JP2010107359A - Capacitance sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance sensor with a simpler structure than conventional ones and capable of quick measurement of a thickness of a film-like medium. <P>SOLUTION: The capacitance sensor 10 detects the thickness of the film-like medium by means of a change in capacitance caused by inserting the film-like medium B into an interval between opposite electrodes comprising two oppositely placed electrodes. The sensor includes a first opposite electrode 14 connected with an AC source 12, a second opposite electrode 16 which is grounded, an inter-electrode wire 18 for electrically connecting between the first and second opposite electrodes in series, and a detector 22 provided at a middle point P of the inter-electrode wire and having an output end 20 for outputting the change in the capacitance. The film-like medium is inserted into the first opposite electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a capacitance sensor that detects the thickness of a film-like medium such as paper.

  By providing a counter electrode comprising two electrodes facing each other at a predetermined interval in the conveyance path of the film-like medium, and outputting a change in capacitance between the electrodes, a film such as paper A capacitance sensor for detecting the thickness of a medium is known.

  By the way, the dielectric constant of a film-like medium such as paper is generally about the same as the dielectric constant of a medium (usually air) existing between the electrodes of the counter electrode. For this reason, in this type of capacitance sensor, when the output changes, it is due to the change in the thickness of the film-like medium, or the change in the dielectric constant of the medium due to the influence of temperature, humidity, etc. It was difficult to separate.

In order to solve this problem, a technique has been proposed in which a second counter electrode that measures a change in the dielectric constant of the medium is provided in addition to the first counter electrode that measures the dielectric constant of the film-like medium (for example, See Patent Document 1.
JP 59-131104 A

  However, in the technique disclosed in Patent Document 1, in order to obtain the change in the dielectric constant derived only from the film-like medium from the outputs of the first and second counter electrodes, excluding the influence of the dielectric constant of the medium, another calculation is performed. It was necessary to provide a circuit.

  For this reason, the technique disclosed in Patent Document 1 may complicate the circuit configuration of the capacitance sensor, and requires a calculation time in the calculation circuit, so that the thickness of the film-like medium cannot be measured quickly. There was a fear.

  The present invention has been made in view of the above-described problems. Accordingly, an object of the present invention is to provide a capacitance sensor that has a simpler structure than the conventional one and can rapidly measure the thickness of a film-like medium.

  The inventor of the present invention electrically connects a first counter electrode into which a film-like medium is inserted and a second counter electrode for evaluating a change in the dielectric constant of the medium in series by inter-electrode wiring. The inventors have conceived that the above-described problem can be solved by taking out a detection signal from the midpoint of the intermediate wiring.

  Therefore, the capacitance sensor of the present invention utilizes the change in capacitance caused by inserting a film-like medium into the gap between the electrodes of the counter electrode composed of two electrodes arranged opposite to each other. The thickness of the film-like medium is detected.

  The capacitance sensor has a first counter electrode connected to an AC power source and a grounded second counter electrode as counter electrodes, and electrically connects the first and second counter electrodes in series. Provided with a detector having an inter-electrode wiring and an output terminal for outputting a detection signal indicating a change in capacitance, provided at a connection midpoint of the inter-electrode wiring, and two of the first counter electrodes A membranous medium is inserted between the electrodes.

  According to a preferred embodiment of this capacitance sensor, a plurality of detectors are arranged in parallel along the traveling direction of the film-like medium, or a plurality of detectors are disposed at right angles to the traveling direction. May be.

  According to another preferred embodiment of the capacitance sensor, the first counter electrode comprises a plurality of first sub counter electrodes connected to a common AC power source, and the plurality of first sub counter electrodes are Between the plurality of sub-electrodes that are arranged in parallel along the traveling direction of the film-like medium, and the inter-electrode wiring electrically connects each of the first sub-counter electrodes and the common second counter electrode in series. Each of the inter-sub-electrode wirings may be provided with a switch for switching the inter-sub-electrode wiring.

  The capacitance sensor of the present invention is configured as described above. As a result, it is possible to obtain a capacitance sensor that has a simpler structure than the conventional one and can quickly measure the thickness of the film-like medium.

  Embodiments of the present invention will be described below with reference to the drawings. Each drawing schematically shows the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood. Moreover, although the preferable structural example of this invention is demonstrated hereafter, the material of each component, a numerical condition, etc. are only a suitable example. Therefore, the present invention is not limited to the following embodiments. Moreover, in each figure, the same code | symbol is attached | subjected to a common component and the description may be abbreviate | omitted.

(Embodiment 1)
The capacitance sensor according to the first embodiment will be described with reference to FIGS.

(Construction)
FIG. 1 is a schematic diagram schematically showing the configuration of the capacitance sensor of this embodiment.

  The capacitance sensor 10 of this embodiment includes a detector 22 having an output terminal 20 that outputs a detection signal representing a change in capacitance.

  The detector 22 includes a first counter electrode 14 connected to the AC power source 12, a grounded second counter electrode 16, and electrodes that electrically connect the first and second counter electrodes 14 and 16 in series. The output end 20 is provided at the connection midpoint P of the interelectrode wiring 18. In addition, the capacitance sensor 10 may preferably include a processing device 29, for example.

  The first counter electrode 14 is a conventionally known parallel plate capacitor, and includes electrodes 14a and 14b facing each other with a predetermined interval. The electrode 14 a is connected to the AC power source 12. The interelectrode wiring 18 is connected to the electrode 14b. As the interelectrode wiring 18, a conventionally known lead wire, printed circuit board wiring, or the like can be used.

  The second counter electrode 16 is a conventionally known parallel plate capacitor, and includes electrodes 16a and 16b facing each other at a predetermined interval. The electrode 16 a is connected to the interelectrode wiring 18. On the other hand, the electrode 16b is grounded.

  The distance between the electrodes of the first and second counter electrodes 14 and 16, that is, the distance d between the electrodes 14a and 14b and the distance d between the electrodes 16a and 16b are preferably set to be equal to each other. . More specifically, the distance between the first and second counter electrodes 14 and 16 is preferably about 5 to 6 mm, for example.

  The electrode areas of the first and second counter electrodes 14 and 16, that is, the areas of the electrodes 14a, 14b, 16a, and 16b are set to be equal to each other.

  Further, a medium having the same dielectric constant is interposed between the electrodes 14 a and 14 b of the first counter electrode 14 and between the electrodes 16 a and 16 b of the second counter electrode 16. In the case of this embodiment, the medium interposed between the electrodes is an atmosphere having a dielectric constant ε≈1. Hereinafter, the dielectric constant of the atmosphere is represented by “ε0”.

  In the capacitance sensor 10 of this embodiment, a change in capacitance caused by inserting a film-like medium B such as a banknote between the electrodes 14a and 14b of the first counter electrode 14 is a change in voltage. And a voltage obtained by synthesizing signals output from the first and second counter electrodes 14 and 16 is output from the output terminal 20 described later. Hereinafter, a change in voltage output from the output terminal 20 is referred to as a “detection signal”.

  The processing device 29 includes an amplifier 24, an A / D converter 26, and a processing unit 28, and performs a process for obtaining the thickness of the film-like medium B from the detection signal as in the conventional case.

  The amplifier 24 has a function of electrically amplifying the detection signal output from the output terminal 20. The detection signal amplified by the amplifier 24 is output to the A / D converter 26.

  The A / D converter 26 is electrically connected to the amplifier 24. The A / D converter 26 converts the detection signal input from the amplifier 24 into a digital signal and outputs the digital signal to the processing unit 28.

  The processing unit 28 is configured as a CPU including a central processing unit (not shown), an internal storage unit, and an input / output unit. The processing unit 28 performs processing for obtaining the thickness of the film-like medium B from the digitized detection signal input from the A / D converter 26. More specifically, the digitized detection signal input from the A / D converter 26 is temporarily stored in an internal storage unit (not shown). The stored detection signal is subjected to a predetermined calculation according to a program read to the central processing unit, and the thickness D of the film-like medium B is obtained.

  The CPU that constitutes the processing unit 28 is well known in the art and is not directly related to the gist of the present invention.

(Operation)
Next, with reference to FIG.1 and FIG.2, operation | movement of the electrostatic capacitance sensor 10 of this embodiment is demonstrated.

  In order to facilitate the understanding of the operation of the capacitance sensor 10, a description will be given in comparison with the conventional capacitance sensor 100 (hereinafter referred to as “conventional sensor 100”) shown in FIG.

  First, the structure of the conventional sensor 100 will be briefly described with reference to FIG. The conventional sensor 100 includes one counter electrode 102. The counter electrode 102 is configured as a parallel plate capacitor. More specifically, in the conventional sensor 100, the electrodes 102a and 102b are arranged to face each other in parallel. Note that the distance between the electrodes 102a and 102b is d. The areas of the electrodes 102a and 102b are S.

  Consider a case where a film-like medium B having a dielectric constant ε is inserted into the counter electrode 102 of the conventional sensor 100. Note that the dielectric constant ε of the film-like medium B is slightly larger than the dielectric constant ε0 of the atmosphere, for example, ε≈10.

  In addition, the thickness D of the film-like medium B is sufficiently thinner than the inter-electrode distance d. Here, “sufficiently thin” indicates that the thickness of the film-like medium B is 1/100 or less of the inter-electrode distance d (D ≦ d / 100).

  At this time, it is assumed that the atmospheric permittivity ε0 slightly changes to ε0 ′ because the temperature and humidity of the atmosphere present in the counter electrode 102 have changed. Here, the change amount Δε0 of ε0, that is, Δε0 = | ε0−ε0 ′ | / ε0 is about 50%.

  In this case, when the dielectric constant ε of the film-like medium B is a very large value (for example, ε = 1000) compared to the atmospheric dielectric constant, the change in the dielectric constant in the atmosphere can be ignored. It is possible to detect a change in capacitance derived from the film-like medium B with sufficient accuracy. As a result, the thickness D of the film-like medium B can be accurately evaluated.

  However, when the dielectric constant ε of the film-like medium B is almost equal to the dielectric constant ε0 of the atmosphere as in this example, a slight change Δε0 of the atmospheric dielectric constant also affects the capacitance measurement. Will be given. That is, the voltage change resulting from the change in the dielectric constant of the atmosphere is a large value that cannot be ignored with respect to the detection signal. As a result, a large error is included in the measurement result of the thickness D of the obtained film-like medium B.

  On the other hand, the capacitance sensor 10 of this embodiment includes a first counter electrode 14 and a second counter electrode 16 that are electrically connected in series. As shown in FIG. 1, the first counter electrode 14 detects the capacitance of the film-like medium B including the changed atmospheric permittivity ε0 ′, and the second counter electrode detects the changed atmospheric dielectric. Only the capacitance with the rate ε0 ′ is detected. Then, the outputs of the first and second counter electrodes 14 and 16, that is, the voltages reflecting the respective capacitances are combined, and a detection signal from the output terminal 20 provided at the midpoint P of the interelectrode wiring 18. Take out as.

  As a result of configuring the capacitance sensor 10 in this manner, the detection signal output from the output terminal 20 is static for the changed atmospheric permittivity ε0 ′ measured by both the first and second counter electrodes 14 and 16. Since the voltage component depending on the electric capacity is canceled, only the detection signal derived from the electrostatic capacity of the film-like medium B can be detected.

(Cancellation mechanism for changes in dielectric constant in the atmosphere)
Hereinafter, with reference to FIGS. 3A to 3C, it will be described in further detail that the capacitance sensor 10 can cancel the change in atmospheric permittivity Δε0.

  First, referring to FIGS. 3A and 3B, even when the film medium B is not inserted into the first counter electrode 14, even if the atmospheric permittivity changes, the capacitance sensor The fact that the detection signal from 10 is unchanged will be described. FIG. 3A is a schematic diagram showing the capacitance sensor 10 as an electric circuit when the permittivity of the atmosphere is ε0. FIG. 3B is a schematic diagram showing the capacitance sensor 10 as an electric circuit when the dielectric constant of the atmosphere is ε0 ′.

  When the dielectric constant of the atmosphere shown in FIG. 3A is ε0, the capacitances C1 and C2 of the first and second counter electrodes 14 and 16 are expressed by the following equations (1) and It is given by (2).

C1 = ε0 × S / d (1)
C2 = ε0 × S / d (2)
Therefore, the detection signal V1 from the output terminal 20 is given by the following equation (3).

V1 = (C2 / C1) × V = V (3)
In Expression (3), V represents a voltage applied to the first counter electrode 14.

  On the other hand, as shown in FIG. 3B, when the dielectric constant of the atmosphere changes to ε0 ′, the capacitances C3 and C4 of the first and second counter electrodes 14 and 16 are as follows according to a conventionally known relationship. It is given by equations (4) and (5).

C3 = ε0 ′ × S / d (4)
C4 = ε0 ′ × S / d (5)
Therefore, the detection signal V2 from the output terminal 20 is given by the following equation (6).

V2 = (C4 / C3) × V = V (6)
Here, comparing Equation (3) with Equation (6), it can be seen that V1 = V2. This is because, when the film-like medium B is not inserted into the first counter electrode 14, even if the dielectric constant ε0 of the air interposed between the first and second counter electrodes 14 and 16 changes, the capacitance sensor 10. It shows that the output voltages from are equal.

  Based on the above, consider the case where the film-like medium B is inserted into the first counter electrode 14 as shown in FIG. In this case, when viewed electrically, as shown in FIG. 3C, three capacitances C1a, C1b, and C1c connected in series are formed between the electrodes 14a and 14b. . FIG. 3C is a schematic diagram showing the capacitance sensor 10 as an electric circuit when the film-like medium B is inserted into the first counter electrode 14.

  In FIG. 3C, C1a is a capacitance formed between the electrode 14a and the film medium B, C1b is a capacitance of the film medium B, and C1c is a film shape. It is a capacitance formed between the medium B and the electrode 14b.

  Incidentally, as described above, since the thickness D of the film-like medium B is sufficiently smaller than the inter-electrode distance d of the first counter electrode 14, it is assumed that the series portions of the capacitances C1a and C1c are equal to C1. Can do.

  From this, it is considered that the three capacitances C1a, C1b, and Clc formed on the first counter electrode 14 are equivalent to those in which the capacitance C1 and the capacitance C1b are connected in series. Can do.

  Therefore, when considering the entire capacitance sensor 10, a circuit in which the capacitances C 1, C 2, and C 1 b are electrically connected in series is formed by inserting the film-like medium B into the first counter electrode 14. Can be considered.

  By the way, as described above, the detection signal does not change even when the atmospheric permittivity changes in the portion where the capacitances C1 and C2 are connected in series. Therefore, the change in the detection signal from the capacitance sensor 10 in which the film-shaped medium B is inserted is derived from the capacitance C1b, that is, the capacitance of the film-shaped medium B.

  That is, even if the dielectric constant in the atmosphere changes, the capacitance sensor 10 cancels the change in the dielectric constant and outputs a detection signal derived from the capacitance C1b of the film-like medium B.

(effect)
(1) In the capacitance sensor 10 of this embodiment, the first counter electrode 14 and the second counter electrode 16 are electrically connected in series, and from the output end 20 provided at the midpoint P of the interelectrode wiring 18. With a simple configuration of taking out the detection signal, the change in the dielectric constant of the medium (atmosphere) interposed between the electrodes 14a and 14b and the electrodes 16a and 16b can be removed from the detection signal. As a result, the thickness D and the number of the film-like medium B can be more accurately evaluated than before.

  More specifically, in the conventional sensor 100, it was only possible to evaluate the number of film-like media B having a thickness D of about 100 μm, but in the capacitive sensor 10 of this embodiment, the thickness D was 50 μm. The number of film-like media B can be evaluated.

  (2) Unlike the technique disclosed in Patent Document 1, the capacitance sensor 10 does not require a complicated arithmetic circuit. Therefore, it is not necessary to consider the time required for the calculation, and the thickness D and the number of the film-like media B can be evaluated more quickly. In addition, since the space for providing the arithmetic circuit can be saved, the capacitance sensor 10 can be made smaller.

(Modification)
(1) In this embodiment, the case where the output end 20 is provided at the midpoint of the interelectrode wiring 18 has been described. However, the output end 20 does not have to be at the position of the midpoint P as long as it is provided in the interelectrode wiring 18. The output end 20 can be provided at any suitable position depending on the design of the capacitance sensor 10.

  In this case, the voltage output from the output terminal 20 may be corrected by comparing with the voltage output from the midpoint P.

  (2) In this embodiment, the case where the medium interposed between the electrodes 14a and 14b and between the electrodes 16a and 16b is the atmosphere has been described. However, the medium is not limited to the atmosphere, and various gaseous media such as nitrogen gas and halogen gas can be used.

  (3) Moreover, in this embodiment, the case where paper, especially a banknote was used as the film-form medium B was demonstrated. However, when the film-like medium B has a dielectric constant ε slightly larger than the dielectric constant ε0 of the atmosphere, specifically, ε0 <ε <10, and the thickness D is 1/100 or less of the inter-electrode distance d, There is no particular limitation. For example, a resin film or cloth may be used.

  (4) In this embodiment, the case where the film-like medium B is inserted into the first counter electrode 14 has been described. However, the film-like medium B may be inserted into the second counter electrode 16. That is, the film-like medium B only needs to be inserted into one of the first and second counter electrodes 14 and 16. Also by configuring in this way, the capacitance sensor 10 has the effects as described above.

(Embodiment 2)
With reference to FIG. 4, the electrostatic capacitance sensor of Embodiment 2 is demonstrated. FIG. 4 is a schematic diagram schematically showing the configuration of the capacitance sensor 30 of this embodiment. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

(Construction)
In the capacitance sensor 30 of this embodiment, a plurality of the detectors 22 described above are arranged in parallel along the traveling direction of the film-like medium B, or a plurality of detectors 22 are arranged perpendicular to the traveling direction. is doing.

  That is, the capacitance sensor 30 includes first to nth detectors 221 to 22n configured in the same manner as the detector 22 described in the first embodiment. The first to n-th detectors 221 to 22n are arranged in parallel along the conveyance direction of the film-like medium B. More specifically, in the first counter electrodes 141 to 14n, the first to nth detectors are used so that the film-like medium B is conveyed between the spaces formed by the electrodes 14a1 to 14an and the electrodes 14b1 to 14bn. 221 to 22n are arranged.

  Further, the electrostatic capacity sensor 30 is provided with a control unit 27 for controlling the operations of the first to nth detectors 221 to 22n. The control unit 27 is configured as a CPU including a central processing unit (not shown), an internal storage unit, and an input / output unit. The CPU constituting the control unit 27 is conventionally well-known and is not directly related to the gist of the present invention, so that further explanation is omitted.

(Operation)
The operations of the individual detectors 221 to 22n constituting the capacitance sensor 30 are the same as those of the capacitance sensor 10 of the first embodiment.

  However, since the electrostatic capacity sensor 30 includes n detectors 221 to 22n, it is necessary to switch them at a predetermined timing in the process of transporting the film-like medium B. This switching is executed according to the program read from the internal storage unit of the control unit 27 to the central processing unit. However, since the specific processing content of this switching is not directly related to the gist of the present invention, further explanation is omitted.

(effect)
The capacitance sensor 30 of this embodiment has the same effect as the capacitance sensor 10 of the first embodiment. Furthermore, the electrostatic capacity sensor 30 is arranged with n detectors 221 to 22n, so that even if the film medium B has a large area or the dielectric constant changes depending on the location of the film medium B, These can be detected independently. As a result, the change in the thickness D of the film-like medium B can be evaluated two-dimensionally.

(Modification)
In this embodiment, the case where the first to n-th detectors 221 to 22n are arranged in one row has been described, but the arrangement of the first to n-th detectors 221 to 22n is not limited to one row. The detectors may be arranged over a plurality of rows. By configuring in this way, it is possible to measure a film medium B having a larger area. Further, with this configuration, the planar distribution of the thickness D of the film-like medium B can be evaluated.

(Embodiment 3)
With reference to FIG. 5, the capacitance sensor of Embodiment 3 will be described. FIG. 5 is a schematic diagram schematically showing the configuration of the capacitance sensor 40 of this embodiment. In FIG. 5, the same components as those in FIG.

(Construction)
In the capacitance sensor 40 of this embodiment, the first counter electrode 14 includes a plurality of first sub counter electrodes 14S1 to 14Sn connected to a common AC power supply 12, and the plurality of first sub counter electrodes 14S1 to 14Sn are arranged in parallel along the traveling direction of the film-like medium B.

  The inter-electrode wiring 18 includes a plurality of inter-sub-electrode wirings 18S1 to 18Sn that electrically connect each of the first sub counter electrodes 14S1 to 14Sn and the common second counter electrode 16 in series. Each of the inter-sub-electrode wirings 18S1 to 18Sn is provided with switches 421 to 42n for switching the inter-sub-electrode wirings 18S1 to 18Sn.

  In the capacitance sensor 40 of this embodiment, the first counter electrode 14 includes first sub counter electrodes 14S1 to 14Sn, and the inter-electrode wiring 18 includes sub-interelectrode wirings 18S1 to 18Sn. Except for the point that the switches 421 to 42n are provided, the configuration is almost the same as the capacitance sensor 10 of the first embodiment. Therefore, in the following description, this difference will be mainly described.

  In the capacitance sensor 40, a common AC power supply 12 is connected to each of the electrodes 14Sa1 to 14San of the first sub counter electrodes 14S1 to 14Sn. Further, inter-sub-electrode wirings 18S1 to 18Sn connecting the common second counter electrode 16 are connected to the electrodes 14Sb1 to 14Sbn, respectively. Furthermore, switches 421 to 42n for switching the first sub counter electrodes 14S1 to 14Sn are provided in the inter-subelectrode wirings 18S1 to 18Sn.

  The output terminal 20 is connected to the processing device 29.

  Furthermore, the electrostatic capacity sensor 40 is provided with a control unit 27 for controlling the entire operation such as switching of the switches 421 to 42n.

(Operation)
The film-like medium B is transported at intervals between the electrodes 14Sa1 to 14San and the electrodes 14Sb1 to 14Sbn by a transport mechanism (not shown). Accordingly, the control unit 27 described above executes the ON / OFF state of the switches 421 to 42n according to the read program. In the ON / OFF control of the switches 421 to 42n by the control unit 27, control is performed so that two or more of the n switches 421 to 42n are not turned on at the same time.

  A detection signal is output from the output terminal 20i of the inter-sub-electrode wiring 18Si provided with the switch 42i (i is an integer satisfying 1 ≦ i ≦ n) in the ON state and processed by the processing device 29.

(effect)
The electrostatic capacity sensor 40 of this embodiment has the same effects as the electrostatic capacity sensor 10 of the first embodiment and the electrostatic capacity sensor 30 of the second embodiment, and the AC power supply 12 and the second counter electrode 16. Therefore, the size can be further reduced as compared with the capacitance sensor 30 of the second embodiment.

(Modification)
The capacitance sensor 40 may arrange the first sub counter electrodes 14S1 to 14Sn in a plurality of rows as in the case of the capacitance sensor 30 of the second embodiment. By configuring in this way, it is possible to measure a film medium B having a larger area. Further, with this configuration, the planar distribution of the thickness D of the film-like medium B can be evaluated.

2 is a schematic diagram schematically showing a configuration of a capacitance sensor according to Embodiment 1. FIG. It is a schematic diagram which shows the schematic structure of a conventional sensor. (A) is the schematic diagram which represented the electrostatic capacitance sensor as an electric circuit, when the dielectric constant of air | atmosphere is (epsilon) 0. (B) is a schematic diagram showing the capacitance sensor as an electric circuit when the atmospheric permittivity is ε0 ′. (C) is a schematic diagram showing the capacitance sensor as an electric circuit when a film-like medium is inserted into the first counter electrode. 6 is a schematic diagram schematically showing a configuration of a capacitance sensor according to a second embodiment. FIG. FIG. 6 is a schematic diagram schematically showing a configuration of a capacitance sensor according to a third embodiment.

Explanation of symbols

10, 30, 40 Capacitance sensor 12 AC power source 14 First counter electrode 14a, 14b, 16a, 16b, 14a1 to 14an, 14b1 to 14bn, 14Sa1 to 14San, 14Sb1 to 14Sbn Electrode 14S1 to 14Sn First sub counter electrode 16 Second counter electrode 18 Inter-electrode wiring 18S1-18Sn Sub-electrode wiring 20 Output terminal 22 Detector 221-22n First to n-th detector 24 Amplifier 26 A / D converter 27 Control unit 28 Processing unit 29 Processing devices 421-42n switch

Claims (3)

A static detection for detecting the thickness of the film-like medium by utilizing the change in capacitance caused by inserting the film-like medium into the gap between the electrodes of the counter electrode composed of two electrodes arranged opposite to each other. In the capacitance sensor,
A first counter electrode connected to an AC power source and a grounded second counter electrode, which are provided as the counter electrodes, respectively, and an inter-electrode wiring electrically connecting the first and second counter electrodes in series; And a detector having an output terminal that is provided at a connection midpoint of the inter-electrode wiring and outputs a detection signal representing a change in capacitance,
A capacitance sensor, wherein a film-like medium is inserted between two electrodes of the first counter electrode.   2. The capacitance sensor according to claim 1, wherein a plurality of the detectors are arranged in parallel along or in a direction perpendicular to the traveling direction of the film-like medium. The first counter electrode includes a plurality of first sub counter electrodes connected to the common AC power source;
A plurality of the first sub counter electrodes are arranged in parallel along the traveling direction of the film medium,
The inter-electrode wiring includes a plurality of inter-electrode wirings that electrically connect each of the first sub counter electrodes and the common second counter electrode in series;
2. The capacitance sensor according to claim 1, wherein each of the inter-sub-electrode wirings is provided with a switch for switching the inter-sub-electrode wirings.

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