JP7215303B2 - measuring device - Google Patents

Description

The present invention relates to measuring devices.

Patent Document 1 below discloses a method for specifying the amount of solvent in a dispersion system in which an insoluble component is dispersed in a solvent. In this method of specifying the amount of solvent, an input electric signal (AC signal) is applied to one of a pair of electrodes in contact with the dispersion system, and the phase difference between the output electric signal obtained from the other of the pair of electrodes and the input electric signal is It measures the concentration of the solute and the electrical conductivity of the dispersed system based on the

Japanese Patent No. 5871237

By the way, in the background art described above, the concentration of a solute and the electrical conductivity of a dispersion system are measured as target physical quantities. must be optimized for each target physical quantity.

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a measuring apparatus capable of measuring a plurality of target physical quantities with higher accuracy.

In order to achieve the above object, the present invention provides a first solution for a measuring device, which includes a detection electrode that contacts an object to be measured, an oscillator that oscillates a predetermined measurement signal, and a plurality of physical quantities to be measured. a plurality of input circuits provided correspondingly for supplying the measurement signals to the detection electrodes; a plurality of detection processing circuits for applying the and control means for inputting a signal for measurement to the detection electrodes.

According to the present invention, as a second solution to the measuring apparatus, in the first solution, the oscillator oscillates the measurement signal with a different frequency for each input circuit.

In the present invention, as a third solution to the measuring apparatus, in the second solution, the detection processing circuit generates the processed detection signal indicating the phase difference between the measurement signal and the detection signal. and outputs it to the computing means.

In the present invention, as a fourth solution to the measuring device, in any one of the first to third solutions, the input circuit transmits the measurement signal to the detection electrode via a predetermined resistor. and the output impedance becomes high when not selected.

In the present invention, as a fifth solution related to the measuring device, in any one of the first to fourth solutions, the plurality of physical quantities to be measured are moisture and electrical conductivity of the measurement object. adopt the means.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the measuring apparatus which can measure several object physical quantities with high precision.

1 is a block diagram showing the functional configuration of a measuring device according to one embodiment of the present invention; FIG. It is a schematic diagram showing the structure of the electrode unit of the measuring device according to one embodiment of the present invention.

An embodiment of the present invention will be described below with reference to the drawings.
The measuring device according to this embodiment is a device for measuring the water content and electrical conductivity of a measurement object. As shown in FIG. 1, this measuring apparatus includes an oscillator 1, a pair of buffer circuits 2A and 2B, a pair of resistors 3A and 3B, a pair of detection electrodes 4X and 4Y, a pair of buffer circuits 5A and 5B, and a pair of detection electrodes. 6A, 6B, a pair of buffer circuits 7A, 7B, a pair of low-pass filters 8A, 8B, a pair of low-pass filters 9A, 9B, a pair of differential amplifiers 10A, 10B, and an MPU 11.

Here, the object to be measured is, for example, soil. Moreover, the water content and electrical conductivity correspond to a plurality of physical quantities to be measured in the present invention. Furthermore, among the above-mentioned components, the components containing "A" in the code are components that contribute only to the measurement of the water content, and the components containing "B" in the code are electrical conductivity It is a component that contributes only to the measurement of

That is, a first buffer circuit 2A, a first resistor 3A, a first buffer circuit 5A, a first detector 6A, a third buffer circuit 7A, a first low-pass filter 8A, and a third low-pass filter 9A. and the first differential amplifier 10A are components related only to water content measurement. Second buffer circuit 2B, second resistor 3B, second buffer circuit 5B, second detector 6B, fourth buffer circuit 7B, second low-pass filter 8B, fourth low-pass filter 9B and the second differential amplifier 10B are components related only to the measurement of electrical conductivity.

The oscillator 1 is of variable frequency type and oscillates two square waves with different repetition frequencies. That is, this oscillator 1 oscillates a square wave with a first repetition frequency f1 and a square wave with a second repetition frequency f2. Such an oscillator 1 outputs a square wave with a first repetition frequency f1 as a first measurement signal to the first buffer circuit 2A, and outputs a square wave with a second repetition frequency f2 as a second measurement signal. It is output as a signal to the second buffer circuit 2A.

Such an oscillator 1 operates, for example, on a positive power supply of +3.3V, so that the first and second measuring signals are square waves with a low potential of 0V and a high potential of +3.3V. Such an oscillator 1 outputs a square wave with a first repetition frequency f1 to the third buffer circuit 5A and the fifth buffer circuit 7A, and outputs a square wave with a second repetition frequency f2 to the fourth buffer circuit. 5B and the sixth buffer circuit 7B.

The first measurement signal is a measurement signal for water content measurement, and the second measurement signal is a measurement signal for electrical conductivity measurement. These first and second measurement signals are square waves with a duty ratio of 50%, and the first and second repetition frequencies f1 and f2 are on the order of several MHz to several tens of MHz, for example. Note that the attribute values of the first and second measurement signals are appropriately set according to the properties of the object to be measured.

The first and second buffer circuits 2A and 2B are current amplifier circuits for current-amplifying the first and second measurement signals, respectively, and the first and second measurement signals after current amplification are transferred to a pair of buffer circuits 2A and 2B. Output to resistors 3A and 3B. That is, the first buffer circuit 2A current-amplifies the first measurement signal and outputs the current-amplified first measurement signal to one end of the first resistor 3A. On the other hand, the second buffer circuit 2B current-amplifies the second measurement signal and outputs the current-amplified second measurement signal to one end of the second resistor 3B.

Further, such first and second buffer circuits 2A and 2B function alternatively based on a switching signal input from the MPU 11. FIG. That is, one of the first and second buffer circuits 2A and 2B selected by the switching signal outputs the measurement signal to the first detection electrode 4X. When selected by the switching signal, the first buffer circuit 2A outputs the first measurement signal to the first detection electrode 4X, and when selected by the switching signal, the second buffer circuit 2B outputs the second measurement signal. is output to the first detection electrode 4X.

Also, such first and second buffer circuits 2A and 2B are three-state buffers whose output impedance is high (for example, several hundred MΩ) when not selected. That is, the first and second buffer circuits 2A and 2B output the measurement signal to the first detection electrode 4X with a relatively low output impedance when selected, but when selected, the output impedance becomes extremely high, and the output impedance becomes extremely high. Stop outputting the signal.

The first and second resistors 3A and 3B are two-terminal electronic elements each having a predetermined resistance value. Of the first and second resistors 3A and 3B, the first resistor 3A has a first resistance value, one end of which is connected to the output end of the first buffer circuit 2A, and the other end of which is the first resistor. It is connected to one detection electrode 4X. The second resistor 3B has a second resistance value, one end is connected to the output end of the second buffer circuit 2B, and the other end is connected to the second detection electrode 4Y.

Such first and second resistors 3A and 3B constitute loads of the first and second buffer circuits 2A and 2B together with the first and second detection electrodes 4X and 4Y. That is, the first resistor 3A constitutes a load of the first buffer circuit 2A together with the first detection electrode 4X and the second detection electrode 4Y, and the second resistor 3B is connected to the first detection electrode 4X. and the second detection electrode 4Y constitute the load of the second buffer circuit 2B.

Such a first resistor 3A is a component that governs the detection dynamic range when detecting the moisture content of the object to be measured. is set appropriately. In addition, the second resistor 3B is a component that governs the detection dynamic range when detecting the electrical conductivity of the object to be measured, and the second resistance value maximizes the electrical conductivity detection dynamic range. is set to

Here, the first and second buffer circuits 2A, 2B and the first and second resistors 3A, 3B constitute an input circuit of the present invention. That is, the first buffer circuit 2A and the first resistor 3A are provided corresponding to the water content among the plurality of physical quantities to be measured, and supply the first measurement signal to the first detection electrode 4X. 1 input circuit. On the other hand, the second buffer circuit 2B and the second resistor 3B are provided corresponding to electrical conductivity among the plurality of physical quantities to be measured, and supply the second measurement signal to the first detection electrode 4X. It constitutes a second input circuit.

The first and second detection electrodes 4X and 4Y are conductive members that come into contact with the object to be measured. These first and second detection electrodes 4X and 4Y are arranged facing each other with a predetermined distance therebetween. constitutes a capacitor C of

That is, as shown in FIG. 2, the first and second detection electrodes 4X and 4Y are configured as an electrode module M set in a facing state by a predetermined support member S, and are embedded in the object to be measured. ing. The first and 2nth detection electrodes 4X and 4Y constitute a capacitor C having an electrostatic capacity that changes according to the water content or electrical conductivity of the object to be measured, and are connected via a predetermined signal line. are connected to the other ends of the first and second resistors 3A and 3B, respectively.

Such a capacitor C, together with the first and second resistors 3A and 3B, constitutes a CR circuit, that is, an integration circuit in the electronic circuit. That is, the capacitor C constitutes a first integration circuit together with the first resistor 3A, and constitutes a second integration circuit together with the second resistor 3B. The first integration circuit has a first time constant τ1 based on the capacitance of the capacitor C and the first resistance value of the first resistor 3A, and the second integration circuit It has a second time constant τ2 based on the capacitance and a second resistance value in the second resistor 3B.

Therefore, the voltage waveforms at the other ends of the first and second resistors 3A and 3B are square waves, and the first measurement signal or the second measurement signal has the first time constant τ1 or the second time constant τ1. The waveform is integrated based on the constant τ2. Since the first and second detection electrodes 4X and 4Y are connected to the input terminals of the first and second detectors 6A and 6B, respectively, the first and second detection electrodes 4X and 4Y are A signal obtained by integrating the first measurement signal or the second measurement signal is output to the first and second detectors 6A and 6B.

The third and fourth buffer circuits 5A and 5B are current amplifier circuits for current-amplifying the first and second measurement signals, respectively, and amplify the current-amplified first and second measurement signals to the first , to the second detectors 6A and 6B, respectively. That is, the third buffer circuit 5A current-amplifies the first measurement signal and outputs the current-amplified first measurement signal to the first detector 6A. On the other hand, the fourth buffer circuit 5B current-amplifies the second measurement signal and outputs the current-amplified second measurement signal to the second detector 6B.

Such third and fourth buffer circuits 5A and 5B are provided to delay the first and second measurement signals by a predetermined time (delay time ΔT). That is, the third buffer circuit 5A delays the first measurement signal by the delay time ΔT and outputs it to the first detector 6A. On the other hand, the fourth buffer circuit 5B delays the second measurement signal by the delay time ΔT and outputs the first measurement signal to the first detector 6A.

The first and second detectors 6A, 6B are phase detectors that detect the phase difference between two input signals. That is, the first detector 6A detects the phase difference between the first detection signal input from the first detection electrode 4X and the first measurement signal input from the third buffer circuit 5A as a first A phase difference is detected, and the first phase difference is output to the first low-pass filter 8A. On the other hand, the second detector 6B converts the phase difference between the second detection signal input from the first detection electrode 4X and the second measurement signal input from the fourth buffer circuit 5B into a second A phase difference is detected, and the second phase difference is output to the second low-pass filter 8B.

The fifth and sixth buffer circuits 7A and 7B are current amplifying circuits that current-amplify the first and second measurement signals, respectively, like the third and fourth buffer circuits 5A and 5B described above. These fifth and sixth buffer circuits 7A and 7B output the current-amplified first and second measurement signals to third and fourth low-pass filters 9A and 9B, respectively. That is, the fifth buffer circuit 7A current-amplifies the first measurement signal and outputs the current-amplified first measurement signal to the third low-pass filter 9A. On the other hand, the sixth buffer circuit 7B current-amplifies the second measurement signal and outputs the current-amplified second measurement signal to the fourth low-pass filter 9B.

The first and second low-pass filters 8A, 8B are integrating circuits having a predetermined cutoff frequency, and extract DC components from the phase difference signals respectively input from the pair of detectors 6A, 6B. That is, the first low-pass filter 8A extracts a DC component from the first phase difference signal input from the first detector 6A, converts the DC component into a first phase difference voltage, and outputs it to the first differential amplifier. Output to 10A. On the other hand, the second low-pass filter 8B extracts a DC component from the second phase difference signal input from the second detector 6B, converts the DC component into a second phase difference voltage, and transfers it to a second differential amplifier. 10B.

The third and fourth low-pass filters 9A and 9B are integration circuits having a predetermined cutoff frequency, and filter the first and second measurement signals input from the fifth and sixth buffer circuits 7A and 7B, respectively. An average DC voltage component is extracted by integration processing. That is, the third low-pass filter 9A extracts the average DC voltage component of the first measurement signal and outputs the average DC voltage component as the first reference voltage to the first differential amplifier 10A.

On the other hand, the fourth low-pass filter 9B extracts the average DC voltage component of the second measurement signal and outputs the average DC voltage component as the second reference voltage to the second differential amplifier 10B. As described above, the first and second measurement signals are square waves having a peak value of +3.3 V and a duty ratio of 50%. Therefore, the first and second reference voltages are 1.65V.

The first and second differential amplifiers 10A and 10B have a predetermined amplification degree, and differentially amplify the first and second phase difference voltages and the first and second reference voltages to generate a difference voltage. , respectively. That is, the first differential amplifier 10A generates a first differential voltage based on the first phase differential voltage and the first reference voltage, and outputs the first differential voltage to the MPU 11. On the other hand, the second differential amplifier 10</b>B generates a second differential voltage based on the second phase differential voltage and the second reference voltage, and outputs the second differential voltage to the MPU 11 .

Here, third and fourth buffer circuits 5A and 5B, first and second detectors 6A and 6B, fifth and sixth buffer circuits 7A and 7B, first and second low-pass filters 8A and 8B , third and fourth low-pass filters 9A and 9B and first and second differential amplifiers 10A and 10B are provided according to a plurality of physical quantities to be measured (moisture content and electrical conductivity). A plurality of detection processing circuits are configured to perform predetermined detection processing on the first and second detection signals obtained from the two detection electrodes 4X and 4Y.

Further, such third and fourth buffer circuits 5A and 5B, first and second detectors 6A and 6B, fifth and sixth buffer circuits 7A and 7B, and first and second low-pass filters 8A , 8B, third and fourth low-pass filters 9A and 9B and first and second differential amplifiers 10A and 10B, a third buffer circuit 5A, a first detector 6A and a fifth buffer circuit 7A. , the first low-pass filter 8A, the third low-pass filter 9A and the first differential amplifier 10A constitute a first detection processing circuit. On the other hand, the fourth buffer circuit 5B, the second detector 6B, the sixth buffer circuit 7B, the second low-pass filter 8B, the fourth low-pass filter 9B and the second differential amplifier 10B are used for the second detection. It constitutes a processing circuit.

The MPU 11 is a microprocessor that estimates the moisture content and electrical conductivity of the object to be measured by performing predetermined information processing on the first and second differential voltages based on a prestored measurement program. In addition to the measurement program, the MPU 11 prestores, for example, a conversion table for estimating water content (moisture content conversion table) and a conversion table for estimating electrical conductivity (electrical conductivity conversion table).

The water content conversion table is a data table showing the relationship between the first differential voltage and the water content of the object to be measured. It is a data table showing the relationship with degree. The MPU 11 extracts the moisture content corresponding to the first differential voltage by searching such a moisture content conversion table with the first differential voltage. Moreover, the MPU 11 extracts the electrical conductivity corresponding to the second differential voltage by searching the electrical conductivity conversion table with the second differential voltage.

Further, the MPU 11 alternatively selects one of the first and second buffer circuits 2A and 2B by outputting a switching signal to the first and second buffer circuits 2A and 2B. That is, the MPU 11 causes the one of the first and second buffer circuits 2A and 2B selected by the switching signal to input the measurement signal to the first detection electrode 4X. The MPU 11 selects the first buffer circuit 2A to input the first measurement signal to the first detection electrodes 4X, and selects the second buffer circuit 2B to input the second measurement signal. It is also a control means for inputting to one detection electrode 4X.

Here, the first and second differential voltages correspond to the processed detection signal of the present invention. That is, the first differential voltage is the output signal of the first detection processing circuit, and the second differential voltage is the output signal of the second detection processing circuit. Further, the MPU 11 corresponds to calculation means for calculating the water content and electrical conductivity (the plurality of physical quantities to be measured) based on such first and second differential voltages (processed detection signals).

Further, among the components described above, the oscillator 1, the first and second buffer circuits 2A and 2B, the third and fourth buffer circuits 5A and 5B, the first and second detection circuits, which are part of the active circuits. The units 6A, 6B and the fifth and sixth buffer circuits 7A, 7B are driven by a positive power supply with an output voltage of +3.3V. The remaining active circuits, ie, the first and second differential amplifiers 10A and 10B and the MPU 11 are driven by a plus power supply with an output voltage of +5.0V.

Next, the operation of the measuring device according to this embodiment will be described in detail.

When measuring the moisture content of the object to be measured using this measuring device, the MPU 11 outputs a switching signal for selecting the first buffer circuit 2A to the first and second buffer circuits 2A and 2B. Since this switching signal is also input to the oscillator 1, the oscillator 1 outputs the first measurement signal to the first buffer circuit 2A. As a result, the first buffer circuit 2A current-amplifies the first measurement signal and supplies it to the first detection electrode 4X via the first resistor 3A.

In this state, the output impedance of the unselected second buffer circuit 2B is set to a high impedance state, so that the effect of the output impedance of the second buffer circuit 2B does not appear in the first detection signal. That is, since the second buffer circuit 2B is in a state equivalent to not being connected to the first detection electrode 4X, it does not affect the detection dynamic range of the first detection signal.

On the other hand, when using this measuring device to measure the electrical conductivity of the object to be measured, the MPU 11 outputs a switching signal for selecting the second buffer circuit 2B to the first and second buffer circuits 2A and 2B. This switching signal is also input to the oscillator 1, and the oscillator 1 outputs the second measurement signal to the second buffer circuit 2A. As a result, the second buffer circuit 2A current-amplifies the second measurement signal and supplies it to the first detection electrode 4X via the second resistor 3B.

In this state, the output impedance of the unselected first buffer circuit 2A is set to a high impedance state, so that the second detection signal is not affected by the output impedance of the first buffer circuit 2A. That is, since the first buffer circuit 2A is in a state equivalent to not being connected to the first detection electrode 4X, it does not affect the detection dynamic range of the second detection signal.

As described above, in the measuring device according to the present embodiment, when measuring the moisture content of a measurement object, the first resistance value (first A first measurement signal is supplied to the first detection electrode 4X via the resistance value of the resistor 3A), and a first detection signal is extracted from the first detection electrode 4X using the first resistance value. be

Further, when measuring the electrical conductivity of the object to be measured, the second resistance value (the resistance value of the second resistor 3B) that is optimally set so as to maximize the detection dynamic range in the measurement is used. A second measurement signal is supplied to the first detection electrode 4X, and a second detection signal is extracted from the first detection electrode 4X using the second resistance value.

Here, if the unselected output impedance of the first and second buffer circuits 2A and 2B remains low instead of high impedance, the combination of the first resistance value and the second resistance value The first and second measurement signals are supplied to the first detection electrode 4X through the resistance value, and the first and second detection signals are extracted from the first detection electrode 4X using the combined resistance value. It will be.

Then, by processing the first detection signal in the first detection processing circuit, a first differential voltage is input to the MPU 11, and by processing the second detection signal in the second detection processing circuit, A second differential voltage is input to the MPU 11 . Then, the MPU 11 obtains the moisture content of the object to be measured based on the first differential voltage, and obtains the electrical conductivity of the object to be measured based on the second differential voltage. Then, the MPU 11 outputs the moisture content and the electrical conductivity to the outside as measured values.

According to this embodiment, the detection dynamic range is set independently for each target physical quantity, that is, for each water content and electrical conductivity, so that a plurality of target physical quantities in the measurement object can be measured with higher accuracy than before. Is possible.

It should be noted that the present invention is not limited to the above-described embodiments, and for example, the following modifications are conceivable.
(1) In the above embodiment, the case where the water content and electrical conductivity of the object to be measured are measured as a plurality of target physical quantities has been described, but the present invention is not limited to this. That is, the present invention can be applied to measurement of target physical quantities other than water content and electrical conductivity.

(2) In the above embodiment, the two target physical quantities, ie, water content and electrical conductivity, have been described laterally, but the present invention is not limited to this. That is, the present invention can be applied laterally to three or more target physical quantities by providing the number of input circuits and detection processing circuits corresponding to the number of target physical quantities.

(3) In the above embodiment, the oscillator 1 that oscillates a square wave is used, but the present invention is not limited to this. Instead of square waves, other waveforms, such as trapezoidal signals, may be generated.

1 oscillator 2A, 2B first and second buffer circuits (input circuits)
3A, 3B first and second resistors (input circuit)
4X, 4Y First and second detection electrodes 5A, 5B Third and fourth buffer circuits (detection processing circuits)
6A, 6B first and second detectors (detection processing circuits)
7A, 7B fifth and sixth buffer circuits (detection processing circuits)
8A, 8B first and second low-pass filters (detection processing circuits)
9A, 9B Third and fourth low-pass filters (detection processing circuits)
10A, 10B first and second differential amplifiers (detection processing circuits)
11 MPUs
M electrode module S support member

Claims (5)

a detection electrode in contact with the object to be measured;
an oscillator that oscillates a predetermined measurement signal;
a plurality of input circuits provided corresponding to a plurality of physical quantities to be measured and supplying the measurement signals to the detection electrodes;
a plurality of detection processing circuits provided corresponding to the plurality of physical quantities to be measured and performing predetermined detection processing on detection signals obtained from the detection electrodes;
computing means for computing a plurality of the physical quantities to be measured based on the processed detection signal input from the detection processing circuit;
a control means for selectively selecting one of the plurality of input circuits and inputting the measurement signal to the detection electrode ;
the input circuit supplies the measurement signal to the detection electrode via a predetermined resistor;
A measuring apparatus , wherein the resistance value of the resistor is set independently for each physical quantity to be measured. 2. The measuring apparatus according to claim 1, wherein the oscillator oscillates the measuring signal with a different frequency for each of the input circuits. 3. The measuring apparatus according to claim 2, wherein the detection processing circuit generates the processed detection signal indicating the phase difference between the measurement signal and the detection signal, and outputs the processed detection signal to the calculation means. 4. The measuring apparatus according to claim 1, wherein the input circuit has a high output impedance when not selected . The measuring apparatus according to any one of claims 1 to 4, wherein the plurality of physical quantities to be measured are moisture and electrical conductivity of the object to be measured.

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