JP2532681B2 - Electric resistance type soil moisture sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric resistance type soil moisture sensor suitable for use in soil moisture management in the agricultural field and the like.

[Conventional technology]

Conventionally, in the soil moisture management in the agricultural field, etc., the soil moisture state is represented by a moisture tension value (pF value) that is directly related to the growing conditions of the crop, and the moisture tension value is suitable for the crop to absorb moisture. As such, it manages the water condition of the soil.

At this time, a sensor member such as gypsum whose water content changes according to the water tension of the soil is buried in the soil, and the water tension is measured based on the electric resistance in the sensor member. A sensor is used.

FIG. 7 is a diagram showing a conventional electric resistance type soil moisture sensor.

In the figure, 10 is a sensor member formed by hardening gypsum, 20a, 20b is a pair of electrodes arranged in the sensor member 10 at a predetermined interval, the electrode 20a in a state where the sensor member 10 is buried in soil. , 20b, the electric resistance of the sensor member 10 is detected, and the water tension value of soil is obtained from the electric resistance value.

When the sensor member 10 is buried in the soil, the water contained in the soil is absorbed in the sensor member 10 by the water absorption of gypsum, etc., but the amount of water in the sensor member 10 depends on the water tension of the soil. It changes, and the amount of water in the sensor member 10 correlates with its electric resistance. Therefore, when the water absorption / release between the soil and the sensor member 10 is in a sufficient equilibrium state, the water tension of the soil and the electric resistance of the sensor member 10 show a correlation.

[Problems to be Solved by the Invention]

However, in this type of sensor, gypsum is used as a material for forming the sensor member 10, and further,
Since the electric resistance value is measured by the water content between the electrodes, there are the following problems.

Moisture transfer from the soil to the gypsum (sensor member) is carried out quickly by the water absorption of the gypsum, but even if the water content of the soil starts to decrease sharply due to drying, the water retention of the gypsum is strong and the gypsum has voids. Due to the small amount, the water transfer from the gypsum to the soil is very slow. For this reason, it takes a long time to reach an equilibrium state between the water state between the electrodes and the water state of the soil, and there is a problem that the response performance is poor. In addition, since the conventional sensor has a small change in the electric resistance value with respect to the change in the water tension, there is a problem that the measurement accuracy is poor and the measurement error is large.

An object of the present invention is to improve the shape or composition of a sensor material in an electric resistance type soil moisture sensor to improve response performance and reduce measurement error.

[Means and Actions for Solving the Problems]

The electric resistance type soil component sensor of the present invention made to solve the above-mentioned problems is characterized in that a trace amount of silicon powder is mixed in the sensor member, and the moisture retention of the sensor member is reduced by the silicon powder, and the sensor The equilibrium state between the member and the soil is quickly achieved.

Further, the electric resistance type soil component sensor of the present invention is characterized in that a small amount of activated carbon powder is mixed in the sensor member, the activated carbon powder facilitates the movement of water in the sensor member, and the equilibrium between the sensor member and soil. State is achieved quickly.

Further, the electric resistance type soil component sensor of the present invention, the sensor member is formed in a thin plate shape, a pair of mesh-shaped and plate-shaped electrode pairs for detecting the electric resistance inside the sensor member in the sensor member. A water-repellent film is placed on both sides of the plate-shaped electrode so as to be opposed to each other, and water that permeates into the plate-shaped electrode surface through the water-repellent film having a small water-holding power. The electric resistance between the electrode pair was changed depending on the amount.

〔Example〕

FIG. 1 is a diagram showing an electric resistance type soil moisture sensor according to an embodiment of the present invention. FIG. 1 (a) is a front view and FIG. 1 (b) is A.
-A sectional drawing and the same figure (c) are BB sectional drawings. In addition,
The thickness of each cross-sectional view is exaggerated.

In the figure, 1 is a plate electrode made of 0.05 mm SuS plate,
2 is a mesh electrode made of 3 mm square SuS wire mesh, 3 is a small amount (1-5%) of silicon powder and 0.5% (0.5-5) based on gypsum
%) Activated carbon powder mixed sensor member, 4 is a water-repellent film that is water-repellent processed by impregnating water-permeable glass fiber filter with silicon grease, and 5 is a plastic inner frame having openings 5a. , 6 is a plastic outer frame having an opening 6a larger than the opening 5a of the inner frame 5, and the sensor of this embodiment has a layered structure symmetrical with respect to the plate electrode 1 on both sides.

The plate-like electrode 1 is fixed by sandwiching the electrode surface between two inner frames 5 with the terminals 1a exposed to the outside, and the opening 5a of the inner frame 5 is fixed.
The water-repellent film 4 is adhered to both surfaces of the plate-like electrode 1 facing the surface.

The two net electrodes 2 are fixed by being sandwiched between the inner frame 5 and the outer frame 6 with the terminals 2a exposed to the outside, and the net electric wires 2 are arranged on both sides of the plate electrode 1 and the water-repellent film 4. Is in a closed state. The sensor member 3 is filled with the thickness from the water-repellent film 4 to the surface of the outer frame 6. An adhesive or the like is used to fix the inner frame 5 and the outer frame 6, and the outer peripheral edge portion is sealed with the adhesive.

In the sensor of this embodiment, the length of the outer frame 6 is 110.
The width is 20 mm and the total thickness is about 6 mm.

As described above, since the sensor member 3 is mixed with a small amount of silicon powder and a small amount of activated carbon powder, the water-repellent property of the silicon powder lowers the water-retaining power of the sensor member 3 itself. Movement of water in the member 3 is facilitated. Therefore, the equilibrium state between the sensor member 3 and the soil is quickly achieved, and excellent response performance is exhibited.

Further, in the sensor of this embodiment, as shown in FIG. 1, only the sensor member 3 and the mesh electrode 2 are provided between the upper end of the opening 5a of the inner frame 5 and the upper end of the opening 6a of the outer frame 6. This portion alone constitutes an evaporation zone 7 for evaporating the moisture of the sensor member 3.

That is, at the time of use, the electrical resistance between both sides of the water-repellent film 4 is set by the terminals 1a and 2a in a state where the mark A (FIG. 1 (a)) is buried in the soil and the evaporation zone 7 is exposed to the atmosphere. To measure.

By exposing the evaporation zone 7 to the atmosphere as described above, the water in the part of the sensor member 3 which is buried in the soil, that is, the part where the water-repellent film 4 is present is evaporated from the evaporation zone 7 to the atmosphere. It Therefore, from the soil to the sensor member 3
The water constantly moves to the side, and the equilibrium state of the sensor member 3 is quickly achieved with respect to the change in the water content of the soil.

Further, the water-repellent film 4 is permeated with water in an amount corresponding to the amount of water (pressure) of the sensor member 3, the permeated water reaches the plate-shaped electrode 1, and the electric resistance is measured by the permeated water. . Therefore, the change in the electric resistance value becomes large with respect to the change in the water tension.

The water-repellent film 4 of this example was manufactured as follows.

First, paste glue silicon grease in a predetermined container with N-
Dissolve in hexane, put 0.26 mm thick glass fiber filter paper in it, and cover the container. Then, the glass fiber filter paper is impregnated with silicon for about 2 days to remove N-hexane, and the glass fiber filter paper impregnated with silicon is cut into a predetermined size. In this example, the amount of silicon impregnated in the glass fiber filter paper was 6.1 mg / cm ² .

FIG. 2 is a diagram showing another embodiment, in which the evaporation zone 7 in the above embodiment is eliminated. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 2, the opening 6 of the outer frame 6 '
The upper end of a'is located at substantially the same position as the upper end of the opening 5a of the inner frame 5, whereby there is no evaporation zone as in the above embodiment.

In the sensor of each of the above embodiments, the sensor member 3 is mixed with the silicon powder and the activated carbon powder, but either the silicon powder or the activated carbon powder may be mixed.

FIG. 3 to FIG. 6 are diagrams showing the measurement results of various sensors in Examples, and the electric resistance value of each sensor is shown as a voltage value with respect to a constant current. For this measurement, as shown in the table below, sensors I to V having a sensor having the same shape as that shown in FIG. 1 or 2 in which silicon powder, activated carbon powder and water-repellent film 4 are appropriately removed are used. ing. In the table below, "○" means "present" and "-" means "absent".

The sensor I has a shape similar to that of the sensor shown in FIG. 2, the sensor member 3 is made of plaster only, and the water-repellent film 4 is removed.

The sensor II is obtained by adding the water-repellent film 4 to the sensor I described above.

The sensor III is the sensor shown in FIG. 2, and the sensor member 3 is a mixture of silicon powder and activated carbon powder.

The sensor IV is the sensor shown in FIG. 1, which is a sensor member 3 in which silicon powder and activated carbon powder are mixed and an evaporation zone is provided.

The sensor V is obtained by removing the activated carbon powder from the sensor member 3 of the sensor IV.

FIG. 3 shows sensor I, sensor II and sensor II.
It is a figure which shows the measurement result of I, and shows the time-dependent change of the electrical resistance value when each sensor is taken out from the soil of a saturated water state to the air, and is naturally dried.

Although the electric resistance value of the sensor I correlates with the moisture content in the sensor member, the increase in the electric resistance value is slow and the response performance and accuracy are poor.

It can be seen that the sensor II has an electric resistance increased earlier than the sensor I, and that the response performance is improved by using the water-repellent film.

Further, the sensor III has a sharper increase in electric resistance than the sensor II, and it can be seen that the responsiveness becomes excellent by mixing the silicon powder and the activated carbon powder in the sensor member.

FIG. 4 is a diagram showing the relationship between the electrical resistance value in the soil that is gradually dried and the actually measured water tension (pF value) of the sensor I and the sensor II.
It can be seen that the electric resistance increases faster than the sensor I and the rate of change is large. The measured value of the water tension was measured using a tension meter.

Fig. 5 shows the response performance (change in voltage value over time, that is, electrical resistance) of sensor I and sensor III when transitioning from soil moisture (DB.45%) to soil moisture (DB.30%). FIG. 3 is a diagram showing a change in the value, and the sensor is similar to the case where the soil is taken out into the atmosphere (FIG. 3).
It can be seen that the response performance of III is superior to that of sensor I.

Fig. 6 shows the sensor IV and sensor V, and the electrical resistance and soil water tension (pF
It is a figure which shows the relationship with the measured value of (value).

As can be seen by comparing FIG. 4 and FIG. 4, the evaporation zone 7
The electric resistances of the sensor IV and the sensor V having the
It can be seen that the rate of change is also large. In addition, Sensor IV
Has a larger change rate than the sensor V, the measurement accuracy of the pF value is improved, and the measurement error can be reduced.

In addition, as shown in FIG. 6, the electric resistance value has a pF value of approximately 1.8 to 2.1.
However, when the pF value is within this range, the soil is in a field state and contains effective water that can be sufficiently absorbed by the crops. Therefore, it is effective to set the target value of the water content management within the above range, and if the measurement accuracy is increased within the above range, the water content management can be effectively performed.

〔The invention's effect〕

As described above, according to the electrical resistance type soil moisture sensor of the present invention, since a minute amount of silicon powder is mixed in the sensor member to reduce the water retention ability, the equilibrium state between the sensor member and soil is prompt. Therefore, the response performance can be improved and the measurement error can be reduced.

In addition, since a small amount of activated carbon powder is mixed with the sensor member to facilitate the movement of water in the sensor member, the equilibrium state between the sensor member and soil is quickly achieved, improving the response performance and reducing the measurement error. be able to.

Further, the electric resistance type soil component sensor of the present invention, the sensor member is formed in a thin plate shape, a pair of mesh-shaped and plate-shaped electrode pairs for detecting the electric resistance inside the sensor member in the sensor member. Since the water-repellent film is adhered to both surfaces of the plate-shaped electrode so as to face each other, the water-repellent film is permeated with an amount of water corresponding to the amount of water (pressure) in the sensor member. The permeated water reaches the plate electrode. In this way, since the electric resistance between the electrode pairs is changed by the amount of water that permeates the plate-shaped electrode surface through the water-repellent film having a small water-holding power, the change in the electric resistance value becomes large, It is possible to improve responsiveness as a sensor and reduce measurement error.

[Brief description of drawings]

FIG. 1 is a diagram showing an electric resistance type soil moisture sensor according to an embodiment of the present invention, FIG. 2 is a diagram showing an electric resistance type soil moisture sensor without an evaporation zone in the same embodiment, and FIGS. The figure which shows the measurement result of the sensor in an example, FIG. 7 is a figure which shows an example of the conventional electrical resistance type soil moisture sensor. 1 ... plate-like electrode, 2 ... net-like electrode, 3 ... sensor member, 4 ... water repellent film.

Claims (3)

(57) [Claims] 1. An electric resistance type soil moisture sensor in which a sensor member for absorbing and releasing water is buried in soil to detect the electric resistance inside the sensor member, wherein the sensor member is An electric resistance type soil moisture sensor characterized by being mixed with silicon powder. 2. An electric resistance type soil moisture sensor in which a sensor member for absorbing and releasing water is buried in soil to detect an electric resistance inside the sensor member, wherein the sensor member is a small amount. An electric resistance type soil moisture sensor characterized by being a mixture of activated carbon powder. 3. An electric resistance type soil moisture sensor in which a sensor member for absorbing and releasing water is embedded in soil to detect the electric resistance inside the sensor member, wherein the sensor member is a thin plate-shaped member. And a mesh-shaped and plate-shaped electrode for detecting the electric resistance, which are arranged so as to face each other in the sensor member, and a water-repellent film impregnated with a water-repellent agent is formed into the mesh-shaped plate and the plate-shaped electrode. An electric resistance type soil moisture sensor, wherein one surface of the electrodes is brought into close contact with the plate-like electrode and the other surface is brought into close contact with the sensor member.