is also kept constant, and the amplitudes of ΔV ₁ and ΔV ₂ are kept equal to each other. It should be noted that even in this case, there is no need to know the magnitude of the amplitude of the volume changes ΔV ₁ and V ₂ ; as long as the amplitudes of both are kept equal, the magnitude of the amplitude will not change due to drift, etc. This means that it is okay to change gradually.

If an attenuator is provided between the speed pickup 36 and the amplifier 32 and its attenuation rate is changed in synchronization with the operation of the solenoid valves 21 and 22, the amplitude ratio of ΔV ₁ and ΔV ₂ can be set to a constant ratio other than 1. It is also possible to control. This is because when the reference volume V ₁ is smaller than the measured volume V ₂ , by making ΔV ₁ smaller than ΔV ₂ , the resulting pressure changes ΔP ₁ and ΔP ₂ can be made to be approximately the same magnitude. This is effective in increasing measurement accuracy. This also applies to the device shown in FIG. In order to keep the magnitudes of ΔV ₁ and ΔV ₂ equal regardless of the magnitude of the load, for example, the spring constant of the cone portion 34 may be increased so that the force due to the gas reaction can be relatively ignored. , various means are applicable. It goes without saying that in the apparatus shown in FIG. 3, various waveforms such as arbitrary periodic signals can be used as ΔV ₁ and ΔV ₂ in addition to sine waves.

In short, the basic idea of the present invention is that the reference volume
Apply alternating volume changes ΔV ₁ and ΔV 2 with a constant ratio of mutual sizes to the gases in V ₁ and the measured volume V ₂ , respectively, and calculate the alternating pressure changes ΔP ₁ and ΔP ₂ that occur at that time _. The purpose is to find V ₂ from the size ratio. The necessary condition here is that the static pressure P of the gas be equal for the two volumes of gas. Although it is desirable that the gas compositions be equal to each other, as explained in connection with the apparatus of FIG. 2, it is not a necessary condition. As a result of the above, unique effects such as being unaffected by temperature and static pressure and being able to rapidly measure the volume of a container with a vent hole are produced. In addition, the magnitude of the volume change itself can vary, and since the pressure change is alternating, an acoustic microphone can be used as a pressure transducer in addition to a normal pressure transducer. This is an extremely advantageous point in manufacturing.

[Brief explanation of drawings]

FIG. 1 shows a device according to an embodiment of the present invention, FIG. 2 shows a device according to a second embodiment of the present invention, FIG. 3 shows the waveform of the rectangular pulse in FIG. 2, and FIG. 4 shows a device according to a third embodiment of the present invention. It is. 1...Reference container, 2...Measurement container, 3...Liquid, 4
...Partition wall, 5-6...Vent hole, 7-8...Bellows,
9-10... Conduit, 11-12... Pressure transducer, 13
~14... Amplifier, 15-16... Rectifier, 17... Divider, 18... Drive device, 19... Lever, 20... Oscillator, 21-22... Solenoid valve, 23-25... Conduit,
26... Pressure transducer, 27... Amplifier, 28... Bandpass filter, 29... Rectifier, 30... Arithmetic device, 31...
Oscillator, 32... Amplifier, 33... Coil section, 34...
Cone part, 35...Small container, 36...Speed pick-up.

Claims (1)

[Claims] 1. A reference container with a reference volume, means for applying alternating volume changes with a fixed mutual size ratio to the gas in this reference volume and the gas in the measured volume of the container to be measured, and the reference container and the container to be measured. and means for detecting the change in pressure inside the reference container and the container to be measured caused by the alternating volume change and calculating the size ratio. A volume meter featuring: