JP3772044B2

JP3772044B2 - Capacitance type detection device

Info

Publication number: JP3772044B2
Application number: JP13073099A
Authority: JP
Inventors: 知岡本; 鎭徳秋山; 正宏天野
Original assignee: ジェイ・エス・ケー株式会社; 株式会社日本オートメーション
Priority date: 1999-05-12
Filing date: 1999-05-12
Publication date: 2006-05-10
Anticipated expiration: 2019-05-12
Also published as: JP2000321113A

Description

【０００１】
【発明の属する技術分野】
本発明は、主として容器や流通配管内の各種液体や粉粒体などの被検出誘電体を外部から静電容量的に検出する手段として利用できる静電容量型検出装置に関するものである。
【０００２】
【従来の技術】
この種の静電容量型検出装置としては、接地状態にある前記容器や流通配管の外側に検出電極を装着し、この検出電極に抵抗を介して矩形波電圧を対地間で印加し、前記抵抗と前記容器や流通配管中の被検出誘電体とを経由して対地間で高周波電流が流れる際の対地間で生じる容量（対地間静電容量）とによって形成されるＲＣ回路による前記検出電極での矩形波電圧の立ち上がり立ち下がりの時間的遅れに基づいて検出信号を出力するようにしたものが知られている。
【０００３】
【発明が解決しようとする課題】
しかして、上記構成の従来の静電容量型検出装置では、容器内の被検出誘電体の表面レベルが検出電極の検出レベルよりも下がった状態や流通配管中に被検出誘電体が流通していない状態であれば、本来は、前記検出電極の対地間静電容量が極減してＲＣ回路が閉成されず、検出電極における矩形波電圧の立ち上がり立ち下がりに時間的遅れが生じなくなり、検出信号が出力されなくなる筈である。しかし、実際には、前記容器や流通配管の内面に、水垢などの汚れ、結露、氷結、あるいは被検出誘電体が強粘性物質である場合の層状の残留付着などが生じている状況では、前記容器や流通配管の内面に高周波回路的に接地状態にある誘電体層が存在することになる結果、当該誘電体層を介して検出電極を経由するＲＣ回路が対地間で閉成され、検出電極における矩形波電圧の立ち上がり立ち下がりに時間的遅れが生じ、検出信号が出力されてしまう。
【０００４】
即ち、容器や流通配管の外側から内部の液体や粉粒体を検出する従来のこの種の静電容量型検出装置は、誤動作が生じ易くて信頼性が低いため、検出対象の被検出誘電体の性状や、容器や配管内部の定期的清掃などの保守面で、相当の好条件が満たされなければ実用に供し得ないものであった。
【０００５】
【課題を解決するための手段】
本発明の第一の目的は、従来のこの種の静電容量型検出装置の最大の問題点である、容器内面や配管内面の汚れや結露、氷結などによる誤動作を解消し、信頼性が高く且つ小型の静電容量型検出装置を提供することにあって、その手段を後述する実施形態の参照符号を付して示すと、被検出誘電体２６との間に非導電性隔壁（容器囲壁２７ａなど）を隔てて配設された検出電極３に抵抗１７を介して矩形波電圧を印加し、前記抵抗１７と被検出誘電体２６とを経由して対地間で高周波電流が流れる際の対地間で生じる静電容量（対地間静電容量）とによって形成されるＲＣ回路の閉成に基づいて検出信号を出力するようにした静電容量型検出装置であって、前記検出電極３に印加される矩形波電圧と同周波数の矩形波電圧を発生するガード電圧発生手段３０（矩形波電圧発生回路１６、可変抵抗器２０、及び位相反転／波形整形回路２４）、第二電極４、及び第三電極５が設けられ、ガード電圧発生手段３０は第二電極４に接続され、第二電極４は前記検出電極３の周囲に配設されて、当該第二電極４の電位により、前記隔壁（容器囲壁２７ａなど）に沿って層状に存在する誘電体を経由するＲＣ回路を遮断するようにし、第三電極５は第二電極４に接続されたもので、前記検出電極３の背面側をカバーするように配設された構成となっている。
【０００６】
また、本発明の第二の目的は、被検出誘電体２６が、水などの液体に比べて比誘電率が非常に小さい粉粒体であっても、精度良く検出することができる静電容量型検出装置を提供することにあって、その手段は、前記第三電極５を第二電極４に接続する代わりに接地した構成となっている。
【０００７】
上記の本発明装置を実施するについて、被検出誘電体が例えば液体であるか粉粒体であるかに応じて使い分けることができるように切り換え手段３２を併用し、この切り換え手段３２により、被検出誘電体２６が比誘電率の大きな液体などである場合には、前記第二電極４及び前記第三電極５の両方を前記ガード電圧発生手段３０に接続し、被検出誘電体２６が比誘電率の小さい粉粒体などである場合には、第二電極４のみを前記ガード電圧発生手段３０に接続するとともに第三電極５を接地することができる。
【０００８】
【発明の実施の形態】
以下に本発明の好適実施形態を添付図に基づいて説明すると、図１及び図２において、１は検出器であって、回路基板２、検出電極３、第二電極４、第三電極５、及びこれらを内蔵するプラスチックケース６から構成され、プラスチックケース６には取り付け用フランジ６ａが設けられている。さらに詳述すると、回路基板２の裏面に取り付けられた第二基板７の表面（回路基板２のある側とは反対側）に第三電極５が形成され、この第三電極５との間に一定空間を隔てるように前記第二基板７に対しスペーサー兼用のピンコネクター８を介して支持された第三基板９の表面（回路基板２のある側とは反対側）に検出電極３と第二電極４とが形成されている。この検出電極３と第二電極４とは、プラスチックケース６の検出作用面を構成する正面壁の内面に接するように配置されているが、第三基板９をプラスチックケース６の検出作用面を構成する正面壁で兼用させるように、このプラスチックケース６の正面壁の内面に直接検出電極３と第二電極４とを形成することもできる。
【０００９】
各電極３〜５は、基板７，９に対して導電膜をプリントする方法や、基板７，９の表面に銅箔や銅板などの薄い導電材を貼付する方法などで構成することができる。しかして、第二電極４は検出電極３の周囲を取り囲む環状に配置され、第三電極５は、検出電極３と第二電極４の背面側の全域をカバーするように配置されている。図示例では、各電極３〜５を矩形（第二電極４は矩形環状）に形成しているが、円形（第二電極４は円形環状）に形成することもできる。
【００１０】
回路基板２上で構成される回路構成について説明すると、図１に示すように、検出電極３は、矩形波電圧発生回路１６の互いに逆位相の矩形波電圧を出力する２つの出力端子の内の一方の出力端子１６ａに抵抗器１７を介して接続されるとともに、位相反転／波形整形回路１８の入力端子１８ａに接続されている。前記矩形波電圧発生回路１６の他方の出力端子１６ｂは、位相反転／波形整形回路１９の入力端子１９ａに可変抵抗器２０を介して接続され、当該位相反転／波形整形回路１９の出力端子１９ｂは、比較回路２１の３つの入力端子２１ａ〜２１ｃの内、入力端子２１ａに接続されて、当該比較回路２１に基準矩形波電圧を印加する。
【００１１】
比較回路２１は、３つの入力端子２１ａ〜２１ｃの電位が全てＬレベルになっている間のみ、出力端子２１ｄの電位がＨレベルからＬレベルに切り替わるように、ダイオードマトリックス回路で構成されたもので、その入力端子２１ｂにおいて前記位相反転／波形整形回路１８の出力端子１８ｂと接続されるとともに、入力端子２１ｃにおいて前記矩形波電圧発生回路１６の出力端子１６ａに接続され、位相反転／波形整形回路１９から与えられる基準矩形波電圧と位相反転／波形整形回路１８から与えられる矩形波電圧とを比較して、前記検出電極３における矩形波電圧の立ち上がり立ち下がりの時間遅れを検出し、その出力端子２１ｄに時間遅れ検出信号を出力する。２２は、前記比較回路２１の出力端子２１ｄに接続される入力端子２２ａと、次段の出力回路２３の入力端子２３ａに接続される出力端子２２ｂとを備えたオンオフ信号発生回路であって、前記比較回路２１からの時間遅れ検出信号に基づいてオンオフ信号を次段の出力回路２３に供給する。出力回路２３は、前記オンオフ信号発生回路２２からのオンオフ信号に基づいて外部出力端子２３ｂの電位を切り換えるもので、接地端子２３ｃとの間に所定の直流電圧が印加される電源端子２３ｄを備えている。
【００１２】
第二電極４と第三電極５とには、位相反転／波形整形回路２４の出力端子２４ｂが接続され、この位相反転／波形整形回路２４の入力端子２４ａは、前記位相反転／波形整形回路１９の入力端子１９ａに接続され、可変抵抗器２０の影響を受けた矩形波電圧が印加されるようになっている。
【００１３】
なお、第三基板９上の検出電極３と第二電極４とは、当該第三基板９を支持するスペーサー兼用のピンコネクター８を介して回路基板２上の所定端子１８ａ，２４ｂに接続されている。
【００１４】
以上のように構成された検出装置の検出器１は、例えば図３Ａに示すように、水などの被検出誘電体２６が収容される容器（タンク）２７の非導電性材料から構成された囲壁２７ａの外側に、前記被検出誘電体２７の有無を検出するレベルに検出電極３が位置するように、そして検出電極３及び第二電極４と囲壁２７ａとの間に空隙が生じないように、取り付けられる。図４及び図５は、この使用状態での各回路の出力乃至は入力の電圧波形を示すもので、図４−列(1) は、検出電極３に対応する検出レベルに被検出誘電体２６が存在しない場合、図４−列(2) は、検出電極３に対応する検出レベルに被検出誘電体２６が存在する場合、図５は、図３Ｂに示すように検出電極３に対応する検出レベルに被検出誘電体２６は存在しないが、囲壁２７ａの内面に水垢や結露、氷結などによる誘電体層２８が形成されている場合を示している。
【００１５】
しかして検出電極３には、矩形波電圧発生回路１６の出力端子１６ａから、図４−行Ａに示す矩形波電圧が抵抗器１７を介して印加される。一方、矩形波電圧発生回路１６の出力端子１６ｂから、図４−行Ｂに示すように前記検出電極３に印加される矩形波電圧（図４−行Ａ）に対し１８０度位相が異なった同周波数の矩形波電圧が出力され、これが可変抵抗器２０を経由することにより、図４−行Ｄに示すように立ち上がり立ち下がりに若干の時間を要した状態で、位相反転／波形整形回路１９の入力端子１９ａに供給される。従って、当該位相反転／波形整形回路１９の出力端子１９ｂ（比較回路２１の入力端子２１ａ）での矩形波電圧の波形は、図４−行Ｆに示すように、位相が１８０度反転されて、図４−行Ａに示す矩形波電圧発生回路１６の出力端子１６ａの出力波形（検出電極３に印加される矩形波電圧の波形）と略同位相になるが、当該図４−行Ａに示す矩形波電圧よりも立ち上がり立ち下がりが時間ｔだけ遅れた矩形波となる。
【００１６】
可変抵抗器２０を経由した矩形波電圧は、前記位相反転／波形整形回路１９と同一の働きをする位相反転／波形整形回路２４にも供給されるので、第二電極４及び第三電極５に印加される矩形波電圧、即ち、位相反転／波形整形回路２４の出力端子２４ｂでの矩形波電圧の波形は、比較回路２１の入力端子２１ａに入力される矩形波電圧（図４−行Ｆ）と同一の波形になる。このことから明らかなように、位相反転／波形整形回路１９の出力端子１９ｂと第二電極４及び第三電極５とを接続して、前記位相反転／波形整形回路２４を省くことも可能である。
【００１７】
以上の回路構成から明らかなように、検出電極３に印加される矩形波電圧に対して、周囲の第二電極４及び背部の第三電極５には略同位相で同周波数の矩形波電圧が印加されている。即ち、検出電極３の背面側をカバーし且つ当該検出電極３と略同位相で同周波数の矩形波電圧が印加されている第三電極５の存在により、検出電極３の背面側に配設されている回路基板２及び当該回路基板２上に構成された回路などから検出電極３に及ぼす静電容量的影響がなくなり、検出電極３の背面側の静電容量が存在しない状態となるとともに、検出電極３そのものが背面側の第三電極５の電位によって付勢される。そして検出電極３の周囲に配置され且つ当該検出電極３と略同位相で同周波数の矩形波電圧が印加されている第二電極４の存在により、検出電極３の正面側周囲に当該検出電極３と略同位相で同周波数の矩形波電圧による電界領域が形成される。
【００１８】
従って、図３Ａに示すように、検出電極３の内側に、第二電極４によって形成される電界領域の影響を受ける深さ（囲壁２７ａに対し直角方向）を越える深さで水などの誘電率の高い被検出誘電体２６が存在するときは、容器囲壁２７ａは高周波回路的に接地されているので、検出電極３は、第二電極４の電界の影響や背面側の回路などの影響を受けずに、当該容器２７内の被検出誘電体２６のみを介して高周波回路的に接地され、対地間で高周波電流が流れることになる。
【００１９】
換言すれば、容器２７内に収容されている被検出誘電体２６の表面レベルが検出電極３の検出レベルよりも低いときは、第二電極４の有る無しに関係なく、検出電極３に印加される矩形波電圧により高周波電流が流れることは確実に防止されるので、図４−列(1) 行Ｅに示すように、比較回路２１の入力端子２１ｂには、単に、矩形波電圧発生回路１６の出力端子１６ａにおける矩形波電圧（図４−列(1) 行Ｃ）の逆位相の矩形波電圧が供給されることになり、その立ち上がり立ち下がりに時間的遅れは生じない。従って、比較回路２１の入力端子２１ｃに供給される矩形波電圧（図４−列(1) 行Ａ）に基づいて、入力端子２１ａに供給される矩形波電圧（図４−列(1) 行Ｆ）と入力端子２１ｂに供給される矩形波電圧（図４−列(1) 行Ｅ）とを比較回路２１において比較した結果、３入力の全ての矩形波電圧が何れもＬレベルになることはないので、その出力端子２１ｄの電位は、図４−列(1) 行Ｉに示すようにＨレベルのままであり、出力回路２３の入力端子２３ａ（オンオフ信号発生回路２２の出力端子２２ｂ）及び外部出力端子２３ｂの電位は、図４−列(1) 行Ｊ，行Ｋに示すようにＨレベルのままである。
【００２０】
これに対して、先に説明したように、容器２７（囲壁２７ａは高周波回路的に接地されている）内に収容されている被検出誘電体２６の表面レベルが検出電極３の検出レベルよりも高いときは、第二電極４の有る無しに関係なく、検出電極３に印加される矩形波電圧により、抵抗器１７、検出電極３、及び被検出誘電体２６を経由して高周波電流が流れるので、図４−列(2) 行Ｃに示すように、位相反転／波形整形回路１８の入力端子１８ａにおける矩形波電圧（検出電極３における矩形波電圧）は、その立ち上がり立ち下がり時に、先に説明した可変抵抗器２０による遅れ時間ｔよりも大きな時間Ｔの遅れが発生する。
【００２１】
従って、比較回路２１の入力端子２１ｂには、時間Ｔだけ立ち上がり立ち下がりが遅れた矩形波電圧（図４−列(2) 行Ｅ）が供給されるので、図４−列(2) 行Ａ，行Ｅ，行Ｆの矩形波電圧波形から明らかなように、比較回路２１の入力端子２１ａの矩形波電圧の立ち下がりから入力端子２１ｂの矩形波電圧の立ち上がりまでの間、比較回路２１の３入力の全ての矩形波電圧が何れもＬレベルになり、その間だけ出力端子２１ｄの電位は、図４−列(2) 行Ｉに示すようにＬレベルとなり、パルス信号が出力される。この結果、オンオフ信号発生回路２２の出力端子２２ｂ（出力回路２３の入力端子２３ａ）及び外部出力端子２３ｂの電位は、図４−列(2) 行Ｊ，行Ｋに示すように、前記パルス信号の立ち上がり時点でＨレベルからＬレベルに切り換えられ、当該外部出力端子２３ｂの電位の変化を利用して、接続された適当な外部制御手段などを介して検出電極３の検出レベルに被検出誘電体２６が存在することを検知できる。
【００２２】
次に、図３Ｂに示すように、検出電極３の検出レベルに被検出誘電体２６は存在しないが、容器２７の囲壁２７ａの内面に濡れ、水垢、結露、氷結などによる誘電体層２８が形成され且つ当該容器２７を介して誘電体層２８が高周波回路的に接地されている場合を説明すると、この誘電体層２８は厚さが最大数ミリメートルと薄いので、前記の如く第二電極４により検出電極３の周囲に形成されている、当該検出電極３と略同位相の電位に付勢された電界領域が、検出電極３が前記誘電体層２８を介して対地間で高周波回路的につながるのを遮断する働きをする。
【００２３】
即ち、図５−列(1) 行Ｃに示すように、前記誘電体層２８を通じて検出電極３が対地間で高周波回路的に接続されるので、抵抗器１７、検出電極３、及び誘電体層２８を通じて高周波電流が流れて、検出電極３に印加される矩形波電圧（位相反転／波形整形回路１８の入力端子１８ａの矩形波電圧）には、その立ち上がり立ち下がりに時間遅れが発生しようとするが、第二電極４に印加される略同位相の矩形波電圧（図５−列(1) 行Ｇ）の電位で検出電極３の周囲の誘電体層２８が付勢される結果、検出電極３における矩形波電圧（図５−列(1) 行Ｃ）の立ち上がり立ち下がりの時間遅れが、第二電極４及び第三電極５に印加される略同位相の矩形波電圧（図５−列(1) 行Ｇ）の立ち上がり立ち下がり時点で強制的に解消され、同時点で検出電極３における矩形波電圧（図５−列(1) 行Ｃ）の立ち上がり立ち下がりが完了する。
【００２４】
従って、比較回路２１の入力端子２１ｂに供給される矩形波電圧（図５−列(1) 行Ｅ）には、その立ち上がり立ち下がりに若干の時間遅れが生じるが、この遅れ時間は、第二電極４及び第三電極５に印加される矩形波電圧（図５−列(1) 行Ｇ）の立ち上がり立ち下がりに生じている遅れ時間、即ち、比較回路２１の入力端子２１ａに供給される矩形波電圧（図５−列(1) 行Ｆ）の立ち上がり立ち下がりに生じる、可変抵抗器２０による遅れ時間ｔと等しいため、結果的には、図５−列(1) 行Ａ，行Ｅ，行Ｆに示すように、比較回路２１における３入力の全てがＬレベルになることはなく、検出電極３の検出レベルに被検出誘電体２６が存在しないときと同様に、出力回路２３の外部出力端子２３ｂの電位が切り替えられることはない。即ち、誘電体層２８は検出されず、誤動作を防止できる。
【００２５】
なお、３つの電極３〜５を備えた検出器１に対し、回路基板２上で構成される回路を別のケーシング内に内装し、両者をコードで接続することもできる。また、金属などの導電性材料から構成された容器（タンク）や流通配管に対して使用するときは、当該容器や配管の導電性材料から構成された囲壁に貫通孔を設け、この孔に検出器１を内嵌固定すれば良い。この場合、被検出誘電体２６と検出電極３及び第二電極４との間の非導電性隔壁は、検出器１のプラスチックケース６となる。
【００２６】
また、被検出誘電体２６の存在により検出電極３に印加される矩形波電圧の立ち上がり立ち下がりに生じる遅れ時間Ｔが、被検出誘電体２６の性状や検出電極３と被検出誘電体２６との間の非導電性隔壁（容器囲壁２７ａや検出器１のプラスチックケース６など）の材質などにより変化するが、可変抵抗器２０は、前記遅れ時間Ｔよりも比較回路２１の入力端子２１ａ、第二電極４及び第三電極５に加えられる矩形波電圧の立ち上がり立ち下がりの遅れ時間ｔが小さくなるように抵抗値が調整される。しかしながら、予想される遅れ時間Ｔの最小値よりも遅れ時間ｔが小さくなれば良いのであるから、前記可変抵抗器２０に代えて、固定抵抗器を使用することもできる。
【００２７】
被検出誘電体２６が水などの液体と比較して比誘電率が大幅に小さい粉粒体である場合（一般的には、液体に比べて粉粒体の比誘電率は１／５〜１／２０程度）は、第二電極４と同様に第三電極５に、検出電極３に印加される矩形波電圧と略同位相且つ同周波数の矩形波電圧を印加すると、この第三電極５の電界の影響を受けて検出電極３から見た被検出誘電体（粉粒体）２６側の静電容量が一層小さくなり、その有無に伴う変化を確実に検出するのが困難になる。
【００２８】
従って、被検出誘電体２６が比誘電率の小さい粉粒体などである場合は、図６に示すように、第二電極４のみを、前記矩形波電圧発生回路１６、可変抵抗器２０、及び位相反転／波形整形回路２４から成るガード電圧発生手段３０に接続し、第三電極５は接地端子３１に接続して接地する。
【００２９】
この図６に示す検出装置によれば、被検出誘電体２６が比誘電率の小さい粉粒体などであっても、検出電極３のレベルに当該被検出誘電体２６が有るときと無いときとで、当該検出電極３の正面側の静電容量変化を確実に捉えさせ、検出電極３のレベルに当該被検出誘電体２６が有るときは、矩形波電圧発生回路１６から当該検出電極３に印加される矩形波電圧により、抵抗器１７、検出電極３、及び被検出誘電体２６を経由するＲＣ回路を閉成させ、以て、図１及び図４に基づいて説明した通り、検出電極３の検出レベルに被検出誘電体２６が存在することの検知信号を出力させることができる。そして、第二電極４は、先に説明した通り、容器囲壁２７ａそのものやその内面に汚れや粉粒体の付着などによって形成される誘電体層の影響を無くす働きがあるので、検出電極３のレベルに粉粒体などの被検出誘電体２６が存在しないにもかかわらず、前記検知信号が出力されるような誤動作を確実に防止できる。
【００３０】
また、図６に示す検出装置は、液体と比較して比誘電率の小さい人体の指先などによるタッチ操作を検出するタッチセンサーなどとしても活用できる。即ち、指先を接触させるためのタッチ面を構成する非導電性材料から成る板材の裏面に検出器１を取り付けるかまたは、プラスチックケース６の正面を指先を接触させるためのタッチ面とし、指先を前記タッチ面に接触させたとき、人体を介して検出電極３が高周波回路的に接地されてＲＣ回路が閉成されるのを、先に説明した粉粒体などの被検出誘電体２６の検出作用と同様の作用で検出させることができる。この場合、前記タッチ面の汚れや雨水などによる水膜の付着による悪影響（誤動作）を第二電極４により防止することができる。
【００３１】
図７は、切り換え手段３２を使用して、第二電極４及び第三電極５の両方を前記ガード電圧発生手段３０に接続する第一状態と、第二電極４のみを前記ガード電圧発生手段３０に接続するとともに第三電極５を接地端子３１に接続する第二状態とに切り換え可能に構成した実施形態を示している。
【００３２】
この図７に示す検出装置によれば、被検出誘電体２６が比誘電率の大きな液体などである場合には、切り換え手段３２により、第二電極４及び第三電極５の両方を前記ガード電圧発生手段３０に接続する第一状態とすることにより、図１〜図５に基づいて説明した通りの検出装置として効果的に使用することができる。一方、被検出誘電体２６が比誘電率の小さい粉粒体などである場合には、切り換え手段３２により、第二電極４のみを前記ガード電圧発生手段３０に接続するとともに第三電極５を接地端子３１に接続する第二状態とすることにより、図６に基づいて説明した通りの検出装置として効果的に使用することができる。
【００３３】
なお、切り換え手段３２を併用する場合、図では機械的な切り換えスイッチを切り換え手段として使用し、電極と回路との接続経路を機械的に変更する構成を示したが、回路上で電気的に接続経路を切り換える方法、例えば、ロジックＩＣを組み込んで印加電圧を変更する方法、アナログスイッチで回路を切り換える方法、回路実装部品を変更する方法なども採用できる。
【００３４】
【発明の効果】
本発明は以上のように実施し使用し得るものであり、請求項１に記載した本発明の静電容量型検出装置では、被検出誘電体は検出位置に存在しないが、検出電極の内側の非導電性隔壁の内面に沿って濡れや汚れなどによる誘電体層が存在する場合、検出電極に印加される矩形波電圧と同周波数の矩形波電圧を印加される第二電極の電位により、前記濡れなどによる誘電体層を経由するＲＣ回路を遮断することができるので、前記非導電性隔壁の内面に形成される濡れや汚れなどによる誘電体層を検出電極により検出してしまうことがない。
【００３５】
しかも、検出電極の背面側をカバーするように第三電極を配設し、この第三電極に、前記第二電極と同様に前記検出電極に印加される矩形波電圧と同周波数の矩形波電圧を印加するように構成したので、検出電極の背面側に静電容量が存在しない状態とし、検出電極背面側の回路などの固定容量による影響を無くすとともに、当該第三電極の電位が検出電極そのものを付勢する作用により、検出電極の正面側におけるガード効果、即ち、検出電極周囲の第二電極による前記作用と同様に、検出電極の正面側の容器囲壁やその内面の汚れなどの誘電体層の影響を受けて誤動作するのを防止する効果が生じ、この結果、検出電極周囲の第二電極の面積を大きくしてそのガード効果を高めたのと同様の結果が得られる。換言すれば、検出電極の周囲の第二電極の面積によって決まる検出器の大きさを、当該第二電極を小さくして小型化することができるのである。
【００３６】
即ち、請求項１に記載の本発明の構成によれば、容器や流通配管の内面の濡れや汚れ、結露、氷結などによる誤動作は勿論のこと、検出電極背面側の回路などによる誤動作を防止して、検出電極が対応する検出位置に被検出誘電体が存在するか否かを容器や流通配管の外部から精度良く検出することができ、被検出誘電体の性状や、容器や流通配管の内部の定期的清掃などの保守作業に影響されない、信頼性の高い、しかも小型化も容易な静電容量型検出装置を得ることができるのである。
【００３７】
被検出誘電体が、高周波回路的に接地された状態ではないと考えられる比誘電率の小さい粉粒体などである場合、検出電極の周囲の前記第二電極によるガード作用により、被検出誘電体と検出電極との間の容量変化量が減殺され、その分だけ検出感度が低下する。この場合、上記のように検出電極の背部に配設される第三電極が前記第二電極に接続されていると、検出感度の低下はさらに顕著になる。勿論、容器内面に付着する粉粒体層は検出されてはならない。
【００３８】
しかして、請求項２に記載の如く、第三電極をアース電極とすることにより、前面の各電極の背面側の容量を一定に固定することにより、結果的に検出電極の前面側（被検出誘電体側）の感度を向上させることができ、比誘電率の小さい粉粒体などを非接触検出するのに特に効果的で、タッチセンサーなどとしても活用可能な静電容量形検出装置を得ることができる。この場合、実施形態に示したように、検出電極とその背部の第三電極との間にピンコネクターなどのスペーサーを介在させて適当な空隙を確保することにより、検出電極の背面側の容量をより一層低く抑えることができ、効果的である。
【００３９】
そして、請求項３に記載の本発明の構成によれば、切り換え手段を切り換えるだけで、被検出対象物が比誘電率の大きな液体がある場合と比誘電率の小さな粉粒体である場合の何れでも、精度良く検出することができる。
【図面の簡単な説明】
【図１】第一実施形態を示す装置全体の回路図である。
【図２】Ａ図は検出器の構成を説明する概略縦断側面図であり、Ｂ図は同一部切り欠き平面図である。
【図３】Ａ図は検出レベル以上に被検出誘電体がある状態を説明する要部の縦断側面図、Ｂ図は検出レベルに被検出誘電体が無く、汚れなどの誘電体層が有る状態を説明する要部の縦断側面図である。
【図４】検出レベルに被検出誘電体の有る状態と無い状態での各端子の電圧波形を説明する図である。
【図５】検出レベルに被検出誘電体が無く、汚れなどの誘電体層が有る状態での各端子の電圧波形を説明する図である。
【図６】第二実施形態の構成を説明する概略図である。
【図７】第三実施形態の構成を説明する概略図である。
【符号の説明】
１検出器
２回路基板
３検出電極
４第二電極
５第三電極
６プラスチックケース
７第二基板
８スペーサー兼用のピンコネクター
９第三基板
１６矩形波電圧発生回路（ガード電圧発生手段）
１７抵抗器
１８位相反転／波形整形回路
１９位相反転／波形整形回路
２０可変抵抗器（ガード電圧発生手段）
２１比較回路
２２オンオフ信号発生回路
２３出力回路
２４位相反転／波形整形回路（ガード電圧発生手段）
２６被検出誘電体
２７容器
２７ａ非導電性材料から成る囲壁
２８汚れなどの誘電体層
３０ガード電圧発生手段
３１接地端子
３２切り換え手段[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a capacitance type detection apparatus that can be used as a means for capacitively detecting a dielectric to be detected such as various liquids and powder particles in containers and distribution pipes from the outside.
[0002]
[Prior art]
  As this type of capacitance-type detection device, a detection electrode is mounted on the outside of the container or the distribution pipe in a grounded state, a rectangular wave voltage is applied to the detection electrode via a resistor, and the resistance And the detected dielectric in the container or distribution pipeAnd the capacitance generated between the ground when high-frequency current flows between the ground (the capacitance between the ground)It is known that a detection signal is output based on a time delay of rising and falling of a rectangular wave voltage at the detection electrode by an RC circuit.
[0003]
[Problems to be solved by the invention]
  Thus, in the conventional capacitance type detection device having the above-described configuration, the detected dielectric is in a state where the surface level of the detected dielectric in the container is lower than the detection level of the detection electrode or in the distribution pipe. If there is no current, the capacitance between the detection electrode and the ground is extremely reduced, the RC circuit is not closed, and there is no time delay in the rising and falling of the rectangular wave voltage at the detection electrode. The signal should not be output.The But in fact,In the situation where dirt such as scale, condensation, icing, or layered residual adhesion occurs when the detected dielectric is a highly viscous material, the inner surface of the container or the distribution pipe As a result, there is a dielectric layer that is grounded as a high-frequency circuit. As a result, the RC circuit that passes through the detection electrode via the dielectric layer is closed between the ground and the rising of the rectangular wave voltage at the detection electrode. A time delay occurs in the fall, and a detection signal is output.
[0004]
  In other words, this type of conventional electrostatic capacitance type detection device that detects the liquid and particles inside the container and the distribution pipe from the outside is prone to malfunction and has low reliability. In terms of the properties and maintenance aspects such as regular cleaning of the inside of the container and piping, it could not be put to practical use unless considerable favorable conditions are satisfied.
[0005]
[Means for Solving the Problems]
  The first object of the present invention is to eliminate malfunctions due to dirt, condensation, icing, etc. on the inner surface of the container and the inner surface of the pipe, which is the biggest problem of this type of conventional electrostatic capacitance type detection device, and has high reliability. Further, in providing a small capacitance type detection device, the means thereof is indicated by reference numerals of embodiments to be described later, and a non-conductive partition wall (container surrounding wall) is provided between the detection dielectric 26 and the device. A rectangular wave voltage is applied to the detection electrodes 3 arranged at a distance from each other through the resistor 17 and the resistor 17 and the detected dielectric 26 are passed through.And electrostatic capacitance generated between the ground when high-frequency current flows between the ground (ground-to-ground capacitance)A capacitance type detection device that outputs a detection signal based on closing of an RC circuit, and generates a guard voltage that generates a rectangular wave voltage having the same frequency as the rectangular wave voltage applied to the detection electrode 3 Means 30 (rectangular wave voltage generation circuit 16, variable resistor 20, and phase inversion / waveform shaping circuit 24), second electrode 4 and third electrode 5 are provided, and guard voltage generation means 30 is provided on second electrode 4. The second electrode 4 is connected around the detection electrode 3, and the electric potential of the second electrode 4 causes the RC to pass through a dielectric that exists in layers along the partition wall (container wall 27 a and the like). The circuit is interrupted, and the third electrode 5 is connected to the second electrode 4 and is arranged to cover the back side of the detection electrode 3.
[0006]
  The second object of the present invention is to provide a capacitance that can be detected with high accuracy even when the detected dielectric 26 is a granular material having a very small relative dielectric constant compared to a liquid such as water. In providing a mold detecting device, the means connects the third electrode 5 to the second electrode 4.Instead ofIt has a grounded configuration.
[0007]
  When implementing the above-described apparatus of the present invention, the switching means 32 is used in combination so that the detected dielectric can be selectively used depending on whether it is a liquid or a granular material. When the dielectric 26 is a liquid having a large relative dielectric constant, both the second electrode 4 and the third electrode 5 are connected to the guard voltage generating means 30, and the detected dielectric 26 is a relative dielectric constant. In the case of a small granular material or the like, only the second electrode 4 can be connected to the guard voltage generating means 30 and the third electrode 5 can be grounded.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
  A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. In FIGS. 1 and 2, reference numeral 1 denotes a detector, which is a circuit board 2, a detection electrode 3, a second electrode 4, a third electrode 5, And a plastic case 6 containing them, and the plastic case 6 is provided with a mounting flange 6a. More specifically, a third electrode 5 is formed on the surface of the second substrate 7 attached to the back surface of the circuit board 2 (the side opposite to the side on which the circuit board 2 is present). The detection electrode 3 and the second electrode are formed on the surface of the third substrate 9 (the side opposite to the side where the circuit substrate 2 is provided) supported by the second substrate 7 via the pin connector 8 serving as a spacer so as to be separated from the second substrate 7. An electrode 4 is formed. The detection electrode 3 and the second electrode 4 are arranged so as to be in contact with the inner surface of the front wall constituting the detection action surface of the plastic case 6, but the third substrate 9 constitutes the detection action surface of the plastic case 6. The detection electrode 3 and the second electrode 4 can also be formed directly on the inner surface of the front wall of the plastic case 6 so that the front wall can be shared.
[0009]
  Each of the electrodes 3 to 5 can be configured by a method of printing a conductive film on the substrates 7 and 9 or a method of attaching a thin conductive material such as a copper foil or a copper plate to the surfaces of the substrates 7 and 9. Thus, the second electrode 4 is disposed in an annular shape surrounding the detection electrode 3, and the third electrode 5 is disposed so as to cover the entire area on the back side of the detection electrode 3 and the second electrode 4. In the illustrated example, each of the electrodes 3 to 5 is formed in a rectangular shape (the second electrode 4 has a rectangular ring shape), but may be formed in a circular shape (the second electrode 4 has a circular ring shape).
[0010]
  The circuit configuration configured on the circuit board 2 will be described. As shown in FIG. 1, the detection electrode 3 is one of the two output terminals of the rectangular wave voltage generation circuit 16 that outputs rectangular wave voltages having opposite phases to each other. The output terminal 16 a is connected to the output terminal 16 a through the resistor 17 and is connected to the input terminal 18 a of the phase inversion / waveform shaping circuit 18. The other output terminal 16b of the rectangular wave voltage generation circuit 16 is connected to the input terminal 19a of the phase inversion / waveform shaping circuit 19 via the variable resistor 20, and the output terminal 19b of the phase inversion / waveform shaping circuit 19 is The comparison circuit 21 is connected to the input terminal 21a among the three input terminals 21a to 21c, and applies a reference rectangular wave voltage to the comparison circuit 21.
[0011]
  The comparison circuit 21 is configured by a diode matrix circuit so that the potential of the output terminal 21d is switched from the H level to the L level only while the potentials of the three input terminals 21a to 21c are all at the L level. The input terminal 21 b is connected to the output terminal 18 b of the phase inversion / waveform shaping circuit 18, and the input terminal 21 c is connected to the output terminal 16 a of the rectangular wave voltage generation circuit 16. Is compared with the rectangular wave voltage supplied from the phase inversion / waveform shaping circuit 18 to detect the time delay of the rising and falling of the rectangular wave voltage at the detection electrode 3, and its output terminal 21d. Outputs a time delay detection signal. Reference numeral 22 denotes an on / off signal generating circuit including an input terminal 22a connected to the output terminal 21d of the comparison circuit 21 and an output terminal 22b connected to the input terminal 23a of the output circuit 23 of the next stage. Based on the time delay detection signal from the comparison circuit 21, an on / off signal is supplied to the output circuit 23 at the next stage. The output circuit 23 switches the potential of the external output terminal 23b based on the on / off signal from the on / off signal generation circuit 22, and includes a power supply terminal 23d to which a predetermined DC voltage is applied between the output circuit 23 and the ground terminal 23c. Yes.
[0012]
  An output terminal 24b of a phase inversion / waveform shaping circuit 24 is connected to the second electrode 4 and the third electrode 5, and an input terminal 24a of the phase inversion / waveform shaping circuit 24 is connected to the phase inversion / waveform shaping circuit 19. Are connected to the input terminal 19a, and a rectangular wave voltage influenced by the variable resistor 20 is applied thereto.
[0013]
  The detection electrode 3 and the second electrode 4 on the third substrate 9 are connected to predetermined terminals 18a and 24b on the circuit board 2 via a pin connector 8 that also serves as a spacer for supporting the third substrate 9. Yes.
[0014]
  As shown in FIG. 3A, for example, the detector 1 of the detection apparatus configured as described above includes a surrounding wall made of a non-conductive material of a container (tank) 27 in which a detected dielectric 26 such as water is accommodated. 27a so that the detection electrode 3 is positioned at a level for detecting the presence or absence of the detected dielectric 27, and no gap is generated between the detection electrode 3 and the second electrode 4 and the surrounding wall 27a. It is attached. 4 and 5 show the voltage waveform of the output or input of each circuit in this use state. FIG. 4-Column (1) shows the detected dielectric 26 at the detection level corresponding to the detection electrode 3. If the detected dielectric 26 is present at the detection level corresponding to the detection electrode 3, FIG. 5 shows the detection corresponding to the detection electrode 3 as shown in FIG. 3B. This shows a case where the detected dielectric 26 does not exist at the level, but the dielectric layer 28 is formed on the inner surface of the surrounding wall 27a by water scale, condensation, icing, or the like.
[0015]
  Thus, the rectangular wave voltage shown in FIG. 4 -row A is applied to the detection electrode 3 from the output terminal 16a of the rectangular wave voltage generation circuit 16 via the resistor 17. On the other hand, from the output terminal 16b of the rectangular wave voltage generating circuit 16, the phase is 180 degrees different from the rectangular wave voltage (FIG. 4-row A) applied to the detection electrode 3 as shown in FIG. A rectangular wave voltage having a frequency is output and passes through the variable resistor 20, so that the phase inversion / waveform shaping circuit 19 takes some time to rise and fall as shown in FIG. It is supplied to the input terminal 19a. Therefore, the waveform of the rectangular wave voltage at the output terminal 19b of the phase inversion / waveform shaping circuit 19 (the input terminal 21a of the comparison circuit 21) is inverted in phase by 180 degrees as shown in FIG. Although it has substantially the same phase as the output waveform of the output terminal 16a of the rectangular wave voltage generation circuit 16 shown in FIG. 4 -row A (the waveform of the rectangular wave voltage applied to the detection electrode 3), it is shown in FIG. A rectangular wave whose rising and falling edge are delayed by time t from the rectangular wave voltage is obtained.
[0016]
  Since the rectangular wave voltage that has passed through the variable resistor 20 is also supplied to the phase inversion / waveform shaping circuit 24 that performs the same function as the phase inversion / waveform shaping circuit 19, the rectangular voltage is supplied to the second electrode 4 and the third electrode 5. The applied rectangular wave voltage, that is, the waveform of the rectangular wave voltage at the output terminal 24b of the phase inversion / waveform shaping circuit 24, is the rectangular wave voltage input to the input terminal 21a of the comparison circuit 21 (FIG. 4-row F). It becomes the same waveform as. As is clear from this, the phase inversion / waveform shaping circuit 24 can be omitted by connecting the output terminal 19b of the phase inversion / waveform shaping circuit 19 to the second electrode 4 and the third electrode 5. .
[0017]
  As apparent from the circuit configuration described above, the rectangular wave voltage applied to the detection electrode 3 has a rectangular wave voltage of substantially the same phase and the same frequency on the surrounding second electrode 4 and the back third electrode 5. Applied. That is, it is disposed on the back side of the detection electrode 3 due to the presence of the third electrode 5 that covers the back side of the detection electrode 3 and is applied with a rectangular wave voltage having substantially the same phase and the same frequency as the detection electrode 3. The capacitive effect on the detection electrode 3 from the circuit board 2 and the circuit configured on the circuit board 2 is eliminated, and the capacitance on the back side of the detection electrode 3 does not exist and is detected. The electrode 3 itself is energized by the potential of the third electrode 5 on the back side. The detection electrode 3 is arranged around the front side of the detection electrode 3 due to the presence of the second electrode 4 disposed around the detection electrode 3 and applied with a rectangular wave voltage having substantially the same phase and the same frequency as the detection electrode 3. An electric field region is formed by a rectangular wave voltage having substantially the same phase and frequency.
[0018]
  Therefore, as shown in FIG. 3A, the dielectric constant of water or the like at a depth exceeding the depth (perpendicular to the surrounding wall 27a) affected by the electric field region formed by the second electrode 4 inside the detection electrode 3. When the high-detection dielectric 26 is present, the container surrounding wall 27a is grounded in a high-frequency circuit, so that the detection electrode 3 is affected by the influence of the electric field of the second electrode 4, the circuit on the back side, and the like. Instead, the high-frequency circuit is grounded only via the detected dielectric 26 in the container 27, and a high-frequency current flows between the ground.
[0019]
  In other words, when the surface level of the detected dielectric 26 accommodated in the container 27 is lower than the detection level of the detection electrode 3, it is applied to the detection electrode 3 regardless of whether the second electrode 4 is present. Therefore, the rectangular wave voltage generating circuit 16 is simply connected to the input terminal 21b of the comparison circuit 21 as shown in row E of FIG. Thus, a rectangular wave voltage having a phase opposite to that of the rectangular wave voltage at the output terminal 16a (FIG. 4, column (1), row C) is supplied, and there is no time delay in the rise and fall. Therefore, based on the rectangular wave voltage supplied to the input terminal 21c of the comparison circuit 21 (FIG. 4-column (1) row A), the rectangular wave voltage supplied to the input terminal 21a (FIG. 4-column (1) row). F) and the rectangular wave voltage supplied to the input terminal 21b (FIG. 4-column (1) row E) are compared in the comparison circuit 21. As a result, all of the three input rectangular wave voltages become L level. Therefore, the potential of the output terminal 21d remains at the H level as shown in FIG. 4 -column (1) row I, and the input terminal 23a of the output circuit 23 (the output terminal 22b of the on / off signal generating circuit 22). The potential of the external output terminal 23b remains at the H level as shown in the column (1) row J and row K in FIG.
[0020]
  On the other hand, as described above, the surface level of the detected dielectric 26 accommodated in the container 27 (the surrounding wall 27a is grounded in a high-frequency circuit) is higher than the detection level of the detection electrode 3. When it is high, a high-frequency current flows through the resistor 17, the detection electrode 3, and the detected dielectric 26 by the rectangular wave voltage applied to the detection electrode 3 regardless of whether the second electrode 4 is present or not. 4-column (2) As shown in row C, the rectangular wave voltage at the input terminal 18a of the phase inversion / waveform shaping circuit 18 (rectangular wave voltage at the detection electrode 3) is described earlier at the rise and fall. A delay of time T larger than the delay time t by the variable resistor 20 is generated.
[0021]
  Accordingly, the input terminal 21b of the comparison circuit 21 is supplied with a rectangular wave voltage (FIG. 4-column (2) row E) whose rise and fall are delayed by time T. As can be seen from the rectangular wave voltage waveforms of, row E and row F, 3 of the comparison circuit 21 from the falling edge of the rectangular wave voltage at the input terminal 21a of the comparison circuit 21 to the rising edge of the rectangular wave voltage at the input terminal 21b. All of the input rectangular wave voltages are at the L level, and during this time, the potential of the output terminal 21d is at the L level as shown in row I of FIG. 4 -column (2), and a pulse signal is output. As a result, the potentials of the output terminal 22b of the on / off signal generation circuit 22 (the input terminal 23a of the output circuit 23) and the external output terminal 23b are set to the pulse signal as shown in FIG. Is switched from the H level to the L level at the time of the rise of the signal, and the detected dielectric material is detected at the detection level of the detection electrode 3 through a suitable connected external control means or the like using the change in potential of the external output terminal 23b. 26 can be detected.
[0022]
  Next, as shown in FIG. 3B, the detected dielectric 26 does not exist at the detection level of the detection electrode 3, but the dielectric layer 28 is formed by wetting on the inner surface of the surrounding wall 27 a of the container 27 due to water scale, condensation, icing, or the like. When the dielectric layer 28 is grounded in the form of a high frequency circuit through the container 27, the dielectric layer 28 has a maximum thickness of several millimeters. An electric field region formed around the detection electrode 3 and biased to a potential substantially in phase with the detection electrode 3 is connected to the ground in a high frequency circuit between the detection electrode 3 and the ground via the dielectric layer 28. It works to shut off.
[0023]
  That is, as shown in FIG. 5 -column (1) row C, the detection electrode 3 is connected to the ground in a high frequency circuit through the dielectric layer 28, so that the resistor 17, the detection electrode 3, and the dielectric layer are connected. The rectangular wave voltage (rectangular wave voltage at the input terminal 18a of the phase inversion / waveform shaping circuit 18) applied to the detection electrode 3 with a high-frequency current flows through 28, and a time delay occurs at the rising and falling edges.try toHowever, as a result of energizing the dielectric layer 28 around the detection electrode 3 with a potential of a rectangular wave voltage (FIG. 5, column (1), row G) of substantially the same phase applied to the second electrode 4, the detection electrode 3 is a rectangular wave voltage having substantially the same phase applied to the second electrode 4 and the third electrode 5 (FIG. 5 column). (1) It is forcibly canceled at the rise and fall time of row G), and the rise and fall of the rectangular wave voltage (FIG. 5-column (1) row C) at detection electrode 3 is completed at the same time.
[0024]
  Accordingly, the rectangular wave voltage supplied to the input terminal 21b of the comparison circuit 21 (FIG. 5—column (1), row E) has a slight time delay in its rise and fall. Delay time generated at the rise and fall of the rectangular wave voltage (FIG. 5—column (1) row G) applied to the electrode 4 and the third electrode 5, that is, the rectangle supplied to the input terminal 21 a of the comparison circuit 21. Since this is equal to the delay time t caused by the variable resistor 20 occurring at the rising and falling of the wave voltage (FIG. 5, column (1), row F), the result is that FIG. As shown in row F, all three inputs in the comparison circuit 21 do not become L level, and the external output of the output circuit 23 is the same as when the detected dielectric 26 does not exist at the detection level of the detection electrode 3. The potential of the terminal 23b is not switched. That is, the dielectric layer 28 is detected.This prevents malfunction.
[0025]
  In addition, with respect to the detector 1 provided with the three electrodes 3-5, the circuit comprised on the circuit board 2 can be built in another casing, and both can also be connected with a cord. In addition, when used for containers (tanks) or distribution pipes made of conductive materials such as metal, through holes are provided in the surrounding walls made of conductive materials for the containers and pipes, and the holes are detected. What is necessary is just to fix the container 1 by internal fitting. In this case, the non-conductive partition between the detected dielectric 26 and the detection electrode 3 and the second electrode 4 becomes the plastic case 6 of the detector 1.
[0026]
  In addition, the delay time T generated at the rising and falling of the rectangular wave voltage applied to the detection electrode 3 due to the presence of the detected dielectric 26 depends on the property of the detected dielectric 26 and the detection electrode 3 and the detected dielectric 26. The variable resistor 20 is connected to the input terminal 21a of the comparison circuit 21 with respect to the delay time T, and the second resistance is changed depending on the material of the non-conductive partition wall (the container enclosure 27a and the plastic case 6 of the detector 1). The resistance value is adjusted so that the delay time t of the rise and fall of the rectangular wave voltage applied to the electrode 4 and the third electrode 5 becomes small. However, since the delay time t only needs to be smaller than the expected minimum value of the delay time T, a fixed resistor can be used in place of the variable resistor 20.
[0027]
  In the case where the detected dielectric 26 is a granular material whose relative dielectric constant is significantly smaller than that of a liquid such as water (generally, the relative dielectric constant of the granular material is 1/5 to 1 compared to that of the liquid) / 20) is applied to the third electrode 5 in the same manner as the second electrode 4, when a rectangular wave voltage having substantially the same phase and frequency as the rectangular wave voltage applied to the detection electrode 3 is applied. Under the influence of the electric field, the capacitance on the detected dielectric (powder) 26 side viewed from the detection electrode 3 is further reduced, and it is difficult to reliably detect a change associated with the presence or absence.
[0028]
  Therefore, when the detected dielectric 26 is a granular material having a low relative dielectric constant, as shown in FIG. 6, only the second electrode 4 is connected to the rectangular wave voltage generating circuit 16, the variable resistor 20, and The third electrode 5 is connected to the ground terminal 31 and grounded, connected to the guard voltage generating means 30 comprising the phase inversion / waveform shaping circuit 24.
[0029]
  According to the detection apparatus shown in FIG. 6, even when the detected dielectric 26 is a granular material having a low relative dielectric constant, the level of the detection electrode 3 includes the detected dielectric 26 and does not exist. Thus, when the electrostatic capacitance change on the front side of the detection electrode 3 is reliably captured and the detected dielectric 26 is present at the level of the detection electrode 3, it is applied from the rectangular wave voltage generation circuit 16 to the detection electrode 3. The RC wave passing through the resistor 17, the detection electrode 3, and the detected dielectric 26 is closed by the rectangular wave voltage, and as described with reference to FIG. 1 and FIG. A detection signal indicating that the detected dielectric 26 exists at the detection level can be output. As described above, the second electrode 4 has a function of eliminating the influence of the dielectric layer formed by dirt, particles, or the like on the container surrounding wall 27a itself or the inner surface thereof. Even if the detected dielectric 26 such as a granular material does not exist in the level, it is possible to surely prevent the malfunction that the detection signal is output.
[0030]
  Further, the detection device shown in FIG. 6 can be used as a touch sensor that detects a touch operation with a fingertip of a human body having a relative dielectric constant smaller than that of a liquid. That is, the detector 1 is attached to the back surface of a plate made of a non-conductive material constituting a touch surface for contacting the fingertip, or the front surface of the plastic case 6 is used as a touch surface for contacting the fingertip, When contacting the touch surface, the detection electrode 3 is grounded via a human body in a high-frequency circuit and the RC circuit is closed. It can be detected by the same action. In this case, the second electrode 4 can prevent an adverse effect (malfunction) due to adhesion of a water film due to dirt on the touch surface or rainwater.
[0031]
  FIG. 7 shows a first state in which both the second electrode 4 and the third electrode 5 are connected to the guard voltage generating means 30 using the switching means 32, and only the second electrode 4 is connected to the guard voltage generating means 30. In the embodiment, the third electrode 5 can be switched to the second state in which the third electrode 5 is connected to the ground terminal 31.
[0032]
  According to the detection apparatus shown in FIG. 7, when the detected dielectric 26 is a liquid having a high relative dielectric constant, the switching means 32 causes both the second electrode 4 and the third electrode 5 to be connected to the guard voltage. By using the first state connected to the generating means 30, it can be effectively used as the detection device as described with reference to FIGS.The on the other hand,When the detected dielectric 26 is a granular material having a small relative dielectric constant, the switching means 32 connects only the second electrode 4 to the guard voltage generating means 30 and connects the third electrode 5 to the ground terminal 31. By setting to the second state connected to, it can be effectively used as a detection device as described with reference to FIG.
[0033]
  Switching means 32In the case of using together, in the figure, a mechanical changeover switch is used as the switching means, and the configuration in which the connection path between the electrode and the circuit is mechanically changed is shown. A method of changing the applied voltage by incorporating a logic IC, a method of switching a circuit with an analog switch, a method of changing a circuit-mounted component, or the like can also be adopted.
[0034]
【The invention's effect】
  The present invention can be implemented and used as described above. In the capacitance type detection device according to the first aspect of the present invention, the detected dielectric does not exist at the detection position, but the inner side of the detection electrode. When there is a dielectric layer due to wetting or dirt along the inner surface of the non-conductive partition wall, the potential of the second electrode to which a rectangular wave voltage having the same frequency as the rectangular wave voltage applied to the detection electrode is applied Since the RC circuit passing through the dielectric layer due to wetting or the like can be cut off, the dielectric layer due to wetting or dirt formed on the inner surface of the non-conductive partition wall is not detected by the detection electrode.
[0035]
  In addition, a third electrode is disposed so as to cover the back side of the detection electrode, and a rectangular wave voltage having the same frequency as the rectangular wave voltage applied to the detection electrode is applied to the third electrode in the same manner as the second electrode. Is applied so that there is no capacitance on the back side of the detection electrode, the influence of the fixed capacitance on the circuit on the back side of the detection electrode is eliminated, and the potential of the third electrode is the detection electrode itself. As in the case of the guard effect on the front side of the detection electrode, that is, the above-mentioned action by the second electrode around the detection electrode, the dielectric layer such as the container wall on the front side of the detection electrode and the dirt on the inner surface thereof As a result, the same effect as that of increasing the guard effect by increasing the area of the second electrode around the detection electrode can be obtained. In other words, the size of the detector determined by the area of the second electrode around the detection electrode can be reduced by making the second electrode smaller.
[0036]
  That is, according to the configuration of the present invention as set forth in claim 1, not only malfunction due to wetting, dirt, condensation, icing, etc. on the inner surface of the container or the distribution pipe, but also malfunction due to the circuit on the back side of the detection electrode is prevented. Therefore, it is possible to accurately detect whether or not the detected dielectric exists at the detection position corresponding to the detection electrode from the outside of the container or the distribution pipe. Therefore, it is possible to obtain a capacitive detection device that is not affected by maintenance work such as periodic cleaning and that is highly reliable and that can be easily downsized.
[0037]
  When the dielectric to be detected is a powder or the like having a small relative dielectric constant, which is considered not to be grounded in a high frequency circuit, the dielectric to be detected is caused by the guard action of the second electrode around the detection electrode. The amount of change in capacitance between the detection electrode and the detection electrode is reduced, and the detection sensitivity decreases accordingly. In this case, when the third electrode disposed on the back of the detection electrode is connected to the second electrode as described above, the decrease in detection sensitivity becomes more remarkable. Of course, the granular material layer adhering to the inner surface of the container must not be detected.
[0038]
  Thus, as described in claim 2, by using the third electrode as a ground electrode, the capacitance on the back side of each electrode on the front side is fixed, and as a result, the front side of the detection electrode (to be detected) Capacitance type detection device that can improve the sensitivity on the dielectric side, is particularly effective for non-contact detection of particles with a low relative dielectric constant, and can also be used as a touch sensor. Can do. In this case, as shown in the embodiment, by interposing a spacer such as a pin connector between the detection electrode and the third electrode at the back thereof to secure an appropriate gap, the capacitance on the back side of the detection electrode is increased. It can be kept even lower and is effective.
[0039]
  And according to the structure of this invention of Claim 3, only by switching a switching means, when a to-be-detected object has a liquid with a large relative dielectric constant, and a case where it is a granular material with a small relative dielectric constant Either can be detected with high accuracy.The
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an entire apparatus showing a first embodiment.
FIG. 2A is a schematic longitudinal sectional side view for explaining the configuration of a detector, and FIG.
FIG. 3A is a longitudinal side view of a main part for explaining a state in which there is a dielectric to be detected above the detection level. FIG. 3B is a state in which there is no dielectric to be detected at the detection level and there is a dielectric layer such as dirt. FIG.
FIG. 4 is a diagram for explaining voltage waveforms at respective terminals in a state where a detected dielectric is present and in a state where a detected dielectric is present;
FIG. 5 is a diagram for explaining voltage waveforms at each terminal in a state where there is no detected dielectric at the detection level and there is a dielectric layer such as dirt.
FIG. 6 is a schematic diagram illustrating a configuration of a second embodiment.
FIG. 7 is a schematic diagram illustrating the configuration of a third embodiment.
[Explanation of symbols]
1 Detector
2 Circuit board
3 detection electrodes
4 Second electrode
5 Third electrode
6 Plastic case
7 Second board
8 Pin connector also used as a spacer
9 Third board
16 Rectangular wave voltage generation circuit (guard voltage generation means)
17 resistors
18 Phase inversion / waveform shaping circuit
19 Phase inversion / waveform shaping circuit
20 Variable resistor (guard voltage generating means)
21 Comparison circuit
22 ON / OFF signal generator
23 Output circuit
24 Phase inversion / waveform shaping circuit (guard voltage generating means)
26 Dielectric to be detected
27 containers
27a Enclosure made of non-conductive material
28 Dielectric layers such as dirt
30 Guard voltage generating means
31 Ground terminal
32    Switching means

Claims

A rectangular wave voltage is applied via a resistor to a detection electrode disposed with a non-conductive partition wall between the dielectric to be detected and a high-frequency current between the ground and the resistance via the resistor and the dielectric to be detected. A capacitance type detection device configured to output a detection signal based on a time delay of rise and fall at the detection electrode by an RC circuit formed by a capacitance generated between the ground and the ground A guard voltage generating means for generating a rectangular wave voltage having the same frequency as the rectangular wave voltage applied to the detection electrode, a second electrode, and a third electrode are provided, and the guard voltage generating means is connected to the second electrode, The second electrode is arranged around the detection electrode, and the electric potential of the second electrode interrupts the RC circuit that passes through the dielectric layered along the partition wall, and the third electrode Connected to two electrodes It is arranged so as to cover the back side of the detection electrode, the capacitive sensing device.

The capacitance type detection device according to claim 1, wherein the third electrode is grounded instead of being connected to the second electrode .

A capacitance type switch comprising switching means for switching between the state in which the third electrode according to claim 1 is connected to the second electrode and the state in which the third electrode according to claim 2 is grounded. Detection device.