JP4420775B2 - Tensiometer - Google Patents

Description

  The present invention relates to a tensiometer used, for example, to detect the amount of water in soil in a farm.

  It is fundamentally important to know the amount of moisture in the soil that is absorbed by plants in order to rationalize plant cultivation, and soil moisture has been measured by various methods from the past. Among them, the most common method for plant cultivation is a method for determining the water potential of soil using a porous cup 120 which is a cocoon made of a porous material such as an unglazed seto as shown in FIG. The feature of this method is that it is possible to measure the amount of water that can be absorbed through the roots of plants, not the total volume content or weight water content of water contained in the soil (see, for example, Patent Document 1).

  As shown in FIG. 5, the tensiometer 100 has a porous cup 120 bonded to one end of a pipe 110 having a diameter of about 20 mm. In addition, a pressure sensor 131 is provided in advance on the porous cup 120 and the pipe 110. Then, water is poured into the porous cup 120 and the pipe 110 and the other end of the pipe 110 is closed with a rubber plug 119. Next, the other end (upper end) provided with the rubber plug 119 and the pressure sensor 131 are left on the ground surface, and the rest is buried in the ground. Further, an indicator 135 for displaying the pressure is provided outside, and the measurement value of the pressure sensor 131 is read from this display unit.

  A so-called capillary phenomenon occurs due to the porous structure of the porous cup 120 and the fine gap between the soil around the porous cup. When the soil is dry, the suction force of water to the outside of the porous cup increases and the suction force increases. When the water is wet, the water suction force to the outside of the porous cup is weakened, and the soaking of water is reduced.

  At this time, if the suction force is large, the pressure in the pipe 110 decreases to around −1 atm. The potential of water can be calculated from this pressure, and is usually displayed in units of pF (potential freeenergy). Further, when the water in the pipe is reduced, the rubber plug 119 is removed and water is supplied manually.

JP 2002-286711 A (page 3-4, FIG. 1)

  According to the conventional method, when water is sucked out of the porous cup and the inside of the pipe becomes negative pressure, air dissolved in the water appears, and water vapor is added as a partial pressure to generate bubbles. When bubbles are generated, pressure balance is reached between the suction force for sucking water outside the porous cup and the negative pressure inside the pipe and the atmospheric pressure outside the porous cup. Go out.

  If the water content of the soil rises again due to rainfall or irrigation after the water is sucked out of the porous cup in this way, the suction force decreases, so the water in the soil flows back into the pipe and reaches pressure equilibrium again. . At this time, the larger the volume of bubbles in the pipe, the greater the amount of water that flows back into the porous cup and the longer it takes to reach equilibrium. Further, since the water that has flowed back is dissolved in the air, it is discharged in the low-pressure cup and the bubbles become larger. Since the upper part of the tensiometer is on the ground, the gas expands and contracts due to solar radiation and the temperature difference between the surface of the day and night, and this amount of water enters and exits the porous cup. Once the bubbles are formed in this way, there is a characteristic that the bubbles are increased synergistically. In addition, other components such as fertilizer are oozing out into the back-flowed water, and the osmotic pressure is different from the pure water originally filled in the pipe. Does not accurately correspond to the amount of water in the soil, and the measured value is also affected, so that the water content in the soil cannot be accurately measured. Further, the water leached from the porous cup gives water to the soil as the object to be measured, and there is a possibility that the roots of the plants gather in the porous cup.

  The objective of this invention is providing the tensiometer which can measure the moisture content in soil more correctly than before.

  In order to solve the above-described problem, a tensiometer according to the present invention includes a porous cup, a pipe having one end connected to the porous cup and the other end opened, a pressure sensor that measures the pressure in the pipe, A tensiometer having a lid that is fitted to the other end of the pipe and seals the inside of the pipe and the porous cup, wherein the pipe and the porous cup include at least a lower chamber including the porous cup and a lower chamber. A separation valve that defines an adjacent upper chamber; and a separation valve opening / closing mechanism that allows the opening and closing of the separation valve to be operated from outside the tensiometer, and the pressure sensor measures the pressure in the lower chamber. It is characterized by that.

  The pipe of the tensiometer is separated into at least a lower chamber containing the interior of the porous cup and an upper chamber adjacent to the lower chamber, and the lower chamber is easily operated with as little air bubbles as possible by operating the lever. The amount of water coming and going can be reduced.

  The tensiometer according to claim 2 of the present invention is the tensiometer according to claim 1, wherein the separation valve slightly supplies water from the upper chamber to the lower chamber by the separation valve opening operation of the separation valve opening / closing mechanism. A first separation valve for flowing in, and a second separation valve for allowing a large amount of water to flow from the upper chamber to the lower chamber, wherein the first separation valve is a second separation when the lower chamber is in a negative pressure state. It is characterized by being opened before the valve.

  First, the first separation valve is opened, and water is slowly allowed to flow into the lower chamber through the narrow passage. When the negative pressure in the lower chamber is reduced, the second separation valve is opened. Since the separation valve has a two-stage opening / closing structure in this way, it prevents the water hammer phenomenon that occurs when water suddenly flows into the lower chamber that is under negative pressure when opening the separation valve, and is sensitive. Prevent shock pressure from acting on the pressure sensor.

  The tensiometer according to claim 3 of the present invention is the tensiometer according to claim 1 or 2, wherein the measured value of the pressure sensor can be confirmed from outside the ground surface in a state where the tensiometer is embedded in soil. The display unit is further provided.

  By providing such a display unit, the state of the soil can always be accurately determined.

  According to the tensiometer of the present invention, bubbles generated in the porous cup can be removed quickly, and the pressure measurement is located in the underground part where there is little temperature influence, thereby reducing the water flow in and out of the porous cup. The time can be advanced, the influence of solar radiation and temperature on the surface can be minimized, the influence on the soil to be measured can be reduced, and the amount of water used can be reduced.

  A tensiometer according to an embodiment of the invention will be described. As shown in FIG. 1, a tensiometer 1 according to an embodiment of the present invention includes a pipe 10, a porous cup 20 provided at the lower end portion of the pipe 10, and a pressure sensor provided in the vicinity of the porous cup of the pipe 10. 31, a plug 19 that closes the upper end opening of the pipe 10, a separation valve 40 provided near the pressure sensor mounting position inside the pipe, a separation valve opening / closing lever 50 extending from the top of the pipe 10, pressure An indicator 35 connected to the sensor 31 is provided.

  The pipe 10 is composed of, for example, a PVC pipe having a diameter of about 18Φ and a length of about 500 mm. As described above, the lower end portion 10a forms a connection portion with the porous cup 20, and the tube wall in the vicinity of the connection portion with the porous cup 20 is used. A pressure measurement hole 10b is formed in the pressure sensor 31, and a pressure sensor 31 is attached to the hole 10b. Further, a step portion 15 for seating the separation valve 40 is continuously formed on the entire inner circumferential direction of the pipe above the hole in the pipe.

  The porous cup 20 provided at the lower end portion of the pipe 10 is made of a jar made of a porous material such as an unglazed seto like the porous cup 120 described above, and the water inside the porous cup 20 is porous in the porous cup 20. It is sucked into the soil by a so-called capillary phenomenon through a fine gap between the pores and the soil around the porous cup.

  Further, the upper end portion 10c of the pipe 10 can be closed with a stopper 19, so that water is injected from the upper end portion of the pipe, and the water injected into the porous cup 20 and the pipe 10 does not enter rainwater or dust. It is designed to accumulate in the state.

  Further, a space formed by the pipe 10 and the porous cup 20 is defined by a lower chamber 11 including the inside of the porous cup and an upper chamber 12 positioned above the lower chamber 11 through a separation valve 40 which will be described later. Water can be separately stored in each space via the valve 40.

  The pressure sensor 31 is for measuring the pressure in the lower chamber including the inside of the porous cup defined by the separation valve 40. The pressure sensor 31 can measure the pressure even when the lower chamber is filled with water. The air or water vapor sucked into the soil from 20 and dissolved in water appears in the lower chamber 11, and the pressure when air and water vapor are mixed in the lower chamber 11 can also be measured. And the pressure sensor 31 sends pressure data to the indicator 35 installed outside the ground surface via an electric wire.

  On the other hand, a traction rope lead-out portion 18 is provided at the top of the pipe 10 and is introduced into the pipe via a traction rope lead-out portion 18 extending from a separation valve opening / closing lever 50 provided at a predetermined distance from the pipe 10. It is connected to a part of a separation valve 40 described later. Then, by operating the separation valve opening / closing lever 50, the traction rope 51 can be slightly led out from the pipe or introduced into the pipe, whereby the separation valve 40 can be opened and closed.

  As shown in detail in FIG. 2, the separation valve 40 includes a first separation valve 41 and a second separation valve 42 disposed so as to partially surround the first separation valve 41. The first separation valve 41 has a needle shape and includes a valve body 41a having an enlarged diameter at a substantially central portion, and a seat 41b of a compression spring 44 at one end. Also, one end of a tension spring 43 is fixed in the vicinity of the other end of the first separation valve 41, the tension spring 43 is wound around the first separation valve 41, and the other end is the first end. The pipe is fixed to a fixing part 17 on the inner wall of the pipe located below the other end of the separation valve 41. The other end of the first separation valve 41 is connected to one end of a traction rope 51 extending from the separation valve opening / closing lever 50 described above.

  The second separation valve 42 has a cylindrical body that can accommodate the valve body 41a of the first separation valve 41 therein. The second separation valve 42 is reduced in diameter at the lower end portion of the second separation valve 42 so that the first separation valve 42 A seating portion 42a for seating 41 is configured. In addition, O-rings 48 and 49 made of, for example, rubber are provided in the vicinity of the seating portion 42a and the outer peripheral edge of the lower end portion of the second separation valve 42. From the upper chamber 12 to the lower chamber 11 when the separation valve is closed. Water is prevented from flowing in. A compression spring 44 is interposed between the lower end surface of the second separation valve 42 and one end of the first separation valve 41.

  In addition, when the first separation valve 41 is pulled upward by the pulling rope 51 when the lower chamber 11 is at a negative pressure, the tension spring 43 and the compression spring 44 are first extended. Only the first separation valve 41 moves upward, whereby water flows into the lower chamber 11 and the pressure in the lower chamber rises, so that the negative pressure from the lower chamber 11 does not act on the second separation valve 42. Each spring constant is designed so that the second separation valve 42 urged by the compression spring 44 moves upward thereafter.

  Then, the actual usage method of this tensiometer 1 is demonstrated. First, the porous cup 20 of the tensiometer 1 is buried vertically with the porous cup 20 at the lower end so as to reach, for example, the depth of the root of the plant in the soil. That is, the pipe 10 is embedded so that the porous cup 20 at the lower end of the pipe has a depth of about 10 cm to 40 cm from the ground surface in accordance with the active range of the root. The upper end of the tensiometer 1 is left protruding from the ground surface in order to remove the plug 19 and allow water to flow in. In addition, the separation valve opening / closing lever 50 is disposed at a suitable position on the ground, and the indicator 35 is disposed at a suitable position on the ground surface.

  Next, the plug 19 is removed and water is poured from the upper end of the pipe 10. At this time, the separation valve opening / closing lever 50 is operated to open the separation valve 40, so that water flows not only into the upper chamber 12 but also into the lower chamber 11. It should be noted that immediately after the tensiometer 1 is buried in the soil, the lower chamber 11 remains at atmospheric pressure, and no negative pressure acts on the second separation valve 42, so that the separation valve opening / closing lever 50 can be operated. Since both the first separation valve 41 and the second separation valve 42 are pulled up at the same time and the separation valve 40 is quickly opened widely, water can efficiently flow into the lower chamber 11 and the upper chamber 12.

  Next, after water is accumulated to the full inside of the tensiometer 1, a stopper 19 is put on the upper end of the pipe 10 to seal the inside of the tensiometer.

  Thus, from the porous cup 20 of the tensiometer 1 buried in the soil, water is sucked into the soil according to the dryness of the soil around the porous cup, the water level in the lower chamber is lowered, and the lower chamber is lowered. Air and water vapor dissolved in the water appear and bubbles are generated, and eventually air accumulates in the upper part of the lower chamber. Thus, the water accumulated in the lower chamber 11 in the pipe is sucked into the soil through the porous cup 20 and becomes a drag when the lower chamber becomes a negative pressure and the water is sucked, and the drag due to the sucking force and the negative pressure. It stabilizes when balanced. In addition, since the suction force will become strong if the soil is dry, the negative pressure in a lower chamber will also become large. And the moisture value in soil is grasped | ascertained by reading the pressure value measured with the pressure sensor 31 with the indicator 35 provided in the appropriate place of the ground surface. The magnitude of the pressure in the lower chamber is almost minus 1 atm when the soil is dry. This device is called a tensiometer because it measures pulling force, that is, tension.

  Here, the tensiometer 1 according to the present embodiment is defined in the lower chamber 11 and the upper chamber 12 via the separation valve 40 outside the tensiometer, so that the lower portion containing the water filled in the porous cup 20 is accommodated. The volume of the chamber 11 is reduced. Therefore, when the water in this space is sucked out of the porous cup 20 and the lower chamber 11 becomes negative pressure, the amount of bubbles generated from the water inside the porous cup can be reduced. Therefore, the following specific actions can be produced.

  Specifically, when water is sucked out and the inside of the pipe 10 becomes a negative pressure, the air dissolved in the water previously put in the pipe 10 appears, and the water evaporates to become water vapor. In addition to this, bubbles are generated in the lower chamber. Water reaches out to reach pressure equilibrium, a significant amount of water is aspirated and finally pressure equilibrium is reached. However, since the volume of the lower chamber 11 in which the tensiometer 1 according to the present embodiment has a negative pressure is smaller than that of the conventional tensiometer, bubbles generated in the tensiometer can be reduced. That is, when the separation valve 40 is closed, the lower chamber 11 is a sealed space having a small volume. Since the lower chamber 11 has such a small volume, it is possible to reduce the amount of air that is first dissolved in water and to reduce the volume of water vapor.

  Since the porous cup 20 is also in contact with the air layer at atmospheric pressure in the ground, the air gradually melts from here, moves into the porous cup, and re-releases air due to the negative pressure inside.

  On the other hand, when the amount of soil water rises due to accumulated water or rainfall, the suction force from the porous cup 20 into the soil decreases, so that the water in the soil flows back into the lower chamber and reaches a pressure equilibrium. However, since the volume of the bubbles in the lower chamber is small as described above, the amount of water flowing back corresponding to this volume can be small. Accordingly, the water that has flowed back in this manner also dissolves other components such as fertilizer, but since the amount of water itself is small, there is little effect on the suction force from the porous cup 20 toward the soil.

  On the other hand, since the upper end portion of the pipe of the tensiometer 1 protrudes from the ground surface, in the conventional tensiometer 100, the upper portion of the pipe is heated by solar radiation or the surface temperature, and the gas inside the pipe expands, and the water corresponding to this volume becomes porous cup. 20 is further sucked out into the ground. And at night, when the air temperature at the surface part decreases, the air inside the pipe is also cooled, so the volume decreases and the pressure inside the pipe decreases, so the water in the soil around the porous cup again flows back from the outside. It was in.

  However, since the lower chamber 11 is in the ground, the tensiometer 1 according to the present embodiment is not affected by solar radiation or the temperature of the ground surface, and can suppress a change in gas volume. Thereby, the expansion | swelling and shrinkage | contraction of the bubble which generate | occur | produced in the lower chamber accompanying the temperature change of the ground surface can be suppressed, and the entrance / exit of the water from the porous cup 20 to soil accompanying this can also be suppressed to the minimum.

  For the reasons described above, it is possible to reduce the entry / exit of water from the porous cup 20 to the soil, suppress the consumption of water in the pipe, and reduce the response time. Along with this, the measurement system composed of the soil around the tensiometer is not affected by the water flowing out to the outside. For example, the root of the plant as in the case where the tensiometer 100 of the conventional example is used. Troubles gathering around the porous cup can be reduced.

  Further, when the water in the lower chamber 11 in the tensiometer is reduced, the water can be easily replenished without causing the pressure sensor 31 to be adversely affected by the water hammer as described below. Hereinafter, this water supply will be described.

  First, after a certain amount of water is sucked into the surrounding soil from the porous cup 20, the air accumulated in the upper portion of the lower chamber 11 is moved to the upper portion of the tensiometer 1 by operating the separation valve 40. Specifically, by operating the separation valve opening / closing lever 50, the first valve body 41 of the separation valve 40 is moved upward against the tensile force of the tension spring 43, as shown in FIG. At this time, since the lower end surface of the second separation valve 42 is pulled downward by the negative pressure in the lower chamber, the compression provided between the first separation valve 41 and the second separation valve 42 is provided. Even by the biasing force of the spring 44, the second separation valve 42 does not immediately move upward. Then, the first separation valve 41 moves upward and a gap is formed between the first separation valve 41 and the second separation valve 42, so that water in the upper chamber flows into the lower chamber little by little. As a result, the water level in the lower chamber rises and the negative pressure in the lower chamber gradually decreases, and eventually the second separation valve 42 is not pulled toward the lower chamber by the negative pressure, as shown in FIG. In addition, the second separation valve 42 is also moved upward by the urging force of the compression spring 44. By opening the second separation valve 42 in this way, a larger amount of water flows into the lower chamber 11 from the upper chamber 12 and the lower chamber 11 can be quickly filled with water.

  In this way, the amount of water flowing from the upper chamber 12 to the lower chamber 11 is reduced initially and increased later, thereby preventing the pressure sensor 31 disposed in the lower chamber from being damaged by the so-called water hammer phenomenon.

  In the above-described embodiment, the separation valve 40 is divided into the first separation valve 41 and the second separation valve 42, and the amount of water flowing from the upper chamber 12 into the lower chamber 11 is changed. Although the water hammer phenomenon has been eliminated to protect the pressure sensor 31, the separation valve 40 is divided into the first separation valve 41 and the second separation valve 42 in this way if there is no fear of damage to the pressure sensor 31. There is no need to configure.

  Further, the plug 19 fitted into the upper portion of the pipe 10 is not limited to a rubber plug, and may be any lid. Further, the diameter, length, and material of the pipe 10 are not necessarily limited to the above-described embodiment. Similarly, various materials such as metal and resin can be considered for the material of the separation valve 40.

  The separation valve 40 is opened and closed via the separation valve opening / closing lever 50 and the traction rope 51. For example, an optical sensor for detecting the generation of bubbles is attached to a position where bubbles in the lower chamber 11 are likely to be generated. The separation valve 40 may be electrically opened and closed by a motor or the like when the generation of bubbles is detected by the optical sensor.

  As described above, when the separation valve 40 is closed, the lower chamber 11 becomes a closed space with a small volume. Since the volume of the lower chamber 11 is cut off from the whole and is small, the amount of air that is initially sunk is reduced, and the volume of water vapor added by partial pressure can be reduced accordingly. Moreover, since the lower chamber 11 is in the ground and the temperature is constant without being affected by solar radiation or the temperature of the ground surface, the volume change of the gas can be suppressed. As a result, extraneous water entry and exit between the porous cup 20 and the surrounding soil can be suppressed as much as possible, the consumption of water in the pipe can be suppressed, and the response time does not need to be reduced. In connection with this, it does not affect the measured system composed of the soil around the tensiometer due to the water flowing out to the outside.

  Further, according to the tensiometer according to the present embodiment, all of the air stored in the lower chamber 11 can be extracted in a short time by simply pulling the separation valve opening / closing lever 50 connected to the traction rope, and water can be filled in the lower chamber 11. it can. Therefore, it is much easier in terms of management of the tensiometer compared to carrying and refilling a water container every time as in the prior art. If water is replenished frequently, the amount of inflow of dissolved water can be reduced, and the responsiveness of the tensiometer itself after the separation valve is closed again is improved.

  When the water in the upper chamber runs out, it must be replenished by opening the stopper. However, since the pressure in the lower chamber does not change at this time, it is not necessary to cause an unnecessary change in the pressure sensor output characteristics.

It is sectional drawing shown in the state which embedded the tensiometer concerning one Embodiment of this invention in soil. FIG. 2 is an enlarged cross-sectional view of a separation valve portion of the tensiometer shown in FIG. 1 and showing a state where the separation valve is closed. FIG. 3 is a cross-sectional view corresponding to FIG. 2, showing a state where only the first separation valve of the separation valve is open. FIG. 3 is a cross-sectional view corresponding to FIG. 2, and is a cross-sectional view showing a state where both a first separation valve and a second separation valve of the separation valve are opened. It is sectional drawing shown in the state which embedded the conventional tensiometer in the soil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tensiometer 10 Pipe 10a Lower end part 10b Hole part 10c Upper end part 11 Lower chamber 12 Upper chamber 15 Step part 17 Fixing part 18 Pulling rope derivation part 19 Plug 20 Porous cup 31 Pressure sensor 35 Display meter 40 Separation valve 41 1st isolation valve 41a Valve body 41b Seating portion 42 Second separation valve 42a Seating portion 43 Tension spring 44 Compression spring 48, 49 O-ring 50 Separation valve opening / closing lever 51 Traction rope 100 Tensiometer 110 Pipe 119 Rubber plug 119
120 Porous cup 131 Pressure sensor 135 Indicator

Claims (3)

With a porous cup,
A pipe having one end connected to the porous cup and the other end opened;
A pressure sensor for measuring the pressure in the pipe;
A tensiometer comprising a lid that is fitted to the other end of the pipe and seals the inside of the pipe and the porous cup,
A separation valve that defines at least the interior of the pipe and the porous cup into a lower chamber including at least the interior of the porous cup and an upper chamber adjacent to the lower chamber; and opening and closing of the separation valve that can be opened and closed from the outside of the tensiometer A tensiometer, wherein the pressure sensor measures the pressure in the lower chamber.   The separation valve includes a first separation valve that slightly allows water to flow from the upper chamber to the lower chamber by opening the separation valve of the opening / closing mechanism, and a second that causes a large amount of water to flow from the upper chamber to the lower chamber. The tensiometer according to claim 1, further comprising a separation valve, wherein the first separation valve is opened before the second separation valve in a state where the lower chamber is in a negative pressure state. The tensiometer according to claim 1 or 2, further comprising a display unit that allows the measurement value of the pressure sensor to be confirmed from outside the ground surface in a state where the tensiometer is embedded in soil.

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