JP7020094B2 - Electrical conductivity estimation device - Google Patents

Description

The present invention relates to an electric conductivity estimation device.

The following patent documents disclose a moisture detection device and method (MOISTURE DETECTION APPARATUS AND METHOD) for detecting the moisture content of a detection object as a capacitance. That is, in this moisture detection device and method, a clock signal (reference signal) having a predetermined frequency is input to a detection electrode in contact with the detection object via a resistor, and the detection object changes depending on the amount of moisture. A detection signal whose rise is slow due to the influence of electric capacity is acquired from the detection electrode, and a DC voltage (output voltage) indicating the amount of water is generated by detecting the phase difference between this detection signal and the reference signal. be.

U.S. Pat. No. 6,904,789

By the way, in addition to the water content of the object to be detected, it may be required to obtain the electric conductivity of the object to be detected. Although the conventional water content detection device can measure the water content, it cannot easily measure the electric conductivity. Therefore, there is a demand for a method that can easily measure the electrical conductivity.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to make it possible to easily estimate the electric conductivity of a detection object.

The present invention adopts the following configuration as a means for solving the problem.

The first invention is an electric conductivity estimation device, which comprises a detection electrode, a signal supply means for supplying a detection input signal to the detection electrode, and the detection input signal having a first frequency to the signal supply means. The detection signal of the detection electrode due to the generation of the detection input signal of the second frequency different from the first frequency and the supply of the detection input signal of the first frequency, and the detection signal of the second frequency. A configuration is adopted in which an arithmetic control means for estimating the electric conductivity of the object to be detected is provided based on the detection signal of the detection electrode due to the supply of the input signal for detection.

In the second invention, in the first invention, the change amount of the detection error included in the detection signal with respect to the unit change of the electric conductivity of the detection object is different from that of the first frequency. Adopt a configuration in which the frequency is increased.

In the third aspect of the invention, in the second invention, the arithmetic control means has the volume of the detection object based on the detection signal of the detection electrode due to the supply of the detection input signal of the first frequency. Adopt a configuration to find the water content.

In the fourth invention, in any one of the first to third inventions, a phase detecting means for detecting the phase difference between the detection signal and the detection input signal and a DC voltage corresponding to the detection input signal are internally provided. A configuration is adopted in which a reference voltage generating means for generating as a reference voltage and an amplification means for differentially amplifying the voltage of the detection signal and the internal reference voltage are provided.

According to the present invention, the detection input signal of the first frequency and the detection input signal of the second frequency are used, and the electric conductivity is determined by the detection signal obtained by inputting the respective detection input signals to the detection electrode. presume. The amount of change in the detection error included in the detection signal with respect to the unit change in the electrical conductivity of the detection object changes depending on the frequency of the detection input signal. Therefore, it is possible to estimate the electrical conductivity of the detection target from the amount of change in the output value of the detection signal using the detection input signals of different frequencies. Therefore, according to the present invention, it is possible to easily estimate the electric conductivity of the object to be detected.

It is a block diagram which shows the functional structure of the electric conductivity estimation apparatus in one Embodiment of this invention. It is a block diagram which shows the functional structure of the detector provided in the electric conductivity estimation apparatus in one Embodiment of this invention. It is a graph which shows the relationship between the output voltage and the volume water content when the electric conductivity is changed. It is a schematic diagram which shows the appearance structure of the detector provided in the electric conductivity estimation apparatus in one Embodiment of this invention. It is a figure explaining the operation of the detector provided in the electric conductivity estimation apparatus in one Embodiment of this invention, (a) the waveform diagram, (b) is the graph which shows the output characteristic.

Hereinafter, an embodiment of the electric conductivity estimation device according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each part is appropriately changed in order to make each part recognizable.

FIG. 1 is a block diagram showing a functional configuration of the electric conductivity estimation device 20 of the present embodiment. The electric conductivity estimation device 20 of the present embodiment is a device that estimates the electric conductivity of a detection target such as soil and calculates the amount of water contained in the detection target. As shown in FIG. 1, the electric conductivity estimation device 20 of the present embodiment includes a detector 30, a calculation control unit 40 (calculation control means) that performs a calculation based on the control of the detector 30 and the detection signal of the detector 30. ) And.

FIG. 2 is a block diagram showing a functional configuration of the detector 30. As shown in FIG. 2, the detector 30 includes a frequency variable oscillator 1, a drive circuit 2, a resistor 3, a pair of detection electrodes 4a and a detection electrode 4b, a delay circuit 5, a phase detector 6, a low-pass filter 7, and a buffer amplifier. 8. The differential amplifier 9, the drive circuit 10, the low-pass filter 11, the buffer amplifier 12, the buffer amplifier 13, the 5V power supply circuit 14, and the 3.3V power supply circuit 15 are provided. Of these components, the components other than the pair of detection electrodes 4a and the detection electrodes 4b constitute the main circuit A of the detector 30.

Here, among these components, the frequency variable oscillator 1, the drive circuit 2, and the resistor 3 constitute a signal supply means for supplying the detection input signal to the detection electrode 4a. Further, the delay circuit 5, the phase detector 6, and the low-pass filter 7 constitute a phase detection means for detecting the phase difference between the detection signal output from the detection electrode 4a and the detection input signal. Further, the drive circuit 10, the low-pass filter 11, and the buffer amplifier 12 constitute a reference voltage generating means for generating a DC voltage corresponding to the detection input signal as an internal reference voltage. Further, the buffer amplifier 8, the differential amplifier 9, and the buffer amplifier 12 constitute an amplification means for differentially amplifying the voltage of the detection signal and the internal reference voltage.

The frequency variable oscillator 1 is, for example, an oscillator that generates a square wave signal (clock signal) having a predetermined frequency and a predetermined detail ratio. This frequency variable oscillator 1 is an oscillator capable of generating square wave signals of different frequencies under the control of the arithmetic control unit 40, and has a first frequency square wave signal capable of accurately measuring the water content and electrical conduction. It is possible to output a square wave signal of the second frequency used for estimating the degree.

Here, the first frequency and the second frequency will be described in more detail. The output voltage of the detector 30 based on the detection signal output from the detection electrode 4a changes depending on the water content (volume water content) contained in the detection target. At this time, if the detection signal contains a slight error, the output voltage (output signal) of the detector 30 also contains a slight error. This error amount varies depending on the frequency of the detection input signal input to the detection electrode 4a, and further, the change state of the error amount greatly differs depending on the frequency depending on the electric conductivity of the detection object. That is, when the frequency of the detection input signal is changed, the amount of change (error amount) of the detection error included in the output signal with respect to the unit change of the electric conductivity of the detection object changes. The first frequency is a frequency at which an error included in the output signal is small with respect to a change in the electrical conductivity of the detection object when the detection input signal of the first frequency is input to the detection electrode 4a. This first frequency is a frequency at which the water content of the detection target can be detected most accurately. On the other hand, the second frequency is a frequency having a larger error included in the output signal when the detection signal of the second frequency is input to the detection electrode 4a than in the case of the detection signal of the first frequency. That is, the second frequency is a frequency in which the amount of change in the detection error included in the output signal with respect to the unit change in the electric conductivity of the detection object is larger than that in the first frequency. For example, the first frequency may be 50 MHz and the second frequency may be 5 MHz. However, the optimum values of the first frequency and the second frequency are appropriately set according to the object to be detected. The duty ratio is, for example, 50%, but the optimum value is appropriately set according to the object to be detected.

FIG. 3 is a graph showing a change in the output voltage of the detector 30 when the detection input signal has a frequency (second frequency) in which the amount of change in the detection error becomes large when the electric conductivity changes. In FIG. 3, the horizontal axis represents the output voltage, and the vertical axis represents the volume moisture content of the object to be detected. Further, FIG. 3 shows the results of measuring the output voltage with four electric conductivitys, and is a graph in which the line type is changed for each electric conductivity. As shown in this figure, it can be seen that even if the volume water content is the same, the output voltage changes greatly when the electric conductivity is different, and the amount of this change is different for each electric conductivity.

Such a variable frequency oscillator 1 outputs a square wave signal to the drive circuit 2, the delay circuit 5, and the drive circuit 10. The drive circuit 2 is a kind of current amplification circuit, and a square wave signal is current-amplified and output to the resistor 3. Since the frequency variable oscillator 1 is operated by the 3.3V power supply supplied from the 3.3V power supply circuit 15, the peak value (amplitude) of the square wave signal (clock signal) is 3.3V.

The resistor 3 is a two-terminal electronic element having a predetermined resistance value, and is provided between the drive circuit 2 and one of the detection electrodes 4a. That is, one end of the resistor 3 is connected to the output end of the drive circuit 2, and the other end is connected to one of the detection electrodes 4a. In such a resistor 3, both the pair of detection electrodes 4a and the detection electrodes 4b constitute a load on the drive circuit 2. Further, the resistor 3 is a component that controls the detection dynamic range of the detector 30, and the resistance value is optimally set so that the detection dynamic range is maximized.

The pair of detection electrodes 4a and 4b are conductive members that come into contact with a detection object such as soil, and are arranged so as to face each other with a predetermined distance between them. Here, the object to be detected is a dielectric having a capacitance having a magnitude corresponding to the amount of water. That is, the pair of detection electrodes 4a and the detection electrode 4b together with the detection target form a capacitor (electronic element) having a capacitance.

Further, since such a pair of detection electrodes 4a and 4b function as a capacitor in a circuit, the CR circuit J in the electronic circuit together with the above-mentioned resistor 3, that is, the capacitance C of the capacitor and the resistor 3 It constitutes a passive circuit having a time constant τ based on the resistance value R. That is, the voltage waveform of the contact P between one of the detection electrodes 4a and the resistor 3 in the CR circuit J is an integral processing of the square wave signal input from the drive circuit 2 as the detection input signal based on the time constant τ. It will be a thing. Such a CR circuit J outputs a signal obtained by integrating a detection input signal (square wave signal) from the contact P, that is, one of the detection electrodes 4a, to the phase detector 6 as a detection signal.

The delay circuit 5 is provided in front of the phase detector 6 and delays the square wave signal input from the frequency variable oscillator 1 by a time corresponding to the delay time of the square wave signal in the drive circuit 2 (delay time τ). Therefore, a square wave signal delayed by the delay time τ is output to the phase detector 6. The delay circuit 5 has exactly the same circuit configuration as, for example, the drive circuit 2.

The phase detector 6 is a phase comparator that compares the phase difference between the square wave signal input from the delay circuit 5 and the detection signal input from the CR circuit J. As is well known, various types of circuits exist in a phase comparator, and the phase detector 6 is a digital comparator that performs phase comparison processing using a detection signal and a square wave signal as digital signals. Such a phase detector 6 outputs a signal (phase difference signal) indicating the phase difference between the detection signal and the square wave signal to the low-pass filter 7.

The low-pass filter 7 is a passive filter circuit having a predetermined cutoff frequency, and a DC voltage (detection voltage) indicating a phase difference between a detection signal and a square wave signal is obtained by extracting a DC component from a phase difference signal. Output to. The buffer amplifier 8 is a kind of impedance converter, and outputs the detected voltage to the differential amplifier 9 by lowering the impedance.

The differential amplifier 9 is a differential amplifier that differentially amplifies the detection voltage input from the buffer amplifier 8 and the internal reference voltage input from the buffer amplifier 12, which will be described later, with a predetermined amplification degree. Since the detected voltage is a relatively low voltage value, for example, on the order of several hundred mV, it needs to be amplified in order to secure a sufficient S / N ratio for output to the outside. The differential amplifier 9 differentially amplifies such a detected voltage by an internal reference voltage, and outputs a signal (output voltage) obtained by the differential amplification to the buffer amplifier 13.

On the other hand, the drive circuit 10 is a kind of current amplification circuit, and a square wave signal (clock signal) input from the frequency variable oscillator 1 is current-amplified and output to the low-pass filter 11. The low-pass filter 11 is a passive filter circuit having a predetermined cutoff frequency, converts a square wave signal into an internal reference voltage which is a DC voltage, and outputs the square wave signal to the buffer amplifier 12. Since the peak value of the square wave signal is set to 3.3V, the internal reference voltage is the average voltage (DC voltage) of the square wave signal, that is, 1.65V.

The buffer amplifier 12 is a kind of impedance converter, and outputs the internal reference voltage to the differential amplifier 9 by lowering the impedance. The buffer amplifier 13 is a kind of current amplification circuit, and the output voltage input from the differential amplifier 9 is current-amplified and output to the outside. The 5V power supply circuit 14 converts an external power supply (for example, a 12V power supply) supplied from the outside into a 5V power supply to convert the voltage into a buffer amplifier 8, a buffer amplifier 12, a buffer amplifier 13, a differential amplifier 9, and a 3.3V power supply circuit 15. Supply to. The 3.3V power supply circuit 15 converts the 5V power supply input from the 5V power supply circuit 14 into a 3.3V power supply and supplies it to the frequency variable oscillator 1, the drive circuit 2, the drive circuit 10, and the phase detector 6.

FIG. 4 is a schematic view showing the external configuration of the detector 30. The detector 30 having the electrical configuration as described above has the mechanical configuration as shown in FIG. That is, the detector 30 includes a printed circuit board B, a connection cable D, and a resin mold E. As shown in the figure, the printed substrate B has a shape having two comb tooth portions b1 and a comb tooth portion b2 facing in parallel, and one of the comb tooth portions b1 and the comb tooth portion b2 has a comb tooth portion b1. One of the above-mentioned detection electrodes 4a is formed as a part of the wiring pattern on the surface or the inside of the other detection electrode 4b, and the other detection electrode 4b is formed on the surface or the inside of the other detection electrode 4b. Further, the above-mentioned main circuit A is formed in a region other than the comb tooth portion b1 and the comb tooth portion b2 in the printed circuit board B, that is, in the body portion b3. Here, when the printed circuit board B is a single layer, the detection electrode 4a and the detection electrode 4b can be formed on the surface. However, when the printed circuit board B is a multilayer printed circuit board, the detection electrode 4a and the detection electrode 4b may be formed on an inner layer portion other than the surface thereof.

The connection cable D is an electric wire for transmitting the above-mentioned external power supply and output voltage, and is composed of a plurality of core wires and a sheath (covering member) covering the core wires. Such a connection cable D is connected to the printed circuit board B by soldering or the like. The detector 30 is used by a person grasping the body portion b3 and inserting the pair of comb tooth portions b1 and the comb tooth portion b2 into a detection object such as soil. The resin mold E is an insulating resin material coated on the body portion b3 in order to electrically and mechanically protect the body portion b3 on which the main circuit A is formed.

Returning to FIG. 1, the arithmetic control unit 40 includes a CPU (Central Processing Unit), a storage device, an input device, an output display, and the like, and is a frequency selection unit as a functional unit embodied by these hardware. It includes 41, a water content calculation unit 42, a water content calculation table storage unit 43, an electric conductivity estimation unit 44, and an electric conductivity estimation table storage unit 45.

The frequency selection unit 41 selects the frequency of the square wave signal to be generated in the frequency variable oscillator 1 based on a command or the like input from the outside, and transmits a command signal to the frequency variable oscillator 1 to generate the selected frequency. Output toward. Here, the frequencies selected by the frequency selection unit 41 are the above-mentioned first frequency and the second frequency. That is, the frequency selection unit 41 has a frequency in which the error included in the detection signal is small with respect to the change in the electric conductivity of the detection object and an error included in the detection signal with respect to the change in the electric conductivity of the detection object. Select a large frequency.

The water content calculation unit 42 calculates the water content contained in the detection target based on the detection signal obtained by inputting the detection input signal of the first frequency to the detection electrode 4a. The water content calculation unit 42 calculates the water content contained in the detection target based on the output voltage of the detector 30 and the water content calculation table stored in the water content calculation table storage unit 43. The water content calculation table storage unit 43 stores a table (water content calculation table) for calculating the water content of the detection target object. This water content calculation table is a table showing the relationship between the output voltage of the detector 30 and the volume water content of the detection target, and is obtained in advance by experiments and simulations.

The electric conductivity estimation unit 44 inputs the detection input signal of the second frequency to the detection electrode 4a, and calculates the electric conductivity of the detection object based on the detection signal obtained as a result. The electric conductivity estimation unit 44 estimates the electric conductivity of the object to be detected based on the output voltage of the detector 30 and the electric conductivity estimation table stored in the electric conductivity estimation table storage unit 45. The electric conductivity estimation table storage unit 45 stores a table (electrical conductivity estimation table) showing the relationship between the output voltage of the detector 30 and the volume moisture content for each electric conductivity. These electrical conductivity estimation tables have been obtained in advance by experiments and simulations. For example, when the object to be inspected is soil, after collecting the soil and drying it once, prepare a plurality of samples whose electrical conductivity and volume moisture content are adjusted by changing the electrical conductivity and volume moisture content. .. After that, the output voltage of the detector 30 is acquired by using the detection input signal of the second frequency for each sample, and the electric conductivity estimation table is created based on the acquisition result.

The electric conductivity estimation unit 44 acquires the volume water content calculated by the water content calculation unit 42 (that is, the volume water content obtained by the detection input signal of the first frequency). Subsequently, in the electric conductivity estimation unit 44, the relationship between the output voltage of the detector 30 obtained by the detection input signal of the second frequency and the volume water content calculated by the water content calculation unit 42 described above is determined. It is determined which of the electric conductivity estimation tables stored for each electric conductivity corresponds to. As a result, the electric conductivity estimation unit 44 estimates, for example, the electric conductivity shown by the electric conductivity estimation table having the highest correlation with the relationship between the output voltage and the volume water content as the electric conductivity of the detection object.

In this embodiment, the water content is obtained using the water content calculation table, and the electric conductivity is obtained using the electric conductivity estimation table. However, for example, it is also possible to store the approximate expression in place of these tables and use the approximate expression to obtain the water content and the electrical conductivity.

Next, the operation of the electric conductivity estimation device 20 of the present embodiment configured in this way will be described in detail. In the following description, it is assumed that the water content calculation table is stored in the water content calculation table storage unit 43 in advance, and the electric conductivity estimation table is stored in the electric conductivity estimation table storage unit 45 in advance.

First, a pair of comb tooth portions b1 and a comb tooth portion b2 of the detector 30 are inserted into a detection object such as soil, and a pair of detection electrodes 4a and a pair of detection electrodes 4a formed on the pair of comb tooth portions b1 and the comb tooth portion b2. The detection electrode 4b comes into contact with a detection object such as soil. In this state, when the start command from the outside is input, the arithmetic control unit 40 selects the first frequency by the frequency selection unit 41, and sends a command signal to the frequency variable oscillator 1 to generate the first frequency. Output toward. As a result, the pair of detection electrodes 4a and the detection electrode 4b function as capacitors having a capacitance C according to the amount of water in the detection object. The pair of detection electrodes 4a and the detection electrode 4b and the resistor 3 having the resistance value R form a CR circuit J having a time constant τ defined by the capacitance C and the resistance value R. ..

In this detector 30, the square wave signal oscillated by the frequency variable oscillator 1 is applied to the CR circuit J via the drive circuit 2. That is, in the CR circuit J, the square wave signal is input to one of the detection electrodes 4a via the resistor 3 as a detection input signal. Then, as shown in FIG. 5A, the CR circuit J outputs a detection signal whose rise of the square wave signal is delayed according to its own time constant τ (that is, capacitance C) to the phase detector 6. do. The delay time of this detection signal with respect to the square wave signal, that is, the phase difference θ between the square wave signal and the detection signal indicates the volume water content of the detection object.

In the phase detector 6, a phase difference signal corresponding to the phase difference θ between the detection signal input from the CR circuit J (that is, one of the detection electrodes 4a) and the square wave signal input from the delay circuit 5 is generated. Will be done. This phase difference signal is a pulse signal whose duty ratio changes according to the phase difference θ. Such a phase difference signal is input to the buffer amplifier 8 as a detection voltage (DC voltage) indicating the water content of the detection target by removing the high frequency component by the low-pass filter 7. Then, this detected voltage is reduced in impedance by the buffer amplifier 8 and input to the + input end (non-inverting input end) of the differential amplifier 9.

In order to normally amplify the detected voltage with this differential amplifier 9, it is necessary to input an internal reference voltage that defines the operating point of differential amplification to the-input end (inverting input end) of the differential amplifier 9. In this detector 30, an internal reference voltage is generated by processing a square wave signal input from the frequency variable oscillator 1 with a drive circuit 10 and a low-pass filter 7.

That is, the internal reference voltage is the average DC voltage (1) of the peak value (3.3 V) of the square wave signal by removing the high frequency component by the low-pass filter 7 after the square wave signal is current-amplified by the drive circuit 10. It is generated as .65V). Then, after adjusting the voltage, the internal reference voltage generated in this way is reduced in impedance by the buffer amplifier 12 and input to the-input end (inverting input end) of the differential amplifier 9.

Here, both the detected voltage and the internal reference voltage input to the differential amplifier 9 are DC voltages generated based on the square wave signal output by the frequency variable oscillator 1, and therefore have the same tendency as the temperature characteristics. That is, the detected voltage and the internal reference voltage show the same tendency to change with respect to the change in ambient temperature. For example, if the detected voltage has a temperature characteristic that rises as the ambient temperature rises, the internal reference voltage also has a temperature characteristic that rises as the ambient temperature rises.

Therefore, according to this detector 30, since the temperature characteristic of the detected voltage and the temperature characteristic of the internal reference voltage show the same tendency, the temperature characteristic is improved in the amplification process of the detected voltage by the differential amplifier 9 as compared with the conventional case. Can be done.

Then, the detected voltage is voltage-amplified by the differential amplifier 9 using the internal reference voltage, further current-amplified by the buffer amplifier 13, and output to the outside as the output voltage of the detector 30. As shown in FIG. 5B, this output voltage has a characteristic that it changes linearly with a change in the water content (volume water content) of the detection object. Such an output voltage is input to the arithmetic control unit 40 by the connection cable D described above.

Further, since the detector 30 is provided with the delay circuit 5, it is possible to eliminate the error factor of the phase comparison in the phase detector 6. That is, when the delay circuit 5 is not provided, the square wave signal input to the phase detector 6 and the detection signal have a time relationship that is deviated by the delay time originally possessed by the drive circuit 2, but the delay circuit 5 When is provided, the time-related deviation is eliminated, so that the phase comparison between the square wave signal and the detection signal becomes possible with higher accuracy. Therefore, according to such a detector 30, it is possible to detect the water content more accurately.

When the output voltage from the detector 30 is input to the arithmetic control unit 40, the water content calculation unit 42 compares it with the water content calculation table stored in the water content calculation table storage unit 43, and detects it based on the output voltage. Calculate the amount of water contained in the object.

Subsequently, the arithmetic control unit 40 selects the second frequency by the frequency selection unit 41, and outputs a command signal to the effect that the second frequency is generated to the frequency variable oscillator 1. Similarly, when the output voltage of the detector 30 is input to the arithmetic control unit 40, the electric conductivity estimation unit 44 compares it with the electric conductivity estimation table stored in the electric conductivity estimation table storage unit 45. Estimate the electrical conductivity of the object to be detected based on the output voltage.

According to the electric conductivity estimation device 20 of the present embodiment as described above, the detection input signal of the first frequency and the detection input signal of the second frequency are used, and each detection input signal is detected by the detection electrode 4a. The electrical conductivity is estimated from the detection signal obtained by inputting to. That is, according to the electric conductivity estimation device 20 of the present embodiment, it is possible to estimate the electric conductivity of the object to be detected only by changing the frequency of the square wave signal generated by the frequency variable oscillator 1. Therefore, according to the electric conductivity estimation device 20 of the present embodiment, it is possible to easily estimate the electric conductivity of the object to be detected.

Further, in the electric conductivity estimation device 20 of the present embodiment, the second frequency has a larger change amount of the detection error included in the detection signal with respect to the unit change of the electric conductivity of the detection object as compared with the first frequency. It is said that the frequency is. Further, in the electric conductivity estimation device 20 of the present embodiment, the volume water content of the object to be detected is obtained based on the detection signal of the detection electrode obtained by supplying the detection input signal of the first frequency. Therefore, the water content (volume water content) of the detection target can be accurately calculated without depending on the electrical conductivity.

Further, in the electric conductivity estimation device 20 of the present embodiment, the phase detecting means (delay circuit 5, phase detector 6 and low-pass filter 7) for detecting the phase difference between the detection signal and the detection input signal, and the detection device. A reference voltage generation means (drive circuit 10, low-pass filter 11 and buffer amplifier 12) that generates a DC voltage corresponding to an input signal as an internal reference voltage, and an amplification means (amplification means) that differentially amplifies the detection signal voltage and the internal reference voltage. It includes a buffer amplifier 8, a differential amplifier 9 and a buffer amplifier 12). Therefore, the temperature characteristic of the detected voltage and the temperature characteristic of the internal reference voltage show the same tendency, and the influence on the temperature measurement result can be reduced.

Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to the above embodiment. The various shapes and combinations of the constituent members shown in the above-described embodiment are examples, and can be variously changed based on design requirements and the like without departing from the spirit of the present invention.

For example, in the above embodiment, a configuration for estimating electrical conductivity using only two frequencies has been described. However, it is also possible to estimate electrical conductivity more accurately using three or more frequencies. That is, although it is possible to estimate the electrical conductivity by using at least two frequencies, the first frequency and the second frequency, it is also possible to use other frequencies in addition to the first frequency and the second frequency. It is also possible to sweep the frequency within a predetermined range, obtain the electric conductivity from each of the detection signals obtained during the sweep, and use the average value of these as the electric conductivity of the object to be detected.

Further, in the above embodiment, the first frequency is assumed to be a frequency at which the water content of the detection target can be accurately calculated. However, when it is not necessary to obtain the water content of the detection target and only the electrical conductivity of the detection target needs to be obtained, it is possible to use a frequency having a large error as the first frequency.

Further, in the above embodiment, the phase detecting means (delay circuit 5, phase detector 6 and low-pass filter 7) for detecting the phase difference between the detection signal and the detection input signal, and the DC voltage corresponding to the detection input signal. Reference voltage generation means (drive circuit 10, low-pass filter 11 and buffer amplifier 12) that generates the internal reference voltage as an internal reference voltage, and amplification means (buffer amplifier 8, differential amplifier) that differentially amplifies the voltage of the detection signal and the internal reference voltage. A configuration including 9 and a buffer amplifier 12) was adopted. However, the present invention is not limited to this. In particular, when it is not necessary to calculate the water content of the object to be detected, a configuration is adopted in which the phase detection means, the reference voltage generation means, and the amplification means are not provided and the electric conductivity is directly obtained from the detection signal. It is also possible.

1 Frequency variable oscillator 2 Drive circuit 3 Resistor 4a Detection electrode 4b Detection electrode 5 Delay circuit 6 Phase detector 7 Low-pass filter 8 Buffer amplifier 9 Differential amplifier 10 Drive circuit 11 Low-pass filter 12 Buffer amplifier 13 Buffer amplifier 14 5V power supply circuit 15 3.3V power supply circuit 20 Electrical conductivity estimation device 30 Detector 40 Calculation control unit (calculation control means)
41 Frequency selection unit 42 Moisture content calculation unit 43 Moisture content calculation table storage unit 44 Electric conductivity estimation unit 45 Electrical conductivity estimation table storage unit A Main circuit B Printed circuit board b1 Comb tooth part b2 Comb tooth part b3 Body part D Connection cable E Resin mold J circuit P contact

Claims (2)

With the detection electrode
A signal supply means for supplying a detection input signal to the detection electrode,
The signal supply means was made to generate the detection input signal of the first frequency or the detection input signal of the second frequency different from the first frequency, and the detection input signal of the first frequency was supplied. An arithmetic control means for estimating the electrical conductivity of the object to be detected based on the detection signal of the detection electrode and the detection signal of the detection electrode due to the supply of the detection input signal of the second frequency. Equipped with
The second frequency is a frequency in which the amount of change in the detection error included in the detection signal with respect to the unit change of the electric conductivity of the detection object is larger than that of the first frequency.
The arithmetic control means is
The detection object is based on the detection signal of the detection electrode obtained by supplying the detection input signal of the first frequency without using the second frequency of the first frequency and the second frequency. To find the volume moisture content of
Based on the volume water content and the detection signal of the detection electrode due to the supply of the detection input signal of the second frequency, the electric conductivity of the detection object is obtained.
An electric conductivity estimation device characterized by this. A phase detection means for detecting the phase difference between the detection signal and the detection input signal, and
A reference voltage generating means that generates a DC voltage corresponding to the detection input signal as an internal reference voltage,
The electric conductivity estimation device according to claim 1 , further comprising an amplification means for differentially amplifying the voltage of the detection signal and the internal reference voltage.

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