JP3678564B2

JP3678564B2 - Method and apparatus for measuring ultrasonic propagation characteristics

Info

Publication number: JP3678564B2
Application number: JP32086397A
Authority: JP
Inventors: 哲哉芦田; 博石橋; 嘉郎羽深; 実岡本; 栄二大沼
Original assignee: Mitsubishi Cable Industries Ltd
Current assignee: Mitsubishi Cable Industries Ltd
Priority date: 1997-11-21
Filing date: 1997-11-21
Publication date: 2005-08-03
Anticipated expiration: 2017-11-21
Also published as: JPH11153584A

Description

【０００１】
【発明の属する技術分野】
本発明は、被検査物の超音波伝搬速度などの超音波の伝搬特性を非破壊的に測定し得る方法およびそのための装置に関する。
【０００２】
【従来の技術】
多くの有機高分子は、熱、日光、放射線あるいはその他の原因により劣化し、劣化の進行と共にその超音波伝搬速度が変化することが知られている。例えば、劣化の進行と共に有機高分子の破断伸び率が低下し、劣化した有機高分子中での超音波の伝搬速度が変化する。この現象を利用して、有機高分子の劣化度を超音波の伝搬速度の変化から診断する方法が周知である。一方、電力ケーブル、通信ケーブル、屋内配電線などの各種絶縁電線は、その電気絶縁層やシースなどの被覆層の劣化により停電や火災事故が生じる可能性があるので、稼働中におけるその被覆層の劣化度は定期的な測定により監視する必要がある。しかもその監視は、電線が稼働中である故にその被覆層を破壊することなく行う必要があるために上記の超音波診断法を絶縁電線の非破壊劣化診断に適用することが提案されている。
【０００３】
例えば、特開平７−３５７３３号公報では、診断対象の電力ケーブルの被覆層の外表面上から超音波をケーブルの半径方向、即ち垂直方向に入射し、被覆層中での超音波伝搬速度Ｖを下式（１）にて求める方法が提案されている。
Ｖ＝２ａ／ｔ（１）
式（１）において、ａは被覆層の厚みであり、ｔは超音波の入射から該被覆層の下層（例えば、導体）の表面で反射して再び入射位置まで帰還するに要した時間である。
【０００４】
ところで上記の方法は、被覆層の厚みａの正しい値が既知である場合には有用であるが、実際上多くの場合においてその値は既知でない。そこで被覆層の厚みａとして絶縁電線の設計基準寸法を採用することが考えられるが、絶縁電線の製造の際には設計基準寸法に対して±１５％もの製造公差が許容されているために、該寸法を用いて算出された伝搬速度は正確さに劣る問題がある。
【０００５】
【発明が解決しようとする課題】
上記に鑑みて本発明が解決しようとする課題は、被検査物の超音波伝搬速度や該速度の相対値などの超音波伝搬特性を非破壊的に、且つより正確に測定する方法、およびそのための測定装置を提供することにある。
【０００６】
【課題を解決するための手段】
上記の課題は、以下に示す測定方法あるいは測定装置にて解決される。
１、超音波送信手段(1) を設置手段(11)を介し、且つ超音波受信手段(2) を設置手段(21)を介してそれぞれ被検査物の表面に設置し、超音波送信手段(1) と超音波受信手段(2) との設置間隔がＬ1 とＬ2 とであるとき、超音波送信手段(1) から送信された超音波が被検査物中を伝搬して超音波受信手段(2)にて受信される迄に要する伝搬時間ｔ1 とｔ2 とをそれぞれ測定して行う超音波伝搬特性の測定方法であって、
前記被検査物は、絶縁電線の被覆層であり、かつ、
前記設置手段(11)および設置手段(21)が、ポリ四フッ化エチレンまたはシリコーンゴムからなることを特徴とする超音波伝搬特性の測定方法。
２、下式（２）から被検査物の超音波伝搬速度Ｖを算出する上記１記載の超音波伝搬特性の測定方法。
Ｖ＝（Ｌ2 −Ｌ1 ）／（ｔ2 −ｔ1 ）（２）
３、被検査物の劣化度の診断のために、被検査物の超音波伝搬速度Ｖの経時的変化を、または設置間隔Ｌ1 とＬ2 との差（Ｌ2 −Ｌ1 ）を常に一定として測定した際に得られる被検査物の（ｔ2 −ｔ1 ）または１／（ｔ2 −ｔ1 ）の経時的変化を測定する上記１または２記載の超音波伝搬特性の測定方法。
４、上記設置手段(11)と絶縁電線の被覆層との間、および上記設置手段(21)と絶縁電線の被覆層との間に、それぞれ、グリスまたは油剤を介在させる上記１〜３のいずれかに記載の超音波伝搬特性の測定方法。
５、上記絶縁電線の被覆層の厚みが、当該測定方法を実施する時点において既知でないことを特徴とする、上記１〜４のいずれかに記載の超音波伝搬特性の測定方法。
６、超音波送信手段(1) とその設置手段(11)、超音波受信手段(2) とその設置手段(21)、および伝搬時間測定手段 (3) を有する、超音波伝搬特性の測定装置であって、
超音波送信手段 (1) の設置手段 (11) は、該送信手段 (1) を被検査物の表面に設置するに際して、該送信手段 (1) から送信された超音波が該設置手段 (11) を通過して被検査物に入射するように、該送信手段 (1) と被検査物の表面との間に介在するものであり、
超音波受信手段 (2) の設置手段 (21) は、該受信手段 (2) を被検査物の表面に設置するに際して、被検査物内を伝搬する超音波が該設置手段 (21) を通過して該受信手段 (2) で受信されるように、該受信手段 (2) と被検査物の表面との間に介在するものであり、
前記伝搬時間測定手段 (3) は、被検査物の表面に設置された超音波送信手段(1)と超音波受信手段(2) との設置間隔がＬ1 とＬ2 とであるときに超音波送信手段(1) から送信された超音波が被検査物中を伝搬して超音波受信手段(2) にて受信される迄に要する伝搬時間ｔ1 とｔ2 とをそれぞれ測定する手段であり、
前記被検査物は、絶縁電線の被覆層であり、かつ、
前記設置手段(11)および設置手段(21)が、ポリ四フッ化エチレンまたはシリコーンゴムからなることを特徴とする超音波伝搬特性の測定装置。
７、伝搬時間ｔ1 とｔ2 とから（ｔ2 −ｔ1 ）または１／（ｔ2 −ｔ1 ）を、あるいは設置間隔Ｌ1 とＬ2 および伝搬時間ｔ1 とｔ2 とから下式（２）により被検査物の超音波伝搬速度Ｖを算出する演算手段(4) をさらに有する上記６記載の超音波伝搬特性の測定装置。
Ｖ＝（Ｌ2 −Ｌ1 ）／（ｔ2 −ｔ1 ）（２）
【０００７】
【作用】
超音波送信手段(1) と超音波受信手段(2) とを被検査物の表面に設置し、該両手段間の設置間隔をＬ1 とＬ2 の二ケースとして、各ケース毎に超音波送信手段(1) から送信された超音波が被検査物中を伝搬して超音波受信手段(2) にて受信される迄の伝搬時間ｔ1 とｔ2 とをそれぞれ測定することにより、後記する説明の通り、上記の式（２）により被検査物の厚みとは無関係に超音波伝搬特性を正確に求めることができる。
【０００８】
【発明の実施の形態】
以下、本発明を図面により詳細に説明する。図１は本発明の測定方法および測定装置についての説明図であり、図２は図１と共に本発明の超音波伝搬特性の測定方法を説明する説明図であり、図３は設置手段(11)と被検査物との界面における超音波の屈折の様子を説明する説明図である。
【０００９】
図１は、本発明の測定装置の実施例であって、電力ケーブルなどの絶縁電線の被覆層の劣化診断装置として応用したものであり、また該実施例の装置による超音波伝搬特性の測定方法をも説明する。
図１の劣化診断装置は、超音波送信手段(1) 、超音波送信制御手段(12)、超音波受信手段(2) 、超音波受信制御手段(22)、伝搬時間測定手段(3) 、演算手段(4) 、距離入力手段(5) 、判定手段(6) 、および表示手段(7) とからなる。
【００１０】
超音波送信手段(1) は、内蔵せる振動子（図示せず）にて超音波を発生し送信し得る機能をなし、また設置手段(11)を有していて設置手段(11)により被検査物の一例たる絶縁電線Ｃの被覆層Ｃ１の表面上に設置されている。超音波送信手段(1) から送信された超音波は、設置手段(11)中を通過して被覆層Ｃ１に入射される。超音波送信制御手段(12)は、超音波送信手段(1) からの超音波の送信時刻などを電気信号にて後記の伝搬時間測定手段(3) に入力する機能をなす。超音波受信手段(2) は、設置手段(21)を有していて設置手段(21)により被覆層Ｃ１の表面上で超音波送信手段(1) から距離Ｌ1 だけ離れた位置に設置されており、被覆層Ｃ１内を伝搬する超音波を設置手段(21)を介して受信する機能をなす。図１では設置手段(11)や設置手段(21)として、有機高分子、例えば、ポリ四フッ化エチレンからなる斜角型ディレーチップを使用することができる。
【００１１】
超音波受信制御手段(22)は、超音波受信手段(2) からの超音波の受信時刻などを電気信号にて伝搬時間測定手段(3) に入力する機能をなす。伝搬時間測定手段(3) は、超音波送信制御手段(12)と超音波受信制御手段(22)とからの各入力を基に、超音波送信手段(1) から送信された超音波が被検査物中を伝搬して超音波受信手段(2) にて受信される迄に要する伝搬時間ｔ1 やｔ2 を測定する機能をなす。残る演算手段(4) 、距離入力手段(5) 、判定手段(6) 、および表示手段(7) の各機能については後記する。
【００１２】
超音波送信手段(1) と超音波受信手段(2) とは、距離Ｌ1 なる間隔をおいて被覆層Ｃ１の表面に設置されている。この状態で超音波送信手段(1) から超音波を送信すると、送信された超音波は設置手段(11)を通過して被覆層Ｃ１内に入射される。入射された超音波は、被覆層Ｃ１内を種々の経路で伝搬するが、超音波送信手段(1) と超音波受信手段(2) との間を最短経路で伝搬する超音波部分も存在するので該超音波部分が超音波受信手段(2) により受信される。
【００１３】
超音波送信手段(1) からの超音波の送信時刻並びに超音波受信手段(2) による超音波の受信時刻が、それぞれ超音波送信制御手段(12)と超音波受信制御手段(22)とから伝搬時間測定手段(3) に入力され、伝搬時間測定手段(3) により上記の設置間隔Ｌ1 に対する超音波の伝搬時間ｔ1 が測定される。
【００１４】
上記の説明から明らかな通り、超音波送信手段(1) から送信された超音波は、図１中に点線で示す経路、即ち設置手段(11)、被覆層Ｃ１、設置手段(21)を順次経由して超音波受信手段(2) に到るのであるが、いま設置手段(11)内での超音波伝搬速度をＶ1 、伝搬距離をＬ11、伝搬時間をｔ11とし、被覆層Ｃ１内での超音波伝搬速度をＶ、伝搬距離をＬ1 、伝搬時間をｔｘとし、また設置手段(21)内での超音波伝搬速度をＶ2 、伝搬距離をＬ2 、伝搬時間をｔ12とすると、下式（３）が成立する。

【００１５】
つぎに超音波送信手段(1) と超音波受信手段(2) との設置間隔を図２に示すようにＬ2 に変更して、上記と同様の方法で設置間隔Ｌ2 に対する超音波の伝搬時間ｔ2 を測定する。その場合、式（３）に対応して下式（４）が成立する。さらに、式（４）と式（３）の差から前記の式（２）が得られる。
ｔ2 ＝（Ｌ11／Ｖ1 ）＋（Ｌ2 ／Ｖ）＋（Ｌ12／Ｖ2 ）（４）
【００１６】
式（２）〜（４）から、Ｌ1 に対するｔ1 を測定する際に使用した設置手段(11)と設置手段(21)とをＬ2 に対するｔ2 を測定する際にも使用するならば、超音波伝搬特性の測定は、原理的にそれら設置手段の形状、寸法、さらには形成材料などに左右されないことが判る。
【００１７】
なお図１および図２においては、上記の式（３）および式（４）の成立を理解し易いように、設置手段(11)と設置手段(21)が被覆層Ｃ１と接する各底面内で超音波の伝搬密度が最高となる辺りをそれぞれ黒丸で示し、各黒丸の位置をもって仮に超音波送信手段(1) と超音波受信手段(2) の設置位置としている。しかし本発明においては超音波送信手段(1) と超音波受信手段(2) の各設置位置は、該黒丸の位置に限る必要はなく、例えば超音波送信手段(1) であれば設置手段(11)の底面の最先端、最後端、あるいはその中間点など任意の位置に決定すればよい。同様のことが超音波受信手段(2) についても該当する。その理由は、上記式（３）と（４）から式（２）を誘導する過程から容易に理解されよう。
【００１８】
上記式（２）から明らかな通り、超音波伝搬速度Ｖは（ｔ2 −ｔ1 ）に逆比例し、１／（ｔ2 −ｔ1 ）に比例する。換言すると、それらの値は超音波伝搬速度Ｖと相対関係にある。よって被検査物の多くの劣化度診断時のように、劣化度の経時的な相対変化だけで十分である場合には、本発明において超音波伝搬特性の測定を常に（Ｌ2 −Ｌ1 ）を一定として行って（ｔ2 −ｔ1 ）や１／（ｔ2 −ｔ1 ）を算出し、それらの数値にて劣化度診断を行うことができる。
【００１９】
上記の測定における設置間隔Ｌ1 とＬ2 とは、距離入力手段(5) にて記憶され、また伝搬時間測定手段(3) にて伝搬時間ｔ1 とｔ2 とが測定される。その後、距離入力手段(5) から設置間隔Ｌ1 とＬ2 とが、一方、伝搬時間測定手段(3) から伝搬時間ｔ1 とｔ2 とがそれぞれ演算手段(4) に入力され、演算手段(4) により伝搬時間差( ｔ2 −ｔ1)や１／( ｔ2 −ｔ1)、あるいは上記式（２）により超音波伝搬速度Ｖが算出される。判定手段(6) は、被覆層Ｃ１を形成する有機高分子についての種々の劣化度における物性、例えば、破断伸び率、引張強度、１００％モジュラスなどと超音波伝搬速度Ｖあるいは該Ｖとの上記相対関係値との相関関係データを保持しており、演算手段(4) から入力されるそれらの値を基に劣化度を判定し、その結果を表示手段(7) に送って劣化度を種々の表示方法、例えば絶縁電線の稼働日数−劣化度の関係グラフなどにて表示せしめる。
【００２０】
超音波送信手段(1) と超音波受信手段(2) との設置間隔を大きくすれば、換言すると、上記の式（３）、式（４）においてＬ1 やＬ2 の値を大きくすれば、理論的にＬ11やＬ12の影響が小さくなって、式（３）あるいは式（４）のみで超音波伝搬特性を測定できることになる。しかし、固体中、特に有機高分子中を伝搬する超音波は、一般的に極めて減衰し易いのでＬ1 やＬ2 の値は数百μｍ〜数十ｍｍ程度とすることが好ましい。その大きさは、実用的な設置手段(11)や設置手段(21)、例えば前記したポリ四フッ化エチレン製斜角型ディレーチップが有するＬ11やＬ12のせいぜい０．５〜５倍程度に過ぎず、このために式（３）あるいは式（４）のみで超音波伝搬特性を測定することは困難である。これらのことから本発明の超音波伝搬特性の測定方法が、実用上からすこぶる有用なることが明らかであろう。
【００２１】
本発明においては、前記したように、設置手段(11)や設置手段(21)を原理的に種々の材料、例えば金属、有機高分子、木材などにて形成してよい。しかしそれら設置手段は、可及的に超音波伝搬速度の遅い材料、就中、被検査物の超音波伝搬速度Ｖ値の１．１倍以下、特に該Ｖ値以下、さらには該Ｖ値の０．９７倍以下のものにて形成することが好ましい。その理由を図３により以下に説明する。
【００２２】
いま設置手段(11)、設置手段(21)が、被検査物の超音波伝搬速度Ｖ値より小さい超音波伝搬速度を有する材料にて形成されている場合を考える。この場合、図３に示す通り被覆層Ｃ１の表面の法線Ａに対して角度θで送信された超音波は、屈折に関するスネルの法則により設置手段(11)と被覆層Ｃ１との界面で大きい角度φにて被覆層Ｃ１内に屈折して入射し、かく入射した超音波の多くの部分が被覆層Ｃ１の外表面に近い層中を進む。また設置手段(21)（図示せず）も被覆層Ｃ１のＶ値より小さい超音波伝搬速度を有する材料にて形成されているので、被覆層Ｃ１の外表面に近い層中を進む高密度の超音波部分は、スネルの法則により設置手段(21)に入り易く、かくして超音波受信手段(2) は、高密度の超音波部分を受信することができる。したがってかかる場合には、超音波送信手段(1) として超音波送信出力が低い安価品を用いることができ、あるいは超音波受信手段(2) としては超音波受信感度の低いやはり安価品を用い得る利点がある。
なお本発明において、超音波送信手段(1) から送信された超音波の被覆層Ｃ１の表面の法線Ａに対する上記の角度θは、２０〜８５°程度が好ましい。
【００２３】
超音波伝搬速度Ｖの値を若干の未劣化状態における有機高分子について紹介すると、ポリエチレン：約１８００ｍ／ｓ、ポリ塩化ビニル：約１８００ｍ／ｓ、エチレン・プロピレン共重合ゴム（ＥＰＭ）：約１３５０ｍ／ｓ、ポリ四フッ化エチレン：約１３００ｍ／ｓ、シリコーンゴム：約１０００ｍ／ｓなどである。したがって、被検査物がポリエチレン、ポリ塩化ビニル、エチレン・プロピレン共重合ゴム（ＥＰＭ）からなる場合、設置手段(11)や設置手段(21)としては、ポリ四フッ化エチレンやシリコーンゴム製のものがスネルの法則上から好適である。
【００２４】
本発明では、被検査物の表面は、曲面や平面などであってよいが、設置手段(11)や設置手段(21)の底面と被検査物の表面との間の接触性が悪くて空気層が存在すると、接触面間で超音波の反射が生じて被検査物内への入射率が低下することがある。かかる場合には、グリスや油剤など、就中低極性の、したがって超音波伝搬速度の遅い材料からなるものを使用して両接触面間に空気層が存在しないようにすることが好ましい。
【００２５】
本発明で使用する超音波の周波数については、一般的には制限はない。なおポリエチレン、ポリ塩化ビニル、エチレン・プロピレン共重合ゴム（ＥＰＭ）などの絶縁電線の被覆層の構成材として多用される有機高分子は、概して超音波の減衰が大きいので、減衰が比較的少ない０．１〜５ＭＨｚ程度、特に０．５〜２ＭＨｚ程度の超音波の使用が好ましい。
【００２６】
【実施例】
外径２１ｍｍ、公称厚さ２．５ｍｍの軟質ポリ塩化ビニルシースを有する製造直後の電力ケーブルを被検査物とし、超音波送信手段(1) と超音波受信手段(2) とをいずれもポリ四フッ化エチレン製斜角型ディレーチップ（傾斜角度：４０°）を使用して両者間の設置間隔Ｌ1 およびＬ2 をそれぞれ１ｍｍと１０ｍｍとして上記の軟質ポリ塩化ビニルシースの表面上に設置し、周波数１．０ＭＨｚの超音波を使用して該シース中の伝搬時間差（ｔ2 −ｔ1 ）を測定した。その結果、（ｔ2 −ｔ1 ）の平均値（ｎ：１０）は４．８６μ秒であり、式（２）から超音波伝搬速度１８５０ｍ／秒を得た。
【００２７】
上記の電力ケーブルを空気が循環するオーブン中で１３０℃で１０日間にわたり加熱劣化し、その後、上記と同じ方法並びに条件にて劣化した軟質ポリ塩化ビニルシース中の伝搬時間差（ｔ2 −ｔ1 ）を測定した。その結果、（ｔ2 −ｔ1 ）の平均値（ｎ：１０）は３．９５μ秒であり、式（２）から超音波伝搬速度２２８０ｍ／秒を得た。
【００２８】
一方、製造直後の上記電力ケーブルの数カ所を解体してシース厚みを測定し、正しいシース厚みは２．４８ｍｍであることを確認した。ついで超音波を電力ケーブルの半径方向に入射する方法並びに前記の式（１）にて該軟質ポリ塩化ビニルシース中の超音波伝搬速度を測定したところ、１０個の測定データの平均値は１８５２ｍ／秒であって、本発明での上記未劣化時の測定データと良好に一致することが確認された。
【００２９】
【発明の効果】
超音波を被検査物の厚み方向に入射する従来方法では該厚みの正しい値の把握が必須であった。これに対して本発明ではその必要がなく、しかも種々の被検査物につきそれらの超音波伝搬特性を非破壊的に正しく測定することができる。よって本発明は、非破壊診断が要求される稼働中にある絶縁電線の被覆層の劣化度診断にすこぶる好適である。
【図面の簡単な説明】
【図１】本発明の測定方法および測定装置についての実施例の説明図である。
【図２】図１と共に本発明の超音波伝搬特性の測定方法を説明する説明図である。
【図３】設置手段と被検査物との界面における超音波の屈折の様子を説明する説明図である。
【符号の説明】
１超音波送信手段
１１設置手段
１２超音波送信制御手段
２超音波受信手段
２１設置手段
２２超音波受信制御手段
３伝搬時間測定手段
４演算手段
Ｃ絶縁電線
Ｃ１被覆層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method capable of nondestructively measuring ultrasonic propagation characteristics such as an ultrasonic propagation velocity of an object to be inspected and an apparatus therefor.
[0002]
[Prior art]
Many organic polymers are known to deteriorate due to heat, sunlight, radiation, or other causes, and the ultrasonic propagation speed changes with the progress of deterioration. For example, as the deterioration progresses, the breaking elongation of the organic polymer decreases, and the propagation speed of ultrasonic waves in the deteriorated organic polymer changes. Using this phenomenon, a method for diagnosing the degree of deterioration of an organic polymer from a change in the propagation speed of ultrasonic waves is well known. On the other hand, various insulated wires such as power cables, communication cables, and indoor distribution lines may cause power outages and fire accidents due to deterioration of the coating layers such as the electrical insulation layer and sheath. The degree of deterioration needs to be monitored by regular measurement. Moreover, since the monitoring needs to be performed without destroying the coating layer because the wire is in operation, it has been proposed to apply the ultrasonic diagnostic method to the non-destructive deterioration diagnosis of the insulated wire.
[0003]
For example, in Japanese Patent Application Laid-Open No. 7-35733, ultrasonic waves are incident on the outer surface of the covering layer of the power cable to be diagnosed in the radial direction of the cable, that is, in the vertical direction, and the ultrasonic propagation velocity V in the covering layer is set. A method of obtaining by the following equation (1) has been proposed.
V = 2a / t (1)
In Equation (1), a is the thickness of the coating layer, and t is the time required to return to the incident position again after being reflected from the surface of the lower layer (for example, a conductor) of the coating layer from the incidence of the ultrasonic wave. .
[0004]
By the way, the above method is useful when the correct value of the thickness a of the coating layer is known, but the value is not known in many cases in practice. Therefore, it is conceivable to adopt the design standard dimension of the insulated wire as the thickness a of the covering layer. However, when manufacturing the insulated wire, a manufacturing tolerance of ± 15% with respect to the design standard dimension is allowed. There is a problem that the propagation velocity calculated using the dimensions is inaccurate.
[0005]
[Problems to be solved by the invention]
In view of the above, the problem to be solved by the present invention is a method for nondestructively and more accurately measuring ultrasonic propagation characteristics such as the ultrasonic propagation speed of the object to be inspected and the relative value of the speed, and therefore It is in providing a measuring device.
[0006]
[Means for Solving the Problems]
The above problem is solved by the following measurement method or measurement apparatus.
1. The ultrasonic transmission means (1) is installed on the surface of the object to be inspected via the installation means (11) and the ultrasonic reception means (2) is installed on the surface of the object to be inspected. When the installation interval between 1) and the ultrasonic wave receiving means (2) is L1 and L2, the ultrasonic wave transmitted from the ultrasonic wave transmitting means (1) propagates through the object to be inspected, and the ultrasonic wave receiving means ( 2) A method for measuring ultrasonic propagation characteristics, which is performed by measuring propagation times t1 and t2 required for reception in 2),
The object to be inspected is a coating layer of an insulated wire, and
The ultrasonic propagation characteristic measuring method, wherein the installation means (11) and the installation means (21) are made of polytetrafluoroethylene or silicone rubber.
2. The method for measuring ultrasonic propagation characteristics according to 1 above, wherein the ultrasonic propagation velocity V of the object to be inspected is calculated from the following equation (2).
V = (L2-L1) / (t2-t1) (2)
3. When diagnosing the degree of deterioration of the inspected object, when measuring the time-dependent change in the ultrasonic propagation velocity V of the inspected object or the difference between the installation intervals L1 and L2 (L2 -L1) is always constant 3. The method for measuring ultrasonic propagation characteristics as described in 1 or 2 above, wherein the change over time of (t2 -t1) or 1 / (t2 -t1) of the inspected object is measured.
4. Any of the above 1 to 3 in which grease or oil is interposed between the installation means (11) and the coating layer of the insulated wire, and between the installation means (21) and the coating layer of the insulated wire, respectively. The method for measuring ultrasonic propagation characteristics according to claim 1.
5. The method for measuring ultrasonic propagation characteristics according to any one of 1 to 4 above, wherein the thickness of the covering layer of the insulated wire is not known at the time of performing the measurement method.
6. Ultrasonic wave propagation characteristic measuring device having ultrasonic wave transmission means (1) and installation means (11), ultrasonic wave reception means (2) and installation means (21), and propagation time measurement means (3) Because
The installation means (11) of the ultrasonic transmission means (1) , when installing the transmission means (1) on the surface of the inspection object, the ultrasonic wave transmitted from the transmission means (1) is the installation means (11 ) Is transmitted between the transmitting means (1) and the surface of the inspection object so as to enter the inspection object through
Mounting means of ultrasonic wave receiving means (2) (21) is passed when placed said receiving means (2) on the surface of the object to be inspected, the ultrasonic wave is the mounting means for propagating in the object to be inspected (21) As received by the receiving means (2) , it is interposed between the receiving means (2) and the surface of the inspection object,
The propagation time measuring means (3) includes an ultrasonic transmission when the installation interval between the ultrasonic receiver ultrasonic transmitting means placed on the surface of the object (1) (2) is L1 and L2 Doo Means for measuring propagation times t1 and t2 required for the ultrasonic wave transmitted from the means (1) to propagate through the object to be received by the ultrasonic wave receiving means (2) ;
The object to be inspected is a coating layer of an insulated wire, and
The ultrasonic propagation characteristic measuring apparatus, wherein the installation means (11) and the installation means (21) are made of polytetrafluoroethylene or silicone rubber.
7. From the propagation times t1 and t2, (t2 -t1) or 1 / (t2 -t1), or from the installation intervals L1 and L2 and the propagation times t1 and t2, 7. The ultrasonic propagation characteristic measuring apparatus according to 6 above, further comprising a calculation means (4) for calculating the propagation velocity V.
V = (L2-L1) / (t2-t1) (2)
[0007]
[Action]
The ultrasonic transmission means (1) and the ultrasonic reception means (2) are installed on the surface of the object to be inspected, and the interval between the two means is set as two cases L1 and L2, and the ultrasonic transmission means for each case. By measuring the propagation times t1 and t2 until the ultrasonic wave transmitted from (1) propagates through the inspection object and is received by the ultrasonic wave receiving means (2), as described later. The ultrasonic wave propagation characteristic can be accurately obtained by the above equation (2) regardless of the thickness of the object to be inspected.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view of the measuring method and measuring apparatus of the present invention, FIG. 2 is an explanatory view of the ultrasonic propagation characteristic measuring method of the present invention together with FIG. 1, and FIG. 3 is an installation means (11). It is explanatory drawing explaining the mode of the refraction | bending of the ultrasonic wave in the interface with a to-be-inspected object.
[0009]
FIG. 1 shows an embodiment of a measuring apparatus according to the present invention, which is applied as a deterioration diagnosis apparatus for a coating layer of an insulated wire such as a power cable, and a method for measuring ultrasonic propagation characteristics using the apparatus of the embodiment. Is also explained.
1 includes an ultrasonic transmission means (1), an ultrasonic transmission control means (12), an ultrasonic reception means (2), an ultrasonic reception control means (22), a propagation time measurement means (3), The calculation means (4), distance input means (5), determination means (6), and display means (7).
[0010]
The ultrasonic transmission means (1) has a function capable of generating and transmitting ultrasonic waves with a built-in vibrator (not shown), and has an installation means (11) which is covered by the installation means (11). It is installed on the surface of the coating layer C1 of the insulated wire C as an example of the inspection object. The ultrasonic wave transmitted from the ultrasonic wave transmission means (1) passes through the installation means (11) and enters the coating layer C1. The ultrasonic transmission control means (12) has a function of inputting the ultrasonic transmission time from the ultrasonic transmission means (1) to the propagation time measuring means (3) described later as an electrical signal. The ultrasonic receiving means (2) has an installation means (21) and is installed on the surface of the coating layer C1 at a position separated from the ultrasonic transmission means (1) by a distance L1 by the installation means (21). The ultrasonic wave propagating in the coating layer C1 is received through the installation means (21). In FIG. 1, an oblique delay chip made of an organic polymer such as polytetrafluoroethylene can be used as the installation means (11) and the installation means (21).
[0011]
The ultrasonic reception control means (22) functions to input the reception time of the ultrasonic waves from the ultrasonic reception means (2) to the propagation time measurement means (3) as an electrical signal. The propagation time measurement means (3) receives the ultrasonic waves transmitted from the ultrasonic transmission means (1) based on the inputs from the ultrasonic transmission control means (12) and the ultrasonic reception control means (22). It functions to measure propagation times t1 and t2 required to propagate through the inspection object and be received by the ultrasonic wave receiving means (2). The remaining functions of the calculation means (4), distance input means (5), determination means (6), and display means (7) will be described later.
[0012]
The ultrasonic transmission means (1) and the ultrasonic reception means (2) are installed on the surface of the coating layer C1 with an interval of a distance L1. When ultrasonic waves are transmitted from the ultrasonic transmission means (1) in this state, the transmitted ultrasonic waves pass through the installation means (11) and enter the coating layer C1. The incident ultrasonic wave propagates in the coating layer C1 through various paths, but there is also an ultrasonic part that propagates between the ultrasonic transmission means (1) and the ultrasonic reception means (2) through the shortest path. Therefore, the ultrasonic wave part is received by the ultrasonic wave receiving means (2).
[0013]
The ultrasonic transmission time from the ultrasonic transmission means (1) and the ultrasonic reception time from the ultrasonic reception means (2) are respectively obtained from the ultrasonic transmission control means (12) and the ultrasonic reception control means (22). Input to the propagation time measuring means (3), and the propagation time measuring means (3) measures the ultrasonic propagation time t1 with respect to the installation interval L1.
[0014]
As is clear from the above description, the ultrasonic wave transmitted from the ultrasonic wave transmission means (1) sequentially passes the path indicated by the dotted line in FIG. 1, that is, the installation means (11), the coating layer C1, and the installation means (21). The ultrasonic wave receiving means (2) is reached via V1, the ultrasonic wave propagation speed in the installation means (11) is V1, the propagation distance is L11, the propagation time is t11, and the wave length in the coating layer C1 is reached. When the ultrasonic propagation velocity is V, the propagation distance is L1, the propagation time is tx, the ultrasonic propagation velocity in the installation means (21) is V2, the propagation distance is L2, and the propagation time is t12, the following equation (3 ) Holds.

[0015]
Next, the installation interval between the ultrasonic transmission means (1) and the ultrasonic reception means (2) is changed to L2 as shown in FIG. 2, and the ultrasonic wave propagation time t2 with respect to the installation interval L2 in the same manner as described above. Measure. In that case, the following equation (4) is established corresponding to the equation (3). Furthermore, said Formula (2) is obtained from the difference of Formula (4) and Formula (3).
t2 = (L11 / V1) + (L2 / V) + (L12 / V2) (4)
[0016]
From the equations (2) to (4), if the installation means (11) and the installation means (21) used for measuring t1 for L1 are also used for measuring t2 for L2, ultrasonic propagation It can be seen that the measurement of characteristics does not depend on the shape and size of the installation means and the forming material in principle.
[0017]
In FIG. 1 and FIG. 2, the installation means (11) and the installation means (21) are within the bottom surfaces where the installation means (11) and the installation means (21) are in contact with the covering layer C1 so that the above equations (3) and (4) can be easily understood. The areas where the ultrasonic propagation density is highest are indicated by black circles, and the positions of the respective black circles are assumed to be the installation positions of the ultrasonic transmission means (1) and the ultrasonic reception means (2). However, in the present invention, the installation positions of the ultrasonic transmission means (1) and the ultrasonic reception means (2) are not necessarily limited to the positions of the black circles. For example, if the ultrasonic transmission means (1), the installation means ( What is necessary is just to determine in arbitrary positions, such as the front end of the bottom of 11), the last end, or the middle point. The same applies to the ultrasonic wave receiving means (2). The reason will be easily understood from the process of deriving the formula (2) from the above formulas (3) and (4).
[0018]
As apparent from the above equation (2), the ultrasonic wave propagation velocity V is inversely proportional to (t2 -t1) and proportional to 1 / (t2 -t1). In other words, these values are relative to the ultrasonic propagation velocity V. Therefore, when only a relative change over time of the degree of deterioration is sufficient as in the case of many deterioration degree diagnoses of the object to be inspected, the ultrasonic propagation characteristics are always measured in the present invention at a constant (L2−L1). (T2−t1) and 1 / (t2−t1) are calculated, and the degree of deterioration can be diagnosed using those numerical values.
[0019]
The installation intervals L1 and L2 in the above measurement are stored in the distance input means (5), and the propagation times t1 and t2 are measured in the propagation time measuring means (3). Thereafter, the installation intervals L1 and L2 from the distance input means (5) and the propagation times t1 and t2 from the propagation time measuring means (3) are input to the calculating means (4), respectively, and the calculating means (4) The ultrasonic wave propagation velocity V is calculated from the propagation time difference (t2-t1), 1 / (t2-t1), or the above equation (2). The judging means (6) is a method for determining the physical properties of the organic polymer forming the coating layer C1 at various degrees of degradation, such as the elongation at break, tensile strength, 100% modulus, and the ultrasonic propagation velocity V or V. Correlation data with relative values are held, and the degree of deterioration is judged based on those values input from the calculation means (4), and the result is sent to the display means (7) to obtain various degrees of deterioration. Display method, for example, a graph showing the relationship between the number of working days of insulated wires and the degree of deterioration.
[0020]
If the interval between the ultrasonic transmitting means (1) and the ultrasonic receiving means (2) is increased, in other words, if the values of L1 and L2 are increased in the above equations (3) and (4), the theory In particular, the influence of L11 and L12 is reduced, and the ultrasonic propagation characteristics can be measured only by the equation (3) or the equation (4). However, since the ultrasonic wave propagating in the solid, particularly in the organic polymer is generally very easily attenuated, the values of L1 and L2 are preferably set to about several hundred μm to several tens of mm. The size is only about 0.5 to 5 times the practical installation means (11) and installation means (21), for example, L11 and L12 of the polytetrafluoroethylene bevel-type delay chip. For this reason, it is difficult to measure the ultrasonic propagation characteristics using only the formula (3) or the formula (4). From these facts, it will be apparent that the method for measuring ultrasonic propagation characteristics of the present invention is extremely useful from a practical point of view.
[0021]
In the present invention, as described above, the installation means (11) and the installation means (21) may in principle be formed of various materials such as metals, organic polymers, and wood. However, these installation means are materials having a slow ultrasonic propagation velocity as much as possible, especially 1.1 times or less of the ultrasonic propagation velocity V value of the object to be inspected. It is preferable to form it by 0.97 times or less. The reason will be described below with reference to FIG.
[0022]
Consider a case where the installation means (11) and the installation means (21) are formed of a material having an ultrasonic propagation velocity smaller than the ultrasonic propagation velocity V value of the object to be inspected. In this case, as shown in FIG. 3, the ultrasonic wave transmitted at an angle θ with respect to the normal A of the surface of the coating layer C1 is large at the interface between the installation means (11) and the coating layer C1 due to Snell's law regarding refraction. Refraction enters the coating layer C1 at an angle φ, and a large part of the incident ultrasonic waves travels in a layer close to the outer surface of the coating layer C1. Further, since the installation means (21) (not shown) is also formed of a material having an ultrasonic wave propagation velocity smaller than the V value of the coating layer C1, the installation means (21) has a high density traveling in the layer close to the outer surface of the coating layer C1. The ultrasonic part easily enters the installation means (21) according to Snell's law, and thus the ultrasonic reception means (2) can receive the high-density ultrasonic part. Therefore, in such a case, an inexpensive product with low ultrasonic transmission output can be used as the ultrasonic transmission means (1), or an inexpensive product with low ultrasonic reception sensitivity can be used as the ultrasonic reception means (2). There are advantages.
In the present invention, the angle θ with respect to the normal A of the surface of the coating layer C1 of the ultrasonic wave transmitted from the ultrasonic wave transmitting means (1) is preferably about 20 to 85 °.
[0023]
Introducing the value of the ultrasonic propagation velocity V for organic polymers in some undegraded states, polyethylene: about 1800 m / s, polyvinyl chloride: about 1800 m / s, ethylene / propylene copolymer rubber (EPM): about 1350 m / s s, polytetrafluoroethylene: about 1300 m / s, silicone rubber: about 1000 m / s. Therefore, when the object to be inspected is made of polyethylene, polyvinyl chloride, ethylene / propylene copolymer rubber (EPM), the installation means (11) and installation means (21) are made of polytetrafluoroethylene or silicone rubber. Is preferable from Snell's law.
[0024]
In the present invention, the surface of the object to be inspected may be a curved surface or a flat surface, but the contact between the bottom surface of the installation means (11) or the installation means (21) and the surface of the object to be inspected is poor. If a layer is present, reflection of ultrasonic waves may occur between the contact surfaces, and the incidence rate into the inspection object may be reduced. In such a case, it is preferable to use a material having low polarity, such as grease or an oil agent, and thus a material having a low ultrasonic propagation speed so that no air layer exists between the contact surfaces.
[0025]
In general, the frequency of the ultrasonic wave used in the present invention is not limited. Organic polymers such as polyethylene, polyvinyl chloride, and ethylene / propylene copolymer rubber (EPM), which are frequently used as constituents of insulation wire coating layers, generally have a high attenuation of ultrasonic waves, and therefore have a relatively low attenuation. It is preferable to use ultrasonic waves of about 1 to 5 MHz, particularly about 0.5 to 2 MHz.
[0026]
【Example】
A power cable immediately after production having a soft polyvinyl chloride sheath having an outer diameter of 21 mm and a nominal thickness of 2.5 mm is used as an object to be inspected, and both the ultrasonic transmission means (1) and the ultrasonic reception means (2) are made of polytetrafluoroethylene. Installed on the surface of the above-mentioned soft polyvinyl chloride sheath using an ethylene fluoride bevel-type delay chip (inclination angle: 40 °) with the installation intervals L1 and L2 being 1 mm and 10 mm, respectively, and a frequency of 1.0 MHz The difference in propagation time (t2 -t1) in the sheath was measured using the ultrasonic wave. As a result, the average value (n: 10) of (t2−t1) was 4.86 μs, and an ultrasonic wave propagation velocity of 1850 m / sec was obtained from the equation (2).
[0027]
The propagation time difference (t2 -t1) in a soft polyvinyl chloride sheath that was deteriorated by heating at 130 ° C. for 10 days in an oven in which air was circulated through the power cable and then deteriorated by the same method and conditions as described above was measured. . As a result, the average value (n: 10) of (t2−t1) was 3.95 μsec, and an ultrasonic wave propagation speed of 2280 m / sec was obtained from the equation (2).
[0028]
On the other hand, several portions of the power cable immediately after production were disassembled and the sheath thickness was measured, and it was confirmed that the correct sheath thickness was 2.48 mm. Then, when the ultrasonic wave propagation velocity in the soft polyvinyl chloride sheath was measured by the method of injecting ultrasonic waves in the radial direction of the power cable and the above equation (1), the average value of 10 measurement data was 1852 m / sec. Thus, it was confirmed that the measurement data in the present invention was in good agreement with the undegraded measurement data.
[0029]
【The invention's effect】
In the conventional method in which ultrasonic waves are incident in the thickness direction of the object to be inspected, it is essential to grasp the correct value of the thickness. On the other hand, in the present invention, this is not necessary, and the ultrasonic propagation characteristics of various inspection objects can be correctly measured nondestructively. Therefore, the present invention is extremely suitable for the deterioration degree diagnosis of the coating layer of the insulated wire in operation that requires nondestructive diagnosis.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of a measuring method and a measuring apparatus according to the present invention.
FIG. 2 is an explanatory view for explaining a method for measuring ultrasonic propagation characteristics according to the present invention together with FIG. 1;
FIG. 3 is an explanatory diagram for explaining the state of ultrasonic wave refraction at the interface between the installation means and the object to be inspected.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ultrasonic transmission means 11 Installation means 12 Ultrasonic transmission control means 2 Ultrasonic reception means 21 Installation means 22 Ultrasonic reception control means 3 Propagation time measurement means 4 Calculation means C Insulated wire C1 Covering layer

Claims

The ultrasonic transmission means (1) is installed on the surface of the object to be inspected via the installation means (11), and the ultrasonic reception means (2) is installed on the surface of the inspection object via the installation means (21). And the ultrasonic wave receiving means (2), the ultrasonic wave transmitted from the ultrasonic wave transmitting means (1) propagates through the inspection object and the ultrasonic wave receiving means (2). Is a method of measuring ultrasonic propagation characteristics by measuring propagation times t1 and t2 required for reception by the
The object to be inspected is a coating layer of an insulated wire, and
The ultrasonic propagation characteristic measuring method, wherein the installation means (11) and the installation means (21) are made of polytetrafluoroethylene or silicone rubber.

2. The method for measuring ultrasonic propagation characteristics according to claim 1, wherein the ultrasonic propagation velocity V of the object to be inspected is calculated from the following equation.
V = (L2-L1) / (t2-t1)

Obtained when measuring the time-dependent change in the ultrasonic wave propagation velocity V of the inspection object or the difference between the installation intervals L1 and L2 (L2 -L1) for the diagnosis of the degree of deterioration of the inspection object. 3. A method for measuring ultrasonic propagation characteristics according to claim 1, wherein a change with time of (t2 -t1) or 1 / (t2 -t1) is measured.

Either grease or an oil agent is interposed between the installation means (11) and the coating layer of the insulated wire, and between the installation means (21) and the coating layer of the insulated wire, respectively. The measuring method of the ultrasonic wave propagation characteristic described in 2.

The method for measuring ultrasonic propagation characteristics according to claim 1, wherein the thickness of the covering layer of the insulated wire is not known at the time when the measurement method is performed.

An ultrasonic propagation characteristic measuring apparatus having an ultrasonic transmission means (1) and its installation means (11), an ultrasonic reception means (2) and its installation means (21), and a propagation time measurement means (3). And
The installation means (11) of the ultrasonic transmission means (1) , when installing the transmission means (1) on the surface of the inspection object, the ultrasonic wave transmitted from the transmission means (1) is the installation means (11 ) Is transmitted between the transmitting means (1) and the surface of the inspection object so as to enter the inspection object.
Mounting means of ultrasonic wave receiving means (2) (21) is passed when placed said receiving means (2) on the surface of the object to be inspected, the ultrasonic wave is the mounting means for propagating in the object to be inspected (21) as received by the receiving means (2) and, which is interposed between said receiving means (2) and the surface of the object,
The propagation time measuring means (3) includes an ultrasonic transmission when the installation interval between the ultrasonic receiver ultrasonic transmitting means placed on the surface of the object (1) (2) is L1 and L2 Doo Means for measuring propagation times t1 and t2 required for the ultrasonic wave transmitted from the means (1) to propagate through the object to be received by the ultrasonic wave receiving means (2) ;
The object to be inspected is a coating layer of an insulated wire, and
The ultrasonic propagation characteristic measuring apparatus, wherein the installation means (11) and the installation means (21) are made of polytetrafluoroethylene or silicone rubber.

Calculate (t2 -t1) or 1 / (t2 -t1) from the propagation times t1 and t2, or calculate the ultrasonic propagation velocity V of the object to be inspected from the installation intervals L1 and L2 and the propagation times t1 and t2. The ultrasonic wave propagation characteristic measuring device according to claim 6, further comprising a calculating means (4) for performing the operation.
V = (L2-L1) / (t2-t1)