JP3633097B2 - Magnetic detector - Google Patents

Description

【００２６】
一方、外部磁界Ｈｅｘが加わると、磁気センサ１に流れる電流は、外部磁界Ｈｅｘ分だけシフトして、例えば、Ｉａ＋ＩｅｘからＩｂ＋Ｉｅｘまで変化するようになる。このとき、交流バイアス電流ｉ１は、Ｉｅｘの分だけシフトすると共に、その応答波形に変化が生じる。そして、交流バイアス電流ｉ１の応答波形が変化し、例えば、交流バイアス電流ｉ１の立ち上がり時間ｔ１が、下記式（１−２）で表されるシフト時間Δｔ１だけ変化することとなる。
【００２７】
【数２】

【００２８】
このように、交流バイアス電流ｉ１の立ち上がり時間ｔ１は、外部磁界Ｈｅｘの変化に応じて変化する。したがって、この磁気センサ１では、交流バイアス電流ｉ１の立ち上がり時間ｔ１のシフト量を検出することにより、外部磁界Ｈｅｘの変化を検出することができる。
【００２９】
なお、この磁気センサ１では、交流バイアス電流ｉ１が、外部磁界Ｈｅｘ分だけ電流値がシフトしてもインダクタンスＬが急峻な変化を示す範囲を包括するように設定する。これにより、上記式（１−２）から明らかなように、外部磁界Ｈｅｘの変化に応じて、シフト時間Δｔ１は、ほぼ直線的に変化することとなる。
【００３０】
したがって、この磁気センサ１は、外部磁界検出時のリニアリティが優れたものとなり、磁界検出用のセンサとして非常に好適に動作する。また、この磁気センサ１では、外部磁界Ｈｅｘの検出に、インダクタンスＬの急峻な変化、すなわちＬｍａｘからＬｍｉｎに至る大きな変化を、常に利用することとなるので、非常に高い感度が得られる。
【００３１】
つぎに、交流バイアス電流ｉ１を反転させた交流バイアス電流ｉ２を磁気センサ１に供給したときの動作について説明する。
【００３２】
ここでは、図２に示すように、磁気センサ１に流れる電流を反転させて、外部磁界Ｈｅｘ＝０のときに磁気センサ１に流れる電流が−Ｉａから−Ｉｂまで変化するように、磁気センサ１に交流バイアス電流ｉ２を供給する。このときも、磁気センサ１のインダクタンスＬは、ＬｍａｘからＬｍｉｎへ変化する。そして、磁気センサ１に印加される電圧の変化が一定であるならば、交流バイアス電流ｉ２の立ち上がり時間ｔ２は、ファラデーの法則によって下記式（１−３）のように表され、上述の立ち上がり時間ｔ１と同じとなる。
【００３３】
【数３】

【００３４】
一方、このように交流バイアス電流ｉ２を供給しているときに、外部磁界Ｈｅｘが加わると、磁気センサ１に流れる電流は、外部磁界Ｈｅｘ分だけシフトして、例えば、−Ｉａ＋Ｉｅｘから−Ｉｂ＋Ｉｅｘまで変化するようになる。このとき、交流バイアス電流ｉ２は、Ｉｅｘの分だけシフトすると共に、その応答波形に変化が生じる。そして、交流バイアス電流ｉ２の応答波形が変化して、例えば、交流バイアス電流ｉ２の立ち上がり時間ｔ２が、下記式（１−４）で表されるシフト時間Δｔ２だけ変化することとなる。
【００３５】
【数４】

【００３６】
このように、交流バイアス電流ｉ１を反転させた交流バイアス電流ｉ２を流したときも、交流バイアス電流ｉ２の立ち上がり時間ｔ２は、外部磁界Ｈｅｘの変化に応じて変化する。そして、このシフト時間Δｔ２は、上述のシフト時間Δｔ１と符号が逆で同じ大きさとなっている。すなわち、シフト時間Δｔ１とシフト時間Δｔ２とは、差動の関係にある。
【００３７】
そこで、順方向に電流を流したときの立ち上がり時間ｔ１＋Δｔ１と、逆方向に電流を流したときの立ち上がり時間ｔ２＋Δｔ２とを測定し、これらの差動を取ることにより、外部磁界Ｈｅｘの変化に応じた信号を、一定の方向にだけ電流を流したときに比べて、約２倍の出力として取り出すことができる。
【００３８】
また、順方向に電流を流したときの立ち上がり時間ｔ１＋Δｔ１と、逆方向に電流を流したときの立ち上がり時間ｔ２＋Δｔ２との差動を取ると、外部磁界Ｈｅｘ＝０のときには、交流バイアス電流の立ち上がり時間が互いにキャンセルされる。したがって、外部磁界Ｈｅｘがない状態である０点を容易に認識することができる。
【００３９】
さらに、磁気センサ１は温度等によってインダクタンスＬの大きさが変化して交流バイアス電流の立ち上がり時間に変化が生じるが、交流バイアス電流の方向を短時間で反転させることにより、このような温度ドリフトや時間ドリフト等の影響を互いにキャンセルすることができる。したがって、この磁気センサでは、温度ドリフトや時間ドリフト等の影響を受けることなく、高精度に外部磁界Ｈｅｘを検出することができる。
【００４０】
つぎに、以上のような磁気センサを用いた磁気探知装置の一構成例について、具体的に説明する。
【００４１】
この磁気探知装置は、図３に示すように、上述のような磁気センサ１０と、磁気センサ１０に流れる電流の方向を反転させるためのバイラテラル・スイッチ１１と、バイラテラル・スイッチ１１に接続された抵抗１２と、磁気センサ１０の両端から導出された配線に接続されたシュミットトリガ回路１３とを備えており、これらにより、無安定マルチバイブレータ回路として動作する発振回路が構成されている。
【００４２】
ここで、磁気センサ１０は、上述したように、リボン状やワイヤー状に形成された細長いアモルファス等からなる磁性体と、この磁性体の長手方向に巻回された銅線等からなるコイルとから構成される。そして、この磁気センサ１０は、スイッチＳＷ１、スイッチＳＷ２、スイッチＳＷ３及びスイッチＳＷ４を備えたバイラテラル・スイッチ１１内に配されており、磁気センサ１０に流れる電流の方向は、このバイラテラル・スイッチ１１によって反転させることができるようになっている。このバイラテラル・スイッチ１１に接続された抵抗１２の一端は、バイラテラル・スイッチ１１を介して磁気センサ１０に対して直列に接続されており、この抵抗１２の他端は、接地されている。
【００４３】
また、シュミットトリガ回路１３は、入力電圧に応じて出力電圧を繰り返し反転させて、方形波発振電圧Ｖ０を出力する。すなわち、シュミットトリガ回路１３は、入力電圧が立ち上がってシュミット電圧ＶｓＨに達したら、出力電圧を反転させて出力し、同様に、入力電圧が立ち下がってシュミット電圧ＶｓＬに達したら出力電圧を反転させて出力し、これらの結果として、方形波発振電圧Ｖ０を出力する。
【００４４】
このように、シュミットトリガ回路１３から方形波発振電圧Ｖ０を出力することにより、上記磁気探知装置は、無安定マルチバイブレータ回路として動作する。ここで無安定マルチバイブレータ回路の時定数は、磁気センサ１０のインダクタンスＬと、抵抗１２の抵抗値Ｒとにより定まる。すなわち、上記磁気探知装置において、磁気センサ１０及び抵抗１２は、無安定マルチバイブレータ回路の時定数決定素子となっている。
【００４５】
そして、無安定マルチバイブレータ回路の発振周期は時定数によって決まるので、この無安定マルチバイブレータ回路の発振周期は、磁気センサ１０のインダクタンスＬと、磁気センサ１０に直列接続された抵抗１２の抵抗値Ｒとにより決定する。
【００４６】
ここで、磁気センサ１０のインダクタンスＬは、外部磁界Ｈｅｘの変化に応じて変化する。したがって、この無安定マルチバイブレータ回路の発振周期は、外部磁界Ｈｅｘの変化に応じて変化する。そこで、この磁気探知装置では、この無安定マルチバイブレータ回路の発振周期、すなわちシュミットトリガ回路１３からの方形波発振電圧Ｖ０の発振周期を測定することにより、外部磁界の強さを検出する。
【００４７】
上記磁気探知装置の動作について、バイラテラル・スイッチ１３によって磁気センサ１０に対して一定の方向に電流が流れるようにしたときの電圧波形のタイムチャートである図４を参照しながら説明する。ここで、図４（ａ）は、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０のタイムチャートを示しており、図４（ｂ）は、磁気センサ１０に生じる電圧、すなわちシュミットトリガ回路１３へ入力する電圧Ｖｒのタイムチャートを示している。
【００４８】
図４（ａ）に示すように、先ず、シュミットトリガ回路１３から、所定の直流バイアス成分を含む電圧Ｖ１が磁気センサ１０に供給され、これにより、磁気センサ１０と抵抗１２とからなる積分回路に流れる電流が立ち上がる。ここで、磁気センサ１０に供給される電圧は直流バイアス成分を含んでいるので、磁気センサ１０に流れる電流は、直流バイアス電流成分を含んでいる。このとき、図４（ｂ）に示すように、磁気センサ１０に生じる電圧、すなわちシュミットトリガ回路１３へ入力する電圧Ｖｒ１の波形は、シュミットトリガ回路１３から出力された電圧Ｖ１に対して、立ち上がり時に遅延が生じた波形となる。この電圧Ｖｒ１の波形は、磁気センサ１０に流れる電流の応答波形に対応するものであり、したがって、この電圧Ｖｒ１の立ち上がり時の遅延は、磁気センサ１０に加わる外部磁界Ｈｅｘの大きさに応じて変化する。そして、シュミットトリガ回路１３は、入力が立ち上がって所定のシュミット電圧ＶｓＨに達したら、図４（ａ）に示すように、出力を反転する。
【００４９】
これにより、シュミットトリガ回路１３から、元の電圧Ｖ１を反転させた電圧Ｖ２が磁気センサ１０に供給され、これにより、磁気センサ１０と抵抗１２とからなる積分回路に流れる電流が立ち下がる。このとき、図４（ｂ）に示すように、磁気センサ１０に生じる電圧、すなわちシュミットトリガ回路１３へ入力する電圧Ｖｒ２の波形は、シュミットトリガ回路１３から出力された電圧Ｖ２に対して、立ち下がり時に遅延が生じた波形となる。この電圧Ｖｒ２の波形は、磁気センサ１０に流れる電流の応答波形に対応するものであり、したがって、この電圧Ｖｒ２の立ち下がり時の遅延は、磁気センサ１０に加わる外部磁界Ｈｅｘの大きさに応じて変化する。そして、シュミットトリガ回路１３は、入力が立ち下がって所定のシュミット電圧ＶｓＬに達したら、出力を反転する。
【００５０】
以上のような動作の繰り返しにより、シュミットトリガ回路１３は、図４（ａ）に示すような方形波発振電圧Ｖ０を出力する。ここで、シュミット電圧ＶｓＬ，ＶｓＨは、磁気センサ１０に流れる電流の立ち上がり時及び立ち下がり時における磁気センサ１０のインダクタンスＬのＬｍａｘからＬｍｉｎへの変化を包括するように設定しておく。すなわち、シュミット電圧ＶｓＬ，ＶｓＨは、磁気センサ１０に流れる発振電流の振幅が、磁気センサ１０のインダクタンスＬが急峻な変化を示す範囲を包括するように設定しておく。
【００５１】
そして、上述したように、シュミットトリガ回路１３に入力する電圧Ｖｒの波形は、磁気センサ１０に流れる電流の応答波形に対応している。したがって、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期は、磁気センサ１０に流れる電流の立ち上がり時間及び立ち下がり時間に対応している。そして、上述したように磁気センサ１０に流れる電流の立ち上がり時間及び立ち下がり時間は外部磁界Ｈｅｘの大きさに依存しているので、このシュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期に基づいて、磁気センサ１０に加わっている外部磁界Ｈｅｘの大きさを検出することができる。
【００５２】
すなわち、この磁気探知装置では、磁気センサ１０に加わった外部磁界Ｈｅｘの変化が、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期の変化として現れる。そこで、この発振周期の変化を検出することにより、外部磁界Ｈｅｘの強さを検出することが可能となる。
【００５３】
ところで、本実施の形態に係る磁気探知装置では、バイラテラル・スイッチ１１によって磁気センサ１０に流れる電流の方向を反転させることができる。すなわち、図３において、スイッチＳＷ１及びスイッチＳＷ４がオンで、スイッチＳＷ２及びスイッチＳＷ３がオフのとき、図３の矢印Ａの向きに電流が流れ、また、スイッチＳＷ１及びスイッチＳＷ４がオフで、スイッチＳＷ２及びスイッチＳＷ３がＯＮのとき、図３の矢印Ｂの向きに電流が流れる。そして、バイラテラル・スイッチ１１によって磁気センサ１０に流れる電流の方向を反転させて外部磁界Ｈｅｘを検出することにより、上述したように、一定の方向にだけ電流を流したときに比べて約２倍の出力が得られ、また、外部磁界Ｈｅｘがない状態である０点を容易に認識することができ、さらには、温度ドリフトや時間ドリフト等の影響を取り除くことができる。
【００５４】
つぎに、磁気センサ１０に加わった外部磁界Ｈｅｘの変化が、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期の変化として現れる原理について、さらに詳細に説明する。
【００５５】
図５に、磁気センサ２０と抵抗２１が直列に接続された積分回路に電流が立ち上がるときの状態をモデル化した回路を示す。このような回路において、スイッチ２２をオフからオンにすると、磁気センサ２０と抵抗２１からなる積分回路に直流電源２３から直流電圧が印加され、磁気センサ２０に電流ｉが流れ出す。ここで、磁気センサ２０に流れる電流ｉは、積分回路に印加される直流電圧の値をＥ、磁気センサ２０のインダクタンスをＬ、抵抗２１の抵抗値をＲ、電流ｉの立ち上がり時間をｔとすると、下記式（１−５）で表される。
【００５６】
【数５】

【００５７】
上記式（１−５）から分かるように、電流ｉの立ち上がり時間ｔは、積分回路の時定数Ｌ／Ｒに比例している。したがって、このような積分回路では、磁気センサ２０のインダクタンスＬや、抵抗２１の抵抗値Ｒの大きさを変えることにより、電流ｉの立ち上がり時間ｔが変化する。
【００５８】
ところで、上述したように、磁気センサのインダクタンスＬは、電流ｉが立ち上がっている間に、ＬｍａｘからＬｍｉｎへ変化する。ここで、上述のシュミット電圧ＶｓＬ，ＶｓＨは、インダクタンスＬのＬｍａｘからＬｍｉｎへの変化を包括するように設定しておく。
【００５９】
そして、磁気センサ２０のインダクタンスＬがＬｍａｘからＬｍｉｎへと変化するため、積分回路に流れる電流ｉは、図６に示すように、初めはインダクタンスＬがＬｍａｘの状態で立ち上がり、やがて、インダクタンスＬがＬｍｉｎの状態で立ち上がることとなる。したがって、積分回路に流れる電流ｉがシュミット電圧ＶｓＨに対応するレベルに達するまで時間Ｔｓは、インダクタンスＬがＬｍａｘの状態での立ち上がり時間Ｔ１と、インダクタンスＬがＬｍｉｎの状態での立ち上がり時間Ｔ２との合計になる。
【００６０】
そして、磁気センサ２０に加わる外部磁界Ｈｅｘが変化すると、この変化分だけ、インダクタンスＬがＬｍａｘからＬｍｉｎに変化する変化点Ｐがシフトするので、外部磁界Ｈｅｘに応じて、積分電流ｉがシュミット電圧ＶｓＨに対応するレベルに達するまでの時間Ｔｓが変化することとなる。
【００６１】
したがって、上述の図４に示したように、外部磁界Ｈｅｘの変化が、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期の変化として現れることとなる。
【００６２】
また、図７に、磁気センサ３０と抵抗３１が直列に接続された積分回路に流れていた電流ｉが立ち下がるときの状態をモデル化した回路を示す。このような回路において、スイッチ３２をオフからオンにすると、直流電源３３からの直流電圧が積分回路に加わらなくなり、磁気センサ３０に流れていた電流に立ち下がりが生じる。ここで、磁気センサ３０に流れる電流ｉは、積分回路に印加されていた直流電圧の値をＥ、磁気センサ３０のインダクタンスをＬ、抵抗３１の抵抗値をＲ、電流の立ち下がり時間をｔとすると、下記式（１−６）で表される。
【００６３】
【数６】

【００６４】
そして、このときも、上述の電流の立ち上がり時と同様に、磁気センサ３０に加わる外部磁界Ｈｅｘが変化すると、この変化分だけ、インダクタンスＬがＬｍａｘからＬｍｉｎに変化する変化点がシフトするので、外部磁界Ｈｅｘに応じて、積分電流ｉがシュミット電圧ＶｓＬに対応するレベルに達するまで時間が変化することとなる。
【００６５】
したがって、電流の立ち下がり時においても、上述の図４に示したように、外部磁界Ｈｅｘの変化が、シュミットトリガ回路１５から出力される方形波発振電圧Ｖ０の発振周期の変化として現れることとなる。
【００６６】
ところで、図３に示したような磁気探知装置において、シュミットトリガ回路１３から出力される方形波発振電圧Ｖ０の発振周期の変化量は、外部磁界Ｈｅｘと、磁気センサ１０の磁性体の長手方向に生じる磁界とが成す角度θに依存している。すなわち、外部磁界Ｈｅｘが一定のとき、図８に示すように、発振周期は、外部磁界Ｈｅｘと、磁気センサ１０の磁性体の長手方向に生じる磁界とが成す角度θに依存して変化する。なお、図８では、外部磁界Ｈｅｘの向きと、磁気センサ１０の磁性体の長手方向に生じる磁界の向きとが同じときを方位０°としている。
【００６７】
図８から分かるように、発振周期は外部磁界Ｈｅｘの方位情報を含んでいる。これは、磁気センサ１０の磁性体の磁化量が、磁気センサ１０に流れる電流による磁化量と、外部磁界Ｈｅｘによる磁化量との合計であり、外部磁界Ｈｅｘによる磁化量が、外部磁界Ｈｅｘと、磁気センサ１０の磁性体の長手方向に生じる磁界とが成す角度θに依存して変化するからである。
【００６８】
すなわち、図９に示すように、磁気センサ１０のコイル１０ｂに流れる電流による磁界Ｈｂは一定であるが、外部磁界Ｈｅｘによって磁気センサ１０の磁性体１０ａに生じる磁界は、外部磁界Ｈｅｘの方向に依存している。したがって、磁気センサ１０で検出される磁界Ｈは、下記式（１−７）で示すように、外部磁界Ｈｅｘのうち、磁性体１０ａの長手方向成分のみとなる。
【００６９】
Ｈ＝Ｈｅｘ・ｃｏｓθ ・・・（１−７）
なお、上記式（１−７）に示すように、磁気センサ１０で検出される磁界Ｈは、外部磁界Ｈｅｘの方位情報を含んでいるので、複数の磁気センサを用いることにより、外部磁界Ｈｅｘの方向を知ることができる。
【００７０】
具体的には、例えば、図１０に示すように、磁気探知装置に２つの磁気センサ１０ｘ，１０ｙを組み込む。なお、この磁気探知装置は、磁気センサを２つ組み込んだ以外は、図３に示した磁気探知装置と同様の回路構成である。ここで、図１１に示すように、磁気センサ１０ｘは、Ｘ軸方向に配置し、磁気センサ１０ｙは、Ｘ軸方向に対して直交するＹ軸方向に配置する。すなわち、磁気センサ１０ｘ及び磁気センサ１０ｙは、互いに直交するように配置する。このとき、図１１に示すように、外部磁界Ｈｅｘの方向と、Ｘ軸方向検出用の磁気センサ１１ｘの磁性体の長手方向とが成す角度をθとすると、Ｘ軸方向検出用の磁気センサ１０ｘによって検出される磁界の大きさＨｘは、下記式（１−８）で表され、Ｙ軸方向検出用の磁気センサ１０ｙによって検出される磁界の大きさＨｙは、下記式（１−９）で表される。
【００７１】
Ｈｘ＝Ｈｅｘ・ｃｏｓθ ・・・（１−８）
Ｈｙ＝Ｈｅｘ・ｓｉｎθ ・・・（１−９）
ここで、Ｘ軸方向検出用の磁気センサ１０ｘによって検出される磁界の大きさＨｘと、Ｙ軸方向検出用の磁気センサ１０ｙによって検出される磁界の大きさＨｙとの比をとると、下記式（１−１０）となる。
【００７２】
Ｈｙ／Ｈｘ＝ｓｉｎθ／ｃｏｓθ＝ｔａｎθ ・・・（１−１０）
したがって、外部磁界Ｈｅｘの方向と、Ｘ軸方向検出用の磁気センサ１０ｘの磁性体の長手方向とが成す角度θは、下記式（１−１１）で表される。ただし、下記式（１−１１）において、Ｈｙ≧０のときは、１８０°≧θ≧０°であり、０＞Ｈｙのときは、３６０°＞θ＞１８０°である。
【００７３】
θ＝ｔａｎ^−１（Ｈｙ／Ｈｘ） ・・・（１−１０）
このように磁気探知装置に、２つの磁気センサ１０ｘ，１０ｙを設けることにより、外部磁界Ｈｅｘの方向を知ることができる。なお、立体空間内での外部磁界Ｈｅｘの方向、すなわち外部磁界Ｈｅｘの３次元での方向まで知りたいときには、互いに直交する３つの磁気センサを用いればよい。
【００７４】
図１０に示した磁気探知装置においても、磁気センサに流れる電流は、シュミットトリガ回路へ入力する電圧と、単一の抵抗とだけによって定まる。したがって、この磁気探知装置においても、磁気センサに流れる電流の向きを反転させても、また、電流を流す磁気センサを切り換えても、磁気センサに接続された抵抗の抵抗値のバラツキ等に起因して検出精度が低下してしまうようなことはない。したがって、この磁気探知装置でも、外部磁界Ｈｅｘの大きさと方向とを、高精度に検出することができる。
【００７５】
【発明の効果】
以上の説明から明らかなように、本発明に係る磁気探知装置では、電流の向きに関わらず、磁気センサには同じ電流が供給されるので、電流の向きによって測定値にバラツキが生じるようなことがなく、外部磁界を高精度に検出することができる。
【００７６】
また、本発明に係る磁気探知装置では、複数のＡＮＤゲートや複数の抵抗等を備える必要が無く、構成を簡単なものとすることができるので、小型化や低価格化を容易に図ることができる。
【図面の簡単な説明】
【図１】本発明を適用した磁気探知装置に用いられる磁気センサの一例を示す模式図である。
【図２】図１に示した磁気センサによる外部磁界検出の原理を説明するための図である。
【図３】本発明を適用した磁気探知装置の一構成例を示す回路図である。
【図４】シュミットトリガ回路から出力される電圧のタイムチャートと、シュミットトリガ回路へ入力する電圧のタイムチャートとを示す図である。
【図５】磁気センサと抵抗からなる積分回路に電流が立ち上がるときの状態をモデル化した回路図である。
【図６】図５に示した積分回路に流れる電流の立ち上がり時の様子を示す図である。
【図７】磁気センサと抵抗からなる積分回路に流れていた電流が立ち下がるときの状態をモデル化した回路図である。
【図８】シュミットトリガ回路から出力される方形波発振電圧の発振周期と、外部磁界Ｈｅｘの方向との関係を示す特性図である。
【図９】磁気センサの磁性体の磁化の様子を示す模式図である。
【図１０】本発明を適用した磁気探知装置の他の構成例を示す回路図である。
【図１１】図１０に示した磁気探知装置の磁気センサの配置の様子を示す模式図である。
【図１２】従来の磁気探知装置の一構成例を示す回路図である。
【図１３】図１２に示した磁気探知装置の一動作例を示す回路図である。
【符号の説明】
１ 磁気センサ、 ２ 磁性体、 ３ コイル、 １０ 磁気センサ、 １１バイラテラル・スイッチ、 １２ 抵抗、 １３ シュミットトリガ回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic detection device including a magnetic sensor in which a coil is wound around a magnetic material, and more particularly to a novel magnetic detection device that achieves high accuracy with a simple structure.
[0002]
[Prior art]
Magnetic detectors that detect external magnetic fields have started to be used for measuring magnetic field detectors and measuring instruments, and in recent years, are widely used in consumer applications such as magnetic switches, magnetic rotary encoders, and geomagnetic sensors.
[0003]
Conventionally, such magnetic detectors include a magnetic detector using a Hall element, a magnetic detector using a fluxgate sensor, and a magnetic detector using a magnetoresistive effect element. Therefore, as a more sensitive magnetic detection apparatus, a magnetic detection apparatus using a magnetro inductance element (hereinafter referred to as MI element) has been put into practical use.
[0004]
The MI element is an element that functions as a magnetic sensor that detects the strength of an external magnetic field, and includes an elongated magnetic body and a coil wound in the longitudinal direction of the magnetic body. Here, as the magnetic material, a magnetic material having an excellent square characteristic exhibiting a steep change in permeability in a weak magnetic field of about several gauss is used. In this MI element, the magnetic permeability of the magnetic material changes according to the change of the external magnetic field, and as a result, the inductance of the coil changes greatly. Therefore, the MI element can detect an external magnetic field by detecting a change in inductance.
[0005]
An example of a magnetic detection apparatus using such a magnetic sensor composed of an MI element is shown in FIG. As shown in FIG. 12, this magnetic detector includes a magnetic sensor 100 composed of the above-described MI element, a Schmitt trigger circuit 101 that outputs an oscillation voltage, and a resistor connected to one terminal C1 of the magnetic sensor 100. 102, a resistor 103 connected to the other terminal C2 of the magnetic sensor 100, and a pair of switches 104 and 105 that alternately connect one of the terminals C1 and C2 of the magnetic sensor 100 to the input of the Schmitt trigger circuit 101, And a pair of AND gates 106 and 107 connected to the DC potential.
[0006]
In the magnetic detection device, the inductance of the magnetic sensor 100 changes in accordance with the change in the external magnetic field, whereby the oscillation period of the oscillation voltage from the Schmitt trigger circuit 101 changes. Therefore, in this magnetic detector, the strength of the external magnetic field is detected by measuring the oscillation period of the oscillation voltage from the Schmitt trigger circuit 101.
[0007]
By the way, when the external magnetic field is actually detected by the magnetic detection device, the direction of the DC bias current flowing in the magnetic sensor 100 is switched in a short time by the pair of switches 104 and the pair of AND gates 105, and each state is detected. Measure the oscillation period of the oscillation voltage at, and find the difference between them. In this way, by switching the direction of the DC bias current supplied to the magnetic sensor 100, it becomes possible to detect the direction of the external magnetic field, and cancel the temperature drift and time drift and apply the external magnetic field with high accuracy. It becomes possible to detect.
[0008]
FIG. 13 shows an equivalent circuit diagram when the input to one AND gate 106 is set to ‘H’ and the input to the other AND gate 107 is set to ‘L’. At this time, the current supplied to the magnetic sensor 100 flows from the terminal C1 to the terminal C2, as indicated by an arrow A1 in FIG. Thus, when the input to one AND gate 106 is set to “H” and the input to the other AND gate 107 is set to “L”, the AND gate 106 functions as a buffer for performing excitation and buffer amplification, and magnetically As a whole, the detection device operates as an astable multivibrator circuit in which the oscillation period of the oscillation voltage changes according to the magnitude of the external magnetic field.
[0009]
[Problems to be solved by the invention]
By the way, in the magnetic detection sensor, when a current is passed as shown in FIG. 13, the amount of current flowing through the magnetic sensor 100 includes the input voltage to the Schmitt trigger circuit 101 and one resistance connected to the magnetic sensor 100. It is determined by the resistance value of 103. Further, when the direction of the current is switched, the amount of current flowing through the magnetic sensor 100 is determined by the input voltage to the Schmitt trigger circuit 101 and the resistance value of the other resistor 102 connected to the magnetic sensor 100. Therefore, in this magnetic detection device, if there is a variation between the resistance value of one resistor 103 connected to the magnetic sensor 100 and the resistance value of the other resistor 102 connected to the magnetic sensor 100, the measurement is performed according to the direction of the current. The values vary, and the magnetic field detection accuracy decreases.
[0010]
In addition, as described above, in the magnetic detection device that controls the flow of current using the AND gates 106 and 107, the configuration becomes very complicated especially when an attempt is made to provide a plurality of magnetic sensors. It becomes difficult to reduce the price. That is, in the above-described magnetic detection device, for example, when three magnetic sensors orthogonal to each other are provided in order to detect the three-dimensional direction of the external magnetic field, it is particularly difficult to reduce the size and the cost. turn into.
[0011]
As described above, the conventional magnetic detection device has a problem that accuracy is lowered due to variations in resistances connected to the magnetic sensor, and it is difficult to reduce the size and cost.
[0012]
The present invention has been proposed in view of such a conventional situation, and has a structure in which variation in resistance connected to a magnetic sensor does not affect accuracy, and can be easily reduced in size and price. An object of the present invention is to provide a magnetic detection device.
[0013]
[Means for Solving the Problems]
Completed to achieve the above objectivesThe present invention  A magnetic circuit that includes an oscillation circuit using a magnetic sensor in which a coil is wound around a magnetic material as part of a time constant determining element, and detects the strength of an external magnetic field by changing the period of an oscillation voltage output from the oscillation circuit. In the detection device, the oscillation circuit includes an astable multivibrator circuit configured using a Schmitt trigger circuit, and includes at least one magnetic sensor in parallel between an input and an output of the Schmitt trigger circuit.Reverse the direction of the current flowing through the magnetic sensorAt least four forBilateral switchAnd a resistor is connected to the input of the Schmitt trigger circuit, the oscillation period of which is the resistance of the resistor connected in series to the magnetic sensor via the bilateral switch and the inductance of the magnetic sensor. Determined by the time constant determined by the valueIt is characterized by this.
[0016]
In the magnetic detection device, the amplitude of the oscillating current flowing in the coil of the magnetic sensor is preferably set so as to cover a range in which the inductance of the magnetic sensor shows a sharp change. The oscillation current flowing through the coil of the magnetic sensor preferably includes a DC bias current component.
[0017]
In the magnetic detection device, a plurality of magnetic sensors may be provided.
[0018]
In the magnetic detection device according to the present invention as described above, the direction of the current flowing through the magnetic sensor is reversed by the bilateral switch. Therefore, in this magnetic detection device, the same current is supplied to the magnetic sensor regardless of the direction of the current. Further, in this magnetic detection device, since the direction of the current flowing through the magnetic sensor is reversed by the bilateral switch, it is not necessary to provide a plurality of AND gates, a plurality of resistors, etc., and the configuration can be simplified. .
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. Note that the present invention is not limited to the following examples, and it goes without saying that modifications can be made without departing from the scope of the present invention.
[0020]
First, an example of a magnetic sensor used in a magnetic detection device to which the present invention is applied will be described.
[0021]
As shown in FIG. 1, a magnetic sensor 1 used in the present embodiment is wound in the longitudinal direction of a magnetic body 2 made of an elongated amorphous or the like formed in a ribbon shape or a wire shape. And a pair of terminals 4 and 5 are led out from both ends of the coil 3. Here, the magnetic material 2 is made of a magnetic material having excellent squareness characteristics that exhibits a steep change in magnetic permeability with a weak magnetic field of several gauss.
[0022]
The principle when the external magnetic field Hex is detected using the magnetic sensor 1 will be described with reference to FIG. FIG. 2 shows the state when the AC bias current i1 or the AC bias current i2 obtained by inverting the AC bias current i1 is supplied to the magnetic sensor 1 in correspondence with the change in the inductance L of the magnetic sensor 1. Is.
[0023]
When the external magnetic field Hex is detected using the magnetic sensor 1, the magnetic sensor 1 is magnetized in the longitudinal direction by passing an AC bias current i 1 including a DC bias current component through the coil 3, and the longitudinal direction of the magnetic sensor 1. An AC bias magnetic field including a DC bias magnetic field component in the direction is generated. Here, the AC bias current i1 supplied to the coil 3 includes a range in which the AC bias magnetic field exhibits a steep change in the inductance L of the magnetic sensor 1 even if the AC bias magnetic field is shifted due to the addition of the external magnetic field Hex. Set as follows.
[0024]
When the AC bias current i1 is supplied so that the current flowing through the coil 3 of the magnetic sensor 1 changes from Ia to Ib when the external magnetic field Hex = 0, the inductance L of the magnetic sensor 1 changes from Lmax to Lmin. . If the change in the voltage applied to the magnetic sensor 1 is constant, the rising time t1 of the AC bias current i1 is expressed by the following equation (1-1) according to Faraday's law.
[0025]
[Expression 1]

[0026]
On the other hand, when the external magnetic field Hex is applied, the current flowing through the magnetic sensor 1 is shifted by the amount of the external magnetic field Hex and changes from, for example, Ia + Iex to Ib + Iex. At this time, the AC bias current i1 is shifted by Iex, and the response waveform changes. Then, the response waveform of the AC bias current i1 changes. For example, the rising time t1 of the AC bias current i1 changes by the shift time Δt1 expressed by the following equation (1-2).
[0027]
[Expression 2]

[0028]
Thus, the rising time t1 of the AC bias current i1 changes according to the change in the external magnetic field Hex. Therefore, in this magnetic sensor 1, a change in the external magnetic field Hex can be detected by detecting the shift amount of the rising time t1 of the AC bias current i1.
[0029]
In the magnetic sensor 1, the AC bias current i1 is set so as to cover a range in which the inductance L shows a steep change even when the current value is shifted by the external magnetic field Hex. Thereby, as is clear from the above equation (1-2), the shift time Δt1 changes substantially linearly in accordance with the change in the external magnetic field Hex.
[0030]
Therefore, this magnetic sensor 1 has excellent linearity when detecting an external magnetic field, and operates very favorably as a magnetic field detection sensor. Further, in the magnetic sensor 1, a steep change of the inductance L, that is, a large change from Lmax to Lmin is always used for detecting the external magnetic field Hex, so that a very high sensitivity can be obtained.
[0031]
Next, an operation when the AC bias current i2 obtained by inverting the AC bias current i1 is supplied to the magnetic sensor 1 will be described.
[0032]
Here, as shown in FIG. 2, the current flowing in the magnetic sensor 1 is reversed so that the current flowing in the magnetic sensor 1 changes from −Ia to −Ib when the external magnetic field Hex = 0. Is supplied with an AC bias current i2. Also at this time, the inductance L of the magnetic sensor 1 changes from Lmax to Lmin. If the change in the voltage applied to the magnetic sensor 1 is constant, the rising time t2 of the AC bias current i2 is expressed by the following equation (1-3) according to Faraday's law, and the rising time described above: It is the same as t1.
[0033]
[Equation 3]

[0034]
On the other hand, when the external magnetic field Hex is applied when the AC bias current i2 is supplied in this way, the current flowing through the magnetic sensor 1 is shifted by the amount of the external magnetic field Hex and changed from, for example, −Ia + Iex to −Ib + Iex. To come. At this time, the AC bias current i2 is shifted by Iex, and the response waveform changes. Then, the response waveform of the AC bias current i2 changes, and for example, the rising time t2 of the AC bias current i2 changes by the shift time Δt2 expressed by the following equation (1-4).
[0035]
[Expression 4]

[0036]
As described above, even when the AC bias current i2 obtained by inverting the AC bias current i1 is supplied, the rising time t2 of the AC bias current i2 changes according to the change in the external magnetic field Hex. The shift time Δt2 has the same sign as that of the shift time Δt1 but opposite in sign. That is, the shift time Δt1 and the shift time Δt2 are in a differential relationship.
[0037]
Therefore, the rise time t1 + Δt1 when the current is passed in the forward direction and the rise time t2 + Δt2 when the current is passed in the reverse direction are measured, and the difference between these is taken to respond to the change in the external magnetic field Hex. The signal can be taken out as about twice as much output as when a current is passed only in a certain direction.
[0038]
Further, if the difference between the rise time t1 + Δt1 when the current flows in the forward direction and the rise time t2 + Δt2 when the current flows in the reverse direction is taken, the rise time of the AC bias current when the external magnetic field Hex = 0. Are cancelled. Therefore, it is possible to easily recognize the zero point where there is no external magnetic field Hex.
[0039]
Further, the magnetic sensor 1 changes in the magnitude of the inductance L depending on the temperature or the like and changes in the rising time of the AC bias current. By reversing the direction of the AC bias current in a short time, such temperature drift and Effects such as time drift can be canceled each other. Therefore, this magnetic sensor can detect the external magnetic field Hex with high accuracy without being affected by temperature drift or time drift.
[0040]
Next, a configuration example of a magnetic detection device using the magnetic sensor as described above will be specifically described.
[0041]
As shown in FIG. 3, this magnetic detector is connected to the magnetic sensor 10 as described above, a bilateral switch 11 for reversing the direction of the current flowing through the magnetic sensor 10, and the bilateral switch 11. And a Schmitt trigger circuit 13 connected to wirings derived from both ends of the magnetic sensor 10, and an oscillation circuit that operates as an astable multivibrator circuit is configured.
[0042]
Here, as described above, the magnetic sensor 10 is composed of a magnetic body made of an elongated amorphous or the like formed in a ribbon shape or a wire shape, and a coil made of a copper wire or the like wound in the longitudinal direction of the magnetic body. Composed. The magnetic sensor 10 is arranged in a bilateral switch 11 including a switch SW1, a switch SW2, a switch SW3, and a switch SW4. The direction of the current flowing through the magnetic sensor 10 is indicated by the bilateral switch 11. Can be reversed. One end of the resistor 12 connected to the bilateral switch 11 is connected in series to the magnetic sensor 10 via the bilateral switch 11, and the other end of the resistor 12 is grounded.
[0043]
Further, the Schmitt trigger circuit 13 repeatedly inverts the output voltage in accordance with the input voltage and outputs a square wave oscillation voltage V0. That is, when the input voltage rises and reaches the Schmitt voltage VsH, the Schmitt trigger circuit 13 inverts and outputs the output voltage. Similarly, when the input voltage falls and reaches the Schmitt voltage VsL, the output voltage is inverted. As a result, a square wave oscillation voltage V0 is output.
[0044]
Thus, by outputting the square wave oscillation voltage V0 from the Schmitt trigger circuit 13, the magnetic detector operates as an astable multivibrator circuit. Here, the time constant of the astable multivibrator circuit is determined by the inductance L of the magnetic sensor 10 and the resistance value R of the resistor 12. That is, in the magnetic detection device, the magnetic sensor 10 and the resistor 12 are time constant determining elements of an astable multivibrator circuit.
[0045]
Since the oscillation period of the astable multivibrator circuit is determined by the time constant, the oscillation period of the astable multivibrator circuit includes the inductance L of the magnetic sensor 10 and the resistance value R of the resistor 12 connected in series to the magnetic sensor 10. And determined by.
[0046]
Here, the inductance L of the magnetic sensor 10 changes according to the change of the external magnetic field Hex. Therefore, the oscillation period of the astable multivibrator circuit changes according to the change in the external magnetic field Hex. Therefore, in this magnetic detector, the intensity of the external magnetic field is detected by measuring the oscillation period of the astable multivibrator circuit, that is, the oscillation period of the square wave oscillation voltage V0 from the Schmitt trigger circuit 13.
[0047]
The operation of the magnetic detector will be described with reference to FIG. 4 which is a time chart of voltage waveforms when a current flows in a certain direction with respect to the magnetic sensor 10 by the bilateral switch 13. 4A shows a time chart of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13, and FIG. 4B shows a voltage generated in the magnetic sensor 10, that is, the Schmitt trigger circuit 13. 6 shows a time chart of the voltage Vr input to the.
[0048]
As shown in FIG. 4A, first, a voltage V1 including a predetermined DC bias component is supplied from the Schmitt trigger circuit 13 to the magnetic sensor 10, whereby an integrating circuit composed of the magnetic sensor 10 and the resistor 12 is supplied. The flowing current rises. Here, since the voltage supplied to the magnetic sensor 10 includes a DC bias component, the current flowing through the magnetic sensor 10 includes a DC bias current component. At this time, as shown in FIG. 4B, the voltage generated in the magnetic sensor 10, that is, the waveform of the voltage Vr1 input to the Schmitt trigger circuit 13, is higher than the voltage V1 output from the Schmitt trigger circuit 13. The waveform is delayed. The waveform of the voltage Vr1 corresponds to the response waveform of the current flowing through the magnetic sensor 10. Therefore, the delay at the rise of the voltage Vr1 changes according to the magnitude of the external magnetic field Hex applied to the magnetic sensor 10. To do. When the input rises and reaches a predetermined Schmitt voltage VsH, the Schmitt trigger circuit 13 inverts the output as shown in FIG.
[0049]
As a result, a voltage V2 obtained by inverting the original voltage V1 is supplied from the Schmitt trigger circuit 13 to the magnetic sensor 10, whereby the current flowing through the integrating circuit composed of the magnetic sensor 10 and the resistor 12 falls. At this time, as shown in FIG. 4B, the voltage generated in the magnetic sensor 10, that is, the waveform of the voltage Vr2 input to the Schmitt trigger circuit 13, falls with respect to the voltage V2 output from the Schmitt trigger circuit 13. Sometimes a delayed waveform occurs. The waveform of the voltage Vr2 corresponds to the response waveform of the current flowing through the magnetic sensor 10. Therefore, the delay when the voltage Vr2 falls depends on the magnitude of the external magnetic field Hex applied to the magnetic sensor 10. Change. The Schmitt trigger circuit 13 inverts the output when the input falls and reaches a predetermined Schmitt voltage VsL.
[0050]
By repeating the above operation, the Schmitt trigger circuit 13 outputs a square wave oscillation voltage V0 as shown in FIG. Here, the Schmitt voltages VsL and VsH are set so as to cover the change from Lmax to Lmin of the inductance L of the magnetic sensor 10 when the current flowing through the magnetic sensor 10 rises and falls. That is, the Schmitt voltages VsL and VsH are set so that the amplitude of the oscillation current flowing through the magnetic sensor 10 covers a range in which the inductance L of the magnetic sensor 10 shows a sharp change.
[0051]
As described above, the waveform of the voltage Vr input to the Schmitt trigger circuit 13 corresponds to the response waveform of the current flowing through the magnetic sensor 10. Therefore, the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13 corresponds to the rise time and fall time of the current flowing through the magnetic sensor 10. As described above, since the rise time and fall time of the current flowing through the magnetic sensor 10 depend on the magnitude of the external magnetic field Hex, the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13 is determined. Based on the above, the magnitude of the external magnetic field Hex applied to the magnetic sensor 10 can be detected.
[0052]
That is, in this magnetic detector, a change in the external magnetic field Hex applied to the magnetic sensor 10 appears as a change in the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13. Therefore, the intensity of the external magnetic field Hex can be detected by detecting the change in the oscillation period.
[0053]
By the way, in the magnetic detection device according to the present embodiment, the direction of the current flowing through the magnetic sensor 10 can be reversed by the bilateral switch 11. That is, in FIG. 3, when the switch SW1 and the switch SW4 are on and the switch SW2 and the switch SW3 are off, current flows in the direction of the arrow A in FIG. 3, and the switch SW1 and the switch SW4 are off and the switch SW2 When the switch SW3 is ON, a current flows in the direction of arrow B in FIG. Then, by reversing the direction of the current flowing through the magnetic sensor 10 by the bilateral switch 11 and detecting the external magnetic field Hex, as described above, the current is about twice as large as when the current is passed only in a certain direction. In addition, the zero point where there is no external magnetic field Hex can be easily recognized, and furthermore, the influence of temperature drift and time drift can be eliminated.
[0054]
Next, the principle that the change in the external magnetic field Hex applied to the magnetic sensor 10 appears as the change in the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13 will be described in more detail.
[0055]
FIG. 5 shows a circuit that models a state when a current rises in an integrating circuit in which a magnetic sensor 20 and a resistor 21 are connected in series. In such a circuit, when the switch 22 is turned from OFF to ON, a DC voltage is applied from the DC power source 23 to the integrating circuit composed of the magnetic sensor 20 and the resistor 21, and a current i flows out to the magnetic sensor 20. Here, the current i flowing through the magnetic sensor 20 is expressed as follows: E is the DC voltage applied to the integrating circuit, L is the inductance of the magnetic sensor 20, R is the resistance of the resistor 21, and t is the rise time of the current i. And represented by the following formula (1-5).
[0056]
[Equation 5]

[0057]
As can be seen from the above equation (1-5), the rise time t of the current i is proportional to the time constant L / R of the integrating circuit. Therefore, in such an integration circuit, the rise time t of the current i changes by changing the inductance L of the magnetic sensor 20 or the resistance value R of the resistor 21.
[0058]
By the way, as described above, the inductance L of the magnetic sensor changes from Lmax to Lmin while the current i rises. Here, the Schmitt voltages VsL and VsH described above are set so as to cover the change of the inductance L from Lmax to Lmin.
[0059]
Since the inductance L of the magnetic sensor 20 changes from Lmax to Lmin, as shown in FIG. 6, the current i flowing through the integrating circuit initially rises when the inductance L is Lmax, and eventually the inductance L becomes Lmin. It will stand up in the state of. Therefore, the time Ts until the current i flowing through the integrating circuit reaches a level corresponding to the Schmitt voltage VsH is the sum of the rise time T1 when the inductance L is Lmax and the rise time T2 when the inductance L is Lmin. become.
[0060]
When the external magnetic field Hex applied to the magnetic sensor 20 changes, the change point P at which the inductance L changes from Lmax to Lmin is shifted by this change, so that the integrated current i is changed to the Schmitt voltage VsH according to the external magnetic field Hex. The time Ts until the level corresponding to is changed.
[0061]
Therefore, as shown in FIG. 4 described above, a change in the external magnetic field Hex appears as a change in the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13.
[0062]
FIG. 7 shows a circuit that models the state when the current i that has flowed through the integrating circuit in which the magnetic sensor 30 and the resistor 31 are connected in series falls. In such a circuit, when the switch 32 is turned on from off, the direct current voltage from the direct current power supply 33 is not applied to the integrating circuit, and the current flowing through the magnetic sensor 30 falls. Here, the current i flowing through the magnetic sensor 30 is represented by E as the value of the DC voltage applied to the integrating circuit, L as the inductance of the magnetic sensor 30, R as the resistance value of the resistor 31, and t as the fall time of the current. Then, it is represented by the following formula (1-6).
[0063]
[Formula 6]

[0064]
At this time as well, when the external magnetic field Hex applied to the magnetic sensor 30 changes, the change point at which the inductance L changes from Lmax to Lmin is shifted by this change, similarly to the above-described rise of the current. Depending on the magnetic field Hex, the time changes until the integrated current i reaches a level corresponding to the Schmitt voltage VsL.
[0065]
Therefore, even when the current falls, the change in the external magnetic field Hex appears as a change in the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 15 as shown in FIG. .
[0066]
Incidentally, in the magnetic detector as shown in FIG. 3, the amount of change in the oscillation period of the square wave oscillation voltage V0 output from the Schmitt trigger circuit 13 varies in the longitudinal direction of the external magnetic field Hex and the magnetic body of the magnetic sensor 10. It depends on the angle θ formed by the generated magnetic field. That is, when the external magnetic field Hex is constant, as shown in FIG. 8, the oscillation period changes depending on the angle θ formed by the external magnetic field Hex and the magnetic field generated in the longitudinal direction of the magnetic body of the magnetic sensor 10. In FIG. 8, when the direction of the external magnetic field Hex is the same as the direction of the magnetic field generated in the longitudinal direction of the magnetic body of the magnetic sensor 10, the azimuth is 0 °.
[0067]
As can be seen from FIG. 8, the oscillation period includes azimuth information of the external magnetic field Hex. This is the sum of the magnetization amount of the magnetic material of the magnetic sensor 10 due to the current flowing through the magnetic sensor 10 and the magnetization amount due to the external magnetic field Hex, and the magnetization amount due to the external magnetic field Hex is the external magnetic field Hex. This is because it changes depending on the angle θ formed by the magnetic field generated in the longitudinal direction of the magnetic body of the magnetic sensor 10.
[0068]
That is, as shown in FIG. 9, the magnetic field Hb caused by the current flowing in the coil 10b of the magnetic sensor 10 is constant, but the magnetic field generated in the magnetic body 10a of the magnetic sensor 10 by the external magnetic field Hex depends on the direction of the external magnetic field Hex. doing. Therefore, the magnetic field H detected by the magnetic sensor 10 is only the longitudinal component of the magnetic body 10a in the external magnetic field Hex, as shown by the following formula (1-7).
[0069]
H = Hex · cos θ (1-7)
As shown in the above formula (1-7), the magnetic field H detected by the magnetic sensor 10 includes the azimuth information of the external magnetic field Hex, so that by using a plurality of magnetic sensors, You can know the direction.
[0070]
Specifically, for example, as shown in FIG. 10, two magnetic sensors 10x and 10y are incorporated in the magnetic detection device. This magnetic detector has the same circuit configuration as the magnetic detector shown in FIG. 3 except that two magnetic sensors are incorporated. Here, as shown in FIG. 11, the magnetic sensor 10x is arranged in the X-axis direction, and the magnetic sensor 10y is arranged in the Y-axis direction orthogonal to the X-axis direction. That is, the magnetic sensor 10x and the magnetic sensor 10y are disposed so as to be orthogonal to each other. At this time, as shown in FIG. 11, assuming that the angle formed by the direction of the external magnetic field Hex and the longitudinal direction of the magnetic body of the magnetic sensor 11x for detecting the X-axis direction is θ, the magnetic sensor 10x for detecting the X-axis direction. The magnetic field magnitude Hx detected by the following equation (1-8) is expressed by the following equation (1-8), and the magnetic field magnitude Hy detected by the Y-axis direction detection magnetic sensor 10y is expressed by the following equation (1-9). expressed.
[0071]
Hx = Hex · cos θ (1-8)
Hy = Hex · sin θ (1-9)
Here, when the ratio of the magnetic field magnitude Hx detected by the X-axis direction detection magnetic sensor 10x and the magnetic field magnitude Hy detected by the Y-axis direction detection magnetic sensor 10y is taken, the following equation is obtained. (1-10).
[0072]
Hy / Hx = sin θ / cos θ = tan θ (1-10)
Accordingly, the angle θ formed by the direction of the external magnetic field Hex and the longitudinal direction of the magnetic body of the magnetic sensor 10x for detecting the X-axis direction is expressed by the following formula (1-11). However, in the following formula (1-11), when Hy ≧ 0, 180 ° ≧ θ ≧ 0 °, and when 0> Hy, 360 °> θ> 180 °.
[0073]
θ = tan^-1(Hy / Hx) (1-10)
Thus, by providing the two magnetic sensors 10x and 10y in the magnetic detector, the direction of the external magnetic field Hex can be known. In order to know the direction of the external magnetic field Hex in the three-dimensional space, that is, the three-dimensional direction of the external magnetic field Hex, three magnetic sensors orthogonal to each other may be used.
[0074]
Also in the magnetic detector shown in FIG. 10, the current flowing through the magnetic sensor is determined only by the voltage input to the Schmitt trigger circuit and a single resistor. Therefore, even in this magnetic detection device, even if the direction of the current flowing through the magnetic sensor is reversed or the magnetic sensor through which the current flows is switched, it is caused by variations in the resistance value of the resistance connected to the magnetic sensor. As a result, the detection accuracy does not deteriorate. Therefore, this magnetic detector can also detect the magnitude and direction of the external magnetic field Hex with high accuracy.
[0075]
【The invention's effect】
As is clear from the above description, in the magnetic detection device according to the present invention, the same current is supplied to the magnetic sensor regardless of the direction of the current, so that the measurement value varies depending on the direction of the current. The external magnetic field can be detected with high accuracy.
[0076]
Further, in the magnetic detection device according to the present invention, it is not necessary to provide a plurality of AND gates, a plurality of resistors, and the like, and the configuration can be simplified. Therefore, it is possible to easily achieve downsizing and cost reduction. it can.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a magnetic sensor used in a magnetic detection device to which the present invention is applied.
2 is a diagram for explaining the principle of external magnetic field detection by the magnetic sensor shown in FIG. 1; FIG.
FIG. 3 is a circuit diagram showing a configuration example of a magnetic detection device to which the present invention is applied.
FIG. 4 is a diagram illustrating a time chart of a voltage output from a Schmitt trigger circuit and a time chart of a voltage input to the Schmitt trigger circuit.
FIG. 5 is a circuit diagram modeling a state when a current rises in an integrating circuit including a magnetic sensor and a resistor.
6 is a diagram illustrating a state when a current flowing through the integration circuit illustrated in FIG. 5 rises. FIG.
FIG. 7 is a circuit diagram modeling a state when a current flowing through an integrating circuit including a magnetic sensor and a resistor falls.
FIG. 8 is a characteristic diagram showing a relationship between an oscillation period of a square wave oscillation voltage output from a Schmitt trigger circuit and a direction of an external magnetic field Hex.
FIG. 9 is a schematic diagram showing a state of magnetization of a magnetic body of a magnetic sensor.
FIG. 10 is a circuit diagram showing another configuration example of the magnetic detection device to which the present invention is applied.
11 is a schematic diagram showing a state of arrangement of magnetic sensors of the magnetic detection device shown in FIG. 10;
FIG. 12 is a circuit diagram showing a configuration example of a conventional magnetic detection device.
13 is a circuit diagram showing an operation example of the magnetic detection device shown in FIG. 12;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetic sensor, 2 Magnetic body, 3 Coil, 10 Magnetic sensor, 11 Bilateral switch, 12 Resistance, 13 Schmitt trigger circuit

Claims (5)

A magnetic circuit that includes an oscillation circuit using a magnetic sensor in which a coil is wound around a magnetic material as part of a time constant determining element, and detects the strength of an external magnetic field by changing the period of an oscillation voltage output from the oscillation circuit. In the detection device,
The oscillation circuit is composed of an astable multivibrator circuit configured using a Schmitt trigger circuit, and in parallel between at least one of the Schmitt trigger circuit and the output , the direction of the current flowing through the magnetic sensor and the magnetic sensor is determined. At least four bilateral switches for inversion are connected, a resistor is connected to the input of the Schmitt trigger circuit, and the oscillation period is determined by the inductance of the magnetic sensor and the bilateral switch via the bilateral switch. A magnetic detection device characterized by being determined by a time constant determined by a resistance value of the resistor connected in series to a magnetic sensor . 2. The magnetic detection device according to claim 1, wherein the amplitude of the oscillating current flowing through the coil of the magnetic sensor is set so as to cover a range in which the inductance of the magnetic sensor shows a steep change. 2. The magnetic detection device according to claim 1, wherein the oscillating current flowing in the coil of the magnetic sensor includes a DC bias current component. The magnetic detection apparatus according to claim 1, comprising a plurality of the magnetic sensors. 2. The magnetic detection device according to claim 1, wherein the magnetic body is used by being magnetized in the longitudinal direction by an oscillating current flowing in the coil.

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