JP2004347493A - Capacitive sensor device having function for detecting abnormality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily detect abnormality of a capacitive sensor device. <P>SOLUTION: The first driving voltage signal V<SB>X1</SB>of a pulse voltage is outputted from a first terminal 1 of a driving signal generation circuit 20. A second driving signal V<SB>X2</SB>that is the pulse voltage or the inversion voltage thereof is outputted from a second terminal 2. The first sensor capacitance C<SB>X1</SB>and the second sensor capacitance C<SB>X2</SB>have the same characteristic. A control signal generation circuit 38 controls which of the pulse voltage and the inversion voltage thereof is to be outputted from the second terminal 2. When the inversion voltage is outputted from the second terminal 2, an electric charge-voltage conversion circuit 26 outputs a voltage value V<SB>OP</SB>corresponding to the value (ΔC<SB>X1</SB>-ΔC<SB>X2</SB>) in which the variation value ΔC<SB>X2</SB>of the second sensor capacitance C<SB>X2</SB>is subtracted from the variation value ΔC<SB>X1</SB>of the first sensor capacitance C<SB>X1</SB>. A determination circuit 36 outputs an abnormality detection signal, on the basis of the output value V<SB>OP</SB>(output V<SB>OUT</SB>of an LPF (low-pass filter) 34, directly). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４７】
上記では、第１センサ素子部２２の動作について説明したが、第２センサ素子部２４でも同様の動作が行われる。これにより、第２センサ容量Ｃ_Ｘ２には、電荷Ｑ_Ｘ２（＝Ｃ_Ｘ２Ｖ_Ｐ＝（Ｃ_Ｒ２＋ΔＣ_Ｘ２）Ｖ_Ｐ）が蓄積される。第２基準容量Ｃ_Ｒ２には、電荷Ｑ_Ｒ２（＝Ｃ_Ｒ２Ｖ_Ｐ）が蓄積される。
よって、第２センサ素子部２４に蓄積された電荷Ｑ_Ｘ２、Ｑ_Ｒ２に起因して、帰還容量Ｃ_Ｆには電荷Ｑ_Ｘ２−Ｑ_Ｒ２が蓄積される。この結果、第２センサ素子部２４に蓄積された電荷Ｑ_Ｘ２、Ｑ_Ｒ２に起因する分のオペアンプ３０の出力電圧Ｖ_ＯＰは、次式（２）となる。

【００４８】
以上から、第１センサ素子部２２に蓄積された電荷Ｑ_Ｘ１、Ｑ_Ｒ１と第２センサ素子部２４に蓄積された電荷Ｑ_Ｘ２、Ｑ_Ｒ２に起因するオペアンプ３０の出力電圧Ｖ_ＯＰは、式（１）のＶ_ＯＰ１と式（２）のＶ_ＯＰ２を加算した次式（３）となる。
Ｖ_ＯＰ＝Ｖ_ＯＰ１＋Ｖ_ＯＰ２＝（ΔＣ_Ｘ１＋ΔＣ_Ｘ２）Ｖ_Ｐ／Ｃ_Ｆ （３）
【００４９】
図２に示すように、期間Ｔ_１４〜Ｔ_１６の間の所定の時点において、制御信号発生回路３８は、サンプル・ホールド回路３２に対して、サンプリング指令信号Ｓ_３を出力する。サンプリング指令信号Ｓ_３が入力されると、サンプル・ホールド回路３２は、オペアンプ３０の出力電圧Ｖ_ＯＰ（図２ではＶ_１）をサンプリングし、その値をホールドする。サンプル・ホールド回路３２の出力信号は、さらにローパス・フィルタ３４に入力される。これにより、ローパス・フィルタ３４からは、高周波成分がカットされ、帯域制限された出力信号Ｖ_ＯＵＴが出力される。
【００５０】
なお、センサモードでは、制御信号発生回路３８から判定回路３６に向けて出力される判定指令信号Ｓ_４はＬｏｗ状態であり、判定動作は行われない。よって、判定回路３６の出力信号Ｖ_ＤＥＴもＬｏｗ状態となっている。
センサモードでは、以上の動作が繰返し行われる。
【００５１】
次に、異常検出モードでの動作について図３のタイミングチャートを参照して説明する。制御信号発生回路３８が出力するモード設定信号Ｓ_１がＨｉ信号の場合は、異常検出モードとなる。異常検出モードでは、制御信号発生回路３８からサンプル・ホールド回路３２に向けて出力されるサンプリング指令信号Ｓ_３はＬｏｗ状態であり、サンプリング動作は行われない。よって、ローパス・フィルタ３４の出力信号Ｖ_ＯＵＴもＬｏｗ状態となっている。異常検出モードでは、センサモードと異なり、第３駆動信号Ｖ_Ｘ２は第１駆動信号Ｖ_Ｘ１に対して逆位相であり、第４駆動信号Ｖ_Ｒ２は第２駆動信号Ｖ_Ｒ１に対して逆位相である。第２駆動信号Ｖ_Ｒ１が第１駆動信号Ｖ_Ｘ１に対して逆位相であるのは、センサモードの場合と同様である。この結果、異常検出モードでは、第２センサ容量Ｃ_Ｘ２と第２基準容量Ｃ_Ｒ２に蓄積される電荷の極性が、センサモードの場合と逆になる。このため、オペアンプ３０の出力電圧Ｖ_ＯＰは、式（１）のＶ_ＯＰ１から式（２）のＶ_ＯＰ２を減算した次式（４）となる。
Ｖ_ＯＰ＝Ｖ_ＯＰ１−Ｖ_ＯＰ２＝（ΔＣ_Ｘ１−ΔＣ_Ｘ２）Ｖ_Ｐ／Ｃ_Ｆ （４）
【００５２】
第１センサ容量Ｃ_Ｘ１と第２センサ容量Ｃ_Ｘ２は正常であれば、先に述べたように、作用する物理量の大きさとは無関係に容量増加値（容量変化値）ΔＣ_Ｘ１とΔＣ_Ｘ２が等しい。このため、オペアンプ３０の出力電圧Ｖ_ＯＰは、センサ素子部２２、２４が正常の場合は、作用する物理量の大きさとは無関係に実質的にゼロとなる。
【００５３】
図３において、期間Ｔ_５４〜Ｔ_５６の間は、センサ素子部２２、２４が正常で、オペアンプ３０の出力電圧Ｖ_ＯＰがゼロとなっている。この出力電圧Ｖ_ＯＰは判定回路３６に入力される。異常検出モードでは、期間Ｔ_５４〜Ｔ_５６の所定の時点で、制御信号発生回路３８から判定回路３６へＨｉ状態の判定指令信号Ｓ_４が出力される。判定回路３６は、判定指令信号Ｓ_４が入力されると、出力電圧Ｖ_ＯＰの値（絶対値）が異常判定値Ｖ_ＴＨ以上か否かを判定する。出力電圧Ｖ_ＯＰの値が異常判定値Ｖ_ＴＨよりも小さい場合は、判定回路３６は、判定信号Ｖ_ＤＥＴとしてＬｏｗ信号（正常である旨を示す信号）を出力する。上記のように出力電圧Ｖ_ＯＰの値が異常判定値Ｖ_ＴＨよりも小さいゼロの場合は、判定回路３６は、判定信号Ｖ_ＤＥＴとしてＬｏｗ信号を出力する。
【００５４】
これに対し、センサ素子部２２、２４に異常がある場合は、（ΔＣ_Ｘ１−ΔＣ_Ｘ２）がほぼゼロにはならない場合が生じる。例えば、センサ容量Ｃ_Ｘ１、Ｃ_Ｘ２を構成する可動電極と固定電極の間に異物（ゴミ等）が挟まった場合は、センサ容量Ｃ_Ｘ１、Ｃ_Ｘ２に所定の物理量が加わっても、可動電極が意図した分だけ変位することができず、意図した容量変化値が得られない場合が生じる。
この場合、オペアンプ３０の出力電圧Ｖ_ＯＰの値がほぼゼロとはならない。
【００５５】
期間Ｔ_６２〜Ｔ_６４の間は、センサ素子部２２、２４に異常が生じており、オペアンプ３０の出力電圧Ｖ_ＯＰががほぼゼロとならず、Ｖ_３となった場合を示している。異常検出モードでは、期間Ｔ_６２〜Ｔ_６４の間の所定の時点で、制御信号発生回路３８から判定回路３６へＨｉ状態の判定指令信号Ｓ_４が出力される。判定回路３６が、その判定指令信号Ｓ_４を受けた時点で、出力電圧Ｖ_ＯＰの値が異常判定値Ｖ_ＴＨ以上の場合は、判定回路３６は、判定信号Ｖ_ＤＥＴとしてＨｉ信号（異常検出信号）を出力する。上記のように、出力電圧Ｖ_ＯＰが異常判定値Ｖ_ＴＨよりも大きいＶ_３の場合は、判定回路３６は、判定信号Ｖ_ＤＥＴとしてＨｉ信号を出力する。
【００５６】
センサ容量Ｃ_Ｘ１、Ｃ_Ｘ２は、異物（ゴミ等）の存在が異常を引き起こす可能性がセンサ装置の中でも相対的に高い。センサ容量Ｃ_Ｘ１、Ｃ_Ｘ２の可動電極と固定電極の間に異物が挟まった場合は、物理量が作用しても可動電極が変位しにくくなり、意図した容量変化値が得られなくなるからである。また、センサ容量Ｃ_Ｘ１、Ｃ_Ｘ２を構成する可動電極は、変位させることを前提した部位である。よって、繰返し使用されることで劣化し、物理量が作用しても意図した変位量（容量変化値）が得られない等の異常が生じる可能性が相対的に高い。
本実施例によると、このように、センサ装置の中でも相対的に異常が生じ易いセンサ素子部２２、２４の異常を、従来よりも簡易に、しかも精度良く検出することができる。
【００５７】
また、制御信号発生回路３８は、第２端子２から図２に示すパルス電圧（第２駆動信号）Ｖ_Ｘ２と、これを反転させた図３に示すパルス電圧（第２駆動信号）Ｖ_Ｘ２を、交互に繰返し出力するように制御可能であることが好ましい。即ち、制御信号発生回路３８は、センサモードと異常検査モードを交互に繰返すように制御可能であることが好ましい。
【００５８】
このようにすると、本実施例のセンサ装置によって、製造後の出荷時における異常検査のみならず、センサ装置の本来の動作であるセンサ動作を行いながら、その合間に異常検査を行うようなオンライン検査をも行うことができる。本実施例では、第２端子２と第４端子４から出力する電圧を反転させるだけで、センサモードと異常検査モードを容易に切換えることができるので、センサモードと異常検査モードを短い時間間隔で繰返すことが容易に行える。
【００５９】
（第２実施例） 図６に示す第２実施例の静電容量式センサ装置は、電荷−電圧変換回路２６を差動入力型にしたものである。第２センサ素子部２４の出力はオペアンプ３０の非反転入力端子に入力される。また、オペアンプ３０の非反転入力端子は、第２帰還容量Ｃ_Ｆ２を介して接地されている。第２帰還容量Ｃ_Ｆ２には、第２スイッチ２９が並列に接続されている。
【００６０】
（第３実施例） 図７に示す第３実施例の静電容量式センサ装置は、駆動信号Ｖ_Ｘ１、Ｖ_Ｘ２、Ｖ_Ｒ１、Ｖ_Ｒ２の電圧波形を方形波から正弦波に変更したものである。また、第１実施例のサンプル・ホールド回路３２に代えて、同期整流回路４０を用いている。また、同期整流回路４０の出力電圧が分岐線４４を通じて判定回路３６に入力される。なお、第２実施例と同様に、電荷−電圧変換回路２６は差動入力型としている。
【００６１】
第２実施例及び第３実施例の静電容量式センサ装置によっても、第１実施例の静電容量式センサ装置と同様の作用効果を得ることができる。
【００６２】
以上、本発明の具体例を詳細に説明したが、これらは例示に過ぎず、特許請求の範囲を限定するものではない。特許請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。
（１）例えば、上記実施例で使用した基準容量Ｃ_Ｒ１に代えて、作用する物理量に応じて容量値がセンサ容量Ｃ_Ｘ１と逆向きに変化し、基準容量値（基準物理量が作用したときの容量値）がセンサ容量Ｃ_Ｘ２とほぼ等しい差動容量を用いてもよい。この構成によると、センサ容量Ｃ_Ｘ１と前記差動容量の基準容量値が相殺され、センサ容量Ｃ_Ｘ１の容量変化値と、前記差動容量の容量変化値の合計値だけを抽出できる。同様に、基準容量Ｃ_Ｒ２に代えて、差動容量を用いてもよい。
（２）また、上記実施例では、帰還容量Ｃ_Ｆと並列にスイッチ２８を設けた場合について説明したが、例えば帰還容量Ｃ_Ｆと並列に抵抗を設けてもよい。このようなスイッチ２８や抵抗を設けることで、電荷−電圧変換回路２６の直流動作点を適切に設定することができる。具体的には、オペアンプ３０の逆相入力端子の直流電位を適切な値に設定することができる。
【００６３】
また、本明細書または図面に説明した技術要素は、単独であるいは各種の組合せによって技術的有用性を発揮するものであり、出願時請求項記載の組合せに限定されるものではない。また、本明細書または図面に例示した技術は複数目的を同時に達成し得るものであり、そのうちの一つの目的を達成すること自体で技術的有用性を持つものである。
【図面の簡単な説明】
【図１】第１実施例の静電容量式センサ装置のブロック図を示す。
【図２】第１実施例の静電容量式センサ装置のセンサモードでの動作を示すタイミングチャートである。
【図３】第１実施例の静電容量式センサ装置の異常検出モードでの動作を示すタイミングチャートである。
【図４】静電容量式センサ装置の動作を説明するための図を示す（１）。
【図５】静電容量式センサ装置の動作を説明するための図を示す（２）。
【図６】第２実施例の静電容量式センサ装置のブロック図を示す。
【図７】第３実施例の静電容量式センサ装置のブロック図を示す。
【符号の説明】
２０：駆動信号発生回路
２２：第１センサ素子部
２４：第２センサ素子部
２６：電荷−電圧変換回路
２８：スイッチ
３０：オペアンプ
３２：サンプル・ホールド回路
３４：ローパス・フィルタ
３６：判定回路
３８：制御信号発生回路
Ｃ_Ｘ１、Ｃ_Ｘ２：センサ容量
Ｃ_Ｒ１、Ｃ_Ｒ２：基準容量
Ｃ_Ｆ：帰還容量
Ｖ_Ｘ１：第１駆動信号
Ｖ_Ｘ２：第２駆動信号
Ｖ_Ｒ１：第３駆動信号
Ｖ_Ｒ２：第４駆動信号
Ｓ_１：モード設定信号
Ｓ_２：リセット信号
Ｓ_３：サンプリング指令信号
Ｓ_４：判定指令信号[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor device and a method of using a sensor capacitance.
[0002]
2. Description of the Related Art A capacitance type sensor device for detecting various physical quantities such as pressure, acceleration, vibration, sound pressure and the like is known. Some of the capacitive sensor devices have an abnormality detection function (also referred to as a failure diagnosis function or a self-diagnosis function) that detects an abnormality in the sensor device (particularly, the sensor element unit) by itself.
[0003]
In a capacitance type sensor device having an abnormality detection function, an electrode pair for abnormality detection is added separately from a sensor capacitance for a sensor, and an abnormality of the sensor device is detected by using the electrode pair. Are known. However, when the electrode pair for abnormality detection is separately added, there is a problem that the configuration of the apparatus becomes complicated. Also, in some sensor devices, it is difficult to add such an electrode pair.
[0004]
On the other hand, Patent Document 1 discloses a sensor device that uses a plurality of sensor capacities for sensors also for detecting an abnormality. According to this sensor device, it is not necessary to separately add a pair of electrodes for abnormality detection.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-40047 (see FIGS. 1 and 3 of the publication, [0040] to [0046])
[0006]
However, according to the capacitance type sensor device disclosed in Patent Document 1, in order to detect an abnormality, it is necessary to separately prepare a voltage source not used for the sensor. was there.
[0007]
An object of the present invention is to realize a technology that can detect an abnormality of a capacitance-type sensor device more easily than before.
[0008]
According to one aspect of the present invention, there is provided a capacitance type sensor device comprising a first means, a second means, a first sensor capacity, a second sensor capacity, It is provided with control means and abnormality detection means.
The first means outputs a first voltage whose amplitude value changes by a predetermined value with time and a second voltage whose amplitude value changes by a value substantially equal to the predetermined value with time or an inverted voltage thereof. The capacitance value of the first sensor capacitance changes according to the applied physical quantity while the first voltage is applied. The second sensor capacitance is applied with the second voltage or its inversion voltage, and has a capacitance value that changes in accordance with a physical quantity that acts, and an absolute value and a reference capacitance value of a capacitance change value when a predetermined physical quantity acts. It is almost equal to the first sensor capacity. The control means controls whether the first means outputs the second voltage or its inverted voltage. The second means, when the second voltage is output together with the first voltage from the first means, a value obtained by adding the absolute value of the capacitance change value of the first sensor capacitance and the absolute value of the capacitance change value of the second sensor capacitance. When the inverted signal of the second voltage is output together with the first voltage from the first means, the capacitance change value of the other sensor capacitance is calculated from the absolute value of the capacitance change value of the one sensor capacitance. And outputs a signal value corresponding to the value obtained by subtracting the absolute value of. The abnormality detection means outputs an abnormality detection signal based on an output signal value of the second means when the inverted voltage of the second voltage is output from the first means.
[0009]
In this aspect, when the first means outputs the second voltage together with the first voltage, the second means determines the absolute value of the capacitance change value of the first sensor capacitance and the absolute value of the capacitance change value of the second sensor capacitance. And outputs a signal value corresponding to the value obtained by adding. In this case, the magnitude of the physical quantity acting on the sensor capacitance can be detected from this signal value.
[0010]
On the other hand, when the first means outputs the inverted voltage of the second voltage together with the first voltage, the second means calculates the capacitance change value of the other sensor capacity from the absolute value of the capacity change value of the one sensor capacity. And outputs a signal value corresponding to the value obtained by subtracting the absolute value of. If the first sensor capacitance and the second sensor capacitance are normal, the absolute value of the capacitance change value when a predetermined physical quantity acts is substantially equal. Therefore, the above subtraction value is almost zero in a normal state. On the other hand, when the subtraction value is not substantially zero, it can be estimated that an abnormality has occurred in the first sensor capacity and / or the second sensor capacity. Therefore, whether or not the first sensor capacity and / or the second sensor capacity has an abnormality can be accurately detected based on whether or not the subtraction value is substantially zero.
[0011]
As described above, in the present mode, when the second voltage is output from the first means, the sensor mode is set, and the second sensor capacitance functions as a sensor element in addition to the first sensor capacitance. Therefore, a physical quantity can be detected with higher sensitivity than in the case where the sensor capacity is one.
[0012]
On the other hand, when an inverted voltage of the second voltage is output from the first means, an abnormality detection mode is set, and the first sensor capacitance and the second sensor capacitance function as elements for abnormality detection. Therefore, it is not necessary to add an electrode pair for abnormality detection separately from the sensor capacitance. Further, in order to switch from the sensor mode to the abnormality detection mode, it is sufficient to switch from a state in which the first means outputs the second voltage to a state in which an inverted voltage of the second voltage is output. Therefore, it is not necessary to separately prepare a voltage source not used for the sensor for abnormality detection.
[0013]
As described above, according to this aspect, it is possible to detect an abnormality of the capacitance type sensor device more easily than before.
[0014]
According to another aspect of the present invention, there is provided a capacitance type sensor device including first means, second means, first sensor capacity, second sensor capacity, control means, and abnormality detection means.
The first means outputs a first terminal whose amplitude value changes by a predetermined value with time, and outputs a second voltage whose amplitude value changes by a value substantially equal to the predetermined value with time or an inverted voltage thereof. And a second terminal. The first sensor capacitance has a pair of electrodes, one of which is connected to the first terminal, and whose capacitance value changes according to the physical quantity that acts. The second sensor capacitor has a pair of electrodes, one of the electrodes is connected to the second terminal, and the capacitance value changes according to the physical quantity that acts, and the capacitance change value when a predetermined physical quantity acts Are substantially equal to the first sensor capacitance. The control means controls which of the second voltage and the inverted voltage is output from the second terminal of the first means. The second means is connected to the other electrode of each sensor capacitor and outputs a signal value corresponding to the amount and polarity of the electric charge accumulated in each sensor capacitor. The abnormality detection means outputs an abnormality detection signal based on the output signal value of the second means.
[0015]
According to this aspect, when one of the second voltage and its inverted voltage is output from the second terminal of the first means, the second means determines the absolute value of the capacitance change value of the first sensor capacity and the second sensor capacity. And outputs a signal value corresponding to the value obtained by adding the absolute value of the capacitance change value. On the other hand, when the other of the second voltage and the inverted voltage is output from the second terminal of the first means, the polarity of the charge accumulated in the second sensor capacitor is opposite to that when the one is output. become. As a result, the second means outputs a signal value corresponding to a value obtained by subtracting the absolute value of the capacitance change value of the other sensor capacitance from the absolute value of the capacitance change value of the other sensor capacitance.
Therefore, according to this aspect, it is possible to more easily detect the abnormality of the capacitance type sensor device than before.
[0016]
The control means is preferably controllable so that the first means alternately and repeatedly outputs the second voltage and its inverted voltage.
[0017]
According to this aspect, the detection of the physical quantity and the abnormality inspection can be performed substantially in parallel.
[0018]
Here, the directions in which the capacitance values of the “first sensor capacitance” and the “second sensor capacitance” change are not limited to the same direction, but may be opposite directions. The fact that the absolute values of the capacitance change values of the first sensor capacitance and the second sensor capacitance are “substantially equal” means that a deviation of about 5% of the absolute value of the capacitance change value is allowed. For example, variations in capacitance change values due to manufacturing errors are allowed, and are included in the applicable range of the present invention.
[0019]
The “signal value according to the added value” includes not only a signal value directly corresponding to the added value but also a signal directly corresponding to a value obtained by superimposing the added value on a reference capacitance value, for example. The value is also included. That is, the present invention is also applied to a configuration in which the reference capacitance value for removing the reference capacitance value of the sensor capacitance and extracting only the change in capacitance is not provided.
[0020]
The above-mentioned "means" are not limited to those realized by hardware, but also include those realized by software and those realized by hardware and software coexisting. Further, each of the “means” may be physically divided into a plurality.
[0021]
The mode "based on the output signal value of the second means" is not limited to the mode of directly using the output signal value of the second means to determine whether or not there is an abnormality and outputting the abnormality detection signal. . For example, when the second means is a charge-to-voltage conversion means, a sample-and-hold means, a filter means, and the like are arranged at the subsequent stage of the means, and it is determined whether or not there is an abnormality using a signal output after passing through these means. And a mode of outputting an abnormality detection signal. Alternatively, in the above case, the entirety of the combination of the charge-voltage conversion means, the sample and hold means, and the filter may be considered as the second means.
[0022]
The “first voltage” is preferably such that the amplitude value periodically changes by a predetermined value. Examples of the voltage waveform of the “first voltage” include a pulse waveform and a sine waveform. It is preferable that the “first voltage” and the “second voltage” are synchronized. It is preferable that the “first voltage” and the “second voltage” have the same phase. It is preferable that the "first voltage" and the "second voltage" have substantially the same voltage waveform shape. Depending on the configuration, an inverted version of the “first voltage” may be used as the “second voltage”. In the aspect of the “inversion voltage of the second voltage”, for example, when the amplitude value of the second voltage is 0 V in the first period, is 5 V in the second period, and the first period and the second period are repeated, ( There are 1) a mode in which the inversion voltage is 5 V in the first period and 0 V in the second period, and (2) a mode in which the inversion voltage is 0 V in the first period and -5 V in the second period.
[0023]
It is preferable that the abnormality detection unit outputs an abnormality detection signal when the absolute value of the output signal value of the second unit when the inverted voltage of the second voltage is output from the first unit is equal to or greater than a predetermined value.
[0024]
The first means inverts a third voltage obtained by inverting the voltage (first voltage) applied to the first sensor capacitor, and a voltage (second voltage or its inverted voltage) applied to the second sensor capacitor. It is preferable to further output the fourth voltage.
Then, while the third voltage is applied, the capacitance value does not substantially change even when a physical quantity acts, and the first reference capacitance value whose reference capacitance value is substantially equal to the first sensor capacitance, and the fourth voltage are applied. In addition, it is preferable that a capacitance value does not substantially change even when a physical quantity acts, and a second reference capacitance having a reference capacitance value substantially equal to the first sensor capacitance is further provided.
Alternatively, the third voltage is applied, and the capacitance value changes in the opposite direction to the first sensor capacitance in accordance with the acting physical quantity, and the first differential capacitance has a reference capacitance value substantially equal to the first sensor capacitance. (4) A second differential capacitance having a capacitance value that changes in the opposite direction to the second sensor capacitance in accordance with a physical quantity that acts upon application of a voltage and has a reference capacitance value substantially equal to the second sensor capacitance. Is preferred.
[0025]
When the reference capacitance or the differential capacitance as described above is further provided, the reference capacitance value can be removed from the sensor capacitance, and only the capacitance change can be extracted. According to the above aspect, even when such a reference capacitance or a differential capacitance is provided, it is possible to easily detect an abnormality.
[0026]
According to another aspect of the present invention, there is provided a method of using a sensor capacitor, comprising: a sensor for changing a capacitance value in accordance with a physical quantity acting thereon and an absolute value and a reference capacitance value of the capacitance variation value when a predetermined physical quantity acts on the two sensors; It is a method of using capacity. This method has a first step and a second step. In the first step, a first voltage whose amplitude value changes by a predetermined value with time is applied to the first sensor capacitor, and a first voltage whose amplitude value changes by a value substantially equal to the predetermined value with time is applied to the second sensor capacitor. By applying two voltages, a value obtained by adding the absolute value of the capacitance change value of the first sensor capacitance and the absolute value of the capacitance change value of the second sensor capacitance is obtained directly or indirectly. In the second step, a first voltage is applied to the first sensor capacitor, and an inverted voltage of the second voltage is applied to the second sensor capacitor, whereby the absolute value of the capacitance change value of one sensor capacitor is used to calculate the other sensor capacitor. Is obtained directly or indirectly by subtracting the absolute value of the capacitance change value.
[0027]
According to this aspect, it is possible to detect the abnormality of the sensor capacity more easily than before.
[0028]
It is preferable that the first step and the second step are alternately repeated.
[0029]
According to this aspect, the detection of the physical quantity and the abnormality inspection can be performed substantially in parallel.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment A capacitive sensor device with an abnormality detection function according to a first embodiment shown in FIG. 1 includes a control signal generation circuit 38, a drive signal generation circuit 20, a first sensor element unit 22, It includes a two-sensor element section 24, a charge-voltage conversion circuit 26, a sample and hold circuit (S / H circuit) 32, a low-pass filter (LPF) 34, and a determination circuit 36. As will be described later, this sensor device has a sensor mode for detecting a physical quantity (for example, pressure, acceleration, vibration, sound pressure, and the like) and an abnormality detection mode for detecting an abnormality of the sensor device (particularly, the sensor element units 22 and 24). Can be set. Note that the sensor mode is a mode in which the sensor device performs its original operation, and thus may be referred to as a normal operation mode. Further, the abnormality detection mode may be referred to as a failure diagnosis mode or a self-diagnosis mode.
[0031]
The control signal generation circuit 38 controls the control signal S ₁ ~ S ₄ Is output. Thereby, the operation of the sensor device is controlled. Specifically, the control signal generation circuit 38 supplies the drive signal generation circuit 20 with the mode setting signal S ₁ Is output. The reset signal S is supplied to the switch 28 of the charge-voltage conversion circuit 26. ₂ Is output. The sampling command signal S is sent to the sample and hold circuit 32. ₃ Is output. The judgment command signal S is sent to the judgment circuit 36. ₄ Is output.
[0032]
The drive signal generation circuit 20 has a first terminal 1, a second terminal 2, a third terminal 3, and a fourth terminal 4. The first drive signal V is independently provided from each of the terminals 1-4. _X1 , The second drive signal V _X2 , The third drive signal V _R1 , The fourth drive signal V _R2 Can be output. These drive signals have an amplitude V _P (See FIGS. 2 and 3).
[0033]
The mode setting signal S from the control signal generation circuit 38 ₁ When the sensor mode setting signal is output as _X2 Is the first drive signal V _X1 Are set to signals having the same voltage waveform and the same phase (see FIG. 2). On the other hand, the mode setting signal S ₁ When the abnormality detection mode setting signal is output as _X2 Is the first drive signal V _X1 Is set to a signal having the same voltage waveform as that of the inverted signal of the same phase (see FIG. 3). In the present embodiment, the first drive signal V _X1 By inverting the phase of a signal having the same voltage waveform and the same phase as the above, the signal is inverted.
[0034]
Third drive signal V _R1 Is the first drive signal V _X1 Is a signal obtained by inverting. In the present embodiment, the third drive signal V _R1 Is the first drive signal V _X1 Are inverted by making the phases opposite (see FIGS. 2 and 3). Fourth drive signal V _R2 Is the second drive signal V _X2 Is a signal obtained by inverting. In the present embodiment, the fourth drive signal V _R2 Is the second drive signal V _X2 Are inverted by making the phases opposite (see FIGS. 2 and 3).
[0035]
The first sensor element unit 22 includes a first sensor capacitor C _X1 And the first reference capacitance C _R1 Having. The second sensor element unit 24 includes a second sensor capacitor C _X2 And the second reference capacitance C _R2 Having. First sensor capacity C _X1 And the second sensor capacitance C _X2 Have equal properties. Also, the first reference capacitance C _R1 And the second reference capacitance C _R2 Have equal properties. Specifically, the first sensor capacitance C _X1 And the second sensor capacitance C _X2 Changes the capacitance value according to the physical quantity that acts. Sensor capacity C _X1 , C _X2 Have a movable electrode and a fixed electrode, respectively. The movable electrode and the fixed electrode are arranged at positions facing each other. When a physical quantity acts, the movable electrode is displaced. Thereby, the distance between the movable electrode and the fixed electrode changes. As a result, the capacitance value changes. In this embodiment, the first sensor capacitance C _X1 And the second sensor capacitance C _X2 Means that when a predetermined physical quantity acts, the capacitance value is ΔC _X1 And ΔC _X2 Only increase. These capacity increase values (capacity change values) ΔC _X1 And ΔC _X2 Are equal. Further, the first sensor capacitance C _X1 And the second sensor capacitance C _X2 Are equal in reference capacity value (capacity value when a reference physical quantity acts).
[0036]
On the other hand, the first reference capacitance C _R1 And the second reference capacitance C _R2 Does not substantially change the capacitance value even when a physical quantity acts. Reference capacity C _R1 , C _R2 Have two fixed electrodes each. That is, even if the physical quantity acts, each reference capacity C _R1 , C _R2 Are fixed, the distance between the electrodes does not change. Therefore, the capacitance value does not change. Reference capacity C _R1 , C _R2 Are respectively the sensor capacitance C _X1 , C _X2 Is designed to be equal to the reference capacitance value. That is, the reference capacity C _R1 , C _R2 Are capacitance change values ΔC, respectively. _X1 , ΔC _X2 Sensor capacity C when is zero _X1, C _X2 Equal to the capacitance value of Reference capacity C _R1 , C _R2 Is the sensor capacity C _X1 , C _X2 From the capacitance change ΔC _X1 , ΔC _X2 It is only for taking out.
[0037]
First sensor capacity C _X1 Is connected to the first terminal 1. First reference capacity C _R1 Is connected to the third terminal 3. Second sensor capacity C _X2 Is connected to the second terminal 2. Second reference capacity C _R2 Is connected to the fourth terminal 4. These capacities C _X1 , C _X2 , C _R1 , C _R2 Is commonly connected to an input terminal of a charge-to-voltage conversion circuit 26 described later (an inverting input terminal of the operational amplifier 30). The non-inverting input terminal of the operational amplifier 30 is grounded. Therefore, for example, the first sensor capacitance C _X1 From the first terminal 1 _P Drive signal V which is a pulse voltage of _X1 Is output, the voltage amplitude value V _P Is the first sensor capacitance C _X1 Is applied. As a result, the voltage value V _P And the first sensor capacitance C _X1 Charge Q obtained by multiplying the capacitance value of _X1 Is the first sensor capacitance C _X1 Is accumulated in Other capacity C _X2 , C _R1 , C _R2 The same applies to
[0038]
The charge-voltage conversion circuit 26 has a sensor capacitance C _X1 , C _X2 And reference capacity C _R1 , C _R2 Is converted into a voltage value and output. This circuit 26 may be referred to as a charge amplifier circuit. The charge-voltage conversion circuit 26 includes an operational amplifier (charge amplifier) 30 and a feedback capacitor C _F And a switch 28. As described above, this circuit 26 has the capacitance C only at the inverting input terminal of the operational amplifier 30. _X1 , C _X2 , C _R1 , C _R2 Are connected to each other, and are of a single input type. Return capacitance C _F And the switch 28 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 30. The switch 28 receives the reset signal S from the control signal generation circuit 38. ₂ Turns on when is input. When the switch 28 is turned on, the feedback capacitance C _F Is short-circuited at both ends, so that the feedback capacitance C _F Is discharged. The output voltage V of the charge-voltage conversion circuit 26 (specifically, the operational amplifier 30) _OP Is input to the sample and hold circuit 32.
[0039]
The sample and hold circuit 32 outputs the sampling signal S from the control signal generation circuit 38. ₃ Is input, the output voltage V of the operational amplifier 30 _OP Is sampled. Then, the value of the sampled signal is held for a predetermined time. The output voltage signal of the sample and hold circuit 32 is input to the low-pass filter 34.
[0040]
The low-pass filter 34 has a predetermined cut-off frequency, cuts a high-frequency component of an output signal of the sample-and-hold circuit 32, and performs a band-limited voltage signal V _OUT Is output. Output voltage V of low-pass filter 34 _OUT Is input to the determination circuit 36.
[0041]
The determination circuit 36 is not used in the sensor mode, but is used in the abnormality detection mode. In the abnormality detection mode, the determination command signal S ₄ Is input, the output voltage V of the charge-voltage conversion circuit 26 (the operational amplifier 30) _OP Is input to the determination circuit 36 through the branch line 42. The judgment circuit 36 outputs the output voltage value V _OP Is a predetermined abnormality determination value (threshold) V _TH The determination signal V _DET Is output. The determination circuit 36 outputs the output voltage value V _OP Is a predetermined threshold value V _TH If the value is smaller than _DET And outputs a signal indicating that it is normal. On the other hand, the judgment circuit 36 outputs the output voltage value V _OP Is a predetermined threshold value V _TH In the above case, the judgment signal V _DET Output an abnormality detection signal.
[0042]
Next, the operation of the capacitance type sensor device having the above configuration will be described. The operation of the sensor device is divided into an operation in a sensor mode and an operation in an abnormality detection mode. First, the operation in the sensor mode will be described with reference to the timing chart of FIG. Note that in FIG. 2 and FIG. 3 described later, the Hi signal is displayed as “H” and the Low signal is displayed as “L”.
As shown in FIG. 2, the mode setting signal S output from the control signal generation circuit 38 ₁ Is a low signal, the sensor mode is set. In the sensor mode, the second drive signal V _X2 Is the first drive signal V _X1 And the same phase. Third drive signal V _R1 Is the first drive signal V _X1 Are in opposite phase with respect to. Fourth drive signal V _R2 Is the third drive signal V _R1 And the same phase.
[0043]
FIG. 4 shows the period T ₁₀ ~ T ₁₂ 3 shows the state of the capacitance-type sensor device. Period T ₁₀ ~ T ₁₂ During the reset signal S ₂ Is a Hi signal. In this case, the switch 28 is turned on. When the switch 28 is turned on, the feedback capacitance C _F Is shorted at both ends. Therefore, the feedback capacitance C _F The electric charge stored in the cell is discharged. Therefore, while the switch 28 is on, the output voltage V of the operational amplifier 30 is _OP Is zero. Also, period T ₁₀ ~ T ₁₂ During the first drive signal V _X1 Is V _P And the third drive signal V _R1 Is zero. In this case, the first sensor capacitance C _X1 Has a Q _X1 = C _X1 V _P = (C _R1 + ΔC _X1 ) V _P Is accumulated.
[0044]
FIG. 5 shows the period T ₁₄ ~ T ₁₆ 3 shows the state of the capacitance-type sensor device. As shown in FIG. ₁₂ At the reset signal S ₂ Is switched from the Hi signal to the Low signal, and during the period T ₁₄ ~ T ₁₆ During the reset signal S ₂ Is a Low signal. In this case, the switch 28 is off. Time T ₁₄ , The first drive signal V _X1 Becomes zero, and the third drive signal V _R1 Is V _P Switch to. Thus, the switch 28 is turned off from the state shown in FIG. 4 as shown in FIG. 5, and the first drive signal V _X1 Becomes zero, the first sensor capacitance C _X1 One electrode (return capacitance C _F Negative electrode accumulated on the first electrode connected to one of the two electrodes) _F Move to the one electrode. Accordingly, the feedback capacitance C _F A positive charge is induced on the other electrode. Thereby, the feedback capacitance C _F Has a first sensor capacitance C _X1 Charge Q equal to the charge stored in _X1 Is accumulated.
[0045]
Further, the third drive signal V _R1 Is V _P , The first reference capacitance C _R1 Has a Q _R1 = C _R1 V _P Is accumulated. In this case, the first reference capacitance C _R1 One electrode (return capacitance C _F Negative electrode is accumulated in the electrode connected to the one electrode). As a result, the feedback capacitance C _F The first reference capacitance C _R1 An electric charge of the opposite sign (that is, a positive electric charge) is induced in the same amount as the negative electric charge stored in the one electrode. Accordingly, the feedback capacitance C _F A negative charge is induced in the other electrode. Thereby, the feedback capacitance C _F Has a first reference capacitance C _R1 Charge Q equal to the charge stored in _R1 Is accumulated.
[0046]
However, the feedback capacitance C _F Charge Q stored in _X1 And Q _R1 Have opposite polarities. Therefore, the charge Q accumulated in the first sensor element unit 22 _X1 , Q _R1 , The feedback capacitance C _F Has a charge Q _X1 −Q _R1 Is accumulated. As a result, the charges Q stored in the first sensor element _X1 , Q _R1 Output voltage V of the operational amplifier 30 due to the _OP1 Is given by the following equation (1) since the non-inverting input terminal is grounded.

[0047]
Although the operation of the first sensor element unit 22 has been described above, the same operation is performed in the second sensor element unit 24. Thereby, the second sensor capacitance C _X2 Has a charge Q _X2 (= C _X2 V _P = (C _R2 + ΔC _X2 ) V _P ) Is accumulated. Second reference capacity C _R2 Has a charge Q _R2 (= C _R2 V _P ) Is accumulated.
Therefore, the charge Q accumulated in the second sensor element unit 24 _X2 , Q _R2 , The feedback capacitance C _F Has a charge Q _X2 −Q _R2 Is accumulated. As a result, the charge Q stored in the second sensor element _X2 , Q _R2 Output voltage V of the operational amplifier 30 due to the _OP Is given by the following equation (2).

[0048]
From the above, the charge Q accumulated in the first sensor element unit 22 _X1 , Q _R1 And the charge Q stored in the second sensor element section 24 _X2 , Q _R2 Output voltage V of the operational amplifier 30 due to the _OP Is V in equation (1) _OP1 And V in equation (2) _OP2 Is added to the following equation (3).
V _OP = V _OP1 + V _OP2 = (ΔC _X1 + ΔC _X2 ) V _P / C _F (3)
[0049]
As shown in FIG. ₁₄ ~ T ₁₆ At a predetermined point in time, the control signal generating circuit 38 sends a sampling command signal S to the sample and hold circuit 32. ₃ Is output. Sampling command signal S ₃ Is input, the sample and hold circuit 32 outputs the output voltage V of the operational amplifier 30. _OP (In FIG. 2, V ₁ ) Is sampled and the value is held. The output signal of the sample and hold circuit 32 is further input to a low-pass filter 34. Thereby, the high-frequency component is cut from the low-pass filter 34, and the band-limited output signal V _OUT Is output.
[0050]
In the sensor mode, the determination command signal S output from the control signal generation circuit 38 to the determination circuit 36 ₄ Is in the Low state, and the determination operation is not performed. Therefore, the output signal V of the determination circuit 36 _DET Are also in the Low state.
In the sensor mode, the above operation is repeatedly performed.
[0051]
Next, the operation in the abnormality detection mode will be described with reference to the timing chart of FIG. Mode setting signal S output from control signal generation circuit 38 ₁ Is a Hi signal, an abnormality detection mode is set. In the abnormality detection mode, the sampling command signal S output from the control signal generation circuit 38 to the sample and hold circuit 32 ₃ Is in a low state, and no sampling operation is performed. Therefore, the output signal V of the low-pass filter 34 _OUT Are also in the Low state. In the abnormality detection mode, unlike the sensor mode, the third drive signal V _X2 Is the first drive signal V _X1 And the fourth drive signal V _R2 Is the second drive signal V _R1 Are in opposite phase with respect to Second drive signal V _R1 Is the first drive signal V _X1 The phase is opposite to that in the case of the sensor mode. As a result, in the abnormality detection mode, the second sensor capacitance C _X2 And the second reference capacitance C _R2 The polarity of the charge stored in the sensor mode is opposite to that in the sensor mode. Therefore, the output voltage V of the operational amplifier 30 _OP Is V in equation (1) _OP1 From equation (2), V _OP2 Is subtracted from the following equation (4).
V _OP = V _OP1 -V _OP2 = (ΔC _X1 −ΔC _X2 ) V _P / C _F (4)
[0052]
First sensor capacity C _X1 And the second sensor capacitance C _X2 Is normal, the capacity increase value (capacity change value) ΔC is independent of the magnitude of the physical quantity acting as described above. _X1 And ΔC _X2 Are equal. Therefore, the output voltage V of the operational amplifier 30 _OP Is substantially zero regardless of the magnitude of the physical quantity that acts when the sensor element portions 22 and 24 are normal.
[0053]
In FIG. 3, the period T ₅₄ ~ T ₅₆ During this period, the sensor element units 22 and 24 are normal and the output voltage V of the operational amplifier 30 is _OP Is zero. This output voltage V _OP Is input to the determination circuit 36. In the abnormality detection mode, the period T ₅₄ ~ T ₅₆ At a predetermined point in time, the control signal generation circuit 38 sends the Hi-state determination command signal S to the determination circuit 36. ₄ Is output. The judgment circuit 36 outputs a judgment command signal S ₄ Is input, the output voltage V _OP (Absolute value) is the abnormality determination value V _TH It is determined whether or not this is the case. Output voltage V _OP Is the abnormality determination value V _TH If it is smaller than the threshold value, the determination circuit 36 _DET And outputs a Low signal (a signal indicating normality). As described above, the output voltage V _OP Is the abnormality determination value V _TH In the case of zero which is smaller than zero, the determination circuit 36 _DET And outputs a Low signal.
[0054]
On the other hand, when there is an abnormality in the sensor element units 22 and 24, (ΔC _X1 −ΔC _X2 ) Does not become almost zero. For example, the sensor capacity C _X1 , C _X2 When a foreign object (such as dust) is caught between the movable electrode and the fixed electrode constituting the sensor, the sensor capacitance C _X1 , C _X2 However, even when a predetermined physical quantity is added, the movable electrode cannot be displaced by an intended amount, and an intended capacitance change value may not be obtained.
In this case, the output voltage V of the operational amplifier 30 _OP Is not almost zero.
[0055]
Period T ₆₂ ~ T ₆₄ During the period, an abnormality has occurred in the sensor element units 22 and 24, and the output voltage V of the operational amplifier 30 is _OP Is not almost zero and V ₃ Shows the case where In the abnormality detection mode, the period T ₆₂ ~ T ₆₄ At a predetermined point in time, the control signal generation circuit 38 sends a high-level determination command signal S to the determination circuit 36. ₄ Is output. The determination circuit 36 outputs the determination command signal S ₄ Output voltage V _OP Is the abnormality determination value V _TH In the above case, the judgment circuit 36 outputs the judgment signal V _DET Output a Hi signal (abnormality detection signal). As described above, the output voltage V _OP Is the abnormality determination value V _TH V greater than ₃ In the case of, the judgment circuit 36 outputs the judgment signal V _DET And outputs a Hi signal.
[0056]
Sensor capacity C _X1 , C _X2 Is more likely to cause an abnormality due to the presence of foreign matter (dust or the like) among sensor devices. Sensor capacity C _X1 , C _X2 This is because, if a foreign object is caught between the movable electrode and the fixed electrode, the movable electrode is unlikely to be displaced even if a physical quantity acts, and the intended capacitance change value cannot be obtained. Also, the sensor capacity C _X1 , C _X2 The movable electrode constituting is a part that is premised on being displaced. Therefore, there is a relatively high possibility of deterioration due to repeated use and occurrence of an abnormality such as an inability to obtain an intended displacement amount (capacity change value) even when a physical quantity acts.
According to the present embodiment, it is possible to detect an abnormality of the sensor element portions 22 and 24, in which an abnormality is relatively likely to occur in the sensor device, more simply and more accurately than in the past.
[0057]
In addition, the control signal generation circuit 38 supplies a pulse voltage (second drive signal) V shown in FIG. _X2 And an inverted pulse voltage (second drive signal) V shown in FIG. _X2 Is preferably controllable so as to be output alternately and repeatedly. That is, it is preferable that the control signal generation circuit 38 can be controlled so as to alternately repeat the sensor mode and the abnormality inspection mode.
[0058]
In this way, the sensor device of the present embodiment performs not only an abnormality inspection at the time of shipment after manufacturing, but also an online inspection that performs an abnormality inspection in the meantime while performing the sensor operation which is the original operation of the sensor device. Can also be performed. In this embodiment, the sensor mode and the abnormality inspection mode can be easily switched only by inverting the voltage output from the second terminal 2 and the fourth terminal 4, so that the sensor mode and the abnormality inspection mode can be switched at short time intervals. It can be easily repeated.
[0059]
Second Embodiment A capacitance type sensor device according to a second embodiment shown in FIG. 6 is configured such that the charge-voltage conversion circuit 26 is of a differential input type. The output of the second sensor element unit 24 is input to the non-inverting input terminal of the operational amplifier 30. The non-inverting input terminal of the operational amplifier 30 is connected to the second feedback capacitance C. _F2 Grounded. Second feedback capacitance C _F2 , A second switch 29 is connected in parallel.
[0060]
Third Embodiment A capacitance type sensor device according to a third embodiment shown in FIG. _X1 , V _X2 , V _R1 , V _R2 Is changed from a square wave to a sine wave. Further, a synchronous rectification circuit 40 is used in place of the sample and hold circuit 32 of the first embodiment. Further, the output voltage of the synchronous rectification circuit 40 is input to the determination circuit 36 through the branch line 44. Note that, similarly to the second embodiment, the charge-voltage conversion circuit 26 is of a differential input type.
[0061]
The same effects as those of the capacitance type sensor device of the first embodiment can also be obtained by the capacitance type sensor devices of the second and third embodiments.
[0062]
As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and alterations of the specific examples illustrated above.
(1) For example, the reference capacitance C used in the above embodiment _R1 In place of the sensor capacitance C according to the physical quantity that acts. _X1 And the reference capacitance value (capacity value when the reference physical quantity acts) becomes the sensor capacitance C. _X2 A differential capacitance approximately equal to the above may be used. According to this configuration, the sensor capacitance C _X1 And the reference capacitance value of the differential capacitance are cancelled, and the sensor capacitance C _X1 And the sum of the capacitance change values of the differential capacitors. Similarly, the reference capacity C _R2 Instead, a differential capacitance may be used.
(2) In the above embodiment, the feedback capacitance C _F The case where the switch 28 is provided in parallel with _F And a resistor may be provided in parallel. By providing such a switch 28 and a resistor, the DC operating point of the charge-voltage conversion circuit 26 can be appropriately set. Specifically, the DC potential of the negative-phase input terminal of the operational amplifier 30 can be set to an appropriate value.
[0063]
Further, the technical elements described in the present specification or the drawings exert technical utility singly or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology illustrated in the present specification or the drawings can simultaneously achieve a plurality of objects, and has technical utility by achieving one of the objects.
[Brief description of the drawings]
FIG. 1 shows a block diagram of a capacitance type sensor device of a first embodiment.
FIG. 2 is a timing chart showing an operation in a sensor mode of the capacitance type sensor device of the first embodiment.
FIG. 3 is a timing chart showing an operation in an abnormality detection mode of the capacitance type sensor device of the first embodiment.
FIG. 4 is a diagram for explaining the operation of the capacitance-type sensor device (1).
FIG. 5 is a diagram for explaining the operation of the capacitance-type sensor device (2).
FIG. 6 is a block diagram showing a capacitance type sensor device according to a second embodiment.
FIG. 7 is a block diagram showing a capacitance type sensor device according to a third embodiment.
[Explanation of symbols]
20: drive signal generation circuit
22: first sensor element unit
24: second sensor element unit
26: charge-voltage conversion circuit
28: Switch
30: Operational amplifier
32: sample and hold circuit
34: Low-pass filter
36: Judgment circuit
38: Control signal generation circuit
C _X1 , C _X2 : Sensor capacity
C _R1 , C _R2 : Reference capacity
C _F : Return capacity
V _X1 : First drive signal
V _X2 : Second drive signal
V _R1 : Third drive signal
V _R2 : Fourth drive signal
S ₁ : Mode setting signal
S ₂ : Reset signal
S ₃ : Sampling command signal
S ₄ : Judgment command signal

Claims (5)

First means for outputting, with a first voltage whose amplitude value changes by a predetermined value over time, a second voltage whose amplitude value changes by a value approximately equal to the predetermined value over time or an inverted voltage thereof,
A first sensor capacitance whose capacitance value changes according to a physical quantity that acts upon application of a first voltage;
When the second voltage or its inversion voltage is applied, the capacitance value changes according to the physical quantity that acts, and the absolute value and the reference capacitance value of the capacitance change value when a predetermined physical quantity acts are substantially equal to the first sensor capacitance. Equal second sensor capacitance;
Control means for controlling which of the second voltage and its inverted voltage is output from the first means;
When the second voltage is output together with the first voltage from the first means, a signal value corresponding to a value obtained by adding the absolute value of the capacitance change value of the first sensor capacitance and the absolute value of the capacitance change value of the second sensor capacitance When the inverted voltage of the second voltage is output together with the first voltage from the first means, the absolute value of the capacitance change value of the other sensor capacitance is subtracted from the absolute value of the capacitance change value of the other sensor capacitance. Second means for outputting a signal value corresponding to the value obtained;
An electrostatic capacitance type sensor device including an abnormality detection unit that outputs an abnormality detection signal based on an output signal value of the second unit when an inverted voltage of the second voltage is output from the first unit. A first terminal that outputs a first voltage whose amplitude value changes by a predetermined value with time, and a second terminal that outputs a second voltage whose amplitude value changes by a value approximately equal to the predetermined value with time or an inverted voltage thereof. First means having;
A first sensor capacitor having a pair of electrodes, one of which is connected to the first terminal, and whose capacitance value changes according to a physical quantity acting thereon;
It has a pair of electrodes, one of the electrodes is connected to the second terminal, the capacitance value changes according to the physical quantity acting, the absolute value of the capacitance change value when a predetermined physical quantity acts, and the reference capacitance A second sensor capacitance whose value is approximately equal to the first sensor capacitance;
Control means for controlling which of the second voltage and its inverted voltage is output from the second terminal of the first means;
A second means to which the other electrode of each sensor capacitor is connected and which outputs a signal value corresponding to the amount and polarity of the electric charge accumulated in each sensor capacitor;
An electrostatic capacitance type sensor device comprising an abnormality detection means for outputting an abnormality detection signal based on an output signal value of the second means. The capacitance type sensor device according to claim 1, wherein the control unit is capable of controlling the first unit to alternately and repeatedly output the second voltage and its inverted voltage. A method of using two sensor capacitors whose capacitance value changes according to a physical quantity that acts and an absolute value and a reference capacitance value of a capacitance change value when a predetermined physical quantity acts are substantially equal,
A first voltage whose amplitude value changes by a predetermined value over time is applied to the first sensor capacitor, and a second voltage whose amplitude value changes by a value substantially equal to the predetermined value over time is applied to the second sensor capacitor. A first step of directly or indirectly obtaining a value obtained by adding the absolute value of the capacitance change value of the first sensor capacitance and the absolute value of the capacitance change value of the second sensor capacitance;
By applying a first voltage to the first sensor capacitor and applying an inverted voltage of the second voltage to the second sensor capacitor, the absolute value of the capacitance change value of one sensor capacitor is used to calculate the capacitance change value of the other sensor capacitor. A method of using a sensor capacitor having a second step of directly or indirectly obtaining a value obtained by subtracting an absolute value. The method according to claim 4, wherein the first step and the second step are alternately repeated.

Images