JPH0786482B2 - Water content measuring device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

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

[Prior art]

Conventionally, a thermal response method and a capacitance method are known as methods for measuring the amount of water content in a substance such as the water content in the soil of a field. The thermal response method measures the amount of water contained in a substance by embedding a heater and a temperature sensor in the substance to be measured, heating the substance by the heater, and detecting the temperature change of the substance by the temperature sensor. Is the way to do it. In the electrostatic capacitance method, a pair of electrodes are separated and inserted into a substance to be measured, and the dielectric constant of the substance is calculated based on the capacitance of a capacitor formed by both electrodes and the substance. It is a method of measuring the amount of water contained in a substance from the correspondence between the rate and the amount of water contained in the substance.

In the thermal response method, since the substance to be measured is heated by the heater, the next measurement cannot be performed until the substance returns to the thermal equilibrium state, and continuous measurement is performed. There is a problem that it takes time to do. Further, since water has a large specific heat, it is necessary to increase the power supplied to the heater in order to heat the substance, which causes a problem that the power consumption is large. Further, since the heater and the temperature sensor must be arranged relatively close to each other, there arises a problem that the measurement result largely changes depending on the measurement place in a substance having a non-uniform density such as soil. On the other hand, the electrostatic capacitance method has an advantage over the thermal response method in that it does not require heating of a substance, and therefore it can perform continuous measurement in a short time and consumes less power.
However, since the absolute value of the capacitance as a capacitor is very small and it is in the order of pF, there are problems that it requires advanced measurement technology, the circuit configuration becomes complicated, and it is easily affected by noise. Although it is conceivable to increase the area of the electrode in order to increase the absolute value of the capacitance, there is a problem of increasing the size. Furthermore, since the capacitance changes depending on the distance between the electrodes and the position of the electrodes, the measurement results are not stable,
There is also a problem that the reliability of the measurement result is low. The present invention is intended to solve the above-mentioned problems, and it is possible to realize with a simple circuit configuration, but the reliability of the measurement result is high, and moreover, it is possible to perform continuous measurement in a short time and low power consumption. The present invention is intended to provide a water content measuring device.

[Means for Solving the Problems]

In the present invention, in order to achieve the above object, a transmission line equivalent to an LC resonant circuit at least a part of which is embedded in a substance to be measured, and an electrical variable that reflects the speed of the electromagnetic wave in the transmission line. A sensor circuit for detecting and a calculation unit for converting the electric variable into the water content of the substance are provided. As the sensor circuit, a frequency detection circuit that detects a frequency in which a standing wave is generated in the transmission line is used, and the frequency can be converted into the water content of the substance in the calculation unit. Further, the sensor circuit is composed of a signal generator that applies a signal to one end of the transmission line, and a time detection unit that detects a delay time required for the signal to reach the other end after being applied to one end of the transmission line. However, the calculation unit may convert the delay time into the water content of the substance. 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 unit that detects the impedance of the transmission line.The frequency detection circuit changes the output frequency of the variable frequency oscillator, detects the impedance, and transmits it. The frequency at which the impedance of the line is minimum or maximum can be the frequency at which a standing wave is generated in the transmission line. As the frequency detection circuit, 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 other of the current phase and the voltage phase of the high-frequency signal passing through the transmission line. Alternatively, the output frequency of the variable frequency oscillator may be changed, the phase angle may be detected, and the frequency at which the positive and negative signs of the phase angle are inverted may be the frequency at which the standing wave is generated in the transmission line. Further, the frequency detection circuit may be an oscillation circuit having a transmission line as a resonance circuit, and the output of the oscillation circuit may be a frequency at which a standing wave is generated in the transmission line. Furthermore, the frequency detection circuit detects a phase difference between a current phase and a voltage phase of a high frequency signal passing through the transmission line and a variable frequency oscillator that applies a high frequency signal to the transmission line, and the phase difference becomes zero. The output frequency of the variable frequency oscillator may be the frequency at which a standing wave is generated in the transmission line. The sensor circuit is preferably packaged in a water resistant case. The transmission line is preferably formed by a pair of conductive core wires and an insulating coating that covers the circumference of the core wires. Further, it is desirable to provide the transmission line with a spacer that keeps both cores in parallel. The spacer may be formed in a shape having through holes at appropriate intervals in the longitudinal direction of both core wires. It is desirable to connect a terminal circuit to the terminal of the transmission line.

[Action]

According to the above configuration, at least a part of the transmission line is embedded in the substance to be measured, and the water content of the substance is measured based on the electrical variable that reflects the velocity of the electromagnetic wave in the transmission line. Since it does not affect the substance to be measured, it is possible to continuously measure in a short time. Moreover, since the substance to be measured has almost no physical influence, energy loss is small and power consumption is also small. In addition, since the frequency at which a standing wave is generated in the transmission line and the signal delay time due to the transmission line are used as the electrical variables that reflect the speed of the electromagnetic wave in the transmission line, the existing technology for frequency measurement and time measurement is used. In view of this, high-accuracy measurement can be performed, the circuit configuration is relatively simple, and it is less susceptible to noise. Further, by appropriately setting the length of the transmission line, it is possible to ignore the influence of the density variation even in a substance having a non-uniform density, and prevent the variation of the measurement result depending on the measurement location. That is, it is possible to perform measurement with high reproducibility of measurement results and high reliability. Also, in the case where the sensor circuit is installed in a water resistant case, the sensor circuit can be embedded in the substance together with the transmission line, and all the parts that generate high frequency signals will be embedded in the substance. It is possible to reduce the radiation noise to the. Alternatively, by exposing a part of the case from the substance, the case can be used as a mark for the embedding position. Further, in the case where the transmission line is provided with an insulating coating, it is not affected by the distributed resistance due to the moisture in the substance, so that the measurement accuracy is further enhanced. Moreover, if a spacer is provided between both cores of the transmission line so that the two cores are parallel to each other, the characteristics will be stable and the reliability of the measurement result will be further enhanced. The influence of the material of the spacer on the measured value is reduced, and highly sensitive measurement can be performed. In addition, if a terminating circuit is provided at the terminal of the transmission line, the characteristics of the transmission line can be stabilized and the reproducibility of the measurement result is further enhanced.

【principle】

In the present invention, the amount of water in a substance is measured by utilizing the fact that the relative permittivity of water is about 80, which is very large compared to other substances. That is, generally, the relative permittivity of a solid substance is about 1 to 10, and there is a large difference from the relative permittivity of water. Therefore, if the amount of water in the substance changes, it will change significantly in the range from the relative permittivity of the substance to the relative permittivity of water. This property is also used in the capacitance method, but in the present invention, instead of burying a pair of electrodes in a substance, a transmission line equivalent to an LC resonance circuit is embedded, and a standing wave is generated in the transmission line. The water content of a substance is obtained by paying attention to the fact that electrical variables such as the frequency (hereinafter referred to as the standing frequency) and the delay time correspond to the speed of the electromagnetic wave on the transmission line. That is, when a high frequency signal having a wavelength on the order of the length of the transmission line passes through the transmission line, the distributed constant of the transmission line affects the transmission characteristics. The distribution constant of the line will correspond to the dielectric constant of the material. As a method of measuring the dielectric constant of a substance, there is the capacitance method described in the conventional example, but in the present invention, if the dielectric constant of the substance changes, the velocity of the electromagnetic wave in the transmission line or the electromagnetic wave in the substance The idea is to detect the velocity of electromagnetic waves in the transmission line based on the knowledge that the propagation velocity also changes.Therefore, changes in the standing frequency and delay time of the transmission line are detected as electrical variables that reflect the velocity of electromagnetic waves. To do. The basic configuration for measuring the standing frequency and delay time of the transmission line will be described below. First, consider the voltage amplitude on the transmission line 1. First
As shown in FIG. 10 (a), a transmission line 1 having an open termination
When a high-frequency signal source S that outputs a high-frequency wave of wavelength λ is connected to one end of, the incident wave W ₁ from the high-frequency signal source S and the reflected wave W ₂ from the end are connected as shown in FIG. 10 (b). A standing wave is generated by the interference, and the distribution of the voltage amplitude on the transmission line 1 is
As shown in Fig. 10 (c), it is minimum at the position (2n-1) · λ / 4 from the end and maximum at the position 2n · λ / 4 (n = 1,2, ...
…). Further, as shown in FIG. 11 (a), when the 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 (b), the distribution of the voltage amplitude on the transmission line 1 due to the interference between the incident wave W ₁ and the reflected wave W ₂ from the high frequency signal source S is as shown in FIG. 11 (c). , (2n-1) ・ λ / 4
The maximum is at the position of 2, and the minimum is at the position of 2n · λ / 4. That is, from the viewpoint 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 the minimum for the open transmission line 1 and the maximum for the short-circuited transmission line 1. become. Conversely, if the length of the transmission line 1 is fixed, the output frequency f of the high frequency signal source S
Impedance characteristics for open transmission line 1
Then, it becomes equivalent to the LC series resonance circuit as shown in FIG. 12, and becomes equivalent to the LC parallel resonance circuit as shown in FIG. However, there are multiple resonance points. When the inductance per unit length of the transmission line 1 is L and the capacitance is C, the standing frequency f _r can be expressed as f _r = κ ₁ / (LC) ^1/2 . However, κ ₁ is a proportional constant.
On the other hand, the capacitance C is proportional to the relative permittivity ε of the material around the transmission line 1, and if the proportional constant is κ ₂ , then C = κ ₂ · ε ... Therefore, from the formula, f _r = κ ₁ / (Κ ₂ · εL) ^1/2 ... That is, if L≈constant, then f _r = κ ₃ / ε ^1/2 . However, κ ₃ is a proportional constant. Here, the inductance L changes according to the relative magnetic permeability of the substance around the transmission line 1, but since the relative magnetic permeability hardly changes depending on the water content in the substance, there is no problem in the process of L≈constant. In addition, the delay time τ per unit length of the transmission line 1
Is τ = κ ₄ · (LC) ^1/2 ... If the proportionality constant is κ ₄ , then τ = κ ₅ · ε ^1/2 ... As described above, the standing wave frequency f _r and the delay time τ of the transmission line 1 depend on the relative permittivity ε of the substance existing around the transmission line. Thus, the water content of the substance existing around the transmission line 1 can be obtained. An example of the relationship between the water content of a substance and the standing wave frequency is
As shown in Fig. 14, it can be seen that the standing wave frequency decreases as the water content increases. Also, comparing the formulas,
Since the standing wave frequency f _r is inversely proportional to the delay time τ, it can be seen that the delay time increases as the water content increases. By the way, it is known that the propagation velocity V of an electromagnetic wave in a substance is V = c / n (c is a light velocity) when the refractive index of the electromagnetic wave in the substance is n. n is the square root of the product of the relative magnetic permeability and the relative permittivity. Since the relative magnetic permeability is about 1 in a nonmagnetic material, V≈c / ε ^1/2 . As can be seen by comparing this formula with the formula and the formula, the transmission line 1
Obtaining the resonance frequency and the delay time of is to indirectly measure the propagation velocity of the electromagnetic wave in the substance. Incidentally, the speed of an electromagnetic wave in the transmission line 1 is proportional to the standing wave frequency f _r, inversely proportional to the delay time tau, by measuring the standing wave frequency f _r and delay time tau, determine the velocity of electromagnetic wave It is equivalent to that. That is, the velocity of the electromagnetic wave in the transmission line 1 also corresponds to the velocity of propagation of the electromagnetic wave in the substance. Here, if the velocity of the electromagnetic wave is measured, the amount of water in the substance can be measured, but since the propagation velocity of the electromagnetic wave is very fast, the device is large-scaled to directly measure the propagation velocity and an error occurs. It tends to occur. On the other hand, if the structure for obtaining the standing wave frequency and the delay time of the transmission line is adopted as described above, the structure of the device can be simplified and a highly reliable measured value can be obtained. .

First Embodiment 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 set as the standing wave frequency of the transmission line. . The transmission line 1 is composed of conductive wires arranged in parallel,
As shown in the figure, it is connected in series to the reference impedance 2. The 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 _a across the series circuit and the voltage V _b across the transmission line 1 is measured. That is, the impedances of the transmission line 1 and the reference impedance 2 with respect to the frequency f are Z _X (f) and Z _A , respectively.
When _{(f), Z X (f} ) / from _{(Z X (f) + Z} A (f)) = relation V _b / V _a is _{satisfied, Z X (f) = Z} A (f) · V _b / (V _a −V _b ) ... where the impedance of reference impedance 2 is
Since Z _A (f) is known, the impedance of the transmission line 1 with respect to the frequency f can be obtained by measuring the voltages V _a and V _b . Therefore, while varying the output frequency of the variable frequency oscillator 3, the voltages V _a and V _b are measured, and Z _X (f) is minimum based on the formula (when the end of the transmission line 1 is open).
Alternatively, if the maximum frequency (when the end of the transmission line 1 is short-circuited) is obtained, it becomes the standing wave frequency of the transmission line 1. Here, in order to easily measure the standing wave frequency of the transmission line 1, control of the output frequency of the variable frequency oscillator 3 and measurement of the voltages V _a and V _b are performed by the microcomputer 4
Has been automated using. That is, which of the voltage V _a between both ends of the series circuit of the transmission line 1 and the reference impedance 2 or the voltage V _b between both ends of the transmission line 1 is selected by the changeover switch 5, and the measured voltage is analog-digital. It is converted into a digital signal by the converter 6. In this way, the measured voltage is input to the microcomputer 4 as a digital signal, the equation is calculated, and the transmission line 1
The impedance of is required. Also, the variable frequency oscillator 3 is controlled so that the output frequency changes stepwise,
The changeover switch 5 is changed within the time period in which the same frequency is maintained, and the two kinds of voltages V _a and V _b are 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-digital converter 6 constitute an impedance detecting section, and the impedance detecting section constitutes the sensor circuit 7 together with the variable frequency oscillator 3. After the measurement of the impedance in the frequency variable range of the variable frequency oscillator 3 is completed as described above, in the microcomputer 4, the impedance is minimum (when the transmission line 1 is an open termination) or maximum (when the transmission line 1 is a short circuit termination). Frequency) is calculated. This frequency is the standing wave frequency of the transmission line 1, and this standing wave frequency is converted into the water content. That is, since the microcomputer 4 calculates the impedance of the transmission line and the standing wave frequency on the basis of the output of the sensor circuit 7, the microcomputer 4 functions as a part of the impedance detection unit (that is, a part of the frequency detection circuit), and the calculation is performed. Function as a department. Next, a case of measuring the amount of water in the soil by the device having the above configuration will be described. In this case, as shown in FIG.
The entire transmission line 1 is buried in the soil E. Also, Sat E
The transmission line 1 is set to an appropriate length so that the influence of the local nonuniformity of the density due to the cavities in the inside is not obtained, and the average value of the range of the length is obtained. For example, if the transmission line 1 of about 1 m is used, the average value in the range of about 1 m can be obtained. Now, if the transmission line 1 having a length of about 1 m is used, an electromagnetic wave with a wavelength of 1 m will be generated in the air. Although it becomes 300MHz, the standing frequency is about 75MHz in air,
As shown in the figure, since the standing wave frequency decreases as the water content increases in the substance, the output frequency of the variable frequency oscillator 3 is several MHz to 100 MHz for this transmission line 1.
It is set in the range of about MHz. It is relatively easy to change the frequency to this extent, and the circuit configuration is simple and stable operation can be expected, which is a preferable condition for a measuring instrument. Here, when an oscillating electric field is applied to water, if the frequency of the oscillating electric field is about 1 GHz, the orientation change of water molecules cannot follow the change of the electric field, and the dielectric constant decreases rapidly. Will be used as the upper limit. That is, the transmission line 1 needs to be at least several tens of cm. On the other hand, when measuring the water content as an average value in a relatively wide range such as in a field, the transmission line 1 can be set to several tens of meters, and in this case, the standing wave frequency becomes lower,
Circuit design becomes easier. The buried depth of the transmission line 1 may be adjusted according to the purpose of measurement, but is usually set to 10 cm or more. The reference impedance 2, the variable frequency oscillator 3, the changeover switch 5, the analog-digital converter 6, and other sensor circuits 7 involved in high frequencies are housed in a water-resistant case 10 and in the soil E together with the transmission line 1. Buried in. Also, a connection line from the case 10 to the microcomputer 4
11 is withdrawn. That is, since all the parts affected by the amount of water in the soil E can be embedded in the soil E, it is possible to prevent variations in the measured values due to the difference in the insertion dimension into the soil E, The reliability of the measured value is enhanced, and the effect of preventing unnecessary radiation noise of high frequency from leaking to the outside can be obtained. If a part of the case 10 is exposed from the soil E, the buried position can be confirmed by the exposed part of the case 10, and the connecting line 11
It is possible to prevent it from being caught by a tractor. As shown in FIG. 3, the transmission line 1 is formed in a feeder line shape in which a waterproof insulating coating 13 is provided around a pair of conductive core wires 12, and a thin wall between the core wires 12 is formed. Spacer 14
Is integrally formed with the insulating coating 13, and the distance between both core wires 12 is kept constant. As described above, by having the insulating coating 13, the influence of the distributed resistance due to the electrolyte dissolved in the moisture of the soil E is prevented, and the increase in power consumption and the increase in the distributed resistance due to the current flowing through the distributed resistance. Selectivity (Q)
Is prevented so that measurement becomes easy.
Further, the insulation coating 13 can prevent the core wire 12 from being corroded.
Here, the presence of the insulating coating 13 slightly reduces the variation range of the measured dielectric constant, but since the impedance can be measured with high accuracy, the influence of the dielectric constant of the insulating coating 13 is negligible. The core wire 12 has an insulating coating 13
The measurement facilitates the measurement as described above, but the insulating coating 13 may be omitted if unnecessary. Also,
As shown in FIG. 4, when the transmission line 1 is formed in a ladder shape by forming the through holes 15 in the spacer 14 at appropriate intervals along the transmission line 1, as compared with the case where the through holes 15 are not formed, ,
Since the surface area of the transmission line 1 is increased and the amount of the spacer 14 which is a dielectric is reduced, it becomes possible to detect the change in the water content of the soil E with high sensitivity. A terminating circuit 16 is provided at the end of the transmission line 1. The terminating circuit 16 is composed of passive circuit components such as a capacitor and a resistor, and can change the impedance of the transmission line 1 and reduce the influence of external electromagnetic waves. Further, since the boundary condition at the end of the transmission line 1 becomes clear, for example, if a capacitor is connected to the end at the open end, the effect of lowering the standing wave frequency and reducing the imperfections of the impedance characteristic can be obtained. When such a capacitor is not connected, as shown by a thin line in FIG. 5, the frequency distribution of impedance often has an irregular portion, which lowers the reliability of the measured value. By providing the above, such a problem is ameliorated as shown by the bold line in FIG. If a resistor is connected to the terminal end, the imperfections in the impedance characteristics can be reduced without affecting the standing wave frequency of the transmission line 1. Further, when the end of the transmission line 1 is short-circuited, the resistance at both ends of the transmission line 1 becomes small. Therefore, in this case, it is desirable to connect a resistor in series to the ground side of the transmission line 1.

Second Embodiment In the present embodiment, as shown in FIG. 7, the fact that the phase angle between the voltage phase and the current phase sharply changes before and after the standing wave frequency of the transmission line 1 is used. Detect the standing wave frequency of the transmission line. That is, when the transmission line 1 has an open termination, as shown by the thick line in FIG. As shown by the thick line in FIG. 7 (b),
It changes from advanced to late. In this way, the positive and negative signs of the phase angle between the voltage phase and the current phase are inverted before and after the standing wave frequency, so if the inversion of the sign of the phase angle is detected,
The standing wave frequency of the transmission line 1 can be obtained. As a circuit configuration for detecting the standing wave frequency in this way, as shown in FIG. 6, a resistor R is connected in series to the transmission line 1 and the high frequency output of the variable frequency oscillator 2 is applied to this series circuit. , The phase difference between both ends of the resistor R may be detected. That is, the voltage phase of the series circuit is detected at the end of the resistor R on the variable frequency oscillator 2 side, and the current phase of the series circuit is detected at the end of the resistor R on the transmission line 1 side. By detecting the phase difference at both ends of R, the phase angle between the voltage phase and the current phase can be detected. To detect the phase difference, the phase difference detection circuit 9 that obtains a voltage output corresponding to the difference in the input phase
Is provided and the output voltage of the phase difference detection circuit 9 is converted into a digital signal by the analog-digital converter 6 and input to the microcomputer 4. The microcomputer 4 controls the variable frequency oscillator 3 to change the output frequency, obtains the output change of the phase difference detection circuit 9 with respect to the frequency, and determines the frequency at which the sign of the phase angle is inverted to the standing wave frequency of the transmission line 1. And The standing wave frequency thus obtained is converted into the water content. As described above, the resistor R, the analog-digital converter 6, and the phase difference detection circuit 9 constitute a phase angle detection section, and the phase angle detection section constitutes the sensor circuit 7 together with the variable frequency oscillator 3. The microcomputer 4 detects the phase angle between the voltage phase and the current phase of the high frequency signal passing through the transmission line and the standing wave frequency as the sensor circuit 7.
Since the calculation is performed based on the output of 1), it functions as a part of the phase angle detection section (that is, a part of the frequency detection circuit) and also as a calculation section.

Third Embodiment In this embodiment, as shown in FIG. 8, the transmission line 1 is used as a resonance circuit of an oscillator 8 by utilizing the property that the transmission line 1 is equivalent to an LF resonance circuit. The standing wave frequency of the transmission line 1 is obtained according to the output frequency of. In FIG. 8, by configuring the oscillator 8 as a modified Clap circuit, there is only one transistor Q that is an active element, and the circuit configuration is very simple. Of course, the oscillator 8 may have another configuration. In this way, by obtaining the standing wave frequency of the transmission line 1 from the output frequency of the oscillator 8, the moisture content of the substance can be converted in the same manner as in the first embodiment.

Fourth Embodiment In this embodiment, as shown in FIG. 9, a resistance R is connected in series to the transmission line 1 and the output of the variable frequency oscillator 2 is applied to this series circuit. The phase-locked loop is configured so that the phase difference between both ends of the 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 described in the second embodiment. The variable frequency oscillator 2 is a voltage controlled oscillator and is controlled by the output voltage of the 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 the frequency becomes stable when the phase difference becomes zero. Since this frequency is the standing wave frequency of the transmission line 1, it is possible to know the standing wave frequency of the transmission line 1 by measuring the output frequency of the variable frequency oscillator 2. Subsequent processing is the same as in Example 1, and the standing wave frequency is converted into the water content of the substance. In this way, the standing wave frequency of the transmission line 1 is obtained by the phase-locked loop, so that the selectivity (Q) of the transmission line 1 has almost no effect and the standing wave frequency of the transmission line 1 is obtained accurately. It is possible.

Fifth Embodiment In the first to fourth embodiments, the standing wave frequency of the transmission line 1 is determined, but in the present embodiment, the transmission line 1 is used.
Is regarded as a distributed constant delay line, and the delay time required for a signal input from one end of the transmission line 1 to reach the other end is measured to correspond to the moisture content of the substance around the transmission line 1. Is. That is, as shown in FIG. 15, the signal generator 20 is connected to one end of the transmission line 1, and the pulse signal is applied to one end of the transmission line 1. Further, the exclusive OR circuit 21 calculates the exclusive OR of the signals at the output end of the signal generator 20 and the other end of the transmission line 1. Here, resistors R ₁ and R ₂ are connected to both ends of the transmission line 1, respectively, and impedance matching is performed. Further, the output of the signal generator 20 is divided by the voltage dividing resistors R ₃ and R ₄ , and both inputs of the exclusive OR circuit 21 are adjusted to have substantially the same level. The output of the exclusive OR circuit 21 is
Integrator circuit 22 consisting of resistor R ₅ , capacitor C, and amplifier circuit OP
The output level of the exclusive OR circuit 21 is "H"
The output of the voltage level corresponding to a certain time is obtained. According to this configuration, as shown in FIG. 16 (a), the signal generator 20 outputs a pulse signal having a pulse width of T ₁ ,
As shown in FIG. 16 (b), if the delay time required for the signal to reach from one end to the other end of the transmission line 1 is T ₂ , the exclusive OR circuit 21 outputs the delay time shown in FIG. ), A pulse output having a pulse width corresponding to the delay time T ₂ of the transmission line 1 is obtained. If the delay time when the transmission line 1 exists in air is T ₂ and the delay time when the transmission line 1 exists in water is T ₃ , then FIG. 16 (b ′)
As described above, since T ₂ <T ₃ , as the output of the exclusive OR circuit 21, a pulse output having a larger pulse width than that in the case of air is obtained as shown in FIG. 16 (c '). Integrator circuit 22
As described above, since the output level of 1 corresponds to the pulse width of the pulse signal output from the exclusive OR circuit 21, as can be seen by comparing FIG. 16 (d) and (d ′),
The output level of the integrating circuit 22 is higher when the transmission line 1 is present in the air than when it is present in the water. That is, when the delay time of the transmission line 1 increases, the output level of the integrating circuit 22 increases. As described above, since the delay time of the transmission line 1 is obtained as the output level of the integrating circuit 22, this delay time is converted into the moisture content of the substance by the arithmetic unit such as a microcomputer. In this embodiment, the pulse signal is output from the signal generator 20, but the signal generator 20 outputs another signal such as a sine wave, and the waveform shaping is performed before the input to the exclusive OR circuit 21. May be performed.

【The invention's effect】

The present invention, as described above, a transmission line equivalent to an LC resonant circuit in which at least a part is embedded in the substance to be measured,
A sensor circuit that detects an electrical variable that reflects the speed of an electromagnetic wave in a transmission line, and a calculation unit that converts the electrical variable into the water content of the substance are provided. At least a part of the transmission line is embedded in and the water content of the substance is measured based on the electrical variable that reflects the velocity of the electromagnetic wave corresponding to the permittivity of the substance in the transmission line. There is an advantage that the measurement can be continuously performed in a short time without affecting the substance. Further, since the substance to be measured has almost no physical influence, energy loss is small and power consumption is small. In addition, since the frequency at which a standing wave is generated in the transmission line and the delay time of the signal due to the transmission line are used as the electrical variable that reflects the velocity of the electromagnetic wave in the transmission line corresponding to the dielectric constant of the substance, Since high-precision measurement can be performed in view of existing techniques of measurement and time measurement, the circuit configuration is relatively simple and is less susceptible to noise. Further, by appropriately setting the length of the transmission line, it is possible to ignore the influence of the density variation even in a substance having a non-uniform density, and prevent the variation of the measurement result depending on the measurement location. That is, there is an effect that the reproducibility of the measurement result is good and the measurement can be performed with high reliability. If the sensor circuit is installed in a water-resistant case, the sensor circuit can be embedded in the substance together with the transmission line, and all the parts that generate high-frequency signals will be embedded in the substance. There is an advantage that noise can be reduced. Alternatively, if a part of the case is exposed from the substance, the case can be used as a mark for the embedding position. Further, in the case where the transmission line is provided with the insulating coating, the measurement accuracy is further improved because the distribution resistance is not affected by the moisture in the substance. Moreover, if a spacer is provided between both cores of the transmission line so that the two cores are parallel to each other, the characteristics will be stable and the reliability of the measurement result will be further enhanced. The influence of the material of the spacer on the measured value is reduced, and highly sensitive measurement can be performed. In addition, if a terminating circuit is provided at the terminal of the transmission line, the characteristics of the transmission line can be stabilized and the reproducibility of the measurement result is further enhanced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory view showing a usage state of the above, FIG. 3 is a perspective view showing a transmission line used in the same, and FIG. 4 is a transmission used in the same. FIG. 5 is a perspective view showing another example of the line, FIG. 5 is an operation explanatory view showing an effect of a termination circuit used in the same, FIG. 6 is a block diagram showing a second embodiment of the present invention, and FIG. FIG. 8 is a circuit diagram of essential parts showing a third embodiment of the present invention, FIG. 9 is a circuit diagram of essential parts showing a fourth embodiment of the present invention, and FIGS. 10 and 11 show transmission lines according to the present invention. Operation explanatory diagram showing the characteristics, FIG. 12 and FIG. 13 is an operation explanatory diagram showing the frequency-impedance characteristic of the transmission line in the present invention, FIG. 14 is a graph explaining the relationship between the standing wave frequency and the water content, FIG. 15 is a circuit diagram showing a fifth embodiment of the present invention, and FIG. 16 is an operation explanatory diagram of the same as above. 1 ... Transmission line, 2 ... Reference impedance, 3 ... Variable frequency oscillator, 4 ... Microcomputer, 5 ...
Changeover switch, 6 ... Analog-digital converter, 7
…… Sensor circuit, 8 …… Oscillation circuit, 9 …… Phase difference detection circuit, 10 …… Case, 11 …… Connecting wire, 12 …… Core wire, 13 ……
Insulation coating, 14 ... Spacer, 15 ... Through hole, 20 ... Signal generator, 21 ... Exclusive OR circuit, 22 ... Integrating circuit, E ...
Sat, R ... resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-135357 (JP, A) JP-A-54-115295 (JP, A) JP-B-57-33551 (JP, B2)

Claims (12)

[Claims] 1. A transmission line equivalent to an LC resonant circuit, at least a part of which is embedded in a substance to be measured, a sensor circuit for detecting an electrical variable that reflects the speed of an electromagnetic wave in the transmission line, and A water content measuring device, comprising: an arithmetic unit for converting an electrical variable into a water content of the substance. 2. The sensor circuit is a frequency detection circuit for detecting a frequency in which a standing wave is generated in a transmission line, and the arithmetic unit converts the frequency into a water content of a substance. Item 1. A water content measuring device according to item 1. 3. The frequency detection circuit includes a variable frequency oscillator for applying a high frequency signal to a transmission line, and an impedance detection section for detecting the impedance of the transmission line, and the output frequency of the variable frequency oscillator is changed and the impedance is also provided. 3. The moisture content measuring device according to claim 2, wherein the frequency at which the impedance of the transmission line is minimum or maximum is detected as the frequency at which a standing wave is generated in the transmission line. 4. A variable frequency oscillator for applying a high frequency signal to a transmission line, and a phase angle for detecting the phase angle of one of the current phase and the voltage phase of the high frequency signal passing through the transmission line. A detector is provided, the output frequency of the variable frequency oscillator is changed, the phase angle is detected, and the frequency at which the positive and negative signs of the phase angle are inverted is set as the frequency at which a standing wave is generated in the transmission line. The water content measuring device according to claim 2. 5. The frequency detecting circuit is an oscillating circuit having a transmission line as a resonance circuit, and the oscillating circuit output has a frequency at which a standing wave is generated in the transmission line. Water content measuring device. 6. The frequency detection circuit detects a phase difference between a current phase and a voltage phase of a high frequency signal passing through the transmission line and a variable frequency oscillator for applying a high frequency signal to the transmission line, and the phase difference is zero. And 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 frequency at which a standing wave is generated in the transmission line. Water content measuring device. 7. The sensor circuit comprises a signal generator for applying a signal to one end of a transmission line, and a time detection for detecting a delay time required for the signal to reach the other end after being applied to one end of the transmission line. The water content measuring device according to claim 1, wherein the operation unit converts the delay time into a water content of a substance. 8. The water content measuring device according to claim 2, wherein the sensor circuit is housed in a water resistant case. 9. The transmission line comprises a pair of conductive core wires,
The water content measuring device according to claim 2, wherein the water content measuring device is formed of an insulating coating that covers the periphery of the core wire. 10. The water content measuring device according to claim 9, wherein the transmission line is provided with a spacer for keeping both core wires in 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 water content measuring device according to claim 2, wherein a terminal circuit is connected to a terminal of the transmission line.