JPS63223529A - Device and method for measuring capacity - Google Patents

Abstract

PURPOSE:To eliminate the need for large facilitates and a drying process and to measure the internal capacity of a container with high accuracy by measuring the detection sensitivity of differential pressure detection for capacity variation previously by using a gas and a capacity adding device. CONSTITUTION:The container 17 to be measured is fitted to measurement-side piping and then while solenoid valves SV3 and SV4 are closed, SV5 and SV6 are opened. Then the solenoid valves SV1 and SV2 are opened to charge air in tanks 13 and 14 to set pressure, and the pressure P'T in the tanks is measured. Then stored tank pressure PT and sensitivity S found by adding the capacity adding device 23 are read out to find correcting sensitivity S'. Then the valves SV1, SV2, SV5, and SV6 are closed and the valves SV3 an SV4 are opened to find the pressure difference between the side of the container 17 to be measured and the side of a reference container 18 by a differential pressure detector 19. Then correcting differential pressure is calculated and the sensitivity S; is used to calculate the corrected capacity difference of the container 17 from the container 18. Thus, not water, but air is used to measure the internal capacity of the container with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an apparatus and method for measuring the internal volume of a container.

``Prior Art'' Conventionally, as a method for accurately measuring the internal volume of a container, for example, a liquid, particularly water, is poured into a container, and the amount of water added until the container is filled is taken as the internal volume.

``Problem to be solved by the invention'' When a large number of containers are measured one after another in the production process, and it is necessary to discard the water and dry the containers after measurement, drainage equipment or collection equipment for the used water is required. Additionally, equipment for drying the container after measurement is also required.

Furthermore, drainage and recovery equipment must take measures to prevent water leakage. Measuring volume using water in this way requires large equipment, and has the drawback of requiring additional equipment and time for drying. Also, handling water is troublesome in many ways.

If we consider measuring volume using a similar method using gas instead of water, since gas is compressible, volume measurement is affected by the pressure of the gas, and is also greatly affected by temperature.

Furthermore, since gas has a lower viscosity than water, leakage of gas from the container itself, the connection between the container and the measuring device, etc. has a large effect.

Therefore, highly accurate measurement was difficult.

The purpose of this invention is to avoid the need for large equipment and drying processes, and to make it possible to measure the internal volume of a container with high precision using gas, especially when measuring variations in the volume of a large number of containers one after another. It is an object of the present invention to provide a suitable volume measuring device and method.

"Means for Solving the Problem" According to the present invention, a pair of tanks having substantially equal volumes for supplying gas to the measurement container side and the reference container side, respectively, and the measurement container and the reference container are provided. means for applying a known change in volume to one side of the container while supplying gas; means for measuring the differential pressure between the container to be measured and the reference container; means for calculating a volume change to differential pressure change ratio representing detection sensitivity from a change in differential pressure before and after the measurement, and means for calculating the volume of the container to be measured from the measured differential pressure and detection sensitivity. It will be done.

Furthermore, the volume measuring method according to the present invention includes the steps of connecting and conducting a sensitivity measurement target container and a reference container to a pair of tanks having substantially equal volumes filled with gas of equal pressure, and performing the sensitivity measurement after the connection. a step of measuring the differential pressure between the container to be measured and the reference container for sensitivity measurement, a step of applying a known volume change to either the container to be measured for sensitivity measurement or the reference container, and a step of measuring the sensitivity after applying the volume change. a step of measuring the differential pressure between the measurement container and the reference container;
a step of calculating a volume change to differential pressure change ratio representing detection sensitivity from the two measured differential pressures and the volume change; and placing the test container and the reference container in the pair of tanks filled with gas of equal pressure. A step of connecting and conducting each, a step of measuring the differential pressure between the container to be measured and the reference container after the connection is made, and a difference in volume of the container to be measured relative to the reference container is calculated from the measured differential pressure and detection sensitivity. The process of
including.

``Example'' Figure 1 shows the mechanical part of a volume measuring device which is an example of the present invention, and in the following description of the example, when the gas used for volume measurement is air. shall be.

The compressed air from the compressed air source 11 is branched and supplied to the inlet sides of the three-way solenoid valves Sv and S V z via a pressure reducing valve 12 via piping. Tanks 13 and 14 each having the same internal volume v7 are connected to the outlet sides of the three-way solenoid valves S1 and SV2 by piping. The tanks 13 and 14 are connected to a measurement side pipe 15 and a reference side pipe 16 via three-way solenoid valves S V3 and S V<, respectively. A container to be measured 17 and a reference container 18 are removably attached to the measurement side piping 15 and the reference side piping 16 via appropriate jigs, respectively.

Further, a differential pressure detector 19 for measuring the differential pressure between the measuring side piping 15 and the reference side piping 16 is connected by piping. Furthermore, measurement side piping 15 and reference side piping 16
are respectively connected to three-way solenoid valves SVS and SV& for exhaust. A tank 13 is provided on the outlet side of the pressure regulating valve 12.
Pressure gauge 2 for visually checking the adjustment of air pressure supplied to 14
1 is connected. Further, in this example, a pressure detector 22 is connected to the tank 13 for detecting the pressure inside the tank 13 or 14, which is data required for volume calculation.

A closed system that includes the tank 13, the container to be measured 17, and the piping section connected to these and which are in gas communication with each other is called the measurement side air system.Similarly, the tank 14 and the reference container 18
A closed system in which gas is conducted to each other, including the air conditioner and the piping portion connected to these, is called the reference side air system. The measurement side piping 15 includes a three-way solenoid valve SV?a volume adder 23 for applying a known volume change to the measurement side air system. A volume adjuster 24 for adjusting the balance between the total volume of the measurement side air system and the total volume of the reference side air system is connected to the reference side piping 16. The volume regulator 24 is composed of a cylinder and a piston, and the piston can be moved by rotating the knob 24-1.

In the above configuration, when the measurement side air system and the reference side air system are left at atmospheric pressure, the solenoid valves SV3゜S Va , S
Vs, S Zero-order solenoid valve sv,,s that closes Vh
The differential pressure detected by the differential pressure detector 19 when the solenoid valves S v+ and S Vz are closed and the solenoid valves SVs and SV4 are opened. Detect how ΔP is expressed.

The volumes of the tanks 13 and 14 including the piping portions are equal to each other (7), and the volume adder 23 is not connected, that is, the solenoid valve SV? VW is the volume including the measured container 17 in a closed state and the measurement side pipe 15 connected thereto, VW is the volume including the reference container 18 and the reference side pipe 16 connected thereto, and is the solenoid valve SVs.

The pressure of the measurement side and reference side air system after opening the SV is Pw, respectively, and the differential pressure detected by the PH1 differential pressure detector is ΔP.
shall be.

V, -V, 4=ΔV -+11PwP,
=ΔP (2) According to Boyle's law, the following equation holds true.

Vt・Pt=(Vt+Vs)・PM−(31V
y・Pt−(Vy+VJ・Pil...(41 formula (1
1, +21 into equation (4) and the PH of equation (3) into the result, VW ・Pt ”(Vy+VM+ΔV)(PM+AP)
From this, ΔP is expressed by the following equation.

Assuming that Δv<< (Vy +VN) holds here, equation (5) can be approximated as follows.

(Vt+Vx) The following can be understood from equation (6). That is, in the configuration shown in FIG. 1, it can be assumed that Vi and Vi do not change, so
When there is a volume difference ΔV between the measurement side air system and the reference side air system, the differential pressure Δ detected after opening the solenoid valves SVs and SV4
P is the initial pressure Pa given to tank 13.14 and the volume difference Δ
■Proportional to the product of.

Its proportionality constant is = Vy/(Vr+VH),
By setting ΔP/Δv=S, equation (6) can be transformed as follows.

ΔP Δ■ S represents the differential pressure detection sensitivity with respect to the volume difference of the differential pressure detector 19 in the configuration shown in FIG.

Initial pressure P given to tank 13.14? If Δv1. is constant, it can be said that equation (7) always holds true within a sufficiently small range of ΔV. Therefore, for different volume differences Δv1. Against Δvt 5
If = API/ΔV + and S = ΔPt/Δv2, the following equation holds true.

ΔV1 ΔV, ΔVt−ΔvI, that is, different volume differences Δv1. When two vessels to be measured giving ΔV2 are connected, the differential pressure ΔP1. Measure ΔP2,
Sensitivity S can be calculated using equation (8). In reality, the differential pressure ΔP1 is first measured for one container to be measured,
Next, a known volume ΔV containing air at atmospheric pressure is added by the volume adder 23, and the differential pressure ΔP2 is similarly measured.

The added volume Δv3 is the change in volume difference (Δv2−Δ■,) in equation (8), and therefore, from equation (8), the sensitivity S
can be calculated.

If the pipes of the measuring side air system and the reference side air system are designed to have the same internal volume, then Δ■ in Equation 11 is equal to
7 and the reference container 18.

Therefore, when the sensitivity S is calculated as described above for the predetermined initial pressure PT, this sensitivity S is used to calculate the volume difference ΔV between the reference container 18 and another measured container 17 having an unknown volume using the following formula. It can be found by

ΔV=ΔP/S (9) Let the volumes of the measured container 17 and the reference container 18 be V, , V, respectively.
, is the volume V of the container 17 to be measured.

is V, -VII +ΔV...
It can be calculated using αω. However, in order to improve measurement accuracy, Δ
It is necessary to fully satisfy the condition v<<('V, +VN), and for this purpose, it is preferable that the volume difference ΔV itself is small. That is, the container to be measured 17 is used as the reference container 18.
It is desirable to select a volume that is as close as possible to the volume of . If you want to measure the variation in volume of a large number of produced containers of the same type, select one of those containers and use it as the reference container 18, and calculate the other containers for that reference container 18 using equation (9). This makes it possible to successively measure the difference in volume between containers.

Generally, the designed volumes of various designed containers to be measured are known in advance, so when changing the type of container to be measured, instead of changing the reference container 18, the volume adjuster 24 can be used to adjust the desired reference volume. Adjustments may be made so that they are approximately the same. This adjustment gives a volume of ΔV to the reference container 18, which is equivalent to mounting a reference container with approximately the same volume as the volume of the container to be measured 17. Volume regulator 2
4, the differential pressures ΔPI and ΔPg are measured as described above, and the sensitivity is calculated from equation (8). In this case, the internal volume of the reference container 18 will be (V, +Δ
Equation αφ is calculated assuming that V). That is, the volume of the container 17 to be measured is calculated using V, -V, +ΔV+ΔV . . . αD.

In the above, it has been assumed that the container to be measured 17 has no leakage, but next we will consider the case where there is a slight leakage. If there is no leakage, solenoid valve SV3. After opening SV4 at time t, the differential pressure between the measurement side and reference side air systems reaches a constant value within a short time δ, as shown by the dashed line (a) in Figure 3, and does not change thereafter. When this is observed with the differential pressure detector 19, for example, if a diaphragm type differential pressure detector is used as the differential pressure detector, the response of the displacement of the diaphragm is slow and the transient phenomenon occurs.
As shown by (IT), the rise is slow and after overshooting, it returns to the constant value. However, if there is a small leak in the container 17 to be measured compared to its internal volume, the pressure in the measurement side air system will decrease over time, and therefore the differential pressure detector 1
The output of 9 also changes.

This change can be regarded as a linear change within a short period of time, so
Considering the response characteristics of the differential pressure detector 19, the detected differential pressure changes as shown by the solid line (c).

Solenoid valve SV3. Immediately after opening the SV (for example, after δ), the amount of air that actually leaked out is so small that it can be ignored, so the differential pressure at that time can be used as the correct differential pressure. The differential pressure is approximately equal to the differential pressure value ΔP0 at the point where the straight line portion of the curve (C) is extended and intersects the vertical axis (differential pressure) at time t0. The differential pressure detected between time points t1 and t2 within the linear region of line (c) is ΔP.

When ΔP2 is assumed, ΔP0 is given by the following equation.

1. If the differential pressure ΔP0 obtained by tapping -1° is used in place of ΔP in equation (9), the volume difference Δ■ with respect to the reference container 18 can be determined with high accuracy even if there is a leak in the measured container 17. can. Although equation (2) represents a correction of the differential pressure for leakage, changes in the differential pressure also occur due to causes other than leakage, such as a decrease in the temperature of the gas in a closed air system. However, if the change can be considered linear within a short period of time, correction is possible as well. After all, the correction by Equation A corrects the overall differential pressure change due to leakage, temperature change, and all other causes.

When the volume difference ΔV of a large number of containers with respect to the reference container 18 is sequentially measured using equation (9) using the same detection sensitivity S, as is clear from equation (7), The initial pressure P7 to be applied must always be the same for each measurement, but if the pressure of the compressed air source 11 changes, P7 will naturally change as well. However, since the volume Va of the tank 13.14 and the daily volume of the reference container 2 do not change, the proportionality constant = VT/(VT+Vg) is constant. If the detection sensitivity at the time is expressed as S', the following equation holds true.

S'-- to -P'a...aS Formula (7) and (to) yield the following formula.

S'=S-P'T/Pd...αO Therefore, in the measurement of each container 17 to be measured, the solenoid valves sv,, sv
Pressure P' of air filled in tank 13.14 after opening z
A can be detected by the pressure detector 22, the sensitivity can be corrected by 200, and the corrected sensitivity S' can be used in place of the sensitivity S in equation (9). It is necessary to measure the sensitivity in advance for each volume measurement. There isn't.

Figure 2 shows a control unit that controls the operation of the volume measuring mechanism shown in Figure 1 and calculates the detection sensitivity S or volume difference ΔV based on various constants and measured values. , a microcomputer 31, and other peripheral circuits.

The micro combinator 31 has a CPU 41. RAM
42. ROM 43, input port 44, output port 4
5, which are connected to each other via a common bus 46.

The outputs of the differential pressure detector 19 and the pressure detector 22 in FIG. 1 are respectively connected to the input side of the multiplexer 32,
One of the differential pressure signal ΔP and the pressure signal PT is selected and connected to the output side. The output side of the multiplexer 32 is connected to an amplifier 33, and the differential pressure signal ΔP or the pressure signal Pt is amplified. The output of the amplifier 33 is connected to the input of the AD converter and converted into a digital signal, and is also connected to a monitor meter 35 for analog display. The output of the AD converter 34 is sent to the computer 31 via an input port 44.
taken within. A keyboard 36 is connected to the input port 44 for inputting set times 'I''+, Tt, Ts of various timers and the added volume value ΔV of the volume adder 23.The output port 45 displays the calculation results. A display 37 for operating the valve and a drive circuit 38 for opening and closing each electromagnetic valve shown in FIG. 1 are connected.ROM
43 stores as a program the operating procedures shown in FIGS. 4 and 5 for measuring the detection sensitivity and measuring the volume difference by the apparatus of the present invention, and the CPU operates the solenoid valve S V by the drive circuit 38 according to this program. In addition to controlling the opening and closing of + to SV, selecting signals at the multiplexer 32, displaying calculation results on the display 37, displaying instructions on the indicator 39, etc., necessary calculations such as detection sensitivity and measurement volume are executed.

Trajectory Creation (Sensitivity Measurement) First, the detection sensitivity S is measured before volumetric measurement is performed using the apparatus of the present invention. For this purpose, a leak-free container 17 to be measured is connected to the measurement side piping 15. Next, pressure gauge 2
While monitoring the instructions in step 1, adjust the pressure reducing valve 12 to remove tank 1.
3. Set the air pressure to be applied in 14. After completing the settings, the operator inputs a start instruction using the keyboard 36.

Hereinafter, the mechanical section shown in FIG. 1 is controlled according to the operation flowchart shown in FIG. 4, and various calculations are performed based on the measured data in the control section shown in FIG.

In step S1, close the solenoid valves SVs and SVn, and SV...
SVa and SVt are opened to the atmosphere.

In step Ss, open solenoid valves SV+ and SV2 in tank 1.
3. Fill with air at the pressure set in 14.

- In step S81, a T+ timer set at a predetermined address in the RAM 42 is started, and it is determined whether time T has elapsed. When TI has elapsed, it is determined that the pressure in the tanks 13 and 14 has reached equilibrium, and the solenoid valve S is activated in step S4.
Close V+, SVz, SVs, SVi, and SVt, and close solenoid valve S V in step S.3. Open S V a. T set at the predetermined address of the RAM 42 in step S.
A low timer is started and it is determined whether the time Tt has elapsed.

When T2 has elapsed, it is determined that the pressures of the measurement side air system and the reference side air system have reached equilibrium, and in step S, the multiplexer 32 selects the differential pressure ΔP to calculate the current value from the differential pressure detector 19. Load detected differential pressure ΔP1 into RAM4
2 at a predetermined address. Step S, solenoid valve S
Vt is opened and a predetermined volume ΔV is added to the measurement side air system. In step S, the T2 timer is started again and it is determined whether time T2 has elapsed. After T2 has elapsed, in step 31+1, the multiplexer 32 selects the differential pressure ΔP and takes in the detected differential pressure ΔP2 from the differential pressure detector 19 and stores it in the RAM.
42 at a predetermined address. In step S, the differential pressure Δ
Calculate the change ΔP between P1 and ΔP, and step SI! Calculate the detection sensitivity S representing the differential pressure change ΔP with respect to the added volume ΔV. Next step SI! Solenoid valve S, V
3°Close SV4 and open solenoid valve SV3. Open the SV& and open (vent) the air system to the atmosphere.6 Next, in step S14, start the timer T again, and when the time T has elapsed, turn on the indicator 39 in step SI8 to end the sensitivity measurement. do. Step SI! The calculated sensitivity S is stored at a predetermined address in the RAM 42.

Study (volume measurement) Next, measure the container 1 according to the flowchart shown in Fig. 5.
Volume difference ΔV between 7 and reference container 18 and/or measured container 1
The operation of measuring the internal volume 1 of 7 will be explained.

After the container 17 to be measured is attached to the measurement side piping 15, when the operator issues a start instruction from the keyboard, the solenoid valves SV, SV4 are closed in step S+, and SVs is activated.

Open SV. In step S2, the solenoid valve S V1. S
Open Vt and fill the tank 13.14 with air at the set pressure. In step S, a timer T set at a predetermined address in the RAM 42 is started, and it is determined whether time T1 has elapsed. If T has elapsed, step S
4, measure the tank internal pressure P'a.

In the sensitivity measurement process in step Ss) lAl'142
Tank pressure P stored in ? Then, the sensitivity S is read out and the corrected sensitivity S' is calculated by 2. Step S, solenoid valve S
Close V+, SVt, SVs, SVa, step S
, solenoid valve SV3. Opening SVJ Next, in step SI, a T2 timer set at a predetermined address in the RAM 42 is started, and it is determined whether time T2 has elapsed. After T2 has elapsed, in step S, the pressure difference ΔP between the air systems on the measurement side and the reference side is loaded into the measurement RAM 42. At step 316, a timer is started with T set at a predetermined address in the RAM 42, and it is determined whether time T4 has elapsed. After T4 has elapsed, in step S, the differential pressure ΔP between the two air systems is measured again and loaded into the RAM 42, step S1! RAM4
2 to the measured differential pressure ΔP+, ΔPg and timer time Tt.

T4, that is, (t+-to) and (tz-t+) are read out, and the corrected differential pressure ΔP0 is calculated by formula. In step 5Iff, the corrected sensitivity S' is read from the RAM 42 and the corrected volume difference ΔV of the measured container 17 with respect to the reference container 18 is calculated using equation (9). Then step 314
In step srs, the volume difference ΔV is displayed on the display 37, and in step srs, the solenoid valves 3V, SV, are closed, and the solenoid valves S Vs , S
Open V&, step SI 6 i' T 3 Start timer, and if time T, has elapsed, step SL'
Turn on the indicator 39 with l to end the measurement. If necessary, step S'1. calculates the volume 1 of the container 17 to be measured between steps S11 and S14 using the formula αω. may be provided as shown by the dotted line.

As mentioned above, when the type of the container I7 to be measured, that is, its volume, changes, the volume adjustment can be performed by adjusting the volume adjuster 24 without replacing the reference container to equivalently change the type of container 17 to be measured. This is the same as installing a reference volume 18 with a volume approximately equal to . Therefore, it is not necessarily necessary to prepare as many reference containers as there are types of containers to be measured, and by providing the volume adjuster 24, it is possible to reduce the number of reference containers that need to be prepared. In this case, the volume change Δvc of the container adjuster 24, which was moved and adjusted before the sensitivity measurement shown in FIG. 4, needs to be maintained as it is during the volume measurement shown in FIG. Therefore, the volume difference measured in steps Sl and I in FIG.
′, equivalent reference volume #lkv, −(v′, +ΔV
It represents the volume difference with respect to c), and the number 20 is transformed as follows.

v, - (v', +ΔV,) = ΔV (2) Therefore, when determining the volume of the container 17 to be measured, in step S'+3 of FIG.
) must be used to calculate. Of course, the volume regulator 24
If it is installed in the air system on the measurement side, (V, +ΔVC) can be used instead of ■ in 200.

In order to perform measurements on a large number of containers, it is sufficient to first determine the detection sensitivity S shown in the flowchart of FIG. 4, and then carry out the measurement shown in FIG. 5 for each container to be measured. Of course, if the initial tank pressure is correctly set to pt for each container to be measured, steps Sa and Ss in FIG. 5 can be omitted.
It is sufficient to use the sensitivity S that is not corrected in step SIS.

What is defined by the formula il+ is always the difference in volume between the measurement side air system and the reference side air system, so the volume adder 23 may be attached to the reference side air system instead of the reference side.

Similarly, the volume adjuster 24 may also be attached to the measurement side air system instead of the reference side.
It is preferable that the volume adjuster 24 can be adjusted to increase or decrease the volume from the neutral point.

The proportionality constant K in equation (6) = V / (VT + V
M)” is V y = V for a given vM,
If you choose l, K will be the maximum. In other words, if the volumes of the containers to be measured are approximately the same,
Optimum sensitivity can be obtained by designing the device by choosing a volume of 3°14 such that v, =V, .

"Operations and Effects of the Invention" As explained above, according to the present invention, the volume of containers to be measured can be measured one after another using gas without using water, and is therefore particularly suitable for volume measurement on a production line. In addition, in order to measure the volume, if you use a volume adder to measure the detection sensitivity of differential pressure changes with respect to volume changes in advance, it will be possible to calibrate even if there is a leak in the container to be measured or the gas pressure changes due to temperature. It is possible to measure the correct volume difference or volume created.

[Brief explanation of drawings]

Figure 1 is a diagram showing the mechanism of the volume measuring device, Figure 2 is a diagram showing the control unit of the volume measuring device, Figure 3 is a diagram showing the output change over time of the differential pressure detector, and Figure 4 is the sensitivity. Flowchart showing measurement operation FIG. 5 is a flowchart showing volume measurement operation. 11: Compressed air source, 12: Pressure reducing valve, 13.14: Tank, 15: Measurement side piping, 16 Two reference side piping, 17: Measured container, 18: Reference container, 19: Differential pressure detector, 21: Pressure meter, 22: pressure detector, 23: volume adder, 24: volume regulator, 35: meter type voltmeter, SV + ~ SV,:
Two-way solenoid valve.

Claims (5)

[Claims] (1) A: A pair of tanks having approximately equal volumes for supplying gas to the measurement container side and the reference container side, respectively; (C) means for measuring the differential pressure between the container to be measured and the reference container; and (D) measuring the volume change and the differential pressure before and after the volume change is applied. A volume measuring device comprising: means for calculating a volume change to differential pressure change ratio representing detection sensitivity from the change; and E means for calculating the volume of the container to be measured from the measured differential pressure and detection sensitivity. (2) a means for measuring the initial pressure of the tank, a means for correcting the detection sensitivity from the initial pressure of the tank given when measuring the detection sensitivity, and the initial pressure of the tank given when measuring the volume; The first claim that includes the means
Container measuring device as described in section. (3) The volume measuring device according to claim 1, further comprising means for calibrating the measured differential pressure from two differential pressure data measured at a predetermined time interval by the differential pressure measuring means. (4) The volume measuring device according to claim 1, further comprising a volume adjusting means attached to either the measured container side or the reference container side for balancing the volumes. (5) Connecting and electrically connecting the container to be measured for sensitivity measurement and the reference container to a pair of tanks having approximately equal volumes filled with gas at the same pressure, and the container to be measured for sensitivity measurement and the reference after the electrical connection. a step of measuring the differential pressure of the container; a step of applying a known volume change to either the container to be measured for sensitivity measurement or the reference container; and the container to be measured for sensitivity measurement after the volume change has been applied. a step of measuring the differential pressure of the reference container; a step of calculating a volume change to differential pressure change ratio representing detection sensitivity from the two measured differential pressures and the volume change; and the pair filled with gas of equal pressure. A step of connecting and electrically connecting the container to be measured and the reference container to the tank, a step of measuring the differential pressure between the container to be measured and the reference container after the electrical connection, and determining the reference container from the measured differential pressure and detection sensitivity. A volume measuring method comprising: calculating a volume difference of the container to be measured with respect to the container.