JPH09189693A - Moisture measuring sensor and moisture meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a moisture meter capable of highly reliable measurement with a simple structure. SOLUTION: A plurality of measuring porous bodies 1-5 which are formed of hydrophilic materials having pores having substantially an uniform diameter distributed therein and mutually differed in diameter of the pores distributed therein, respectively, have electrodes 8a, 8b extending over these porous bodies as measuring electrodes. A reference porous body 6 formed of a hydrophilic material having pores distributed therein and having a pore diameter substratially equal to or properly smaller than the pore diameter of the measuring porous body having the minimum pores of the measuring porous bodies 1-5 is provided near the measuring porous bodies 1-5, and electrodes 8a, 8b are provided on the reference porous body 6 as reference electrodes. The water quantity in a sample is arithmetically calculated from the ratio of the composed impedance of the measuring porous bodies 1-5 to the impedance of the reference porous body 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture measuring sensor and a moisture meter suitable for measuring moisture contained in soil.

[0002]

2. Description of the Related Art Generally, the water content of soil is held in the pores of the aggregate of soil particles by a capillarity-like absorption power, and as the soil dries, the water content gradually increases from the pores of large diameter. Will be lost.

On the basis of such knowledge, a plurality of measuring porous bodies made of a hydrophilic material in which pores of substantially uniform diameter are distributed, and the diameters of the pores distributed in each are different from each other, A moisture measuring sensor has been proposed which comprises an impedance measuring electrode provided on each of a plurality of measuring porous bodies (Japanese Patent Laid-Open No. 63-298143, Japanese Utility Model Publication 4-).
30535 publication).

The basic configuration of the moisture measuring sensor according to the above conventional technique will be described below with reference to FIG. In FIG. 4, (A) is a partial external front view of the moisture measurement sensor,
(B) is a partial rear view of the inside thereof. Codes 1 to 5
Is a measuring porous body made of a hydrophilic material, and the pore diameters thereof increase in order from 1 to 5. This measuring porous body 1
5, impedance measuring electrodes 8 are attached to the impedance measuring electrodes 8, lead wires 11 are connected to the impedance measuring electrodes 8, 8 ... And the lead wires 11, 11 ... Are bundled by a lead wire bundle 12. These measuring porous bodies 1
To 5, impedance measuring electrodes 8, 8 ..., Lead wire 1
1, 11, ..., The lead wire bundle 12 and the like are housed in a support tube 15, and the measurement porous bodies 1 to 5 below the support tube 15.
The housing portion is obliquely inclined so that the surfaces of the measurement porous bodies 1 to 5 are exposed and the tube surface is sealed by the sealing body 16. The support tube 15 can be inserted and buried up to an arbitrary depth in the sample S such as soil.
The surfaces of the measurement porous bodies 1 to 5 can be covered with a protection porous body (not shown) having a small pore size, if necessary.

When the moisture measuring sensor having such a structure is inserted and embedded in the sample, the moisture W in the sample is sequentially absorbed from the one having the smallest pore size of the porous bodies 1 to 5 for measurement, and the empty as the sample dries. Moisture W in order of increasing pore size
Lose. Whether or not each of the measuring porous bodies 1 to 5 absorbs the water W can be grasped as an impedance change between the impedance measuring electrodes 8 and 8.

FIG. 5 shows a circuit configuration for catching this impedance change. In FIG. 5, 81a and 81b
Through 85a and 85b are impedance measuring electrodes, electrodes 81a and 81b are on the measuring porous body 1, and electrodes 82a and 8b are
2b is the measuring porous body 2, electrodes 83a and 83b are the measuring porous body 3, and electrodes 84a and 84b are the measuring porous body 4.
The electrodes 85a and 85b are provided on the measuring porous body 5, respectively.

Reference numerals 11a to 11f are lead wires attached to the impedance measuring electrodes 81a, 81b to 85a, 85b, respectively, which are bundled by a lead wire bundle 12 and led to a detection circuit.

Reference numerals 91a, 91b to 95a, 95b are diodes forming a clipping circuit, and those having forward voltages as equal as possible are used. A ₃ is an operational amplifier which forms a summing circuit together with the input resistors R ₁₁ to R ₁₅ and the feedback resistor R ₁₆ . S _AC is a voltage source for measurement, and is composed of, for example, a DC / AC converter. T ₀ is an output terminal.

Now, the measuring porous body 1 having the smallest pore diameter absorbs water in the sample, and the impedance measuring electrode 81
When the impedance decreases until a current of a certain level or more flows between a and 81b, the diode 91 corresponding to this electrode
A constant voltage is generated at a and 91b and is applied to the operational amplifier A ₃ via the input resistor R ₁₁ .

Similarly, when the measuring porous bodies 2 to 5 absorb more than a certain amount of water, a certain voltage is generated in the diode corresponding to each of them and is applied to the operational amplifier A ₃ . Therefore, by dividing the output voltage of the output terminal T _{0 by} the voltage applied from each diode, it is possible to know the number of the porous bodies for measurement that absorb a certain amount of water or more, and immediately after that, the water content of the sample can be determined. Or the degree of dryness can be determined.

[0011]

In the moisture measuring sensor according to the above-mentioned prior art, the number of lead wires is required according to the number of impedance measuring electrodes, and the lead wire bundle becomes thick, which is not convenient to handle. The connection may be unreliable. Further, even if the amount of water is the same, the impedance changes depending on the conductivity of the absorbed water, so that it is necessary to take out a constant voltage by the clip circuit, and the circuit configuration is complicated. Further, when the conductivity of the absorbed water is extremely low, the impedance is not sufficiently lowered even if a certain amount of water or more is absorbed, and a constant voltage is not generated in the diode, which may cause a measurement error. An object of the present invention is to provide a moisture measuring sensor having a simple structure and capable of highly reliable measurement in view of the above-mentioned conventional technique.

[0012]

SUMMARY OF THE INVENTION The present invention comprises a plurality of measuring porous bodies made of a hydrophilic material in which pores of substantially uniform diameter are distributed, and the diameter of the pores distributed in each is different from each other. And a pair of measuring electrodes that exist over each of the plurality of measuring porous bodies and that are formed substantially in a single unit, thereby providing a moisture measuring sensor. It is a solution to the inconvenience.

That is, when a pair of measuring electrodes are formed substantially in a single structure over each of the measuring porous bodies,
The reciprocal of the obtained impedance is the sum of the reciprocal of the impedance of each individual porous body for measurement. And
This impedance can be taken out as a signal with two lead wires regardless of the number of porous bodies for measurement.
The lead wire bundle does not become unnecessarily thick and the connection reliability is improved.

Further, according to the present invention, the pore diameter is made of a hydrophilic material, and the pore diameter thereof is substantially equal to the pore diameter of the measuring porous body having the smallest pore size among the plurality of measuring porous bodies. By providing a reference porous body that is appropriately small in the vicinity of the measurement porous body, and by providing a pair of reference electrodes provided on the reference porous body, it is possible to perform accurate measurement regardless of the conductivity of the absorbed moisture. It enables various measurements.

That is, even if the impedance between the measurement electrodes changes due to the conductivity of the absorbed water, the impedance between the reference electrodes also changes, so that the change in the conductivity of the water can be compensated.

Here, the pore diameter distributed in the reference porous body is approximately equal to or appropriately smaller than the pore diameter of the measuring porous body having the smallest pore size among the plurality of measuring porous bodies. This is to ensure that when any of the measurement porous bodies absorbs and holds water, the reference porous body also always absorbs and holds water.

The reference porous body is provided in the vicinity of the measurement porous body so as to absorb water which is homogeneous with the water absorbed by the measurement porous body. However, it is not always necessary to store the porous body for measurement in the same support tube.

Further, according to the present invention, the pore diameter is made of a hydrophilic material, and the pore diameter thereof is substantially equal to the pore diameter of the measuring porous body having the smallest pore size among the plurality of measuring porous bodies. The protective porous body, which is appropriately small, is adhered to the surface of the measuring porous body that comes into contact with the sample through the water-permeable conductive film, and this water-permeable conductive film is used as one of the pair of measurement electrodes. Thus, the moisture sensor can be integrally formed with a simple structure. In addition, the reason why the water-permeable conductive film is used is to prevent the movement of water from the protective porous body to the measuring porous body.

Further, the present invention provides a moisture meter characterized by calculating the amount of moisture in a sample from the ratio of the impedance obtained from the pair of measurement electrodes and the impedance obtained from the pair of reference electrodes. However, it is possible to obtain the water content in the sample from the signal obtained from the water content measurement sensor.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on embodiments shown in the drawings. FIG. 1 shows a moisture meter according to the present invention. In FIG. 1, reference numerals 1 to 5 are the same measuring porous bodies as in FIG. Although the number is set to 5 for convenience of explanation, it may be increased or decreased as appropriate according to the variation range of the water content of the sample. Further, the arrangement of the porous body for measurement is not particularly limited, and can be variously changed according to the shape of the entire moisture measuring sensor. For example, as shown in FIG. 4, the lower portion of the support pipe may be linearly arranged on the surface of the sealing body that obliquely seals.
As shown in FIGS. 6 and 7 of the publication, when a support having a brim-shaped protrusion at the lower end of a rod-shaped body is used, the protrusions may be arranged in a circle.

Reference numeral 6 is a reference porous body, and reference numeral 9 is a protective porous body, all of which are approximately equal to or appropriate to the pore diameter of the measurement porous body having the smallest diameter of the plurality of measurement porous bodies. The small holes are distributed. The reference porous body is provided in the vicinity of the measurement porous body, but it does not have to be integrated.

The protective porous body 9 is the measurement porous body of the sample S.
It is closely attached to the surface in contact with and is configured to protect the measurement porous body from the sample. As a result, it is possible to eliminate the possibility that fine particles of the sample enter the measuring porous body having a large diameter and cause a measurement error due to a change in the diameter of the pores. In the example in FIG. 1, the protective porous body is provided in close contact with both the measuring porous body and the adjacent reference porous body, but it is not necessary to configure the protective porous body so as to protect it. Not necessarily.

Reference numerals 8a and 8b are electrodes for impedance measurement. The electrode 8a is a water-permeable conductive film made of, for example, gold paste, and is used for measuring porous bodies 1 to 5 and reference porous body 6.
Exists between the protective porous bodies 9 and also serves as an adhesive between the porous bodies. The electrodes 8b and 8c are also conductive films, and the electrode 8b is the electrode 8a of the porous bodies 1 to 5 for measurement.
It is attached to the side that opposes. The electrode 8c is attached to the side of the reference porous body that faces the electrode 8a.

Here, the electrodes 8a and 8b correspond to a pair of measuring electrodes formed substantially in a single unit, and the electrodes 8a and 8c correspond to a pair of reference electrodes. These pair of electrodes are provided at appropriately separated positions of the measurement or reference porous body,
The mounting position is not particularly limited. For example, it is attached between the measuring porous body or the reference porous body and the protective porous body, or on the back surface or the side surface of the measuring porous body.

Incidentally, the electrode which is formed substantially in one piece is
In addition to the electrodes 8a and 8b formed of a homogeneous thin film of a conductive material as an electrode having an integral structure, each electrode individually formed in each measuring porous body is a separate electrical connection member,
For example, a lead wire, another conductive film, a solder, or the like, which is integrated later, is also included.

Lead wires 11a, 11b and 11c are attached to the electrodes 8a, 8b and 8c, respectively, and they are bound by a lead wire bundle 12.

These measuring porous bodies 1 to 5, reference porous body 6, electrodes 8a, 8b, 8c, lead wires 11a, 11b,
11 c, the lead wire bundle 12, and the like are housed in a watertight and insulating support (not shown). The shape of the support is not particularly limited, and may be composed of, for example, a support tube and an obliquely inclined sealing body as in FIG. 4, or as a support having a flange-shaped protrusion at the lower end of the tubular body. Is also good. In short, it suffices that the surfaces of the measurement porous bodies 1 to 5 and the reference porous body 6 are in contact with the sample S directly or through the protective porous body 9.

A ₁ is an operational amplifier, S _AC is a voltage source for measurement,
R _f is a circuit stabilizing resistor, and T ₀ is an output terminal.

The operation of the moisture meter shown in FIG. 1 will be described with reference to the equivalent circuit diagram shown in FIG. In FIG. 2, R _{1 to} R ₅ are electrodes 8a and 8b via the measurement porous bodies 1 to 5, respectively.
It is the equivalent resistance of the impedance obtained between the two. Also,
R _r is the equivalent resistance of the impedance obtained between the electrodes 8 a and 8 c via the reference porous body 6.

Now, these equivalent resistance and circuit stabilizing resistance R
The impedance value of _f is set to R ₁ ~
Expressed by R ₅ , R _r , and R _f , the values of the combined impedance Z _i that is the input resistance of the operational amplifier A ₁ that forms the non-inverting amplifier circuit and the combined impedance Z _f that is the feedback resistance are These are expressed by the following formulas 1 and 2, respectively.

[0031]

1 / Z _i = 1 / R ₁ + 1 / R ₂ + 1 / R ₃ + 1 / R
₄ + 1 / R ₅

[0032]

[Formula 2] Z _f = R _r · R _f / (R _r + R _f )

If R _f is selected so that R _f >> R _r , then this equation 2 becomes the following equation 3.

[0034]

[Formula 3] Z _f ≈R _r · R _f / R _f = R _r

Therefore, the output voltage of the measuring voltage source S _AC is set to E
_In , and the output voltage at the output terminal T ₀ are E _out , the following formula 4 is obtained.

[0036]

[Equation 4] E _out = (1 + Z _f / Z _i ) · E _in ≈E _in + R _r (1 / R ₁ + 1 / R ₂ + 1 / R ₃ + 1 / R ₄ +
1 / R ₅ ) ・ E _in

In Equation 4, when the measuring porous bodies 1 to 5 lose water, the impedance significantly increases, and the corresponding 1 / R ₁ , 1 / R ₂ , 1 / R ₃ , 1 / R ₄ , 1 /
Since R ₅ is almost zero, the amount of water in the measurement porous body can be determined from the value of the output voltage E _out , up to how much of the porous body for measurement absorbs and holds water.

Next, a change in conductivity of water in the sample will be examined. If the conductivity of water in the sample is C, then R
₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R _r are represented by the following formulas 5 to 10. In addition, K ₁ in Equation 5 to Equation 10,
K ₂ , K ₃ , K ₄ , K ₅ , and K _r are generally called cell constants, and are constants determined by the properties of the measuring porous body and the mechanical dimensions of the impedance measuring electrode.

[0039]

[Equation 5] R ₁ = K ₁ / C

[0040]

[Equation 6] R ₂ = K ₂ / C

[0041]

[Equation 7] R ₃ = K ₃ / C

[0042]

[Formula 8] R ₄ = K ₄ / C

[0043]

[Equation 9] R ₅ = K ₅ / C

[0044]

[Equation 10] R _r = K _r / C

By substituting the equations 5 to 10 into the equation 4, the following equation 11 is obtained.

[0046]

[Equation 11] E _out ≈ E _in + K _r (1 / K ₁ + 1 / K ₂ + 1 /
K ₃ + 1 / K ₄ + 1 / K ₅ ) ・ E _in

That is, the output voltage E _out is not affected by the change in conductivity of water in the sample. In addition, K ₁ , K ₂ , K ₃ ,
It is desirable that K ₄ and K ₅ are substantially equal to each other.

Next, another embodiment of the present invention will be described with reference to the equivalent circuit diagram shown in FIG. In FIG. 3, A ₂ is an operational amplifier, and R _g is a circuit stabilizing resistor. Further, the value of the impedance of the circuit stabilizing resistor R _g, represented by R _g by the same reference numerals. The other parts having the same configurations as those in FIG.

In the present embodiment, the value of the combined impedance Z _j which is the input resistance of the operational amplifier A ₂ forming the inverting amplifier circuit is expressed by the following formula 12.

[0050]

## EQU12 ## 1 / Z _j = 1 / R ₁ + 1 / R ₂ + 1 / R ₃ + 1 /
R ₄ + 1 / R ₅ + 1 / R _g

Where R _g >> R ₁ , R ₂ , R ₃ , R ₄ , R ₅ ,
If R _g is selected so that
It looks like 3.

[0052]

1 / Z _j ≈1 / R ₁ + 1 / R ₂ + 1 / R ₃ + 1 /
R ₄ + 1 / R ₅

The value of the combined impedance Z _f , which is the feedback resistance, is expressed by the equation 2 as in the embodiment shown in FIG.
It is represented by Therefore, the output voltage of the measurement voltage source S _AC is E
_When the output voltage at the output terminal T _{0 is} in and E _out , the following formula 14 is obtained under the condition of R _f >> R _r .

[0054]

E _out = − (Z _f / Z _i ) · E _in ≈−R _r (1 / R ₁ + 1 / R ₂ + 1 / R ₃ + 1 / R ₄ + 1 /
R ₅ ) ・ E _in

From this equation, the water content of the sample can be obtained in the same manner as the embodiment shown in FIG. The change in the conductivity of water in the sample can be dealt with in the same manner as the embodiment shown in FIG.

In each of the above-described embodiments, the reference porous body is provided separately from the protective porous body, but the protective porous body 9 can also be used as the reference porous body. As a result, the reference porous body 6 can be omitted, and a simpler electrode configuration can be obtained.
In this case, the electrode 8c is attached to the protective porous body 9 at a position appropriately separated from the electrode 8a.

[0057]

As described above, according to the moisture measuring sensor of the present invention, basically two lead wires are sufficient regardless of the number of measuring porous bodies, and the impedance of the reference porous body is measured. 3 wires are enough even if you add a lead wire to do. Therefore, the lead wire bundle is not thick and easy to handle, and the connection reliability is high.

Further, according to the moisture measuring sensor and the moisture meter of the present invention, the ratio of the impedance obtained from the measurement electrode to the impedance obtained from the reference electrode is used to determine whether the sample to be absorbed has high or low conductivity. The amount of water in it can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a diagram showing a moisture meter according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the moisture meter.

FIG. 3 is an equivalent circuit diagram of a moisture meter according to another embodiment of the present invention.

FIG. 4 shows an example of a conventional moisture measurement sensor,
(A) is a front view of an external portion, and (B) is a rear view of an internal portion.

FIG. 5 is a circuit diagram of a conventional moisture meter using a moisture measuring sensor.

[Explanation of symbols]

1, 2, 3, 4, 5 Porous body for measurement 6 Porous body for reference 8, 8a, 8b, 8c Electrode 9 Protective porous body 11, 11a, 11b, 11c, 11d, 11e, 11
f Lead wire R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R _r Equivalent resistance R _f , R _g Circuit stabilization resistance A ₁ , A ₂ , A ₃ Operational amplifier S _AC Measurement voltage source T ₀ output Terminal

Claims (4)

[Claims] 1. A plurality of measuring porous bodies each made of a hydrophilic material in which pores having substantially uniform diameters are distributed, and the diameters of the pores distributed in each are different from each other, and the plurality of measuring porous bodies. A moisture measuring sensor which is present over each of the porous bodies, and which comprises a pair of measuring electrodes formed substantially in a single unit. 2. A porous material made of a hydrophilic material having pores distributed therein, the pore diameter of which is approximately equal to or appropriately smaller than the pore diameter of the measurement porous body having the smallest pore size among the plurality of measurement porous bodies. 2. The moisture measuring sensor according to claim 1, wherein the reference porous body that has been soaked is provided in the vicinity of the measurement porous body, and a pair of reference electrodes provided on the reference porous body is provided. 3. A porous material made of a hydrophilic material having pores distributed therein, the pore diameter of which is approximately equal to or appropriately smaller than the pore diameter of the measuring porous body having the smallest diameter of the plurality of measuring porous bodies. The protective porous body that has been soaked is brought into close contact with the surface of the measurement porous body that comes into contact with the sample through a water-permeable conductive film, and the water-permeable conductive film is one of the pair of measurement electrodes. The moisture measuring sensor according to claim 1 or 2. 4. A moisture measuring sensor according to claim 2 or 3, wherein the amount of moisture in a sample is calculated from a ratio of an impedance obtained from the pair of measurement electrodes and an impedance obtained from the pair of reference electrodes. Moisture meter characterized by calculating.