JP3035262B2 - Moisture sensor, moisture measuring device, and water supply method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture sensor suitable for measuring the moisture concentration in soil for cultivating plants, and a moisture measuring method and a water supplying method using the same. It is possible to measure the thermal conductivity of the object, thereby detecting the moisture content of the object with almost no change in the temperature of the object, thereby supplying appropriate moisture to the object. The present invention relates to a moisture sensor, a moisture measurement method, and a water supply method that can perform water supply.

[0002]

2. Description of the Related Art In cultivating plants, it is extremely important to control the water content of the soil on which the plants are planted. Conventionally, the determination of the water content for soil moisture management often relies solely on human intuition, such as looking at the color of the soil or feeling when the soil is taken up and collapsed. On the other hand, recently, attempts have been made to obtain the water content of the soil as electrical data by physical means for the purpose of appropriately managing the water content of the soil and automating the soil management.

[0003] Several methods have already been developed as a method for measuring the moisture content in soil. One of the methods is to measure the water content in the soil based on the height of the water column based on the capillary phenomenon caused by the surface tension of the moisture in the soil. is there. However, this method is not suitable for easily measuring the moisture content of soil on a farm due to the large scale of the device. Further, as other simple methods for measuring the water content, there are a tensiometer method for measuring the water absorbing power by capillary action of the water in the soil through a porous Lamix, and a method for measuring their electrical resistance and the like. . However, these have a large sensor shape, and there are problems to be solved in response and the like, and the study of their practical use is in progress. In addition, there are an electric resistance method and a capacitance method for measuring changes in the electric resistance and the dielectric constant of soil, and these may be affected by ionic substances such as fertilizers.

Recently, a heat conduction type moisture sensor utilizing the fact that the heat conductivity of soil changes depending on the water content has been studied. For example, means for measuring the thermal conductivity of soil with a thermal probe having a heater and a temperature sensor built in a sealed stainless protective tube (for example, Japanese Patent Application Laid-Open No. 63-193049)
And Japanese Patent Application Laid-Open No. 63-193051). Further, in order to improve the accuracy and sensitivity, a reference sensor is provided (Japanese Patent Application Laid-Open No. 61-233350),
Means using two probes (JP-A-5-164711)
Has been proposed. In addition, a means for improving the measurement accuracy by installing a temperature compensation sensor (Japanese Utility Model Application
No. 12725). Each of these means basically measures the thermal conductivity of soil.

[0005]

However, the conventional moisture sensor does not give a large temperature change to soil provided in a small space such as a cell tray in which plant seedlings and the like are planted, and has a high sensitivity and a high moisture content. It is not suitable for measuring with high accuracy. In the measurement of soil moisture in a small space such as a seedling raising cell tray, in order to continuously measure at a low heating temperature that does not affect the seedling raising, it is necessary to improve the sensitivity and accuracy of the sensor structure and its measurement method. There are fundamental issues to consider.

When measuring the moisture content of soil in a small cell tray for raising seedlings as a main object, it is necessary to use a probe which is small enough to fit in the cell tray.
It is necessary to reduce the temperature rise for measurement so as not to affect the seedling raising and to enable continuous measurement. For that purpose, it is necessary to reduce the heat capacity of the moisture sensor and improve the temperature responsiveness. A conventional heat conduction type moisture sensor cannot meet such a demand.

SUMMARY OF THE INVENTION In view of the problems of the conventional moisture sensor, the present invention measures the water content of an object to be measured, such as soil, with high accuracy, high sensitivity, and responsiveness at a low heating temperature using a small probe. It is an object of the present invention to provide a moisture sensor that can be used, and a moisture measuring method and a water supply method using the same.

[0008]

In order to achieve the above-mentioned object, according to the present invention, the outer wall of the probe 14 is formed of a metal heat radiating pipe 1 having a high thermal conductivity, and is closely attached to the inner surface of the heat radiating pipe 1. The heater 2 was arranged, and a temperature measuring point 19 of the temperature measuring element was provided in close contact with the inner surface of the heat radiation pipe 1. Further, one end of the heat radiating pipe 1 is sealed with a sealing material 6, and a sealing material is also provided between the tube 7 for guiding the lead wire 5 of the heater 2 and the temperature measuring element to the outside of the probe 14 and the other end of the heat radiating pipe 1. 6 and sealed.

That is, the moisture sensor according to the present invention is housed in a probe 14 arranged in an object to be measured,
A heater 2 for heating the periphery of the probe 14 and a probe 1
4 and a temperature measuring element for measuring the temperature around the probe 14. The moisture sensor includes a heat radiating pipe 1 made of a metal having a high thermal conductivity that forms an outer wall of the probe 14, a heater 2 disposed in close contact with an inner surface of the heat radiating pipe 1, and a winding of the heater 2. The temperature measuring element provided with a temperature measuring point 19 in close contact with the inner surface of the heat radiating pipe 1 and the lead wire 5 of the heater 2 and the lead wire of the temperature measuring element are guided to the outside of the probe 14 while being insulated from each other. Tube 7
And a sealing material 6 made of a thermal insulator for sealing an end of the heat radiating pipe 1.

In such a moisture sensor, the probe 14
Is formed of a metal heat radiating pipe 1 having a high thermal conductivity, and the end of the heat radiating pipe 1 is sealed with a sealing material 6 made of a thermal insulator. Can be reduced. Since the heater 2 is arranged in close contact with the inner surface of the heat radiating pipe 1 and is heated, it is possible to heat the heat radiating pipe 1 with small electric power and with good responsiveness. Furthermore, by providing the temperature measuring point 19 of the temperature measuring element in close contact with the inner surface of the heat radiating pipe 1, the temperature of the heat radiating pipe 1 can be measured with high sensitivity and high accuracy. Thereby, a temperature change appears sensitively at a low heating temperature, the temperature change of the measurement object around the probe 14 can be measured, and its thermal conductivity can be measured.

The temperature measuring element generally comprises a thermocouple 3, which is connected from the temperature measuring point 19 to the tube 7 without a connection point.
Through the outside of the probe 14 and the same probe 14
And is connected to a zero point compensation circuit 9 for performing zero point compensation of the thermocouple in the relay box 11. Accordingly, since only the temperature measuring points 19 of the heater 2 and the thermocouple 3 need to be basically arranged inside the probe 14, the probe 14 can be downsized. Also, the heater 2 and the temperature measuring points 19 of the temperature measuring element are inserted inside the heat radiating pipe 1 together with the insulating pipe 4 while being fixed to the outer periphery of the insulating pipe 4 and fixed, so that the heater 2 The temperature measuring points 19 can be easily incorporated and can be easily replaced.

In order to measure the water content of a measuring object such as soil using such a moisture sensor, the probe 14 is arranged in the measuring object, and from the time t1 when the measurement is started to the time t when the heating is stopped.
The current is passed through the heater 2 of the heat radiating pipe 1 to 2, and then the heat radiating pipe 1 is allowed to cool naturally. After a predetermined time has elapsed from the time t2 when the heating is stopped, the measurement ends at time t3. Then, the temperature measured by the temperature measuring element 3 at the time determined from the measurement start time t1 to the measurement end time t3, or the measurement start time t
The integral value of the measured temperature from 1 to the end time t3 of the measurement, or the integral value of the drop in the measured temperature from the time t2 when the heating is stopped to the time t3 when the measurement is completed is defined as a parameter proportional to the water content of the object to be measured. The moisture content of the object to be measured is measured by the parameter.

By doing so, it is possible to accurately measure the water content of the measurement object without error without being affected by the variation in the measurement temperature. Further, the electromotive force generated at the temperature measuring point 19 of the thermocouple 3 is converted into a current value by the temperature conversion circuit 10 in the relay box 11 near the probe 14 and transmitted to the control box 15. Therefore, even if the distance from the relay box 11 to the control box 15 is large, an error due to the distance is prevented.

Further, using such a moisture measurement method, when the temperature or the integrated value for a predetermined time exceeds a predetermined value, an opening / closing signal is supplied to a valve, and a predetermined amount of water is supplied to an object to be measured. Supply. This makes it possible to replenish an appropriate amount of water to the measurement object such as soil and to maintain the water content at a predetermined value.

[0015]

Embodiments of the present invention will now be described specifically and in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing the structure of the probe 14 of the moisture sensor. A cylindrical insulating pipe 4 made of an insulator such as plastics such as epoxy resin or ceramics such as alumina and having a low thermal conductivity is prepared.
Is wound around the heater 2.

As the temperature measuring element, for example, a thermocouple 3 such as chromel-alumel, copper-constantan, etc. is used, the tip of which is welded as a temperature measuring point 19, and the temperature measuring point 19 is connected to the insulating pipe 4. It is located outside. Heater 2
The surface of the thermocouple wire 3 at the temperature measuring point 19 is coated with paint or
It is covered with a thin wrap film etc. and is electrically insulated.

The insulating pipe 4 is fitted into the heat radiating pipe 1, and the temperature measuring points 19 of the heater 2 and the thermocouple 3 are brought into close contact with the inner surface of the heat radiating pipe 1 so that there is no gap. This state
In the state, the temperature measuring point 19 of the thermocouple 3 is located between the windings of the heater 2.
positioned. The heat radiating pipe 1 is a cylindrical pipe made of a metal having a high thermal conductivity and a small heat capacity, for example, Cu, and has an inner diameter slightly larger than that of the insulating pipe 4 .

Both ends of the heater 2 are connected to a thick lead wire 5 in the insulating pipe 4 and guided outside the heat radiating pipe 1.
The thermocouple wire 3 is led outside without a connection point. The lead wire 5 and the thermocouple 3 guided to the outside are housed in a tube 7 made of vinyl or the like, and are insulated by an inorganic insulating material such as an insulating paint. Actually, lead wire 5 and thermocouple 1
Using a composite sheath cable containing the set, the distal end of the tube 7 as the sheath is peeled off, the lead wire 5 and the distal end of the thermocouple 3 are taken out, and these are set on the insulating pipe 4.

The distal end of the heat radiating pipe 1 is sealed together with the insulating pipe 4 by a sealing material 6. At this time, the connection end portion between the heater 2 and the lead wire 5 may be embedded in the sealing material 6 and fixed. At the other end of the heat radiating pipe 1, the tube 7 is fitted into the insulating pipe 4. In this state, the gap between the tube 7 and the heat radiating pipe 1 is sealed by the sealing material 6 together with the insulating pipe 4. As the sealing material 6, an insulating material having a low thermal conductivity such as plastics such as epoxy resin or ceramics such as alumina is used, so that the heat radiation pipe 1 and the tube 7 are thermally insulated. .

FIG. 2 schematically shows a state in which the probe 14 of the moisture sensor is embedded in the soil 12 and the thermocouple 3 is connected to the zero point compensation circuit 9 in the relay box 11. Soil 1
An externally controlled current is supplied to a heater 2 in a heat radiation pipe 1 embedded in the heat radiation pipe 2. The thermocouple 3 is guided from the temperature measuring point 19 in the heat radiation pipe 1 to the relay box 11 without a connection point. Since the zero point compensation circuit 9 is provided inside the relay box 11 and the zero point compensation of the thermocouple 3 is performed, it is not necessary to incorporate a temperature compensation circuit inside the probe 14. Thereby, the probe 14 can be miniaturized and the temperature in the soil can be measured accurately.

The electromotive force generated at the temperature measuring point 19 of the thermocouple 3 is converted into a current value by current control by the temperature conversion circuit 10 in the relay box 11, and the remote control box 15 described later with reference to FIG. Sent to. By controlling the heating current of the heater 2 and the electromotive force of the thermocouple 3 in this manner, the relay box 11 and the control box 1 are controlled.
Signal attenuation due to the distance between 5 can be prevented.

FIG. 3 shows the measured current value sent from the temperature conversion circuit 10 processed by a sequencer, a computer, or the like, and shows the time change of the temperature. The temperature at the measurement start time t1 indicates the temperature in the soil before the measurement.
A predetermined current is applied from the measurement start time t1 to the heating stop time t2, and then the device is cooled naturally, and the measurement is completed at the measurement completion time t3.

In this case, the speed at which the heat radiating pipe 1 is naturally cooled by the heat conduction of the measurement object can be obtained from the shape of the cooling curve. However, in an actual measurement, a smooth curve is not obtained due to noise. Then the curve ab
The integral value surrounded by de is a parameter indicating the speed at which the heat radiation pipe 1 is naturally cooled by heat conduction. Since this parameter is proportional to the water content, the water content in the soil can be determined from this parameter.

In addition, as a parameter directly indicating the degree of cooling of the temperature, a curve bcd or an integrated value surrounded by a curve bdf may be used. This is the integral value of the temperature drop from the time t2 when the heating is stopped to the time t3 when the measurement is completed. In other words, it is the temperature integrated value from the heating stop time t2 to the measurement completion time t3 with the temperature at the measurement completion time t3 as the reference value 0. Alternatively, as a simple method, the temperature at a predetermined time between the measurement start time t1 and the measurement end time t3 may be used as a parameter proportional to the water content.

FIG. 4 shows the relationship between the temperature integrated value and the water content in soil. The actual water content in the soil may be determined by directly measuring the potential of water, or simply adding a predetermined amount of water to a sufficiently dried soil of a predetermined volume or weight to artificially produce a soil having a known water content. You may make it. in this way,
Based on the correlation between the water content of the known soil and the temperature integrated value obtained therefrom, the water content can be converted from the temperature integrated value and the water content can be estimated by measurement.

FIG. 5 shows a flow chart for realizing the above-mentioned measurement. After the measurement is started, conditions are set, whereby the heating time is set by a timer. If the soil temperature is measured by the thermocouple 3, the heat radiation pipe 4 is heated by the heater 2.
Is started, and at the same time, the temperature of the radiating pipe 4 is measured by the thermocouple 3. The temperature integrated value is obtained from the time and the measured temperature. When the heating time is less than the predetermined time, the heating is continued, and when the heating time reaches the predetermined time, the heating is stopped. The temperature integrated value is recorded, and when this value exceeds the specified value, an open signal is output to the watering valve 16 and the water supply valve 17 described later with reference to FIG. , 17 are closed. After the water supply, the radiator pipe 1 is heated by the heater 2 while measuring the temperature of the radiator pipe 4 with the thermocouple 3 in the same manner as described above, and the temperature integrated value is obtained again. At this time, the measurement is completed within a predetermined measurement time. Such a measurement operation can be repeated periodically to continuously measure the moisture content of the soil.

FIG. 6 shows an example in which the above-mentioned moisture sensor is applied to a device for automatically supplying water to soil in a seedling raising cell tray 13. In the cell tray 13, seedlings and the like of plants are vegetated. This cell tray 13 is installed on the irrigation gutter 20,
Only when the water level in the irrigation gutter 20 exceeds a predetermined water level, the cell tray 13 is moved from the irrigation gutter 20 by capillary action.
Moisture is taken up into the soil inside. In the irrigation gutter 20,
Water is supplied when the water supply valve 17 is opened. A watering nozzle 21 is provided on the cell tray 13, and the watering nozzle 21 sprays water toward the cell tray when the watering valve 16 is opened.

The probe 14 is placed on the soil in the cell tray 13.
The probe 14 is connected to the relay box 11 as described above, and the relay box 11 is connected to the control box 15. The signal obtained in the control box 15 is input to the computer 18 and required data processing such as the above-described calculation of the temperature integrated value is performed.
Also, the result of the data processing is input to the control box 15,
Thereby, the control box 15 is connected to the heater 2 (FIGS. 1 and 2).
) And the watering valve 16 and the water supply valve 17 are controlled.

As described above, as a result of measuring the water content in the soil, if the temperature integrated value obtained by the computer 18 exceeds the specified value, the control box 15 sends a water supply signal to the watering valve 16 or the water supply valve 17. Is output, and a predetermined amount of water is supplied. After the water supply, the heat radiation pipe 1 is heated by the heater 2 while measuring the temperature of the heat radiation pipe 4 by the thermocouple 3, and the temperature integrated value is obtained again. When the value is below the specified value, the measurement is performed. finish. Such a measuring operation is periodically repeated to continuously measure the moisture content of the soil,
Thus, by supplying moisture to the soil of the cell tray 13, moisture in the soil of the cell tray 13 is always properly maintained.

As described above, the moisture sensor according to the present invention is not intended to measure the absolute moisture content of a measuring object such as soil, but to keep the moisture content of the measuring object such as soil constant. The purpose is to obtain the electrical information necessary to determine the necessity of water supply. In addition,
As an object to be measured, the description is given taking soil as an example.In addition to soil, the powder according to the present invention may be used as long as it is a powder or fine granules, and the permeation and diffusion of water are performed by capillary action. Sensors and moisture measurement methods are applicable. For example, the moisture sensor and the moisture measuring method according to the present invention can be applied for the purpose of keeping the moisture content of flour as a food material constant.

[0031]

According to the invention described in the above embodiment, the following effects can be obtained. In the moisture sensor, the heat radiating pipe 4, which is a heat radiating body, is made of a metal having high thermal conductivity and does not use a metal protection pipe or the like for protecting other sensors.
Temperature changes due to thermal diffusion in the measurement object can be sensitively reflected. Furthermore, since the probe 14 can be made small, it can be easily installed in a small-capacity soil such as a cell tray for raising seedlings.

Since the heater 2 is installed in close contact with the inside of the heat radiating pipe, the heating efficiency at the time of heating can be increased, and a precisely set amount of heat can be supplied to the heat radiating pipe. Further, since the temperature change of the heat radiating pipe 4 is measured by the thermocouple 3 set in close contact with the inside of the heat radiating pipe 4, the temperature change of the heat radiating pipe 4 can be sensitively measured. For this reason, the temperature of the measurement target can be measured to be 10 ° C. or lower from the normal temperature without increasing the temperature of the measurement target, and the environment of the measurement target is not affected. Even short-time repeated measurement does not affect the measurement. Therefore, it is suitable for measuring moisture in soil when cultivating plants and the like.

The temperature of the heat radiating pipe 4 is measured at the temperature measuring point 19 of the thermocouple 3 in the probe 14, and the zero point compensation is performed in the relay box 11 outside the probe 14.
4 can be downsized and further simplified.
Also in this regard, the heat capacity of the probe 14 can be reduced, and the temperature and the temperature change of the measurement object can be measured accurately and with high sensitivity.

The relay box 11 is arranged near the probe 14. The electromotive force generated at the temperature measuring point 19 of the thermocouple 3 is converted into a current by the temperature conversion circuit 10 and transmitted. Even if the distance between the control box 15 and the computer 18 is large, errors due to the distance can be prevented. In addition, since the probe 14 and the relay box 11 are installed at a plurality of locations and their signals are controlled by the single control box 15 and the computer 18 and data processing can be performed, the water content at many points can be measured simultaneously. The data of many points is repeatedly measured by the computer 18 for a long time, data is processed, and when the temperature integrated value obtained as a result of the calculation becomes equal to or less than a specified value, a signal of water supply start is output, so that water supply is started. An automated and unmanned water supply system can be realized.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a probe part of an example of a moisture sensor according to the present invention.

FIG. 2 is a conceptual diagram showing a state where a probe of the moisture sensor is embedded in soil and a relay box in the vicinity thereof.

FIG. 3 is a graph showing an example of a time change of a temperature measured at a temperature measuring point of a thermocouple incorporated in the probe, and showing a means for calculating a temperature integral value which is a parameter proportional to a water content.

FIG. 4 is a graph showing an example of a qualitative relationship between the temperature integrated value and the water content in soil.

FIG. 5 is a flowchart showing a procedure of a method of measuring moisture in soil using the moisture sensor and controlling a valve based on the result.

FIG. 6 illustrates the moisture sensor and a method of measuring moisture by the moisture sensor.
It is a system conceptual diagram which shows the example applied to the automatic plant watering apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat radiating pipe 2 Heater 3 Thermocouple 4 Insulating pipe 5 Lead wire 6 Sealing material 7 Tube 9 Zero compensation circuit 10 Temperature conversion circuit 11 Relay box 12 Soil 13 Cell tray 14 Probe 15 Control box 16 Watering valve 17 Water supply valve 18 Computer 19 Temperature measurement Point 20 Irrigation gutter 21 Sprinkling nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Norihiko Sugimoto 38 Shinkocho, Hitachinaka City, Ibaraki Prefecture Inside Hitachinaka Techno Center Co., Ltd. (56) References JP-A-63-47644 (JP, A) (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 25/00-25/72 JICST file (JOIS)

Claims (8)

(57) [Claims] 1. A heater (2) housed in a probe (14) arranged in an object to be measured and heating a periphery of the probe (14), and a probe housed in the probe (14). In a moisture sensor having a temperature measuring element for measuring an ambient temperature of (14), a metal heat radiating pipe (1) having a high thermal conductivity and forming an outer wall of the probe (14).
A heater (2) disposed in close contact with the inner surface of the heat radiating pipe (1), and a heater (2) closely contacting the inner surface of the heat radiating pipe (1) at a position between the windings of the heater (2). To measure the temperature (19)
The probe (1) is provided in such a manner that the temperature measuring element provided with the heater, the lead wire (5) of the heater (2) and the lead wire of the temperature measuring element are insulated from each other.
4) A moisture sensor comprising: a tube (7) leading to the outside; and a sealing material (6) made of a thermal insulator for sealing an end of the heat radiating pipe (1). 2. The moisture sensor according to claim 1, wherein the temperature measuring element comprises a thermocouple (3). 3. The thermocouple (3) passes from the temperature measuring point (19) to the probe (1) through the tube (7) without a connection point.
A zero point compensation circuit (9) that is guided to a relay box (11) arranged outside the probe (14) and near the probe (14) and performs zero point compensation of the thermocouple in the relay box (11). The moisture sensor according to claim 2, wherein the moisture sensor is connected. 4. A temperature measuring point (1) of a heater (2) and a temperature measuring element.
9) is mounted on the outer circumference of the insulating pipe (4),
The moisture sensor according to any one of claims 1 to 3, wherein the moisture sensor is inserted and fixed inside the heat radiation pipe (1) together with the insulating pipe (4). 5. Using the moisture sensor according to any one of claims 1 to 4, arranging the probe (14) in an object to be measured, and starting heating (t1) to stopping heating (t1).
An electric current is applied to the heater (2) of the heat radiating pipe (1) until 2), and then the heat radiating pipe (1) is naturally cooled.
3) from the start of the measurement (t1) to the end of the measurement (t
Moisture measurement characterized by obtaining a parameter proportional to the water content of the object to be measured from the temperature measured by the temperature measuring element (3) until 3), and measuring the water content of the object to be measured with the parameter. Method. 6. From the start of measurement (t1) to the end of measurement (t1).
The integrated value of the measured temperature up to 3) or when the heating is stopped (t
The integral value of the decrease in the measured temperature from 2) to the end of the measurement (t3) is set as a parameter proportional to the water content of the measurement object, and the water content of the measurement object is measured using the parameter. The moisture measurement method according to claim 5, wherein 7. An electromotive force generated at a temperature measuring point (19) of a thermocouple (3) is converted into a current value by a temperature conversion circuit (10) in a relay box (11) near a probe (14). The method according to claim 5, wherein the data is transmitted to a control box (15). 8. The method according to claim 5, wherein the probe (14) is installed in an object to be measured, and the temperature or the integrated value at the predetermined time is a predetermined value. A water supply method characterized in that when the value is exceeded, an open signal is supplied to the valves (16) and (17) to supply a predetermined amount of water to the object to be measured.