JP2001317983A - Method for measuring liquid level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a simple measurement of the liquid level of a liquid to be measured, in which its specific gravity is not known beforehand. SOLUTION: In the method for measuring liquid level, a liquid 3 to be measured is put in a container 1, and the specific gravity of the liquid 3 is calculated from the relationship between the pressure difference of a first pressure when the liquid 3 arrives at a first set point P1 and a second pressure when the liquid arrives at a second set point P2 higher than the point P1, and a pressure of a reference liquid having a known specific gravity. Then, a measured lower limit value and a measured upper limit value of the liquid 3 are calculated from the specific gravity of the reference liquid, calculated specific gravity and first, second set points P1, P2 and the proportional relationship between the liquid level of the liquid 3 and the pressure as a liquid level data table is obtained. The pressure-measured value of the liquid 3 which is actually filled in the container 1 is collated with the liquid level data table, and the actual liquid level is calculated and measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level measuring method, and more particularly to a back pressure type liquid level measuring method for measuring the liquid level (height to liquid level) of liquid stored in various industrial fields. Regarding improvement.

[0002]

2. Description of the Related Art Conventionally, for measuring the liquid level of a liquid stored in a container, for example, there is a method using gas pressure.

[0006] That is, as shown in FIG. 6, a liquid 3 to be measured is stored in a container 1, and one end of a pipe 7 is connected to a gas supply device 5 for feeding an inert gas (gas) under pressure. It is inserted into the liquid 3 to be measured, and bubbles 9 are always generated in the liquid 3 to be measured from the tip of the pipe 7, and a liquid level measuring device 11 is connected in the middle of the pipe 7, and the gas pressure in the pipe 7 This is a measurement method for measuring the liquid level through the measurement of the liquid level.

[0004] Reference numeral 13 in FIG.
1 is a joint inserted in the middle of the pipe 7 to connect the two.

Generally, when a liquid 3 to be measured having a specific gravity ρ is stored in a container 1 and a virtual reference surface is considered at an arbitrary depth H from the liquid surface, the pressure P on the reference surface is represented by the gravitational acceleration g. Then, P = ρgH, and the depth H can be expressed as follows. H = P / ρg (1)

According to this, if the specific gravity ρ of the liquid 3 to be measured is known, the liquid level H can be known by measuring the pressure P.

In the above-described liquid level measurement method of the back pressure type, the gas pressure (static pressure) at the tip of the pipe 7 is equal to the gas pressure in the pipe 7, and the gas pressure in the pipe 7 increases as the liquid level increases. Therefore, if the gas supply from the gas supply device 5 is adjusted so as to generate bubbles 9 from the tip of the pipe 7 in a state where the liquid 3 to be measured is fully stored in the container 1, the liquid 3 to be measured is full. From the state to the empty state, the gas level in the pipe 7 is measured by the liquid level measuring device 11, and the liquid level H can be obtained by applying the above equation (1).

As a means for forming the liquid level measuring device 11 and measuring the pressure of gas in the middle of the pipe 7, a back pressure type pressure sensor is used.

[0009]

However, the above-described back pressure type liquid level measuring method is suitable for measuring the liquid level of the liquid 3 to be measured whose specific gravity is known in advance. If the specific gravity of the liquid 3 is different, the pressure will also be different. Therefore, it is difficult to measure the liquid level of the liquid 3 whose specific gravity is unknown.

In the case of the container 1 for storing the liquid 3 to be measured, if the container has an arbitrary shape, the measured liquid level does not always have a predetermined proportional relationship, and it is difficult to accurately measure the remaining volume. Was.

Further, when a semiconductor wafer is processed in a chemical solution in a semiconductor manufacturing process or the like, the specific gravity of the chemical solution easily changes in accordance with the number of times the semiconductor wafer is processed, and the liquid surface level is changed with the change in the specific gravity. It has been difficult to measure accurately.

The present invention has been made to solve such a conventional problem, and has as its object to provide a liquid level measuring method capable of measuring the liquid level of a liquid to be measured whose specific gravity is not known in advance. .

It is another object of the present invention to provide a liquid level measuring method capable of accurately measuring the remaining volume of a liquid to be measured stored in a container having an arbitrary shape.

Still another object of the present invention is to provide a liquid level measuring method capable of accurately measuring the liquid level even when the specific gravity of the liquid to be measured changes for each processing of the processing object.

[0015]

In order to solve such a problem, a first method according to the present invention is to insert a pipe into a liquid to be measured placed in a container and supply a gas at a predetermined pressure. In the liquid level measurement method of measuring the liquid level of the liquid to be measured by measuring the back pressure in a state where bubbles are generated in the liquid to be measured from the end of the pipe, the liquid to be measured is previously stored in the container. The first set point when the first set point is reached
The specific gravity of the liquid to be measured is determined from the proportional relationship between the pressure of the reference liquid and the pressure difference between the pressure of the reference liquid and the second pressure when the pressure reaches the second set point higher than the first set point. A first step of calculating, and a second step of obtaining a liquid level data table indicating a proportional relationship between the pressure of the liquid to be measured and the liquid level at least between the first and second set points based on the calculated specific gravity. And a third step of measuring the liquid level by making the pressure value of the liquid to be measured put in the container correspond to the liquid level data table as the main measurement.

In the first method, as a second step,
The measurement lower limit level and the measurement upper limit level of the liquid to be measured corresponding to the measurement lower limit level and the measurement upper limit level of the reference liquid are calculated from the calculated specific gravity, the reference liquid specific gravity, and the first and second set points. The proportional relationship between the pressure and the liquid level may be obtained as the liquid level data table.

According to a second method of the present invention, in the liquid level measuring method for measuring the liquid level of the liquid to be measured, the volume of the container and the liquid level when a reference liquid whose specific gravity is known in advance are filled A fourth step of obtaining a relationship with the level as a volume data table;
From the pressure difference between the third pressure when the set point is reached and the fourth pressure when the set point is higher than the third set point, and the pressure due to the reference liquid. A fifth step of calculating the specific gravity of the liquid to be measured, a sixth step of correcting the volume data table with the calculated specific gravity, and a pressure data of the liquid to be measured placed in the container as the main measurement in the volume data table. And a seventh step of measuring the remaining volume of the liquid to be measured.

Further, a fourth method according to the present invention is the liquid level measuring method for measuring the liquid level of the liquid to be measured, wherein the object to be processed is processed a plurality of times in the liquid to be measured placed in the container. An eighth step of setting an initial specific gravity before the processing and a specific gravity after the plurality of processings, a ninth step of calculating a change specific gravity for each processing number from the initial specific gravity and the specific gravity after the processing, A tenth step of correcting the pressure measurement value of the liquid to be measured for each number of times with a change specific gravity corresponding to the number of times of processing at the time of the pressure measurement to measure a liquid level.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. First, for convenience, a liquid level measurement device that implements the liquid level measurement method of the present invention will be described.

FIG. 1 is a block diagram showing a liquid level measuring device for implementing the liquid level measuring method of the present invention, and corresponds to, for example, the liquid level measuring device 11 in FIG.

In FIG. 1, reference numeral 15 denotes a back pressure type pressure sensor which is disposed in the liquid level measuring device 11 in FIG. 6 and outputs an analog measurement signal having a level corresponding to the gas pressure fed through the pipe 7. The sensor is connected to the input unit 17. As the pressure sensor, for example, a semiconductor pressure sensor or other conventionally known sensor elements are used.

The input unit 17 converts the measurement signal from the pressure sensor 15 into a digital signal by A / D conversion at a predetermined timing, and is connected to the calculation unit 19.

The operation unit 19 includes a CPU 19a for executing a main operation, calculation or judgment function of the present invention,
It is formed having a ROM 19b storing the operation program of 9a and an input / output interface 19c, and is connected to the storage unit 21, the display unit 23, the setting unit 25, and the alarm unit 27. The function of the calculation unit 19 will be described later.

The storage unit 21 is a built-in or external memory for storing a liquid level data table and other data tables, which will be described later, and various kinds of data.

The display unit 23 is a liquid crystal display or the like that displays the liquid level calculated by the calculation unit 19 in mm or%, or displays other items.

When the set point is reached, the setting section 25 inputs the height of the liquid level, and instructs tamping to take in the pressure value from the input section 17 and store it in the storage section 21 as described later. , Etc., are input from the outside and the storage unit 2
1 and a keyboard and an online connection unit.

The liquid (pure water) having a specific gravity of 1 has a height of 100
A pressure value of 0 mm 9.807 kPa (measurement upper limit), 0 kP
a (measurement lower limit) and the like may be fixedly input and set in advance from the setting unit 25 or at the time of manufacture.

The alarm unit 27 is a liquid crystal display or a buzzer that issues an alarm to the outside when the liquid level calculated by the calculation unit 19 or the like is out of the measurement range, and is configured as a part of the display unit 23. It may be done.

As shown in FIG. 6 described above, the measurement liquid 3 for which the liquid level is to be actually measured is flowed into the container 1 in advance and, for example, 250 mm from the bottom of the container 1 (first position) as shown in FIG.
The set point P1) and the pressure when the pressure reaches 400 mm (the second set point P2) are taken in according to an instruction from the setting unit 25,
It has a function of storing in the storage unit 21. The first and second set points P1 and P2 are arbitrary.

FIG. 2 shows the case where the pressures when the liquid 3 reaches 250 mm (first set point P1) and 400 mm (second set point P2) are 1.961 kPa and 3.923 kPa, respectively. The relationship between the pressure and the liquid level between these two points is virtually shown as a linear relationship.

The calculating section 19 calculates the pressure values of the first and second set points P1 and P2 and the specific gravity of the reference liquid 9.807.
From kPa, the specific gravity of the liquid 3 to be measured is calculated by the following formula,
State of 0 kPa (measurement lower limit) in pure water and 9.807
It has a function of calculating a measurement lower limit value and a measurement upper limit value of the measured liquid 3 corresponding to a state of kPa (measurement upper limit).

Calculated specific gravity = [1000 mm × (3.923 kPa−1.96 kPa) /9.807 kPa] / 400 mm−250 mm = 1.333 (2) Measurement lower limit = 250 mm − [(1000 mm × 1.961 kPa / 9.807 kPa) / 1.333 ...] = 100 mm (3) Upper limit of measurement = (400 mm-250 mm) / [(3.923 kPa-1.961 kPa) /9.807 kPa] +100 mm = 850 mm (9) Here, 9.807 kPa is 1000 mm of pure water. Is the pressure equivalent value of the depth.

That is, the calculating section 19 calculates the ratio of the specific gravity of the reference liquid to 9.807 kPa to the pressure value difference (3.923 kPa to 1.961 kPa) at the first and second set points P1 and P2 of the liquid 3 to be measured. A function of calculating the specific gravity of the liquid 3 to be measured with respect to the specific gravity 1 of pure water from the ratio of the distance between the first and second set points P1 and P2 (400 mm-250 mm).

The calculating section 19 calculates the ratio of the pressure of the reference liquid 9.807 kPa to the pressure (1.961 kPa) of the first set point P1 for the liquid 3 to be measured and the calculated specific gravity of the liquid 3 to be measured (1. 333) and the first set point P1 to calculate the measurement lower limit value of the liquid 3 to be measured.
And the distance between the second set points P1 and P2 (400 mm−
250 mm) and the ratio of the reference liquid pressure 9.807 kPa to the pressure value difference (3.923 kPa-1.961 kPa) between the first and second set points P1 and P2, and the liquid at the first set point P1. It has a function of calculating the measurement upper limit value of the liquid 3 to be measured from the surface level.

Further, the calculating unit 19 calculates the calculated specific gravity,
It has a function of creating a liquid level data table (see FIG. 2) in which the relationship between the pressure level and the liquid level is linearized from the measurement lower limit value and the measurement upper limit value, and storing it in the storage unit 21.

The arithmetic unit 19 compares the pressure value input from the input unit 17 with the liquid level data table for the liquid 3 to be measured placed in the container 1 as the main measurement, and determines the corresponding pressure value and liquid level. In addition to the function to be displayed on the display unit 23, it has various functions described below.

Next, a first method according to the liquid level measuring method of the present invention will be described. FIG. 3 is a flowchart for explaining the operation of the above-described liquid level measuring device and the main part of the first method according to the present invention.

As shown in FIG. 6, the other end (end) of the pipe 7 having one end connected to the gas supply device 5 is inserted into the liquid 3 to be measured in the container 1 from the liquid level. An inert gas is pressure-fed from the pipe 7 to form a state in which bubbles 9 are always generated from the tip of the pipe 7, and 9.807 kP which is a pressure value of a pure water level of 1000 mm from the setting unit 25 in FIG.
a, pure water at 0 kPa (measurement lower limit) and 9.807
Each pressure value in the kPa (measurement upper limit) state is set in the setting unit 2
5 to the storage unit 21 in advance.

When the program is started in step 300, a first set point P1 is set in step 301 based on an instruction from the setting section 25, and when the measured liquid 3 reaches the first set point P1, At step 302, the first pressure value is fetched in accordance with an instruction from the setting unit 25, and step 303
Is determined by the computing unit 19 as to whether or not the first pressure is within the measurable range of the liquid level measuring device 11.

If the first pressure is the liquid level measurement device 1
If it is out of the preset measurable range in step 1 and N is determined, in step 311 the arithmetic unit 19 performs a processing to indicate that there is a specific gravity correction error due to the liquid 3 to be measured, and the display unit 23 informs the display unit 23 of that. The message is displayed and an alarm is output to the alarm unit 27, and the flow proceeds to the return of step 312.

In the case of Y within the measurable range, the process proceeds from step 303 to step 304 to input and set the second set point P2 based on the instruction from the setting section 25, and the liquid 3 to be measured is When the set point P2 is reached, step 304
At the time, the second pressure is taken in according to an instruction from the setting unit 25,
In step 306, the calculation unit 19 determines whether the second pressure is within the measurable range of the liquid level measuring device.

If it is out of the measurable range and N, the above-described error processing is performed in step 311. If it is in the measurable range and Y, the arithmetic unit 19 is executed in step 307.
Performs specific gravity calculation processing using the above-described equation (2), and in step 308, the calculation unit 19 determines whether or not the calculated specific gravity is within the measurable range.

If it is out of the measurable range and N, the arithmetic unit 19 performs the above-described error processing in step 311,
In the case of Y within the measurable range, in step 309, the calculation unit 19 performs the calculation processing of the measurement lower limit value using the above formula (3), and in step 310, the measurement upper limit value using the formula (4). Is performed to create a liquid level data table, and the flow proceeds to the return of step 312.

After the liquid level data table is created, in the actual measurement of the liquid level of the liquid 3 to be measured, the pressure value input from the input unit 17 by the arithmetic unit 19 is stored in the liquid level data in the storage unit 21. The table is collated with the table, and the corresponding liquid level is output to the display unit 23 to be displayed.

As described above, the first method according to the present invention comprises:
The first pressure when the liquid 3 to be measured is previously placed in the container 1 and the first set point P1 is reached from the bottom of the container 1 and the second pressure when the second set point P2 higher than the first set point P2 is reached The specific gravity of the liquid 3 to be measured is calculated from a proportional relationship between the pressure difference between the measured liquid 3 and the pressure value due to pure water (first step). Measurement lower limit level and measurement upper limit level are calculated specific gravity,
The specific gravity of the reference liquid is calculated from the first and second set points P1 and P2, and the proportional relationship between the pressure and the liquid level is determined as a liquid level data table (second step). The actual liquid level was measured by associating the pressure value of the liquid 3 to be measured with the liquid level data table (third step).

Therefore, it is possible to measure the liquid level of the liquid 3 to be measured whose specific gravity is unknown only by using the reference liquid whose specific gravity is known in advance, for example, the specific gravity of pure water. Is simplified.

Further, in the above-described first method, the calculated specific gravity, the specific gravity of the reference liquid, the first and second set points P1, P2
The lower limit value and the upper limit value of the measurement are calculated from the above and the liquid level data table is created. Since the pressure and the height of the liquid to be measured are in a proportional relationship, the first and second set points P1, P
Even if 2 is arbitrarily selected, there is an advantage that the widest possible measurement range can be automatically secured.

However, if the first set point P1 is selected at a position near the measurement lower limit and the second set point P2 is set at a position near the measurement upper limit, at least the first and second set points are set. Between P1 and P2, it is possible to measure the liquid level of the liquid 3 to be measured whose specific gravity is unknown.

Therefore, it is not always necessary to calculate the measurement lower limit level and the measurement upper limit level of the liquid 3 to be measured, which correspond to the measurement lower limit level and the measurement upper limit level of the reference liquid.

Next, a second method of the liquid level measuring method according to the present invention will be described. In order to carry out the second method, the calculation unit 19 and the storage unit 21 shown in FIG. 1 have the following functions in addition to the functions described above.

The computing unit 19 has a function of creating a relationship between a predetermined liquid level in an arbitrary container 29 and the remaining volume for each liquid level as a volume data table and storing it in the storage unit 21. .

That is, as shown in FIG. 4, 1 liter, 6 liters, 12 liters,
9 liters, 27 liters, 36 liters, 45 liters, 53 liters, 60 liters, 66 liters, 71
The operator reads the liquid level when the liter is charged from the outside, and inputs the liquid level and volume of these 11 points from the setting unit 25. When the operator inputs the liquid level and volume from the setting unit 25, the calculating unit 19 calculates The relationship with the capacity is created as a volume data table and stored in the storage unit 21.

Further, similarly to the first method (see FIGS. 2 and 3), the calculating section 19 puts the liquid 3 to be measured for actually measuring the liquid level in the container 29 and, for example, from the bottom of the container 29 220 mm (third set point P3) and 420 mm (fourth
(The third and fourth pressures) when the pressure reaches the set point P4) is stored in the storage unit 21 according to the instruction from the setting unit 25, and the measured liquid 3 is calculated by the above-described equation (2). Has a function of correcting the liquid level in the volume data table from pure water to a liquid level corresponding to the specific gravity of the liquid 3 to be measured by the calculated specific gravity, and rewriting and storing the storage unit 21. I have.

Then, for the liquid 3 to be measured in the container 29, the arithmetic unit 19 checks the pressure value input from the input unit 17 during the main measurement with the corrected volume data table, and determines the remaining volume corresponding to the measured pressure. It has a function of displaying on the display unit 23 and calculating and displaying the amount of change from the previous measured pressure.

As described above, the second method according to the present invention comprises:
The relationship between the volume of the container 29 and the liquid level when a reference liquid having a known specific gravity is charged is stored as a volume data table (fourth step). The third pressure when reaching the third set point P3 from the bottom and the fourth set point P4 higher than the third set point P3
The specific gravity of the liquid 3 to be measured is calculated from the relationship between the pressure difference from the fourth pressure when the pressure reaches the pressure and the pressure of the reference liquid whose specific gravity is known (fifth step), and the volume data table is calculated. Corrected by the specific gravity and stored (sixth step), and the actual remaining volume is measured by associating the pressure value of the liquid 3 to be measured in the container 29 with the volume data table as the main measurement (seventh step). ), Even if the container 29 for storing the liquid 3 to be measured is not of a simple cylindrical shape, the remaining volume and the amount of change from the previous measurement pressure can be measured by measuring the pressure of the liquid 3 to be measured.

Moreover, for the liquid 3 to be measured whose specific gravity is not known in advance, the specific gravity is calculated using the pressure between the third and fourth set points P3 and P4 and the pressure of the reference liquid whose specific gravity is known.
Since the volume data table is corrected by the calculated specific gravity, the remaining volume can be measured by putting the measured liquid 3 having an unknown specific gravity into an arbitrary container 29.

When a semiconductor wafer is processed in a chemical solution, the specific gravity of the chemical solution changes according to the number of times of the processing. Therefore, the third method is useful for accurately measuring the liquid level from the measured pressure. It is.

Hereinafter, a third method of the liquid level measuring method according to the present invention will be described. To implement the third method,
The calculation unit 19 and the storage unit 21 illustrated in FIG. 1 have the following functions.

The calculating section 19 is provided for measuring the liquid 3 to be measured stored in the container 1.
With respect to the initial specific gravity, the end specific gravity in a state where the predetermined number of processes have been completed, and when the number of processes is input from the setting unit 25, a change in the number of processes and a change in the specific gravity for each process are created as specific gravity table data, It has a function of storing in the storage unit 21.

That is, in the third method, as shown in FIG. 5A, the specific gravity of the liquid 3 to be measured in the initial state is compared with the specific gravity of FIG.
The specific gravity after processing the object 31 once and taking it out as described above, and further, as shown in FIG. Is what you do.

The calculating section 19 stores the object 31 to be measured in the liquid 3 to be measured.
When the number of times of processing is input from the setting unit 25, the pressure value input from the input unit 17 is compared with the specific gravity data table to calculate the corresponding liquid level, and displayed. It has a function of outputting to the unit 23.

As described above, the third method according to the present invention comprises:
The initial specific gravity before the treatment and the specific gravity after the plurality of treatments in the case where the predetermined treatment is performed a plurality of times in the liquid to be measured 3 placed in the container 3 are measured (eighth step), and the initial specific gravity and the treatment are measured. The relationship between the specific gravity and the pressure is stored from the subsequent specific gravity and the relationship between the specific gravity and the pressure (a ninth step), and the pressure measurement value of the liquid to be measured is changed according to the number of processes during the pressure measurement. Since the liquid surface level is measured by correcting with the specific gravity (tenth step), even if the specific gravity of the liquid 3 to be measured changes for each processing of the processing object 31, the specific gravity automatically changes according to the number of times of processing. Is corrected to
Accurate liquid level measurement is possible.

In the liquid level measurement method of the present invention, when the end of the pipe 7 is opened, that is, when the pressure of the gas to be pumped is empty while the containers 1 and 29 are empty, the pressure value is determined to be a predetermined value. Is determined to be within the range of the initial value, and if it is within the range of the initial value, the measurement is advanced, and if it is out of the range of the initial value, an alarm signal is outputted to the alarm unit 27. Is preferred.

[0064]

As described above, according to the first method of the liquid level measuring method of the present invention, the liquid level of the liquid to be measured whose specific gravity is not known in advance can be measured. Then, in the first method, by adding a method of calculating the measurement lower limit value and the measurement upper limit value, there is an advantage that a wider range of the liquid level can be measured. Further, according to the second method of the present invention, it is possible to measure the remaining volume of the liquid to be measured stored in a container having an arbitrary shape. further,
According to the third method of the present invention, if the initial specific gravity, the final specific gravity, and the number of times of processing of the liquid to be measured are input and set in advance, even if the specific gravity of the liquid to be measured changes for each processing of the processing object, accurate measurement is possible. The liquid level can be measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a liquid level measuring device for implementing a liquid level measuring method of the present invention.

FIG. 2 is a characteristic diagram illustrating a first method relating to the liquid level measurement method of the present invention.

FIG. 3 is a flowchart for explaining a first method relating to the liquid level measurement method of the present invention.

FIG. 4 is a diagram illustrating a second method relating to the liquid level measurement method of the present invention.

FIG. 5 is a diagram illustrating a third method relating to the liquid level measurement method of the present invention.

FIG. 6 is a reference drawing of the liquid level measurement method of the related art and the present invention.

[Explanation of symbols]

 1, 29 container 3 liquid to be measured 5 gas supply device 7 pipe 9 air bubble 11 liquid level measurement device 13 joint 15 sensor 17 input unit 19 operation unit 21 storage unit 23 display unit 25 setting unit 27 alarm unit

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Katsuo Takahashi 1164 Sano, Yachiyo-cho, Yuki-gun, Ibaraki Prefecture Inside Rika Industry Co., Ltd. (72) Inventor Hideaki Oka 1164, Sano, Yachiyo-cho, Yuki-gun, Ibaraki Prefecture In-house (72) Inventor Shigeru Nakamura 1164 Sano, Yachiyo-cho, Yuki-gun, Ibaraki Pref.

Claims (4)

[Claims] 1. A pipe is inserted into a liquid to be measured placed in a container, a gas at a predetermined pressure is supplied, and a back pressure is measured in a state where bubbles are generated in the liquid to be measured from the tip of the pipe. Thus, in the liquid level measuring method for measuring the liquid level of the liquid to be measured, the liquid to be measured is put in advance in the container, and the first pressure and the first pressure when the liquid reaches the first set point are set. Second higher than the set point of
A first step of calculating the specific gravity of the liquid to be measured from a pressure difference from the second pressure when the set point is reached, and a specific relationship between the specific gravity and the pressure of the known reference liquid; A second step of obtaining a liquid level data table indicating a proportional relationship between the pressure of the liquid to be measured and the liquid level at least between the first and second set points; and A third step of measuring the liquid level by associating the pressure value of the liquid to be measured with the liquid level data table. 2. The method according to claim 2, wherein the measuring upper limit level and the measuring lower limit level of the liquid to be measured corresponding to the measurement lower limit level and the measurement upper limit level of the reference liquid are calculated by the calculation specific gravity,
2. The liquid level measuring method according to claim 1, wherein the liquid level is calculated from a reference liquid specific gravity and first and second set points, and a proportional relationship between the pressure and the liquid level during the calculation is obtained as the liquid level data table. 3. A back pressure is measured in a state where a pipe is inserted into a liquid to be measured placed in a container and a gas of a predetermined pressure is supplied to generate bubbles in the liquid to be measured from the tip of the pipe. Thus, in the liquid level measurement method for measuring the liquid level of the liquid to be measured, the relationship between the volume of the container and the liquid level when a reference liquid having a known specific gravity is previously placed in the container is represented by volume data. A fourth step of obtaining a table, a step of previously placing the liquid to be measured in the container, a third pressure when the liquid reaches a third set point, and a fourth pressure higher than the third set point.
A fifth step of calculating the specific gravity of the liquid to be measured from a pressure difference between the fourth pressure when the set point is reached and the pressure by the reference liquid; and calculating the volume data table. 6th correction with specific gravity
And a seventh step of measuring the remaining volume of the liquid to be measured by associating the pressure value of the liquid to be measured put in the container with the volume data table as the main measurement. Level measurement method. 4. A back pressure is measured in a state in which a pipe is inserted into a liquid to be measured placed in a container and gas of a predetermined pressure is supplied to generate bubbles in the liquid to be measured from the end of the pipe. Thus, in the liquid level measuring method for measuring the liquid level of the liquid to be measured, the initial specific gravity before the processing and the multiple times when the object to be processed is processed a plurality of times in the liquid to be measured placed in the container An eighth step of measuring the specific gravity after the processing, a ninth step of obtaining a change specific gravity for each of the processing times from the initial specific gravity and the post-processing specific gravity, and a pressure value of the liquid to be measured for each of the processing times. And a tenth step of measuring the liquid level by correcting with a change specific gravity according to the number of processings at the time of the pressure measurement.