JP2005069727A - Multi-channel strain measuring circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use in common a bridge constitutional resistance in all channels, and to use a switching element of a high ON-state resistance value of a semiconductor relay or the like as a switching element in a bridge. <P>SOLUTION: In the case of one gage method, a constant current is sent in a route: an amplifier AMP2→a switch element Sa for selective scanning→a connection terminal Ta→a strain gage Ga→a connection terminal Tc→a switch element Sc'→a switch element SW2→a resistance Rb. A potential of the connection terminal Ta to which one end of the strain gage Ga is connected is extracted by an amplifier AMP4, and an error voltage portion in the ON-state resistance of the switch element Sc' and the switch element SW2 is extracted by an amplifier AMP5. A series circuit of the bridge constitutional resistances Rd, Rc is inserted between output terminals of the amplifiers AMP4, AMP5, and the output potential on one side is acquired from a connection point between resistances Rd, Rc. The output potential on the other side is acquired from a connection terminal Tb connected to the other end of the strain gage Ga. The voltage between the output potentials is extracted by a differential amplifier AMP1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１６】
これを、「１ゲージ法のブリッジ非直線性」と称し、この非直線性による誤差が無視できない場合には、測定と同時、あるいは測定後に、（１）式に従った補正処理を行なう必要があった。
なお、２ゲージ法測定モードにおいても、測定対象となるひずみをアクティブゲージとしての第１のひずみゲージで受け、第２のひずみゲージがダミーゲージとして温度補償のために使用される場合には、そのブリッジは、１ゲージ法の場合とほぼ同様の特性を示すので、上述したような非直線性が発生する。
【００１７】
【発明が解決しようとする課題】
上述したように、各チャンネルにそれぞれ各測定点で測定を行なうためのひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なうための多チャンネルひずみ測定回路においては、一組のブリッジ構成用抵抗素子を各チャンネルで共用することができ、しかもブリッジ内の切替え素子として、従来オン抵抗値が高過ぎて使用することができなかった半導体リレー等の高オン抵抗値の切替え素子を使用可能にする回路の実現が待たれていた。また、１ゲージ法測定モードおよび２つのひずみゲージの一方をアクティブゲージ、他方をダミーゲージとして用いる２ゲージ法測定モードにおいては、いわゆる１ゲージ法のブリッジ非直線性による測定誤差が発生するという問題があった。
本発明は、上述した事情に鑑みてなされたもので、１ゲージ法測定モード、２ゲージ法測定モードおよび４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、ブリッジ構成用抵抗を全チャンネルで共用することを可能とし且つブリッジ内の切替え素子として半導体リレー等の高オン抵抗値の切替え素子を使用することを可能とする多チャンネルひずみ測定回路を提供することを目的としている。
【００１８】
すなわち、本発明の請求項１の目的は、特に、少なくとも１ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することを可能とする多チャンネルひずみ測定回路を提供することにある。
また、本発明の請求項２の目的は、特に、少なくとも２ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することを可能とする多チャンネルひずみ測定回路を提供することにある。
本発明の請求項３の目的は、特に、１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における非直線性を防止し且つブリッジ励振電源を全チャンネルで共用することを可能とする多チャンネルひずみ測定回路を提供することにある。
【００１９】
本発明の請求項４の目的は、特に、少なくとも１ゲージ法および２ゲージ法測定モードにおいて、共通の励振電源による定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源およびブリッジ構成用抵抗素子を全チャンネルで共用することを可能とする多チャンネルひずみ測定回路を提供することにある。
本発明の請求項５の目的は、特に、定電圧励振の４ゲージ法測定モードによる測定をも可能とする多チャンネルひずみ測定回路を提供することにある。
本発明の請求項６の目的は、特に、１ゲージ法および２ゲージ法測定モードと実質的に共通の定電流励振を用いる４ゲージ法測定モードによる測定をも可能とし、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源を全チャンネルで共用することを可能とする多チャンネルひずみ測定回路を提供することにある。
本発明の請求項７の目的は、特に、ひずみゲージの接続状態に応じた測定回路の接続構成の自動的な選択設定を可能とする多チャンネルひずみ測定回路を提供することにある。
【００２０】
【課題を解決するための手段】
請求項１に記載した本発明に係る多チャンネルひずみ測定回路は、上述した目的を達成するために、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、
第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、
第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することを特徴としている。
【００２１】
請求項２に記載した本発明に係る多チャンネルひずみ測定回路は、上述した目的を達成するために、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記２ゲージ法測定モードによる測定時には、第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、
定電流の分流阻止と電位抽出のために用いられる第１のバッファ増幅器および第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することを特徴としている。
【００２２】
請求項３に記載した本発明に係る多チャンネルひずみ測定回路は、請求項１または請求項２の多点ひずみ測定回路であって、
前記１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における前記ブリッジ励振電流を供給するブリッジ励振電源を、単一の定電流源で構成することにより、ブリッジ方式における非直線性を無くし、各ひずみゲージの抵抗値変化に比例した出力を得ることを特徴としている。
【００２３】
請求項４に記載した本発明に係る多チャンネルひずみ測定回路は、上述した目的を達成するために、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として励振電源よりブリッジ励振電流を流して、
第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、
第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定するとともに、
前記２ゲージ法測定モードによる測定時には、前記第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として前記励振電源よりブリッジ励振電流を流して、
定電流の分流阻止と電位抽出のために用いられる前記第１のバッファ増幅器および前記第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、
前記第１のバッファ増幅器の出力端と前記第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の前記第２の抵抗素子と前記第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定する
ことにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することを特徴としている。
【００２４】
請求項５に記載した本発明に係る多チャンネルひずみ測定回路は、請求項１〜請求項４のうちのいずれか１項の多チャンネルひずみ測定回路であって、
前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路に定電圧を供給する定電圧励振回路を含む測定回路を構成することを特徴としている。
請求項６に記載した本発明に係る多チャンネルひずみ測定回路は、請求項１〜請求項５のうちのいずれか１項の多チャンネルひずみ測定回路であって、
前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路から切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流す定電流励振回路を含む測定回路を構成することを特徴としている。
【００２５】
請求項７に記載した本発明に係る多チャンネルひずみ測定回路は、請求項１〜請求項６のうちのいずれか１項の多チャンネルひずみ測定回路であって、
前記所定の第１、第２、第３および第４の端子からひずみゲージ側を見た回路特性を検出して、これら第１〜第４の端子に対するひずみゲージの測定モードを判別し、判別された測定モードに応じて測定回路の接続構成を選択設定するモード切替え手段をさらに含むことを特徴としている。
【００２６】
【作用】
すなわち、本発明の請求項１による多チャンネルひずみ測定回路は、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、
第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、
第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去する。
【００２７】
このような構成により、１ゲージ法測定モード、２ゲージ法測定モードおよび４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路は、特に、少なくとも１ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００２８】
また、本発明の請求項２による多チャンネルひずみ測定回路は、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記２ゲージ法測定モードによる測定時には、第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、
定電流の分流阻止と電位抽出のために用いられる第１のバッファ増幅器および第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去する。
このような構成により、特に、少なくとも２ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００２９】
本発明の請求項３による多チャンネルひずみ測定回路は、請求項１または請求項２の多点ひずみ測定回路において、前記１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における前記ブリッジ励振電流を供給するブリッジ励振電源を、単一の定電流源で構成することにより、ブリッジ方式における非直線性を無くし、各ひずみゲージの抵抗値変化に比例した出力を得る。
このような構成により、特に、１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における非直線性を防止し且つブリッジ励振電源を全チャンネルで共用することが可能となる。
【００３０】
本発明の請求項４による多チャンネルひずみ測定回路は、
ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、
少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、
前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として励振電源よりブリッジ励振電流を流して、
第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、
第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、
前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定するとともに、
前記２ゲージ法測定モードによる測定時には、前記第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として前記励振電源よりブリッジ励振電流を流して、
定電流の分流阻止と電位抽出のために用いられる前記第１のバッファ増幅器および前記第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、
前記第１のバッファ増幅器の出力端と前記第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の前記第２の抵抗素子と前記第３の抵抗素子を直列に接続し、
これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することにより、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去する。
このような構成により、特に、少なくとも１ゲージ法および２ゲージ法測定モードにおいて、共通の励振電源による定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源およびブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００３１】
本発明の請求項５による多チャンネルひずみ測定回路は、請求項１〜請求項４のうちのいずれか１項の多チャンネルひずみ測定回路において、前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路に定電圧を供給する定電圧励振回路を含む測定回路を構成する。
このような構成により、特に、定電圧励振の４ゲージ法測定モードによる測定が可能となる。
本発明の請求項６による多チャンネルひずみ測定回路は、請求項１〜請求項５のうちのいずれか１項の多チャンネルひずみ測定回路において、前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路から切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流す定電流励振回路を含む測定回路を構成する。
このような構成により、特に、１ゲージ法および２ゲージ法測定モードと実質的に共通の定電流励振を用いる４ゲージ法測定モードによる測定をも可能とし、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源を全チャンネルで共用することが可能となる。
【００３２】
本発明の請求項７による多チャンネルひずみ測定回路は、請求項１〜請求項６のうちのいずれか１項の多チャンネルひずみ測定回路において、前記所定の第１、第２、第３および第４の端子からひずみゲージ側を見た回路特性を検出して、これら第１〜第４の端子に対するひずみゲージの測定モードを判別し、判別された測定モードに応じて測定回路の接続構成を選択設定するモード切替え手段をさらに含む。
このような構成により、特に、ひずみゲージの接続状態に応じた測定回路の接続構成の自動的な選択設定が可能となる。
【００３３】
【発明の実施の形態】
以下、本発明に係る実施の形態に基づき、図面を参照して本発明の多チャンネルひずみ測定回路を詳細に説明する。
図１は、本発明の一つの実施の形態に係る多チャンネルひずみ測定回路の具体的な回路構成を示している。
図１に示す多チャンネルひずみ測定回路は、各チャンネルに共通の、励振電源Ｅｉｎ、増幅器ＡＭＰ１、ＡＭＰ２、ＡＭＰ３、ＡＭＰ４、ＡＭＰ５、モード切替え用のスイッチ素子ＳＷ１、ＳＷ２、ＳＷ３、ＳＷ４、ＳＷ５、ＳＷ６およびブリッジ構成用抵抗Ｒｂ、Ｒｃ、Ｒｄ、ならびに各チャンネル毎にそれぞれ設けられる、接続端子Ｔａ、Ｔｂ、Ｔｃ、Ｔｄおよび選択走査用のスイッチ素子Ｓａ、Ｓａ′、Ｓｂ、Ｓｃ、Ｓｃ′、Ｓｄを具備している。
選択走査用のスイッチ素子Ｓａ、Ｓａ′、Ｓｂ、Ｓｃ、Ｓｃ′、Ｓｄは、各チャンネル毎に連動して各チャンネル毎の走査切替え素子ＳＳＷを構成し、チャンネル単位で逐次選択的にオン動作することによりチャンネルの選択走査を行なう。これら走査切替え素子ＳＳＷ、その連動するスイッチ素子Ｓａ、Ｓａ′、Ｓｂ、Ｓｃ、Ｓｃ′、Ｓｄおよびゲージ接続用の接続端子Ｔａ、Ｔｂ、Ｔｃ、Ｔｄは、参照符号の桁数の増大による説明の煩雑さを避けて、理解を容易にするために、各チャンネル毎に共通の参照符号を付して示している。
【００３４】
なお、図１には、多チャンネルのうちの３チャンネル分のみを示しているが、４チャンネル以上の多チャンネルについても同様に構成することは言うまでもない。
モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６は、いずれも１つの可動選択端を測定モードに応じて２つの被選択端のいずれか一方に選択的に切替え接続される切替えスイッチである。すなわち、スイッチ素子ＳＷ１は、１ゲージ法測定モード（１Ｇ）および２ゲージ法測定モード（２Ｇ）では、可動選択端を一方の被選択端（１−２Ｇ）に接続し、定電圧４ゲージ法測定モード（４Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を他方の被選択端（４Ｇ／４ＧＩ）に接続する。スイッチ素子ＳＷ２は、１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を一方の被選択端（１−２Ｇ／４ＧＩ）に接続し、定電圧４ゲージ法測定モード（４Ｇ）では、可動選択端を他方の被選択端（４Ｇ）に接続する。スイッチ素子ＳＷ３は、１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を一方の被選択端（１−２Ｇ／４ＧＩ）に接続し、定電圧４ゲージ法測定モード（４Ｇ）では、可動選択端を他方の被選択端（４Ｇ）に接続する。
【００３５】
スイッチ素子ＳＷ４は、１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を一方の被選択端（１−２Ｇ／４ＧＩ）に接続し、定電圧４ゲージ法測定モード（４Ｇ）では、可動選択端を他方の被選択端（４Ｇ）に接続する。スイッチ素子ＳＷ５は、１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を一方の被選択端（１−２Ｇ／４ＧＩ）に接続し、定電圧４ゲージ法測定モード（４Ｇ）では、可動選択端を他方の被選択端（４Ｇ）に接続する。スイッチ素子ＳＷ６は、２ゲージ法測定モード（２Ｇ）、定電圧４ゲージ法測定モード（４Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）では、可動選択端を一方の被選択端（２Ｇ／４Ｇ／４ＧＩ）に接続し、１ゲージ法測定モード（１Ｇ）では、可動選択端を他方の被選択端に接続する。
接続端子Ｔａは、選択走査用のスイッチ素子Ｓａ′およびＳａのそれぞれに接続されている。接続端子Ｔｂは、選択走査用のスイッチ素子Ｓｂに接続されている。接続端子Ｔｃは、選択走査用のスイッチ素子Ｓｃ′およびＳｃのそれぞれに接続されている。
【００３６】
そして接続端子Ｔｄは、スイッチ素子Ｓｄに接続されている。選択走査用のスイッチ素子Ｓａ′は、モード切替え用のスイッチ素子ＳＷ４の可動選択端に接続され、選択走査用のスイッチ素子Ｓａには、増幅器ＡＭＰ２の出力端が接続されている。選択走査用のスイッチ素子Ｓｂは、増幅器ＡＭＰ１の反転入力端（−）に接続されている。選択走査用のスイッチ素子Ｓｃ′は、モード切替え用のスイッチ素子ＳＷ２の可動選択端に接続され、選択走査用のスイッチ素子Ｓｃは、モード切替え用のスイッチ素子ＳＷ３の可動選択端に接続されている。選択走査用のスイッチ素子Ｓｄは、モード切替え用のスイッチ素子ＳＷ１の定電圧４ゲージ法測定モード（４Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記他方の被選択端に接続されている。これらは、各チャンネルに共通の構成である。
励振電源Ｅｉｎの一方、この場合正側、の出力端は、増幅器ＡＭＰ２の非反転入力端（＋）に接続され、励振電源Ｅｉｎの他方、この場合負側、の出力端は、増幅器ＡＭＰ３の非反転入力端（＋）および共通電位（アース）のそれぞれに接続されている。増幅器ＡＭＰ２の反転入力端（−）には、モード切替え用のスイッチ素子ＳＷ５の可動選択端が接続されている。
【００３７】
増幅器ＡＭＰ３の反転入力端（−）には、モード切替え用のスイッチ素子ＳＷ２の定電圧４ゲージ法測定モード（４Ｇ）で選択される前記他方の被選択端が接続されている。モード切替え用のスイッチ素子ＳＷ２の１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端は、スイッチ素子ＳＷ５の１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端に接続されると共に、スイッチ素子ＳＷ６の１ゲージ法測定モード（１Ｇ）で選択される被選択端のそれぞれに接続されている。モード切替え用のスイッチ素子ＳＷ５の１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端は、ブリッジ構成用抵抗Ｒｂを介して共通電位に接続されている。モード切替え用のスイッチ素子ＳＷ５の定電圧４ゲージ法測定モード（４Ｇ）で選択される前記他方の被選択端は、スイッチ素子ＳＷ４の定電圧４ゲージ法測定モード（４Ｇ）で選択される前記他方の被選択端に接続されている。増幅器ＡＭＰ３の出力端は、スイッチ素子ＳＷ３の定電圧４ゲージ法測定モード（４Ｇ）で選択される前記他方の被選択端に接続されている。
【００３８】
スイッチ素子ＳＷ４の１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端は、増幅器ＡＭＰ４の非反転入力端（＋）に接続されている。増幅器ＡＭＰ４の反転入力端（−）には、増幅器ＡＭＰ４の出力端が接続されている。モード切替え用のスイッチ素子ＳＷ３の１ゲージ法測定モード（１Ｇ）、２ゲージ法測定モード（２Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端は、増幅器ＡＭＰ５の非反転入力端（＋）に接続されている。増幅器ＡＭＰ５の反転入力端（−）には、スイッチ素子ＳＷ６の可動選択端が接続されている。モード切替え用のスイッチ素子ＳＷ６の２ゲージ法測定モード（２Ｇ）、定電圧４ゲージ法測定モード（４Ｇ）および定電流４ゲージ法測定モード（４ＧＩ）で選択される前記一方の被選択端には、増幅器ＡＭＰ５の出力端が接続されている。ブリッジ構成用抵抗ＲｄとＲｃは、直列に接続され、これらブリッジ構成用抵抗ＲｄとＲｃの直列回路の抵抗Ｒｄ側の端部は、増幅器ＡＭＰ４の出力端に接続され、ブリッジ構成用抵抗ＲｄとＲｃの直列回路の抵抗Ｒｃ側の端部は、増幅器ＡＭＰ５の出力端に接続されている。ブリッジ構成用抵抗ＲｄとＲｃの相互の接続点は、スイッチ素子ＳＷ１の１ゲージ法測定モード（１Ｇ）および２ゲージ法測定モード（２Ｇ）で選択される前記一方の被選択端に接続されている。
【００３９】
１ゲージ法測定モードの場合には、ひずみゲージＧａとしていわゆる３ワイヤ式のひずみゲージを用い、このひずみゲージＧａのゲージ抵抗の一端に接続された第１端は、接続端子Ｔａに接続され、ひずみゲージＧａのゲージ抵抗の他端に接続された第２端は接続端子Ｔｂに接続され、ひずみゲージＧａのゲージ抵抗の他端に前記第２端と共通に接続された第３端は接続端子Ｔｃに接続される。
２ゲージ法測定モードの場合には、ひずみゲージＧａのゲージ抵抗の一端に接続された第１端は、接続端子Ｔａに接続され、ひずみゲージＧａのゲージ抵抗の他端に接続された第２端は接続端子Ｔｂに接続される。ひずみゲージＧｂのゲージ抵抗の一端に接続された第１端は、ひずみゲージＧａの前記第２端と共に接続端子Ｔｂに接続され、ひずみゲージＧｂのゲージ抵抗の他端に接続された第２端は接続端子Ｔｃに接続される。
４ゲージ法測定モードの場合には、定電圧励振および定電流励振のいずれにおいても、ひずみゲージＧａのゲージ抵抗の一端に接続された第１端は、接続端子Ｔａに接続され、ひずみゲージＧａのゲージ抵抗の他端に接続された第２端は接続端子Ｔｂに接続される。
【００４０】
ひずみゲージＧｂのゲージ抵抗の一端に接続された第１端は、ひずみゲージＧａの前記第２端と共に接続端子Ｔｂに接続され、ひずみゲージＧｂのゲージ抵抗の他端に接続された第２端は接続端子Ｔｃに接続される。ひずみゲージＧｃのゲージ抵抗の一端に接続された第１端は、ひずみゲージＧｂの前記第２端と共に接続端子Ｔｃに接続され、ひずみゲージＧｃのゲージ抵抗の他端に接続された第２端は接続端子Ｔｄに接続される。ひずみゲージＧｄのゲージ抵抗の一端に接続された第１端は、ひずみゲージＧｃの前記第２端と共に接続端子Ｔｄに接続され、ひずみゲージＧｄのゲージ抵抗の他端に接続された第２端は、ひずみゲージＧａの前記第１端と共に接続端子Ｔａに接続される。なお、図１においては、第１番目のチャンネルに１ゲージ法測定モード、第２番目のチャンネルに２ゲージ法測定モード、そして第３番目のチャンネルに４ゲージ法測定モードにそれぞれ従ってひずみゲージを接続した状態を示しているが、もちろんどのチャンネルにどの測定モードでひずみゲージの接続を行なっても良い。
【００４１】
ブリッジ構成用抵抗Ｒｂ、ＲｃおよびＲｄは、ひずみゲージと組み合わせてブリッジを構成する。ブリッジ励振電源Ｅｉｎは、ブリッジ励振用の基準電圧を供給する。増幅器ＡＭＰ１はブリッジ出力を増幅する差動増幅器であり、増幅器ＡＭＰ２はブリッジ励振用の第１の電源増幅器、増幅器ＡＭＰ３はブリッジ励振用の第２の電源増幅器である。増幅器ＡＭＰ４は、ブリッジ励振電流が抵抗Ｒｄと抵抗Ｒｃの辺へ分流することを阻止するための第１のバッファ増幅器であり、増幅器ＡＭＰ５は、１ゲージ法測定モードでの接続時には切替え素子の抵抗による電圧発生分を抽出する差動増幅器として動作し、２ゲージ法測定モードでの接続時には増幅器ＡＭＰ４と同様に抵抗Ｒｄと抵抗Ｒｃの辺へのブリッジ電流の分流を阻止するバッファとして動作する第２のバッファ増幅器である。モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６は、測定モードに応じて各回路素子を所要の測定方式に従って接続するためのスイッチである。なお、図１においては、モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６は、２ゲージ法測定モードにおける選択状態が示されており、各チャンネル毎の走査切替え素子ＳＳＷを構成する選択走査用のスイッチ素子Ｓａ、Ｓａ′、Ｓｂ、Ｓｃ、Ｓｃ′、Ｓｄは、非選択状態として示されている。
以下、図１に示した多チャンネルひずみ測定回路における各測定モード毎の接続状態および動作を説明する。
【００４２】
〈（１）１ゲージ法〉
図１の多チャンネルひずみ測定回路の構成において、１ゲージ法測定モードとして接続した場合、すなわちモード切替え用のスイッチ素子ＳＷ１〜ＳＷ５を図１に示されるように被選択端が選択された状態とし、モード切替え用のスイッチ素子ＳＷ６を図１とは異なる被選択端が選択された状態とした場合、の実質的な回路を図２に示す。この図２には、１ゲージ法測定モードにおける動作に関連する素子および回路だけを示している。例えば、モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６のうち、図２に示されているのはスイッチ素子ＳＷ２だけであるが、このスイッチ素子ＳＷ２以外のモード切替え用の各スイッチ素子ＳＷ１、ＳＷ３〜ＳＷ６は、その特性等が測定精度の検討に実質的に大きく影響しないので、図２の回路上に明示していない。
すなわち、図２に示す接続状態においては、増幅器ＡＭＰ１の非反転入力端（＋）にブリッジ構成用抵抗ＲｄとＲｃの接続点が接続されており、増幅器ＡＭＰ５の非反転入力端（＋）に選択走査用のスイッチ素子Ｓｃが接続されており、増幅器ＡＭＰ４の非反転入力端（＋）に選択走査用のスイッチ素子Ｓａ′が接続されており、そして増幅器ＡＭＰ２の反転入力端（−）はブリッジ構成用抵抗Ｒｂを介して共通電位に接続されている。
【００４３】
増幅器ＡＭＰ２の反転入力端（−）には、また、モード切替え用のスイッチ素子ＳＷ２を介して選択走査用のスイッチ素子Ｓｃ′が接続されている。増幅器ＡＭＰ５の反転入力端（−）は、増幅器ＡＭＰ２の反転入力端（−）と接続されている。
この状態で、ひずみゲージＧａには、増幅器ＡＭＰ２→接続端子Ｔａ→ひずみゲージＧａ→接続端子Ｔｃ→スイッチ素子Ｓｃ′→スイッチ素子ＳＷ２→抵抗Ｒｂの経路で定電流を流す。その電流は、ブリッジ構成用抵抗Ｒｂの両端の電圧が、ブリッジ励振電源Ｅｉｎの基準電圧（Ｅｉｎ）に等しくなるように、増幅器ＡＭＰ２により制御された一定の電流である。
バッファ増幅器ＡＭＰ４により、ひずみゲージＧａのゲージ抵抗の一端に対応する第１端に接続された接続端子Ｔａの電位を抽出し、さらに上述の電流経路の選択走査用のスイッチ素子Ｓｃ′とモード切替え用のスイッチ素子ＳＷ２のオン抵抗（数百Ω以下）に、電流が流れることによって発生する誤差電圧分を増幅器ＡＭＰ５により抽出し、増幅器ＡＭＰ４と増幅器ＡＭＰ５との出力端間に、互いに等しい抵抗値を有するブリッジ構成用抵抗ＲｄとＲｃの直列回路を挿入した回路を構成して、抵抗ＲｄとＲｃの接続点から、従来方式のブリッジ回路における正の出力に相当する一方の出力電位を得る。
【００４４】
また、ひずみゲージＧａのゲージ抵抗の他端に対応する第２端に接続された接続端子Ｔｂからは、従来方式のブリッジ回路における負の出力に相当する他方の出力電位を得る。
これら正負の出力電位間の電圧がひずみゲージの抵抗値変化に比例した出力、すなわちひずみ出力となる。この実施の形態においては、差動増幅器ＡＭＰ１によって、正負出力電位間の差の電圧を抽出し、必要とあれば増幅する。
図２の構成において、ひずみゲージＧａの接続ケーブルにおけるリード線の抵抗値を考慮した場合の回路構成を図３に示している。ひずみゲージＧａと接続端子Ｔａ、ＴｂおよびＴｃの間にそれぞれ挿入されている抵抗値ＲＬがひずみゲージのリード線抵抗値であり、これらは同じ抵抗値と考えて良い。
ひずみゲージリード線抵抗値ＲＬを考慮した場合の図３の回路の等価回路を図４に示している。以下、この図４の等価回路に基づいて、詳細に説明する。
ひずみゲージＧａのゲージ抵抗（抵抗値もＧａとする）に流れる電流Ｉは、ブリッジ励振電源電圧Ｅｉｎおよびブリッジ構成用抵抗値Ｒｂに基づいて次式であらわされる。
【００４５】
【数２】

【００４６】
ブリッジ励振電源電圧Ｅｉｎおよびブリッジ構成用抵抗値Ｒｂは、共に固定値であるから、電流値Ｉは一定の電流、つまり定電流、である。
接続端子Ｔａの電位、すなわち増幅器ＡＭＰ４の出力の電位Ｅａｍｐ４は、次式であらわされる。
Ｅａｍｐ４＝Ｉ×（Ｇａ＋Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２＋２×ＲＬ）… （３）
ここで、Ｒｓｃ′とＲｓｗ２は、それぞれ選択走査用のスイッチ素子Ｓｃ′とモード切替え用のスイッチ素子ＳＷ２のオン抵抗値である。
また、増幅器ＡＭＰ５の出力の電位Ｅａｍｐ５は、次式であらわされる。
Ｅａｍｐ５＝Ｉ×（Ｒｓｃ′＋Ｒｓｗ２） … （４）
したがって、ブリッジ構成用抵抗Ｒｄとブリッジ構成用抵抗Ｒｃの接続点の電位Ｅ１は、次式であらわされる。
【００４７】
【数３】

【００４８】
また、接続端子Ｔｂの電位Ｅ２は、次式であらわされる。
Ｅ２＝Ｉ×（Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２＋ＲＬ） … （６）
ここで、ひずみゲージＧａのゲージ抵抗（Ｇａ）は、初期状態、つまり無負荷時、では、ブリッジ構成用抵抗Ｒｂと等しいので、ゲージ抵抗Ｇａからひずみによる抵抗値変化分ΔＧａを分離して、Ｇａ＝Ｇａ＋ΔＧａ＝Ｒｂ＋ΔＧａとおけば、（５）式は、次のようになる。
【００４９】
【数４】

【００５０】
すなわち、ブリッジ出力に相当する電位Ｅ１とＥ２の電位差Ｅｏは、（６）式および（７）式より、次式であらわされる。
【００５１】
【数５】

【００５２】
電流値Ｉは、一定であるから、最終的な出力Ｅｏとしては、ひずみゲージＧａの抵抗値変化ΔＧａに完全に比例した出力が得られる。
〈（２）２ゲージ法〉
図１の多チャンネルひずみ測定回路の構成において、２ゲージ法測定モードとして接続した場合、すなわちモード切替え用のスイッチ素子ＳＷ１〜ＳＷ６を図１に示されるように被選択端が選択された状態とした場合、の実質的な回路を図５に示す。この図５には、２ゲージ法測定モードにおける動作に関連する素子および回路だけを示している。例えば、モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６のうち、図５に示されているのはスイッチ素子ＳＷ２だけであるが、このスイッチ素子ＳＷ２以外のモード切替え用の各スイッチ素子ＳＷ１、ＳＷ３〜ＳＷ６は、その特性等が測定精度の検討に実質的に大きく影響しないので、図５の回路上に明示していない。
【００５３】
すなわち、図５に示す接続状態においては、増幅器ＡＭＰ１の非反転入力端（＋）にブリッジ構成用抵抗ＲｄとＲｃの接続点が接続されており、増幅器ＡＭＰ５の非反転入力端（＋）に選択走査用のスイッチ素子Ｓｃが接続されており、増幅器ＡＭＰ４の非反転入力端（＋）に選択走査用のスイッチ素子Ｓａ′が接続されており、そして増幅器ＡＭＰ２の反転入力端（−）はブリッジ構成用抵抗Ｒｂを介して共通電位に接続されている。増幅器ＡＭＰ２の反転入力端（−）には、また、モード切替え用のスイッチ素子ＳＷ２を介して選択走査用のスイッチ素子Ｓｃ′が接続されている。増幅器ＡＭＰ５の反転入力端（−）には、その増幅器ＡＭＰ５の出力端が接続されている。
この状態で、２個のひずみゲージＧａおよびＧｂには、増幅器ＡＭＰ２→接続端子Ｔａ→ひずみゲージＧａ→接続端子Ｔｂ→ひずみゲージＧｂ→接続端子Ｔｃ→スイッチ素子Ｓｃ′→スイッチ素子ＳＷ２→抵抗Ｒｂの経路で定電流を流す。その電流は、ブリッジ構成用抵抗Ｒｂの両端の電圧が、ブリッジ励振電源Ｅｉｎの基準電圧（Ｅｉｎ）に等しくなるように、増幅器ＡＭＰ２により制御された一定の電流である。
【００５４】
バッファ増幅器ＡＭＰ４により、ひずみゲージＧａのゲージ抵抗の前記一端に対応する第１端に接続された接続端子Ｔａの電位を抽出し、さらにバッファ増幅器ＡＭＰ５により、ひずみゲージＧｂのゲージ抵抗の前記他端に対応する第２端に接続された接続端子Ｔｃの電位を抽出して、増幅器ＡＭＰ４と増幅器ＡＭＰ５との出力端間に、互いに等しい抵抗値のを有するブリッジ構成用抵抗ＲｄとＲｃの直列回路を挿入した回路を構成して、抵抗ＲｄとＲｃの接続点から、従来方式のブリッジ回路における正の出力に相当する一方の出力電位を得る。また、ひずみゲージＧａのゲージ抵抗の前記他端に対応する第２端に接続されるとともにひずみゲージＧｂのゲージ抵抗の前記一端に対応する第１端に接続された接続端子Ｔｂからは、従来方式のブリッジ回路における負の出力に相当する他方の出力電位を得る。
これら正負の出力電位間の電圧がひずみゲージの抵抗値変化に比例した出力、すなわちひずみ出力となる。この実施の形態においては、差動増幅器ＡＭＰ１によって、正負出力電位間の差の電圧を抽出し、必要とあれば増幅する。
【００５５】
２個のひずみゲージＧａおよびＧｂを励振する電流の経路にある選択走査用のスイッチ素子Ｓｃ′とモード切替え用のスイッチ素子ＳＷ２のオン抵抗（数百Ω以下）に電流が流れることによって発生する電圧は、差動増幅器ＡＭＰ１に対して同相電圧として入力されるので、ひずみ測定値に影響しない。
図５の構成において、２個のひずみゲージＧａおよびＧｂの接続ケーブルにおけるリード線の抵抗値を考慮した場合の回路構成を図６に示している。ひずみゲージＧａ、Ｇｂの各両端と接続端子Ｔａ、Ｔｂ、Ｔｃの間に挿入されている抵抗値ＲＬがリード線抵抗値であり、これらは同じ抵抗値と考えて良い。
ひずみゲージリード線抵抗値ＲＬを考慮した場合の図６の回路の等価回路を図７に示している。以下、この図７の等価回路に基づいて、詳細に説明する。
ひずみゲージＧａおよびＧｂのゲージ抵抗（抵抗値もＧａおよびＧｂとする）に流れる電流Ｉは、上述の１ゲージ法測定モードの場合と同様にブリッジ励振電源電圧Ｅｉｎおよびブリッジ構成用抵抗値Ｒｂに基づいて（２）式であらわされ、一定の電流、すなわち定電流、である。
【００５６】
接続端子Ｔａの電位、すなわち増幅器ＡＭＰ４の出力の電位Ｅａｍｐ４は、選択走査用のスイッチ素子Ｓｃ′のオン抵抗値Ｒｓｃ′とモード切替え用のスイッチ素子ＳＷ２のオン抵抗値Ｒｓｗ２を用いて。次式であらわされる。
Ｅａｍｐ４＝Ｉ×（Ｇａ＋Ｇｂ＋Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２＋４×ＲＬ）… （９）
また、増幅器ＡＭＰ５の出力の電位Ｅａｍｐ５は、次式であらわされる。
Ｅａｍｐ５＝Ｉ×（Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２） … （１０）
したがって、ブリッジ構成用抵抗Ｒｄとブリッジ構成用抵抗Ｒｃの接続点の電位Ｅ１は、次式であらわされる。
【００５７】
【数６】

【００５８】
また、接続端子Ｔｂの電位Ｅ２は、次式であらわされる。
Ｅ２＝Ｉ×（Ｇｂ＋Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２＋２×ＲＬ）… （１２）
ここで、初期状態、つまり無負荷時、では、ひずみゲージＧａのゲージ抵抗（Ｇａ）とひずみゲージＧｂのゲージ抵抗（Ｇｂ）とは、互いに等しいので、
Ｇａ＝Ｇｂとおき、ゲージ抵抗ＧａおよびＧｂからひずみによる抵抗値変化分ΔＧａおよびΔＧｂをそれぞれ分離して、Ｇａ＝Ｇｂ＋ΔＧａ、Ｇｂ＝Ｇｂ＋ΔＧｂとおけば、Ｅ１を示す（１１）式は、次のようになる。
【００５９】
【数７】

【００６０】
となる。同様にＥ２を示す（１２）式は、次のようになる。
Ｅ２＝Ｉ×（ΔＧｂ＋Ｇｂ＋Ｒｂ＋Ｒｓｃ′＋Ｒｓｗ２＋２×ＲＬ）… （１４）
すなわち、ブリッジ出力に相当する電位Ｅ１とＥ２の電位差Ｅｏは、（１３）式および（１４）式より、次式であらわされる。
【００６１】
【数８】

【００６２】
電流値Ｉは、一定であるから、最終的な出力Ｅｏとしては、２個のひずみゲージＧａ、Ｇｂの抵抗値変化ΔＧａ、ΔＧｂに完全に比例した出力が得られる。
【００６３】
〈（３）定電圧（定電圧励振）４ゲージ法〉
図１の多チャンネルひずみ測定回路の構成において、定電圧励振の４ゲージ法、つまり定電圧４ゲージ法測定モードとして接続した場合、すなわちモード切替え用のスイッチ素子ＳＷ１〜ＳＷ５を図１とは異なる被選択端が選択された状態とし、モード切替え用のスイッチ素子ＳＷ６を図１に示されるように被選択端が選択された状態とした場合、の実質的な回路を図８に示す。この図８には、定電圧４ゲージ法測定モードにおける動作に関連する素子および回路だけを示している。例えば、モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６は、その特性等が測定精度の検討に実質的に大きく影響しないので、図８の回路上に明示していない。
すなわち、図８に示す接続状態においては、増幅器ＡＭＰ１の非反転入力端（＋）に選択走査用のスイッチ素子Ｓｄが接続されており、増幅器ＡＭＰ３の反転入力端（−）に選択走査用のスイッチ素子Ｓｃ′が接続されており、増幅器ＡＭＰ３の出力端は選択走査用のスイッチ素子Ｓｃに接続されており、そして増幅器ＡＭＰ２の反転入力端（−）に選択走査用のスイッチ素子Ｓａ′が接続されている。このような図８の接続構成の等価回路を図９に示している。
【００６４】
図９に示す構成において、接続端子ＴａおよびＴｃの電位がそれぞれ基準電圧Ｅｉｎおよび０Ｖの共通電位となるように増幅器ＡＭＰ２およびＡＭＰ３が制御するので、ブリッジ励振電圧は基準電圧Ｅｉｎとなる。
この図９の等価回路は、一般的な定電圧励振による４ゲージ法測定モードの測定回路である。この定電圧４ゲージ法測定モードは、ロードセルを始めとして加速度変換器、変位計、トルク変換器など種々のひずみゲージ式変換器を接続する際に使用する。各変換器には、定電圧励振電源により較正された較正係数が付属されており、多チャンネルのひずみ測定システムとしては必須の測定モードである。
【００６５】
〈（４）定電流（定電流励振）４ゲージ法〉
図１の多チャンネルひずみ測定回路の構成において、定電流励振の４ゲージ法、つまり定電流４ゲージ法測定モードとして接続した場合、すなわちモード切替え用のスイッチ素子ＳＷ１を図１とは異なる被選択端が選択された状態とし、モード切替え用のスイッチ素子ＳＷ２〜ＳＷ６を図１に示されるように被選択端が選択された状態とした場合、の実質的な回路を図１０に示す。この図１０には、定電流４ゲージ法測定モードにおける動作に関連する素子および回路だけを示している。例えば、モード切替え用のスイッチ素子ＳＷ１〜ＳＷ６のうち、図１０に示されているのはスイッチ素子ＳＷ２だけであるが、このスイッチ素子ＳＷ２以外のモード切替え用の各スイッチ素子ＳＷ１、ＳＷ３〜ＳＷ６は、その特性等が測定精度の検討に実質的に大きく影響しないので、図１０の回路上に明示していない。
【００６６】
すなわち、図１０に示す接続状態においては、増幅器ＡＭＰ１の非反転入力端（＋）に選択走査用のスイッチ素子Ｓｄが接続されており、増幅器ＡＭＰ２の反転入力端（−）はブリッジ構成用抵抗Ｒｂを介して共通電位に接続されている。増幅器ＡＭＰ２の反転入力端（−）には、また、モード切替え用のスイッチ素子ＳＷ２を介して選択走査用のスイッチ素子Ｓｃ′が接続されている。このような図１０の接続構成の等価回路を図１１に示している。
この図１１の等価回路は、一般的な定電流励振による４ゲージ法測定モードの測定回路である。この定電流４ゲージ測定モードは、接続ケーブル長が数百〜数千メートルと長くなることも多いひずみゲージ式土木用変換器等を接続する際に効果的に使用することができる。定電流励振であるためにケーブルのリード線抵抗による電圧降下の影響を受けることがなく、ブリッジ励振電圧の低下による感度変化を生じることがない。このような測定モードも多チャンネルのひずみ測定システムとしては必須の測定モードである。
【００６７】
基準抵抗となるブリッジ構成用抵抗Ｒｂの両端における電圧が、励振電源基準電圧Ｅｉｎに等しくなるように増幅器ＡＭＰ２により制御された電流が、増幅器ＡＭＰ２→接続端子Ｔａ→４ゲージブリッジ（Ｇａ、Ｇｂ、Ｇｃ、Ｇｄ）→接続端子Ｔｃ→スイッチ素子Ｓｃ′→スイッチ素子ＳＷ２→抵抗Ｒｂの経路で流れる。なお、４ゲージブリッジ（Ｇａ、Ｇｂ、Ｇｃ、Ｇｄ）部分は、ひずみゲージＧａとＧｂの直列回路と、ひずみゲージＧｄとＧｃの直列回路との並列接続である。
選択走査用のスイッチ素子Ｓｃ′とモード切替え用のスイッチ素子ＳＷ２のオン抵抗の総和（Ｒｓｃ′＋Ｒｓｗ２）は、その抵抗値がひずみゲージと同程度、例えば数百Ωという大きな値であっても、接続端子Ｔｄにあらわれる出力電位Ｅ１と接続端子Ｔｂにあらわれる出力電位Ｅ２との間のブリッジ出力（Ｅ１−Ｅ２）の同相電圧として差動増幅器ＡＭＰ１に入力されるので、前記オン抵抗の総和（Ｒｓｃ′＋Ｒｓｗ２）の影響は差動増幅器ＡＭＰ１によって除去される。
【００６８】
以上において説明した通り、図１に示す本発明の実施の形態に係る多チャンネルひずみ測定回路は、４種類のゲージ法による測定モードを全て包含して、チャンネル毎に選択的に切替えて適用することが可能であり、且つブリッジ構成用抵抗を全チャンネルで共用することが可能であって、しかもブリッジ内の切替え素子として半導体リレー等の高オン抵抗値の切替え素子を使用することが可能である。
従来の技術において、図１２に示す測定回路から図１３に示す測定回路へ変更することにより、ブリッジ構成用抵抗を大幅に削減することが可能となるが、図１３のような抵抗の共用は測定のためのブリッジの辺を切り替えることになり、誤差を許容範囲に抑えるためには、切替え素子のオン抵抗値が数ｍΩ以下に制限されるために、スイッチ素子として使用可能な素子の選択範囲が制限されていた。
これに対して、上述した実施の形態に示すような本発明に係る多チャンネルひずみ測定回路は、かかる制限を取り除くことができ、数百Ωのオン抵抗値を持つ半導体スイッチも使用可能となる。
【００６９】
すなわち、本発明の多チャンネルひずみ測定回路によれば、数百Ωのオン抵抗を持つスイッチを使用してもその誤差を除去して適正なひずみ測定データを得ることができる（（８）式を参照されたい）。このような、本発明に従った多チャンネルひずみ測定回路により得られる効果は、半永久的な長寿命化、切替えの高速化、そして低価格化と多岐にわたっている。
図１の本発明の実施の形態に係る多チャンネルひずみ測定回路の構成と図１３の従来回路の構成とを比較すれば明らかであるが、本発明方式による追加回路部品は、数個の利得設定抵抗を伴う２個のバッファ増幅器と数個のモード切り換えスイッチだけである。これらの部品は、従来の構成に用いられている回路部品と比較して特に高精度である必要はなく、同程度の部品でよい。したがって、多チャンネルのひずみ測定システムを構成する場合にも僅かな部品追加で本発明に係る多チャンネルひずみ測定回路を実施することが可能である。
【００７０】
また、上述した構成においては、１ゲージ法測定モードと２ゲージ法測定モードに定電流励振を採用したことにより、定電圧励振で見られるようなひずみゲージの抵抗値変化によるブリッジの当該辺を流れる電流変化により生じるブリッジ出力の非直線性の発生が無く、ひずみゲージ抵抗値変化に完全に比例した出力が得られる（（１５）式を参照されたい）。
なお、１ゲージ法測定モードおよび２ゲージ法測定モードにおける定電流方式のひずみ測定回路は、図１５および図１６にそれぞれ示すような回路が典型的である。図１５および図１６のいずれにおいても２個の定電流電源ＣＣＳ１およびＣＣＳ２を具備し、それら定電流電源ＣＣＳ１およびＣＣＳ２の出力電流は、ブリッジ基準電圧Ｅｉｎをもとにして作られ、両方とも同じ値（Ｉ１）である。これら定電流電源ＣＣＳ１およびＣＣＳ２の出力電流Ｉ１が、図１５の構成では、ひずみゲージＧａおよびブリッジ構成用抵抗Ｒｂにそれぞれ供給され、図１６の構成では、ひずみゲージＧａおよびＧｂにそれぞれ供給されて、出力電位Ｅ１およびＥ２を得る。これら出力電位Ｅ１とＥ２との間の電圧を差動増幅器ＡＭＰ１０で抽出している。
【００７１】
これら図１５および図１６の回路でも、ひずみゲージの抵抗値変化に比例した出力を得ることができるが、２個の定電流源ＣＣＳ１およびＣＣＳ２を使用することにより、それぞれの電流源固有の独立したノイズが重畳した出力となるため、そのノイズは差動増幅器ＡＭＰ１において充分に除去することはできず、定電圧励振に比して高精度な測定には不向きであった。本発明に係る図１の回路では、定電流源は１個であるから、定電流源自身が持つノイズやゆっくりとしたノイズである漂動は、同相成分として正負両方のひずみ出力に重畳するので差動増幅器で効果的に除去することができる。したがって、従来の定電流励振電源によるひずみ測定回路と比較しても、より高精度で且つ高安定な測定が可能となる。
また、モード切替え用スイッチ素子ＳＷ１〜ＳＷ６によるモード切替えは、予め各チャンネルの適用モードを、目視または接続記録メモ等に従ってマニュアル操作で不揮発性の記憶手段等に登録しておき、チャンネルの切替え走査に伴って登録された測定モードに従って逐次モード切替え用スイッチ素子ＳＷ１〜ＳＷ６を切り替えるようにしても良い。
【００７２】
しかしながら、接続端子Ｔａ〜Ｔｄに対するひずみゲージの測定モードに従った接続状態は、接続端子Ｔａ〜Ｔｄにおける端子間の抵抗値等パラメータに基づいて判別することが可能であるので、自動的に、各チャンネルの接続端子Ｔａ〜Ｔｄを順次走査して、各チャンネル毎の測定モードを判別して登録する手段をさらに設け、最初の測定時、測定走査時にその都度、または一定期間毎に、測定に先立って各チャンネルの接続端子Ｔａ〜Ｔｄを順次走査して、各チャンネル毎の測定モードを判別して登録し、チャンネルの切替え走査に伴って登録された測定モードに従って逐次モード切替え用スイッチ素子ＳＷ１〜ＳＷ６を切り替えるようにしても良い。
【００７３】
【発明の効果】
以上述べたように、本発明によれば、１ゲージ法測定モード、２ゲージ法測定モードおよび４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、ブリッジ構成用抵抗を全チャンネルで共用することを可能とし且つブリッジ内の切替え素子として半導体リレー等の高オン抵抗値の切替え素子を使用することを可能とする多チャンネルひずみ測定回路を提供することができる。
すなわち、本発明の請求項１の多チャンネルひずみ測定回路によれば、ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することによって、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することにより、特に、少なくとも１ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００７４】
また、本発明の請求項２の多チャンネルひずみ測定回路によれば、ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、前記２ゲージ法測定モードによる測定時には、第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流して、定電流の分流阻止と電位抽出のために用いられる第１のバッファ増幅器および第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することによって、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することにより、特に、少なくとも２ゲージ法測定モードにおいて、定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、ブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００７５】
本発明の請求項３の多チャンネルひずみ測定回路によれば、請求項１または請求項２の多点ひずみ測定回路において、前記１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における前記ブリッジ励振電流を供給するブリッジ励振電源を、単一の定電流源で構成することにより、ブリッジ方式における非直線性を無くし、各ひずみゲージの抵抗値変化に比例した出力を得ることにより、特に、１ゲージ法測定モードおよび２ゲージ法測定モードの少なくとも一方における非直線性を防止し且つブリッジ励振電源を全チャンネルで共用することが可能となる。
【００７６】
本発明の請求項４の多チャンネルひずみ測定回路によれば、ひずみゲージを接続するための所定の第１、第２、第３および第４の端子を各チャンネル毎に有し、前記第１の端子と前記第２の端子との間に単一のひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間が短絡される１ゲージ法測定モードと、前記第１の端子と前記第２の端子との間に１つのひずみゲージが接続され且つ前記第２の端子と前記第３の端子との間に他の１つのひずみゲージが接続される２ゲージ法測定モードと、前記第１の端子と前記第２の端子との間、前記第２の端子と前記第３の端子との間、前記第３の端子と前記第４の端子との間、そして前記第４の端子と前記第１の端子との間にそれぞれ１つずつの異なる４個のひずみゲージがそれぞれ接続される４ゲージ法測定モードを含む測定モードで選択的に各チャンネルにひずみゲージを接続し、前記各チャンネルを選択的に切り替えて、各チャンネル毎の前記ひずみゲージによる測定を行なう多チャンネルひずみ測定回路において、少なくとも前記１ゲージ法測定モードおよび２ゲージ法測定モードの測定で使用するブリッジ構成用抵抗素子を全チャンネルで１組だけ具備して各チャンネルに共通に使用し、前記１ゲージ法測定モードによる測定時には、ひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として励振電源よりブリッジ励振電流を流して、第１のバッファ増幅器により、前記ブリッジ励振電流の分流を阻止し且つ前記ひずみゲージの一方の接続端の電位を抽出し、第２のバッファ増幅器により、前記電流経路における前記切替え素子のオン抵抗により発生する電圧を抽出し、前記第１のバッファ増幅器の出力端と第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の第２の抵抗素子と第３の抵抗素子を直列に接続し、これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記ひずみゲージの他方の接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定するとともに、前記２ゲージ法測定モードによる測定時には、前記第１および第２のひずみゲージから切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流として前記励振電源よりブリッジ励振電流を流して、定電流の分流阻止と電位抽出のために用いられる前記第１のバッファ増幅器および前記第２のバッファ増幅器により、アクティブゲージである第１のひずみゲージの一方の接続端およびダミーゲージである第２のひずみゲージの一方の接続端の電位をそれぞれ抽出し、前記第１のバッファ増幅器の出力端と前記第２のバッファ増幅器の出力端との間に、抵抗値の等しいブリッジ構成用の前記第２の抵抗素子と前記第３の抵抗素子を直列に接続し、これら第２の抵抗素子と第３の抵抗素子との相互間の接続点から一方の出力電位を得るともに、前記第１および第２のひずみゲージの各他方の接続端が共通に接続された共通接続端から他方の出力電位を得て、これら両出力電位の差の電圧を測定することによって、前記電流経路に入っている切替え素子のオン抵抗による誤差を除去することにより、特に、少なくとも１ゲージ法および２ゲージ法測定モードにおいて、共通の励振電源による定電流励振を採用し、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源およびブリッジ構成用抵抗素子を全チャンネルで共用することが可能となる。
【００７７】
本発明の請求項５の多チャンネルひずみ測定回路によれば、請求項１〜請求項４のうちのいずれか１項の多チャンネルひずみ測定回路において、前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路に定電圧を供給する定電圧励振回路を含む測定回路を構成することにより、特に、定電圧励振の４ゲージ法測定モードによる測定が可能となる。
【００７８】
本発明の請求項６の多チャンネルひずみ測定回路によれば、請求項１〜請求項５のうちのいずれか１項の多チャンネルひずみ測定回路において、前記４ゲージ法測定モードによる測定時には、４個の前記ひずみゲージからなるブリッジ回路から切替え素子を経て基準抵抗となるブリッジ構成用の前記第１の抵抗素子を通る電流経路で、前記第１の抵抗素子の両端間にあらわれる電圧を所定の電圧とする定電流としてブリッジ励振電流を流す定電流励振回路を含む測定回路を構成することにより、特に、１ゲージ法および２ゲージ法測定モードと実質的に共通の定電流励振を用いる４ゲージ法測定モードによる測定をも可能とし、電流経路における切替え素子のオン抵抗による誤差を除去するとともに、非直線性の発生を防止して、励振電源を全チャンネルで共用することが可能となる。
本発明の請求項７の多チャンネルひずみ測定回路によれば、請求項１〜請求項６のうちのいずれか１項の多チャンネルひずみ測定回路において、前記所定の第１、第２、第３および第４の端子からひずみゲージ側を見た回路特性を検出して、これら第１〜第４の端子に対するひずみゲージの測定モードを判別し、判別された測定モードに応じて測定回路の接続構成を選択設定するモード切替え手段をさらに含むことにより、特に、ひずみゲージの接続状態に応じた測定回路の接続構成の自動的な選択設定が可能となる。
【図面の簡単な説明】
【図１】本発明の一つの実施の形態に係る多チャンネルひずみ測定回路の構成を模式的に示す回路構成図である。
【図２】図１の多チャンネルひずみ測定回路の１ゲージ法測定モードにおける測定回路の接続構成を模式的に示す回路構成図である。
【図３】図２の測定回路において、ひずみゲージを接続するケーブルのリード線抵抗を考慮した場合の接続構成を模式的に示す回路構成図である。
【図４】図３の回路構成を説明するための等価回路を示す回路構成図である。
【図５】図１の多チャンネルひずみ測定回路の２ゲージ法測定モードにおける測定回路の接続構成を模式的に示す回路構成図である。
【図６】図５の測定回路において、ひずみゲージを接続するケーブルのリード線抵抗を考慮した場合の接続構成を模式的に示す回路構成図である。
【図７】図６の回路構成を説明するための等価回路を示す回路構成図である。
【図８】図１の多チャンネルひずみ測定回路の定電圧４ゲージ法測定モードにおける測定回路の接続構成を模式的に示す回路構成図である。
【図９】図８の回路構成を説明するための等価回路を示す回路構成図である。
【図１０】図１の多チャンネルひずみ測定回路の定電流４ゲージ法測定モードにおける測定回路の接続構成を模式的に示す回路構成図である。
【図１１】図１０の回路構成を説明するための等価回路を示す回路構成図である。
【図１２】従来の多チャンネルひずみ測定回路の一例の構成を模式的に示す回路構成図である。
【図１３】従来の多チャンネルひずみ測定回路の他の一例の構成を模式的に示す回路構成図である。
【図１４】従来の定電圧励振による１ゲージ法測定モードにおける非直線性を説明するための真のひずみ量対ひずみゲージブリッジ出力の特性を示す図である。
【図１５】従来一般的に考えられていた定電流励振による１ゲージ法測定モードの原理的な構成を模式的に示す回路構成図である。
【図１６】従来一般的に考えられていた定電流励振による２ゲージ法測定モードの原理的な構成を模式的に示す回路構成図である。
【符号の説明】
Ｅｉｎ 励振電源（基準電圧）
ＡＭＰ１〜ＡＭＰ５ 増幅器
ＳＷ１〜ＳＷ６ モード切替え用のスイッチ素子
Ｒｂ〜Ｒｄ ブリッジ構成用抵抗
Ｔａ〜Ｔｄ 接続端子
Ｓａ〜Ｓｄ，Ｓａ′，Ｓｃ′ 選択走査用のスイッチ素子
ＳＳＷ 走査切替え素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a strain gauge type measurement system on the premise that a strain gauge or a strain gauge type transducer is used, and in particular, predetermined first, second, third and fourth for connecting a strain gauge. A terminal is provided for each channel, a single strain gauge is connected between the first terminal and the second terminal, and a short circuit is established between the second terminal and the third terminal. One strain gauge measurement mode, one strain gauge is connected between the first terminal and the second terminal, and another one is connected between the second terminal and the third terminal. 2-gauge method measurement mode in which a strain gauge is connected; between the first terminal and the second terminal; between the second terminal and the third terminal; Between the fourth terminal and between the fourth terminal and the first terminal A strain gauge is selectively connected to each channel in a measurement mode including a four-gauge method measurement mode in which four different strain gauges are connected to each channel, and each channel is selectively switched. The present invention relates to a multi-channel strain measurement circuit for performing measurement with each strain gauge.
[0002]
[Prior art]
For example, when measuring using a strain gauge or a strain gauge type transducer in strain measurement, this type of strain gauge type measuring device has a plurality of measurement modes due to differences in strain gauge connection methods. Specifically, for example, a 1-gauge method measurement mode using only a single strain gauge, a 2-gauge method measurement mode using two strain gauges in a half-bridge connection, and four strain gauges using a full-bridge connection. The 4-gauge method measurement mode is a typical measurement mode. In general, the connection terminals used to connect strain gauge type measuring instruments have been standardized to some extent, and the connection method such as strain gauges for connection terminals consisting of multiple terminals must be uniquely determined for each measurement mode. There are many. On the measuring instrument side, at least one of the power supply method, power supply location, measurement information, measurement location, and input / output resistance differs depending on these measurement modes, so depending on the measurement mode applied to the connection of strain gauges, etc. Therefore, the measurement mode must be set individually on the measuring instrument side.
[0003]
On the other hand, in strain measurement, it is often necessary to measure a strain at a remote place by connecting the measuring device to a strain gauge installed at a location away from the measuring device via a connection cable. In particular, a large number of various sensors, including strain gauges and strain gauge transducers, are installed in a large number of locations such as dams and large buildings and facilities, or construction sites, and each channel consists of multiple terminals. In a multi-channel measurement system in which measurement is performed by connecting each multi-channel connection terminal via a cable and selectively scanning these multi-channel connection terminals to a measuring instrument, each individual channel is related to the scan connection. You must set the connection mode.
[0004]
<(1) Common use of bridge resistance and restriction of switching elements>
The common use of the bridge resistance and the limitation of the switching element in the conventional multichannel strain measurement circuit will be described.
FIG. 12 shows an example of a conventional general multi-channel distortion measuring circuit. The multi-channel distortion measurement circuit of FIG. 12 includes an excitation power source E1in and amplifiers AMP11, AMP12, AMP13 common to each channel, and terminals T1a, T1b, T1b ′, T1c, T1d, T1d ′, T1d ″, resistors for each channel. R1b, R1c, R1d and switch elements S1a, S1a ′, S1b, S1c, S1c ′, S1d are provided.
The switch elements S1a, S1a ′, S1b, S1c, S1c ′, and S1d constitute a scan switching element SSW1 for each channel in conjunction with each channel, and perform channel scanning by selectively turning on. These scanning switching elements SSW1, their associated switching elements S1a, S1a ′, S1b, S1c, S1c ′, S1d, gauge connection terminals T1a, T1b, T1b ′, T1c, T1d, T1d ′, T1d ″ and for bridge configuration The bridge resistances R1b, R1c, and R1d are shown with a common reference symbol for each channel in order to avoid the complicated explanation due to the increase in the number of digits of the reference symbol and to facilitate understanding. Therefore, each component of each channel is individually provided for each channel even though they are given the same reference numerals.
[0005]
The terminal T1a is connected to each of the switch elements S1a ′ and S1a. The terminal T1b is connected to the switch element S1b. The terminal T1b ′ is connected to the terminal T1c via the resistor R1b. The terminal T1c is connected to each of the switch elements S1c ′ and S1c. The terminal T1d is connected to the switch element S1d. The terminal T1d ′ is connected to the terminal T1c through the resistor R1c. The terminal T1d ″ is connected to the terminal T1a via the resistor R1d. The switch element S1a ′ is connected to the inverting input terminal (−) of the amplifier AMP12, and the switch element S1a is connected to the output terminal of the amplifier AMP12. The switch element S1b is connected to the inverting input terminal (−) of the amplifier AMP11, the switch element S1c ′ is connected to the inverting input terminal (−) of the amplifier AMP13, and the switch element S1c includes The switch element S1d is connected to the non-inverting input terminal (+) of the amplifier AMP11, which has a common configuration for each channel.
The output terminal of one of the excitation power sources E1in, in this case the positive side, is connected to the non-inverting input terminal (+) of the amplifier AMP12, and the other output terminal of the excitation power source E1in, in this case the negative side, is the non-inverting input terminal of the amplifier AMP13. It is connected to each of the inverting input terminal (+) and the common potential (earth).
[0006]
In the case of the 1 gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T1a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is A third end connected to the terminal T1b and connected to the other end of the gauge resistor of the strain gauge Ga in common with the second end is connected to the terminal T1b ′, and the terminals T1d, T1d ′ and the terminal T1d ″ are shunted to each other. Is done.
In the case of the two-gauge measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T1a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is Connected to terminal T1b. The first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the terminal T1b together with the second end of the strain gauge Ga, and the second end connected to the other end of the gauge resistance of the strain gauge Gb is the terminal. Connected to T1c. The terminals T1d, T1d ′ and the terminal T1d ″ are shunted.
[0007]
In the case of the 4-gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T1a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is Connected to terminal T1b. The first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the terminal T1b together with the second end of the strain gauge Ga, and the second end connected to the other end of the gauge resistance of the strain gauge Gb is the terminal. Connected to T1c. A first end connected to one end of the gauge resistance of the strain gauge Gc is connected to the terminal T1c together with the second end of the strain gauge Gb, and a second end connected to the other end of the gauge resistance of the strain gauge Gc is a terminal. Connected to T1d. The first end connected to one end of the gauge resistance of the strain gauge Gd is connected to the terminal T1d together with the second end of the strain gauge Gc, and the second end connected to the other end of the gauge resistance of the strain gauge Gd is The first end of the strain gauge Ga is connected to the terminal T1a.
For the selection switching of the 1 gauge method, 2 gauge method and 4 gauge method measurement mode, each channel corresponding to each measurement point is provided with bridge resistors R1b, R1c and R1d, and connected to the connected strain gauge. The bridge circuit is configured by combination.
[0008]
Since a bridge is formed for each channel, there are many types of switch elements S1a to S1d that can be used for the scan switching element SSW1 for channel switching, and various switch elements can be selected from mechanical relays to semiconductor relays. it can. On the other hand, in the configuration of FIG. 12, three high-precision resistors are required for each channel. For example, when a multi-channel strain measurement system for multi-point measurement having a maximum of 1000 measurement points is configured. It had the disadvantage of becoming expensive. In order to solve such a drawback, only one set of bridge-constituting resistance elements corresponding to the resistances R1b, R1c and R1d in FIG. 12 is provided, and this resistance element is used in common for the measurement of each channel. Strain measuring circuits with a greatly reduced number are also used. A general example of such a strain measurement circuit is shown in FIG.
The multi-channel distortion measurement circuit of FIG. 13 includes an excitation power source E2in common to each channel, amplifiers AMP21, AMP22, AMP23, mode switching switch elements SW21, SW22, SW23, bridge configuration resistors R2b, R2c, R2d, and each Terminals T2a, T2b, T2c, T2d for each channel and switch elements S2a, S2a ′, S2b, S2c, S2c ′, S2d for selective scanning are provided.
[0009]
The switch elements S2a, S2a ′, S2b, S2c, S2c ′, and S2d for selective scanning constitute a scan switching element SSW2 for each channel in conjunction with each channel, and are selectively turned on to operate the channel. Perform selective scanning. These scanning switching elements SSW2, their associated switching elements S2a, S2a ', S2b, S2c, S2c', S2d and gauge connection terminals T2a, T2b, T2c, T2d are denoted by reference numerals as in FIG. In order to avoid the complicated explanation due to the increase in the number and to facilitate the understanding, common reference numerals are given to the respective channels.
Of the switch elements SW21, SW22, and SW23 for mode switching, the switch element SW21 is a changeover switch that selectively switches and connects one movable selection end to one of the two selected ends according to the measurement mode. The switch elements SW22 and SW23 are switches that are turned on / off according to the measurement mode. That is, the switch element SW21 connects the movable selection end to one selected end (1-2G) in the 1 gauge method and the 2 gauge method measurement mode, and connects the movable selection end to the other selected end in the 4 gauge method measurement mode. Connect to the selected end. The switch element SW22 is turned on in the 1 gauge method measurement mode and turned off in the 2 gauge method and the 4 gauge method measurement mode.
[0010]
The switch element SW23 is turned on in the 2 gauge method and the 4 gauge method measurement mode, and is turned off in the 1 gauge method measurement mode.
The terminal T2a is connected to each of the switch elements S2a ′ and S2a. The terminal T2b is connected to the switch element S2b. The terminal T2c is connected to each of the switch elements S2c ′ and S2c. The terminal T2d is connected to the switch element S2d. The switch element S2a ′ is connected to the inverting input terminal (−) of the amplifier AMP22, and the output terminal of the amplifier AMP22 is connected to the switch element S2a. The switch element S2b is connected to the inverting input terminal (−) of the amplifier AMP21. The switch element S2c ′ is connected to the inverting input terminal (−) of the amplifier AMP23 via the switch element SW23 that is turned on in the 2-gauge method and the 4-gauge method measurement mode. The output terminal of the amplifier AMP23 is connected via R2b. The switch element S2d is connected to the other selected end selected in the 4-gauge method measurement mode of the switch element SW21. These are common configurations for each channel.
[0011]
The output terminal of one of the excitation power supplies E2in, in this case, the positive side is connected to the non-inverting input terminal (+) of the amplifier AMP22, and the other output terminal of the excitation power supply E2in, in this case, the negative side, is connected to the non-inverting input terminal of the amplifier AMP23. It is connected to each of the inverting input terminal (+) and the common potential (earth). The bridge configuration resistors R2d and R2c are connected in series, and the end of the series circuit of the bridge configuration resistors R2d and R2c on the side of the resistor R2d is connected to the non-inverting input terminal (+) of the amplifier AMP22. The end of the series circuit of the resistors R2d and R2c on the resistor R2c side is connected to the non-inverting input terminal (+) of the amplifier AMP23. The mutual connection point of the bridge configuration resistors R2d and R2c is connected to the one selected end selected in the 1 gauge method and the 2 gauge method measurement mode of the switch element SW21. The movable selection end of the switch element SW21 is connected to the non-inverting input end (+) of the amplifier AMP21. A switch element SW22 that is turned on in the 1-gauge method measurement mode is connected between the inverting input terminal (−) and the output terminal of the amplifier AMP23.
In the case of the 1 gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T2a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is A third end connected to the terminal T2b and connected to the other end of the gauge resistance of the strain gauge Ga in common with the second end is connected to the terminal T2c.
[0012]
In the two-gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T2a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is Connected to terminal T2b. A first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the terminal T2b together with the second end of the strain gauge Ga, and a second end connected to the other end of the gauge resistance of the strain gauge Gb is a terminal. Connected to T2c.
In the case of the 4-gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the terminal T2a, and the second end connected to the other end of the gauge resistance of the strain gauge Ga is Connected to terminal T2b. A first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the terminal T2b together with the second end of the strain gauge Ga, and a second end connected to the other end of the gauge resistance of the strain gauge Gb is a terminal. Connected to T2c. A first end connected to one end of the gauge resistance of the strain gauge Gc is connected to the terminal T2c together with the second end of the strain gauge Gb, and a second end connected to the other end of the gauge resistance of the strain gauge Gc is a terminal. Connected to T2d. A first end connected to one end of the gauge resistance of the strain gauge Gd is connected to the terminal T2d together with the second end of the strain gauge Gc, and a second end connected to the other end of the gauge resistance of the strain gauge Gd is Together with the first end of the strain gauge Ga, it is connected to the terminal T2a.
[0013]
The measurement circuit of FIG. 13 has only one set of bridge configuration resistors R2b, R2c, R2d for all measurement points, that is, all channels, and is used in common for each channel. When the 1 gauge method measurement mode is connected in this circuit, the switch element for selective scanning of the scan switching element SSW2 (switch element S2c in the example of FIG. 13) enters the side of the bridge. It is necessary to use a switch having a low resistance value, that is, an on-resistance, for example, a mechanical switch having an on-resistance of several mΩ or less. That is, the semiconductor switch has a high on-resistance of several Ω to several tens of Ω and cannot be used in the circuit as shown in FIG.
However, unlike semiconductor switches that can be used semi-permanently, mechanical switches have a lifetime of 10 ⁷ -10 ⁸ About times. In particular, in the case of multi-channels, the ratio of the number of switch elements of the switching element in the entire measurement system is large, and the system shown in FIG. 13 has a major drawback in terms of failure rate. Also, the advantages of semiconductor switches in terms of switching speed and component price are increasing year by year, and from this point of view, the resistance element for bridge configuration can be shared by each channel, and semiconductor switches can be used as switching elements. The realization of a circuit that can be used has been awaited.
[0014]
<(2) Non-linearity in the 1 gauge method>
In the measurement of the one gauge method in which a bridge including a strain gauge is excited using a constant voltage excitation power source, the current flowing through the strain gauge itself changes due to a change in the resistance value of the strain gauge. For this reason, there is a problem that the bridge output does not become linear with respect to the change in the resistance value of the strain gauge, that is, the strain output. The influence of the error due to this problem is shown in FIG. 14 as the relationship between the true strain amount and the bridge output. As shown in FIG. 14, for a positive strain, the current flowing through the strain gauge decreases as the resistance value of the strain gauge increases, and the output voltage of the bridge is obtained by multiplying the resistance value change of the strain gauge and the current value. Therefore, the actual bridge output voltage becomes smaller with respect to the true distortion amount. On the other hand, for negative strain, the value of the current flowing through the strain gauge increases, so that the actual bridge output voltage increases with respect to the true strain amount. The relationship between the true strain amount ε and the bridge output Eo is expressed by the following equation.
[0015]
[Expression 1]

[0016]
This is referred to as “one-gauge bridge nonlinearity”, and if the error due to this nonlinearity cannot be ignored, it is necessary to perform correction processing according to equation (1) simultaneously with or after the measurement. there were.
Even in the 2-gauge method measurement mode, when the strain to be measured is received by the first strain gauge as the active gauge and the second strain gauge is used as a dummy gauge for temperature compensation, Since the bridge exhibits substantially the same characteristics as in the case of the 1 gauge method, the nonlinearity as described above occurs.
[0017]
[Problems to be solved by the invention]
As described above, a strain gauge for measuring at each measurement point is connected to each channel, and each channel is selectively switched to perform multi-channel strain measurement with the strain gauge for each channel. In a measurement circuit, a set of bridge configuration resistance elements can be shared by each channel, and as a switching element in the bridge, a conventional on-resistance value is too high to be used, such as a semiconductor relay. The realization of a circuit that can use a switching element having a high on-resistance value has been awaited. Further, in the one-gauge method measurement mode and the two-gauge method measurement mode in which one of the two strain gauges is used as an active gauge and the other is used as a dummy gauge, there is a problem that a measurement error due to bridge nonlinearity of the so-called one-gauge method occurs. there were.
The present invention has been made in view of the above-described circumstances. A strain gauge is selectively connected to each channel in a measurement mode including a 1 gauge method measurement mode, a 2 gauge method measurement mode, and a 4 gauge method measurement mode. In a multi-channel strain measurement circuit that selectively switches each channel and performs measurement with the strain gauge for each channel, it is possible to share the resistance for the bridge configuration in all channels, and a semiconductor relay as a switching element in the bridge An object of the present invention is to provide a multi-channel distortion measuring circuit that makes it possible to use a switching element having a high on-resistance value.
[0018]
That is, the object of claim 1 of the present invention is to employ constant current excitation, particularly in at least one gauge method measurement mode, to eliminate errors due to the on-resistance of the switching element in the current path, and to generate non-linearity. An object of the present invention is to provide a multi-channel distortion measuring circuit which can prevent and share a bridge-forming resistance element in all channels.
The object of claim 2 of the present invention is to employ constant current excitation, particularly in at least the two-gauge measurement mode, to eliminate errors due to the on-resistance of the switching element in the current path, and to generate non-linearity. An object of the present invention is to provide a multi-channel distortion measuring circuit which can prevent and share a bridge-forming resistance element in all channels.
The object of claim 3 of the present invention is to provide a multi-channel which can prevent non-linearity in at least one of the 1-gauge method measurement mode and the 2-gauge method measurement mode, and can share the bridge excitation power source for all channels. It is to provide a strain measurement circuit.
[0019]
The object of claim 4 of the present invention is to adopt constant current excitation by a common excitation power source, particularly in at least the 1 gauge method and the 2 gauge method measurement mode, and to eliminate an error due to the ON resistance of the switching element in the current path. Another object of the present invention is to provide a multi-channel distortion measuring circuit that prevents the occurrence of non-linearity and makes it possible to share the excitation power source and the bridge configuration resistance element in all channels.
A fifth object of the present invention is to provide a multi-channel distortion measuring circuit that enables measurement in a 4-gauge method measurement mode of constant voltage excitation.
The object of claim 6 of the present invention is to enable the measurement in the 4-gauge method measurement mode using constant current excitation substantially common to the 1-gauge method and the 2-gauge method measurement mode. An object of the present invention is to provide a multi-channel distortion measuring circuit that eliminates errors due to on-resistance and prevents the occurrence of nonlinearity, and enables an excitation power source to be shared by all channels.
A seventh object of the present invention is to provide a multi-channel strain measurement circuit that enables automatic selection and setting of the connection configuration of the measurement circuit according to the connection state of the strain gauge.
[0020]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the multi-channel distortion measuring circuit according to the present invention described in claim 1 is provided.
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. By measuring the voltage of the difference, an error due to the on-resistance of the switching element in the current path is removed.
[0021]
In order to achieve the above-mentioned object, the multi-channel distortion measuring circuit according to the present invention described in claim 2 is provided.
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the two-gauge method measurement mode, both ends of the first resistance element are passed through a current path that passes from the first and second strain gauges through the switching element and through the first resistance element for bridge configuration that becomes a reference resistance. Let the bridge excitation current flow as a constant current with the voltage appearing between
The first buffer amplifier and the second buffer amplifier, which are used for blocking the constant current shunting and extracting the potential, have one connection end of the first strain gauge as the active gauge and the second strain gauge as the dummy gauge. Extract the potential at one connection end of
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. By obtaining the other output potential from the connection end and measuring the voltage between the two output potentials, an error due to the on-resistance of the switching element in the current path is eliminated.
[0022]
A multi-channel strain measurement circuit according to the present invention described in claim 3 is the multi-point strain measurement circuit according to claim 1 or claim 2, wherein
By configuring the bridge excitation power source that supplies the bridge excitation current in at least one of the 1 gauge method measurement mode and the 2 gauge method measurement mode with a single constant current source, the nonlinearity in the bridge system is eliminated, The output is proportional to the change in resistance value of the strain gauge.
[0023]
In order to achieve the above-mentioned object, the multi-channel distortion measuring circuit according to the present invention described in claim 4 is provided.
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow from the excitation power source as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. While measuring the difference voltage,
At the time of measurement in the two-gauge method measurement mode, the first resistance element is a current path that passes from the first and second strain gauges through the switching element to the bridge-structured first resistance element serving as a reference resistance. The bridge excitation current is passed from the excitation power source as a constant current with a voltage appearing between both ends of the
By means of the first buffer amplifier and the second buffer amplifier used for preventing a constant current from being shunted and extracting a potential, one connection end of the first strain gauge which is an active gauge and a second gauge which is a dummy gauge are used. Extract the potential at one end of the strain gauge,
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, the second resistance element and the third resistance element for bridge configuration having the same resistance value are connected in series. ,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. Obtain the other output potential from the connection end and measure the voltage difference between these two output potentials.
Thus, an error due to the on-resistance of the switching element in the current path is removed.
[0024]
The multi-channel distortion measuring circuit according to the present invention described in claim 5 is the multi-channel distortion measuring circuit according to any one of claims 1 to 4,
In the measurement in the 4-gauge method measurement mode, a measurement circuit including a constant voltage excitation circuit for supplying a constant voltage to a bridge circuit including the four strain gauges is configured.
The multi-channel distortion measuring circuit according to the present invention described in claim 6 is the multi-channel distortion measuring circuit according to any one of claims 1 to 5,
At the time of measurement in the 4-gauge method measurement mode, the first resistor is connected through a current path that passes from the bridge circuit composed of the four strain gauges through the switching element to the bridged first resistance element serving as a reference resistance. The measuring circuit includes a constant current excitation circuit that causes a bridge excitation current to flow as a constant current with a voltage appearing between both ends of the element as a predetermined voltage.
[0025]
A multi-channel distortion measurement circuit according to the present invention described in claim 7 is the multi-channel distortion measurement circuit according to any one of claims 1 to 6,
The circuit characteristics of the first, second, third, and fourth terminals as viewed from the strain gauge side are detected, and the strain gauge measurement modes for these first to fourth terminals are determined to be determined. It further includes mode switching means for selectively setting the connection configuration of the measurement circuit in accordance with the measurement mode.
[0026]
[Action]
That is, the multi-channel distortion measuring circuit according to claim 1 of the present invention is:
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. By measuring the difference voltage, an error caused by the on-resistance of the switching element in the current path is removed.
[0027]
With such a configuration, a strain gauge is selectively connected to each channel in a measurement mode including a 1 gauge method measurement mode, a 2 gauge method measurement mode, and a 4 gauge method measurement mode, and each channel is selectively switched, The multi-channel strain measurement circuit that performs measurement with the strain gauge for each channel employs constant current excitation, particularly in at least one gauge method measurement mode, and removes an error due to the on-resistance of the switching element in the current path. It is possible to prevent the occurrence of non-linearity and share the bridge configuration resistance element in all channels.
[0028]
A multi-channel distortion measuring circuit according to claim 2 of the present invention is
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the two-gauge method measurement mode, both ends of the first resistance element are passed through a current path that passes from the first and second strain gauges through the switching element and through the first resistance element for bridge configuration that becomes a reference resistance. Let the bridge excitation current flow as a constant current with the voltage appearing between
The first buffer amplifier and the second buffer amplifier, which are used for blocking the constant current shunting and extracting the potential, have one connection end of the first strain gauge as the active gauge and the second strain gauge as the dummy gauge. Extract the potential at one connection end of
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. By obtaining the other output potential from the connection end and measuring the voltage difference between the two output potentials, an error due to the on-resistance of the switching element in the current path is eliminated.
With such a configuration, in particular, at least in the 2-gauge method measurement mode, constant current excitation is adopted, and an error due to the on-resistance of the switching element in the current path is removed, and the occurrence of non-linearity is prevented. It is possible to share the resistance element for all channels.
[0029]
A multi-channel strain measurement circuit according to claim 3 of the present invention is the multi-point strain measurement circuit according to claim 1 or 2, wherein the bridge excitation current in at least one of the 1-gauge method measurement mode and the 2-gauge method measurement mode is determined. By configuring the bridge excitation power supply to be a single constant current source, the nonlinearity in the bridge system is eliminated, and an output proportional to the resistance value change of each strain gauge is obtained.
With such a configuration, it is possible to prevent non-linearity in at least one of the 1 gauge method measurement mode and the 2 gauge method measurement mode, and to share the bridge excitation power source in all channels.
[0030]
A multi-channel distortion measuring circuit according to claim 4 of the present invention is
A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow from the excitation power source as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. While measuring the difference voltage,
At the time of measurement in the two-gauge method measurement mode, the first resistance element is a current path that passes from the first and second strain gauges through the switching element to the bridge-structured first resistance element serving as a reference resistance. The bridge excitation current is passed from the excitation power source as a constant current with a voltage appearing between both ends of the
By means of the first buffer amplifier and the second buffer amplifier used for preventing a constant current from being shunted and extracting a potential, one connection end of the first strain gauge which is an active gauge and a second gauge which is a dummy gauge are used. Extract the potential at one end of the strain gauge,
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, the second resistance element and the third resistance element for bridge configuration having the same resistance value are connected in series. ,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. By obtaining the other output potential from the connection end and measuring the voltage difference between the two output potentials, an error due to the on-resistance of the switching element in the current path is eliminated.
With such a configuration, in particular, at least in the 1-gauge method and the 2-gauge method measurement mode, constant current excitation by a common excitation power source is adopted, an error due to the on-resistance of the switching element in the current path is removed, and nonlinearity is achieved. Therefore, it is possible to share the excitation power source and the bridge configuration resistance element in all channels.
[0031]
The multi-channel strain measurement circuit according to claim 5 of the present invention is the multi-channel strain measurement circuit according to any one of claims 1 to 4, wherein the four-channel strain measurement circuit is configured to measure the four channel strain measurement circuits in the 4-gauge method measurement mode. A measurement circuit including a constant voltage excitation circuit for supplying a constant voltage to a bridge circuit made of a strain gauge is configured.
With such a configuration, in particular, measurement in a constant voltage excitation 4 gauge method measurement mode is possible.
The multi-channel strain measurement circuit according to claim 6 of the present invention is the multi-channel strain measurement circuit according to any one of claims 1 to 5, wherein the four channel strain measurement circuits are configured to perform the measurement in the four-gauge method measurement mode. In a current path that passes from the bridge circuit composed of a strain gauge through the switching element to the first resistance element for bridge configuration that serves as a reference resistance, a voltage that appears between both ends of the first resistance element is defined as a predetermined voltage. A measurement circuit including a constant current excitation circuit that supplies a bridge excitation current as a current is configured.
With such a configuration, it is possible to perform measurement in the 4-gauge method measurement mode using constant current excitation substantially in common with the 1-gauge method and the 2-gauge method measurement mode, and an error due to the on-resistance of the switching element in the current path. And the occurrence of non-linearity can be prevented, and the excitation power supply can be shared by all channels.
[0032]
A multi-channel distortion measuring circuit according to a seventh aspect of the present invention is the multi-channel distortion measuring circuit according to any one of the first to sixth aspects, wherein the predetermined first, second, third and fourth. Detects the circuit characteristics when the strain gauge side is viewed from the terminals, determines the strain gauge measurement mode for these first to fourth terminals, and selects and sets the connection configuration of the measurement circuit according to the determined measurement mode Further, mode switching means is included.
With such a configuration, in particular, it is possible to automatically select and set the connection configuration of the measurement circuit according to the connection state of the strain gauge.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, based on the embodiment concerning the present invention, the multichannel distortion measuring circuit of the present invention is explained in detail with reference to drawings.
FIG. 1 shows a specific circuit configuration of a multi-channel distortion measuring circuit according to one embodiment of the present invention.
The multi-channel distortion measurement circuit shown in FIG. 1 includes an excitation power source Ein, amplifiers AMP1, AMP2, AMP3, AMP4, AMP5, mode switching switch elements SW1, SW2, SW3, SW4, SW5, SW6, common to each channel. The bridge configuration resistors Rb, Rc, Rd, and connection terminals Ta, Tb, Tc, Td and selective scanning switch elements Sa, Sa ′, Sb, Sc, Sc ′, Sd are provided for each channel. doing.
The switch elements Sa, Sa ′, Sb, Sc, Sc ′, and Sd for selective scanning constitute a scanning switching element SSW for each channel in conjunction with each channel, and are selectively turned on in units of channels. Thus, channel selective scanning is performed. These scanning switching elements SSW, their associated switching elements Sa, Sa ′, Sb, Sc, Sc ′, Sd and gauge connection connection terminals Ta, Tb, Tc, Td are explained by increasing the number of digits of the reference symbols. In order to avoid complications and facilitate understanding, common reference numerals are assigned to the respective channels.
[0034]
FIG. 1 shows only three of the multi-channels, but it goes without saying that the same configuration is applied to multi-channels of four or more channels.
Each of the switch elements SW1 to SW6 for mode switching is a changeover switch that selectively connects one movable selection end to either one of the two selected ends according to the measurement mode. That is, the switch element SW1 connects the movable selection end to one selected end (1-2G) in the 1 gauge method measurement mode (1G) and the 2 gauge method measurement mode (2G), and performs the constant voltage 4 gauge method measurement. In the mode (4G) and the constant current 4-gauge method measurement mode (4GI), the movable selection end is connected to the other selected end (4G / 4GI). In the 1-gauge method measurement mode (1G), the 2-gauge method measurement mode (2G), and the constant current 4-gauge method measurement mode (4GI), the switch element SW2 has one movable selected end (1-2G / 4GI). In the constant voltage 4-gauge method measurement mode (4G), the movable selection end is connected to the other selected end (4G). In the 1-gauge method measurement mode (1G), the 2-gauge method measurement mode (2G), and the constant current 4-gauge method measurement mode (4GI), the switch element SW3 has one movable selection end (1-2G / 4GI). In the constant voltage 4-gauge method measurement mode (4G), the movable selection end is connected to the other selected end (4G).
[0035]
In the 1 gauge method measurement mode (1G), the 2 gauge method measurement mode (2G), and the constant current 4 gauge method measurement mode (4GI), the switch element SW4 has a movable selection end as one of the selected ends (1-2G / 4GI). In the constant voltage 4-gauge method measurement mode (4G), the movable selection end is connected to the other selected end (4G). In the 1-gauge method measurement mode (1G), the 2-gauge method measurement mode (2G), and the constant current 4-gauge method measurement mode (4GI), the switch element SW5 has one movable selection end (1-2G / 4GI). In the constant voltage 4-gauge method measurement mode (4G), the movable selection end is connected to the other selected end (4G). In the 2 gauge method measurement mode (2G), the constant voltage 4 gauge method measurement mode (4G), and the constant current 4 gauge method measurement mode (4GI), the switch element SW6 has one movable selected end (2G / 4G). / 4GI), and in the 1 gauge method measurement mode (1G), the movable selection end is connected to the other selected end.
The connection terminal Ta is connected to each of the selective scanning switch elements Sa ′ and Sa. The connection terminal Tb is connected to the switch element Sb for selective scanning. The connection terminal Tc is connected to each of the switching elements Sc ′ and Sc for selective scanning.
[0036]
The connection terminal Td is connected to the switch element Sd. The switch element Sa ′ for selective scanning is connected to the movable selection end of the switch element SW4 for mode switching, and the output terminal of the amplifier AMP2 is connected to the switch element Sa for selective scanning. The switch element Sb for selective scanning is connected to the inverting input terminal (−) of the amplifier AMP1. The switch element Sc ′ for selective scanning is connected to the movable selection end of the switch element SW2 for mode switching, and the switch element Sc for selective scanning is connected to the movable selection end of the switch element SW3 for mode switching. . The switch element Sd for selective scanning is connected to the other selected end selected in the constant voltage 4 gauge method measurement mode (4G) and the constant current 4 gauge method measurement mode (4GI) of the mode switching switch element SW1. Has been. These are common configurations for each channel.
The output terminal of one of the excitation power supplies Ein, in this case, the positive side is connected to the non-inverting input terminal (+) of the amplifier AMP2, and the other output terminal of the excitation power supply Ein, in this case, the negative side, is connected to the non-inverting input terminal of the amplifier AMP3. It is connected to each of the inverting input terminal (+) and the common potential (earth). The movable selection terminal of the switch element SW5 for mode switching is connected to the inverting input terminal (−) of the amplifier AMP2.
[0037]
The other selected end selected in the constant voltage 4 gauge method measurement mode (4G) of the switching element SW2 for mode switching is connected to the inverting input terminal (−) of the amplifier AMP3. The one selected end selected in the 1-gauge method measurement mode (1G), 2-gauge method measurement mode (2G) and constant current 4-gauge method measurement mode (4GI) of the switch element SW2 for mode switching is the switch element The SW5 is connected to the one selected end selected in the 1 gauge method measurement mode (1G), the 2 gauge method measurement mode (2G), and the constant current 4 gauge method measurement mode (4GI), and the switch element SW6 It is connected to each of the selected ends selected in the 1 gauge method measurement mode (1G). The one selected end selected in the 1-gauge method measurement mode (1G), the 2-gauge method measurement mode (2G), and the constant current 4-gauge method measurement mode (4GI) of the switch element SW5 for mode switching is a bridge configuration. It is connected to the common potential via the resistor Rb. The other selected end selected in the constant voltage 4 gauge method measurement mode (4G) of the switching element SW5 for mode switching is the other selected end in the constant voltage 4 gauge method measurement mode (4G) of the switch element SW4. Connected to the selected end. The output terminal of the amplifier AMP3 is connected to the other selected terminal selected in the constant voltage 4-gauge method measurement mode (4G) of the switch element SW3.
[0038]
The one selected end selected in the 1-gauge method measurement mode (1G), the 2-gauge method measurement mode (2G) and the constant current 4-gauge method measurement mode (4GI) of the switch element SW4 is the non-inverting input of the amplifier AMP4. Connected to the end (+). The output terminal of the amplifier AMP4 is connected to the inverting input terminal (−) of the amplifier AMP4. The one selected end selected in the 1-gauge method measurement mode (1G), 2-gauge method measurement mode (2G) and constant current 4-gauge method measurement mode (4GI) of the switching element SW3 for mode switching is the amplifier AMP5. Is connected to the non-inverting input terminal (+). The movable selection terminal of the switch element SW6 is connected to the inverting input terminal (−) of the amplifier AMP5. The one selected end selected in the 2-gauge method measurement mode (2G), the constant voltage 4-gauge method measurement mode (4G) and the constant current 4-gauge method measurement mode (4GI) of the switching element SW6 for mode switching The output terminal of the amplifier AMP5 is connected. The bridge configuration resistors Rd and Rc are connected in series. The end of the series circuit of the bridge configuration resistors Rd and Rc on the side of the resistor Rd is connected to the output end of the amplifier AMP4, and the bridge configuration resistors Rd and Rc. The end of the series circuit on the resistor Rc side is connected to the output terminal of the amplifier AMP5. The mutual connection point of the bridge configuration resistors Rd and Rc is connected to the one selected end selected in the 1 gauge method measurement mode (1G) and the 2 gauge method measurement mode (2G) of the switch element SW1. .
[0039]
In the 1-gauge method measurement mode, a so-called three-wire strain gauge is used as the strain gauge Ga, and the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the connection terminal Ta, and the strain gauge Ga The second end connected to the other end of the gauge resistance of the gauge Ga is connected to the connection terminal Tb, and the third end connected to the other end of the gauge resistance of the strain gauge Ga in common with the second end is the connection terminal Tc. Connected to.
In the two-gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the connection terminal Ta, and the second end connected to the other end of the gauge resistance of the strain gauge Ga. Is connected to the connection terminal Tb. The first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the connection terminal Tb together with the second end of the strain gauge Ga, and the second end connected to the other end of the gauge resistance of the strain gauge Gb is Connected to the connection terminal Tc.
In the case of the 4-gauge method measurement mode, the first end connected to one end of the gauge resistance of the strain gauge Ga is connected to the connection terminal Ta in both the constant voltage excitation and the constant current excitation. The second end connected to the other end of the gauge resistor is connected to the connection terminal Tb.
[0040]
The first end connected to one end of the gauge resistance of the strain gauge Gb is connected to the connection terminal Tb together with the second end of the strain gauge Ga, and the second end connected to the other end of the gauge resistance of the strain gauge Gb is Connected to the connection terminal Tc. The first end connected to one end of the gauge resistance of the strain gauge Gc is connected to the connection terminal Tc together with the second end of the strain gauge Gb, and the second end connected to the other end of the gauge resistance of the strain gauge Gc is Connected to the connection terminal Td. The first end connected to one end of the gauge resistance of the strain gauge Gd is connected to the connection terminal Td together with the second end of the strain gauge Gc, and the second end connected to the other end of the gauge resistance of the strain gauge Gd is The strain gauge Ga is connected to the connection terminal Ta together with the first end. In FIG. 1, a strain gauge is connected to the first channel according to the 1 gauge method measurement mode, the second channel according to the 2 gauge method measurement mode, and the third channel according to the 4 gauge method measurement mode. Of course, the strain gauge may be connected to any channel in any measurement mode.
[0041]
The bridge constituting resistors Rb, Rc and Rd constitute a bridge in combination with a strain gauge. The bridge excitation power supply Ein supplies a reference voltage for bridge excitation. The amplifier AMP1 is a differential amplifier that amplifies the bridge output, the amplifier AMP2 is a first power amplifier for bridge excitation, and the amplifier AMP3 is a second power amplifier for bridge excitation. The amplifier AMP4 is a first buffer amplifier for preventing the bridge excitation current from being shunted to the sides of the resistors Rd and Rc, and the amplifier AMP5 depends on the resistance of the switching element when connected in the 1-gauge method measurement mode. A second amplifier that operates as a differential amplifier that extracts a voltage generation amount and operates as a buffer that prevents a branch current from being shunted to the sides of the resistors Rd and Rc when connected in the two-gauge measurement mode, similarly to the amplifier AMP4. It is a buffer amplifier. The switch elements SW1 to SW6 for mode switching are switches for connecting each circuit element according to a required measurement method according to the measurement mode. In FIG. 1, the switching elements SW1 to SW6 for mode switching are shown in the selected state in the 2-gauge method measurement mode, and the switching element Sa for selective scanning that constitutes the scanning switching element SSW for each channel. , Sa ′, Sb, Sc, Sc ′, Sd are shown as non-selected states.
Hereinafter, the connection state and operation for each measurement mode in the multi-channel distortion measurement circuit shown in FIG. 1 will be described.
[0042]
<(1) 1 gauge method>
In the configuration of the multi-channel strain measurement circuit of FIG. 1, when connected as a one-gauge method measurement mode, that is, the mode-switching switch elements SW1 to SW5 are selected as shown in FIG. FIG. 2 shows a substantial circuit when the switch element SW6 for mode switching is in a state where a selected end different from that in FIG. 1 is selected. FIG. 2 shows only elements and circuits related to the operation in the 1 gauge measurement mode. For example, among the switch elements SW1 to SW6 for mode switching, only the switch element SW2 is shown in FIG. 2, but the switch elements SW1 and SW3 to SW6 for mode switching other than the switch element SW2 are These characteristics are not clearly shown on the circuit of FIG. 2 because they do not substantially affect the measurement accuracy.
That is, in the connection state shown in FIG. 2, the connection point of the bridge-constituting resistors Rd and Rc is connected to the non-inverting input terminal (+) of the amplifier AMP1, and is selected as the non-inverting input terminal (+) of the amplifier AMP5. The scanning switch element Sc is connected, the selective scanning switch element Sa ′ is connected to the non-inverting input terminal (+) of the amplifier AMP4, and the inverting input terminal (−) of the amplifier AMP2 is a bridge configuration. It is connected to the common potential via the resistor Rb.
[0043]
A switch element Sc ′ for selective scanning is connected to the inverting input terminal (−) of the amplifier AMP2 via a switch element SW2 for mode switching. The inverting input terminal (−) of the amplifier AMP5 is connected to the inverting input terminal (−) of the amplifier AMP2.
In this state, a constant current is passed through the strain gauge Ga through the path of the amplifier AMP2, the connection terminal Ta, the strain gauge Ga, the connection terminal Tc, the switch element Sc ′, the switch element SW2, and the resistor Rb. The current is a constant current controlled by the amplifier AMP2 so that the voltage across the bridge configuration resistor Rb is equal to the reference voltage (Ein) of the bridge excitation power supply Ein.
The buffer amplifier AMP4 extracts the potential of the connection terminal Ta connected to the first end corresponding to one end of the gauge resistance of the strain gauge Ga, and further switches the current path selection scanning switch Sc 'and the mode switching function. An error voltage generated by the current flowing into the ON resistance (several hundreds Ω or less) of the switch element SW2 is extracted by the amplifier AMP5, and has an equal resistance value between the output terminals of the amplifier AMP4 and the amplifier AMP5. A circuit in which a series circuit of bridge configuration resistors Rd and Rc is inserted is configured, and one output potential corresponding to a positive output in the conventional bridge circuit is obtained from the connection point of the resistors Rd and Rc.
[0044]
Further, the other output potential corresponding to the negative output in the conventional bridge circuit is obtained from the connection terminal Tb connected to the second end corresponding to the other end of the gauge resistance of the strain gauge Ga.
The voltage between these positive and negative output potentials is an output proportional to the change in resistance value of the strain gauge, that is, a strain output. In this embodiment, the differential amplifier AMP1 extracts the difference voltage between the positive and negative output potentials and amplifies it if necessary.
In the configuration of FIG. 2, a circuit configuration in consideration of the resistance value of the lead wire in the strain gauge Ga connection cable is shown in FIG. 3. The resistance value RL inserted between the strain gauge Ga and the connection terminals Ta, Tb and Tc is the lead wire resistance value of the strain gauge, and these may be considered as the same resistance value.
FIG. 4 shows an equivalent circuit of the circuit of FIG. 3 in consideration of the strain gauge lead wire resistance value RL. Hereinafter, a detailed description will be given based on the equivalent circuit of FIG.
The current I flowing through the gauge resistance (the resistance value is also Ga) of the strain gauge Ga is expressed by the following equation based on the bridge excitation power supply voltage Ein and the bridge configuration resistance value Rb.
[0045]
[Expression 2]

[0046]
Since the bridge excitation power supply voltage Ein and the bridge configuration resistance value Rb are both fixed values, the current value I is a constant current, that is, a constant current.
The potential of the connection terminal Ta, that is, the potential Eamp4 of the output of the amplifier AMP4 is expressed by the following equation.
Eamp4 = I × (Ga + Rb + Rsc ′ + Rsw2 + 2 + × RL) (3)
Here, Rsc ′ and Rsw2 are on-resistance values of the switch element Sc ′ for selective scanning and the switch element SW2 for mode switching, respectively.
Further, the potential Eamp5 of the output of the amplifier AMP5 is expressed by the following equation.
Eamp5 = I × (Rsc ′ + Rsw2) (4)
Therefore, the potential E1 at the connection point between the bridge configuration resistor Rd and the bridge configuration resistor Rc is expressed by the following equation.
[0047]
[Equation 3]

[0048]
Further, the potential E2 of the connection terminal Tb is expressed by the following equation.
E2 = I × (Rb + Rsc ′ + Rsw2 + RL) (6)
Here, since the gauge resistance (Ga) of the strain gauge Ga is equal to the bridge configuration resistance Rb in the initial state, that is, when there is no load, the resistance value change ΔGa due to strain is separated from the gauge resistance Ga, and Ga = Ga + ΔGa = Rb + ΔGa, the formula (5) becomes as follows.
[0049]
[Expression 4]

[0050]
That is, the potential difference Eo between the potentials E1 and E2 corresponding to the bridge output is expressed by the following equation from the equations (6) and (7).
[0051]
[Equation 5]

[0052]
Since the current value I is constant, an output that is completely proportional to the resistance value change ΔGa of the strain gauge Ga is obtained as the final output Eo.
<(2) 2 gauge method>
In the configuration of the multi-channel strain measurement circuit of FIG. 1, when connected as the two-gauge method measurement mode, that is, the mode switching switch elements SW1 to SW6 are in a state where the selected end is selected as shown in FIG. In this case, a substantial circuit is shown in FIG. FIG. 5 shows only elements and circuits related to operation in the 2-gauge measurement mode. For example, among the switch elements SW1 to SW6 for mode switching, only the switch element SW2 is shown in FIG. 5, but the switch elements SW1 and SW3 to SW6 for mode switching other than the switch element SW2 are The characteristics and the like do not substantially affect the examination of the measurement accuracy, and are not clearly shown on the circuit of FIG.
[0053]
In other words, in the connection state shown in FIG. 5, the connection point between the bridge configuration resistors Rd and Rc is connected to the non-inverting input terminal (+) of the amplifier AMP1, and is selected as the non-inverting input terminal (+) of the amplifier AMP5. The scanning switch element Sc is connected, the selective scanning switch element Sa ′ is connected to the non-inverting input terminal (+) of the amplifier AMP4, and the inverting input terminal (−) of the amplifier AMP2 is a bridge configuration. It is connected to the common potential via the resistor Rb. The selective scanning switch element Sc ′ is connected to the inverting input terminal (−) of the amplifier AMP2 via the mode switching switch element SW2. The output terminal of the amplifier AMP5 is connected to the inverting input terminal (−) of the amplifier AMP5.
In this state, the two strain gauges Ga and Gb include amplifier AMP2 → connection terminal Ta → strain gauge Ga → connection terminal Tb → strain gauge Gb → connection terminal Tc → switching element Sc ′ → switching element SW2 → resistance Rb. A constant current is passed through the path. The current is a constant current controlled by the amplifier AMP2 so that the voltage across the bridge configuration resistor Rb is equal to the reference voltage (Ein) of the bridge excitation power supply Ein.
[0054]
The potential of the connection terminal Ta connected to the first end corresponding to the one end of the strain resistance of the strain gauge Ga is extracted by the buffer amplifier AMP4, and further, the other end of the gauge resistance of the strain gauge Gb is extracted by the buffer amplifier AMP5. The potential of the connection terminal Tc connected to the corresponding second end is extracted, and a series circuit of bridge configuration resistors Rd and Rc having the same resistance value is inserted between the output ends of the amplifiers AMP4 and AMP5. Thus, one output potential corresponding to the positive output in the conventional bridge circuit is obtained from the connection point of the resistors Rd and Rc. In addition, the connection terminal Tb connected to the second end corresponding to the other end of the gauge resistance of the strain gauge Ga and connected to the first end corresponding to the one end of the gauge resistance of the strain gauge Gb is a conventional method. The other output potential corresponding to the negative output in the bridge circuit is obtained.
The voltage between these positive and negative output potentials is an output proportional to the change in resistance value of the strain gauge, that is, a strain output. In this embodiment, the differential amplifier AMP1 extracts the difference voltage between the positive and negative output potentials and amplifies it if necessary.
[0055]
Voltage generated by current flowing through the ON resistance (several hundred Ω or less) of the switch element Sc ′ for selective scanning and the switch element SW2 for mode switching in the path of current for exciting the two strain gauges Ga and Gb Is input as a common-mode voltage to the differential amplifier AMP1, and does not affect the distortion measurement value.
In the configuration of FIG. 5, a circuit configuration in consideration of the resistance value of the lead wire in the connection cable of two strain gauges Ga and Gb is shown in FIG. 6. The resistance value RL inserted between the both ends of the strain gauges Ga and Gb and the connection terminals Ta, Tb and Tc is the lead wire resistance value, and these may be considered as the same resistance value.
FIG. 7 shows an equivalent circuit of the circuit of FIG. 6 in consideration of the strain gauge lead wire resistance value RL. Hereinafter, a detailed description will be given based on the equivalent circuit of FIG.
The current I flowing through the gauge resistances of the strain gauges Ga and Gb (the resistance values are also Ga and Gb) is based on the bridge excitation power supply voltage Ein and the bridge configuration resistance value Rb, as in the above-described one-gauge method measurement mode. (2) is a constant current, that is, a constant current.
[0056]
The potential of the connection terminal Ta, that is, the potential Eamp4 of the output of the amplifier AMP4 is obtained by using the on-resistance value Rsc ′ of the selective scanning switch element Sc ′ and the on-resistance value Rsw2 of the mode switching switch element SW2. It is expressed by the following formula.
Eamp4 = I × (Ga + Gb + Rb + Rsc ′ + Rsw2 + 4 × RL) (9)
Further, the potential Eamp5 of the output of the amplifier AMP5 is expressed by the following equation.
Eamp5 = I × (Rb + Rsc ′ + Rsw2) (10)
Therefore, the potential E1 at the connection point between the bridge configuration resistor Rd and the bridge configuration resistor Rc is expressed by the following equation.
[0057]
[Formula 6]

[0058]
Further, the potential E2 of the connection terminal Tb is expressed by the following equation.
E2 = I × (Gb + Rb + Rsc ′ + Rsw2 + 2 × RL) (12)
Here, in the initial state, that is, when there is no load, the gauge resistance (Ga) of the strain gauge Ga and the gauge resistance (Gb) of the strain gauge Gb are equal to each other.
When Ga = Gb is set and the resistance changes ΔGa and ΔGb due to strain are separated from the gauge resistances Ga and Gb, respectively, and Ga = Gb + ΔGa and Gb = Gb + ΔGb are set, E1 is expressed as follows: become.
[0059]
[Expression 7]

[0060]
It becomes. Similarly, the equation (12) indicating E2 is as follows.
E2 = I × (ΔGb + Gb + Rb + Rsc ′ + Rsw2 + 2 × RL) (14)
That is, the potential difference Eo between the potentials E1 and E2 corresponding to the bridge output is expressed by the following equation from the equations (13) and (14).
[0061]
[Equation 8]

[0062]
Since the current value I is constant, an output that is completely proportional to the resistance value changes ΔGa and ΔGb of the two strain gauges Ga and Gb is obtained as the final output Eo.
[0063]
<(3) Constant voltage (constant voltage excitation) 4 gauge method>
In the configuration of the multi-channel strain measurement circuit of FIG. 1, when connected in the constant voltage excitation 4-gauge method, that is, the constant voltage 4-gauge method measurement mode, that is, the mode switching switch elements SW1 to SW5 are different from those in FIG. FIG. 8 shows a substantial circuit when the selected end is selected and the mode switching switch element SW6 is selected as shown in FIG. FIG. 8 shows only elements and circuits related to the operation in the constant voltage 4-gauge measurement mode. For example, the switching elements SW1 to SW6 for mode switching are not clearly shown on the circuit of FIG. 8 because their characteristics do not substantially affect the examination of measurement accuracy.
That is, in the connection state shown in FIG. 8, the selective scanning switch element Sd is connected to the non-inverting input terminal (+) of the amplifier AMP1, and the selective scanning switch is connected to the inverting input terminal (−) of the amplifier AMP3. The element Sc ′ is connected, the output terminal of the amplifier AMP3 is connected to the switch element Sc for selective scanning, and the switch element Sa ′ for selective scanning is connected to the inverting input terminal (−) of the amplifier AMP2. ing. FIG. 9 shows an equivalent circuit of such a connection configuration of FIG.
[0064]
In the configuration shown in FIG. 9, the amplifiers AMP2 and AMP3 control the connection terminals Ta and Tc so that the potentials of the connection terminals Ta and Tc become the common potentials of the reference voltage Ein and 0 V, respectively, so that the bridge excitation voltage becomes the reference voltage Ein.
The equivalent circuit of FIG. 9 is a measurement circuit in a 4-gauge method measurement mode by general constant voltage excitation. This constant voltage 4-gauge measurement mode is used when connecting various strain gauge transducers such as an acceleration transducer, a displacement meter, and a torque transducer as well as a load cell. Each converter is attached with a calibration coefficient calibrated by a constant voltage excitation power source, which is an essential measurement mode for a multi-channel strain measurement system.
[0065]
<(4) Constant current (constant current excitation) 4-gauge method>
In the configuration of the multi-channel strain measurement circuit of FIG. 1, when connected as a constant-current excitation 4-gauge method, that is, a constant-current 4-gauge measurement mode, that is, the mode switching switch element SW1 is different from that shown in FIG. FIG. 10 shows a substantial circuit when the mode selection switch element SW2 to SW6 is selected and the selected end is selected as shown in FIG. FIG. 10 shows only elements and circuits related to the operation in the constant current 4-gauge measurement mode. For example, among the switch elements SW1 to SW6 for mode switching, only the switch element SW2 is shown in FIG. 10, but the switch elements SW1 and SW3 to SW6 for mode switching other than the switch element SW2 are Since the characteristics and the like do not substantially affect the examination of the measurement accuracy, they are not clearly shown on the circuit of FIG.
[0066]
That is, in the connection state shown in FIG. 10, the switch element Sd for selective scanning is connected to the non-inverting input terminal (+) of the amplifier AMP1, and the inverting input terminal (−) of the amplifier AMP2 is the bridge configuration resistor Rb. Are connected to a common potential via The selective scanning switch element Sc ′ is connected to the inverting input terminal (−) of the amplifier AMP2 via the mode switching switch element SW2. FIG. 11 shows an equivalent circuit of such a connection configuration of FIG.
The equivalent circuit of FIG. 11 is a measurement circuit in a 4-gauge method measurement mode by general constant current excitation. This constant current 4-gauge measurement mode can be effectively used when connecting a strain gauge type civil engineering transducer or the like whose connection cable length is often several hundred to several thousand meters. Since it is a constant current excitation, it is not affected by a voltage drop due to the cable lead wire resistance, and a sensitivity change due to a decrease in the bridge excitation voltage does not occur. Such a measurement mode is also an essential measurement mode for a multi-channel strain measurement system.
[0067]
The current controlled by the amplifier AMP2 so that the voltage at both ends of the bridge configuration resistor Rb serving as the reference resistance is equal to the excitation power supply reference voltage Ein is the amplifier AMP2 → the connection terminal Ta → the 4-gauge bridge (Ga, Gb, Gc). , Gd) → connection terminal Tc → switch element Sc ′ → switch element SW2 → resistance Rb. The 4-gauge bridge (Ga, Gb, Gc, Gd) portion is a parallel connection of a series circuit of strain gauges Ga and Gb and a series circuit of strain gauges Gd and Gc.
The total on-resistance (Rsc ′ + Rsw2) of the switch element Sc ′ for selective scanning and the switch element SW2 for mode switching is approximately the same as the strain gauge, for example, a large value of several hundred Ω, Since it is input to the differential amplifier AMP1 as a common-mode voltage of the bridge output (E1-E2) between the output potential E1 appearing at the connection terminal Td and the output potential E2 appearing at the connection terminal Tb, the sum of the on-resistances (Rsc ′ The effect of + Rsw2) is eliminated by the differential amplifier AMP1.
[0068]
As described above, the multi-channel strain measurement circuit according to the embodiment of the present invention shown in FIG. 1 includes all four measurement modes by the gauge method, and is selectively switched for each channel. In addition, it is possible to share the resistance for bridge configuration in all channels, and it is possible to use a switching element having a high on-resistance value such as a semiconductor relay as the switching element in the bridge.
In the prior art, by changing from the measurement circuit shown in FIG. 12 to the measurement circuit shown in FIG. 13, it is possible to greatly reduce the resistance for the bridge configuration. In order to suppress the error to an allowable range, the on-resistance value of the switching element is limited to several mΩ or less, so that the selection range of elements that can be used as a switching element is limited. It was restricted.
On the other hand, the multi-channel distortion measuring circuit according to the present invention as shown in the above-described embodiment can remove such limitation, and a semiconductor switch having an on-resistance value of several hundreds Ω can be used.
[0069]
That is, according to the multi-channel strain measurement circuit of the present invention, even if a switch having an on-resistance of several hundred Ω is used, the error can be removed and appropriate strain measurement data can be obtained (Equation (8) See). The effects obtained by the multi-channel strain measurement circuit according to the present invention have a wide range of effects such as a semi-permanent extension of life, a high-speed switching, and a low price.
As apparent from a comparison between the configuration of the multichannel distortion measuring circuit according to the embodiment of the present invention shown in FIG. 1 and the configuration of the conventional circuit shown in FIG. 13, the additional circuit component according to the present invention has several gain settings. There are only two buffer amplifiers with resistors and a few mode selector switches. These parts do not need to be particularly highly accurate as compared with the circuit parts used in the conventional configuration, and may be the same parts. Therefore, even when a multi-channel strain measurement system is configured, the multi-channel strain measurement circuit according to the present invention can be implemented with a few additional components.
[0070]
Further, in the above-described configuration, by adopting constant current excitation in the 1 gauge method measurement mode and the 2 gauge method measurement mode, the current flows through the corresponding side of the bridge due to a change in the resistance value of the strain gauge as seen in constant voltage excitation. There is no non-linearity of the bridge output caused by the current change, and an output that is completely proportional to the strain gauge resistance value change can be obtained (see equation (15)).
The constant current type strain measurement circuits in the 1 gauge method measurement mode and the 2 gauge method measurement mode are typically circuits as shown in FIGS. 15 and 16, respectively. 15 and 16 includes two constant current power supplies CCS1 and CCS2, and the output currents of the constant current power supplies CCS1 and CCS2 are generated based on the bridge reference voltage Ein, both of which have the same value. (I1). The output currents I1 of the constant current power supplies CCS1 and CCS2 are respectively supplied to the strain gauge Ga and the bridge configuration resistor Rb in the configuration of FIG. 15, and are supplied to the strain gauges Ga and Gb in the configuration of FIG. Output potentials E1 and E2 are obtained. The voltage between these output potentials E1 and E2 is extracted by the differential amplifier AMP10.
[0071]
15 and 16 can obtain an output proportional to the change in the resistance value of the strain gauge. However, by using two constant current sources CCS1 and CCS2, independent currents specific to each current source can be obtained. Since the output is superimposed with noise, the noise cannot be sufficiently removed by the differential amplifier AMP1, and is not suitable for high-precision measurement as compared with constant voltage excitation. In the circuit of FIG. 1 according to the present invention, since there is one constant current source, the noise of the constant current source itself and the drift that is slow noise are superimposed on both positive and negative distortion outputs as in-phase components. It can be effectively removed with a differential amplifier. Therefore, even when compared with a conventional strain measurement circuit using a constant current excitation power supply, a highly accurate and highly stable measurement is possible.
In addition, mode switching by the mode switching switch elements SW1 to SW6 is performed in advance by registering the application mode of each channel in the nonvolatile storage means or the like manually or visually according to a connection record memo or the like. The sequential mode switching switch elements SW1 to SW6 may be switched according to the registered measurement mode.
[0072]
However, since the connection state according to the measurement mode of the strain gauge with respect to the connection terminals Ta to Td can be determined based on parameters such as resistance values between the terminals of the connection terminals Ta to Td. A means for sequentially scanning the channel connection terminals Ta to Td to discriminate and register the measurement mode for each channel is provided, and at the time of the first measurement, at the time of the measurement scan, or every predetermined period, prior to the measurement. The connection terminals Ta to Td of each channel are sequentially scanned to determine and register the measurement mode for each channel, and the sequential mode switching switch elements SW1 to SW6 according to the measurement mode registered with the channel switching scan. May be switched.
[0073]
【The invention's effect】
As described above, according to the present invention, a strain gauge is selectively connected to each channel in a measurement mode including a 1 gauge method measurement mode, a 2 gauge method measurement mode, and a 4 gauge method measurement mode. In a multi-channel strain measurement circuit that selectively switches and performs measurement with the strain gauge for each channel, it is possible to share the resistance for the bridge configuration with all channels, and as a switching element in the bridge, a semiconductor relay or the like can be used. It is possible to provide a multi-channel distortion measurement circuit that makes it possible to use a switching element having an on-resistance value.
That is, according to the multi-channel strain measuring circuit of claim 1 of the present invention, the first, second, third and fourth terminals for connecting a strain gauge are provided for each channel, and the first A 1-gauge method measurement mode in which a single strain gauge is connected between the first terminal and the second terminal, and the second terminal and the third terminal are short-circuited; One strain gauge is connected between the second terminal and the second terminal, and another one strain gauge is connected between the second terminal and the third terminal. And between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and There are four different strain gauges, one between each of the four terminals and the first terminal. A multi-channel which performs a measurement with each strain channel by selectively connecting a strain gauge to each channel in a measurement mode including a four-gauge method measurement mode connected to each channel, and selectively switching each channel. In the strain measurement circuit, at least one set of bridge-forming resistance elements used in the measurement in the 1-gauge method measurement mode and the 2-gauge method measurement mode is provided for all channels, and is used in common for each channel. At the time of measurement in the measurement mode, a voltage appearing between both ends of the first resistance element is set to a predetermined voltage in a current path passing through the first resistance element for the bridge configuration that becomes the reference resistance from the strain gauge through the switching element. A bridge excitation current is passed as a constant current, and the first buffer amplifier is used to distribute the bridge excitation current. And the potential at one connection end of the strain gauge is extracted, the voltage generated by the on-resistance of the switching element in the current path is extracted by the second buffer amplifier, and the first buffer amplifier Between the output end and the output end of the second buffer amplifier, a second resistance element and a third resistance element for a bridge configuration having the same resistance value are connected in series, and the second resistance element and the third resistance element are connected to each other. By obtaining one output potential from the connection point between the two resistance elements, obtaining the other output potential from the other connection end of the strain gauge, and measuring the difference voltage between these two output potentials, By removing the error due to the on-resistance of the switching element in the current path, in particular, at least in the one-gauge method measurement mode, constant current excitation is adopted, and the switching element in the current path It is possible to remove the error due to the on-resistance and prevent the occurrence of non-linearity so that the bridge-constituting resistive element can be shared by all channels.
[0074]
According to the multi-channel strain measuring circuit of claim 2 of the present invention, the first, second, third and fourth terminals for connecting a strain gauge are provided for each channel, and the first A 1-gauge method measurement mode in which a single strain gauge is connected between the first terminal and the second terminal, and the second terminal and the third terminal are short-circuited; One strain gauge is connected between the second terminal and the second terminal, and another one strain gauge is connected between the second terminal and the third terminal. And between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and There are four different strain gauges, one between each of the four terminals and the first terminal. Multi-channel strain measurement in which a strain gauge is selectively connected to each channel in a measurement mode including a connected 4-gauge method measurement mode, and each channel is selectively switched to perform measurement with the strain gauge for each channel. In the circuit, at least one set of bridge configuration resistance elements used in the measurement of the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel. At the time of measurement, the voltage appearing between both ends of the first resistance element is determined in a current path passing through the first resistance element for the bridge configuration that becomes the reference resistance from the first and second strain gauges through the switching element. The bridge excitation current is passed as a constant current of a constant current, which is used for blocking the constant current and extracting the potential. The first buffer amplifier and the second buffer amplifier, respectively, extract potentials at one connection end of the first strain gauge that is the active gauge and one connection end of the second strain gauge that is the dummy gauge, Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series, and A common connection end in which one output potential is obtained from a connection point between the two resistance elements and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. In particular, by removing the error due to the on-resistance of the switching element in the current path by measuring the voltage of the difference between the two output potentials by obtaining the other output potential from In the 2-gauge method measurement mode, constant current excitation is used to eliminate errors caused by the on-resistance of the switching element in the current path and to prevent non-linearity. It becomes possible to do.
[0075]
According to the multi-channel strain measurement circuit of claim 3 of the present invention, in the multi-point strain measurement circuit of claim 1 or 2, the bridge excitation in at least one of the 1-gauge method measurement mode and the 2-gauge method measurement mode. By constructing the bridge excitation power supply for supplying current with a single constant current source, non-linearity in the bridge system is eliminated, and an output proportional to the resistance value change of each strain gauge is obtained. Non-linearity in at least one of the method measurement mode and the two-gauge method measurement mode can be prevented, and the bridge excitation power source can be shared by all channels.
[0076]
According to the multi-channel strain measuring circuit of claim 4 of the present invention, the first, second, third and fourth terminals for connecting a strain gauge are provided for each channel, and the first A one-gauge measurement mode in which a single strain gauge is connected between the terminal and the second terminal and the second terminal and the third terminal are short-circuited; and the first terminal A two-gauge measurement mode in which one strain gauge is connected between the second terminal and the second terminal, and another strain gauge is connected between the second terminal and the third terminal; Between the first terminal and the second terminal; between the second terminal and the third terminal; between the third terminal and the fourth terminal; and Four different strain gauges are connected between the terminal and the first terminal. In a multi-channel strain measurement circuit that selectively connects a strain gauge to each channel in a measurement mode including a four-gauge method measurement mode and selectively switches each channel to perform measurement with the strain gauge for each channel. In addition, at least one set of bridge configuration resistance elements used in the measurement in the 1-gauge method measurement mode and the 2-gauge method measurement mode is provided for all channels, and is commonly used for each channel. Occasionally, a current path that passes from the strain gauge through the switching element to the first resistance element for bridge configuration that serves as a reference resistance is excited as a constant current with a voltage appearing at both ends of the first resistance element as a predetermined voltage. A bridge excitation current is supplied from a power source, and the bridge excitation current is reduced by a first buffer amplifier. A first buffer amplifier for extracting a voltage generated by an on-resistance of the switching element in the current path by a second buffer amplifier, and extracting a potential at one connection end of the strain gauge; The second resistance element and the third resistance element for the bridge configuration having the same resistance value are connected in series between the output terminal of the second buffer amplifier and the output terminal of the second buffer amplifier. And obtaining one output potential from the connection point between the three resistance elements, obtaining the other output potential from the other connection end of the strain gauge, measuring the voltage between these two output potentials, At the time of measurement in the two-gauge method measurement mode, the first and second strain gauges pass through the switching element, the current path passing through the first resistance element for the bridge configuration that becomes a reference resistance, and the first gauge The first buffer amplifier and the second buffer amplifier used for blocking a constant current and extracting a potential by causing a bridge excitation current to flow from the excitation power source as a constant current having a voltage appearing between both ends of the resistance element as a predetermined voltage. The two buffer amplifiers extract potentials at one connection end of the first strain gauge that is the active gauge and one connection end of the second strain gauge that is the dummy gauge, and output the first buffer amplifier. The second resistance element and the third resistance element for bridge configuration having the same resistance value are connected in series between the second resistance element and the output terminal of the second buffer amplifier, A common connection end in which one output potential is obtained from a connection point between the third resistance element and the other connection ends of the first and second strain gauges are connected in common. In particular, by removing the error due to the on-resistance of the switching element in the current path by measuring the voltage of the difference between the two output potentials by obtaining the other output potential, In the two-gauge method measurement mode, constant current excitation using a common excitation power supply is adopted to eliminate errors due to the on-resistance of the switching element in the current path and to prevent the occurrence of nonlinearity. The resistance element can be shared by all channels.
[0077]
According to the multi-channel strain measurement circuit of claim 5 of the present invention, in the multi-channel strain measurement circuit according to any one of claims 1 to 4, when measuring in the 4-gauge method measurement mode, By configuring a measurement circuit including a constant voltage excitation circuit for supplying a constant voltage to the bridge circuit composed of the strain gauge, it is possible to measure in particular in the 4-gauge method measurement mode of constant voltage excitation.
[0078]
According to the multi-channel strain measurement circuit of claim 6 of the present invention, in the multi-channel strain measurement circuit according to any one of claims 1 to 5, when measuring in the 4-gauge method measurement mode, A voltage that appears between both ends of the first resistance element in a current path that passes through the first resistance element for the bridge configuration that serves as a reference resistance from the bridge circuit that includes the strain gauge via a switching element is defined as a predetermined voltage. By configuring a measurement circuit including a constant current excitation circuit for supplying a bridge excitation current as a constant current to be generated, a 4-gauge method measurement mode using a constant-current excitation substantially in common with the 1-gauge method and the 2-gauge method measurement mode, in particular. Measurement, and the error due to the on-resistance of the switching element in the current path is removed, and non-linearity is prevented, and the excitation power supply is turned off. It is possible to share in the channel.
According to the multi-channel distortion measuring circuit of the seventh aspect of the present invention, in the multi-channel distortion measuring circuit according to any one of the first to sixth aspects, the predetermined first, second, third and The circuit characteristics of the strain gauge side viewed from the fourth terminal are detected, the strain gauge measurement mode for these first to fourth terminals is determined, and the connection configuration of the measurement circuit is determined according to the determined measurement mode. By further including mode switching means for selecting and setting, it is possible to automatically select and set the connection configuration of the measurement circuit according to the connection state of the strain gauge.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram schematically showing a configuration of a multi-channel distortion measurement circuit according to an embodiment of the present invention.
2 is a circuit configuration diagram schematically showing a connection configuration of a measurement circuit in a 1-gauge method measurement mode of the multi-channel strain measurement circuit of FIG. 1; FIG.
3 is a circuit configuration diagram schematically showing a connection configuration in consideration of a lead wire resistance of a cable connecting a strain gauge in the measurement circuit of FIG. 2; FIG.
4 is a circuit configuration diagram showing an equivalent circuit for explaining the circuit configuration of FIG. 3; FIG.
5 is a circuit configuration diagram schematically showing a connection configuration of a measurement circuit in a 2-gauge method measurement mode of the multi-channel strain measurement circuit of FIG. 1; FIG.
6 is a circuit configuration diagram schematically showing a connection configuration in consideration of a lead wire resistance of a cable connecting a strain gauge in the measurement circuit of FIG. 5;
7 is a circuit configuration diagram showing an equivalent circuit for explaining the circuit configuration of FIG. 6; FIG.
8 is a circuit configuration diagram schematically showing a connection configuration of a measurement circuit in a constant voltage 4-gauge method measurement mode of the multi-channel strain measurement circuit of FIG. 1; FIG.
9 is a circuit configuration diagram showing an equivalent circuit for explaining the circuit configuration of FIG. 8;
10 is a circuit configuration diagram schematically showing a connection configuration of a measurement circuit in a constant current 4-gauge method measurement mode of the multi-channel strain measurement circuit of FIG. 1; FIG.
11 is a circuit configuration diagram showing an equivalent circuit for explaining the circuit configuration of FIG. 10;
FIG. 12 is a circuit configuration diagram schematically showing the configuration of an example of a conventional multi-channel distortion measurement circuit.
FIG. 13 is a circuit configuration diagram schematically showing another example of the configuration of a conventional multi-channel distortion measurement circuit.
FIG. 14 is a diagram showing characteristics of true strain amount versus strain gauge bridge output for explaining nonlinearity in a one-gauge method measurement mode by conventional constant voltage excitation.
FIG. 15 is a circuit configuration diagram schematically showing a basic configuration of a one-gauge method measurement mode by constant current excitation, which has been generally considered conventionally.
FIG. 16 is a circuit configuration diagram schematically showing a basic configuration of a 2-gauge method measurement mode by constant current excitation, which has been generally considered in the past.
[Explanation of symbols]
Ein excitation power supply (reference voltage)
AMP1 to AMP5 amplifier
SW1 to SW6 Mode switching element
Rb to Rd Bridge configuration resistors
Ta to Td connection terminal
Sa to Sd, Sa ′, Sc ′ Switch elements for selective scanning
SSW Scan switching element

Claims (7)

A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. An error due to an on-resistance of the switching element in the current path is removed by measuring a difference voltage, and the multi-channel distortion measuring circuit is characterized in that A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the two-gauge method measurement mode, both ends of the first resistance element are passed through a current path that passes from the first and second strain gauges through the switching element and through the first resistance element for bridge configuration that becomes a reference resistance. Let the bridge excitation current flow as a constant current with the voltage appearing between
The first buffer amplifier and the second buffer amplifier, which are used for blocking the constant current shunting and extracting the potential, have one connection end of the first strain gauge as the active gauge and the second strain gauge as the dummy gauge. Extract the potential at one connection end of
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. A multi-channel distortion characterized by removing the error due to the on-resistance of the switching element in the current path by obtaining the other output potential from the connection end and measuring the voltage of the difference between the two output potentials Measuring circuit. By configuring the bridge excitation power source that supplies the bridge excitation current in at least one of the 1 gauge method measurement mode and the 2 gauge method measurement mode with a single constant current source, the nonlinearity in the bridge system is eliminated, The multipoint strain measurement circuit according to claim 1 or 2, wherein an output proportional to a change in resistance value of the strain gauge is obtained. A predetermined first, second, third and fourth terminal for connecting a strain gauge is provided for each channel, and a single strain gauge is provided between the first terminal and the second terminal. 1 strain gauge measurement mode in which the second terminal and the third terminal are short-circuited, and one strain gauge is connected between the first terminal and the second terminal. And a two-gauge method measurement mode in which another strain gauge is connected between the second terminal and the third terminal, between the first terminal and the second terminal, One each between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal. Select each of the measurement modes, including the four-gauge method measurement mode, in which four different strain gauges are connected. Strain Connect gauge Yan'neru, by switching each channel selectively, in a multi-channel strain measurement circuit performs measurement by the strain gauges for each channel,
At least one set of resistance elements for bridge configuration used in the measurement in the 1 gauge method measurement mode and the 2 gauge method measurement mode is provided for all channels, and is used in common for each channel.
At the time of measurement in the one-gauge method measurement mode, a voltage that appears between both ends of the first resistance element is predetermined in a current path that passes from the strain gauge through the switching element to the bridge-forming first resistance element. Let the bridge excitation current flow from the excitation power source as a constant current of
The first buffer amplifier prevents branching of the bridge excitation current and extracts a potential at one connection end of the strain gauge;
A second buffer amplifier extracts a voltage generated by an on-resistance of the switching element in the current path;
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, a second resistance element and a third resistance element for bridge configuration having the same resistance value are connected in series,
One output potential is obtained from the connection point between the second resistance element and the third resistance element, and the other output potential is obtained from the other connection end of the strain gauge. While measuring the difference voltage,
At the time of measurement in the two-gauge method measurement mode, the first resistance element is a current path that passes from the first and second strain gauges through the switching element to the bridge-structured first resistance element serving as a reference resistance. The bridge excitation current is passed from the excitation power source as a constant current with a voltage appearing between both ends of the
By means of the first buffer amplifier and the second buffer amplifier used for preventing a constant current from being shunted and extracting a potential, one connection end of the first strain gauge which is an active gauge and a second gauge which is a dummy gauge are used. Extract the potential at one end of the strain gauge,
Between the output terminal of the first buffer amplifier and the output terminal of the second buffer amplifier, the second resistance element and the third resistance element for bridge configuration having the same resistance value are connected in series. ,
One output potential is obtained from a connection point between the second resistance element and the third resistance element, and the other connection ends of the first and second strain gauges are connected in common. A multi-channel distortion characterized by removing the error due to the on-resistance of the switching element in the current path by obtaining the other output potential from the connection end and measuring the voltage of the difference between the two output potentials Measuring circuit. 5. A measurement circuit including a constant voltage excitation circuit for supplying a constant voltage to a bridge circuit composed of four strain gauges at the time of measurement in the four gauge method measurement mode. The multi-channel distortion measuring circuit according to any one of the above. At the time of measurement in the four-gauge method measurement mode, the first resistor is connected in a current path that passes from the bridge circuit composed of the four strain gauges through the switching element to the first resistance element for bridge configuration that becomes a reference resistance. 6. A measurement circuit including a constant current excitation circuit that causes a bridge excitation current to flow as a constant current with a voltage appearing between both ends of the element as a predetermined voltage. The multi-channel distortion measuring circuit according to Item. The circuit characteristics of the first, second, third and fourth terminals as viewed from the strain gauge side are detected, and the strain gauge measurement modes for these first to fourth terminals are determined to be determined. The multi-channel distortion measurement circuit according to claim 1, further comprising mode switching means for selectively setting a connection configuration of the measurement circuit according to the measurement mode.

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