JP2014041034A - Measuring device and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a proper electrostatic capacitance.SOLUTION: A snow density sensor 1A includes: an electrode pair 11; a reference section 20a having a capacitor; a detection section 24 for detecting an output of the electrode pair 11 and an output of the capacitor of the reference section 20a; and a switch section 23 for connecting the detection section 24 to the electrode pair 11 and the capacitor of the reference section 20a. The snow density sensor 1A further includes an electrostatic capacitance calculation section 26 for calculating electrostatic capacitance between the electrode pair 11 with the use of the output of the electrode pair 11 connected to the detection section 24 by the switch section 23 and the output of the capacitor of the reference section 20a connected to the detection section 24 by the switch section 23. The reference section 20a is provided and the output of the capacitor of the reference section is used so that electrostatic capacitance between the electrode pair 11, which changes according to a measurement environment, is properly measured and a dielectric constant and measuring precision of the snow density sensor are improved.

Description

  The present invention relates to a measuring apparatus and a measuring method.

  A technology for measuring the capacitance between electrodes by placing a pair of electrodes on the measurement target material, a technology for measuring the relative dielectric constant of the material based on the measured capacitance, and the measured dielectric constant Techniques for determining the density of a substance based on the rate are known. For example, a technique is known in which snow is an object to be measured, the capacitance and relative permittivity of snow are measured using electrodes, and the density of snow is obtained from the measured values.

  As a measurement technique using capacitance, a capacitive humidity sensor that measures humidity based on capacitance between electrodes is known.

JP-A-6-288888 JP 2007-248065 A

  In the conventional measurement technology, there is a case where an appropriate capacitance between the electrodes cannot be measured due to the form of the measurement object, the measurement environment, or the influence of the change. Thus, when the electrostatic capacitance between electrodes is not measured appropriately, it may happen that the relative permittivity and density of the measurement object between the electrodes cannot be measured with high accuracy.

  For example, when the object to be measured is snow, the change in relative dielectric constant accompanying the change in density is as small as about 1.5 to 4, and the change in capacitance is also small. There is a risk of variations in relative permittivity and density. In addition, when the measurement target is snow, the measurement is performed outdoors, so the circuit of the measurement device installed outdoors is easily affected by the measurement environment and its change, and there is a possibility that appropriate capacitance or the like may not be obtained. is there.

  According to an aspect of the present invention, a pair of electrodes, a reference unit including a first capacitor, a detection unit that detects an output of the pair of electrodes and the first capacitor, and the detection unit as the pair of electrodes or A switch unit connected to the first capacitor; a first output of the pair of electrodes connected to the detection unit by the switch unit; and a second of the first capacitor connected to the detection unit by the switch unit. A measurement device is provided that includes a first calculation unit that calculates a first capacitance between the pair of electrodes using an output.

  Moreover, according to one viewpoint of this invention, the measuring method using a measuring device is provided.

  According to the disclosed technology, by using the capacitor of the reference unit, it is possible to appropriately measure the capacitance that can change in the form of the measurement target and the measurement environment existing between the electrodes of the detection unit.

It is a figure which shows an example of the relationship between the output voltage of an electrode, and an electrostatic capacitance. It is a figure which shows the structural example of the snow density sensor which concerns on 1st Embodiment. It is a figure which shows an example of the snow density measurement process which concerns on 1st Embodiment. It is explanatory drawing of the correction process of the characteristic curve which concerns on 1st Embodiment. It is a figure which shows the structural example of the snow density sensor which concerns on 2nd Embodiment. It is a figure which shows the 1st example of the snow density measurement process which concerns on 2nd Embodiment. It is a figure which shows the 2nd example of the snow density measurement process which concerns on 2nd Embodiment. It is a figure which shows the 3rd example of the snow density measurement process which concerns on 2nd Embodiment.

Hereinafter, the measuring device will be described in detail by taking a measuring device (snow density sensor) for measuring snow density as an example.
For example, for the purpose of water utilization, it is very effective to measure the amount of snow and predict the amount of water obtained from snow. The prediction of the amount of water obtained from snow can be calculated, for example, by measuring snow density and snow depth. As a snow density sensor, a sensor is known that measures the relative dielectric constant of snow between electrodes from the capacitance between opposing electrodes and measures the density of snow using the relative dielectric constant. By using such a snow density sensor, the snow density can be measured over time.

  By the way, the change of the dielectric constant accompanying the change of the snow density is very small, and the relative dielectric constant is about 1.5 to 4. Therefore, in the conventional snow density sensor, the capacitance change between the opposing electrodes is small, and the circuit characteristics of the snow density sensor are affected by the measurement environment and the change, and the measurement value may vary. . Since the snow density sensor is assumed to be installed outdoors, it is easily affected by the measurement environment and its change.

  In addition, as a method of increasing the change in capacitance, a method of increasing the area of the opposing electrodes or reducing the distance between the opposing electrodes can be considered. However, when the electrode area is increased, there is a possibility of increasing the manufacturing cost and the installation area. When the distance between the electrodes is reduced, no snow is accumulated between the electrodes, or it is not accumulated uniformly. It can lead to a situation.

  In addition to measuring electrodes (measurement electrodes), a reference electrode (reference electrode) is prepared separately as a method of correcting the influence of the measurement environment when measuring capacitance. There is also known a method of correcting the measurement value of the measurement electrode by using.

  The relationship between the output voltage of the electrode and the capacitance is represented by a characteristic curve as shown in FIG. 1, for example. In FIG. 1, the vertical axis represents the output voltage of the electrode, and the horizontal axis represents the capacitance. In the characteristic curve 30a, the inclination (sensitivity) m and the offset n vary mainly depending on the temperature. If the characteristic curve 30a indicated by the solid line in FIG. 1 is the reference temperature, the characteristic curve 30a may be changed like the characteristic curve 30b and the characteristic curve 30c indicated by the dotted line in FIG. 1 due to the influence of temperature.

  Therefore, even when the measurement electrode and the reference electrode as described above are used, the correction needs to be performed not only for the offset n but also for two fluctuations of the inclination m and the offset n. As described above, since the change in the relative permittivity and the change in the capacitance due to the change in the snow density are small, the correction error can greatly affect the measurement result of the snow density.

  Further, in the snow density sensor, in order to measure a minute dielectric constant, for example, a large electrode of several tens of centimeters or more may be used. Therefore, when both the measurement electrode and the reference electrode are prepared as described above, there is a possibility that the installation area of the electrode, the installation cost and the manufacturing cost of the snow density sensor increase.

In view of the above points, a snow density sensor as described below as an embodiment is used here.
First, the first embodiment will be described.

FIG. 2 is a diagram illustrating a configuration example of the snow density sensor according to the first embodiment.
A snow density sensor 1 </ b> A shown in FIG. 2 includes a detection unit 10 and a detection circuit 20. The detection unit 10 includes a pair of electrodes 11a and an electrode 11b (electrode pair 11). The detection circuit 20 includes a first reference unit 21 and a second reference unit 22 (reference unit 20a), a switch unit 23, a detection unit 24, a recording unit 25, a capacitance calculation unit 26, a relative dielectric constant calculation unit 27, and a snow density. A calculation unit 28 and a snow density output unit 29 are included.

  When measuring the snow density, the detection unit 10 is installed outdoors, and the detection circuit 20 is installed outdoors with waterproofing measures taken, for example, in a waterproof case. In the snow density sensor 1A, the detection unit 10 and the detection circuit 20 are both installed outdoors as described above.

  The electrode 11a and the electrode 11b of the electrode pair 11 of the detection unit 10 can be, for example, a pair of electrode plates arranged to face each other. In addition, various arrangements (such as being arranged side by side on a plane) and shapes (such as a disc and a square plate) can be employed for the electrode 11a and the electrode 11b. A conductive material such as metal can be used for the electrode 11a and the electrode 11b.

  The first reference unit 21 of the detection circuit 20 includes a first capacitor 21a having a known capacitance (first fixed capacitance). The second reference unit 22 includes a second capacitor 22a having a known capacitance (second fixed capacitance) different from the first capacitor 21a. The capacitances of the first capacitor 21a and the second capacitor 22a are set in a range of 1 pF to 10 pF, for example.

  The first capacitor 21 a of the first reference unit 21 and the second capacitor 22 a of the second reference unit 22 can be connected to the switch unit 23. Similarly to the first capacitor 21 a and the second capacitor 22 a, the electrode pair 11 of the detection unit 10 can be connected to the switch unit 23. The switch unit 23 is connected to the detection unit 24, and switches the connection destination of the detection unit 24 to any one of the electrode pair 11, the first capacitor 21a, and the second capacitor 22a.

  The detection unit 24 generates an input signal to the electrode pair 11, the first capacitor 21a, and the second capacitor 22a. The detection unit 24 supplies the generated input signal to any one of the electrode pair 11, the first capacitor 21a, and the second capacitor 22a connected to the detection unit 24 by the switch unit 23, and outputs the output signal thereby. To detect.

  That is, when the detection unit 24 and the electrode pair 11 are connected by the switch unit 23, the detection unit 24 supplies an input signal to the electrode pair 11, and between the electrode 11 a and the electrode 11 b of the electrode pair 11. An output signal corresponding to the capacitance is detected. When the detection unit 24 and the first capacitor 21a are connected by the switch unit 23, the detection unit 24 supplies an input signal to the first capacitor 21a, and according to the capacitance from the first capacitor 21a. The output signal is detected. When the detection unit 24 and the second capacitor 22a are connected by the switch unit 23, the detection unit 24 supplies an input signal to the second capacitor 22a and corresponds to the capacitance from the second capacitor 22a. The output signal is detected.

  For example, the detection unit 24 applies an AC voltage to one electrode (application electrode) of each of the electrode pair 11, the first capacitor 21a, and the second capacitor 22a as an input signal, and applies to the other electrode (detection electrode). A flowing current value is detected, converted into a voltage, and detected as an output signal.

  The recording unit 25 records the output signal from the electrode pair 11 detected by the detection unit 24, the output signal from the first capacitor 21a, and the output signal from the second capacitor 22a. A storage device such as a memory is used for the recording unit 25.

  The capacitance calculating unit 26 calculates the capacitance between the electrode pair 11 based on the output signals from the electrode pair 11, the first capacitor 21a, and the second capacitor 22a. The capacitance calculating unit 26 includes a reference characteristic curve (relational expression) obtained by experiments and simulations on the relationship between the output signal from the electrode pair 11 and the capacitance between the electrode pair 11. . Further, the capacitance calculating unit 26 includes information on the capacitance (fixed capacitance) of the first capacitor 21a and the second capacitor 22a. The electrostatic capacity calculation unit 26 corrects the reference characteristic curve based on the output signals from the first capacitor 21a and the second capacitor 22a and their electrostatic capacity (fixed capacity). The capacitance calculation unit 26 calculates the capacitance between the electrode pair 11 using the corrected characteristic curve and the output signal from the electrode pair 11 detected by the detection unit 24.

  The relative permittivity calculation unit 27 uses the capacitance between the electrode pair 11 calculated by the capacitance calculation unit 26, and the ratio of the substance to be measured that exists between the electrode pair 11 here, that is, snow. Calculate the dielectric constant.

The snow density calculator 28 calculates the density of the snow using the relative permittivity of the snow existing between the electrode pairs 11 calculated by the relative permittivity calculator 27.
The snow density output unit 29 outputs the snow density data calculated by the snow density calculation unit 28 to the outside of the detection circuit 20. The snow density output unit 29 is, for example, a communication connector, and transmits data to other devices (computer, storage device, etc.) outside the snow density sensor 1A.

Next, the snow density measurement process of the snow density sensor 1A having the above configuration will be described.
FIG. 3 is a diagram illustrating an example of a snow density measurement process according to the first embodiment.

When measuring the snow density, the snow density sensor 1 </ b> A is installed in a predetermined environment such as outdoors, and snow as a measurement target exists between the electrode pair 11.
In the snow density sensor 1A, first, the switch unit 23 switches the connection destination of the detection unit 24 to the electrode pair 11 of the detection unit 10 (step S1). Then, a predetermined input signal is supplied to the electrode pair 11 by the detection unit 24, and an output signal (output voltage) corresponding to the electrostatic capacitance is detected from the electrode pair 11 in which snow is present (step S2). The detected output voltage of the electrode pair 11 is recorded in the recording unit 25.

  Next, the switch unit 23 switches the connection destination of the detection unit 24 to the first capacitor 21a of the first reference unit 21 (step S3). Then, a predetermined input signal is supplied to the first capacitor 21a by the detection unit 24, and an output signal (output voltage) corresponding to the capacitance of the first capacitor 21a is detected from the first reference unit 21 (step) S4). The detected output voltage of the first reference unit 21 is recorded in the recording unit 25.

  Next, the switch unit 23 switches the connection destination of the detection unit 24 to the second capacitor 22a of the second reference unit 22 (step S5). Then, the detection unit 24 supplies a predetermined input signal to the second capacitor 22a, and an output signal (output voltage) corresponding to the capacitance of the second capacitor 22a is detected from the second reference unit 22 (step). S6). The detected output voltage of the second reference unit 22 is recorded in the recording unit 25.

  Next, a standard characteristic curve is calculated by the capacitance calculation unit 26 based on the capacitances of the first reference unit 21 and the second reference unit 22 and the output voltages of the first reference unit 21 and the second reference unit 22. Is corrected (step S7). Then, the corrected characteristic curve and the output voltage of the electrode pair 11 are used, and the capacitance between the electrode pair 11 is calculated (step S8).

Here, a reference characteristic curve correction process and a capacitance calculation process using the corrected characteristic curve will be described.
FIG. 4 is an explanatory diagram of the characteristic curve correction processing according to the first embodiment.

  The reference characteristic curve 30a (relational expression) before the correction process has a relationship as shown by a solid line in FIG. 4, for example. Such a reference characteristic curve 30a is obtained by experiments or simulations. The capacitance calculating unit 26 includes the reference characteristic curve 30a obtained in this way.

The reference characteristic curve 30a is expressed by the following equation (1a).
C = f (V) (1a)
In the formula (1a), C is a capacitance, and V is an output voltage. f (V) is a function of the output voltage V, and is determined by the circuit configuration of the snow density sensor 1A.

A characteristic curve 30b including a change in circuit characteristics due to a temperature change in the measurement environment has a relationship as shown by a dotted line in FIG. 4 and can be expressed as the following equation (1b).
C = a × f (V) + b (1b)
In Expression (1b), C is an electrostatic capacity, V is an output voltage, a is a sensitivity correction coefficient with respect to a temperature change in the measurement environment, and b is an offset coefficient with respect to a temperature change in the measurement environment.

  The sensitivity correction coefficient a and the offset coefficient b are obtained based on the output voltage from the first capacitor 21 a of the first reference unit 21 and the output voltage from the second capacitor 22 a of the second reference unit 22. Now, the known capacitance of the first capacitor 21a is Cr1, the known capacitance of the second capacitor 22a is Cr2, the output voltage from the first capacitor 21a is Vr1, and the output voltage from the second capacitor 22a is Vr2. To do. Further, in the reference characteristic curve 30a, the output voltage corresponding to the capacitance Cr1 is Vrr1, and the output voltage corresponding to the capacitance Cr2 is Vrr2. At this time, the sensitivity correction coefficient a and the offset coefficient b can be approximated by the following expressions (2) and (3), respectively.

a = [(Vr2-Vr1) / (Cr2-Cr1)] / [(Vrr2-Vrr1) / (Cr2-Cr1)] (2)
b = [[Cr1-a * f (Vr1)] + {Cr2-a * f (Vr2)}] / 2 (3)
The detected output voltages Vr1 and Vr2, the known capacitances Cr1 and Cr2, and the output voltages Vrr1 and Vrr2 obtained from the reference characteristic curve 30a are used. From the equations (2) and (3), the sensitivity correction coefficient a and the offset coefficient b are obtained. By applying the obtained sensitivity correction coefficient a and offset coefficient b to the equation (1b), a corrected characteristic curve 30b including fluctuations in circuit characteristics due to temperature changes in the measurement environment is obtained. In the obtained corrected characteristic curve 30b (formula (1b)), the output voltage detected from the electrode pair 11 (for example, the output voltage Ve in FIG. 4) is substituted, whereby the electrostatic capacitance between the electrode pair 11 is determined. The capacity (for example, the electrostatic capacity Ce in FIG. 4) is calculated.

  In the capacitance calculating unit 26, the reference characteristic curve 30a is corrected in this way to obtain a corrected characteristic curve 30b, and the capacitance between the electrode pair 11 is obtained using the characteristic curve 30b. Is calculated.

  The capacitance calculating unit 26 may be provided with a characteristic curve obtained by experiments or simulations under a predetermined temperature condition (for example, 0 ° C.) as a reference characteristic curve 30a. In addition, for each environment where the snow density sensor 1 </ b> A is installed, the capacitance calculation unit 26 displays a characteristic curve obtained under conditions (for example, + 10 ° C. and −10 ° C.) in consideration of the temperature of the environment. The reference characteristic curve 30a may be provided. When the measured temperature is close to the temperature condition when the reference characteristic curve 30a is obtained, the relationship between the actually measured output voltage and the capacitance becomes closer to the reference characteristic curve 30a, and the reference characteristic curve 30a is more approximate. The capacitance can be calculated from the corrected characteristic curve 30b close to.

  In addition, the capacitances of the first reference unit 21 and the second reference unit 22 are set to a predetermined value that is set in advance, regardless of the standard characteristic curve 30a (regardless of the temperature condition when obtained). Can do. Each value and their difference (interval) can also be set for each reference characteristic curve 30a (for each temperature condition when obtained). As the capacitance of the first reference unit 21 and the second reference unit 22, for example, a capacitance value corresponding to a relatively linear portion of the characteristic curve 30a or the characteristic curve 30b can be set. As a result, the accuracy of the sensitivity correction coefficient a (and the offset coefficient b using the sensitivity correction coefficient a) expressed by the ratio of the rate of change between two points in the characteristic curve 30a or the characteristic curve 30b can be increased.

  Returning to FIG. 3, after the capacitance calculation between the electrode pairs 11 by the capacitance calculation unit 26 (steps S <b> 7 and S <b> 8), the relative permittivity of the snow between the electrode pairs 11 is calculated by the relative dielectric constant calculation unit 27. A rate is calculated (step S9).

When the electrostatic capacitance between the electrode pair 11 is C and the relative dielectric constant of snow between the electrode pair 11 is εr, the relative dielectric constant εr is expressed by the following equation (4a).
εr = k × C / ε0 (4a)
In equation (4), ε0 is the dielectric constant of vacuum. k is a conversion coefficient. For example, when the area of the electrodes 11a and 11b facing each other in the electrode pair 11 is A and the distance between the electrodes 11a and 11b is L, the following equation (4b) is expressed. .

k = L / A (4b)
The relative dielectric constant calculator 27 has a relationship (relational expression) as expressed by the equations (4a) and (4b). The relative permittivity calculation unit 27 uses the vacuum permittivity ε0 and the conversion coefficient k (area A and distance L), and the capacitance C between the electrode pair 11 calculated by the capacitance calculation unit 26. From the equations (4a) and (4b), the relative dielectric constant εr of the snow between the electrode pair 11 is calculated.

After calculating the relative dielectric constant of the snow between the electrode pair 11 by the relative dielectric constant calculating unit 27, the snow density calculating unit 28 calculates the snow density (step S10).
Assuming that the relative dielectric constant of snow between the electrode pair 11 is εr and the snow density is ρ, the snow density ρ is expressed by the following equation (5).

ρ = j × εr (5)
In Expression (5), j is a coefficient obtained by experiment or simulation. The snow density calculation unit 28 has a relationship (relational expression) as expressed by Expression (5). In the snow density calculation unit 28, the coefficient j and the relative dielectric constant εr calculated by the relative dielectric constant calculation unit 27 are used, and the density ρ of the snow between the electrode pair 11 is calculated from the equation (5). .

The calculated snow density ρ is output to the outside of the detection circuit 20 by the snow density output unit 29 (step S11).
As described above, in the snow density sensor 1 </ b> A, the reference characteristic curve is corrected using the first reference unit 21 and the second reference unit 22 each having a capacitor with a different known capacitance, and the gap between the electrode pair 11 is corrected. Calculate the capacitance. Then, the relative dielectric constant is calculated from the calculated capacitance, and the snow density is further calculated. According to the snow density sensor 1A, even when there is a change in circuit characteristics due to a temperature change or the like in the measurement environment, an appropriate capacitance between the electrode pair 11 can be measured, and the relative permittivity and snow density can be increased. It can be measured with high accuracy.

  Here, the output voltage is detected in the order of the electrode pair 11, the first reference portion 21, and the second reference portion 22 (steps S1 to S6), the reference characteristic curve 30a is corrected (step S7), and the corrected voltage is corrected. The case where the capacitance is calculated using the characteristic curve 30b (step S8) is illustrated. The order of these processes is not limited to the above example. The output voltages of the first reference unit 21 and the second reference unit 22 are detected before the correction of the reference characteristic curve 30a, and the output of the electrode pair 11 before the calculation of the capacitance using the corrected characteristic curve 30b. It is sufficient that the voltage is detected.

  Moreover, although the case where two of the first reference part 21 and the second reference part 22 having a known capacitance are provided is illustrated here, three or more reference parts having a known capacitance are provided. You can also. Even when three or more reference parts are provided, the same snow density measurement process as described above can be performed. By increasing the number of reference portions with known capacitances, it is possible to increase the accuracy when correcting the standard characteristic curve 30a.

  The processing function of the detection circuit 20 of the snow density sensor 1A uses elements such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an ASIC (Application Specific Integrated Circuit), and a PLD (Programmable Logic Device). Is feasible. The processing function of the detection circuit 20 may be realized by using one of these elements, or the processing function of the detection circuit 20 may be realized by combining two or more of these elements.

Next, a second embodiment will be described.
FIG. 5 is a diagram illustrating a configuration example of a snow density sensor according to the second embodiment.
The snow density sensor 1B shown in FIG. 5 includes a reference unit 31 including a variable capacitance capacitor 31a having a variable capacitance in the detection circuit 20, and a variable capacitance control unit 32 that controls the capacitance of the variable capacitance capacitor 31a. Is included.

  The capacitance of the variable capacitor 31a of the reference unit 31 in the snow density sensor 1B is set to a range of 1 pF to 10 pF by the variable capacitance control unit 32, for example. The variable capacitor 31 a of the reference unit 31 can be connected to the switch unit 23. The switch unit 23 switches the connection destination of the detection unit 24 to one of the electrode pair 11 of the detection unit 10 and the variable capacitor 31 a of the reference unit 31. The detection unit 24 supplies an input signal to either the electrode pair 11 or the variable capacitor 31a connected to the detection unit 24 by the switch unit 23, and detects an output signal output thereby.

  The variable capacitance control unit 32 sets (controls) the electrostatic capacitance of the variable capacitance capacitor 31a of the reference unit 31 to two or more values. When the detection unit 24 is connected to the variable capacitance capacitor 31a set to the first value capacitance by the switch unit 23, the detection unit 24 supplies an input signal to the variable capacitance capacitor 31a set to the capacitance. The output signal corresponding to the electrostatic capacity is detected. When the switch unit 23 is connected to the variable capacitor 31a set to the second value capacitance by the switch unit 23, the detection unit 24 supplies an input signal to the variable capacitor 31a set to the capacitance. The output signal corresponding to the electrostatic capacity is detected. Similarly, when the capacitance of the variable capacitor 31a is set to a third or subsequent value, an output signal corresponding to the value is detected.

  Similarly to the above, when the detection unit 24 is connected to the electrode pair 11 by the switch unit 23, the detection unit 24 supplies an input signal to the electrode pair 11, and the static electricity between the electrode 11 a and the electrode 11 b is supplied from the electrode pair 11. An output signal corresponding to the electric capacity is detected.

  For example, the detection unit 24 applies an AC voltage to one electrode (application electrode) of each of the electrode pair 11 and the variable capacitor 31a as an input signal, and detects a current value flowing through the other electrode (detection electrode). Then, it is converted into a voltage and detected as an output signal.

The recording unit 25 records the output signal from the electrode pair 11 detected by the detection unit 24 and the output signal from the variable capacitor 31a.
The capacitance calculating unit 26 calculates the capacitance between the electrode pair 11 based on the output signals from the electrode pair 11 and the variable capacitor 31a.

  For example, the capacitance calculation unit 26 includes a reference characteristic curve (relational expression) obtained through experiments or simulations. Further, the capacitance calculating unit 26 includes information on the capacitance of the variable capacitor 31 a changed by the variable capacitance control unit 32. The capacitance calculating unit 26 corrects the reference characteristic curve based on the output signal from the variable capacitor 31 a whose capacitance has been changed to a plurality of values, and the corrected characteristic curve and the detection unit 24 The capacitance between the electrode pair 11 is calculated using the detected output signal from the electrode pair 11.

  The capacitance calculating unit 26 may be configured not to have a reference characteristic curve. In this case, the capacitance calculating unit 26 generates a characteristic curve based on the output signal from the variable capacitor 31 a whose capacitance has been changed to a plurality of values, and the generated characteristic curve and the detection unit 24 The capacitance between the electrode pair 11 is calculated using the detected output signal from the electrode pair 11. Alternatively, the capacitance calculating unit 26 detects the output signal while changing the capacitance of the variable capacitor 31 a, and determines the capacitance when matching or approximating the output signal from the electrode pair 11 as the electrode pair 11. The capacitance is between.

The relative dielectric constant calculator 27 calculates the relative dielectric constant of the snow existing between the electrode pair 11 using the electrostatic capacitance between the electrode pair 11 calculated by the electrostatic capacity calculator 26.
The snow density calculator 28 calculates the density of the snow using the relative permittivity of the snow existing between the electrode pairs 11 calculated by the relative permittivity calculator 27.

The snow density output unit 29 outputs the snow density data calculated by the snow density calculation unit 28 to the outside of the detection circuit 20.
Next, the snow density measurement process of the snow density sensor 1B having the above configuration will be described.

First, a first example of snow density measurement processing will be described.
FIG. 6 is a diagram illustrating a first example of the snow density measurement process according to the second embodiment.
When measuring the snow density, the snow density sensor 1 </ b> B is installed in a predetermined environment such as outdoors, and snow as a measurement target exists between the electrode pair 11.

  In the first example shown in FIG. 6, first, the switch unit 23 switches the connection destination of the detection unit 24 to the electrode pair 11 of the detection unit 10 (step S20). Then, a predetermined input signal is supplied to the electrode pair 11 by the detection unit 24, and an output signal (output voltage) corresponding to the capacitance is detected from the electrode pair 11 in which snow exists between them (step S21). The detected output voltage of the electrode pair 11 is recorded in the recording unit 25.

  Next, the switch unit 23 switches the connection destination of the detection unit 24 to the variable capacitor 31a of the reference unit 31 (step S22). The variable capacitance capacitor 31a of the reference unit 31 is set (changed) to a predetermined capacitance by the variable capacitance control unit 32 (step S23). Then, a predetermined input signal is supplied to the variable capacitor 31a by the detector 24, and an output signal (output voltage) corresponding to the capacitance of the variable capacitor 31a is detected from the reference unit 31 (step S24). . The detected output voltage of the reference unit 31 is recorded in the recording unit 25.

  In the snow density sensor 1B, the processes in steps S23 and S24 are repeated N times (N is an integer of 2 or more) (step S25). The value of the capacitance of the variable capacitor 31 a is changed by the variable capacitance control unit 32 each time it is repeated, and the output voltage corresponding to the value is detected by the detection unit 24 and recorded in the recording unit 25.

  Next, the reference characteristic curve is corrected by the capacitance calculation unit 26 based on the output voltage from the variable capacitor 31a of the reference unit 31 whose capacitance has been changed to a plurality of values (step S26). . Then, the corrected characteristic curve and the output voltage from the electrode pair 11 are used, and the capacitance between the electrode pair 11 is calculated (step S27).

  The reference characteristic curve 30a has, for example, the relationship shown by the solid line in FIG. The capacitance calculating unit 26 includes the reference characteristic curve 30a obtained in this way. The capacitance calculating unit 26 includes information on the capacitance of the variable capacitor 31a. The capacitance calculating unit 26 corrects the reference characteristic curve 30a based on the output voltage from the variable capacitor 31a whose capacitance is changed to a plurality of values.

  For example, a case is assumed in which the output voltage is detected from each of the variable capacitors 31a whose capacitance has been changed to two values (when N = 2). In this case, the two capacitances of the variable capacitor 31a are Cr1 and Cr2, respectively, the output voltages are Vr1 and Vr2, and the output voltages corresponding to the capacitances Cr1 and Cr2 in the reference characteristic curve 30a are Vrr1 and Vrr2. . At this time, the sensitivity correction coefficient a and the offset coefficient b can be approximated by the above equations (2) and (3), respectively.

  The detected output voltages Vr1 and Vr2, the electrostatic capacitances Cr1 and Cr2 of the variable capacitor 31a, and the output voltages Vrr1 and Vrr2 obtained from the reference characteristic curve 30a are used. From the equations (2) and (3), Sensitivity correction coefficient a and offset coefficient b are obtained. By applying the obtained sensitivity correction coefficient a and offset coefficient b to the above equation (1b), a corrected characteristic curve 30b including fluctuations in circuit characteristics due to temperature changes in the measurement environment is obtained. In the obtained corrected characteristic curve 30b (formula (1b)), the output voltage detected from the electrode pair 11 (for example, the output voltage Ve in FIG. 4) is substituted, whereby the electrostatic capacitance between the electrode pair 11 is determined. The capacity (for example, the electrostatic capacity Ce in FIG. 4) is calculated.

In the capacitance calculating section 26, the reference characteristic curve 30a is corrected in this way, and the capacitance between the electrode pair 11 is calculated using the corrected characteristic curve 30b.
For the reference characteristic curve 30a, a characteristic curve 30a that is obtained by experiments and simulations under a predetermined temperature condition, or that is obtained under conditions that take into account the temperature of the installation environment of the snow density sensor 1B is used. Can do. Further, the plurality of types of capacitance realized by the variable capacitor 31a can be set to predetermined values. Depending on the installation environment of the snow density sensor 1B, each capacitance value or a difference between them may be set.

  After the capacitance calculation between the electrode pair 11 by the capacitance calculation unit 26, the relative dielectric constant calculation unit 27 calculates the relative dielectric constant of the snow between the electrode pair 11 (step S28). The relative dielectric constant calculator 27 has a relational expression as expressed by the above equations (4a) and (4b). In the relative dielectric constant calculator 27, the vacuum dielectric constant ε0 and the conversion coefficient k (area A and distance L) in the equations (4a) and (4b), and the electrode pair 11 calculated by the capacitance calculator 26 are shown. The relative dielectric constant εr of the snow between the electrode pair 11 is calculated.

  After the relative permittivity of the snow between the electrode pair 11 is calculated by the relative permittivity calculating section 27, the snow density calculating section 28 calculates the snow density (step S29). The snow density calculation unit 28 has a relational expression as expressed by the above expression (5). In the snow density calculation unit 28, the coefficient j in the equation (5) and the relative dielectric constant εr calculated by the relative dielectric constant calculation unit 27 are used to calculate the density ρ of the snow between the electrode pair 11.

The calculated snow density ρ is output to the outside of the detection circuit 20 by the snow density output unit 29 (step S30).
As described above, in the snow density measurement process shown in the first example of the snow density sensor 1B, the reference characteristic curve is corrected using the reference unit 31 including the variable capacitor 31a having a variable capacitance, and the electrode pair The capacitance between 11 is calculated. Then, the relative dielectric constant is calculated from the calculated capacitance, and the snow density is further calculated. Thereby, even when there is a change in circuit characteristics due to a temperature change or the like in the measurement environment, an appropriate capacitance between the electrode pair 11 can be measured, and a relative permittivity and a snow density can be measured with high accuracy. Can do.

  Here, the output voltage is detected in the order of the electrode pair 11 and the reference unit 31 (steps S20 to S25), the standard characteristic curve 30a is corrected (step S26), and the corrected characteristic curve 30b is used for electrostatic detection. The case where the capacity is calculated (step S27) is illustrated. The order of these processes is not limited to the above example. It is sufficient that the output voltage of the reference unit 31 is detected before the correction of the reference characteristic curve 30a and the output voltage of the electrode pair 11 is detected before the calculation of the capacitance using the corrected characteristic curve 30b. .

  In addition, the processing function of the detection circuit 20 in the snow density sensor 1B that performs the snow density measurement process as shown in the first example is, for example, one or more elements such as a CPU, MPU, ASIC, and PLD. It can be realized using.

Subsequently, a second example of the snow density measurement process will be described.
FIG. 7 is a diagram illustrating a second example of the snow density measurement process according to the second embodiment.
In the second example shown in FIG. 7, first, the switch unit 23 switches the connection destination of the detection unit 24 to the electrode pair 11 of the detection unit 10 (step S <b> 40), and snow exists between the detection unit 24. An output voltage corresponding to the capacitance is detected from the electrode pair 11 (step S41). The detected output voltage of the electrode pair 11 is recorded in the recording unit 25.

  Next, the switch unit 23 switches the connection destination of the detection unit 24 to the variable capacitor 31a of the reference unit 31 (step S42), and the variable capacitance control unit 32 sets the capacitance of the variable capacitor 31a to a predetermined value. It is set (changed) (step S43). Then, a predetermined input signal is supplied to the variable capacitor 31a by the detecting unit 24, and an output voltage corresponding to the capacitance of the variable capacitor 31a is detected from the reference unit 31 (step S44). The detected output voltage of the reference unit 31 is recorded in the recording unit 25.

  In the snow density sensor 1B, the processes in steps S43 and S44 are repeated N times (N is an integer of 2 or more) (step S45). The value of the capacitance of the variable capacitor 31 a is changed by the variable capacitance control unit 32 each time it is repeated, and the output voltage corresponding to the value is detected by the detection unit 24 and recorded in the recording unit 25.

  Next, based on the output voltage from the variable capacitor 31a whose capacitance has been changed to a plurality of values by the capacitance calculation unit 26, the relational expression between the output voltage and the capacitance using the least square method, That is, a characteristic curve is generated (step S46). Then, the generated characteristic curve and the output voltage from the electrode pair 11 are used, and the capacitance between the electrode pair 11 is calculated (step S47).

Here, a characteristic curve generation process and a capacitance calculation process using the generated characteristic curve will be described.
The generated characteristic curve is expressed by the following equation (6a).

C = f2 (V) (6a)
In Expression (6a), C is an electrostatic capacity, and V is an output voltage. f2 (V) is a function of the output voltage V, and is obtained using the least square method based on the output voltage measured from the variable capacitor 31a whose capacitance has been changed to a plurality of values. Although f2 (V) depends on the number of times of measurement, for example, it is expressed as the following equation (6b) using coefficients a2, b2, c2, and d2.

f2 (V) = a2 × V ³ + b2 × V ² + c2 × V + d2 (6b)
The capacitance C between the electrode pair 11 is calculated by substituting the output voltage V measured from the electrode pair 11 into the equation of the characteristic curve obtained using the least square method.

  Note that the plurality of types of capacitance realized by the variable capacitor 31a can be set to predetermined values. Depending on the installation environment of the snow density sensor 1B, each capacitance value or a difference between them may be set.

  After the capacitance calculation between the electrode pair 11 by the capacitance calculation unit 26, the relative dielectric constant of the snow between the electrode pair 11 is calculated by the relative dielectric constant calculation unit 27 (step S48). The relative dielectric constant calculator 27 has a relational expression as expressed by the above equations (4a) and (4b). In the relative dielectric constant calculator 27, the vacuum dielectric constant ε0 and the conversion coefficient k (area A and distance L) in the equations (4a) and (4b), and the electrode pair 11 calculated by the capacitance calculator 26 are shown. The relative dielectric constant εr of the snow between the electrode pair 11 is calculated.

  After the calculation of the relative dielectric constant of the snow between the electrode pairs 11 by the relative dielectric constant calculation unit 27, the snow density calculation unit 28 calculates the snow density (step S49). The snow density calculation unit 28 has a relational expression as expressed by the above expression (5). In the snow density calculation unit 28, the coefficient j in the equation (5) and the relative dielectric constant εr calculated by the relative dielectric constant calculation unit 27 are used to calculate the density ρ of the snow between the electrode pair 11.

The calculated snow density ρ is output to the outside of the detection circuit 20 by the snow density output unit 29 (step S50).
As described above, in the snow density measurement process shown in the second example of the snow density sensor 1B, the characteristic curve is generated using the reference unit 31 including the variable capacitor 31a having a variable capacitance, and The capacitance between them is calculated. Then, the relative dielectric constant is calculated from the calculated capacitance, and the snow density is further calculated. Thereby, even when there is a change in circuit characteristics due to a temperature change or the like in the measurement environment, an appropriate capacitance between the electrode pair 11 can be measured, and a relative permittivity and a snow density can be measured with high accuracy. Can do.

  Here, the output voltage is detected in the order of the electrode pair 11 and the reference unit 31 (steps S40 to S45), a characteristic curve is generated (step S46), and the capacitance is calculated using the generated characteristic curve (step S46). Step S47) was exemplified. The order of these processes is not limited to the above example. It is sufficient that the output voltage of the reference unit 31 is detected before the generation of the characteristic curve, and the output voltage of the electrode pair 11 is detected before the calculation of the capacitance using the generated characteristic curve.

  In addition, the processing function of the detection circuit 20 in the snow density sensor 1B that performs the snow density measurement process as shown in the second example described above is, for example, one or more elements such as a CPU, MPU, ASIC, and PLD. It can be realized using.

  In the second example, the characteristic curve is generated using the variable capacitor 31a. In addition to this, a plurality of capacitors (capacitances that are known and different in capacitance) are used to generate a characteristic curve using the capacitances and the output voltages from them. You can also

Subsequently, a third example of the snow density measurement process will be described.
FIG. 8 is a diagram illustrating a third example of the snow density measurement process according to the second embodiment.
In the second example shown in FIG. 8, first, the switch unit 23 switches the connection destination of the detection unit 24 to the electrode pair 11 of the detection unit 10 (step S60), and snow exists between the detection unit 24. An output voltage corresponding to the capacitance of the electrode pair 11 is detected (step S61). The detected output voltage of the electrode pair 11 is recorded in the recording unit 25.

  Subsequently, the switch unit 23 switches the connection destination of the detection unit 24 to the variable capacitor 31a of the reference unit 31 (step S62). Next, the variable capacitance control unit 32 sets the capacitance of the variable capacitance capacitor 31a of the reference unit 31 to a predetermined value, in this example, the median value of the variable capacitance range of the variable capacitance capacitor 31a (step S63). And the output voltage according to the electrostatic capacitance of the variable capacitor 31a is detected by the detection unit 24 (step S64). The detected output voltage of the reference unit 31 is recorded in the recording unit 25.

  Next, the capacitance calculating unit 26 obtains a difference between the output voltage measured from the variable capacitor 31a of the reference unit 31 and the output voltage measured from the electrode pair 11 (step S65). The capacitance calculating unit 26 determines whether or not the obtained difference between the output voltages of the variable capacitor 31a and the electrode pair 11 is equal to or less than a set threshold (step S66). In the capacitance calculation unit 26, when it is determined that the difference is equal to or less than the threshold, the capacitance of the variable capacitor 31 a whose output voltage at the time of the determination is measured is set as the capacitance between the electrode pair 11. (Step S67).

  When the capacitance calculation unit 26 determines that the difference between the obtained output voltage of the variable capacitor 31a and the electrode pair 11 exceeds the set threshold value (step S66), the variable capacitance control unit 32 Then, the capacitance of the variable capacitor 31a is changed to a predetermined value (step S68). At that time, the variable capacitance control unit 32 changes the capacitance of the variable capacitance capacitor 31a according to the difference between the output voltages of the variable capacitance capacitor 31a and the electrode pair 11. When [output voltage of variable capacitor 31a]> [output voltage of electrode pair 11], the capacitance of variable capacitor 31a is changed to a smaller value. In the case of [output voltage of variable capacitor 31a] <[output voltage of electrode pair 11], the capacitance of variable capacitor 31a is changed to a larger value.

  After the capacitance of the variable capacitor 31a is changed in this way, the processes after step S64 are executed. That is, the detection unit 24 detects the output voltage of the variable capacitor 31a after the capacitance change (step S64), and obtains the difference between the output voltage and the output voltage of the electrode pair 11 (step S65). It is determined whether or not the difference is less than or equal to a threshold value (step S66). When it is determined that the difference exceeds the threshold value, the capacitance of the variable capacitor 31a is changed (step S68). The capacitance calculation unit 26 and the variable capacitance control unit 32 repeat such processing until the difference becomes equal to or less than the threshold value.

When changing the capacitance of the variable capacitor 31a, the change amount of the capacitance may be a change amount by a fixed amount or a change amount based on a binary search.
In the snow density sensor 1B, the capacitance of the variable capacitance capacitor 31a when the difference between the output voltages of the variable capacitance capacitor 31a and the electrode pair 11 is equal to or smaller than the threshold value as the capacitance between the electrode pair 11 as described above. It is determined (step S67).

  After calculating the capacitance between the electrode pair 11 by the capacitance calculating unit 26, the relative dielectric constant calculating unit 27 calculates the relative dielectric constant of snow between the electrode pair 11 (step S69). The relative dielectric constant calculator 27 has a relational expression as expressed by the above equations (4a) and (4b). In the relative dielectric constant calculator 27, the vacuum dielectric constant ε0 and the conversion coefficient k (area A and distance L) in the equations (4a) and (4b), and the electrode pair 11 calculated by the capacitance calculator 26 are shown. The relative dielectric constant εr of the snow between the electrode pair 11 is calculated.

  After calculating the relative dielectric constant of the snow between the electrode pairs 11 by the relative dielectric constant calculating unit 27, the snow density calculating unit 28 calculates the snow density (step S70). The snow density calculation unit 28 has a relational expression as expressed by the above expression (5). In the snow density calculation unit 28, the coefficient j in the equation (5) and the relative dielectric constant εr calculated by the relative dielectric constant calculation unit 27 are used to calculate the density ρ of the snow between the electrode pair 11.

The calculated snow density ρ is output to the outside of the detection circuit 20 by the snow density output unit 29 (step S71).
As described above, in the snow density measurement process shown in the third example of the snow density sensor 1B, the reference unit 31 including the variable capacitor 31a having a variable capacitance is used. In the snow density measurement process shown in the third example, the capacitance of the variable capacitor 31a when the output voltage at which the difference from the output voltage of the electrode pair 11 is equal to or less than the threshold is obtained from the reference unit 31, It is determined as the capacitance between the electrode pair 11. Then, the relative dielectric constant is calculated from the determined capacitance, and the snow density is further calculated. Thereby, even when there is a change in circuit characteristics due to a temperature change or the like in the measurement environment, an appropriate capacitance between the electrode pair 11 can be measured, and a relative permittivity and a snow density can be measured with high accuracy. Can do.

  Here, the case where the output voltage is detected in the order of the electrode pair 11 and the reference unit 31 (steps S60 to S64) has been illustrated, but the detection order is not limited to the above example, and the reference unit 31 is not limited thereto. The output voltage may be detected in the order of the electrode pair 11.

  In addition, the processing function of the detection circuit 20 in the snow density sensor 1B that performs the snow density measurement process as shown in the third example is, for example, one or more elements such as CPU, MPU, ASIC, and PLD. It can be realized using.

  In the third example, the variable capacitor 31a is used, and when the difference between the output voltage of the electrode pair 11 and the output voltage of the electrode pair 11 exceeds the threshold value, the capacitance of the variable capacitor 31a is changed. In addition, a plurality of capacitors (capacitances that are known and have different capacitances) can also be used. In this case, first, the difference between the output voltage of one of the capacitors and the output voltage of the electrode pair 11 is compared with a threshold value, and if the difference exceeds the threshold value, another one similarly The difference between the output voltage and the output voltage of the electrode pair 11 is compared with a threshold value. The capacitance of the capacitor when the difference is equal to or less than the threshold is determined as the capacitance between the electrode pair 11.

  As described above, the snow density sensors 1A and 1B have been described as examples. However, the above method can be applied to various measurement devices in addition to the snow density sensor. For example, the above method can be similarly applied to a measuring device that measures the capacitance, relative dielectric constant, density, moisture content, and the like of soil.

  In the above description, after obtaining the electrostatic capacity between the electrode pair, the relative dielectric constant of the substance between the electrode pair is obtained from the electrostatic capacity, and the relative dielectric constant is between the electrode pair. The measuring device which calculated | required the density of the substance and output the density was illustrated. In addition, it is possible to realize a capacitance measuring device that obtains and outputs the capacitance, and a relative dielectric constant measuring device that obtains and outputs the relative permittivity.

Regarding the embodiment described above, the following additional notes are further disclosed.
(Supplementary note 1) a pair of electrodes;
A reference unit comprising a first capacitor;
A detection unit for detecting outputs of the pair of electrodes and the first capacitor;
A switch unit that connects the detection unit to the pair of electrodes or the first capacitor;
Using the first output of the pair of electrodes connected to the detection unit by the switch unit and the second output of the first capacitor connected to the detection unit by the switch unit, between the pair of electrodes And a first calculation unit that calculates a first capacitance.

(Supplementary Note 2) The reference unit includes a second capacitor,
The detection unit detects outputs of the pair of electrodes, the first capacitor, and the second capacitor,
The switch unit connects the detection unit to the pair of electrodes, the first capacitor, or the second capacitor,
The first calculation unit calculates the first capacitance using the first output, the second output, and a third output of the second capacitor connected to the detection unit by the switch unit. The measuring apparatus according to Supplementary Note 1, wherein:

(Supplementary Note 3) The first capacitor is a variable capacitor,
The first calculation unit calculates the first capacitance using the first output, the second output, and a third output of a second capacitor obtained by changing a capacitance of the first capacitor. The measuring device according to appendix 1, characterized by:

(Supplementary Note 4) It has a relational expression between the capacitance between the pair of electrodes and the output from the pair of electrodes,
The first calculation unit includes:
Based on the capacitances of the first capacitor and the second capacitor, and the second output and the third output, the relational expression is corrected,
The measurement apparatus according to appendix 2 or 3, wherein the first capacitance is calculated using the corrected relational expression and the first output.

(Supplementary Note 5) The first calculation unit includes:
Based on the capacitances of the first capacitor and the second capacitor, and the second output and the third output, a relational expression between the capacitance between the pair of electrodes and the output from the pair of electrodes. Produces
The measurement apparatus according to appendix 2 or 3, wherein the first capacitance is calculated using the generated relational expression and the first output.

(Supplementary Note 6) The first calculation unit includes:
Calculating a first difference between the first output and the second output and comparing the first difference with a set value;
When the first difference is less than or equal to the set value, the capacitance of the first capacitor is determined as the first capacitance;
Calculating a second difference between the first output and the third output and comparing the second difference with the set value;
4. The measuring device according to appendix 2 or 3, wherein when the second difference is equal to or less than the set value, the capacitance of the second capacitor is determined as the first capacitance.

  (Supplementary note 7) Any one of Supplementary notes 1 to 6, further comprising a second calculation unit that calculates a relative dielectric constant of the substance between the pair of electrodes using the calculated first capacitance. The measuring device described in 1.

(Additional remark 8) The measuring apparatus of Additional remark 7 characterized by further including the 3rd calculation part which calculates the density of the said substance using the calculated said relative dielectric constant.
(Supplementary note 9) The measuring apparatus according to any one of supplementary notes 1 to 8, wherein the pair of electrodes and the reference portion are arranged in an equivalent temperature environment.

(Additional remark 10) A reference part provided with a pair of electrodes, a first capacitor, a detection part for detecting outputs of the pair of electrodes and the first capacitor, and the detection part as the pair of electrodes or the first capacitor Using the switch unit to be connected, the first output of the pair of electrodes connected to the detection unit by the switch unit, and the second output of the first capacitor connected to the detection unit by the switch unit, A measurement method using a measurement device including a calculation unit that calculates a first capacitance between the pair of electrodes,
Arranging the pair of electrodes with a substance to be measured interposed therebetween;
Connecting the detection unit to the pair of electrodes by the switch unit, and detecting the first output by the detection unit;
Connecting the detection unit to the first capacitor by the switch unit, and detecting the second output by the detection unit;
A step of calculating the first capacitance using the first output and the second output by the calculation unit.

(Supplementary Note 11) The reference unit includes a second capacitor,
Connecting the detection unit to the second capacitor by the switch unit, and detecting a third output of the second capacitor by the detection unit;
(Supplementary note 10) In the step of calculating the first capacitance by the calculation unit, the first capacitance is calculated using the first output, the second output, and the third output. Measurement method described in 1.

(Supplementary Note 12) The first capacitor is a variable capacitor,
In the step of calculating the first capacitance by the calculation unit, the first output, the second output, and the third output of the second capacitor in which the capacitance of the first capacitor is changed, The measurement method according to appendix 10, wherein the first capacitance is calculated.

(Additional remark 13) It has the relational expression of the electrostatic capacitance between the pair of electrodes and the output from the pair of electrodes,
The step of calculating the first capacitance by the calculation unit includes:
Correcting the relational expression based on capacitances of the first capacitor and the second capacitor, and the second output and the third output;
The method according to claim 11 or 12, further comprising: calculating the first capacitance using the corrected relational expression and the first output.

(Supplementary Note 14) The step of calculating the first capacitance by the calculation unit includes:
Based on the capacitances of the first capacitor and the second capacitor, and the second output and the third output, a relational expression between the capacitance between the pair of electrodes and the output from the pair of electrodes. Generating
The method according to claim 11 or 12, further comprising: calculating the first capacitance using the generated relational expression and the first output.

(Supplementary Note 15) The step of calculating the first capacitance by the calculation unit includes:
Calculating a first difference between the first output and the second output and comparing the first difference with a set value;
Determining the capacitance of the first capacitor as the first capacitance when the first difference is less than or equal to the set value;
Calculating a second difference between the first output and the third output and comparing the second difference with the set value;
The method according to claim 11 or 12, further comprising: determining the capacitance of the second capacitor as the first capacitance when the second difference is equal to or less than the set value. .

  (Supplementary note 16) In any one of supplementary notes 11 to 16, further comprising a step of arranging the pair of electrodes and the reference portion in an equivalent temperature environment before the step of arranging the pair of electrodes. The measurement method described.

DESCRIPTION OF SYMBOLS 1A, 1B Snow density sensor 10 Detection part 11 Electrode pair 11a, 11b Electrode 20 Detection circuit 20a, 31 Reference part 21 1st reference part 21a 1st capacitor 22 2nd reference part 22a 2nd capacitor 23 Switch part 24 Detection part 25 Recording Unit 26 capacitance calculation unit 27 relative permittivity calculation unit 28 snow density calculation unit 29 snow density output unit 30a, 30b, 30c characteristic curve 31a variable capacitance capacitor 32 variable capacitance control unit

Claims (9)

A pair of electrodes;
A reference unit comprising a first capacitor;
A detection unit for detecting outputs of the pair of electrodes and the first capacitor;
A switch unit that connects the detection unit to the pair of electrodes or the first capacitor;
Using the first output of the pair of electrodes connected to the detection unit by the switch unit and the second output of the first capacitor connected to the detection unit by the switch unit, between the pair of electrodes And a first calculation unit that calculates a first capacitance. The reference unit includes a second capacitor,
The detection unit detects outputs of the pair of electrodes, the first capacitor, and the second capacitor,
The switch unit connects the detection unit to the pair of electrodes, the first capacitor, or the second capacitor,
The first calculation unit calculates the first capacitance using the first output, the second output, and a third output of the second capacitor connected to the detection unit by the switch unit. The measuring apparatus according to claim 1. The first capacitor is a variable capacitor;
The first calculation unit calculates the first capacitance using the first output, the second output, and a third output of a second capacitor obtained by changing a capacitance of the first capacitor. The measuring device according to claim 1. A relational expression between the capacitance between the pair of electrodes and the output from the pair of electrodes;
The first calculation unit includes:
Based on the capacitances of the first capacitor and the second capacitor, and the second output and the third output, the relational expression is corrected,
The measuring apparatus according to claim 2, wherein the first capacitance is calculated using the corrected relational expression and the first output. The first calculation unit includes:
Based on the capacitances of the first capacitor and the second capacitor, and the second output and the third output, a relational expression between the capacitance between the pair of electrodes and the output from the pair of electrodes. Produces
The measurement apparatus according to claim 2, wherein the first capacitance is calculated using the generated relational expression and the first output. The first calculation unit includes:
Calculating a first difference between the first output and the second output and comparing the first difference with a set value;
When the first difference is less than or equal to the set value, the capacitance of the first capacitor is determined as the first capacitance;
Calculating a second difference between the first output and the third output and comparing the second difference with the set value;
4. The measuring device according to claim 2, wherein when the second difference is equal to or less than the set value, the capacitance of the second capacitor is determined as the first capacitance.   7. The apparatus according to claim 1, further comprising a second calculation unit that calculates a relative dielectric constant of the substance between the pair of electrodes using the calculated first capacitance. Measuring device.   The measurement apparatus according to claim 7, further comprising a third calculation unit that calculates the density of the substance using the calculated relative dielectric constant. A pair of electrodes, a reference unit including a first capacitor, a detection unit for detecting outputs of the pair of electrodes and the first capacitor, and a switch unit for connecting the detection unit to the pair of electrodes or the first capacitor And the first output of the pair of electrodes connected to the detection unit by the switch unit and the second output of the first capacitor connected to the detection unit by the switch unit, A measurement method using a measurement device including a calculation unit that calculates a first capacitance between
Arranging the pair of electrodes with a substance to be measured interposed therebetween;
Connecting the detection unit to the pair of electrodes by the switch unit, and detecting the first output by the detection unit;
Connecting the detection unit to the first capacitor by the switch unit, and detecting the second output by the detection unit;
A step of calculating the first capacitance using the first output and the second output by the calculation unit.

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