JP2021173585A - Measurement device and measurement method - Google Patents

Abstract

To provide a measurement device and a measurement method that can perform accurate measurement with a simplified structure.SOLUTION: An aspect of the present invention is a measurement device including a detection unit including a pair of detection electrodes, a signal generation unit that generates a detection AC signal with a predetermined frequency and varies the frequency of the detection AC signal in a predetermined range, a phase shift unit that includes an LC circuit including a coil and a capacitor, is connected to the pair of detection electrodes, and shifts the phase of the detection AC signal in accordance with the frequency, a phase comparison unit that obtains the phase difference between the detection AC signal and the signal with the phase shifted by the phase shift unit, and a calculation unit that determines the frequency of the detection AC signal where the phase difference obtained by the phase comparison unit is 90° to be a reference frequency, obtains a resistance component between the pair of detection electrodes in accordance with the change quantity of the phase difference obtained by the phase comparison unit when the frequency of the detection AC signal is changed in a predetermined range with the reference frequency as a center, and obtains a capacity component between the pair of detection electrodes in accordance with the reference frequency.SELECTED DRAWING: Figure 1

Description

The present invention relates to a measuring device and a measuring method, and more particularly to a measuring device and a measuring method for detecting the electric conductivity and the amount of water of a measurement object such as soil.

As a device for measuring a physical quantity of an object to be measured, Patent Document 1 describes a fuel dielectric constant detection device that is not affected by changes in fuel conductivity or power supply voltage, has good accuracy, and is suitable for mass production. Is disclosed. Further, Patent Document 2 discloses an inductive proximity detector capable of detecting a ferrous metal object and a non-ferrous metal object in the same range by using a simple means and by highly reliable identification. Will be done.

Patent Document 3 discloses a fuel mixing ratio detecting device that accurately detects the alcohol mixing ratio in the mixed fuel regardless of the magnitude of the electric conductivity of the alcohol mixed fuel. Patent Document 4 discloses a magnetic permeability detecting device that stably performs an operation of detecting magnetic permeability such as toner concentration and improves the sensitivity of magnetic permeability detection.

Further, Patent Document 5 discloses a quantification method and a quantification device for a living body, which has a speed close to real time and easily detects a specific number of living bodies. Patent Document 6 discloses a concentration specifying method for specifying the concentration of an ionic solute contained in a solvent in a dispersion system in which an insoluble component insoluble in the solvent is dispersed in the solvent.

Japanese Unexamined Patent Publication No. 05-126778 Japanese Unexamined Patent Publication No. 07-294489 Japanese Unexamined Patent Publication No. 07-306172 Japanese Unexamined Patent Publication No. 2002-296240 JP-A-2007-071766 International release WO2011 / 158812

When an electric signal is used in a device for measuring electric conductivity or water content in a medium such as soil, a high frequency signal such as several megahertz (MHz) to 100 MHz or a microwave is often used. For this reason, it is necessary to complicate the circuit and take measures against high frequencies, which tends to increase the cost and increase the power consumption. In addition, when measuring electrical conductivity and water content, if the values affect each other, it becomes difficult to measure each value independently and accurately.

An object of the present invention is to provide a measuring device and a measuring method capable of performing accurate measurement while simplifying the configuration.

In order to solve the above problems, one aspect of the present invention is a detection unit having a pair of detection electrodes and a signal generation unit that generates a detection AC signal of a predetermined frequency and changes the frequency of the detection AC signal within a predetermined range. A phase shift unit that has an LC circuit with a coil and a capacitor, is connected to a pair of detection electrodes, and shifts the phase of the detection AC signal according to the frequency, a detection AC signal, and a phase shift unit. The detection AC signal is set in a predetermined range centered on the reference frequency, with the frequency of the detection AC signal at which the phase difference obtained by the phase comparison unit is 90 ° as the reference frequency and the phase comparison unit that obtains the phase difference from the signal. It is a measuring device provided with a calculation unit for obtaining a resistance component between a pair of detection electrodes according to the amount of change in the phase difference obtained by the phase comparison unit when the frequency of the above is changed.

According to such a configuration, at the reference frequency where the phase difference between the detection AC signal and the signal whose phase is shifted by the phase shift portion is 90 °, the phase difference is 90 regardless of the resistance component between the pair of detection electrodes. It becomes °. Further, the amount of change in the phase difference with respect to the frequency change in a predetermined range centered on the reference frequency changes according to the resistance component regardless of the capacitance component between the pair of detection electrodes. Therefore, the resistance component is obtained without being affected by the capacitance component between the pair of detection electrodes by the amount of change in the phase difference when the frequency of the detection AC signal is changed within a predetermined range centered on the reference frequency. Can be done.

The measuring device further includes a storage unit for storing electrical conductivity data indicating the relationship between the amount of change in the phase difference and the electrical conductivity of the object to be measured, and the calculation unit is the electrical conductivity data stored in the storage unit. The electrical conductivity corresponding to the phase difference may be output with reference to. As a result, electrical conductivity can be obtained without being affected by the capacitance component between the pair of detection electrodes.

One aspect of the present embodiment includes a detection unit having a pair of detection electrodes, a signal generation unit that generates a detection AC signal of a predetermined frequency and changes the frequency of the detection AC signal within a predetermined range, and a coil and a capacitor. A phase shift unit having an LC circuit, connected to a pair of detection electrodes, and shifting the phase of the detection AC signal according to the frequency, and a phase difference between the detection AC signal and the phase-shifted signal in the phase shift unit. A phase comparison unit that obtains It is a measuring device equipped with.

According to such a configuration, the reference frequency at which the phase difference between the detection AC signal and the phase-shifted signal at the phase shift portion is 90 ° depends on the capacitance component regardless of the resistance component between the pair of detection electrodes. Will shift. Therefore, by obtaining the reference frequency, the capacitance component can be obtained without being affected by the resistance component between the pair of detection electrodes.

The measuring device further includes a storage unit that stores water content data indicating the relationship between the reference frequency and the water content of the object to be measured, and the calculation unit obtains the water content data by referring to the water content data stored in the storage unit. The amount of water corresponding to the reference frequency may be output. As a result, the amount of water can be obtained without being affected by the resistance component between the pair of detection electrodes.

In the above measuring device, it is preferable that the signal generation unit supplies the detection AC signal to the phase shift unit while changing the frequency at 1 megahertz (MHz) or less. As described above, since the measurement can be performed by a signal of 1 MHz or less, the complexity of the circuit is suppressed, and excessive high frequency countermeasures are not required.

One aspect of the present invention is a method of measuring a physical quantity of a measurement object by bringing a pair of detection electrodes into contact with the measurement object, generating a detection AC signal having a predetermined frequency, and determining the frequency of the detection AC signal. A step of varying within a predetermined range, a step of shifting the phase of the detection AC signal according to the capacitance component and resistance component between the pair of detection electrodes, and the frequency, a detection AC signal, and a phase-shifted signal. A pair of detections according to the amount of change in the phase difference when the frequency of the detection AC signal is changed within a predetermined range centered on the reference frequency, with the frequency of the detection AC signal having a phase difference of 90 ° as the reference frequency. This is a measurement method including a step of obtaining a resistance component between electrodes.

According to such a configuration, at the reference frequency where the phase difference between the detection AC signal and the phase shift signal of the detection AC signal is 90 °, the phase difference is large regardless of the resistance component between the pair of detection electrodes. It becomes 90 °. Further, the amount of change in the phase difference with respect to the frequency change in a predetermined range centered on the reference frequency changes according to the resistance component regardless of the capacitance component between the pair of detection electrodes. Therefore, the resistance component is obtained without being affected by the capacitance component between the pair of detection electrodes by the amount of change in the phase difference when the frequency of the detection AC signal is changed within a predetermined range centered on the reference frequency. Can be done.

In the above measurement method, in the step of obtaining the resistance component, the electric conductivity corresponding to the phase difference may be output based on the relationship between the amount of change in the phase difference obtained in advance and the electric conductivity of the object to be measured. good. As a result, electrical conductivity can be obtained without being affected by the capacitance component between the pair of detection electrodes.

One aspect of the present invention is a method of measuring a physical quantity of a measurement object by bringing a pair of detection electrodes into contact with the measurement object, generating a detection AC signal having a predetermined frequency, and determining the frequency of the detection AC signal. A step of varying within a predetermined range, a step of shifting the phase of the detection AC signal according to the capacitance component and resistance component between the pair of detection electrodes, and the frequency, a detection AC signal, and a phase-shifted signal. This is a measurement method including a step of obtaining a capacitance component between a pair of detection electrodes according to a reference frequency, with the frequency of a detection AC signal having a phase difference of 90 ° as a reference frequency.

According to such a configuration, the reference frequency at which the phase difference between the detection AC signal and the phase shift signal of the detection AC signal is 90 ° becomes a capacitance component regardless of the resistance component between the pair of detection electrodes. It will shift accordingly. Therefore, by obtaining the reference frequency, the capacitance component can be obtained without being affected by the resistance component between the pair of detection electrodes.

In the above measuring method, in the step of obtaining the capacitance component, the water content corresponding to the reference frequency may be output based on the relationship between the reference frequency obtained in advance and the water content of the measurement object. As a result, the amount of water can be obtained without being affected by the resistance component between the pair of detection electrodes.

In the above measurement method, the frequency of the detection AC signal is preferably 1 MHz or less. As described above, since the measurement can be performed by a signal of 1 MHz or less, the complexity of the circuit is suppressed, and excessive high frequency countermeasures are not required.

According to the present invention, it is possible to provide a measuring device and a measuring method capable of performing accurate measurement while simplifying the configuration.

It is a circuit diagram which illustrates the structure of the measuring apparatus which concerns on this embodiment. (A) and (b) are diagrams illustrating a phase comparison unit using an analog multiplier. (A) and (b) are diagrams illustrating a phase comparison unit using a comparator. It is an equivalent circuit diagram explaining the measurement principle of the measuring apparatus which concerns on this embodiment. It is a figure which illustrates the frequency characteristic of a phase difference θ. It is a figure (enlarged view) which illustrates the frequency characteristic of a phase difference θ. It is a figure which shows the circuit example which converts the phase difference characteristic into a voltage (detection voltage) with a resistance component _{RL as a parameter.} It is a figure which shows the frequency characteristic of the detection voltage Vm with the _{resistance component RL} as a parameter in the circuit example shown in FIG. 7. It is a figure which shows the circuit example which converts the phase difference characteristic into a voltage (detection voltage) with the capacitance component C _{2 as a parameter.} Is a diagram showing a frequency characteristic of the detection voltage Vm in which the capacitive component C ₂ as a parameter in the circuit example shown in FIG. It is a figure which shows the frequency characteristic of the detection voltage Vm with the EC value of a solution as a parameter. It is a figure explaining the method of obtaining the EC value from the change of the detection voltage Vm. It is a figure which shows the relationship between Vx (Vm) and EC value. It is a figure which shows the relationship between the reference frequency fc and the water content. It is a figure which shows the other circuit example. It is a figure which shows the frequency characteristic of the output signal with the capacitance component C _{2 as a parameter.} It is a figure which shows the frequency characteristic of the output signal with the resistance component _{RL as a parameter.}

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same members are designated by the same reference numerals, and the description of the members once described will be omitted as appropriate.

(Measuring device configuration)
FIG. 1 is a circuit diagram illustrating the configuration of the measuring device according to the present embodiment.
As shown in FIG. 1, the measuring device 1 according to the present embodiment is a device for obtaining a resistance component and a capacitance component of the measurement object W. For example, when the object W to be measured is soil, the measuring device 1 is applied as a device for obtaining the electric conductivity (also referred to as an EC value) based on the resistance component and obtaining the water content from the volume component.

The measuring device 1 includes a detection unit 10 having a pair of detection electrodes 11 and 12, a signal generation unit 20 that generates a detection AC signal of a predetermined frequency, and a phase shift unit 30 that shifts the phase of the detection AC signal. A phase comparison unit 40 for obtaining a phase difference and a calculation unit 50 for obtaining a measurement result are provided. In the measuring device 1, the measurement object W is arranged between the pair of detection electrodes 11 and 12 of the detection unit 10, or the pair of detection electrodes 11 and 12 are inserted into the measurement object W to measure the object. Obtain the resistance component and capacitance component of W.

The pair of detection electrodes 11 and 12 of the detection unit 10 may be parallel flat plates made of a conductive material, or may be parallel bars (round bars, prism bars, etc.). As an example, in the present embodiment, stainless steel plates having a length of 20 mm (mm), a width of 2 mm, a thickness of 2 mm, and a distance between electrodes of 10 mm are used as the detection electrodes 11 and 12.
The detection unit 10 may be provided with a thermometer 15. The temperature measured by the thermometer 15 is sent to the calculation unit 50 and used for correction of calculation and the like.

The signal generation unit 20 generates a detection AC signal having a predetermined frequency, and outputs the detection AC signal with a variable frequency within a predetermined range. A control signal is sent from the control unit 60 to the signal generation unit 20, and the frequency of the detection AC signal generated by the control signal is changed.

In the present embodiment, the signal generation unit 20 generates an AC signal for detection having a frequency of 1 MHz or less and supplies it to the phase shift unit 30 in the subsequent stage. The variable range of frequency is, for example, several tens of kHz to several hundreds of kHz. In the measuring device 1 according to the present embodiment, since the measurement is performed by a relatively low frequency signal of 1 MHz or less as the detection AC signal, the complexity of the circuit is suppressed and excessive high frequency countermeasures are not required.

The phase shift unit 30 has an LC circuit 310 with a coil 311 and a capacitor 312. The phase shift unit 30 is connected to the pair of detection electrodes 11 and 12 and shifts the phase of the detection AC signal according to the frequency. In the example shown in FIG. 1, the detection electrode 11 is connected to the connection point between the coil 311 and the capacitor 312 of the LC circuit 310, and the detection electrode 12 is connected to the ground side of the capacitor 312. As a result, in the phase shift unit 30, the resistance component _RL and the capacitance component C ₂ between the pair of detection electrodes 11 and 12 contribute to the characteristics of the LC circuit 310, and the phase of the detection AC signal is changed to the resistance component _RL and It is shifted according to the capacitance component C _2.

The phase comparison unit 40 obtains the phase difference θ between the detection AC signal and the signal phase-shifted by the phase shift unit 30. The phase comparison unit 40 compares the input signal (detection AC signal) of the phase shift unit 30 with the output signal of the phase shift unit 30, and outputs a phase difference signal based on the phase difference θ. That is, the phase comparison unit 40 obtains the phase difference θ by comparing the detection AC signal with the phase-shifted signal in the phase shift unit 30 with reference to the detection AC signal.
In the following description, when the term "phase difference θ" is used, it means the phase difference between the detection AC signal and the signal whose phase is shifted by the phase shift unit 30.

Here, a configuration example of the phase comparison unit 40 will be described.
2 (a) and 2 (b) are diagrams illustrating a phase comparison unit using an analog multiplier.
As shown in FIG. 2A, the phase comparison unit 40 includes a multiplier 41 that multiplies the input signal (detection AC signal) of the phase shift unit 30 and the output signal of the phase shift unit 30, and the multiplier 41. It has an integrator circuit 42 that integrates the output of. Thereby, the detection voltage Vm based on the phase difference θ can be obtained. FIG. 2B shows the relationship between the detection voltage Vm by the phase comparison unit 40 shown in FIG. 2A and the phase difference θ.

3A and 3B are diagrams illustrating a phase comparison unit using a comparator.
As shown in FIG. 3A, the phase comparison unit 40 includes a first comparator 45, a second comparator 46, a logical operation unit 47, and an integration circuit 42.

The input signal (detection AC signal) of the phase shift unit 30 is input to the first comparator 45, and the output signal of the phase shift unit 30 is input to the second comparator 46. The reference signals of the first comparator 45 and the second comparator 46 are common.

The outputs of the first comparator 45 and the second comparator 46 are input to the logical operation unit 47. The logical operation unit 47 calculates the exclusive OR. By integrating the output of the logical operation unit 47 with the integration circuit 42, the detection voltage Vm based on the phase difference θ can be obtained. FIG. 3B shows the relationship between the detection voltage Vm by the phase comparison unit 40 shown in FIG. 3A and the phase difference θ. Here, the detection voltage at which the phase difference θ is 90 ° is defined as Vm (90).

As the phase comparison unit 40, one using the multiplier 41 shown in FIG. 2, one using the comparators (first comparator 45, second comparator 46) shown in FIG. 3, and one using a circuit configuration other than these. Either of them may be used, but in the present embodiment, the phase comparison unit 40 using the comparator shown in FIG. 3 will be described as an example.

The calculation unit 50 uses the reference frequency fc as the frequency of the detection AC signal at which the phase difference θ obtained by the phase comparison unit 40 is 90 °, and uses this reference frequency fc to resist between the pair of detection electrodes 11 and 12. Calculations are performed to obtain the _{component RL} and the volume component C _2.

_{Here, the resistance component RL} between the pair of detection electrodes 11 and 12 is the phase difference obtained by the phase comparison unit 40 when the frequency of the detection AC signal is changed within a predetermined range centered on the reference frequency fc. It is obtained according to the amount of change in θ.
_{Further, the capacitance component C 2} between the pair of detection electrodes 11 and 12 is obtained according to the reference frequency fc.

In the measuring device 1 according to the present embodiment, the pair of detection electrodes 11 and 12 are used by using the reference frequency fc in which the phase difference θ between the detection AC signal and the signal phase-shifted by the phase shift unit 30 is 90 °. The resistance component _RL and the capacitance component C ₂ between them can be measured independently without being affected by each other.

Further, the measuring device 1 may be provided with a storage unit 70. The storage unit 70 may store electrical conductivity data indicating the relationship between the amount of change in the phase difference θ and the electrical conductivity of the object W to be measured. In this case, the calculation unit 50 refers to the electric conductivity data stored in the storage unit 70 and outputs the electric conductivity corresponding to the phase difference θ. As a result, electrical conductivity can be obtained without being affected by the capacitance component between the pair of electrodes.

Further, the storage unit 70 may store water content data indicating the relationship between the reference frequency fc and the water content of the measurement object W. In this case, the calculation unit 50 may output the water content corresponding to the obtained reference frequency fc by referring to the water content data stored in the storage unit 70. As a result, the amount of water can be obtained without being affected by the resistance component between the pair of electrodes.

(Measurement principle)
Next, the measurement principle of the measuring device 1 according to the present embodiment will be described.
FIG. 4 is an equivalent circuit diagram illustrating the measurement principle of the measuring device according to the present embodiment.
In FIG. 4, the voltage of the detection AC signal generated by the signal generation unit 20 is e _S , the internal resistance of the signal generation unit 20 is _RS , the reactor of the coil 311 of the LC circuit 310 is L, and the capacitance of the capacitor 312 is C _1. , _C 2, the _{R L,} capacitance component and the resistance component between the voltage of the signal input to the LC circuit 310 _e i, the voltage of the output of the LC circuit 310 _{e o,} the pair of sensing electrodes 11, 12 C = Let C ₁ + C ₂ and the angular frequency of the detection AC signal generated by the signal generation unit 20 be ω. The resistance component _RL and the capacitance component C ₂ include the resistance value and capacitance value of the measurement object W between the pair of detection electrodes 11 and 12, and the unique resistance based on the material and structure of the pair of detection electrodes 11 and 12. Contains values and unique capacity values.
Each voltage on the input side and the output side of the LC circuit 310 is represented by the following equations (1) and (2).

From equations (1) and (2), the transfer function is represented by the following equation (3).

If the real part and the imaginary part of this transfer function are separated and the real part is A and the imaginary part is B, the following equations (4) and (5) are obtained.

When the phase difference θ is calculated from the real part A and the imaginary part B, the following equation (6) is obtained.

Here, since ω = 2πf, the graphs of the input / output phase difference θ of the LC circuit 310 as frequency characteristics are as shown in FIGS. 5 and 6. FIG. 6 is an enlarged view of FIG. As an example, the circuit constants adopted here are L = 100 μH and C = 470 pF. In FIGS. 5 and 6, the parameter of the graph is the resistance component _RL .

As shown in FIGS. 5 and 6, it can be seen that the frequency characteristic of the phase difference θ shows a constant phase difference θ at a constant frequency, although the change characteristic of the phase difference θ changes depending on _{the resistance component RL.} This constant phase difference θ is 90 °. The frequency at which the phase difference θ becomes 90 ° is referred to as the reference frequency fc.

_{The measuring device 1 according to the present embodiment measures the resistance component RL} and the capacitance component C ₂ between the pair of detection electrodes 11 and 12 by utilizing the frequency characteristic of the phase difference θ as described above.

First, the frequency characteristics of _{the resistance component RL} between the pair of detection electrodes 11 and 12 will be described.
FIG. 7 is a diagram showing an example of a circuit that converts a phase difference characteristic into a voltage (detection voltage) with _{the resistance component RL as a parameter.} FIG. 7 is a circuit example using the first comparator 45, the second comparator 46, the logical operation unit 47, and the integrator circuit 42. Let Vm be the detection voltage output from this circuit.

FIG. 8 is a diagram showing the frequency characteristics of the detection voltage Vm with the _{resistance component RL} as a parameter in the circuit example shown in FIG. 7. Here, no load means that the pair of detection electrodes 11 and 12 are open in the air.
In the graph shown in FIG. 8, a cross point having a constant phase difference θ occurs at a constant frequency regardless _{of the resistance component RL.} The frequency of this cross point is the reference frequency fc, and the detection voltage Vm at the reference frequency fc is the detection voltage Vm (90) at which the phase difference θ is 90 °.

On the other hand, _{the change in the resistance component RL} appears as a frequency characteristic (degree of change) centered on the cross point. The frequency characteristics of any of the resistance components _RL are point-symmetrical characteristics centered on the cross point.

Next, the frequency characteristics of _{the capacitance component C 2} between the pair of detection electrodes 11 and 12 will be described.
FIG. 9 is a diagram showing an example of a circuit that converts a phase difference characteristic into a voltage (detection voltage) using _{the capacitance component C 2 as a parameter.} The circuit example shown in FIG. 9 is the same as the circuit example shown in FIG. 7, but _{only the capacitance component C 2} between the pair of detection electrodes 11 and 12 is used as a parameter.

FIG. 10 is a diagram showing the frequency characteristics of the detection voltage Vm with the _{capacitance component C 2 as a parameter in the circuit example shown in FIG.}
In the graph shown in FIG. 10, the frequency characteristics of the detection voltage Vm although shifted in accordance with the capacitance component C _2, the frequency characteristics (degree of change) appears substantially equal.

Next, using the circuit examples shown in FIGS. 7 and 9, the frequency characteristics of the detection voltage Vm were measured using the measurement object W as a solution. As an example, as a pair of detection electrodes 11 and 12, stainless steel plates having a length of 20 mm (mm), a width of 2 mm, a thickness of 2 mm, and a distance between electrodes of 10 mm were used. The measurement result is shown in FIG. FIG. 11 is a diagram showing the frequency characteristics of the detection voltage Vm with the EC value of the solution as a parameter.

The reference voltage of the detection voltage Vm shown in FIG. 11 is a voltage at which the phase difference θ is 90 °. The EC values of the solution are 0.002 milliemens (mS / cm), 0.1 mS / cm, 0.5 mS / cm, 1 mS / cm, 3.5 mS / cm, 7 mS / cm and no load. The no-load state is a state in which the pair of detection electrodes 11 and 12 are opened in the air. Therefore, it can be said that the frequency characteristic of the detection voltage Vm in the case of no load is a characteristic in a state where the EC value is very low (about 0.002 mS / cm) and the water content is very low.

Since the solution is the object W to be measured, the water content is 100% except when there is no load. In the measurement results other than when there is no load, the slope of the change in the detection voltage Vm differs depending on the EC value, centering on the reference frequency fc, which is a frequency indicating the reference voltage. Further, in the frequency characteristics of each EC value, the change of the detection voltage Vm centered on the reference frequency fc is substantially point-symmetrical about the intersection of the reference frequency fc and the reference voltage.

On the other hand, when the frequency characteristics of the detection voltage Vm are compared between the case where the EC value is 0.002 mS / cm and the case where there is no load, the slope of the change in the detection voltage Vm is almost the same, but the frequency that becomes the reference voltage (that is, that is). The frequency at which the phase difference θ is 90 °) is shifted. From this, it can be seen that the EC value is not affected by the amount of water and is determined by the slope of the change in the detection voltage Vm.

(EC value)
FIG. 12 is a diagram illustrating a method of obtaining an EC value from a change in the detection voltage Vm.
FIG. 12 shows an enlarged view centered on the reference frequency fc of FIG.
As described above, the EC value is determined according to the slope of the change in the detection voltage Vm. Further, the change of the detection voltage Vm is substantially point-symmetrical about the intersection of the reference frequency fc and the reference voltage. Therefore, the EC value can be obtained by setting a predetermined frequency range Wf centering on the reference frequency fc and obtaining the difference between the maximum detection voltage V2 and the minimum detection voltage V1 in that range.

In the example shown in FIG. 12, the reference frequency fc is set to 710 MHz, and the frequency range Wf is set to 60 kHz as an example. Therefore, the maximum value of the frequency in the frequency range Wf is 740 kHz, and the minimum value is 680 kHz. Then, the detection voltage V2 at the maximum frequency value of 740 kHz and the detection voltage V1 at the minimum frequency value of 680 kHz are obtained, and V2-V1 is calculated. Here, Vx (Vm) = V2-V1.

The value of Vx (Vm) is equivalent to the slope of the change of the detection voltage Vm, and is determined by the frequency characteristic according to the EC value. Therefore, the EC value can be obtained from the correlation between the Vx (Vm) value and the EC value.

FIG. 13 is a diagram showing the relationship between Vx (Vm) and the EC value.
The relationship shown in FIG. 13 is that the frequency range Wf is swept in advance using solutions of various EC values to obtain the detection voltages V1 and V2, Vx (Vm) is obtained, and the correspondence between the EC value and Vx (Vm) is obtained. It is a plot. Interpolation is performed between plots by an appropriate method. The relationship shown in FIG. 13 shows the conversion characteristics between Vx (Vm) and the EC value.

The measuring device 1 according to the present embodiment uses the conversion characteristics of Vx (Vm) and the EC value shown in FIG. 13 as electrical conductivity data. The electrical conductivity data is stored in, for example, the storage unit 70. The measuring device 1 measures the detection voltages V1 and V2 of the object W to be measured, obtains Vx (Vm) by the calculation unit 50, and outputs an EC value from Vx (Vm) with reference to the electrical conductivity data. As a result, the EC value can be obtained without being affected by _{the capacitance component C 2} between the pair of detection electrodes 11 and 12.

(amount of water)
FIG. 14 is a diagram showing the relationship between the reference frequency fc and the amount of water.
The relationship shown in FIG. 14 is obtained by obtaining the relationship between the reference frequency fc and the water content (%) in advance using objects having various water content. The measuring device 1 according to the present embodiment uses the relationship between the reference frequency fc and the water content (%) shown in FIG. 14 as the water content data. The water content data is stored in, for example, the storage unit 70. The measuring device 1 uses the calculation unit 50 to obtain a frequency (reference frequency fc) that is a detection voltage (reference voltage) at which the phase difference θ is 90 ° from the detection voltage Vm of the object W to be measured. The calculation unit 50 outputs the water content (%) from the reference frequency fc with reference to the water content data. As a result, the amount of water can be obtained without being affected by _{the resistance component RL} between the pair of detection electrodes 11 and 12.

(Other circuit examples)
FIG. 15 is a diagram showing another circuit example.
This circuit example has a configuration in which the connection between the coil 311 and the capacitor 312 of the LC circuit 310 is replaced with respect to the circuit example described above. For convenience of explanation, a circuit in which the connection between the coil 311 and the capacitor 312 of the LC circuit 310 is exchanged is referred to as a CL circuit 320. Even with the configuration using the CL circuit 320, the same result as the configuration using the LC circuit 310 described above can be obtained.

Each voltage on the input side and the output side of the CL circuit 320 is represented by the following equations (7) and (8).

From equations (7) and (8), the transfer function is represented by the following equation (9).

When the real part and the imaginary part of this transfer function are separated and the real part is A and the imaginary part is B, the following equations (10) and (11) are obtained.

When the phase difference θ is calculated from the real part A and the imaginary part B, the following equation (12) is obtained.

この結果は、ＬＣ回路３１０を用いた構成と全く同じである。したがって、位相差検出特性として周波数特性も全く同じ結果を得ることができる。

This result is exactly the same as the configuration using the LC circuit 310. Therefore, it is possible to obtain exactly the same result as the frequency characteristic as the phase difference detection characteristic.

(Difference between this embodiment and the resonant circuit)
Here, a resonance circuit (so-called tank circuit) is generally used as a circuit configuration for measuring a physical quantity of an object by utilizing a change in the phase of an AC signal. Although the measuring device 1 according to the present embodiment uses a reactance element (inductance and capacitance), it is completely different in measurement principle from a general resonant circuit.

For example, when resonance is used in the equivalent circuit diagram of the measuring device 1 shown in FIG. 4, the frequency characteristics are as shown in FIG. In FIG. 16, the voltage of the output signal eo is measured when the voltage of the input signal is kept constant and the frequency is swept from 500 kHz to 1 MHz. The circuit constants are resistance components _RL = 100 kΩ, L = 100 μH, and C ₁ = 470 pF.

In FIG. 16, the parameter is the volume component C ₂ . When the capacitance component C ₂ is 0 pF, the water content is zero, and the peak frequency can be read by the series resonance between _{L and C 1.} It can be seen that the capacitance component C ₂ increases as the water content increases, and the peak frequency shifts in the lower direction. _{Therefore, the capacitance component C 2} can be found by measuring the peak frequency, and the water content can be calculated from the capacitance component C _2. However, the voltage of the output signal eo decreases as the capacitance component C _{2 increases.}

FIG. 17 is a diagram showing the frequency characteristics of the output signal with the _{resistance component RL as a parameter.}
In FIG. 17, the voltage of the output signal eo when the voltage of the input signal is kept constant and the frequency is swept from 500 kHz to 1 MHz is measured. The circuit multiplier is L _{= 100 μH, C 1} = 470 pF, and capacitance component C _{2 = 0 pF.} The volume component C ₂ = 0 pF assumes a state in which the amount of water does not exist.

In FIG. 17, the parameter is the resistance component _RL . From this frequency characteristic, since the voltage of the peak of the output signal eo is reduced by a decrease in the resistance component R _L, it is possible to obtain the resistance component R _L by reading the voltage of the peak. However, _{due to the decrease in the resistance component RL} , the voltage of the output signal eo and the waveform become dull. In this example, when the resistance component _RL becomes 1 kΩ or less, it becomes difficult to read the peak voltage due to the blunting of the waveform. When the resistance component _RL is 100Ω or less, there is no peak voltage.

Further, in the frequency characteristics shown in FIG. 17, it can be seen that the peak frequency shifts in the lower direction even though the _{capacitance component C 2 is fixed.} This phenomenon is because the _{resonance frequency due to the resonance circuit does not change much in the range where the resistance component RL} is sufficiently high, but when the resistance component _RL becomes low, it becomes dominant as an impedance network and series resonance does not hold.
Since the resistance component _RL of 1 kΩ or less corresponds to a value of 0.1 mS / cm to 0.5 mS / cm or more as an EC value, the water content cannot be measured or accurate measurement is performed in a situation where the EC value is high. It is thought that it cannot be done.

On the other hand, the measuring device 1 according to the present embodiment is a method of detecting the input / output phase difference θ of the LC circuit 310 (or CL circuit 320). As the phase difference θ is 90 ° and becomes frequency reference frequency fc, the slope of the detection voltage Vm at a predetermined frequency range around the reference frequency fc is unaffected by the capacitance component C _2, also the reference frequency fc resistance Utilizing the fact that the component _RL is not affected, it is possible to accurately measure the water content and the EC value without being affected by each other.

(Measuring method)
The measuring method according to the present embodiment is a method of measuring the physical quantity of the measurement target W by bringing the pair of detection electrodes 11 and 12 into contact with the measurement target W, and has the following steps.

(A1) A step of generating a detection AC signal of a predetermined frequency and changing the frequency of the detection AC signal within a predetermined range (A2) A capacitance component C ₂ and a resistance component _RL between the pair of detection electrodes 11 and 12. Further, a step of shifting the phase of the detection AC signal according to the frequency (A3) The frequency of the detection AC signal at which the phase difference between the detection AC signal and the phase-shifted signal is 90 ° is set as the reference frequency fc. Step of obtaining the resistance component between the pair of detection electrodes 11 and 12 according to the amount of change in the phase difference when the frequency of the detection AC signal is changed in a predetermined range centered on the reference frequency fc. By having (A3), the resistance component _RL can be obtained _{without being affected by the capacitance component C 2} between the pair of detection electrodes 11 and 12.

Further, in the above step (A3), the electric conductivity corresponding to the phase difference θ may be output based on the relationship between the amount of change in the phase difference θ obtained in advance and the electric conductivity of the object W to be measured. good. As a result, the electrical conductivity of the object to be measured W can be obtained without being affected by _{the capacitance component C 2} between the pair of detection electrodes 11 and 12.

In addition, the measurement method according to this embodiment has the following steps.
(B1) A step of generating a detection AC signal of a predetermined frequency and changing the frequency of the detection AC signal within a predetermined range (B2) A capacitance component C ₂ and a resistance component _RL between the pair of detection electrodes 11 and 12. Further, the step of shifting the phase of the detection AC signal according to the frequency (B3) The frequency of the detection AC signal at which the phase difference between the detection AC signal and the phase-shifted signal is 90 ° is set as the reference frequency fc. _{Step of obtaining the capacitance component C 2} between the pair of detection electrodes according to the reference frequency fc By having the above steps (B1) to (B3), the resistance component _RL between the pair of detection electrodes 11 and 12 is affected. The volume component C ₂ can be obtained without receiving it.

Further, in the above step (B3), the water content corresponding to the reference frequency fc may be output based on the relationship between the reference frequency fc obtained in advance and the water content of the measurement object W. As a result, the amount of water can be obtained without being affected by _{the resistance component RL} between the pair of detection electrodes 11 and 12.

In the above measurement method, the frequency of the detection AC signal is preferably 1 MHz or less. As described above, since the measurement can be performed by a signal of 1 MHz or less, the complexity of the circuit is suppressed, and excessive high frequency countermeasures are not required.

As described above, according to the measuring device 1 and the measuring method according to the embodiment, it is possible to provide a measuring device and a measuring method capable of performing accurate measurement while simplifying the configuration.

Although the present embodiment and its modifications have been described above, the present invention is not limited to these examples. For example, the circuit configuration of the phase shift unit 30 and the circuit configurations of other parts are not limited to the configurations described above as long as they have the same functions. In addition, those skilled in the art appropriately adding, deleting, or changing the design of each of the above-described embodiments or application examples thereof, and those in which the features of each embodiment are appropriately combined are also included in the present invention. As long as it has a gist, it is included in the scope of the present invention.

The present invention can be applied to foods (bread dough, etc.), clay, concrete, skin, paper (copier), etc., as well as soil, as objects to be measured. Further, the present invention can be applied to the measuring device 1 as a soil moisture sensor used by burying it in the soil in the field of sediment-related disasters as well as in the field of agriculture.

1 ... Measuring device 10 ... Detection units 11, 12 ... Detection electrode 20 ... Signal generation unit 30 ... Phase shift unit 40 ... Phase comparison unit 41 ... Multiplier 42 ... Integrator circuit 45 ... First comparator 46 ... Second comparator 47 ... Logic Calculation unit 50 ... Calculation unit 60 ... Control unit 70 ... Storage unit 310 ... LC circuit 311 ... Coil 312 ... Capacitor 320 ... CL circuit A ... Real part B ... Imaginary part C ₁ ... Capacitance C ₂ ... Capacitance component e _S , e _i , E _o ... Voltage L ... Reactance _RL ... Resistance component _RS ... Internal resistance V1, V2, Vm ... Detection voltage W ... Measurement target Wf ... Frequency range fc ... Reference frequency θ ... Phase difference

Claims (10)

A detection unit having a pair of detection electrodes and
A signal generator that generates a detection AC signal of a predetermined frequency and changes the frequency of the detection AC signal within a predetermined range.
A phase shift unit having an LC circuit consisting of a coil and a capacitor, connected to the pair of detection electrodes, and shifting the phase of the detection AC signal according to the frequency.
A phase comparison unit for obtaining the phase difference between the detection AC signal and the signal phase-shifted by the phase shift unit.
When the frequency of the detection AC signal is changed within a predetermined range centered on the reference frequency with the frequency of the detection AC signal at which the phase difference is 90 ° obtained by the phase comparison unit as a reference frequency. A calculation unit that obtains a resistance component between the pair of detection electrodes according to the amount of change in the phase difference obtained by the phase comparison unit, and a calculation unit.
A measuring device equipped with. Further, a storage unit for storing electrical conductivity data indicating the relationship between the amount of change in the phase difference and the electrical conductivity of the object to be measured is provided.
The measuring device according to claim 1, wherein the calculation unit refers to the electric conductivity data stored in the storage unit and outputs the electric conductivity corresponding to the phase difference. A detection unit having a pair of detection electrodes and
A signal generator that generates a detection AC signal of a predetermined frequency and changes the frequency of the detection AC signal within a predetermined range.
A phase shift unit having an LC circuit consisting of a coil and a capacitor, connected to the pair of detection electrodes, and shifting the phase of the detection AC signal according to the frequency.
A phase comparison unit for obtaining the phase difference between the detection AC signal and the signal phase-shifted by the phase shift unit.
A calculation unit for obtaining a capacitance component between the pair of detection electrodes according to the reference frequency, with the frequency of the detection AC signal having a phase difference of 90 ° obtained by the phase comparison unit as a reference frequency.
A measuring device equipped with. A storage unit for storing water content data indicating the relationship between the reference frequency and the water content of the object to be measured is further provided.
The measuring device according to claim 3, wherein the calculation unit outputs the water content corresponding to the obtained reference frequency with reference to the water content data stored in the storage unit. The measuring device according to any one of claims 1 to 4, wherein the signal generation unit supplies the detection AC signal to the phase shift unit while changing the frequency at 1 MHz or less. A method of measuring a physical quantity of a measurement object by bringing a pair of detection electrodes into contact with the measurement object.
A process of generating a detection AC signal of a predetermined frequency and changing the frequency of the detection AC signal within a predetermined range.
A step of shifting the phase of the detection AC signal according to the capacitance component and the resistance component between the pair of detection electrodes and the frequency, and
The detection AC signal has a phase difference of 90 ° between the detection AC signal and the phase-shifted signal, and the detection AC signal has a frequency within a predetermined range centered on the reference frequency. A step of obtaining a resistance component between the pair of detection electrodes according to the amount of change in the phase difference when the frequency is changed, and a step of obtaining the resistance component between the pair of detection electrodes.
Measurement method with. The step of obtaining the resistance component includes outputting the electric conductivity corresponding to the phase difference based on the relationship between the amount of change in the phase difference obtained in advance and the electric conductivity of the object to be measured. Item 6. The measuring method according to Item 6. A method of measuring a physical quantity of a measurement object by bringing a pair of detection electrodes into contact with the measurement object.
A process of generating a detection AC signal of a predetermined frequency and changing the frequency of the detection AC signal within a predetermined range.
A step of shifting the phase of the detection AC signal according to the capacitance component and the resistance component between the pair of detection electrodes and the frequency, and
The capacitance component between the pair of detection electrodes is set according to the reference frequency, with the frequency of the detection AC signal at which the phase difference between the detection AC signal and the phase-shifted signal is 90 ° as a reference frequency. The desired process and
Measurement method with. The measurement according to claim 8, wherein the step of obtaining the volume component includes outputting the water content corresponding to the reference frequency based on the relationship between the reference frequency and the water content of the measurement object obtained in advance. Method. The measuring method according to any one of claims 6 to 9, wherein the frequency of the detection AC signal is 1 MHz or less.

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