JP2010054260A - Liquid level measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure the liquid level, even if distribution resistance of a detection pipe varies and the pressurized gas supply source side changes over time, in a liquid level measuring device that includes a pressurized gas supply source connected to the detection pipe whose tip is immersed in liquid and a pressure sensor connected to the detection pipe, and measures the liquid level based on the detected value of the pressure sensor in a pressurized gas supply stop state after the pressurized gas supply from the pressurized gas supply source to the detection pipe. <P>SOLUTION: After stopping the pressurized gas supply from the pressurized gas supply source 2A, an arithmetic means 14 calculates the liquid level based on the detected value of the pressure sensor 5 in response to the fact that a pressure stabilization determining means 12 determines that the pressure in the detection pipe 3 becomes stable based on the change of the detected value of the pressure sensor 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a detection tube that immerses the tip in a liquid whose liquid level is to be measured, and a pressurized gas supply source connected to the detection tube to leak pressurized gas from the tip of the detection tube. A pressure sensor connected to the detection tube so as to detect the pressure in the detection tube, and in a state where the pressurized gas supply is stopped after the pressurized gas is supplied from the pressurized gas supply source to the detection tube. The present invention relates to a liquid level measuring apparatus that measures a liquid level based on a detection value of the pressure sensor.

When the tip of the detection tube is immersed in the liquid to be measured, the pressurized gas from the pump driven at regular intervals leaks out from the tip of the detection tube, and a predetermined time has elapsed after the pump has stopped operating Patent Document 1 has already known that the pressure in the detection tube is stabilized and the pressure is detected and the liquid level is measured based on the pressure.
JP 2007-78413 A

  However, as disclosed in Patent Document 1, the pressure in the detection tube is detected when a predetermined time has elapsed after the pump is stopped. If the flow resistance of the detection tube changes due to a change in distance or constriction or crushing of the detection tube, the pressure in the detection tube may still be in an unstable state when a predetermined time has elapsed after the pump has stopped operating. In such a state, if the liquid level is measured based on the detection value of the pressure sensor, the measurement value becomes inaccurate.

  In addition, the flow rate of the pressurized gas supplied from the pressurized gas supply source decreases due to variations in the discharge amount from the pump and deterioration over time due to clogging of the filter, etc. until the pressurized gas leaks from the tip of the detection tube. Even when a long time is required, the replacement of the pressurized gas in the detection tube cannot be completed within a predetermined time, and the measurement value becomes inaccurate.

  The present invention has been made in view of such circumstances, and a liquid level that can accurately measure the liquid level even if there is a change in flow resistance of the detection tube or a change over time on the pressurized gas supply side. An object is to provide a level measuring device.

  In order to achieve the above object, the invention according to claim 1 is characterized in that a detection tube in which a tip is immersed in a liquid whose liquid level is to be measured, and a pressurized gas is leaked from the tip of the detection tube. A pressurized gas supply source connected to the detection tube; and a pressure sensor connected to the detection tube so as to detect a pressure in the detection tube; In a liquid level measuring apparatus for measuring a liquid level based on a detection value of the pressure sensor in a state where supply of pressurized gas is stopped after supply of pressurized gas, the pressure in the detection pipe is based on a change in the detection value of the pressure sensor. The pressure stabilization determining means for determining whether the pressure is stable, and the pressure stabilization determining means for determining that the pressure in the detection tube has stabilized after the supply of the pressurized gas from the pressurized gas supply source is stopped. According to the detection value of the pressure sensor Based characterized in that it comprises a calculating means for calculating a liquid surface level.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the pressurized gas supply from the pressurized gas supply source is started at a predetermined time interval from the pressurized gas supply source. The pressure stabilization determination means determines that the pressure in the detection tube has stabilized after the start of supply of pressurized gas from the pressurized gas supply source. Supply stop timing control means for controlling the pressurization gas supply stop timing from the pressurization gas supply source so as to stop the pressurization gas supply from the pressurization gas supply source according to To do.

  The pump 2A of the first embodiment corresponds to the pressurized gas supply source of the present invention.

  According to the first aspect of the present invention, when the pressure stabilization determining means determines that the pressure in the detection tube is stable based on the change in the detected value of the pressure sensor after the supply of the pressurized gas from the pressurized gas supply source is stopped. In addition, since the liquid level is calculated based on the detection value of the pressure sensor, the liquid level is measured in a state where the pressure in the detection tube becomes a stable value corresponding to the liquid level, The distance from the pressurized gas supply source to the tip of the detection tube changes, the flow resistance of the detection tube changes due to constriction and crushing of the detection tube, and there is deterioration over time on the pressurized gas supply source side However, it is possible to accurately measure the liquid level.

  According to the second aspect of the present invention, it is possible to prevent useless operation of the pressurized gas supply source, thereby contributing to shortening of the measurement time and energy saving. That is, when the supply of the pressurized gas from the pressurized gas supply source is started, the pressure in the detection tube increases, and the pressurized gas supply amount from the pressurized gas supply source and the pressurized gas leakage amount from the tip of the detection tube The pressure in the detection tube reaches its peak value due to the balance with the After the start of supply of pressurized gas from the pressurized gas supply source, the time until the pressure in the detection tube reaches the peak value varies. However, when the pressure stabilization judgment means judges that the pressure in the detection tube has stabilized after the pressurized gas supply from the pressurized gas supply source is started, it is judged that the pressure in the detection tube has reached the peak value and the pressurized gas is supplied. Since the pressurized gas supply from the source is stopped, regardless of the flow resistance of the detection tube, a sufficient amount of pressurized gas is present in the detection tube, By appropriately stopping the pressurized gas supply, wasteful operation of the pressurized gas supply source can be prevented, and energy saving can be achieved while shortening the measurement time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples of the present invention shown in the accompanying drawings.

  1 to 7 show a first embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a liquid level measuring device, FIG. 2 is a block diagram showing a configuration of a control panel, and FIG. 3 is a diagram of a control unit. FIG. 4 is a flowchart showing a procedure for measuring the liquid level, FIG. 5 is a diagram showing an example of a pressure change in the detection tube, and FIG. 6 is a diagram showing a setting state of the first and second pressure thresholds. FIG. 7 is a diagram showing changes in pressure in two types of detection tubes having different lengths.

  First, in FIG. 1, a liquid that is a liquid level measurement target is stored in a tank 1, and a detection tube 3 is connected to the tip of the tank 1 in order to measure a liquid level L in the tank 1. It is inserted to a position close to the bottom 1a, and the tip of the detection tube 3 is immersed in the liquid.

  On the other hand, a pump 2A, which is a pressurized gas supply source, is fixedly disposed outside the tank 1, and the detection tube 3 is connected to the pump 2A via a check valve 4 that prevents backflow to the pump 2A side. Connected to. A pressure sensor 5 for detecting the pressure in the detection pipe 3 is connected to the branch pipe 3 a branched from the detection pipe 3 on the downstream side of the check valve 4.

  Referring also to FIG. 2, the operation of the pump 2 </ b> A is controlled by the control panel 6, and the detected value of the pressure sensor 5 is also input to the control panel 6. Thus, the control panel 6 includes a control unit 7 composed of a microcomputer, a keyboard 8 and a display 9 connected to the control unit 7, and a drive connected to the control unit 7 so as to drive the pump 2A. Circuit 10.

  In FIG. 3, the control unit 7 is driven by determining the supply start timing of the pressurized gas so as to start the supply of the pressurized gas from the pump 2 </ b> A every first predetermined time T <b> 1 set by the keyboard 8. Based on the change in the detected value of the pressure sensor 5 before and after the supply start timing control means 11 for inputting the drive signal to the circuit 10 and the second predetermined time T2 set by the keyboard 8 are opened. Pressure stabilization determination means 12 for determining whether or not the pressure in the detection tube 3 is stable, and the pressure stabilization when the pressure in the detection tube 3 is stabilized after the supply of pressurized gas from the pump 2A is started. In response to the judgment by the judgment means 11, a timing for stopping the supply of pressurized gas from the pump 2A is determined so as to stop the supply of pressurized gas from the pump 2A, and a drive stop signal is input to the drive circuit 10. The supply stop timing control means 13 and the pressure stabilization determination means 12 determine that the pressure in the detection tube 3 has stabilized after the supply of pressurized gas from the pump 2A is stopped. Calculation means 14 for calculating the liquid level based on the detection value, third and fourth predetermined times T3 and T4 set by the keyboard 8, first and second pressure thresholds h1 and h2, and the supply start timing And an abnormality determination means 15 for determining an abnormality of the pump 2A or the detection tube 3 based on the determination of the supply start timing of the pressurized gas by the control means 11 and the pressure stability determination result by the pressure stabilization determination means 12.

  Such a control unit 7 measures the liquid level L according to the procedure shown in FIG. The driving of the pump 2A is started by inputting the driving signal. In step S3, it is determined whether or not a third predetermined time T3, for example, 1 minute has elapsed after the operation of the pump 2A is started.

  Thus, in step S4 after it is determined in step S3 that the elapsed time after the start of the operation of the pump 2A is equal to or less than the third predetermined time T3, the pressure stabilization determination means 12 performs the second predetermined time T2, for example, 0. It is determined whether or not the pressure in the detection tube 3 is stabilized based on the change in the detection value of the pressure sensor 5 before and after the interval of 5 seconds. That is, it is determined in step S4 whether or not the detection value PA of the previous pressure sensor 5 is equal to the detection value PB of the current pressure sensor 5 after the second predetermined time T2 has elapsed from the previous time. When PA = PB, the process proceeds from step S4 to step S5. When PA ≠ PB, the process returns from step S4 to step S2. In the determination in step S4, when | PA-PB | is within a predetermined range, PA = PB.

  When it is determined in step S4 that PA = PB, that is, when the pressure stabilization determination means 12 determines that the pressure in the detection tube 3 is stable, the supply stop timing control means 13 is connected to the drive circuit 10 in step S5. The drive stop signal is input to stop the pump 2A, and the pressurized gas supply from the pump 2A is stopped.

  In step S6 after the pump 2A is stopped, it is determined whether or not a fourth predetermined time T4, for example, 1 minute has elapsed after the pump 2A is stopped, and the elapsed time after the pump 2A is stopped is a fourth predetermined time. In step S7 after determining in step S6 that the time T4 is less than or equal to time T4, the pressure stabilization determination means 12 is based on the change in the detected value of the pressure sensor 5 before and after the second predetermined time T2 is opened. Therefore, when the pressure stabilization determination means 12 determines that the pressure in the detection tube 3 is stable, the process proceeds from step S7 to step S8. Note that a predetermined time may be required when proceeding to step S8 after determining that PA = PB in step S7.

  In step S8, it is determined whether or not the detected pressure of the pressure sensor 5 is less than the first pressure threshold value h1, and when it is determined in step S8 that the detected pressure is greater than or equal to the first pressure threshold value h1, the process proceeds to step S9. It is determined whether or not the detected pressure of the pressure sensor 5 exceeds a second pressure threshold h2 that is larger than the first pressure threshold h1.

  When it is determined in step S9 that the detected pressure is equal to or lower than the second pressure threshold value h2, the process proceeds to step S10, where the calculation means 14 calculates the liquid level L based on the detection value of the pressure sensor 5 and starts measurement. It will be. Thus, when the pressure in the detection tube 3 is stable when the pump 2A is stopped, the pressure in the detection tube 3 is a value corresponding to the water head pressure h from the tip of the detection tube 3 to the liquid level L. It has become. Therefore, the pressure sensor 5 can detect the water head pressure h, that is, the pressure corresponding to the liquid level L, and the calculating means 14 can calculate the liquid level L corresponding to the detection value of the pressure sensor 5, and the liquid level The level L is displayed on the display unit 9.

  In the next step S11, it is determined whether or not the first predetermined time T1 has elapsed since the intermittent time, that is, the driving of the pump 2A has been started. Driving will be started.

  By executing the processing of step S1 to step S11, as shown in FIG. 5, in the process in which the pressure in the detection tube 3 increases from the start of driving the pump 2A, the second predetermined time T2 from time t1. The driving of the pump 2A is not stopped at the time t2 when elapses, and at the time t4 when the second predetermined time T2 elapses from the time t3 when the pressure in the detection tube 3 reaches the peak. The pump 2A stops because the pressure has stabilized. Thereafter, in the process in which the pressure in the detection tube 3 decreases due to the stop of the pump 2A, the measurement is not started at the time t6 when the second predetermined time T2 has elapsed from the time t5, and the pressure in the detection tube 3 is reduced. The measurement of the liquid level L is started at the time t8 when the second predetermined time T2 has elapsed from the time t7 in the state where the water head pressure h has been lowered.

  When the elapsed time from the start of operation of the pump 2A exceeds the third predetermined time T3, the abnormality determination means 15 determines that an abnormality has occurred in the pump 2A or the detection tube 3 and determines in step S3. From step S12, an error is displayed on the display unit 9, a signal for forcibly stopping the drive of the pump 2A is input to the drive circuit 10 in step S13, and measurement is stopped in step S14.

  In addition, when it is determined in step S6 that the elapsed time from the stop of the operation of the pump 2A exceeds the fourth predetermined time T4, the abnormality determining means 15 determines that the detection tube 3 is clogged and determines from step S6 to step S6. In S15, an error is displayed on the display unit 9, a signal for forcibly stopping the driving of the pump 2A is input to the drive circuit 10 in Step S16, and the measurement is stopped in Step S17.

  Further, the abnormality determination unit 15 determines that the detected pressure of the pressure sensor 5 is the first pressure threshold value in step S8 when the pressure stabilization determination unit 12 determines that the pressure in the detection pipe 3 has stabilized after the pump 2A is stopped. When it is determined that it is less than h1, it is determined that a leak has occurred from the detection tube 3, the process proceeds from step S8 to step S18, an error is displayed on the display 9, and the pump 2A is forcibly driven in step S19. A signal for stopping is input to the drive circuit 10, and the measurement is stopped in step S20.

  Here, if the detected pressure of the pressure sensor 5 changes as indicated by the curve A in FIG. 6 in a state where neither the pump 2A nor the detection pipe 3 is abnormal, the first pressure threshold value h1 is the tank 1 The pressure is set as a pressure corresponding to a level lower than the lowest value of the liquid level L, and in the state where leakage has occurred from the detection pipe 3, as shown by the curve B, the first pressure is set after the pump 2A is stopped. Since the detection value of the pressure sensor 5 decreases to less than the threshold value h1, it is possible to determine that a leak has occurred in the detection tube 3.

  The second pressure threshold value h2 is set as a pressure corresponding to a level higher than the maximum value of the liquid level L in the tank 1, and the abnormality determination means 15 is set in the detection tube 3 after the pump 2A stops operating. If it is determined in step S9 that the pressure stabilization determination means 12 has determined that the pressure has been stabilized and the detected pressure of the pressure sensor 5 exceeds the second pressure threshold value h2, the detection tube 3 is clogged. Then, the process proceeds from step S9 to step S21 to display an error on the display unit 9. In step S22, a signal for forcibly stopping the driving of the pump 2A is input to the drive circuit 10, and measurement is further performed in step S23. Stop.

  Thus, as shown by curve C in FIG. 6, when the detection tube 3 is clogged, the detection value of the pressure sensor 5 increases to a value exceeding the second pressure threshold value h2 after the pump 2A is stopped. 3 makes it possible to determine that a blockage has occurred.

  Next, the operation of the first embodiment will be described. When the pressure in the detection tube 3 is stabilized based on the change in the detection value of the pressure sensor 5 after the supply of pressurized gas from the pump 2A is stopped, the pressure stabilization determination means 12 Since the liquid level L is calculated based on the detection value of the pressure sensor 5, the liquid in the state where the pressure in the detection tube 3 becomes a stable value corresponding to the liquid level L is calculated. Even if the flow resistance of the detection tube 3 is changed by measuring the surface level L, the distance from the pump 2A to the tip of the detection tube 3 is changed, or the detection tube 3 is constricted or crushed, Even if there is deterioration with time on the pump 2A side, the liquid level L can be accurately measured.

  By the way, when the supply of the pressurized gas from the pump 2A is started, the pressure in the detection tube 3 increases, and the pressurized gas supply amount from the pump 2A and the pressurized gas leakage amount from the tip of the detection tube 3 are balanced. As a result, the pressure in the detection tube 3 becomes a peak value, but depending on the distance from the pump 2A to the tip of the detection tube 3 and the change in flow resistance due to constriction or crushing in the middle of the detection tube 3, the pump The time until the pressure in the detection tube 3 reaches the peak value changes after the pressurized gas supply from 2A starts. However, the pressurized gas is supplied from the pump 2A to the detection tube 3 at intervals of the first predetermined time T1, and the pressure is stabilized based on the change in the detected value of the pressure sensor 5 after the pressurized gas supply from the pump 2A is started. When the determination means 12 determines that the pressure in the detection tube 3 has stabilized, it is determined that the pressure in the detection tube 3 has reached the peak value, and the supply of pressurized gas from the pump 2A is stopped. Therefore, even if the distance from the pump 2A to the tip of the detection tube 3 changes greatly, or the flow resistance of the detection tube 3 changes due to the constriction or collapse of the detection tube 3, a sufficient amount in the detection tube 3 The pressurized gas supply from the pump 2A can be appropriately stopped in the state where the pressurized gas exists. That is, regardless of the flow resistance of the detection tube 3, the supply of the pressurized gas from the pump 2A is appropriately stopped in a state where a sufficient amount of pressurized gas exists in the detection tube 3, and the pump 2A It is possible to prevent useless operation and save energy while shortening the measurement time.

  Here, when two types of detection tubes 3 having different lengths are used, the pressure in the detection tube 3 changes as shown in FIG. 7, and when the detection tube 3 having a short length LA is used. While the drive of the pump 2A is stopped at the time t9, when the detection tube 3 having a long length LB is used, the time t10 that is later than the time t9 although the start time of the pump 2A is the same. Therefore, even if the distance from the pump 2A to the tip of the detection tube 3 changes greatly, the pump 2A is still in a state where a sufficient amount of pressurized gas exists in the detection tube 3. It is possible to appropriately stop the supply of pressurized gas from.

  8 and 9 show a second embodiment of the present invention. FIG. 8 is a diagram showing the configuration of the liquid level measuring device, and FIG. 9 is a flowchart showing the procedure for measuring the liquid level.

  First, in FIG. 8, a pressurized gas supply source 2 </ b> B disposed outside the tank 1 is constituted by a pump 16 and a buffer tank 17 connected in series to the pump 16, and this pressurized gas supply source 2B is connected to the detection tube 3 via a pressure regulating valve 18, a throttle 19 and an electromagnetic valve 20 for adjusting the supply pressure of the pressurized gas from the pressurized gas supply source 2B to be constant. A pressure sensor 5 for detecting the pressure in the detection tube 3 is connected to the branch tube 3a branched from the detection tube 3 on the downstream side.

  The opening / closing operation of the electromagnetic valve 20 is controlled by the control panel 6, and the detection value of the pressure sensor 5 is also input to the control panel 6. The pump 16 in the pressurized gas supply source 2B is turned on / off by a pressure switch (not shown) attached to the buffer tank 17 so that the pressure in the buffer tank 17 becomes a value within a predetermined range. It is driven intermittently.

  Thus, the liquid level L is measured according to the procedure shown in FIG. 9 by the control unit 7 (see the first embodiment) provided in the control panel 6, and the measurement is stopped in step S31, and in step S32. The solenoid valve 20 is opened. In the next step S33, it is determined whether or not a measurement start time set in advance as a time when the pressure in the detection tube 3 reaches a peak value after the pressurized gas is supplied to the detection tube 3 has been determined. When it is determined that the measurement start time has elapsed, the process proceeds to step S34, where the electromagnetic valve 20 is closed and the supply of pressurized gas to the detection tube 3 is stopped.

  In step S35 after the supply of the pressurized gas to the detection tube 3 is stopped, it is determined whether or not a fourth predetermined time T4, for example, 1 minute has elapsed after the supply of the pressurized gas is stopped, and a pressurized gas supply source is determined. In step S36 after it is determined in step S35 that the elapsed time after the supply of pressurized gas from 2B is stopped is equal to or shorter than the fourth predetermined time T4, the second predetermined time T2, for example, 0.5 seconds is left between them. Whether or not the pressure in the detection tube 3 is stable is determined based on the change in the detection value of the pressure sensor 5 before and after the determination. When it is determined that the pressure in the detection tube 3 is stable, step S36 is performed. To Step S37.

  In step S37, it is determined whether or not the detected pressure of the pressure sensor 5 is less than the first pressure threshold value h1, and when it is determined in step S37 that the detected pressure is greater than or equal to the first pressure threshold value h1, the process proceeds to step S38. It is determined whether or not the detected pressure of the pressure sensor 5 exceeds a second pressure threshold h2 that is larger than the first pressure threshold h1.

  When it is determined in step S38 that the detected pressure is equal to or lower than the second pressure threshold value h2, the process proceeds to step S39 and measurement is started. Thus, when the pressure in the detection tube 3 is stable after the supply of pressurized gas to the detection tube 3 is stopped after the pressure in the detection tube 3 reaches the peak value, the pressure in the detection tube 3 is maintained. Is a value corresponding to the water head pressure h from the tip of the detection tube 3 to the liquid level L. Therefore, the pressure sensor 5 can detect the water head pressure h, that is, the pressure corresponding to the liquid level L, and can calculate the liquid level L based on the detected value of the pressure sensor 5.

  In step S40 after the measurement is started in step S39, it is confirmed whether or not a predetermined time set in advance as the measurement start time interval has elapsed. When the elapse of the predetermined time is confirmed, the process returns to step S31. Further, when it is determined in step S35 that the elapsed time after the supply of pressurized gas into the detection tube 3 has stopped exceeds the fourth predetermined time T4, it is determined that the detection tube 3 is clogged, and from step S35. In step S41, an error is displayed, and measurement is stopped in step S42.

  In step S37 in which it is determined that the pressure in the detection tube 3 has stabilized after the supply of pressurized gas into the detection tube 3 is stopped, it is determined that the detected pressure of the pressure sensor 5 is less than the first pressure threshold value h1. If it is determined that there is a leak from the detection tube 3, the process proceeds from step S37 to step S43 to display an error, and the measurement is stopped in step S44.

  Further, in step S38 when it is determined that the pressure in the detection tube 3 has stabilized after the supply of pressurized gas into the detection tube 3 is stopped, it is determined that the detected pressure of the pressure sensor 5 exceeds the second pressure threshold h2. Sometimes, it is determined that the detection tube 3 is clogged, the process proceeds from step S38 to step S45, an error is displayed, and the measurement is stopped in step S46.

  Also according to the second embodiment, when it is determined that the pressure in the detection tube is stabilized after the supply of the pressurized gas from the pressurized gas supply source 2B is stopped by closing the electromagnetic valve 20, the detection value of the pressure sensor 5 is detected. Since the liquid level L is calculated based on the pressure level, the liquid level L is measured in a state where the pressure in the detection tube 3 becomes a stable value corresponding to the liquid level L, and the pressure is increased. Even if the distance from the gas supply source 2B to the tip of the detection tube 3 changes, or the flow resistance of the detection tube 3 changes due to constriction or crushing of the detection tube 3, the pressure gas supply source 2B side also changes. Even if there is deterioration with time, the liquid level L can be accurately measured.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

  For example, a pressure cylinder may be used as the pressurized gas supply source.

It is a figure which shows the structure of the liquid level measuring apparatus of 1st Example. It is a block diagram which shows the structure of a control panel. It is a block diagram which shows the structure of a control unit. It is a flowchart which shows the measurement procedure of a liquid level. It is a figure which shows an example of the pressure change in a detection tube. It is a figure which shows the setting condition of the 1st and 2nd pressure threshold value. It is a figure which shows the pressure change in two types of detection tubes from which length differs. It is a figure which shows the structure of the liquid level measuring apparatus of 2nd Example. It is a figure which shows the measurement procedure of a liquid level.

Explanation of symbols

2A: Pressurized gas supply source 2B ... Pressurized gas supply source 3 ... Detection tube 5 ... Pressure sensor 11 ... Supply start timing control means 12 ... Pressure stabilization judgment Means 13: Supply stop timing control means 14 ... Calculation means

Claims (2)

  A detection tube (3) in which the tip is immersed in the liquid whose liquid level is to be measured, and a pressure tube connected to the detection tube (3) to leak pressurized gas from the tip of the detection tube (3). A pressurized gas supply source (2A, 2B) and a pressure sensor (5) connected to the detection tube (3) so as to detect the pressure in the detection tube (3), Liquid level measurement that measures the liquid level based on the detection value of the pressure sensor (5) in a state where the pressurized gas supply is stopped after the pressurized gas is supplied from the sources (2A, 2B) to the detection tube (3). In the apparatus, pressure stabilization determining means (12) for determining whether or not the pressure in the detection tube (3) is stabilized based on a change in the detection value of the pressure sensor (5), and the pressurized gas supply After the supply of pressurized gas from the source (2A, 2B) is stopped, the pressure in the detection tube (3) is stabilized. And a calculation means (14) for calculating a liquid level based on a detection value of the pressure sensor (5) according to the determination by the pressure stabilization determination means (12). Level measuring device.   Supply start timing control means for controlling the pressurized gas supply start timing from the pressurized gas supply source (2A) so as to start the pressurized gas supply from the pressurized gas supply source (2A) at a predetermined time interval. (11) and when the pressure stabilization determining means (12) determines that the pressure in the detection tube (3) is stabilized after the pressurized gas supply from the pressurized gas supply source (2A) is started. The supply stop timing control means (13) for controlling the supply stop timing of the pressurized gas from the pressurized gas supply source (2A) so as to stop the supply of the pressurized gas from the pressurized gas supply source (2A). The liquid level measuring apparatus according to claim 1, comprising:

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