JP5063050B2 - Capacitance type detection device - Google Patents

Description

  The present invention relates to an apparatus for detecting the presence or absence of a dielectric material such as the amount of moisture in soil.

  Patent Document 1 includes a ground plate, a sensor plate, and a shield plate, and when an article to be detected approaches the plate, it cooperates with the article to exhibit a capacitance that changes as the article approaches. Three plates, an oscillator whose frequency is a function of the capacitance, a central conductance connected to the sensor plate, an inner shield connected to the shield plate, and an outer shield connected to the ground plate A sensor system is described that includes a single triple coaxial cable connected thereto.

  Referring to FIG. 1 and FIG. 2 of Patent Document 1, the sensor of the present invention has a ground plate 1, a sensing plate 2, and a shield plate 3, and these plates are laminated, and the sensing plate 2 and the shield plate 3 There is a glass layer in between. The shield plate 3 is driven by the voltage follower 14 via the inner shield 9.

  In Patent Document 2, a rectangular wave voltage is applied via a resistor to a detection electrode disposed with a non-conductive partition wall between the detection dielectric and the detected dielectric, and then passes through the resistor and the detected dielectric. A moisture detection device configured to output a detection signal based on a time delay of rising and falling of a rectangular wave voltage at the detection electrode by an RC circuit, the same as the rectangular wave voltage applied to the detection electrode. A second electrode to which a rectangular wave voltage of the same phase and frequency is applied is provided, and the RC circuit via a dielectric such as water existing in layers along the partition is cut off by the potential of the second electrode. A moisture detector is described which is adapted to do so. When this moisture detection device is disposed in a tank that accommodates an object to be detected, a ground electrode is disposed in the tank at an appropriate distance from the tank wall, and between the detection electrode and the ground electrode. Describes that the RC circuit passing through the object to be detected is formed.

Patent Document 3 discloses a substrate detection device for detecting whether or not a substrate is present at a substrate detection position in a non-contact manner with a non-conductive partition wall at a position spaced from the substrate detection position. A detection electrode arranged at a distance, and arranged to surround the detection electrode, opposed to the substrate detection position across the non-conductive partition wall, and for eliminating an electric field component along the surface of the non-conductive partition wall A substrate detection probe having a guard electrode, and a rectangular wave voltage is applied to the detection electrode via a resistor, and a time constant of an RC circuit formed between the resistor and the ground is detected via the resistor and the detection electrode Accordingly, a substrate detection circuit that detects the presence or absence of a substrate at the substrate detection position, and a guard that applies a rectangular wave voltage having the same phase and the same potential as the rectangular wave voltage applied to the detection electrode to the guard electrode. Substrate detection device which comprises a square wave application circuit for electrode is described.
Japanese Patent Publication No. 8-510093 JP 2000-65775 A JP 2001-68534 A

  If the accuracy is such that the presence or absence of the substrate or the presence or absence of water is confirmed by the change in capacitance, the degree of detection of the time constant of the RC circuit formed between the ground as described in Patent Document 2 or 3 The detection device can be used. For example, in an apparatus for the purpose of grasping the amount of water in the soil instead of the presence or absence of water, it is necessary to accurately detect a change in capacitance. For this purpose, it is desirable that the area of the electrode involved in the capacitance is fixed. An example of such a device is a device that includes a sensing portion in which both electrodes for forming a capacitance are integrated. However, in the type in which plate-like electrodes are stacked as described in Patent Document 1, most of the capacitance is determined by the portion where the layers are stacked, and the rate at which the capacitance fluctuates due to the influence of the outside world is small. Therefore, it is difficult to accurately detect a change in dielectric constant of an object in the outside world.

  One embodiment of the present invention is an apparatus for outputting a detection signal based on a change in capacitance between a first electrode and a second electrode, and includes a flat first electrode and a second electrode. Is a plate portion that is formed into a flat plate shape using a non-conductive material, and at least a part of the first electrode and the second electrode are arranged in parallel along the surface of the plate portion. A plate portion and a third electrode disposed between the first electrode and the second electrode arranged in parallel in the plate portion, wherein the width of the third electrode is the width of the second electrode The distance between the third electrode and the second electrode is smaller than the distance between the third electrode and the first electrode.

  In this apparatus, the flat first and second electrodes for forming the electrostatic capacitance are disposed inside the plate portion formed in a flat plate shape by a non-conductive material, for example, resin or glass. Instead of being stacked in the thickness direction, they are arranged along the plane of the plate portion, for example, in parallel in the width direction. That is, inside the plate portion, the first and second electrodes are arranged in parallel so that the flat surfaces of the respective electrodes are parallel to the flat surface of the plate portion so that the flat surfaces do not face each other. Has been. Therefore, the electric lines of force appearing in a direction perpendicular to the flat surface of these electrodes extend to the outside of the plate portion, and influence the dielectric constant of substances including liquid, gas, solid, etc. existing outside the plate portion. receive. For this reason, the electrostatic capacitance between the first and second electrodes is likely to fluctuate due to the influence of the dielectric constant of the substance existing around the plate portion, that is, outside.

  Furthermore, the device has a third electrode disposed between the first electrode and the second electrode disposed in parallel in the plate portion. The third electrode forms a capacitance with a part of the first electrode, and prevents electric lines of force between the first and second electrodes from passing through the inside of the plate portion. . As a result, the capacitance between the first and second electrodes is easily affected by the periphery of the plate portion, and the amount of change (change rate) of the capacitance can be increased.

  In this apparatus, an RC circuit including a capacitance passing through the periphery of the plate portion is formed between the first and second electrodes, and the capacitance caused by a change in the dielectric constant of the substance existing in the periphery. The change of is detected. Therefore, the third electrode is not intended to block the RC circuit that passes through the material outside the plate portion, and is not intended to eliminate the electric field component along the surface of the plate portion. Therefore, the width of the third electrode is smaller than the width of the second electrode, and the distance between the third electrode and the second electrode is narrower than the distance between the third electrode and the first electrode. That is, the spread of the electric lines of force between the first and third electrodes may be such that the electric lines of force between the first and second electrodes are spread outside the plate portion. Increasing the width (area) leads to a reduction in the effective width (area) of the first electrode on the ground side. Therefore, the width of the third electrode is preferably smaller than the width of the second electrode on the sensor side. In addition, the electric current between the first and second electrodes is arranged closer to the second electrode on the sensor side than the third electrode is arranged in the center of the first and second electrodes. It is easy to obtain the effect of spreading the lines of force outside the plate portion.

  The typical form of the plate portion is a strip shape, and the typical form of the flat first electrode and the second electrode is such that each electrode is a strip shape and is arranged in parallel in the width direction of the plate portion. It is what has been. In order to increase the capacitance variation due to the material outside the plate portion, it is desirable that the length of the electric lines of force between the first and second electrodes is short, and further, the first and second It is desirable that the electrode area of these electrodes be large. The strip-shaped plate portion and the strip-shaped electrode are examples of suitable forms that satisfy these conditions, and are easy to insert into the ground, and are therefore suitable for a device for detecting soil moisture.

In this apparatus, an RC circuit that detects a change in capacitance between the first and second electrodes is formed, and a signal that changes according to its time constant is obtained . That is, this apparatus is for supplying electric power including a frequency component to the RC circuit, the first resistance component for forming the capacitance between the first electrode and the second electrode, the RC circuit, and the RC circuit. further comprising a drive circuit and a circuit for generating a detection signal based on a change of the time constant of the RC circuit. In this device, the second electrode is connected to the drive circuit via the first resistance component which is a detection resistor, and the third electrode is connected to the drive circuit, whereby the first electrode on the ground side is connected. Between the first electrode and the third electrode, the electric field lines (auxiliary field) suitable for spreading the electric field lines (electric field for detection) between the first electrode and the second electrode on the sensor side to the outside of the plate portion. Electric field).

  The third electrode is disposed in the vicinity of the second electrode on the sensor side. Therefore, in order to reduce the influence of the capacitance between the second electrode and the third electrode, a second resistance component is connected between the third electrode and the drive circuit, and the third It is desirable to control the drive voltage applied to the electrodes.

  One form of a circuit for generating a detection signal includes an EXOR circuit for calculating an exclusive OR of signals at both ends of the first resistance component, and a circuit for smoothing the output of the EXOR circuit. Circuit. When a voltage signal at both ends of the first resistance component is detected, if a substance having a high dielectric constant such as moisture increases outside the plate portion, the output of the EXOR circuit is caused by a time difference (phase difference) in the voltage signal at both ends. And the voltage of the signal smoothed by the smoothing circuit increases. Therefore, when the measurement target is a moisture content, a detection signal whose voltage increases or decreases with the moisture content outside the plate portion can be output. For this reason, the amount of water is output by a system having a device that outputs a detection signal and a device that includes a function that estimates the amount of water in a portion where the plate portion is in contact with the detection signal based on an appropriate function, Processing corresponding to the amount of water, for example, watering can be automatically performed.

  Furthermore, it is preferable to have a thermistor for temperature measurement arranged in the plate portion. The dielectric constant of a material can vary with temperature. In addition, the measurement-side conditions such as the dielectric constant of the non-conductive material constituting the plate portion may vary depending on the temperature. Therefore, by measuring the temperature together with the variation in capacitance, it is possible to more accurately calculate the physical quantity that is to be obtained from the variation in capacitance, for example, the amount of water.

  Furthermore, it is desirable to further have a layer for absorbing liquid disposed outside the plate portion. For example, it may be desirable to further have a porous layer disposed outside the plate portion. When a plate portion is inserted or buried in the soil, if a gap is generated between the soil and the plate portion, the variation in capacitance due to the moisture in the soil becomes small, which causes a decrease in the accuracy of measuring the amount of water. By disposing a layer for absorbing liquid or a porous layer outside the plate portion and forming a layer containing moisture on the outer surface of the plate portion, it is possible to suppress a decrease in measurement accuracy.

  In FIG. 1, the schematic structure of the watering system of one Embodiment of this invention is shown. The watering system 1 includes a sensor 10 inserted into the soil 3 in which the plant 2 is planted, a measuring device 5 having a function of obtaining a moisture amount by receiving a signal from the sensor 10, and a signal from the measuring device 5. And a sprinkler 9 for starting watering.

  FIG. 2 shows a schematic configuration of the sensor 10. FIG. 2A is a plan view of the sensor 10, and FIG. 2B is a side view of the sensor 10. FIG. 2C shows a type in which a layer 19 for water absorption is provided on the surface around the plate portion 18 of the sensor 10. The sensor 10 is a device for outputting a detection signal Sd based on a change in the capacitance Cm between the first electrode 11 and the second electrode 12. The sensor 10 includes a printed circuit board 15 having flat belt-like first electrodes 11 and second electrodes 12 formed on the surface thereof, and a non-conductive material mold resin 16 so as to include the printed circuit board 15 inside. And a plate portion 18 formed into a flat plate shape. The overall shape of the plate portion 18 obtained by molding the strip-shaped printed circuit board 15 with the resin 16 is a strip shape, and the tip 18 a is slightly narrowed so as to be easily inserted into the soil 3.

  On the substrate 15 of the plate portion 18, the strip-like first electrode 11 and the second electrode 12 are arranged so as to extend in the longitudinal direction L in parallel with the width direction W of the plate portion 18. More specifically, the second electrode 12 is disposed in the center of the surface of the substrate 15 so as to extend substantially in a straight line in the longitudinal direction L, and has a U-shape that is long in the longitudinal direction L along the periphery of the surface of the substrate 15. The first electrode 11 is disposed so as to surround the second electrode 12 at the center of the substrate. An example of the substrate 15 is made of glass epoxy (Garaepo), and may be another material such as Teflon (registered trademark). An example of the mold resin 16 is a polyolefin with low water absorption. The plate portion 18 may be formed of other non-conductive material such as glass.

  On the substrate 15 of the plate portion 18, a third electrode 13 is further disposed between the first electrode 11 and the second electrode 12 that are disposed in parallel. The third electrode 13 is also strip-shaped, the width (area) of which is smaller than the width (area) of the second electrode, and the third electrode 13 has a U shape that is long in the longitudinal direction L of the substrate 15. It is arranged in the vicinity of the second electrode 12 so as to surround the second electrode 12. Accordingly, the interval Wd2 between the third electrode 13 and the second electrode 12 is narrower than the interval Wd1 between the third electrode 13 and the first electrode 11. The ratio of the width We1 of the first electrode 11, the width We2 of the second electrode 12, and the width We3 of the third electrode 13 is, for example, 2.5: 2.0: 0.3. The ratio of the distance Wd1 between the first electrode 11 and the third electrode 13 and the distance Wd2 between the second electrode 12 and the third electrode 13 is 2.2: 1.

  A waveform generation / detection circuit 20 is mounted on the other end of the substrate 15 and is integrally covered with the plate portion 18 by the mold resin 16. The first electrode 11, the second electrode 12, and the third electrode 13 are connected to a waveform generation / detection circuit 20, and the current or / and voltage signals obtained by these electrodes 11, 12, and 13 are waveform generation / detection signals. Processed by the detection circuit 20, the detection signal Sd is output to the measurement device 5 via the cable 29. Further, a thermistor 31 capable of measuring the temperature around the sensor 10 is mounted on the substrate 15.

  FIG. 3 shows a circuit configuration of the sensor 10. The waveform generation / detection circuit 20 forms an RC circuit for detecting a change in the capacitance Cm between the first electrode 11 and the second electrode 12, and outputs a signal Sd that changes according to its time constant. The waveform generation / detection circuit 20 includes a capacitance Cm between the first electrode 11 and the second electrode 12, a first resistance component R1 for forming an RC circuit, and a frequency component in the RC circuit. A drive circuit 21 for supplying power, a signal generation circuit 22 for generating a detection signal Sd based on a change in the time constant of the RC circuit, and a circuit 23 for correcting the temperature of the detection signal Sd are included. The signal generation circuit 22 includes an EXOR circuit 25 for calculating an exclusive OR with the voltage signals Sn1 and Sn2 at both ends of the first resistance component R1, and a smoothing circuit 26 for smoothing the output of the EXOR circuit 25. Including.

  FIG. 4 shows an outline of the waveform of each signal. The drive circuit 21 is connected to the second electrode 12 via the first resistance component R1, and supplies a signal Sn1 of a rectangular wave of several MHz to the second electrode 12 on the sensor side. The first electrode 11 is connected to a common (ground). The first electrode 11 and the second electrode 12 function as capacitors, and the waveform of the input signal Sn2 obtained via the resistance component R1 is blunted (delayed) by the capacitance Cm. Therefore, the EXOR circuit 25 detects a deviation (time difference, phase difference) between the input signal Sn2 having a delayed waveform and the input signal Sn1 having the original rectangular wave, whereby the first electrode 11 and the second electrode 12 are detected. Can be detected. The drive circuit 21 is a circuit for supplying power including frequency components to the RC circuit, and the signal Sn1 supplied to the second electrode 12 is not limited to a rectangular wave. However, a rectangular wave is one suitable waveform for driving to detect a time difference.

  In this waveform generation / detection circuit 20, as indicated by a broken line in FIG. 4, when the capacitance Cm increases, the deviation of the input signal Sn2 increases, and the pulse output from the EXOR circuit 25 due to the time difference from the input signal Sn1. The width of the signal Sn3 increases. Therefore, the voltage Vd of the detection signal Sd obtained by smoothing the output signal Sn3 by the smoothing circuit 26 using a resistor and a capacitor increases. For this reason, if the measurement target of the sensor 10 is the amount of moisture, the detection signal Sd whose voltage increases or decreases with the amount of moisture outside the plate portion 18 can be output.

  That is, the capacitance Cm varies with the dielectric constant of the substance 50 outside the plate portion 18 of the sensor 10. For this reason, a change in the situation around the sensor 10 can be detected as a change in the capacitance Cm. For example, when the sensor 10 is embedded in the soil 3, since the dielectric constant of water is high, the capacitance Cm increases due to the amount of water in the soil 3, and the voltage of the detection signal Sd increases. Therefore, the measuring device 5 can convert the voltage of the detection signal Sd into a moisture content by using an appropriate function or a lookup table, and can display and control the sprinkler 9.

  The dielectric constant of water varies with temperature. Therefore, the detection signal Sd may fluctuate due to a change in temperature around the sensor 10 (soil) even though there is no change in water content. In the sensor 10, a thermistor 31 is disposed on the plate portion 18. In the temperature correction circuit 23, the resistance value of the thermistor 31 is added to the output of the detection signal Sd to divide the voltage, thereby suppressing the detection signal Sd from fluctuating due to a change in ambient temperature.

  Furthermore, it is desirable that the capacitance Cm greatly varies depending on the moisture of the soil around the plate portion 18. Therefore, by connecting the third electrode 13 to the drive circuit 21, the first electrode 11 is driven between the first electrode 11 and the third electrode 13 on the ground side by being driven by the rectangular wave signal Sn1. And electric field lines (auxiliary electric field) suitable for spreading the electric field lines (detection electric field) between the second electrode 12 on the sensor side to the outside of the plate portion 18.

  FIG. 5 shows a schematic configuration of a sensor 90 for comparison with the embodiment of the present invention. The sensor 90 includes a plate portion 18 in which a first electrode 11 and a second electrode 12 are arranged in parallel. Accordingly, the sensor 90 includes a flat first electrode 11 and a second electrode 12 for forming a capacitance for detecting the state of the outside world. 12 is common to the sensor 10 in that the 12 flat surfaces are not opposed to each other, that is, the flat surfaces of the respective electrodes 11 and 12 are parallel to the flat surface of the plate portion 18. To do. These electrodes 11 and 12 are arranged in parallel in the width direction of the plate portion, instead of being stacked in the thickness direction of the plate portion formed of a nonconductive material such as resin or glass. For this reason, the electric field 71 caused by the electric field lines that run in a direction perpendicular to the flat surfaces of the electrodes 11 and 12 extends outside the plate portion 18, and the dielectric constant of the substance 50 existing outside the plate portion 18. Be susceptible. Therefore, the capacitance Cm between the first electrode 11 and the second electrode 12 varies under the influence of the dielectric constant of the substance 50 existing around the plate portion 18, that is, outside the plate portion 18. It's easy to do.

  In the sensor 90 having such an electrode arrangement, the electrodes 11 and 12 may have substantially the same size, and the electrodes 11 and 12 have a capacitance Cm due to a substance 50 such as moisture in the periphery when the area is larger. The change is great. Furthermore, as the electrodes 11 and 12 are as close as possible, the change in the capacitance Cm due to the surrounding substance 50 is large. However, if the electrodes 11 and 12 are close, the change in the capacitance Cm should increase, but the capacitance affected by the inside of the plate portion 18, that is, the mold resin 16, tends to increase. For this reason, if the electrodes 11 and 12 are too close to make the sensor small, the rate at which the capacitance Cm changes due to the surrounding substance 50 becomes small.

  In the sensor 90 in which the electrodes 11 and 12 are arranged in parallel, the electric field 71 for measurement spreads outside the plate portion 18, so that the capacitance Cm between the electrodes 11 and 12 is the material 50 around the plate portion 18. It is suitable for measurement of the surrounding substance 50, for example, the amount of water. However, when the distance between the electrodes 11 and 12 is small and the ratio of the capacity of the mold resin 16 to the electrostatic capacity Cm between these electrodes is large, there are few substances having a large dielectric constant such as moisture around the plate portion 18. Even in this case, there is a possibility that the time difference (phase shift) between the input signals Sn1 and Sn2 becomes large and the output Sn3 of the EXOR circuit 25 is saturated. Output saturation can be suppressed by lowering the value of the resistance component R1 for detection. Further, by connecting an appropriate capacitor C in parallel with the resistance component R1, the phase shift can be reduced, and the saturation of the output can be suppressed. However, in these methods, it is difficult to increase the rate of change of the capacitance Cm by the surrounding substance 50 and further improve the sensitivity of the capacitance type sensor.

  FIG. 6 shows a type in which a layer 19 having water absorption is provided on the surface around the plate portion 18 of the sensor 90. The water absorption layer 19 is, for example, a ceramic layer, and preferably has a moisture absorption capacity equivalent to that of the surrounding material 50. For example, if the substance 50 around the sensor 90 is soil, it is desirable that the water absorption layer 19 has a moisture absorption capacity comparable to that of the soil. Such materials include water-absorbing cloth, paper, resin, ceramic and the like. When the measurement object of the sensor 90 is moisture, the capacity Cm is increased by disposing the water-absorbing layer 19 in a place where the density of the electric field lines of the measurement electric field 71 is highest outside the mold resin 16. Fluctuates easily under the influence of the amount of moisture. Therefore, the sensitivity of the sensor 90 can be improved. The water absorbing layer 19 can be formed by coating or sticking a suitable water absorbing material on the surface 18 s of the plate portion 18. Further, a water-absorbing material may be put on the plate portion 18 like a sheath or a cover.

  FIG. 7 shows a schematic configuration of a sensor 92 further different from the above. The sensor 92 includes a plate portion 18 in which a first electrode 11 and a second electrode 12 are arranged in parallel, and a small third electrode 13 is arranged between the electrodes 11 and 12. . Thus, by inserting the third electrode 13 between the two electrodes 11 and 12, and forming a sub electric field 72 between the electrodes 11 and 13, the electric field between the electrode 11 and the electrode 12 is formed. It is possible to suppress the electric lines of force 71 from passing through the mold resin 16. This sub electric field 72 does not block or eliminate the electric field (electric field) 71 that passes through the substance 50 outside the plate portion 18, but within the electric field 71 formed by the electrodes 11 and 12. This is to reduce the electric field component passing through the inside of the portion 18 as much as possible. That is, when the electrode 13 is inserted between the electrodes 11 and 12 that are spaced apart, the electric lines of force connecting the electrodes 11 and 12 are placed outside the electrode 13 instead of connecting the electrodes 11 and 12 linearly. Spreading and increasing the rate of passing through the material 50 outside the plate portion 18.

  Further, as shown in FIG. 3, by increasing the distance between the electrode 11 and the electrode 13 and narrowing the distance between the electrode 12 and the electrode 13, the lines of electric force between the electrodes 11 and 13 are concentrated in a narrow range. And the spread of the sub electric field 72 can be increased. For this reason, the spread of the electric lines of force connecting the electrodes 11 and 12 is further increased, the electric lines of force passing through the inside of the mold resin 16 can be reduced, and at the same time, the main electric field 71 is further expanded to the outside of the mold resin 16. be able to. For this reason, it is possible to increase the rate at which the capacitance Cm between the electrodes 11 and 12 varies depending on the substance 50 outside the plate portion 18.

  Thus, by forming the sub electric field 72 for the guard, the sensitivity of the capacitance Cm can be improved. In order to suppress the concentration of the electric field lines of the sub electric field 72, the distance Wd1 between the first electrode 11 and the third electrode 13, the distance Wd2 between the second electrode 12 and the third electrode 13, It is desirable that the interval Wd2 is narrower and the interval Wd1 is wider than 1: 1. If the interval Wd1 is too wide with respect to the interval Wd2, the gap between the electrodes 11 and 12 is too wide, or the gap between the electrodes 13 and 12 is too narrow, which affects the improvement of the sensitivity of the capacitance Cm. there is a possibility. Therefore, the ratio of the interval Wd1 to the interval Wd2 is preferably greater than 1: 1 and less than 10: 1, and more preferably 1.5: 1 to 4: 1. In the sensor 10 shown in FIG. 3, the ratio between the intervals Wd1 and Wd2 is set to 2.2: 1.

  The sub electric field 72 is intended to spread the main electric field 71 to the outside of the plate portion 18, and it is desirable that the capacitance Cs is small. In addition, it is desirable to reduce the ratio of the area of the ground-side electrode 11 that is paired with the third electrode 13 and that is split to form the sub electric field 72. Therefore, the area (width) of the third electrode 13 is desirably small, and is desirably at least smaller than the area (width) of the second electrode 12 on the sensor side. The ratio of the width We2 of the second electrode 12 to the width We3 of the third electrode 13 is preferably in the range of 2: 1 to 20: 1, for example, and preferably in the range of 4: 1 to 10: 1. Further preferred. In the sensor 10 shown in FIG. 3, the ratio of the electrode widths We2 and We3 is set to 20: 3.

  Even if the area of the electrode 13 is small, the signal generated in the electrode 12 may be greatly affected by the signal applied to the electrode 13 due to the proximity of the electrode 12 and the electrode 13. Therefore, as shown in FIG. 3, it is desirable to insert a resistance component R2 between the electrode 13 and the drive circuit 21 to suppress the signal intensity supplied to the third electrode 13 to an appropriate value. For example, the thickness of the resin 16 that molds the electrodes 11, 12, and 13 and forms the plate portion 18 may vary depending on the object to be measured. In that case, if the distance between the electrode 12 and the electrode 13 is adjusted in accordance with the thickness of the mold resin 16, the electric field 71 is effectively spread outward so that the electric lines of force effectively pass through the substance to be measured. Can be. The intensity of the guard sub electric field 72 can be controlled by the second resistance component R2.

  8 and 9 show different examples of the waveform generation / detection circuit 20, respectively. In these examples, the drive circuit 21 for driving the RC circuit and the detection resistor R1 for configuring the RC circuit are included, but are not shown in the drawing. These circuits 20 supply the signal of the thermistor 31 to the measuring device 5 as it is, thereby displaying the temperature of the plate portion 18 in the measuring device 5 or correcting the detection signal Sd using the temperature of the plate portion 18. It can be converted into moisture content. The circuit 20 shown in FIG. 8 is a type that outputs the detection signal Sd based on the change in the capacitance Cm and the signal of the thermistor 31 in four lines. The circuit 20 shown in FIG. 9 is a type that outputs the detection signal Sd and the signal of the thermistor 31 by three lines, and includes diodes D1 and D2. The circuit 20 can switch between the measurement of the capacitance Cm and the temperature measurement by the thermistor 31 by changing the power-on direction.

  As described above, the sensor 10 including the first electrode 11, the second electrode 12, and the third electrode 13 disposed on the second electrode 12 side between them includes the plate portion 18. The electric field 71 for measurement can be efficiently spread outside. For this reason, the sensor 10 can accurately detect a change in the dielectric constant of the space around the plate portion 18 or the substance 50 as a change in capacitance. Therefore, the capacitance type sensor 10 can be used for various applications. In particular, since the sensor 10 is highly sensitive to changes in the dielectric constant of the surrounding material 50, it detects not only the presence or absence of objects with different dielectric constants, but also the density or concentration of objects or substances with different dielectric constants and variations thereof. Suitable for the purpose.

  The example shown in FIG. 1 and FIG. 2 is a sensor for detecting the moisture content (moisture concentration) of the soil 3, and the increase or decrease in the moisture content is measured by the measuring device 5 or a preset moisture content. Thus, the sprinkler 9 can be operated. The set value of the amount of water for operating the sprinkler 9 can be changed by the plant 2 planted in the soil 3. In order to further improve the sensitivity of the sensor 10, rather than having a gap around the plate portion 18, the sensor 10 is in close contact with the soil 3, or at least moisture corresponding to the moisture concentration of the soil 3 is on the surface 18 s of the plate portion 18. It is preferable that it exists in.

  In the sensor 10 shown in FIG. 2C, a ceramic layer 19 is formed on the surface 18 s of the plate portion 18. If the ceramic layer 19 is partially in contact with the soil 3, the ceramic layer 19 absorbs moisture from the soil 3. For this reason, even if the entire surface 18 s of the plate portion 18 is not in contact with the soil 3, water corresponding to the amount of water in the soil 3 exists in many portions of the surface 18 s of the plate portion 18. The sensitivity can be further improved. The ceramic layer 19 is porous and absorbs water, has high strength and durability, and is suitable as a material for coating the surface 18 s of the plate portion 18 of the sensor 10. Instead of the ceramic layer 19, a water-absorbing cloth, paper, resin, or the like may be attached to the surface 18 s of the plate portion 18, applied, or molded.

  The sensor 10 can be used not only for soil but also for applications such as detecting the amount of water contained in other powders or granules, or detecting the presence or absence of objects having different dielectric constants. In addition, the shape of the electrode sensor and the electrode arrangement shown in FIG. 2 are examples, and the present invention is not limited to this. For example, the electrodes may extend linearly, may be arranged in a zigzag manner, or may be arranged in another curved shape such as a spiral shape.

The figure which shows schematic structure of a watering system. It is a figure which shows schematic structure of a sensor, FIG. 2 (a) is a top view, FIG.2 (b) is a side view, FIG.2 (c) is a side view of the sensor further provided with the ceramic layer. The figure which shows the circuit structure of a sensor. The figure which shows each signal of the circuit of a sensor. The figure which shows the circuit structure of a sensor (comparative example). The figure which shows the example which provided the water absorption layer. The figure which shows the circuit structure of a different sensor. The figure which shows the example from which a waveform generation / detection circuit differs. The figure which shows the further different example of a waveform generation and detection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Watering system, 3 Soil, 5 Measuring apparatus, 9 Sprinkler 10 Sensor, 11 1st electrode, 12 2nd electrode, 13 3rd electrode 15 Board | substrate, 16 Mold resin, 18 Plate part 20 Waveform generation and detection circuit, 21 drive circuit, 22 signal generation circuit

Claims (9)

An apparatus for outputting a detection signal based on a change in capacitance between a first electrode on a ground side and a second electrode to which power is supplied ,
A flat plate portion that includes the flat first electrode and the second electrode and is formed into a flat plate shape using a non-conductive material, and includes at least a part of the first electrode and the second electrode. A plate portion arranged in parallel along the surface of the plate portion;
A third electrode disposed between the first electrode and the second electrode disposed in parallel in the plate portion and supplied with power ;
A first resistance component that forms an RC circuit with a capacitance between the first electrode and the second electrode;
A drive circuit for supplying power including a frequency component to the RC circuit;
A circuit for generating the detection signal based on a change in a time constant of the RC circuit ,
The second electrode is connected to the drive circuit via the first resistance component, the third electrode is connected to the drive circuit, and
The width of the third electrode is smaller than the width of the second electrode, and the distance between the third electrode and the second electrode is the distance between the third electrode and the first electrode. Narrower than the device.   The apparatus according to claim 1, wherein the plate portion has a strip shape, the first electrode and the second electrode have a strip shape, and are arranged in parallel in the width direction of the plate portion. 3. The width We3 of the third electrode, the width We2 of the second electrode, a distance Wd2 between the third electrode and the second electrode, and the third electrode according to claim 1 or 2, The apparatus satisfy | fills the following conditions with the space | interval Wd1 with a said 1st electrode.
2 <We2 / We3 <20
1.5 <Wd1 / Wd2 <4 4. The apparatus according to claim 1 , further comprising a second resistance component for connecting the third electrode and the driving circuit. In any one of claims 1 to 4, a circuit for the generation smoothes an EXOR circuit, an output of the EXOR circuit for calculating an exclusive OR of both ends of the signal of the first resistance component And a circuit comprising: 6. The apparatus according to claim 1 , further comprising a temperature measurement thermistor disposed on the plate portion. 7. The apparatus according to claim 1 , further comprising a layer for absorbing liquid disposed outside the plate portion. 8. A device according to any preceding claim, further comprising a porous layer disposed outside the plate portion. An apparatus according to any of claims 1 to 8 ,
A system having a function of estimating a moisture content of a portion in contact with the plate portion based on the detection signal.