JP3562703B2

JP3562703B2 - Measuring device

Info

Publication number: JP3562703B2
Application number: JP03557899A
Authority: JP
Inventors: 孝桑原
Original assignee: Yokogawa Electric Corp
Current assignee: Yokogawa Electric Corp
Priority date: 1999-02-15
Filing date: 1999-02-15
Publication date: 2004-09-08
Anticipated expiration: 2019-02-15
Also published as: JP2000235053A

Description

【０００１】
【発明の属する技術分野】
本発明は、４線式抵抗測定方法及び計測装置の改善に関し、特に４線式抵抗測定の高速化と高精度化を実現するとともに、被測定物と計測装置を接続する配線等の接触不良または断線等によって発生しうる誤測定を防止することが可能な計測装置に関するものである。
【０００２】
【従来の技術】
従来の４線式抵抗測定を行う計測装置の構成を図５を用いて説明する。同図は従来の高精度４線式デジタルマルチメータの４線式抵抗測定回路の一例である。
【０００３】
同図において、被測定物である被測定抵抗１の一端は、測定装置１００のプラス電流端子３及びプラス電圧端子４に接続され、被測定抵抗１の他の一端は、測定装置１００のマイナス電流端子６及びマイナス電圧端子５に接続されている。
【０００４】
測定装置１００の内部では、基準電圧４８が基準抵抗９を介してプラス電流端子３に印加されている。また、マイナス電流端子６は、非反転入力端子をゼロ電位点に接続され反転入力端子を前記プラス電流端子３に接続された演算増幅器１０の出力端子に接続されている。更にこの演算増幅器１０の出力は、位相補償用コンデンサ１４を介して負帰還されている。
【０００５】
更に、プラス電圧端子４とマイナス電圧端子５はＦＥＴスイッチ１１と１２の一端にそれぞれ接続され、このＦＥＴスイッチ１１と１２の他の一端は、演算増幅器を利用した非反転型アンプであるプリアンプ７の入力に接続されている。このプリアンプ７の出力が被測定抵抗１の測定電圧信号として後段の制御回路１３に入力され、ここでデジタル値に変換された後、適切な演算処理が施され、その結果が被測定抵抗１の抵抗値として表示器（図示せず。）等に表示される。また、この制御回路１３は、ＦＥＴスイッチ１１と１２のオンオフ動作も管理している。
【０００６】
このように被測定抵抗１と接続された計測装置１００は、被測定抵抗１に既知の定電流Ｉｓをプラス電流端子３からマイナス電流端子６に向かって流し、被測定抵抗１の両端に発生する電圧をプラス電圧端子４とマイナス電圧端子５から測定し、この電圧を定電流Ｉｓで除算して被測定抵抗１の抵抗値を求める。
【０００７】
上記の定電流Ｉｓは、基準電圧４８と基準抵抗９及び演算増幅器１０によって発生され、その大きさは、基準抵抗９の下端ａが演算増幅器１０の作用によってゼロ電位に制御されるため、基準電圧４８の電圧値を基準抵抗９の抵抗値で除算して得られた値となる。
【０００８】
制御回路１３は、この定電流Ｉｓを被測定抵抗１に流し、この被測定抵抗１のプラス側に発生する電圧Ｒｖ＋をＦＥＴスイッチ１１をオン、ＦＥＴスイッチ１２をオフとすることによって、プリアンプ７に入力し検出すると共にこの値を記憶し、次にこの被測定抵抗１のマイナス側に発生する電圧Ｒｖ−をＦＥＴスイッチ１１をオフ、ＦＥＴスイッチ１２をオンとすることによって、プリアンプ７に入力し検出すると共にこの値を記憶する。
【０００９】
制御回路１３は、上記の動作によって記憶した被測定抵抗１のプラス側に発生する電圧Ｒｖ＋からマイナス側に発生する電圧Ｒｖ−を減算し、その値を定電流Ｉｓの電流値で除算して被測定抵抗１の抵抗値を求める。
【００１０】
このような構成の計測装置では、シンプルな構成の非反転アンプをプリアンプとして用いることが可能であると共に、２回の測定を行ってプラス側に発生する電圧とマイナス側に発生する電圧の差を求めることにより、前記プリアンプのオフセット電圧によるドリフトをキャンセルすることが可能となり、被測定抵抗１の抵抗値を高精度に測定することが可能となる。
【００１１】
また、他の従来例として図６に示す構成のものがある。同図は、生産ラインに用いる計測装置のように、高速測定を行う用途に用いられる計測装置の一例である。同図において、図５と同様のものは同一の符号を付しその説明を省略する。
【００１２】
図６の回路において、被測定抵抗１に定電流Ｉｓを流してその両端に発生する電圧から抵抗値を求めるという原理は図５の計測装置と同様であるが、図６の計測装置では、プラス電圧端子４とマイナス電圧端子５をプリアンプ７の非反転入力と反転入力にそれぞれ接続し、プリアンプ７を差動アンプとして用いている。
【００１３】
図６の回路では、上記に示すようにプリアンプ７を差動アンプとして用いることにより、被測定抵抗１に定電流Ｉｓを流してその両端に発生する電圧を１回の測定で求めることができるため、高速測定が可能となる。
【００１４】
【発明が解決しようとする課題】
しかしながら図５に示した従来の計測装置では、被測定抵抗１の両端に発生する電圧を求めるために、２回の測定を行う必要があることから測定に要する時間が長くかかり、高速測定を行うことができないという問題点があった。
【００１５】
また、図６に示した従来の計測装置では、プリアンプ７を差動アンプとして用いることにより、１回の測定で被測定抵抗１の両端に発生する電圧を測定することが可能であるが、このような構成の計測装置では、その測定精度がプリアンプ７の精度に依存してしまうという問題点がある。つまり、高精度の測定を行うためにはプリアンプ７を構成する抵抗の絶対値のマッチングに、期待する測定精度以上の精度が必要となる。現実的にはトリマ抵抗で微調整の作業が必要となり作業工数が増えてしまう。また、市販の差動アンプでゲイン誤差が０．０２％程度と比較的良いものもあるが高価であり、更に市販品でそれ以上の精度を望むことは難しい。従って、差動アンプを用いる電圧測定回路は、高精度測定を行う計測装置には適用できないという問題点があった。
【００１６】
本発明は、上記課題を解決するもので、高精度測定と高速測定を同時に実現することが可能な４線式抵抗測定を行う計測装置を提供することを目的とする。
【００１７】
【課題を解決するための手段】
このような目的を達成するために請求項１に記載の発明では、プラス電流端子及びマイナス電流端子を介して被測定物に定電流を供給するとともに、プラス電圧端子及びマイナス電圧端子を介して前記被測定物の両端に発生する電圧を検出して前記被測定物の抵抗値を測定する４線式抵抗測定を行う計測装置において、前記プラス電流端子及びマイナス電流端子に定電流を供給する測定用定電流源回路と、出力端子を前記マイナス電流端子に接続し、非反転入力端子をゼロ電位点に接続し、反転入力端子を前記プラス電圧端子に接続した演算増幅器と、
前記マイナス電圧端子とゼロ電位点との電位差を検出するプリアンプを備え、
前記演算増幅器によって前記プラス電圧端子の電位をゼロ電位となるように制御し、前記プリアンプによって前記マイナス電圧端子とゼロ電位点との間に発生する負電圧を検出することによって、前記被測定物の両端に発生する電圧を測定し、これを抵抗値換算して前記被測定物の抵抗を求めるように構成されたことを特徴とするものである。
【００１８】
これにより、被測定物に発生する電圧を差動アンプを用いることなく１回の測定で測定することが可能となる。
【００１９】
請求項２記載の発明では、請求項１に記載の計測装置に用いる定電流源回路を簡単な回路構成で実現することが可能となる。
【００２０】
請求項３に記載の発明では、４線式抵抗測定を行う計測装置において、
前記プラス電流端子及びマイナス電流端子に定電流を供給する測定用定電流源回路と、出力端子を前記マイナス電流端子に接続し、非反転入力端子をゼロ電位点に接続し、反転入力端子を前記プラス電圧端子に接続した演算増幅器と、前記マイナス電圧端子とゼロ電位点との電位差を検出するプリアンプから成る抵抗測定回路と、
前記プラス電流端子の電圧を入力とするコンパレータと、前記プリアンプの入力電圧をプルアップするプリアンプ用プルアップ回路と、前記演算増幅器の反転入力に接続された断線検知用定電流源回路と、前記プリアンプの出力を入力するバッファアンプと、前記バッファアンプの入力端子に前記コンパレータの出力を制御端子に入力するスイッチ回路を介して接続されたバッファアンプ用プルアップ回路から成る断線検知回路を備えたことを特徴とするものである。
【００２１】
これにより、請求項１に記載の計測装置に簡単な回路を付加するだけで、断線検知回路を実現することが可能となる。
【００２２】
請求項４から７に記載の発明では、請求項３に記載の計測装置と被測定物を接続する各配線がオープン状態となったことを、前記バッファアンプの出力をプラス側に出力することによって検知することが可能となる。
【００２３】
請求項８記載の発明では、請求項３に記載の計測装置に用いる定電流源回路を簡単な回路構成で実現することが可能となる。
【００２４】
【発明の実施の形態】
以下図面を用いて本発明を詳しく説明する。図１は本発明に係る計測装置の一実施例を示す回路図である。同図において従来例で説明した図５と同一のものは同一の符号を付し、その説明を省略する。
【００２５】
図１において、基準電圧４８は測定用定電流源回路４９に基準電圧を供給し、測定用定電流源回路４９の出力はプラス電流端子３に接続される。また、出力端子をマイナス電流端子６に接続された演算増幅器１０の反転入力はプラス電圧端子４に接続され、プリアンプ７の入力はマイナス電圧端子５に接続される。
【００２６】
ここで用いるプリアンプ７は、演算増幅器を利用して構成された非反転アンプである。
【００２７】
このような構成の計測装置１０１において、測定用定電流源回路４９から流れ出た定電流Ｉｓは被測定抵抗１を通って演算増幅器１０に流れ込む。演算増幅器１０はプラス電圧端子４をゼロ電位に制御しているので、プリアンプ７によってゼロ電位を基準にマイナス電圧端子５の電圧を測定すれば、被測定抵抗１の両端に発生した電圧を１回の測定で検出することが可能である。尚、プリアンプ７で測定されるマイナス電圧端子５の電圧は、マイナス電位の電圧である。
【００２８】
ここで、測定用定電流源回路４９の実施例を図２に示す。同図において測定用定電流源回路４９は、基準電圧４８を印加されて直列接続された基準抵抗５１と５２の共通接続点ｋを演算増幅器５４の非反転入力に接続し、前記基準電圧４８の印加点ｊを基準抵抗５３を介して前記演算増幅器５４の反転入力に接続し、前記演算増幅器５４の出力をＦＥＴ５５のゲートに接続し、前記ＦＥＴ５５のソースを前記演算増幅器５４に負帰還し、前記ＦＥＴ５５のドレインから定電流Ｉｓを出力するように構成されている。
【００２９】
上記のように構成された計測装置の測定精度は、電圧検出を行うプリアンプ７をシンプルな非反転アンプとしたため、プリアンプ７の構成部品である演算増幅器のオフセット電圧と抵抗の精度によって決定される。また、プリアンプ７の回路内のオフセットとゲインはソフトウェアによって根付けしてしまうので、各素子の絶対値は問題とならず、温度係数と経年変化の小さいものを使用すれば良い。従って、プリアンプ７を容易に高精度化することが可能であるため、計測装置１０１の高精度化が容易である。。
【００３０】
また、抵抗測定を行う場合、一般的に測定レンジに対応して被測定抵抗１に流す定電流Ｉｓの大きさを変化させるため、被測定抵抗１の両端に発生する電圧は測定レンジに依らず、比較的大きな電圧（例えば１０Ｖフルスケール）に標準化することが可能である。従って、プリアンプ７は極端に小さな電圧を測定する必要が無く比較的大きな電圧を測定するため、測定電圧に対するオフセット電圧のドリフトによる影響は相対的に小さくなる。このため、図５に示した計測装置のように２回測定を行ってオフセット電圧のドリフトによる影響を除去しなくても、充分高精度な測定を行うことが可能である。
【００３１】
また、図１のように構成された計測装置の断線検知手段を図３を用いて説明する。同図は、図１の計測装置に断線検知用回路を付加して構成された計測装置の一実施例である。同図において図１と同様のものは、同一の符号を付しその説明を省略する。
【００３２】
図３の計測装置において、プリアンプ７の出力は抵抗６４を介してバッファアンプ６５の入力に接続されており、このバッファアンプ６５の出力が制御回路１３に入力される。
【００３３】
また、例えば−１５Ｖの負基準電圧８１が印加された断線検知用定電流源回路６６は演算増幅器１０の反転入力に接続され、プルアップ抵抗６７に例えば＋１５Ｖのプルアップ電圧８２を印加して構成されたプリアンプ用プルアップ回路８４がプリアンプ７の入力に接続されている。
【００３４】
更に、プラス電流端子３に接続された測定用電流源回路４９の出力にはコンパレータ６１の入力が接続されており、このコンパレータ６１の出力は、スイッチ回路６２の制御端子に接続されている。このスイッチ回路６２の可動接点ｅにはプルアップ抵抗６３に例えば＋１５Ｖのプルアップ電圧８３印加して構成されたバッファアンプ用プルアップ回路８５が接続されており、このスイッチ回路６２の固定接点ｆはバッファアンプ６５の入力が接続されている。
【００３５】
このような構成の計測装置１０２において、計測装置１０２から被測定抵抗１に接続される４本の接続線ａ，ｂ，ｃ、ｄがオープン状態となった場合の動作について下記に説明する。
【００３６】
まず、プラス電流端子３から被測定抵抗１を接続する接続線ａがオープン状態となった場合、定電流Ｉｓが被測定抵抗１に流れなくなるため、プリアンプ７の出力はゼロになるが、測定用定電流源回路４９の負荷抵抗が無限大となるため、プラス電流端子３の電圧が基準電圧４８の電圧レベル付近まで上昇する。このプラス電流端子３の電圧はコンパレータ６１で監視されており、この電圧が予めコンパレータ６１に設定された電圧範囲を超過した場合、コンパレータ６１は出力をハイとする。コンパレータ６１の出力は、スイッチ回路６２の制御端子に接続されており、スイッチ回路６２は、この制御端子の信号がハイ状態となるとスイッチを閉じるように構成されている。これによって、バッファアンプ用プルアップ回路８５がバッファアンプ６５の入力に接続されるため、バッファアンプ６５の入力には＋１５Ｖであるプルアップ電圧８３とプリアンプ７の出力を、プルアップ抵抗６３と抵抗６４で分圧した電圧が入力される。
【００３７】
バッファアンプ６５の出力電圧は、全ての前記接続線ａ〜ｄがオープン状態とならず確実に接続された状態（以下、正常状態という。）であればマイナス電位の電圧であるが、接続線ａがオープン状態となった場合、上記の作用によりバッファアンプ６５の出力にはプラス電位の電圧が出力される。また、仮にプリアンプ７の出力がマイナス側に張り付いてもバッファアンプ６５の入力が常にプラス側になるような値にプルアップ抵抗６３と抵抗６４の抵抗値を決めておけば、接続線ａがオープン状態となった場合、制御回路１３には常にプラスの電圧が入力される。
【００３８】
制御回路１３は、マイナス電位の電圧が入力された場合、これを正常状態で測定された電圧であると認識し適切な演算処理を施し抵抗値換算を行うが、プラス側の電圧が入力された場合、これをオープン状態で測定された電圧であると認識し、断線検知処理を行う。この断線検知処理とは、例えば被測定抵抗１の抵抗値をスケールオーバーさせて表示し、測定者に異常の発生を認識させるものである。
【００３９】
プラス電圧端子４から被測定抵抗１を接続する接続線ｂがオープン状態となった場合、演算増幅器１０の反転入力端子の電流が断線検知用定電流源回路６６に流れ込むため、演算増幅器１０の出力からプラス側の電圧が出力される。従って、マイナス電流端子６に接続されているプラス電圧端子５の電圧もプラス電位となりプリアンプ７の出力電圧がプラス側となり最終的にバッファアンプ６５の出力にプラス電位の電圧が出力される。制御回路１３はこのプラス電位の電圧を検知して断線検知処理を行う。
【００４０】
また、ここで用いる断線検知用低電流源回路６６は、正常状態で測定を行っている場合、測定用定電流源回路４９の電流を差し引いてしまうので、断線検知用定電流源回路６６の定電流Ｉｏは測定用定電流源回路４９の定電流Ｉｓの１／１００以下程度の大きさにする必要があるが、定電流Ｉｏの大きさは、演算増幅器１０の出力をプラス側に引っ張るために必要な大きさ（例えば１００ｎＡ程度）があればよいため、問題とならない。また、断線検知用定電流源回路６６の精度も測定用定電流源回路４９の精度に比べて１００倍程度悪くても良いため、安価な汎用部品で構成することが可能である。
【００４１】
マイナス電圧端子５から被測定抵抗１を接続する接続線ｃがオープン状態となった場合、プリアンプ用プルアップ回路８４によって、プリアンプ７にプラス電位の電圧が入力され最終的にバッファアンプ６５の出力にプラス電位の電圧が出力される。制御回路１３はこのプラス電位の電圧を検知して断線検知処理を行う。
【００４２】
また、正常状態で測定を行っている時は、マイナス電圧端子５はマイナス電流端子６と接続されているため、低インピーダンスであるのでプリアンプ用プルアップ回路８４は測定に影響を及ぼさない。
【００４３】
マイナス電流端子６から被測定抵抗１を接続する接続線ｄがオープン状態となった場合、測定用定電流源回路４９の負荷抵抗が無限大となるため、マイナス電圧端子５の電圧が基準電圧４８の電圧レベル付近まで上昇する。これによってプリアンプ７にプラス電位の電圧が入力され最終的にバッファアンプ６５の出力にプラス電位の電圧が出力される。制御回路１３はこのプラス電位の電圧を検知して断線検知処理を行う。
【００４４】
上記には各配線が１本だけオープン状態となった場合の動作について説明したが、複数の配線が同時にオープン状態となった場合であっても、上記に説明した原理のいずれかを用いて断線検知が可能である。図４にオープン状態となった箇所と制御回路に入力される電圧及びその原理の関係を示す。
【００４５】
なお、以上の説明は、本発明の説明および例示を目的として特定の好適な実施例を示したに過ぎない。したがって本発明は、上記実施例に限定されることなく、その本質から逸脱しない範囲で更に多くの変更、変形をも含むものである。
【００４６】
【発明の効果】
以上説明したことから明らかなように、本発明によれば次のような効果がある。
請求項１に記載の発明では、４線式抵抗測定を高速且つ高精度に行うことが可能な計測装置をシンプルな回路構成で実現することが可能である
【００４７】
請求項３から７に記載の発明では、請求項１に記載された発明の計測装置に安価でシンプルな回路を付加するだけで、断線検知を実現することが可能である。
【００４８】
請求項２及び８に記載の発明では、請求項１及び３に記載された発明において、定電流源回路を安価でシンプルな回路構成で実現することが可能である。
【図面の簡単な説明】
【図１】本発明に係る計測装置の一実施例を示す構成図である。
【図２】本発明に係る計測装置の定電流源回路の一実施例を示す構成図である。
【図３】本発明に係る計測装置の断線検知回路の一実施例を示す構成図である。
【図４】本発明に係る計測装置の断線検知回路を説明する図である。
【図５】従来の計測装置の一例を示す構成図である。
【図６】従来の計測装置の他の一例を示す構成図である。
【符号の説明】
１被測定抵抗
３プラス電流端子
４プラス電圧端子
５マイナス電圧端子
６マイナス電流端子
７プリアンプ
９基準抵抗
１０演算増幅器
１３制御回路
４９測定用定電流源回路
６１コンパレータ
６２スイッチ回路
６３、６７プルアップ抵抗
８２，８３プルアップ電圧
Ｉｓ，Ｉｏ定電流
６４抵抗
６５バッファアンプ
４８，８１基準電圧
８４プリアンプ用プルアップ回路
８５バッファアンプ用プルアップ回路
１００，１０１，１０２計測装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement of a four-wire resistance measurement method and a measurement device, and more particularly to realizing a high-speed and high-accuracy four-wire resistance measurement, and to improve a contact failure of wiring or the like connecting an object to be measured and a measurement device. The present invention relates to a measurement device capable of preventing erroneous measurement that may occur due to disconnection or the like.
[0002]
[Prior art]
The configuration of a conventional measuring device for performing four-wire resistance measurement will be described with reference to FIG. FIG. 1 shows an example of a conventional 4-wire resistance measuring circuit of a high-precision 4-wire digital multimeter.
[0003]
In the figure, one end of a resistance 1 to be measured, which is an object to be measured, is connected to a positive current terminal 3 and a positive voltage terminal 4 of the measurement device 100, and another end of the resistance 1 to be measured is It is connected to terminal 6 and negative voltage terminal 5.
[0004]
Inside the measuring device 100, a reference voltage 48 is applied to the positive current terminal 3 via the reference resistor 9. The negative current terminal 6 has a non-inverting input terminal connected to the zero potential point and an inverting input terminal connected to the output terminal of the operational amplifier 10 connected to the positive current terminal 3. Further, the output of the operational amplifier 10 is negatively fed back via the phase compensation capacitor 14.
[0005]
Further, the positive voltage terminal 4 and the negative voltage terminal 5 are connected to one ends of FET switches 11 and 12, respectively, and the other ends of the FET switches 11 and 12 are connected to a preamplifier 7 which is a non-inverting amplifier using an operational amplifier. Connected to input. The output of the preamplifier 7 is input as a measurement voltage signal of the resistance 1 to be measured to the control circuit 13 at the subsequent stage, where it is converted into a digital value, and then an appropriate arithmetic processing is performed. It is displayed on a display (not shown) or the like as a resistance value. The control circuit 13 also manages the on / off operation of the FET switches 11 and 12.
[0006]
The measuring device 100 connected to the resistance under test 1 in this manner causes a known constant current Is to flow through the resistance under test 1 from the positive current terminal 3 to the negative current terminal 6 and is generated at both ends of the resistance under test 1. The voltage is measured from the positive voltage terminal 4 and the negative voltage terminal 5, and this voltage is divided by the constant current Is to determine the resistance value of the resistance 1 to be measured.
[0007]
The constant current Is is generated by the reference voltage 48, the reference resistor 9, and the operational amplifier 10. The magnitude of the constant current Is is controlled by the operation of the operational amplifier 10 to zero potential. A value obtained by dividing the voltage value of 48 by the resistance value of the reference resistor 9 is obtained.
[0008]
The control circuit 13 supplies the constant current Is to the resistance 1 to be measured, and applies a voltage Rv + generated on the plus side of the resistance 1 to be measured to the preamplifier 7 by turning on the FET switch 11 and turning off the FET switch 12. This value is input and detected, and this value is stored. Then, the voltage Rv- generated on the negative side of the resistance to be measured 1 is input to the preamplifier 7 by turning off the FET switch 11 and turning on the FET switch 12 for detection. And store this value.
[0009]
The control circuit 13 subtracts the voltage Rv− generated on the negative side from the voltage Rv + generated on the positive side of the resistance 1 to be measured stored by the above operation, divides the value by the current value of the constant current Is, and performs control. The resistance value of the measurement resistor 1 is obtained.
[0010]
In a measuring device having such a configuration, a non-inverting amplifier having a simple configuration can be used as a preamplifier, and the difference between the voltage generated on the plus side and the voltage generated on the minus side can be obtained by performing two measurements. By calculating, the drift due to the offset voltage of the preamplifier can be canceled, and the resistance value of the measured resistance 1 can be measured with high accuracy.
[0011]
FIG. 6 shows another conventional example. FIG. 1 is an example of a measuring device used for high-speed measurement, such as a measuring device used in a production line. 5, the same components as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.
[0012]
In the circuit of FIG. 6, the principle of flowing a constant current Is through the resistance to be measured 1 and obtaining the resistance value from the voltage generated at both ends thereof is the same as that of the measuring device of FIG. 5, but the measuring device of FIG. The voltage terminal 4 and the negative voltage terminal 5 are connected to the non-inverting input and the inverting input of the preamplifier 7, respectively, and the preamplifier 7 is used as a differential amplifier.
[0013]
In the circuit of FIG. 6, since the preamplifier 7 is used as a differential amplifier as described above, a constant current Is flows through the resistance under test 1 and a voltage generated at both ends can be obtained by one measurement. , High-speed measurement becomes possible.
[0014]
[Problems to be solved by the invention]
However, in the conventional measuring device shown in FIG. 5, it is necessary to perform two measurements in order to find the voltage generated at both ends of the resistance 1 to be measured. There was a problem that it was not possible.
[0015]
Further, in the conventional measuring device shown in FIG. 6, by using the preamplifier 7 as a differential amplifier, it is possible to measure the voltage generated at both ends of the measured resistance 1 in one measurement. The measuring device having such a configuration has a problem that the measurement accuracy depends on the accuracy of the preamplifier 7. That is, in order to perform high-precision measurement, matching of the absolute value of the resistance constituting the preamplifier 7 requires an accuracy higher than the expected measurement accuracy. Practically, fine adjustment work is required with the trimmer resistance, and the number of work steps increases. In addition, some commercially available differential amplifiers have a relatively good gain error of about 0.02%, but are expensive, and it is difficult to obtain higher accuracy with a commercially available amplifier. Therefore, there is a problem that the voltage measurement circuit using the differential amplifier cannot be applied to a measurement device that performs high-accuracy measurement.
[0016]
An object of the present invention is to solve the above-described problems and to provide a measuring device for performing a four-wire resistance measurement capable of simultaneously realizing high-accuracy measurement and high-speed measurement.
[0017]
[Means for Solving the Problems]
In order to achieve such an object, in the invention described in claim 1, a constant current is supplied to the device under test via a positive current terminal and a negative current terminal, and the constant current is supplied via a positive voltage terminal and a negative voltage terminal. A measuring device for detecting a voltage generated at both ends of a device under test and performing a four-wire resistance measurement for measuring a resistance value of the device under test for supplying a constant current to the positive current terminal and the negative current terminal A constant current source circuit, an operational amplifier having an output terminal connected to the negative current terminal, a non-inverting input terminal connected to a zero potential point, and an inverting input terminal connected to the positive voltage terminal,
A preamplifier for detecting a potential difference between the negative voltage terminal and a zero potential point,
By controlling the potential of the positive voltage terminal to be zero potential by the operational amplifier, and detecting the negative voltage generated between the negative voltage terminal and the zero potential point by the preamplifier, It is characterized in that a voltage generated at both ends is measured, and this is converted into a resistance value to obtain the resistance of the object to be measured.
[0018]
This makes it possible to measure the voltage generated in the device under test in one measurement without using a differential amplifier.
[0019]
According to the second aspect of the present invention, the constant current source circuit used for the measuring device according to the first aspect can be realized with a simple circuit configuration.
[0020]
According to a third aspect of the present invention, in the measuring device for performing a four-wire resistance measurement,
A constant current source circuit for measurement that supplies a constant current to the positive current terminal and the negative current terminal, an output terminal is connected to the negative current terminal, a non-inverting input terminal is connected to a zero potential point, and an inverting input terminal is An operational amplifier connected to a positive voltage terminal, and a resistance measuring circuit including a preamplifier for detecting a potential difference between the negative voltage terminal and a zero potential point;
A comparator to which the voltage of the plus current terminal is input, a preamplifier pull-up circuit to pull up an input voltage of the preamplifier, a disconnection detection constant current source circuit connected to an inverting input of the operational amplifier, and the preamplifier And a disconnection detection circuit comprising a buffer amplifier pull-up circuit connected to an input terminal of the buffer amplifier via a switch circuit for inputting the output of the comparator to a control terminal. It is a feature.
[0021]
Thus, it is possible to realize a disconnection detection circuit by simply adding a simple circuit to the measuring device according to the first aspect.
[0022]
According to the inventions described in claims 4 to 7, the fact that each wiring connecting the measuring device according to claim 3 and the device under test is in an open state is output by outputting the output of the buffer amplifier to the plus side. It becomes possible to detect.
[0023]
According to the eighth aspect of the present invention, the constant current source circuit used for the measuring device according to the third aspect can be realized with a simple circuit configuration.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the measuring device according to the present invention. In this figure, the same components as those in FIG. 5 described in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.
[0025]
In FIG. 1, a reference voltage 48 supplies a reference voltage to a measuring constant current source circuit 49, and an output of the measuring constant current source circuit 49 is connected to the plus current terminal 3. The inverted input of the operational amplifier 10 whose output terminal is connected to the negative current terminal 6 is connected to the positive voltage terminal 4, and the input of the preamplifier 7 is connected to the negative voltage terminal 5.
[0026]
The preamplifier 7 used here is a non-inverting amplifier configured using an operational amplifier.
[0027]
In the measuring device 101 having such a configuration, the constant current Is flowing out of the constant current source circuit 49 for measurement flows into the operational amplifier 10 through the resistance 1 to be measured. Since the operational amplifier 10 controls the positive voltage terminal 4 to zero potential, if the voltage of the negative voltage terminal 5 is measured by the preamplifier 7 based on the zero potential, the voltage generated at both ends of the resistance 1 to be measured is once measured. Can be detected by the measurement of The voltage of the negative voltage terminal 5 measured by the preamplifier 7 is a voltage of a negative potential.
[0028]
Here, an embodiment of the constant current source circuit 49 for measurement is shown in FIG. In the figure, a measuring constant current source circuit 49 connects a common connection point k of reference resistors 51 and 52 connected in series by applying a reference voltage 48 to a non-inverting input of an operational amplifier 54. The application point j is connected to the inverting input of the operational amplifier 54 via the reference resistor 53, the output of the operational amplifier 54 is connected to the gate of the FET 55, and the source of the FET 55 is negatively fed back to the operational amplifier 54, The constant current Is is output from the drain of the FET 55.
[0029]
The measurement accuracy of the measuring device configured as described above is determined by the accuracy of the offset voltage and the resistance of the operational amplifier, which is a component of the preamplifier 7, because the preamplifier 7 that performs voltage detection is a simple non-inverting amplifier. Further, since the offset and gain in the circuit of the preamplifier 7 are established by software, the absolute value of each element does not matter, and an element having a small temperature coefficient and small aging can be used. Therefore, since the precision of the preamplifier 7 can be easily increased, the accuracy of the measuring apparatus 101 can be easily increased. .
[0030]
In addition, when resistance measurement is performed, the magnitude of the constant current Is flowing through the resistance 1 to be measured is generally changed in accordance with the measurement range. Therefore, the voltage generated at both ends of the resistance 1 to be measured does not depend on the measurement range. Can be standardized to a relatively large voltage (eg, 10 V full scale). Therefore, since the preamplifier 7 does not need to measure an extremely small voltage and measures a relatively large voltage, the influence of the offset voltage drift on the measured voltage is relatively small. Therefore, sufficiently high-accuracy measurement can be performed without performing the measurement twice and removing the influence of the drift of the offset voltage as in the measurement device illustrated in FIG.
[0031]
Further, a disconnection detecting means of the measuring device configured as shown in FIG. 1 will be described with reference to FIG. FIG. 3 shows an embodiment of a measuring device configured by adding a disconnection detecting circuit to the measuring device of FIG. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0032]
3, the output of the preamplifier 7 is connected to the input of a buffer amplifier 65 via a resistor 64, and the output of the buffer amplifier 65 is input to the control circuit 13.
[0033]
Further, the disconnection detection constant current source circuit 66 to which the negative reference voltage 81 of, for example, -15 V is applied is connected to the inverting input of the operational amplifier 10, and is configured by applying a pull-up voltage 82 of, for example, +15 V to the pull-up resistor 67. The pre-amplifier pull-up circuit 84 is connected to the input of the pre-amplifier 7.
[0034]
Further, the output of the measuring current source circuit 49 connected to the positive current terminal 3 is connected to the input of the comparator 61, and the output of the comparator 61 is connected to the control terminal of the switch circuit 62. The movable contact e of the switch circuit 62 is connected to a buffer amplifier pull-up circuit 85 configured by applying a pull-up voltage 83 of, for example, +15 V to a pull-up resistor 63. The fixed contact f of the switch circuit 62 is The input of the buffer amplifier 65 is connected.
[0035]
In the measuring device 102 having such a configuration, an operation when the four connection lines a, b, c, and d connected from the measuring device 102 to the resistance 1 to be measured are in an open state will be described below.
[0036]
First, when the connection line a connecting the positive resistance terminal 3 to the resistance 1 to be measured is in an open state, the constant current Is does not flow through the resistance 1 to be measured, so that the output of the preamplifier 7 becomes zero. Since the load resistance of the constant current source circuit 49 becomes infinite, the voltage of the plus current terminal 3 rises to near the voltage level of the reference voltage 48. The voltage of the positive current terminal 3 is monitored by the comparator 61. When this voltage exceeds a voltage range set in the comparator 61 in advance, the comparator 61 sets the output to high. The output of the comparator 61 is connected to a control terminal of a switch circuit 62, and the switch circuit 62 is configured to close the switch when the signal of the control terminal goes to a high state. As a result, the buffer amplifier pull-up circuit 85 is connected to the input of the buffer amplifier 65, so that the input of the buffer amplifier 65 is supplied with the pull-up voltage 83 of +15 V and the output of the preamplifier 7, and the pull-up resistor 63 and the resistor 64. The divided voltage is input.
[0037]
The output voltage of the buffer amplifier 65 is a negative potential voltage when all of the connection lines a to d are securely connected without being opened (hereinafter referred to as a normal state). Is in an open state, a positive potential voltage is output to the output of the buffer amplifier 65 by the above operation. Also, if the resistance values of the pull-up resistor 63 and the resistor 64 are determined so that the input of the buffer amplifier 65 is always on the plus side even if the output of the preamplifier 7 is stuck on the minus side, the connection line a becomes In the open state, a positive voltage is always input to the control circuit 13.
[0038]
When a voltage of a negative potential is input, the control circuit 13 recognizes this as a voltage measured in a normal state, performs appropriate arithmetic processing, and performs resistance value conversion, but a positive voltage is input. In this case, this is recognized as the voltage measured in the open state, and disconnection detection processing is performed. The disconnection detection processing is, for example, to display the resistance value of the resistance 1 to be measured in a scale-over manner so that the measurer can recognize the occurrence of the abnormality.
[0039]
When the connection line b connecting the resistance 1 to be measured from the positive voltage terminal 4 is in an open state, the current at the inverting input terminal of the operational amplifier 10 flows into the disconnection detecting constant current source circuit 66. Outputs a positive voltage. Accordingly, the voltage of the plus voltage terminal 5 connected to the minus current terminal 6 also becomes a plus potential, and the output voltage of the preamplifier 7 becomes the plus side, and finally a plus potential voltage is output to the output of the buffer amplifier 65. The control circuit 13 detects the positive voltage and performs a disconnection detection process.
[0040]
The disconnection detection low current source circuit 66 used here subtracts the current of the measurement constant current source circuit 49 when the measurement is performed in a normal state. The current Io needs to be about 1/100 or less of the constant current Is of the constant current source circuit 49 for measurement, but the magnitude of the constant current Io is required to pull the output of the operational amplifier 10 to the plus side. This is not a problem because it is sufficient that a required size (for example, about 100 nA) is provided. In addition, the accuracy of the disconnection detection constant current source circuit 66 may be about 100 times lower than the accuracy of the measurement constant current source circuit 49, so that it is possible to use inexpensive general-purpose components.
[0041]
When the connection line c connecting the resistance 1 to be measured from the negative voltage terminal 5 is in an open state, a positive potential voltage is input to the preamplifier 7 by the preamplifier pull-up circuit 84 and finally to the output of the buffer amplifier 65. A positive voltage is output. The control circuit 13 detects the positive voltage and performs a disconnection detection process.
[0042]
When the measurement is performed in a normal state, the negative voltage terminal 5 is connected to the negative current terminal 6 and has a low impedance, so that the preamplifier pull-up circuit 84 does not affect the measurement.
[0043]
When the connection line d connecting the negative current terminal 6 to the resistance 1 to be measured is in an open state, the load resistance of the constant current source circuit 49 for measurement becomes infinite, so that the voltage of the negative voltage terminal 5 becomes the reference voltage 48. Rise to near the voltage level of As a result, a positive potential voltage is input to the preamplifier 7, and finally a positive potential voltage is output to the output of the buffer amplifier 65. The control circuit 13 detects the positive voltage and performs a disconnection detection process.
[0044]
In the above, the operation in the case where only one of the wirings is in the open state has been described. However, even in the case where the plurality of wirings are in the open state at the same time, the disconnection is performed by using any of the principles described above. Detection is possible. FIG. 4 shows the relationship between the open state, the voltage input to the control circuit, and the principle thereof.
[0045]
It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of explanation and illustration of the present invention. Therefore, the present invention is not limited to the above-described embodiment, but includes many more changes and modifications without departing from the spirit thereof.
[0046]
【The invention's effect】
As is apparent from the above description, the present invention has the following effects.
According to the first aspect of the present invention, it is possible to realize a measuring device capable of performing a four-wire resistance measurement at high speed and with high accuracy with a simple circuit configuration.
According to the third to seventh aspects of the present invention, disconnection detection can be realized only by adding an inexpensive and simple circuit to the measuring apparatus of the first aspect.
[0048]
According to the second and eighth aspects of the present invention, in the first and third aspects, the constant current source circuit can be realized with an inexpensive and simple circuit configuration.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a measuring device according to the present invention.
FIG. 2 is a configuration diagram showing one embodiment of a constant current source circuit of the measuring device according to the present invention.
FIG. 3 is a configuration diagram showing one embodiment of a disconnection detection circuit of the measuring device according to the present invention.
FIG. 4 is a diagram illustrating a disconnection detection circuit of the measuring device according to the present invention.
FIG. 5 is a configuration diagram illustrating an example of a conventional measurement device.
FIG. 6 is a configuration diagram showing another example of a conventional measurement device.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 resistance to be measured 3 plus current terminal 4 plus voltage terminal 5 minus voltage terminal 6 minus current terminal 7 preamplifier 9 reference resistor 10 operational amplifier 13 control circuit 49 measurement constant current source circuit 61 comparator 62 switch circuit 63, 67 pull-up resistor 82 , 83 Pull-up voltage Is, Io Constant current 64 Resistance 65 Buffer amplifier 48, 81 Reference voltage 84 Pre-amplifier pull-up circuit 85 Buffer amplifier pull-up circuit 100, 101, 102 Measuring device

Claims

A constant current is supplied to the device under test through a positive current terminal and a negative current terminal, and a voltage generated at both ends of the device under test is detected through a positive voltage terminal and a negative voltage terminal to detect the voltage of the device under test. In a measuring device that performs a four-wire resistance measurement for measuring a resistance value,
A constant current source circuit for measurement for supplying a constant current to the positive current terminal and the negative current terminal,
An operational amplifier having an output terminal connected to the negative current terminal, a non-inverting input terminal connected to a zero potential point, and an inverting input terminal connected to the positive voltage terminal,
A preamplifier for detecting a potential difference between the negative voltage terminal and a zero potential point,
By controlling the potential of the positive voltage terminal to be zero potential by the operational amplifier, and detecting the negative voltage generated between the negative voltage terminal and the zero potential point by the preamplifier, A measuring apparatus characterized in that a voltage generated at both ends is measured, and this is converted into a resistance value to obtain a resistance of the object to be measured.

The constant current source circuit for measurement connects a common connection point of a series-connected reference resistance to which a reference voltage is applied, to a non-inverting input of an operational amplifier, and connects the application point of the reference voltage via the reference resistance to the calculation point. Connected to the inverting input of the amplifier, connected to the output of the operational amplifier to the gate of the FET, negatively fed back the source of the FET to the operational amplifier, and output a constant current from the drain of the FET. The measuring device according to claim 1, wherein:

A constant current is supplied to the device under test through a positive current terminal and a negative current terminal, and a voltage generated at both ends of the device under test is detected through a positive voltage terminal and a negative voltage terminal to detect the voltage of the device under test. In a measuring device that performs a four-wire resistance measurement for measuring a resistance value,
A constant current source circuit for measurement for supplying a constant current to the positive current terminal and the negative current terminal,
An operational amplifier having an output terminal connected to the negative current terminal, a non-inverting input terminal connected to a zero potential point, and an inverting input terminal connected to the positive voltage terminal,
A resistance measuring circuit comprising a preamplifier for detecting a potential difference between the negative voltage terminal and a zero potential point,
A comparator that receives the voltage of the positive current terminal as an input,
A preamplifier pull-up circuit for pulling up the input voltage of the preamplifier,
Disconnection detection constant current source circuit connected to the inverting input of the operational amplifier,
A buffer amplifier for receiving an output of the preamplifier;
A measuring apparatus comprising: a disconnection detection circuit including a buffer amplifier pull-up circuit connected to an input terminal of the buffer amplifier via a switch circuit that inputs an output of the comparator to a control terminal.

The disconnection detecting circuit, when the wiring connected from the positive current terminal to the device under test is disconnected, detects a voltage increase of the positive current input terminal caused by the disconnection by the comparator, and closes the switch circuit. An output is generated, a voltage of the buffer amplifier pull-up circuit is applied to an input of the buffer amplifier, and an output of the buffer amplifier is output to a positive side to detect disconnection. The measuring device according to claim 3.

The disconnection detection circuit, when the wiring connected from the positive voltage terminal to the device under test is disconnected, the disconnection detection constant current source circuit allows a current to flow from the inverting input of the operational amplifier, A positive voltage is induced in the output, a positive voltage is applied to the input of the preamplifier connected thereto, and the disconnection is detected by outputting the output of the preamplifier to the positive side. The measuring device according to claim 3, characterized in that:

The disconnection detecting circuit, when the wiring connected to the device under test from the negative voltage terminal is disconnected, a voltage on the positive side to the input of the preamplifier connected to the negative voltage terminal by the preamplifier pull-up circuit. 4. The measuring device according to claim 3, wherein the measuring device is configured to apply the voltage and output the output of the preamplifier to a positive side to detect a disconnection.

The disconnection detection circuit, when the wiring connected to the device under test from the negative current terminal is disconnected, a voltage on the positive side to the input of the preamplifier connected to the negative current terminal by the preamplifier pull-up circuit. 4. The measuring device according to claim 3, wherein the measuring device is configured to apply the voltage and output the output of the preamplifier to a positive side to detect a disconnection.

The constant current source circuit for measurement connects a common connection point of a series-connected reference resistance to which a reference voltage is applied, to a non-inverting input of an operational amplifier, and connects the application point of the reference voltage via the reference resistance to the calculation point. Connected to the inverting input of the amplifier, connected to the output of the operational amplifier to the gate of the FET, negatively fed back the source of the FET to the operational amplifier, and output a constant current from the drain of the FET. The measuring device according to claim 3, wherein: