JP2002286711A - Tensiometer for measuring water content of soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tensiometer as improvement of a conventional one equipped with a pressure converter involving such problems as degradation of the measuring accuracy and promotion of cumulation of the leaching air owing to the use of a pressure converter for air, degradation of the responsiveness and an increase of the amount of the leaching air resulting from forming the body from a polyvinyl chloride pipe, and turbulence of the periphery of a porous cup, destruction of the pressure converter, etc., likely when the leaching air is to be removed. SOLUTION: The tensiometer is composed of a transparent polyvinyl chloride pipe 2 furnished with a P-cock 1 ranging from the top to below, an upper and a lower valve socket 3 made of polyvinyl chloride connected to the pipe, a full-bore type ball valve 4, nipple 5, and cheese pipe 6 provided between the valve sockets, a bushing 7 and pressure converter 8 installed beside the cheese pipe, a stainless steel pipe 9 connected with below the valve sockets, and the porous cup 10 having water permeability connected to the stainless steel pipe, whereby the arrangement is partitioned into upper and lower parts by closing the full-bore ball valve so that the upper part is used as an air sump while the lower part is formed as a measuring system, and the water content of soil is determined by measuring the water tension of negative pressure in the measuring system by the pressure converter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soil moisture sensor for detecting soil moisture in, for example, agricultural horticulture.
In particular, the present sensor provides a fast responsive soil moisture sensor for use in an automatic irrigation controller.

[0002]

2. Description of the Related Art When performing soil moisture measurement with a tensiometer, the most problematic is leaching air which is always generated from water filling the tensiometer due to negative pressure. The expansion and contraction of the leached air greatly increases the measurement error of the tensiometer. For this purpose, deaerated water (water obtained by applying a negative pressure to air dissolved in water and leaching it) is used for filling water, but the air dissolves due to shaking during transportation and the elapsed time, and the remaining effect is It is important to reduce the amount of leached air itself and to simplify the elimination of leached air.

As a prior art, Japanese Patent Laid-Open No. Hei 6-160 discloses a structure in which a pressure-sensitive sensor for measuring soil moisture is housed in a porous cup so as to be less affected by the outside air temperature.
No. 378, the size of the porous cup itself is large to accommodate the pressure sensor, and the amount of filling water is large due to the complicated water supply pipe and water supply valve connected to the inside of the porous cup, and the supply and exhaust pipe and the supply and exhaust valve. As a result, the amount of leached air does not decrease, and exhausting time is not easy.

[0004] Japanese Patent Laid-Open No. 8-1 discloses a method of filling water.
No. 70959 can reduce the amount of filling water, but in order to eliminate the leached air that always occurs, the sensor must be excavated by excavating the sensor from the soil each time, and it can be said that it is a simple exhaust operation. Absent.

[0005] A commercially available tensiometer that automatically refills filling water with a solenoid valve and a timer is expensive because it has a large sensor device and is difficult to handle.

As is well known, commercially available tensiometers equipped with a pressure transducer have come to be attached to the tensiometer because the precision of the semiconductor pressure transducer has become very good in recent years, but most of them are inexpensive air pressure transducers. A transducer is installed, and air is present from the beginning in the space up to the pressure receiving chip made of single crystal silicon, which is installed in the pressure transducer, and the expansion and contraction of the leached air in the tensiometer due to temperature changes. It is conducive to and inaccurate for long-term measurements.

[0007] A further important deficiency that has been overlooked in the past is that since Henderson (1964) recommended the use of inexpensive and readily available vinyl chloride tubing for the body constituting the tensiometer, it has been published worldwide in the American Soil Society Journal. The PVC pipe tensiometer has been used for a long time. It became clear from the experiment.

[0008] In other words, the main body of the PVC pipe contracts due to the soil water tension and the negative pressure due to the suction force of the root of the crop, and discharges more contracted water than the porous cup. However, when the negative pressure is relaxed, the PVC pipe body expands, and the expanded water must be taken in from the soil, but the tensiometer also measures the suction power of the roots of the crop, and sufficient soil water is taken up. The structure cannot maintain the mechanical equilibrium by further expanding the leached air in the measurement system.

In addition, conventionally, every time leaching air is discharged,
The rubber stopper attached to the top was removed and the inside of the measurement system was opened to the atmosphere, and water or degassed water was filled. However, it takes a lot of time and labor to inject the water, and the water in the porous cup at the lower end becomes positive pressure, so that water permeates to the outside and disturbs the soil moisture condition around the porous cup and recovers to the previous measured value It took a long time to re-equilibrate. More seriously, the removal and pushing of the rubber stopper destroyed the pressure receiving surface of the sensitive pressure transducer.

[0010]

SUMMARY OF THE INVENTION The present invention is intended to reduce the measurement accuracy and accumulate leaching air due to the use of a pressure transducer for air, and to reduce the responsiveness and leaching caused by constituting a main body of a vinyl chloride tube. Reducing problems with conventional tensiometers with pressure transducers, such as increasing the amount of air, turbulence around the porous cup during the operation of removing leached air, and destruction of the pressure transducer, reduces the amount of leached air itself. It is intended to provide a tensiometer with a pressure transducer which can reduce the number of discharge operations, simplify the discharge operation, and facilitate maintenance.

[0011]

SUMMARY OF THE INVENTION The present invention has the following structure to provide a tensiometer with a pressure transducer that reduces the amount of leached air itself to reduce the number of discharge operations and facilitates the discharge operation. And A full-bore type ball valve (4) is provided at the center, and the upper portion of the closed full-bore type ball valve is separated into an air reservoir system and the lower portion into a measurement system. A pressure transducer (8) with a double diaphragm structure without any air in the transducer is used for the pressure transducer. A stainless steel tube (9) having almost no contraction / expansion with respect to increase / decrease of negative pressure is used for the tensiometer body of the measurement system. In order to prevent the pressure transducer from breaking, a peacock (1) is used at the leaching air exhaust port. In order to avoid the influence of the air temperature and the ground temperature on the tensiometer, a porous cup (10) having good water permeability that does not leak even at -98.1 KPa is used. In order to further reduce the amount of degassed water that fills the inside of the measurement system, the stainless steel pipe (9) connecting the porous cup (10) and the pressure transducer has a smaller diameter as shown in FIG. 4 or a stainless steel pipe as shown in FIG. (9) and porous cup (10)
An insertion rod (13) having an outer diameter slightly smaller than the inner diameter is inserted into. (9 ') is a small diameter stainless steel pipe, (1)
0 ′) is a small-diameter porous cup.

This overcomes the following defects caused by the conventional leaching of air.

A double-diaphragm pressure transducer, in which the space up to the pressure-receiving chip in the pressure transducer is sealed with silicone oil, is slightly more expensive than a conventionally used pneumatic pressure transducer. The portion is a stainless steel flat plate exposed to the outside, suitable for measuring the negative pressure of the liquid in the Tensio cup, and capable of long-term measurement without the presence of air. When the response of the tensiometer equipped with the pressure transducer having the double diaphragm structure was measured, it was 2-3.
It shows quick operation characteristics in seconds and has electrical output, so it can be used as a soil moisture control sensor.

The contraction and expansion of the PVC pipe can be overcome by using an inexpensive stainless steel pipe, and most of the stainless steel pipe is buried in the soil, so that the influence of thermal expansion due to direct sunlight is small.

The operation of discharging the leached air in the measurement system generated by the negative pressure is performed by filling the closed peacock (1), the transparent vinyl chloride pipe (2), and water (11) such as water or deaerated water. Open the full-bore ball valve (4), which is always closed at the time of measurement, in the upper air reservoir system, quickly move the air accumulated in the measurement system upward, and close the full-bore ball valve (4) again. Just do these three
There is almost no disturbance of soil moisture around the porous cup for the opening and closing operation for 5 seconds. In the operation of discharging air in the upper air reservoir system, only the peacock (1) at the upper end is opened while the full-bore type ball valve (4) is closed, and water or deaerated water is injected to discharge air. , This involves
It takes some time, but there is no need to panic and maintenance is easy.

The ball valve is defined as a full-bore type ball valve (4) which does not shrink in diameter. The reason for this is that a transparent PVC pipe (2) and a stainless steel pipe (9) have the same diameter cross section so that leached air can be obtained. The transparent vinyl chloride tube (2) in the upper air reservoir system was used to confirm whether or not the leached air was excluded from the measurement system.

As described above, the present invention is intended to simplify the operation of introducing a pressure transducer (8) having a double diaphragm structure, introducing a stainless steel pipe (9) of a measuring system body of a tensiometer, and discharging leached air. In addition to reducing the amount of leached air itself by introducing a full-bore type ball valve (4), the operation for removing the leached air can be performed simply and rationally to obtain easy maintenance and good measurement accuracy of the tensiometer. Was.

When the amount of leached air generated is measured, the cheese tube (6) and the porous cup (10) in the measuring system are connected to each other with respect to the water tension of 0 to -900 cm in the tensiometer having the shape shown in FIG. Stainless steel pipe (9)
Of the leaching air generated by using a conventional transparent vinyl chloride pipe (2) with an inner diameter of 13 mm and an outer diameter of 18 mm
In the case of the stainless steel tube (9) having an inner diameter of 15 mm and an outer diameter of 19 mm according to the present invention, the ratio is 1/17, and a resin insertion rod (1) having an outer diameter of 13 mm is inserted into the stainless steel tube (9).
If the absolute amount of the water (11) to be filled by inserting 3) was reduced, it became 1/135.

Similarly, the measurement accuracy of the water tension of each material of the tube connecting the cheese tube (6) and the porous cup (10) has an error of ± 8% in the conventional vinyl chloride tube as shown in FIG. , But within ± 2% for the stainless steel tube (9) of the present invention.

[0020]

According to the tensiometer with a pressure transducer of the present invention, as shown in FIG. 1, a peacock (1) made of gunmetal, a transparent vinyl chloride pipe (2), a full-bore type ball valve (4) made of gunmetal,
Steel cheese tube (6), pressure transducer with double diaphragm structure (8), stainless steel tube (9), leak pressure -98.1
It consists of a porous cup (10) with good water permeability of KPa or more, and the inside of the tensiometer is water or deaerated water (11).
Fill with. The procedure for discharging the leached air was as described above. The frequency of the discharging operation in the midsummer of the site was conventionally performed once a day, but was extremely low, about once a week to once every 10 days.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Peacock (1) made of gunmetal, transparent vinyl chloride pipe (2), full-bore type ball valve (4) made of gunmetal,
The steel cheese tube (6), the stainless steel tube (9), and the porous cup (10) use a unitary size of 1/2 inch. The pressure transducer (8) of the double diaphragm structure
The PA800-102V manufactured by Copal Electronics Co., Ltd. is used.
It is necessary to insert one bushing fitting of 1/2 × PF3 / 8. (14) is a support plate provided between the small-diameter stainless steel pipe (9 ') and the vinyl chloride valve socket (3).

[0022]

The present invention solves the problem of measuring soil moisture with a tensiometer, that is, simplification of maintenance work and improvement of measurement accuracy by reducing the amount of leached air generated in the tensiometer. At the same time, a tensiometer with a pressure transducer that has simplified the process of eliminating leached air,
To be able to be used for soil moisture measurement, and to be able to use the tensiometer with the pressure transducer as a soil moisture sensor in an automatic irrigation controller in farming situations, and to have easy maintenance and good measurement accuracy of the tensiometer And the like.

The use of an inexpensive stainless steel pipe eliminates the conventional problems caused by shrinkage and expansion of the vinyl chloride pipe, and most of the stainless steel pipe is buried in the soil. There is a benefit in reducing the effects of thermal expansion due to sunlight.

[Brief description of the drawings]

FIG. 1 is a front view showing a soil moisture measuring tensiometer of the present invention.

FIG. 2 is a flowchart showing measurement accuracy of a soil moisture measuring tensiometer according to the present invention.

FIG. 3 is a sectional view showing another soil moisture measuring tensiometer according to the present invention.

FIG. 4 is a sectional view showing still another soil moisture measuring tensiometer according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Peacock 2 Transparent vinyl chloride pipe 3 Vinyl chloride valve socket 4 Full bore type ball valve 5 Nipple 6 Cheese pipe 7 Bushing 8 Pressure transducer 9 Stainless steel pipe 9 'Small diameter stainless steel pipe 10 Porous cup 10' Small diameter porous cup 11 Water or Deaerated water 12 Soil 13 Insertion rod 14 Support plate

Claims (2)

[Claims] 1. A transparent vinyl chloride pipe (2) having a peacock (1) downward from an upper end, a pair of upper and lower vinyl chloride valve sockets (3) connected to the transparent vinyl chloride pipe, and A full bore ball valve (4), a nipple (5) and a cheese tube (6) provided between the valve sockets (3), and a bushing (7) and a pressure transducer ( 8)
And the lower valve socket made of vinyl chloride (3)
And a porous cup (10) connected to the stainless steel pipe (9) and impermeable to air but permeable to air. The porous cup (10) is connected to the soil (12). ), The full-bore type ball valve (4) located at the center is closed to divide it into upper and lower parts, and this upper part is used as an air reservoir system.
A soil moisture measuring tensiometer having a configuration in which a lower portion is formed in a measuring system, and the soil pressure is detected by measuring the negative tension moisture in the measuring system with the pressure transducer (8). 2. A cheese tube (6), a stainless steel tube (9), an air-permeable but water-permeable porous cup (9) in order to reduce the amount of water (11) filled in the measuring system of the tensiometer. An insertion rod (13) having an outer diameter slightly smaller than the inner diameter is inserted into the measuring system constituted by (10), or a stainless steel pipe (9) or a porous cup (10) which is a constituent member of the measuring system is inserted. The tensiometer for measuring soil moisture according to claim 1, wherein the diameter is reduced.