JP2005221432A - Liquid sensor and measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid sensor which reduces power consumption. <P>SOLUTION: A pump within a liquid level measurement device 1 is operated to measure the liquid level of a liquid from the pressure (back pressure) within a measurement tube 2 measured under the condition that air bubbles are slightly emitted from a lower end 2A of the measurement tube 2. When starting the operation of the pump, the pressure within the measurement tube 2 is monitored. When the pressure becomes constant, that is, when air bubbles start to be emitted from the lower end 2A, the operation of the pump is ceased. The present invention can be applied to an air-purge type liquid level measurement apparatus. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In particular, the present invention relates to an air purge type liquid sensor and a measurement method capable of suppressing power consumption.

  Conventionally, an air purge type liquid level meter has been used as a means for measuring the level of liquid stored in a tank or the like (Patent Document 1).

The air purge type liquid level measuring device supplies a gas such as air to a measurement tube extending in a liquid, and measures the back pressure when a slight bubble comes out from the lower end of the measurement tube. Since the back pressure measured at this time is proportional to the height of the liquid level, it becomes possible to measure the water level of the liquid.
JP 7-49252 A

  By the way, in order to measure the water level with the liquid level measuring device, a power source is naturally necessary. In particular, since the power consumption by driving the pump inside the liquid level measuring device is large, for example, the power source When using a built-in battery, there was a problem that the water level could not be measured continuously for a long time. In addition, this pump is for supplying gas to the measuring pipe with which a liquid level measuring device is equipped.

  The present invention has been made in view of such a situation. For example, the power consumption of a liquid sensor for measuring the level of a liquid level can be suppressed.

  The liquid sensor according to the present invention is an air purge type liquid sensor, and detects that the pressure in the measurement tube becomes constant by driving the supply unit and the supply unit supplying gas to the measurement tube extending in the liquid surface direction. And a drive control means for stopping the drive of the supply means.

  This liquid sensor measures the water level of various liquids such as liquid chemicals, drinking water, and oil stored in a tank or the like. Also, those that measure the height from the bottom of the tank to the liquid level, those that measure the height from the tip of the measuring tube that extends into the liquid to the liquid level, Any one that measures the pressure measured by multiplying the specific gravity of the liquid sensor is included in the liquid sensor.

  The air purge method is a method in which a gas such as air is supplied to a measuring tube extending to the liquid surface (in the liquid) and the water level is measured from a back pressure measured in a state where bubbles are generated from the lower end of the measuring tube. .

  Here, the constant pressure in the measurement tube means a state in which the pressure does not increase. For example, as shown in FIG. 2, the pressure fluctuates in a minute range due to bubbles coming out from the lower end of the measurement tube. Including the state.

  The supply means is constituted by, for example, the pump 21 of FIG. 3, and includes a cylinder that supplies gas in addition to the pump.

  The drive control means is configured by, for example, the pump drive control unit 32 of FIG. By stopping the drive of the supply means by the drive control means, the water level can be measured with the minimum required drive of the supply means. That is, power consumption can be suppressed.

  The liquid sensor of the present invention may further include a battery that supplies power. The built-in battery eliminates the need to connect a cord or the like for supplying power from a nearby outlet to the liquid sensor.

  The measurement method of the present invention is a measurement method of an air purge type liquid sensor provided with a supply means for supplying gas to a measurement tube extending in the liquid surface direction, and the pressure in the measurement tube becomes constant by driving the supply means. And a drive control step of stopping driving of the supply means when it is detected.

  The drive control step corresponds to, for example, step S4 in FIG.

  In the liquid sensor and measurement method of the present invention, when the gas is supplied by the supply means to the measurement tube extending in the liquid surface direction, and it is detected that the pressure in the measurement tube becomes constant by driving the supply means, the supply means Is stopped.

  According to the present invention, power consumption can be suppressed.

  Further, according to the present invention, the water level can be measured for a long time even when the built-in battery is used as a power source.

  FIG. 1 is a diagram showing an example of the appearance of a liquid level measuring device 1 to which the present invention is applied.

  The liquid level measuring instrument 1 is an air purge type measuring instrument that measures the level of liquid stored in a tank or the like, and is fixed at a position higher than the liquid level, for example, as shown in FIG.

  The liquid level measuring instrument 1 basically has an external appearance composed of a lid member 11 and a fixing member 12 for fixing the measuring tube 2 extending in the water surface direction, and the lid member 11 and the fixing member 12 are combined. In the internal space that is sometimes formed, for example, a pump for supplying a gas such as air to the measuring tube 2, a battery for driving the pump, a controller (chip) for controlling the driving of the pump, and the like are disposed. A substrate or the like is provided.

  That is, the liquid level measuring device 1 is driven by a built-in battery, and a cord for supplying power from a nearby outlet or the like is not connected.

  The liquid level measuring device 1 supplies air to the measuring tube 2 by driving an internal pump, and when the air bubbles slightly come out from the lower end 2A of the measuring tube 2 as shown in FIG. The water level of the liquid is measured from the pressure (back pressure) in the measurement tube 2 to be measured.

  Here, measurement of the liquid level or pressure of the liquid will be described. Depending on the measurement method, the liquid level sensor (liquid level measuring device 1) is classified into the following three types.

  Type 1 (Sensor that measures the height H from the bottom of the tank to the liquid level)

In FIG. 1, when variables are defined as follows, the height H from the tank bottom surface to the liquid surface can be obtained from the following equations (1) to (4). However, the unit of pressure is Kg / cm ² , the unit of height is cm, and the unit of specific gravity is Kg / cm ³ .

P0: Atmospheric pressure P1: Pressure in the pipe when the measuring pipe 2 is filled with air L: Height from the bottom of the tank at the lower end 2A of the measuring pipe 2 s: Specific gravity of the liquid in the tank P: Output from the pressure sensor Pressure value

First, the pressure in the pipe when the inside of the measuring pipe 2 is filled with air is obtained from the following equation (1).
P1 = P0 + (HL) * s (1)

Since a normal pressure sensor outputs a differential pressure from the atmospheric pressure, the pressure value P is expressed by the following equation (2).
P = P1-P0 (2)

The following equation (3) is obtained from equations (1) and (2).
P = (HL) * s (3)

When formula (3) is modified, the following formula (4) is obtained.
H = P / s + L (4)

  The type 1 liquid level sensor having the water level of the height H obtained from the equation (4) strictly determines the height of the liquid level from the tank bottom, and from the tank bottom of the lower end 2A of the measuring tube 2 Since the data of the height L and the specific gravity s of the liquid are required, these data are stored in advance in the liquid level sensor.

  In reality, there are cases where there is no practical problem even with a liquid level sensor that measures using a type 2 or type 3 method, which will be described later, and in this case, type 2 or type 3 sensors are also used.

  Type 2 (sensor for measuring the height H1 from the lower end 2A of the measuring tube 2 to the liquid level)

From the following equation (5), the height H1 from the lower end 2A of the measuring tube 2 to the liquid level is obtained.
H1 = (HL) = P / s (5)

  In this type 2 liquid level sensor, the height L of the lower end 2A of the measuring tube 2 is regarded as the bottom surface of the tank, and when the bottom of the tank is not flat or the tank has a certain remaining amount. This is used when you want to manage the liquid level of the tank.

  In the case of Type 2, there is no need to measure the value of the height L or store it in advance, and it is only necessary to know the value P of the pressure sensor and the value of the specific gravity s.

  Type 3 (sensor for measuring a value H2 (pressure) obtained by multiplying the height H1 from the center 2A of the measuring tube 2 to the liquid level by a specific gravity s)

The value H2 is obtained from the following equation (6).
H2 = H1 * s = P (6)

  This type 2 liquid level sensor is used when it is only necessary to measure a rough liquid level, or when only liquids having the same specific gravity are always handled.

  The liquid level measuring device 1 in FIG. 1 may be any of the above three types.

  Returning to the explanation of FIG. 1, the liquid level measuring device 1 supplies air from the pump, measures the pressure in the measuring tube 2, and when bubbles come out from the lower end 2 </ b> A of the measuring tube 2, Stop the pump drive. The state in which bubbles emerge from the lower end 2A of the measuring tube 2 is detected based on the pressure in the measuring tube 2 that changes as shown in FIG. The horizontal axis in FIG. 2 represents time, and the vertical axis represents the pressure in the measurement tube 2.

When the drive of the pump is started at time 0, the value of the pressure is gradually increased from the pressure P ₁ is the initial value, after time t ₁ it becomes a state in which the bubble leaves from the lower end 2A of the measuring tube 2, It becomes almost constant at the pressure P ₂ . When the pressure becomes almost constant in this way, the liquid level measuring device 1 determines that bubbles are generated from the lower end 2A of the measuring tube 2, and stops driving the pump.

  Thus, by stopping the driving of the pump when bubbles come out from the lower end 2A, it is naturally possible to measure the water level and to consume more than when the pump is continuously driven thereafter. It becomes possible to suppress electric power. Therefore, even when a built-in battery is used as a power source, the water level can be measured for a long time.

  Processing for controlling the driving of the pump by the liquid level measuring device 1 will be described later with reference to a flowchart.

  FIG. 3 is a diagram illustrating an internal configuration example of the liquid level measuring device 1.

  As shown in FIG. 3, the internal space formed when the lid member 11 and the fixing member 12 are combined contains a pump 21 that supplies air from the supply pipe 22 to the measurement pipe 2, and a battery such as a dry cell. And a substrate 25 on which a controller for controlling the overall driving of the liquid level measuring instrument 1 and the like are provided.

  The storage unit 23 can store, for example, two AA-type dry batteries. Moreover, the measurement result of the water level by the liquid level measuring device 1 is wirelessly transmitted to a nearby terminal by a wireless communication module disposed on the substrate 25, for example.

  FIG. 4 is a block diagram illustrating an example of a functional configuration realized by a controller disposed on the substrate 25 of FIG.

  When the driving of the pump 21 is started, the pressure monitoring unit 31 starts monitoring the measurement result by the pressure sensor 24, and the pressure in the measuring tube 2 becomes constant as described with reference to FIG. At this time, the pump drive control unit 32 stops the drive of the pump 21.

  The state in which the pressure in the measuring tube 2 is constant means a state in which the pressure does not increase. As shown in FIG. 2, the pressure fluctuates in a very small range due to bubbles coming out from the lower end 2A. Includes state.

  The pump drive control unit 32 controls the drive of the pump 21 and manages the supply of air to the measurement pipe 2. When instructed to measure the water level, the pump drive control unit 32 starts driving the pump 21 and stops driving the pump 21 in accordance with an instruction given from the pressure monitoring unit 31 at a predetermined timing.

  Next, the drive control process of the pump 21 by the liquid level measuring device 1 will be described with reference to the flowchart of FIG.

  The pressure monitoring unit 31 starts monitoring the measurement result by the pressure sensor 24 in step S1.

  In step S <b> 2, the pump drive control unit 32 drives the pump 21 to start supplying air into the measurement tube 21.

In step S <b> 3, the pressure monitoring unit 31 determines whether or not the pressure in the measurement pipe 2 has reached a constant state based on the measurement result by the pressure sensor 24, and waits until it is determined that the pressure has reached a constant state. . In this standby state, the pressure in the measuring tube 2 gradually increases from the pressure P ₁ as in the period up to time t _{1 in} FIG.

On the other hand, if the pressure monitoring unit 31 determines in step S3 that the pressure in the measurement tube 2 has become constant, the pressure monitoring unit 31 proceeds to step S4 and causes the pump drive control unit 32 to stop driving the pump 21. As a result, the drive of the pump 21 is stopped immediately after the time t _{1 in} FIG. 2 when the pressure in the measurement tube 2 becomes constant, and the pump 21 is turned on even after the pressure in the measurement tube 2 becomes constant. Compared with the case where it continues to drive, the consumption of electric power by driving the pump 21 can be suppressed.

  In step S5, the pressure monitoring unit 31 measures the pressure and calculates the liquid level by any one of the above-described types 1 to 3.

In the above description, the pump 21 is stopped when it is detected that the pressure in the measuring tube 2 has become constant. However, the time t _{1 in} FIG. Prediction based on the result, the pressure measurement cycle may be shortened slightly before the predicted time t _1, and the driving of the pump 21 may be stopped when the pressure becomes constant. This also makes it possible to measure the water level with the minimum required drive of the pump 21 and to suppress power consumption.

  In the above description, the liquid level measuring device 1 is driven by using a built-in battery. However, the liquid level measuring device 1 may be driven by a power source supplied from a nearby outlet via a cord. Also in this case, as described above, by stopping the driving of the pump 21 when the pressure in the measurement tube 2 becomes constant, the power consumption can be suppressed as in the case of using the built-in battery.

It is a figure which shows the structural example of the liquid level measuring device to which this invention is applied. It is a figure shown about transition of the pressure in a measurement pipe. It is a figure which shows the example of an internal structure of a liquid level measuring device. It is a block diagram which shows the function structural example implement | achieved by the controller. It is a flowchart explaining the drive control processing of a liquid level measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid level measuring device 2 Measuring pipe 21 Pump 22 Supply pipe 23 Storage part 24 Pressure sensor 25 Board | substrate 31 Pressure monitoring part 32 Pump drive control part

Claims (3)

In air purge type liquid sensor,
Supply means for supplying gas to a measuring tube extending in the liquid surface direction;
A liquid sensor comprising: drive control means for stopping driving of the supply means when it is detected that the pressure in the measurement tube has become constant by the drive of the supply means. The liquid sensor according to claim 1, further comprising a battery that supplies power. In a measuring method of an air purge type liquid sensor comprising a supply means for supplying gas to a measuring tube extending in the liquid surface direction,
A measurement method comprising: a drive control step of stopping the drive of the supply means when it is detected that the pressure in the measurement tube has become constant by the drive of the supply means.

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