JPH02238353A - Apparatus for measuring water content rate - Google Patents

Abstract

PURPOSE:To measure the rate of water content of a material continuously in a short time by detecting the dielectric constant of the material as the electric variable of a transmitting line, and converting the electric variable into the percent of water contents of the material. CONSTITUTION:When the amount of water in the ground is measured, a transmission line 1 is embedded in the ground. The resonant frequency of the line 1 is decreased when the percentage of water content is increased. At this time, the voltage across both ends of a series circuit of the line 1 and reference impedance 2 and the voltage across both ends of the line 1 are measured with a variable frequency oscillator 3. The values are inputted into a CPU 4 through an A/D converter 6. In the CPU 4, the measured results are operated, and the impedance of the line 1 is obtained. After the measurement of the impedance, the frequency at which the impedance becomes the minimum value (the terminating end of the line 1 is opened) or the maximum value (the terminating end of the line 1 is shorted) is obtained. This frequency is the resonant frequency of the line 1. This resonant frequency is converted into the percentage of the water content.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a moisture content measuring device that measures the amount of water contained in a substance.

[Conventional technology]

Conventionally, the thermal response method and the capacitance method have been known as methods for measuring the water content in substances, such as the water content in soil in fields. Thermal response method measures the amount of water contained in the material by embedding a heater or temperature sensor in the material to be measured, heating the material with the heater, and detecting temperature changes in the material with the temperature sensor. This is the way to do it. In addition, in the capacitance method, a pair of electrodes is inserted into the material to be measured at a distance, and the dielectric constant of the material is determined based on the capacitance of the capacitor formed by both electrodes and the material. This is a method of measuring the amount of water contained in a substance based on the correspondence between the ratio and the amount of water contained in the substance. (The problem that the invention aims to solve!!!) In the thermal response method, the substance to be measured is heated by a heater, so the next measurement cannot be performed until the substance returns to a state of thermal equilibrium. The problem is that it takes time to perform continuous measurements. In addition, since water has a high specific heat, it is necessary to supply a large amount of power to the heater to heat the substance, leading to the problem of high power consumption. Furthermore, since the heater and temperature sensor must be placed relatively close to each other, there is the problem that measurement results vary greatly depending on the measurement location in materials with uneven density, such as soil. On the other hand, in the capacitance kζ method, compared to the thermal response method,
Since there is no need to heat the substance, measurements can be taken continuously in a short period of time, and it also has the advantage of low power consumption. However, since the absolute value of the capacitance as a capacitor is very small, on the order of pF, there are problems in that it requires sophisticated measurement techniques, the circuit configuration becomes complex, and it is susceptible to noise. One way to increase the absolute value of capacitance is to increase the area of the electrode, but this poses the problem of increasing the size. Furthermore, since the capacitance changes depending on the distance between the electrodes and the position of the electrodes, there is a problem that the measurement results are unstable and the reliability of the measurement results is low. The present invention aims to solve the above-mentioned problems, and since it can be realized with a simple circuit configuration, the reliability of the measurement results is high, and it is possible to perform continuous measurements in a short time and at low cost. The present invention aims to provide a device for determining water content>+S based on power consumption.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a transmission line that is at least partially buried in a substance that is a measured lunar phenomenon;
A sensor circuit that detects the dielectric constant of the material as an electrical variable of the transmission line, and a calculation section that converts the electrical variable into the water content of the material are provided. A frequency detection circuit that detects the resonant frequency of the transmission line is used as the sensor circuit, and the resonant frequency can be converted into the water content of the material in the calculation section. In addition, the sensor circuit consists of a signal generator that applies a signal to one end of the transmission line, and a time detection unit that detects the delay time required from when the signal is applied to one end of the transmission line until it reaches the other end. However, the delay time may be converted into the water content of the substance in the arithmetic unit. The frequency detection circuit is composed of a variable frequency oscillator that applies a high frequency signal to the transmission line, and an impedance detection section that detects the impedance of the transmission line. The frequency at which the impedance of the line is minimum or maximum can be taken as the resonant frequency of the transmission line. The frequency detection circuit also includes a variable frequency oscillator that applies a high frequency signal to the transmission line, and a phase angle detection section that detects the phase angle of the current phase and voltage phase of the high frequency signal passing through the transmission line with respect to the other. The output frequency of the variable frequency oscillator may be changed, the phase angle may be detected, and the frequency at which the sign of the phase angle is reversed may be set as the resonant frequency of the transmission line. Furthermore, the frequency detection circuit can be an oscillation circuit using the transmission line as a resonant circuit, and the output of the oscillation circuit can be the resonant frequency of the transmission line. Furthermore, the frequency detection circuit includes a variable frequency oscillator that applies a high frequency signal to the transmission line, and detects the phase difference between the current phase and voltage phase of the high frequency signal passing through the transmission line, and the phase difference becomes zero. The output frequency of the variable frequency oscillator may be set to the resonant frequency of the transmission line. It is desirable to package the sensor circuit in a water-resistant case. The transmission line is preferably formed of a pair of conductive core wires and an insulating coating surrounding the core wires. Further, it is desirable to provide the transmission line with a spacer that keeps both core wires parallel. The spacer is preferably formed in a shape having through holes at appropriate intervals in the longitudinal direction of both core wires. It is desirable to connect a termination circuit to the terminal of the transmission line.

[Operation] According to the above configuration, at least a portion of the transmission line is buried in the substance to be measured, and the moisture content of the substance is measured based on the electrical variable of the transmission line corresponding to the dielectric constant of the substance. , it does not affect the substance to be measured during the measurement, and measurements can be carried out continuously in a short period of time. Because it does not feed, there is less energy loss and less power consumption. In addition, while using the resonant frequency of the transmission line and the delay time of the signal due to the transmission line as the electrical variable of the transmission line that corresponds to the dielectric constant of the material, high-precision measurement is possible using existing frequency measurement and time measurement techniques. This makes the circuit configuration relatively simple and less susceptible to noise. In addition, by setting the length of the transmission line appropriately, it is possible to ignore the effects of density variations even in materials with non-uniform densities, and it is possible to prevent variations in measurement results depending on the measurement location. In other words, measurements with good reproducibility and high reliability can be performed. In addition, if the sensor circuit is housed in a water-resistant case, the sensor circuit can be buried in the material along with the transmission line, and all parts that generate high-frequency signals are buried in the material, making it easier to This makes it possible to reduce radiated noise. Alternatively, if a portion of the case is exposed from within the substance, the case can be used as a marker for the buried position. Furthermore, when the transmission line is provided with an insulating coating, it is not affected by distributed resistance due to moisture in the substance, which further increases measurement accuracy. Furthermore, if a spacer is provided between both core wires of the transmission line so that the two core wires are parallel to each other, the characteristics will be stabilized and the reliability of the measurement results will be further increased. This reduces the influence of the spacer material on the measured values, allowing highly sensitive measurements. In addition, by providing a termination circuit at the end of the transmission line, the characteristics of the transmission line can be stabilized, further increasing the reproducibility of measurement results.

【principle】

In the present invention, the amount of water in a substance is measured by taking advantage of the fact that the dielectric constant of water is approximately 80, which is extremely large compared to other substances. That is, the relative permittivity of solid substances is generally about 1 to 10, and there is a large difference in the relative permittivity of water. Therefore, if the amount of water in a substance changes, there will be a large change in the range from the specific dielectric constant of the substance to the dielectric constant of water. This property is also used in the capacitance method, but in the present invention, instead of burying a pair of electrodes in the material, a transmission line is buried, and electrical variables such as the resonant frequency and delay time of the transmission line are However, the water content of a substance is determined by focusing on the point that corresponds to the dielectric constant of the substance. In other words, when a high-frequency signal with a wavelength on the order of the length of the transmission line passes through the transmission line, the distribution constant of the transmission line affects the transmission characteristics. The distribution constant of the line corresponds to the dielectric constant of the material. Therefore, the resonant frequency and delay time of the transmission line change, and the present invention is based on the knowledge that by measuring these electrical variables on the transmission line, it is possible to determine the water content of the substance. The basic configuration for measuring the resonant frequency and delay time of a transmission line is explained below. First, consider the voltage amplitude on the transmission line 1. As shown in FIG. 10[g(a), when a high-frequency signal source S that outputs a high-frequency wave with a wavelength λ is connected to one end of the transmission line 1 having an open termination, a high-frequency Due to the interference between the incident wave W from the signal source S and the reflected wave W2 from the terminal end, the voltage amplitude distribution on the transmission line 1 is
As shown in Figure (C), the minimum occurs at the position (2n-1)·λ/4 from the end, and the maximum occurs at the position 2n·λ/4 (n=1.
2,...). Furthermore, when a high-frequency signal source S is connected to one end of the transmission line 1 having a short-circuit termination as shown in FIG. 11(a), the incident wave from the high-frequency signal source S as shown in FIG. 11(b) Due to the interference between the reflected wave W} and the reflected wave W2, the voltage amplitude distribution on the transmission line 1 is maximized at the position of (2n-1)·λ/4 and becomes 2n·λ, as shown in FIG. 11(e).
It becomes minimum at position /4. That is, from the perspective of the high-frequency signal source S, the position λ/4 from the end of the transmission line 1 is the position where the impedance is minimum if the transmission line 1 has an open termination, and the position where the impedance is maximum if the transmission line 1 is short-terminated. become. Conversely, if the length of the transmission line 1 is fixed, the impedance characteristics with respect to the output frequency f of the high-frequency signal source S will be equivalent to that of an LC series resonant circuit in the open-terminated transmission line 1, as shown in Figure 12, and in the case of a short-circuited termination. The transmission line 1 is equivalent to an LC parallel resonant circuit as shown in Figure 13. However, there are multiple resonance points. Let the inductance per unit length of the transmission line 1 be C and the capacitance be C, then at the resonant frequency, f,=κ+/(L
It can be expressed as C)””...■. However, κ. is a proportionality constant. On the other hand, the capacitance C is proportional to the relative dielectric constant ε of the material surrounding the transmission line 1, and if the proportionality constant is κ2, then C=κ2・ε ...■. According to the formula, f,= κ,/(κ2・εL)1″...■.In other words, if L# is constant, f,=κ,/ε1″...■. However, κ is a proportionality constant. Here, the inductance changes depending on the relative magnetic permeability of the material surrounding the transmission line 1, but since the relative magnetic permeability hardly changes depending on the old water content in the material, there is no problem with the assumption that L is constant. Also, the delay time τ per unit length of the transmission line 1 is τ=κ4・(LC)''...■, if the proportionality constant is κ4, so when L''=.constant,■ [F] By formula, τ=κ5・
ε． ．． ．． ■It becomes. As mentioned above, since the resonant frequency 1 and the delay time τ of the transmission line 1 depend on the dielectric constant ε'' of the material existing around the transmission line, it is possible to find the resonant frequency and delay time of the transmission line 1. Therefore, the moisture content of the material existing around the transmission line 1 can be determined. An example of the relationship between the water content of a substance and the resonant frequency is as follows.
It can be seen that the resonance frequency decreases as the water content increases. Furthermore, if we compare the formulas, it can be seen that the resonance frequency f7 is inversely proportional to the delay time, so as the water content increases, the darkness at the time of delay increases. By the way, it is known that the propagation speed of electromagnetic waves in a substance is ■ = c/n (c is the speed of light) when the refractive index of electromagnetic waves in the substance is n, and the refractive index is n is the square root of the product of relative magnetic permeability and relative permittivity, and since the relative magnetic permeability of non-magnetic materials is about 1, V ``t (/ε1''
becomes. As can be seen by comparing this formula with formulas ■ and ■, finding the resonant frequency and delay time leap of transmission line 1 is as follows:
This means that the propagation speed of electromagnetic waves in materials is indirectly measured. In other words, by measuring the propagation speed of electromagnetic waves in a material, it is possible to measure the amount of water in the material, but since the propagation speed of electromagnetic waves is extremely fast, direct measurement of the propagation speed requires large-scale equipment. As a result, errors are more likely to occur. On the other hand, if the propagation speed of electromagnetic waves in materials is measured indirectly using the resonant frequency and delay time of the transmission line as described above, the configuration of the device can be simplified and the reliability can be improved. Therefore, high measured values can be obtained.

[Example 1
] In this embodiment, the impedance of the transmission line is measured while changing the frequency of the high-frequency signal flowing through the transmission line, and the frequency at which the impedance is minimum or maximum is determined as the resonant frequency of the transmission line. The transmission line 1 is made up of conductive wires arranged in parallel.
As shown in the figure, it is connected in series to the reference impedance 2. The terminal end of the transmission line 1 may be open or short-circuited. The output voltage of the variable frequency oscillator 3 is applied to the series circuit of the transmission line 1 and the reference impedance 2, and the ratio between the voltage V across the series circuit and the voltage across the transmission line 1 is measured. That is, the impedances of the transmission line 1 and the reference impedance 2 for the frequency f are respectively Zu(f),
Let ZA(f) be Z. m/(Z x (f) + Z A (f)) = V
．． /V. Since the relationship holds true, z. (r)=Z A(f)・V. /(V.-Vb)
...■, and since the impedance ZA(f) of the reference impedance 2 is known, the voltage V.
,V. By measuring , the impedance of the transmission line 1 with respect to the frequency f can be determined. Therefore, while varying the output frequency of the variable frequency oscillator 3, the voltage V −
, Vb, and find the frequency at which Zx(f) is minimum (when the end of transmission line 1 is open) or maximum (when the end of transmission line 1 is short-circuited) based on formula becomes the resonant frequency of transmission line 1. Here, in order to easily measure the resonant frequency of the transmission line 1, the output frequency of the variable frequency oscillator 3 is controlled and the voltage V. ,V. The measurement is automated using a microcomputer 4. That is, the voltage across the series circuit of the transmission line 1 and the reference impedance 2 is Vt.
The voltage across the transmission line 1 is V. Which of the following is to be measured is selected by the changeover switch 5, and the voltage to be measured is converted into a digital signal by the analog-to-digital converter 6.5The voltage to be measured is thus inputted to the microcomputer 4 as a digital signal, and the voltage to be measured is inputted to the microcomputer 4 as a digital signal. The impedance of the transmission line 1 is obtained by calculating the impedance of the transmission line 1. Further, the variable frequency oscillator 3 is controlled so that the output frequency changes stepwise, and the changeover switch 5 is switched within the time period during which the output frequency is maintained at the same frequency, and the output frequency is changed between two types of voltage V. ,V. is measured. Therefore, the switching timing of the changeover switch 5 is also controlled by the microcomputer 4. That is, the reference impedance 2, the changeover switch 5, and the analog-to-digital converter 6 constitute an impedance detection section, and this impedance detection section, together with the variable frequency oscillator 3, constitutes the sensor circuit 7. After the impedance measurement in the variable frequency range of the variable frequency oscillator 3 is completed as described above, the microcomputer 4 determines whether the impedance is the minimum (if the transmission line 1 has an open termination) or the maximum (if the transmission line 1 has a short-circuit termination). Find the frequency that satisfies (case). This frequency is the resonant frequency of the transmission line 1, and this resonant frequency is converted into the water content. That is, since the microcomputer 4 calculates the impedance and resonance frequency of the transmission line based on the output of the sensor circuit 7, it functions as a part of the impedance detection section (that is, a part of the frequency detection circuit), and also functions as a calculation section. Function. Next, we will explain how to measure the moisture content in soil using the device with the above configuration. In this case, as shown in Figure 2,
The entire transmission line 1 is buried in soil E. Also, soil E
The transmission line 1 is set to an appropriate length so as to avoid the influence of local non-uniform density due to cavities in the transmission line 1, and to obtain an average value over the length range. For example, 1l
If a transmission line 1 of about 100 MHz is used, an average value in a range of about 1 liter can be obtained, and the resonant frequency of this transmission line 1 is about 75 MHz in air, and as shown in Fig. Since the resonant frequency decreases as the water content increases, for this transmission line 1, the output frequency of the variable frequency oscillator 3 is from several MHz to 100 MHz.
It is set to a range of about z. It is relatively easy to vary the frequency to this degree, and the circuit configuration is simple and stable operation can be expected, which are desirable conditions for a measuring instrument. Here, when an oscillating electric field is applied to water, when the frequency of the oscillating electric field reaches about IGHz, the change in the orientation of water molecules cannot follow the change in the electric field, and the dielectric constant decreases rapidly, so in practical terms, it is about 500M82. will be used as the upper limit. That is, the transmission line 1 requires at least several tens of CJI. On the other hand, when measuring the moisture content as an average value over a relatively wide area, such as in a field, the transmission line 1 can be set to several tens of liters, and in this case, the resonant frequency becomes even lower, so the circuit design becomes even easier. The depth at which the transmission line 1 is buried may be adjusted depending on the measurement purpose, but is usually set to 10 cm or more. A sensor circuit 7 that is involved in high frequencies, such as a reference impedance 2, a variable frequency oscillator 3, a changeover switch 5, and an analogue digital converter 6, is housed in a water-resistant case 10, and is connected to the soil E along with the transmission line 1. It is buried inside. Also, case 1
A connection line 11 to the microcomputer 4 is drawn out from o. That is, since all parts affected by the moisture content in the soil E can be buried in the soil E, it is possible to prevent variations in measured values due to differences in the dimensions of insertion into the soil E. The reliability of measured values is increased, and unnecessary high-frequency radiation noise is prevented from leaking to the outside. Also, if a part of the gauge 10 is exposed from the soil E, the exposed part of the gauge 1o can be buried. This makes it possible to prevent the connecting wire 11 from being caught by a tractor or the like. The transmission line 1, as shown in FIG. Spacer 14 is insulated F! J! 13, and the distance between both core wires 12 is kept constant. In this way, by having the insulated FW 13, it is possible to prevent the influence of distributed resistance caused by the electrolyte dissolved in the moisture of soil E, and to prevent the increase in power consumption due to current flowing through the distributed resistance and the increase in distributed resistance. This prevents selectivity (Q) from decreasing and facilitates measurement. Further, the insulation coating 13 can also prevent corrosion of the core wire 12. Here, insulation coating 1
Due to the presence of 3, the range of change in the measured dielectric constant becomes slightly smaller, but impedance can be measured with high accuracy.
The influence of the dielectric constant of the insulation coating 13 is negligible. Note that by applying the insulation coating 13 to the core wire 12, the measurement becomes easier as described above, but the insulation coating 13 may be omitted if it is not necessary. Further, as shown in FIG. 4, if the transmission line 1 is formed into a ladder shape by forming through holes 15 in the spacer 14 at appropriate intervals along the transmission line 1,
Compared to the case where the through hole 15 is not formed, the surface area of the transmission line 1 becomes larger, and the spacer 1 which is a dielectric material
Since the amount of 4 decreases, changes in the moisture content of soil E can be detected with high accuracy. A termination circuit 16 is provided at the end of the transmission line 1. The termination circuit 16 is composed of passive circuit components such as capacitors and resistors, and can change the impedance of the transmission line 1 and reduce the influence of external electromagnetic waves. In addition, since the boundary conditions at the end of the transmission line 1 are clear, for example, if a capacitor is connected to the open end, the resonance frequency will be lowered and the fluctuations in the impedance characteristics will be reduced. If such a capacitor is not connected, irregular portions often appear in the frequency distribution of impedance, as shown by the thin line in FIG. 5, and the reliability of the measured value decreases. By providing this, such problems can be improved, as shown by the thick line in Figure 5. By connecting a resistor to the terminal end, it is possible to reduce fluctuations in impedance characteristics without affecting the resonant frequency of the transmission line 1. Furthermore, when the ends of the transmission line 1 are short-circuited, the resistance between both ends of the transmission line 1 becomes small, so in this case, it is desirable to connect a resistor in series to the ground side of the transmission line 1.

[Embodiment 2] In this embodiment, as shown in FIG. 7, the transmission line is In other words, when the transmission line 1 has an open termination, the current phase changes from lagging to leading with respect to the voltage phase, as shown by the bold line in Figure 7(a). , in the case of a short-circuit termination, the phase changes from leading to lagging, as shown by the thick line in FIG. 7(b). In this way, the sign of the phase angle between the voltage phase and the current phase reverses before and after the resonant frequency, so if the reversal of the sign of the phase angle is detected, the resonant frequency of the transmission line 1 can be determined. It is possible. As shown in FIG. 6, the circuit configuration for detecting the resonance frequency in this way is to connect a resistor R in series to the transmission line 1, apply the high frequency output of the variable frequency oscillator 2 to this series circuit, and apply the high frequency output of the variable frequency oscillator 2 to the series circuit. It is sufficient to detect the phase difference between both ends of R. That is, at the end of the resistor R on the variable frequency oscillator 2 side, the voltage phase of the series circuit is detected, and at the end of the resistor R on the transmission line 1 side, the current phase of the series circuit is detected. By detecting the phase difference at both ends of R, the phase angle between the voltage phase and current phase can be detected. To detect the phase difference, a phase difference detection circuit 9 is provided which can obtain a voltage output corresponding to the input phase difference, and the output voltage of the phase difference detection circuit 9 is converted into a digital signal by the analog-to-digital converter 6 and converted into a digital signal. Just enter it into computer 4. The microcomputer 4 controls the variable frequency oscillator 3 so that the output frequency changes, determines the change in the output of the phase difference detection circuit 9 with respect to the frequency, and selects the frequency at which the sign of the phase angle is reversed to the transmission line 1.
This is the resonant frequency of . The resonant frequency thus obtained is converted to water content. As described above, the resistor R, the analog-to-digital converter 6
, a phase angle detection section is configured by the phase difference detection circuit 9,
This phase angle detection section constitutes the sensor circuit 7 together with the variable frequency oscillator 3. Since the microcomputer 4 calculates the phase angle between the voltage phase and the current phase of the high-frequency signal passing through the transmission line and the resonance frequency based on the output of the sensor circuit 7, It functions as a part of the detection circuit) and as an arithmetic unit.

[Embodiment 3] In this embodiment, as shown in section 8, the transmission line 1 is an LC
Utilizing the property of being equivalent to a resonant circuit, the transmission line 1 is used as a resonant circuit for the oscillator 8, and the resonant frequency of the transmission line 1 is determined from the output frequency of the oscillator 8. In FIG. 8, by configuring the oscillator 8 as a modified Clapp circuit, there is only one transistor Q, which is an active element, and the circuit configuration is extremely simple. It goes without saying that the oscillator 8 may have other configurations. By determining the common wave number of the transmission line 1 from the output frequency of the oscillator 8 in this way, it can be converted to the water content of the substance in the same manner as in Example 1.

[Embodiment 4] In this embodiment, as shown in FIG.
are connected in series, and the output of the variable frequency oscillator 2 is applied to this series circuit, forming a phase-locked loop so that the phase difference between both ends of the resistor R is zero. That is, the phase difference between both ends of the resistor R corresponds to the phase difference between the voltage phase and the current phase, as explained in the second embodiment. Further, the variable frequency oscillator 2 is a voltage controlled oscillator, and is controlled by the output voltage of a phase difference detection circuit 9 that generates a voltage corresponding to the phase difference. Therefore, the variable frequency oscillator 2 is adjusted to reduce the phase difference, and when the phase difference becomes zero, the frequency becomes stable. Since this frequency is the resonant frequency of the transmission line 1, the resonant frequency of the transmission line 1 can be determined by measuring the output frequency of the variable frequency oscillator 2. The subsequent processing is the same as in Example 1, and the resonant frequency is converted into the water content of the substance. In this way, since the resonant frequency of the transmission line 1 is determined using the phase-locked groove, there is almost no influence of the selectivity (Q) of the transmission line 1, and the resonant frequency of the transmission line 1 can be determined accurately. It is.

[Embodiment 5] In Embodiments 1 to 4, the resonant frequency of the transmission line 1 was determined, but in this embodiment, the transmission line 1 is regarded as a distributed constant delay line, and the resonance frequency is determined from one end of the transmission line 61. By measuring the delay time required for the input signal to reach the other end, it can be made to correspond to the moisture content of the material surrounding the transmission line 1. That is, as shown in FIG. 15, a signal generator 20 is connected to one end of the transmission line 1, and a pulse signal is applied to one end of the transmission line 1. Further, an exclusive OR circuit 21 calculates the exclusive OR of the signals from the output end of the signal generator 20 and the other end of the transmission line 1 . Here, resistors R + and R x are connected to both ends of the transmission line 1, respectively, for impedance matching. Further, the output of the signal generator 20 is connected to a voltage dividing resistor R 3 . The voltage is divided by R4 and adjusted so that both inputs of the exclusive OR circuit 21 are at approximately the same level. The output of the exclusive OR circuit 21 is integrated by an integrating circuit 22 consisting of a resistor R5, a capacitor C, and an amplifier circuit oP, and outputs a voltage level corresponding to the time when the output level of the exclusive OR circuit 21 is "H". is now available. According to this configuration, as shown in FIG. 16(a), a pulse signal having a pulse width of TI is output from the signal generator 20, and as shown in FIG. 16(b), one end of the transmission line 1 The delay time required for the signal to reach the other end is T2
, the exclusive OR circuit 21 outputs the 16th
As shown in Figure (c), a pulse output with a pulse width corresponding to the delay time T2 of the transmission line 1 is obtained. If the delay time when the transmission line 1 exists in the air is T2, and the delay time when the transmission line 1 exists in the water is T, then the 16th r5! i(b′》Noyouni, T 2 <
T)):- As the output of the exclusive OR circuit 21, a pulse output having a larger pulse width than that in the air is obtained as shown in FIG. 16(C'). As mentioned above, the output level of the integrating circuit 22 corresponds to the pulse width of the pulse signal output from the exclusive OR circuit 21, so it can be seen by comparing FIGS. 16(cl) and (d'). As shown, the output level of the integrating circuit 22 is higher when the transmission line 1 is in the air than when it is in the water. That is, as the delay time of the transmission line 1 increases, the output level of the integrating circuit 22 increases. As described above, the delay time of the transmission line 1 is obtained as the output level of the integrating circuit 22, so this delay time is
In this embodiment, the signal generator 20 outputs a pulse signal, but the signal generator 20 may output other signals such as a sine wave. Outputs exclusive OR circuit 2
Waveform shaping may be performed before input to 1.

【Effect of the invention】

As described above, the present invention includes a transmission line that is at least partially buried in a substance to be measured, a sensor circuit that detects the dielectric constant of the substance as an electrical variable of the transmission line, and a sensor circuit that detects the dielectric constant of the substance as an electrical variable of the transmission line. At least a part of the transmission line is buried in the substance to be measured, and the electric variable of the transmission line corresponding to the dielectric constant of the substance is calculated. Since the moisture content of a substance is measured based on the above, there is an advantage that the measurement does not affect the substance to be measured during the measurement, and measurements can be carried out continuously in a short period of time. Additionally, since it has almost no physical effect on the substance being measured, there is less energy loss and less power consumption. In addition, the resonant frequency of the transmission line and the delay time of the signal due to the transmission line are used as the electrical variables of the transmission line that correspond to the dielectric constant of the material. This makes the circuit configuration relatively simple and less susceptible to noise. Furthermore, by appropriately setting the length of the transmission line, it is possible to ignore the influence of variations in density even within a substance with non-uniform density, and it is possible to prevent variations in measurement results depending on the measurement location. That is, there is an effect that the reproducibility of measurement results is good and highly reliable measurements can be performed. If the sensor circuit is packaged in a water-resistant case, the sensor circuit can be buried in the material along with the transmission line, and all the parts that generate high-frequency signals are buried in the material, reducing radiation to the outside. This has the advantage of being able to reduce noise. Alternatively, if a part of the case is exposed from the material, the case can be used as a marker for the burial location. Furthermore, if the transmission line is provided with an insulating coating, it will not be affected by distributed resistance due to moisture in the substance, so the measurement accuracy will be further improved. Moreover, if a spacer is provided between both core wires of the transmission line so that the two core wires are parallel to each other, the characteristics will be stabilized and the reliability of the measurement results will be further increased. , the influence of the spacer material on the measured values is reduced, and highly sensitive measurements can be performed. In addition, by providing a termination circuit at the end of the transmission line, the characteristics of the transmission line can be stabilized, further increasing the reproducibility of measurement results.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing Embodiment 1 of the present invention, Fig. 2 is an explanatory diagram showing the usage state of the same, Fig. 3 is a perspective view showing a transmission line used in the above, and Fig. 4 is a transmission line used in the same. A perspective view showing another example of the line, FIG. 5 is an operation explanatory diagram showing the effect of the termination circuit used in the above, FIG. 6 is a block diagram showing Embodiment 2 of the present invention, and FIG. 7 is an operation explanation of the same as above. 8 is a circuit diagram of a main part showing a third embodiment of the present invention, FIG. 9 is a circuit diagram of a main part showing a fourth embodiment of the present invention, and FIGS. 10 and 11 are diagrams of a transmission line in the present invention. Operation explanatory diagram showing properties, 12th
The diagram and FIG. 13 show the frequency of the transmission line in the present invention.
FIG. 14 is a graph explaining the relationship between resonance frequency and water content; FIG. 15 is a circuit diagram showing Embodiment 5 of the present invention; FIG. 16 is an explanatory diagram of the same operation. It is. ．． 1. ...Transmission line, 2...Reference impedance, 3
... variable frequency oscillator, 4... microcomputer, 5... changeover switch, 6... T-narrow-to-digital converter, 7... sensor circuit, 8... oscillation circuit,
9... Phase difference detection circuit, 10... Case, 11-...
・Connection wire, 12...core wire, 13...insulation coating, l4
...Suberi, 15...Through hole, 20...Signal generator, 2]...Exclusive OR circuit, 22...Integrator circuit, E
...10 [Eh...resistance, agent patent attorney Ishida]
Long 7 Figure 5 Figure 6K Figure 7 (a) hf (b) ゐgf Figure 10 Figure 11 Figure 8 Figure 9 Figure 2 lO9f Figure 13 b, f

Claims (12)

[Claims] (1) A transmission line that is at least partially buried in a substance to be measured; a sensor circuit that detects the dielectric constant of the substance as an electrical variable of the transmission line; and a sensor circuit that detects the dielectric constant of the substance as an electrical variable of the transmission line; 1. A moisture content measuring device comprising: a calculating section for converting into a moisture content. (2) The moisture content measurement according to claim 1, wherein the sensor circuit is a frequency detection circuit that detects a resonance frequency of a transmission line, and the calculation unit converts the resonance frequency into a moisture content of a substance. Device. (3) The frequency detection circuit includes a variable frequency oscillator that applies a high frequency signal to the transmission line, and an impedance detection section that detects the impedance of the transmission line, and changes the output frequency of the variable frequency oscillator and detects the impedance. 3. The water content measuring device according to claim 2, wherein the frequency at which the impedance of the transmission line is minimum or maximum is set as the resonant frequency of the transmission line. (4) The frequency detection circuit includes a variable frequency oscillator that applies a high frequency signal to the transmission line, and a phase angle detection unit that detects the phase angle of the current phase and voltage phase of the high frequency signal passing through the transmission line with respect to the other. 3. The transmission line according to claim 2, wherein the output frequency of the variable frequency oscillator is changed and the phase angle is detected, and a frequency at which the sign of the phase angle is reversed is set as the resonant frequency of the transmission line. Moisture content measuring device. (5) The water content measuring device according to claim 2, wherein the frequency detection circuit is an oscillation circuit that uses a transmission line as a resonant circuit, and the oscillation circuit output is the resonant frequency of the transmission line. (6) The frequency detection circuit detects the phase difference between the variable frequency oscillator that applies a high frequency signal to the transmission line and the current phase and voltage phase of the high frequency signal passing through the transmission line, and the phase difference becomes zero. 3. The water content measuring device according to claim 2, further comprising a phase difference detection circuit that adjusts the output frequency of the variable frequency oscillator so that the output frequency of the variable frequency oscillator is the resonance frequency of the transmission line. (7) The sensor circuit includes a signal generator that applies a signal to one end of the transmission line, and a time detection unit that detects the delay time required from when the signal is applied to one end of the transmission line until it reaches the other end. 2. The moisture content measuring device according to claim 1, wherein the calculation unit converts the delay time into the moisture content of the substance. (8) The moisture content measuring device according to any one of claims 2 to 7, wherein the sensor circuit is housed in a water-resistant case. (9) The moisture content measurement according to any one of claims 2 to 8, wherein the transmission line is formed of a pair of conductive core wires and an insulating coating that covers the core wires. Device. (10) The water content measuring device according to claim 9, wherein the transmission line includes a spacer that keeps both core wires parallel. (11) The water content measuring device according to claim 10, wherein the spacer is formed in a shape having through holes at appropriate intervals in the longitudinal direction of both core wires. (12) The moisture content measuring device according to any one of claims 2 to 11, characterized in that a termination circuit is connected to a terminal of the transmission line.