JPS6245500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring capacitance of a capacitive element.

Conventionally, the first capacitance measuring device for capacitive elements
The configuration described below with reference to the figure is proposed.

That is, e ₀ = E ₀ sinωt (1) (where E ₀ is the amplitude, ω is the angular frequency,
t is time) It has an AC constant voltage source 1 that can obtain an AC constant voltage e ₀ , and current-voltage conversion is performed through a capacitive element 2 to be measured represented by a parallel equivalent circuit of a capacitance C _p and a conductance g. The input side of the circuit 3 is connected, and from the output side of this current-voltage conversion circuit 3, based on the AC current supplied from the AC constant voltage source 1 side through the capacitive element 2 to be measured, e ₁ = -E ₀ R _S (ωC _P cosωt+gsinωt)
......(2) The electrostatic capacitance C _P of the capacitive element 2 to be measured is expressed as
The AC voltage e ₁ is the sum (vector sum) of the AC voltage proportional to the conductance g and the AC voltage proportional to the conductance g. In this case, the current-voltage conversion circuit 3 has an input terminal a connected to the AC constant voltage source 1 through the capacitive element 2 to be measured, an input terminal b connected to the ground and having the opposite polarity to the input terminal a, It consists of an operational amplifier 4 having an output terminal c having a polarity opposite to that of an input terminal a, and a resistor R _S connected between the output terminal c and the input terminal a.

Also, the input side of the phase shift circuit 5 is connected to the AC constant voltage source 1, and from the output side of the phase shift circuit 5, based on the AC constant voltage _e0 , e ₃ =-E ₀ /R ₁ ωC ₁ sin (ωt−π/2)=E ₀ /
R ₁ ωC ₁ cosωt (3) An AC voltage e ₃ having a phase difference of 90° with respect to an AC constant voltage e ₀ is obtained. In this case, the phase shift circuit 5 includes an operational amplifier 6 having an input terminal a, an input terminal b connected to ground and having a polarity opposite to that of the input terminal a, and an output terminal c having a polarity opposite to the input terminal a. , consisting of a resistor R ₁ whose one end is connected to the input terminal a of the operational amplifier 6 and the other end connected to the AC constant voltage source 1, and a capacitor C ₁ connected between the output terminal c and the input terminal a of the operational amplifier 6. .

The AC voltage e ₁ obtained from the current-voltage conversion circuit 3 is then supplied to one input terminal of the multiplier circuit 8 through an amplifier 7 with polarity inversion as required.
On the other hand, the AC voltage _e3 obtained from the phase shift circuit 5 is supplied to the other input terminal of the multiplier circuit 8 through an amplifier 9 as required, and the AC voltage e3 is supplied from the multiplier circuit 8 as required.
Based on e ₁ and e ₃ , E ₁ = K ₁ K ₃ E ₀ ² R _S C _P /2P ₁ C ₁ ......(4) The capacitance C _P of the capacitive element 2 to be measured is expressed as
It is designed to obtain a DC voltage E ₁ proportional to . In this case, the multiplier circuit 8 is e ₄ =K ₁ e ₁・K ₃ e ₃ =K ₁ E ₀ R _S (ωC _P cosωt+gsinωt)・K ₃ E ₀ /R ₁ ωC ₁ cosωt = K ₁ K ₃ E ₀ ² R _S C _P (1+cos2ωt)/2R ₁ C ₁ +K ₁ K ₃ E ₀ ² R _S gsin2ωt/2
R ₁ ωC ₁ =K ₁ K ₃ E ₀ ² R _S C _P /2R ₁ C ₁ +K ₁ K ₃ E ₀ ² R _S (ωC _P cos2ωt+gsin2ωt)
/2R ₁ ωC ₁ ...(5) (however, K ₁ and K ₃ are constants), AC voltage
Multiplier circuit main body 10 configured to obtain output e ₄ of the product of the voltage based on e ₁ and the voltage based on AC voltage e ₃
and a low frequency converter 11 configured to obtain a DC voltage E ₁ expressed by equation (4) based on the output e ₄ connected to the output side thereof.

The above is a capacitance measuring device for a capacitive element that has been proposed conventionally.
Although the capacitance C _P seen in the parallel equivalent circuit of the capacitive element 2 to be measured can be determined by _E1 , the multiplier circuit 8, particularly the multiplier circuit main body 10, can be determined by the current that uniquely handles only one signal. - It is difficult to determine the accuracy of voltage conversion circuit 3, phase shift circuit 5, amplifiers 7 and 9, etc. because it requires a complex circuit configuration that handles two signals. Is Umono.

Therefore, in the case of the conventional device described above in FIG.
This has the drawback that the capacitance C _P that can be determined from the DC voltage E ₁ obtained from the multiplier circuit 8 cannot be made highly accurate.

Therefore, the present invention aims to propose a novel capacitance measuring device for a capacitive element that does not have such drawbacks, and this will become clear from the detailed description below.

FIG. 2 shows an example of an apparatus for measuring the capacitance of a capacitive element according to the first invention of the present application, and corresponding parts to those in FIG. It has an AC constant voltage source 1 that can obtain an AC constant voltage e ₀ expressed by equation 1 ₎ , and a first The input side of the current-voltage conversion circuit 3 consisting of the operational amplifier 4 and the resistor R _S is connected in the same way as described above in the figure, and the output side of the current-voltage conversion circuit 3 is connected as described above in FIG. 1. Similarly, it can be expressed by equation (2) mentioned above,
The AC voltage e ₁ is the sum of an AC voltage proportional to the capacitance C _P of the capacitive element 2 to be measured and an AC voltage proportional to the conductance g.

Also, the input side of a phase shift circuit 5 consisting of an operational amplifier 6, a resistor R ₁ and a capacitor C ₁ is connected to the AC constant voltage source 1 as described above in FIG. From the output side, an AC voltage e ₃ having a phase difference of 90° with respect to the AC constant voltage e ₀ expressed by equation (3) described above is obtained in the same way as shown in FIG. 1. .

Therefore, the AC voltage e ₁ from the current-voltage conversion circuit 3
is supplied to one input side of a multiplier circuit 8 consisting of a multiplier circuit main body 10 and a low-frequency amplifier 11 through an amplifier 7 with polarity inversion if necessary, as described above in FIG. The alternating current voltage _e3 obtained from the phase shift circuit 5 is supplied to the other input side of the multiplier circuit 8 through the amplifier 9 as described above in FIG. The output e ₄ expressed by equation (5) mentioned above in
Through the process of obtaining , the DC voltage E ₁ expressed by the above-mentioned equation (4) is obtained.

Also, the AC voltage obtained from the current-voltage conversion circuit 3
e ₁ is supplied to one input terminal of another multiplier circuit 12 through the above-mentioned amplifier 7 as necessary, and the other input terminal of the multiplier circuit 12 is supplied with an AC constant voltage source 1.
An alternating current constant voltage e ₀ is supplied as necessary through the amplifier 13, and therefore, based on the alternating current voltages e ₀ and e ₁ from the multiplier circuit 12, E ₂ =K ₀ K ₁ E ₀ ² R _S g/2 . . . . . . (6) A DC voltage E ₂ proportional to the conductance g of the capacitive element 2 to be measured is obtained as shown in (6). In this case, the multiplier circuit 12 is e ₅ =K ₀ e ₀・K ₁ e ₁ =K ₀ E ₀ sinωt・K ₁ E ₀ R _S (ωC _P cosωt+gsinωt) =K ₀ K ₁ E ₀ ² R _S ω _C Psin2ωt/ 2+K ₀ K ₁ E ₀ ² R _S g (1-cos2ωt)/2 = K ₀ K ₁ E ₀ ² R _S g/2+K ₀ K ₁ E ₀ ² R _S (ωC _P sin2ωt-gcos2ωt)/2...
(7) (where K ₀ and K ₁ are constants), AC voltage
Multiplier circuit main body 14 configured to obtain output e ₅ which is the product of the output based on e ₀ and the output based on AC voltage e ₁
and a low frequency wave generator 15 connected to its output side and configured to obtain a DC voltage F ₂ expressed by equation (6) based on the output e ₅ .

Further, the AC voltage e ₁ obtained from the current-voltage conversion circuit 3 is supplied to the AC-DC conversion circuit 20 through the amplifier 7 with polarity reversal as required, and from this, based on the AC voltage e ₁ , E ₃ ∝K ₄ ｜e ₁ ｜ =K ₄ ｜−E ₀ R _S (ωC _P cosωt+gsinωt)｜ =K ₄ E ₀ R _S (ω ² C ² _P g ² ) = K ₄ E ₀ R _S ｜Y｜ ………( 8) (where K ₄ is a constant) DC voltage E ₃ proportional to admittance |Y| of capacitive element 2 to be measured
It is designed so that you can get

Furthermore, the AC constant voltage obtained from the AC constant voltage source 1
e ₀ is connected to other alternating current through amplifier 21 as necessary.
It is supplied to the DC conversion circuit 22, and from this, based on the AC constant voltage e ₀ , it is expressed as E ₄ ∝K ₅ |e| =K ₅ |E ₀ sinωt| =K ₅ E ₀ (9) (however, K ₅ is a constant), so that a DC voltage E ₄ proportional to the amplitude E ₀ of the AC constant voltage e ₀ can be obtained.

The DC voltages E ₁ and E ₂ obtained from the multiplier circuits 8 and 12 are supplied to the multiplier circuit 24 of the arithmetic circuit 23, and based on the DC voltages E ₁ and F ₂ , E ₂ /E ₁ =K ₀ K ₁ E ₀ ² R _S g/2・2R ₁ C ₁
/K ₁ K ₃ E ₀ ² R _{S CP} = K ₀ R ₁ C ₁ /K ₃・g/ _CP = s/ω _{0 CP} = tan δ = D ......(10) Capacitance to be measured The arrangement is such that an output Q1 representing the loss D of the element 2 is obtained.

Further, the DC voltages E ₃ and E ₄ obtained from the AC-DC conversion circuits 20 and 22 are supplied to another division circuit 25 of the arithmetic circuit 23, from which the DC voltages E ₃ and E 4 are
Based on E ₄ , E ₃ /E ₄ =K ₄ E ₀ R _S |Y| /K ₅ E ₀ =K ₄ /K ₅・R _S |Y| =K ₇ R _S |Y| ………(11 ) The admittance of the capacitive element 2 to be measured is expressed as |
An output Q2 representing Y| is obtained.

Furthermore, the output Q obtained from the division circuits 24 and 25
1 and Q2 are supplied to the calculator 26, and based on the outputs Q1 and Q2, using the known angular frequency ω of the constant AC voltage e ₀ , |Y|/ω(1+D ² )== _CP ... ...(12) An output Q3 representing the electrostatic capacitance C _P of the capacitive element 2 to be measured expressed as follows is obtained. Note that the fact that the output Q3 of equation (12) is obtained in the arithmetic unit 26 based on the outputs Q1 and Q2 is because K ₀ , K ₃ , R ₁ and C ₁ in equation (10) representing the output Q1 are known. , therefore ω
₀ is known, and in equation (11) representing the output Q2,
It will be understood that K ₇ and R _S are known.

The above is an example of the capacitance measuring device for a capacitive element according to the first invention of the present application. Capacitive element to be measured 2
The capacitance C _P seen from the parallel equivalent circuit of can be determined, but the output Q3 is the result of the output Q2 representing the admittance |Y| of the capacitive element 2 to be measured obtained from the divider circuit 25 and the output Q2 obtained from the divider circuit 25. The calculation based on the above-mentioned equation (12) is performed based on the output Q1 representing the loss D of the capacitive element 2 to be measured.

Therefore, according to an example of the first invention of the present application, the capacitance C _P of the capacitive element 2 to be measured is determined based on the admittance |Y| of the capacitive element 2 to be measured and the loss D of the capacitive element 2 to be measured, It is configured as desired.

Here, the output Q2 is generated by the current-voltage conversion circuit 3 based on the fact that the AC current is supplied to the current-voltage conversion circuit 3 from the AC constant voltage source 1 side from which the AC constant voltage e ₀ is obtained through the capacitive element 2 to be measured. The AC voltage e ₁ obtained from the above is simply converted into a DC voltage E ₃ which corresponds to converting the AC voltage e 1 into a DC voltage in the AC-DC conversion circuit 20, and the AC constant voltage e ₀ obtained from the AC constant voltage source 1 is simply converted into an AC voltage E 3 which corresponds to converting the AC voltage e 1 obtained from the
The output Q2 is simply divided by the dividing circuit 25 by the DC voltage _E4 equivalent to that converted into a DC voltage by the DC conversion circuit 22, and the output Q2 is the amplitude of the AC constant voltage _e0.
It is an output that can be obtained without depending on E ₀ , and therefore the output Q2 cannot be obtained from a circuit that includes a multiplication circuit that is difficult to construct with high precision. Therefore, the output Q2 can be easily obtained with high precision.

Therefore, according to an example of the first invention of the present application, the capacitance C _P of the capacitive element 2 to be measured is determined based on the admittance |Y| of the capacitive element 2 to be measured and the loss D of the capacitive element 2 to be measured. If configured as above, the admittance |Y| can be obtained with high precision.

The output Q1 is an AC voltage having a phase difference of 90° with respect to the AC voltage e ₁ obtained from the current-voltage conversion circuit 3 and the AC constant voltage e ₀ obtained from the AC constant voltage source 1 obtained from the phase shift circuit 5. Multiplying circuit 8 with voltage e ₃
The multiplier circuit 12 is composed of the DC component E ₁ of the AC voltage e ₄ multiplied by the AC voltage e ₁ obtained from the current-voltage conversion circuit 3 and the AC constant voltage e ₀ obtained from the AC constant voltage source 1 The output Q1 is a DC output obtained by dividing the AC voltage e ₅ multiplied by the DC component E ₂ by the division circuit 24. Therefore, the output Q1 is a multiplication circuit that is difficult to configure with high precision. This can be obtained from a circuit containing Therefore, it cannot be said that it is easy to obtain the output Q1 with high precision.

Therefore, according to an example of the first invention of the present application, the capacitance C _P of the capacitive element 2 to be measured is determined based on the admittance |Y| of the capacitive element 2 to be measured and the loss D of the capacitive element 2 to be measured. If the configuration is as follows, it is difficult to obtain the loss D described above with high precision.

However, the loss D of the capacitive element 2 to be measured is generally D
Since there is a relationship of ≪1, even if it is difficult to obtain the loss D with high precision, there is no problem as much as on the left,
This means that the capacitance C _P of the capacitive element 2 to be measured is determined based on the admittance |Y| of the capacitive element 2 to be measured and the loss D of the capacitive element 2 to be measured. The loss D is used as D ² as shown in equation (12) when calculating the capacitance C _P just described, and this is especially true since in this case D has a relationship of <<1. According to an example of the device for measuring the capacitance of a capacitive element according to the first invention of the present application, the capacitance C _P that can be determined from the output Q3 obtained from the arithmetic circuit 23 is made to have high accuracy. It has the great feature of being able to do

Next, an example of an apparatus for measuring the capacitance of a capacitive element according to the second invention of the present application will be described in detail with reference to FIG. 3. Parts corresponding to those in FIG. Although omitted, in the configuration described above in FIG. 2, the output side of the amplifier 7 and the multiplier circuit 8
and 12, an arithmetic circuit 31 is inserted between one input side of the circuit 12, and is configured to obtain an output voltage having a substantially constant level even when the level of the input voltage changes;
Therefore, from this amplifier circuit 31, based on the AC voltage e ₁ , e ₂ =K ₂ E ₀ R _S (ωC _P cosωt + gsinωt)
......(2) An alternating current voltage e ₂ with a nearly constant level expressed as ′
Accordingly, the output e ₄ from the multiplier circuit 8 expressed by the equation (5) mentioned above is
In place of the DC voltage E ₁ expressed by the above-mentioned equation (4) obtained through the process of obtaining in the multiplier circuit main body 10, e ₄ ′=e ₂・K ₃ e ₃ = according to the above-mentioned equation (5) K ₂ E ₀ R _S (ωC _P cosωt + gsinωt)・K ₃ E ₀ /R ₁ ωC ₁ cosωt) = K ₂ K ₃ E ₀ ² P _S C _P (1 + cos2ωt) / 2R ₁ C ₁ +K ₂ K ₃ E ₀ ² R _S gsin2ωt/2
R ₁ ωC ₁ =K ₂ K ₃ E ₀ ² R _S C _P /2R ₁ C ₁ +K ₂ K ₃ E ₀ ² R _S C _P 2R ₁ C ₁ +K ₂ K ₃ E ₀ ² R _S (ω
C _P cos2ωt+gsin2ωt)/2R ₁ ωC ₁ ......(5)' Through the process in which the output _{e 4} expressed _{as 3} E ₀ ² R _S C _P /2R ₁ C ₁ ………(4
)' can be obtained, and from the multiplier circuit ₁₂ , the output expressed by equation (7) mentioned above can be obtained.
Instead of the DC voltage E ₂ expressed by the above-mentioned equation (6) obtained through the process of obtaining e 5 in the multiplier circuit main body ₁₄ , e ₅ ′=e ₂・K ₀ e according to the above-mentioned equation (7) ₀ = K ₂ E ₀ R _S (ωC _P cosωt + gsinωt)・K ₀ E ₀ sinωt = K ₀ K ₂ E ₀ ² R _S ωC _P sin2ωt/2+K ₀ K ₂ E ₀ ² R _S g (1-cos2ωt)/2 =K ₀ K ₂ E ₀ ² R _S g/2+K ₀ K ₂ E ₀ ² R _S ( _ωCP sin2ωt−gcos2ωt)/2……
After the process in which the output e ₅ ' expressed by (7)' is obtained in the multiplier circuit main body 14, E ₂ '=K ₀ K ₂ E ₀ ² R _S g/2 according to the above-mentioned equation (6)... It has the same configuration as the case in FIG. 2 except that a DC voltage E ₂ ' expressed by (6)' is obtained.

It should be noted that the fact that the AC voltage e ₂ obtained from the amplifier circuit 31 has a constant level is expressed as |e ₂ |=K ₂ E ₀ R _S (ω ² C _P ² +g ² ) = (13) This means that the absolute value |e ₂ | of the AC voltage e ₂ has a substantially constant level, and the amplifier circuit 31 is designed to obtain such an AC voltage e ₂ .
Even if the capacitance C _P and conductance g of the capacitive element 2 to be measured change within the expected range, that is, (9)
Even if C _P and g in the equation change within the expected range, the coefficient K ₂ (amplification degree) changes accordingly, so that the AC voltage e ₂ can be obtained at a substantially constant level. It consists of an amplifier circuit with AGC function.
Further, the output Q1 obtained from the division circuit 24 of the arithmetic circuit 23 is divided by the DC voltages E ₁ ' and E ₂ ' obtained from the multiplication circuits 8 and 12 in the division circuit 24 according to equation (10) described above. Therefore, the division circuit 24 of the arithmetic circuit 23 in the case of FIG.
Therefore, the output Q3 obtained from the arithmetic unit 26 of the arithmetic circuit 23 is the same as the output Q3 obtained from the arithmetic unit 26 of the arithmetic circuit 23 in the case of FIG. Output Q3
This is obtained as follows.

The above is an example of the capacitance measuring device for a capacitive element according to the second invention of the present application. The output Q representing the loss D of the capacitive element 2 to be measured obtained from the division circuit 24 of the arithmetic circuit 23 is similar to the example of the capacitive element capacitance measuring device according to the first invention of the present application described above.
1. Capacitive element to be measured 2 obtained from the division circuit 25
Since the output Q2 representing _the admittance |Y| of Similarly to the above case, the capacitance C _P of the capacitive element 2 to be measured, which can be determined from the output Q3 obtained from the arithmetic circuit 23, can be determined with high precision. However, in this case, the output Q1 obtained from the dividing circuit 24 is the capacitance C of the capacitive element 2 to be measured.
In this application, the capacitance C _P of the capacitive element 2 to be measured, which can be determined from the output Q3, can be obtained with high resolution regardless of the values of _P and conductance g, and is described above in FIG. It is possible to have higher resolution than the case according to the first invention.

To explain the reason now, it is because the output Q1 is obtained from the multiplier circuits 8 and 12 and is divided into the divider circuit 24 by the DC voltages E' ₁ and E' ₂ shown in equations (4)' and (6)', respectively. The output obtained by dividing the DC voltages E ₁ ' and E ₂ ' by the AC voltages e ₃ and e ₀ for the multiplier circuits 8 and 12, respectively, is the output of the capacitance to be measured. Capacitance C _P of element 2
Since the alternating current voltage e ₂ is at an approximately constant level regardless of the value of the conductance g, the multiplier circuits 8 and 1
2, the multiplier circuit 8 can obtain the DC voltages E ₁ ′ and E ₂ ′ with high resolution regardless of the values of the capacitance C _P and conductance g of the capacitive element 2 to be measured.
The AC voltages multiplied by the AC voltages e ₃ and e ₀ for and 12, respectively, are the capacitance C of the capacitive element 2 to be measured.
This is easier than the case of _the first invention of the present application described above in _FIG .
Therefore, the output Q1 is the capacitance C of the capacitive element 2 to be measured.
This is because, regardless of the values of _P and conductance g, it is easier to obtain higher resolution than in the case of the first invention of the present application described above with reference to FIG.

In the above description, based on the outputs Q1 and Q2 expressed by the expressions (10) and (11) from the arithmetic unit 26 of the arithmetic circuit 23, the output Q3 expressed by the expression (12) is obtained. When capacitive element 2 is expressed as a parallel equivalent circuit with capacitance C _P and conductance g, its capacitance C
This describes the case where _P can be determined. Based on the outputs Q1 and Q2 expressed by equations (10) and (11) from the arithmetic unit 26 of the arithmetic circuit 23, |Y|(1+D ² )〓/ω=C _P (1+D ² )=C _S ……
(12) Obtain the output represented by ', and use this to make it possible to determine the capacitance C _S when the capacitive element 2 to be measured is represented by a series equivalent circuit of a capacitance C _S and a resistor. It is also possible.

Also, between each of the multiplication circuits 8 and 12 and the division circuit 24, between the husbands of the AC-DC conversion circuits 20 and 22 and the division circuit 25, and between each of the division circuits 24 and 25 and the arithmetic unit 26. Amplifying circuits can be inserted in each case as necessary, and multiplier circuits 8 and 1 can also be inserted.
2 can be constructed such that the multiplier circuit bodies 10 and 14 are replaced with a synchronous detection circuit in place of the synchronous detection circuit body, and various other modifications and changes can be made without departing from the spirit of the present invention. Will.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a conventional capacitance measuring device for a capacitive element, FIG. 2 is a system diagram showing an example of a capacitance measuring device for a capacitive element according to the first invention of the present application, and FIG. 3 is a system diagram showing an example of a capacitance measuring device of the present invention. FIG. 7 is a system diagram showing an example of a capacitance measuring device for a capacitive element according to a second invention. In the figure, 1 is an AC constant voltage source, 2 is a capacitive element to be measured, C _P is capacitance, g is conductance, 3 is a current-voltage conversion circuit, 5 is a phase shift circuit, 8 and 12
is a multiplication circuit, 10 and 14 are multiplication circuit bodies, 11
20 and 22 are AC-DC conversion circuits, 23 is an arithmetic circuit, 24 and 25 are division circuits, 26 is an arithmetic unit, and 31 is an amplifier circuit, respectively.

Claims (1)

[Scope of Claims] 1. An AC constant voltage source, which is connected to the AC constant voltage source through a capacitive element to be measured, and which is connected to the AC constant voltage source through the capacitive element to be measured based on the AC current supplied from the AC constant voltage source side through the capacitive element to be measured. a current-voltage conversion circuit configured to obtain a first alternating current voltage that is the sum of an alternating current voltage proportional to the capacitance of the capacitive element and an alternating current voltage proportional to the conductance; and an alternating current constant voltage obtained from the above alternating current constant voltage source. a phase shift circuit configured to obtain a third alternating current voltage having a phase difference of 90 degrees with respect to the first alternating voltage; a first multiplier circuit or a synchronous detection circuit configured to obtain a proportional first DC voltage; and a first multiplier circuit or a synchronous detection circuit configured to obtain a proportional first DC voltage; a second multiplier circuit or a synchronous detection circuit configured to obtain a second DC voltage proportional to the conductance; and a third DC voltage proportional to the admittance of the capacitive element to be measured based on the first AC voltage. and an arithmetic circuit configured to obtain an output representing the capacitance of the capacitive element to be measured based on the first, second, and third DC voltages. A capacitance measuring device for a capacitive element, which is characterized by: 2 connected to the AC constant voltage source through an AC constant voltage source and a capacitive element to be measured, and measuring the capacitance of the capacitive element to be measured based on the AC current supplied from the AC constant voltage source through the capacitive element to be measured; a current-voltage conversion circuit configured to obtain a first alternating voltage that is the sum of an alternating current voltage proportional to conductance and an alternating current voltage proportional to conductance; and a second alternating current voltage having a constant level based on the first alternating voltage. an amplification circuit configured to obtain a third AC voltage having a phase difference of 90° with respect to the AC constant voltage obtained from the AC constant voltage source; , a first multiplier circuit or a synchronous detection circuit configured to obtain a first DC voltage proportional to the capacitance of the capacitive element to be measured based on the second and third AC voltages, and the AC constant voltage a second multiplier circuit or a synchronous detection circuit configured to obtain a second DC voltage proportional to the conductance of the capacitive element to be measured based on the AC voltage obtained from the source and the second AC voltage; an AC-DC conversion circuit configured to obtain a third DC voltage proportional to the admittance of the capacitive element to be measured based on the first AC voltage; 1. A capacitance measuring device for a capacitive element, comprising: an arithmetic circuit configured to obtain an output representing the capacitance of the capacitive element to be measured.