JP3766824B2 - Method and apparatus for measuring temperature of conductive fluid in pipe - Google Patents

Description

ここで、記号上の「・」はベクトルを表し、ｊ＝√（−１）、ω＝２πｆは周波数ｆの正弦波交流の角周波数であり、第１の誘導コイルと第２の誘導コイルでの配管と計測コイルとの間の相互インダクタンスＭ₄ は等しいと仮定している。更に数１に回路条件を加えて整理すると次のようになる。
【数２】

ここで、Ｘ＝ωＬは自己インダクタンスＬによるリアクタンスであり、Ｒは抵抗である。なお、添え字はＮがナトリウム中、Ｓが配管表面を表している。
【００１９】
数２において、括弧内の２＋（Ｒ_N ＋ｊＸ_N ）／（Ｒ_S ＋ｊＸ_S ）は、定数２に対して温度変化による抵抗変化が極めて小さいので、殆ど定数と見なすことができる。またω² Ｍ₁ Ｍ₄ Ｉ₁ も電流、周波数及び各コイルの相対的配置が一定であれば定数である。これらのことから、計測コイルに誘導される電圧Ｅ₄ の誘導コイルの電流と同相の成分は、配管と配管内ナトリウム中の電流経路における電気抵抗の和に関連付けることが可能である。
【数３】

ここでＡは定数である。Ｒ_N はナトリウム温度に依存するので、校正試験によって電圧値とナトリウム温度との関係を数３に基づいて把握しておけば、計測コイルの電圧値から配管内部のナトリウム温度を求めることができる。ただし、Ｒ_S は表面温度に依存するので、表面温度は別途計測する必要がある。実際の校正においては、計測コイルの電圧とナトリウム温度との関係を次の簡略式で求めることができる。
【数４】

ここで、ｔ_N ，ｔ_S は配管内ナトリウムと配管表面の温度、Ａ，Ｂ，Ｃは定数であり、校正試験によって決定する。以上のように、電気的等価回路に基づく検討から、差動コイル式の電磁誘導温度計測法が可能であることが分かる。
【００２０】
図４は本発明に係る配管内導電性流体の温度計測装置の構成例を示すブロック図である。発振器３０の出力で交流定電流増幅器３２の出力を制御し、該交流定電流増幅器３２の出力電流は端子と出力ケーブルの間に挿入した５０Ａ→５０ｍＶのシャント抵抗３４の電圧降下を電圧計３６で測定して監視しつつ、配管１０に設けた誘導コイル１２に供給する。計測コイル１４に現れた電圧信号は、１：１００の増幅トランス３８で増幅した後、同軸ケーブルで２位相ロックインアンプ４０の入力端子に入力する。またロックインアンプ４０の参照信号は、交流定電流増幅器３２の出力端子から取る。そしてロックインアンプ４０のアナログ信号をデータ収録装置４２で配管表面等の温度データと一緒に計測する。またロックインアンプ４０のアナログ信号はオシロスコープ４４で観測できるようになっている。計測装置の各ブロックは、１台の装置内に組み込むこともできるが、それぞれのブロックに合わせて多数の装置を組み合わせてもよい。
【００２１】
図５は、その信号とデータの流れを示す説明図である。発振部（発振器）は一定周波数の信号を発生する部分であり、電力増幅部（交流定電流増幅器）は発振部の信号に基づいて一定周波数、一定電流の励磁電流を誘導コイルに供給する。計測コイルに誘導された電圧信号（計測信号）は、測定部で増幅し、位相分離した上でＡ／Ｄ変換される。位相分離に必要な参照信号は電力増幅部の出力から分岐して得る。校正を行う場合の計測データは校正部に収録する。収録は何度か繰り返して行い、温度と電圧の相関から校正曲線（校正式）を作成する。この校正式は、通常、数４に示す１次式でよいが、高精度が要求される場合は、多項式の使用、または配管温度をパラメータとして計測を繰り返す等により校正式の精度を上げる。実際に温度を計測する場合の計測データは、比較校正部で校正曲線（校正式）に当てはめて温度に換算する。温度に換算されたデータは、表示・出力部によって表示及び外部装置への出力を行う。
【００２２】
計測結果の一例（周波数：５７０Ｈｚ）を図６に示す。計測対象は、温度が周期的に変動する配管内の液体ナトリウムである。図６において、「Ｎａ中温度」はナトリウム中に熱電対を差し込んで計測した温度、「外面温度」は配管表面に熱電対を取り付けて計測した温度、「電磁誘導」は本発明方法により計測した電圧を「Ｎａ中温度」と「外面温度」を使って校正した温度である。図６の結果から、電磁誘導による校正結果（本発明方法による結果）は、「Ｎａ中温度」とほぼ一致しており、また「外面温度」とは温度変動の位相がずれている。このことから「電磁誘導（により求めた温度）」は、外面温度ではなく、ナトリウム温度を示していることが確認できた。
【００２３】
図７は温度検出部の具体例を示す斜視図であり、パッケージ化した例である。Ａは配管取付前の状態を、Ｂは配管取付後の状態を、それぞれ示している。配管５０の外周を取り囲むような絶縁性円筒体を２つ割り構造として取付ベース５２ａ，５２ｂとする。該取付ベース５２ａ，５２ｂは、断熱材で半円筒状に成形されており、配管の保温材を兼ねている。一方の取付ベース５２ａの内側面には誘導コイルの半分５４ａを設け、他方の取付ベース５２ｂの内側面には誘導コイルの半分５４ｂと計測コイル５６を設ける。これらは、配管を挟むように組み合わせられ、クランプ等で固定される。取付ベース５２ａ，５２ｂを配管５０の外側に施工した後、巻き返しコイル側に出るリード線は交流電源に接続し、もう一方の周回コイル側の誘導用電線はリード線５８で相互に接続する。なお、取付ベース５２ｂには配管の表面温度計測用の熱電対６０も取り付ける。
【００２４】
図８は、本発明に係る配管内導電性流体の温度計測方法の他の例を示す説明図であり、誘導電位差法の例である。内部をナトリウムが流動する配管８０の外周に誘導コイル８２を設け、配管外面に計測用電線８４を直接接続する。誘導コイルは前記実施例の第１の誘導コイルと同様の構造でよい。即ち、誘導コイル８２は、配管８０の外周に沿って同一周上に誘導用電線を半周ずつ巻き互いに逆回りに同じ電流が流れるようにした構造であり、交流定電流電源８４により交流電流が供給される。誘導コイル８２を流れる交流電流による電磁誘導によって配管及び導電性流体に誘導電流が流れる。誘導コイル８２を流れるある瞬間の電流は、配管８０を挟んで取り付けた２本の誘導コイルに沿って互いに反対方向に流れるので、電流は１周することができない。このため誘導電流は、矢印で示すように、途中から配管内のナトリウム中を通る経路で流れる。図８では、誘導電流は配管下方と配管上方で分流・合流するように、ナトリウム内を上下方向に流れる。計測用電線８４は、誘導コイルが対向する位置（誘導電流の分流・合流点に対応した位置）の配管表面に圧着やスポット溶接などによって取り付ける。誘導コイル８２に交流電流を供給し、計測用電線８４間の電圧を電圧計測手段８８で計測して、それを温度に変換する。図９に、その電気的等価回路を示す。
【００２５】
計測用電線に現れる電圧と配管内の抵抗の関係は、次のようになる。
【数５】

数５において、Ｅ_N の抵抗と同相の成分Ｅ_NRは、配管内ナトリウムの抵抗Ｒ_N の関数として表すことができ、その電圧からナトリウム温度を求めることが可能である。ステンレス鋼製の配管内のナトリウム温度を計測する場合は、簡略化して次のようにナトリウム温度ｔ_N を求めることが可能である。
【数６】

数６におけるＡ，Ｂは定数であり、校正において行う最小二乗法の未定係数となる。
【００２６】
以上のことから分かるように、誘導電位差式温度計測方法は、計測値から直接ナトリウム温度を計算できるという利点があり、前述の差動コイル式よりも簡便な温度計測方法である。但し、誘導電位差式温度計測方法は、計測用電線を圧着やスポット溶接等によって配管に取り付ける必要があるので、非接触での配管内ナトリウム温度の計測は行えない。しかし、計測用電線には殆ど電流が流れないので細い電線を使用することができ、計測用電線の接続にスポット溶接を使用したとしても、配管の強度に与える影響は無視できる程度である。
【００２７】
ところで本発明において、差動コイル法では、計測コイルが差動コイルとなっているので、誘導コイル相互の影響は相殺されるが、配管内を流れる電流には若干の影響が考えられる。このため、第１の誘導コイルと第２の誘導コイルの軸方向離間距離は、お互いのコイルによる電磁的影響が及ばないような距離にすることが望ましい。温度計測の精度にも関係するが、実用上の目安としては、誘導コイルと配管表面との距離に対する誘導用電線相互の離隔距離を数十倍以上とすることである。また、誘導コイルを巻き返すときに電線が空中を通るが、配管に近づきすぎると配管に直接巻いた誘導用電線による誘導電流を打ち消してしまう。従って、これもお互いに影響を与えない程度の離隔距離が必要である。試作品では、どちらも配管直径に相当する離隔距離をとっている。なお、離隔距離が大きい場合は特に問題はないが、それそれのコイル位置での配管温度に差があると誤差の原因になる。
【００２８】
誘導コイルに供給する交流電流の周波数は、配管内の交流電流の表皮効果と誘導起電力によって制限を受ける。配管中心付近に電流を流すためには、表皮効果が小さい低周波の方が有利である。他方、電磁誘導によって配管に誘導される起電力は周波数が高い方が有利である。差動コイル法では、計測コイルに十分な誘導起電力を発生させる必要があることから、少し高めの周波数を設定する必要がある。配管内の流れが乱流で、配管内の温度が比較的均一であり、配管の肉厚が薄い場合には、１ｋＨｚ以上の周波数まで使用できる。実用上は数百Ｈｚ〜１ｋＨｚ程度が望ましい。試作品によって、外径７６mm、肉厚４．７mmのステンレス鋼配管内のナトリウム温度を計測した結果、１．３ｋＨｚでもナトリウムの温度変化に対応する電圧を計測することができた。誘導電位差法の場合は、配管内の電気抵抗による電圧降下を計測線で直接計測するので、比較的低い周波数（数十〜数百Ｈｚ）で使用することができる。
【００２９】
配管中のナトリウム温度を計測するための誘導コイル及び計測コイル、計測用電線には、高温大気中で使用しても溶融、酸化、劣化（著しい抵抗変化など）が生じない材質であれば、任意の電線が使用可能である。例えばセラミックス長繊維あるいはシリカ長繊維で被覆したニッケル線、ステンレス鋼線、あるいは丹銅（黄銅）線などの金属線が有用である。
【００３０】
上記の実施例では、１筆書きのルートを１回たどるように誘導コイルを設けているが、小電流で大きな誘導電流を得る必要がある場合には、同じルートで複数回たどるように誘導コイルを設けてもよい。それらにおいて使用上の違いは生じない。また、計測コイルについても、巻き回数を多くすることで検出感度を上げることができる。
【００３１】
誘導コイルと計測コイルは、配管に対して絶縁されている必要はないが、配管と導通している箇所が２箇所以上の場合は、配管を通る電流経路ができるので、計測誤差が大きくなり、最悪の場合は計測できなくなる。配管と電線及び電線相互が完全に絶縁されていれば、問題が発生することはない。電線には、薄い被覆の絶縁電線を使うのが好ましい。
【００３２】
上記の実施例では誘導コイルは、配管を挟んで２本の電線を対向させた配置としている。誘導電流路を規制し計測精度を上げるためには、そのような構成が好ましいが、計測コイルを沿わせた側のコイルだけでも差動コイル式温度計測法として機能する。その場合、第１の誘導コイルと計測コイルの長さは、計測対象に合わせてその距離を任意に変更してもよい。また、誘導電位差式温度計測法においても、同様に片側だけで機能させることができる。
【００３３】
本発明により温度を計測する対象は、ナトリウムに限らず、導電性を有し電気抵抗が温度依存性を有する流体であればよい。原理的には、導電性を有し電気抵抗が温度依存性を有する物質に適用可能である。但し、計測対象に適合したコイルや電源装置などを用いることになる。
【００３４】
ところで、従来、交流電流を用いた厚肉配管などの内部の非破壊検査は、表皮効果により電流が試料の表面に集中するため困難である。本発明方法のように誘導電流が試料を横切るように誘導コイルを配置すると、非破壊検査を行いやすくなる。従って、本発明のような誘導コイルにより誘導電流を流す方法は、非破壊検査にも応用可能である。
【００３５】
【発明の効果】
本発明は上記のように、電磁誘導によって配管及び内部の導電性流体に電流を流すようにした配管内導電性流体の温度計測方法及び装置であるので、大電流を供給する電流電極が不要となり、そのため配管に大掛かりな溶接箇所がないために配管に応力集中箇所が生じず、特に高温環境下での安全性・信頼性が著しく向上する。
【００３６】
差動コイル式では非接触検査とすることができるので着脱が可能であり、計測用電線を配管に接続する必要がある誘導電位差法に比べて計測場所の移動が容易で高速検査が可能である。また、コイル等の絶縁材料を耐熱性とすれば高温環境下での検査にも適用できる。
【図面の簡単な説明】
【図１】本発明に係る配管内導電性流体の温度計測方法の一実施例を示す説明図。
【図２】その電流の流れを示す説明図。
【図３】その電気的等価回路図。
【図４】その装置構成例を示すブロック図。
【図５】その信号とデータの流れを示す説明図。
【図６】それによる計測結果の一例を示すグラフ。
【図７】温度検出部の具体例を示す斜視図。
【図８】本発明に係る配管内導電性流体の温度計測方法の他の実施例の説明図。
【図９】その電気的等価回路図。
【符号の説明】
１０ 配管
１２ 誘導コイル
１４ 計測コイル
１６ 交流定電流電源
１８ 電圧計測手段
２０ 第１の誘導コイル
２２ 第２の誘導コイル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for measuring the temperature of a conductive fluid such as sodium existing in a pipe using the temperature dependence of the electrical resistance of the conductive fluid. More specifically, the present invention relates to a method and an apparatus for measuring the temperature of a conductive fluid in a pipe that allows current to flow through the pipe and the conductive fluid in the pipe by electromagnetic induction.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent No. 2972749 gazette
Regardless of the form of the sample, a method using a thermocouple is generally used to measure the temperature of the sample. For example, when measuring the temperature of liquid sodium flowing in a pipe, a protective tube containing a thermocouple is inserted and fixed in a through hole provided in the pipe so that the tip of the sodium comes into contact with sodium. However, in this method, the tip of the protective tube is always exposed to flowing sodium, so even if it is designed to ensure sufficient strength of the protective tube, it may be damaged by unexpected external force. There is.
[0004]
Therefore, as a method for measuring the temperature of a conductive fluid such as sodium flowing in the pipe, a method utilizing the temperature dependence of the electrical resistance has been proposed (see Patent Document 1). This is done by installing a pair of current electrodes on the outer surface of the pipe so that the conductive fluid in the pipe is energized by energizing between the electrodes, and the potential difference due to the voltage drop caused thereby is detected by the voltage detection electrode. The temperature is calculated from the detected value. That is, the resistance value based on Ohm's law is calculated from the current and voltage flowing through the conductive fluid.
[0005]
Such a potential difference method includes a method in which a direct current is passed through a conductive fluid and a method in which an alternating current is passed. The DC potential difference method has a simple principle and is easy to apply, but there are problems such as that the thermoelectromotive force is superimposed on the measured value and that it is easily influenced by external noise. The AC potential difference method has some problems such as the fact that the apparatus is somewhat complicated and the skin effect appears, but it is not affected by the thermoelectromotive force and the influence of external noise can be eliminated.
[0006]
[Problems to be solved by the invention]
However, in the potential difference method, it is generally necessary to supply a large current. Therefore, the current electrode for that purpose must be connected to the pipe so that the electrical resistance can be kept as low as possible. In particular, in a high temperature environment, an oxide film is likely to be formed on the pipe surface, so that the current electrode is usually attached by welding. However, since the welded portion becomes discontinuous in terms of material and structure, stress concentration is likely to occur, and there is a risk that cracks will occur from there.
[0007]
In addition, since the current electrode must be fixed to the pipe in a low resistance state by welding or the like, it is extremely difficult to change the measurement location.
[0008]
The object of the present invention is to eliminate the need for a current electrode for supplying a large current, so that there are no large welded portions in the piping, so stress concentration points do not occur, and safety and reliability in a high temperature environment are remarkably improved. The object is to provide a temperature measuring method and apparatus for a conductive fluid in a pipe. Another object of the present invention is to provide a method and an apparatus for measuring the temperature of a conductive fluid in a pipe that can be attached and detached, and therefore can easily change the measurement location.
[0009]
[Means for Solving the Problems]
The present invention measures the temperature of a conductive fluid that correlates with the electrical resistance by passing a current through the pipe and the conductive fluid inside by electromagnetic induction and detecting the voltage caused by the electrical resistance in the current path. Technology. Here, there are two modes for detecting the voltage. One is a method of detecting an induced electromotive force caused by a current flowing through a pipe and a current flowing through an internal conductive fluid using a differential measurement coil (this is referred to as a “differential coil method”). One of them is a method of detection using a thin measuring wire directly attached to a pipe by spot welding or the like (this is referred to as an “induced potential difference method”). In particular, the differential coil method has an advantage that temperature measurement is possible (non-contact) while being insulated from the piping.
[0010]
That is, the present invention relates to a method for measuring the temperature of a conductive fluid existing in a pipe using the temperature dependence of the electrical resistance of the conductive fluid, and for guiding the same along the outer circumference of the pipe. By supplying an alternating current to the first induction coil in which the same current flows in the opposite direction by winding the electric wire half a turn, an induction current flows through the piping and the conductive fluid by electromagnetic induction. By supplying the same alternating current as the first induction coil to the second induction coil that circulates the induction wire along the outer periphery of the pipe away from the one induction coil, the induction current flows through the pipe by electromagnetic induction. Thus, a method for measuring a temperature of a conductive fluid in a pipe is characterized by measuring a difference between electromotive forces induced in a measuring coil by both induced currents and converting the measured voltage into a temperature. This is the differential coil method.
[0011]
An apparatus for carrying out this differential coil method is a first induction coil in which an induction wire is wound around the same circumference along the outer circumference of a conductive fluid pipe so that the same current flows in the opposite direction. A second induction coil that is continuous with the first induction coil and that circulates the induction wire along the outer periphery of the pipe that is away from the first induction coil; and an alternating current in the first and second induction coils An AC constant-current power source for supplying an induction current to the pipe and the conductive fluid by electromagnetic induction, a measuring wire arranged along one half-circular winding induction wire of the first induction coil, and a second In-pipe conductivity comprising a differential measurement coil in which measurement wires arranged along the induction wire for a half circumference of the induction coil are continuous, and a voltage measurement means provided between both ends of the measurement coil This is a fluid temperature measuring device.
[0012]
Further, the present invention provides a method for measuring the temperature of a conductive fluid existing in a pipe by using the temperature dependence of the electrical resistance of the conductive fluid, and for guiding the same along the outer circumference of the pipe. By supplying alternating current to an induction coil that is wound half a turn around the wire so that the same current flows in the opposite direction, the induction current flows through the conductive fluid by electromagnetic induction, and the electrical resistance of the conductive fluid inside the pipe Is a method for measuring the temperature of a conductive fluid in a pipe, characterized in that the voltage generated by the above is measured and the measured voltage is converted into temperature. This is the induced potential difference method.
[0013]
An apparatus for carrying out this induction potential difference method includes an induction coil in which induction wires are wound half a turn on the same circumference along the outer circumference of a conductive fluid pipe, and the same current flows in the opposite direction to each other. AC constant-current power supply that sends induction current to piping and conductive fluid by electromagnetic induction by supplying alternating current to the induction coil, and measurement connected to the outer peripheral surface position of the pipe corresponding to the diversion point and confluence of the induction current It is the temperature measuring apparatus of the conductive fluid in piping which has the voltage measuring means provided between the electric wire for electric wires and both the electric wires for measurement.
[0014]
【Example】
FIG. 1 is an explanatory view showing an example of a method for measuring the temperature of a conductive fluid in a pipe according to the present invention, which is an example of a differential coil method. An induction coil 12 and a differential measurement coil 14 are provided on the outer periphery of a pipe 10 through which a conductive fluid (here, sodium; Na) flows. An AC constant current power supply 16 is connected to the induction coil 12 to supply an AC current, a difference in electromotive force induced in the measurement coil 14 is measured by the voltage measuring means 18, and the measured voltage is converted into a temperature.
[0015]
The induction coil 12 includes a first induction coil 20 in which induction wires are wound on the same circumference along the outer periphery of the pipe 10 by half a circumference so that the same current flows in the opposite directions, and the first induction coil is continuous with the first induction coil. And a second induction coil 22 in which a guide wire is wound once along the outer periphery of the pipe away from the first induction coil. Accordingly, the same alternating current is supplied to the first and second induction coils 20 and 22. An induction current flows through the pipe and the conductive fluid by electromagnetic induction due to an alternating current flowing through the first induction coil 20, and an induction current flows through the pipe due to electromagnetic induction due to the same alternating current flowing through the second induction coil 22.
[0016]
The current at a certain moment induced on the pipe surface by the current flowing through the induction coil 12 flows differently between the first induction coil 20 and the second induction coil 22. In the portion of the second induction coil 22, current flows around the piping surface along the coil. On the other hand, in the portion of the first induction coil 20, currents in opposite directions flow along the two induction coils attached with the pipe interposed therebetween, so that the current cannot make one turn, and the inside of the pipe starts from the middle. Flowing through the sodium. The current flow by the first induction coil 20 is indicated by arrows in FIG. In FIG. 2, the induced current flows in the vertical direction in the sodium so that it is divided and merged at the lower part of the pipe and the upper part of the pipe.
[0017]
The differential measurement coil 14 is a half circumference of the first measurement wire and the second induction coil 22 arranged along one half-turn induction wire (indicated by a thick line) of the first induction coil 20. The second measuring wire arranged along the guiding wire (indicated by a thick line) is continuous, and voltage measuring means 18 is provided between both ends of the measuring coil 14. In this case, the measurement coil 14 is attached at a position where the direction is the same when the stroke is written along the induction coil 12. As a result, the electromotive forces induced from the first induction coil 20 and the second induction coil 22 to the measurement coil 14 cancel each other. Further, in a portion parallel to the measurement coil, the electromotive force induced from the first and second induction coils 20 and 22 to the pipe surface is the same in both coils, and flows in the pipes at the first and second induction coil positions. Since the electromotive force induced in the measurement coil by the current acts differentially on each side of the measurement coil, a voltage depending on the electrical resistance in the current path in the pipe appears in the measurement coil 14. From the voltage, the sodium temperature inside the pipe having a correlation with the electric resistance can be obtained.
[0018]
An electrical equivalent circuit of the differential coil method is shown in FIG. Focusing on the relationship between the half circumference of each induction coil and the piping surface, the first induction coil 20 portion and the second induction coil 22 portion are equal. However, since the induced current caused by the first induction coil 20 flows through the sodium in the pipe (see FIG. 2), an impedance corresponding thereto is added. In FIG. 3, the electromotive force E ₄ (vector amount) induced in the measurement coil can be expressed as follows.
[Expression 1]

Here, “·” on the symbol represents a vector, j = √ (−1), ω = 2πf is an angular frequency of a sinusoidal alternating current of frequency f, and is expressed by the first induction coil and the second induction coil. It is assumed that the mutual inductance M ₄ between the pipe and the measuring coil is equal. Further, when the circuit conditions are added to Equation 1 and arranged, the result is as follows.
[Expression 2]

Here, X = ωL is the reactance due to the self-inductance L, and R is the resistance. In addition, the subscript represents N in sodium and S represents the pipe surface.
[0019]
In Equation 2, 2+ (R _N + jX _N ) / (R _S + jX _S ) in parentheses can be considered almost constant because resistance change due to temperature change is extremely small compared to constant 2. Ω ² M ₁ M ₄ I ₁ is also a constant if the current, frequency, and relative arrangement of the coils are constant. From these facts, the component in phase with the current of the induction coil of voltage E ₄ induced in the measurement coil can be related to the sum of the electrical resistance in the current path in the pipe and sodium in the pipe.
[Equation 3]

Here, A is a constant. Since R _N is dependent on the sodium temperature, if grasped based on the relationship between the voltage value and the sodium temperature the number 3 by the calibration test, it is possible to obtain the sodium temperature inside the piping from a voltage value of the measuring coil. However, since R _S depends on the surface temperature, it is necessary to measure the surface temperature separately. In actual calibration, the relationship between the voltage of the measuring coil and the sodium temperature can be obtained by the following simplified formula.
[Expression 4]

Here, t _N and t _S are sodium in the pipe and the temperature of the pipe surface, and A, B and C are constants, and are determined by a calibration test. As described above, it is understood from the examination based on the electrical equivalent circuit that a differential coil type electromagnetic induction temperature measuring method is possible.
[0020]
FIG. 4 is a block diagram showing a configuration example of the temperature measuring device for conductive fluid in a pipe according to the present invention. The output of the AC constant current amplifier 32 is controlled by the output of the oscillator 30, and the output current of the AC constant current amplifier 32 is a voltage drop of a 50 A → 50 mV shunt resistor 34 inserted between the terminal and the output cable by a voltmeter 36. While being measured and monitored, it is supplied to the induction coil 12 provided in the pipe 10. The voltage signal appearing in the measuring coil 14 is amplified by a 1: 100 amplification transformer 38 and then input to the input terminal of the two-phase lock-in amplifier 40 through a coaxial cable. The reference signal for the lock-in amplifier 40 is taken from the output terminal of the AC constant current amplifier 32. The analog signal of the lock-in amplifier 40 is measured by the data recording device 42 together with the temperature data of the pipe surface and the like. The analog signal of the lock-in amplifier 40 can be observed with an oscilloscope 44. Each block of the measuring device can be incorporated in one device, but a number of devices may be combined in accordance with each block.
[0021]
FIG. 5 is an explanatory diagram showing the flow of signals and data. The oscillation part (oscillator) is a part that generates a signal with a constant frequency, and the power amplification part (AC constant current amplifier) supplies an excitation current with a constant frequency and a constant current to the induction coil based on the signal of the oscillation part. A voltage signal (measurement signal) induced in the measurement coil is amplified by the measurement unit, phase-separated, and A / D converted. A reference signal necessary for phase separation is obtained by branching from the output of the power amplifier. Measurement data for calibration is recorded in the calibration section. Recording is repeated several times, and a calibration curve (calibration formula) is created from the correlation between temperature and voltage. The calibration equation may be a linear equation represented by Equation (4). However, when high accuracy is required, the accuracy of the calibration equation is increased by using a polynomial or repeating measurement using the piping temperature as a parameter. The measurement data when actually measuring the temperature is converted into temperature by applying it to a calibration curve (calibration equation) in the comparative calibration unit. The data converted into temperature is displayed and output to an external device by the display / output unit.
[0022]
An example of the measurement result (frequency: 570 Hz) is shown in FIG. The measurement target is liquid sodium in the pipe whose temperature varies periodically. In FIG. 6, “temperature in Na” is a temperature measured by inserting a thermocouple into sodium, “outside surface temperature” is a temperature measured by attaching a thermocouple to the pipe surface, and “electromagnetic induction” is measured by the method of the present invention. The voltage is calibrated using “Na medium temperature” and “outside surface temperature”. From the result of FIG. 6, the calibration result by electromagnetic induction (result by the method of the present invention) almost coincides with “temperature in Na”, and the phase of temperature fluctuation is shifted from “outside surface temperature”. From this, it was confirmed that “electromagnetic induction (temperature determined by)” indicates not the external surface temperature but the sodium temperature.
[0023]
FIG. 7 is a perspective view showing a specific example of the temperature detection unit, which is a packaged example. A shows the state before the pipe is attached, and B shows the state after the pipe is attached. The insulating base body surrounding the outer periphery of the pipe 50 is divided into two, and the mounting bases 52a and 52b are formed. The mounting bases 52a and 52b are formed of a heat insulating material in a semi-cylindrical shape, and also serve as a heat insulating material for piping. An induction coil half 54a is provided on the inner side surface of one mounting base 52a, and an induction coil half 54b and a measuring coil 56 are provided on the inner side surface of the other mounting base 52b. These are combined so as to sandwich the pipe, and are fixed by a clamp or the like. After the mounting bases 52 a and 52 b are installed on the outside of the pipe 50, the lead wire that goes out to the winding coil side is connected to the AC power source, and the induction wire on the other side coil side is connected to each other through the lead wire 58. A thermocouple 60 for measuring the surface temperature of the pipe is also attached to the attachment base 52b.
[0024]
FIG. 8 is an explanatory view showing another example of the method for measuring the temperature of the conductive fluid in the pipe according to the present invention, and is an example of the induced potential difference method. An induction coil 82 is provided on the outer periphery of a pipe 80 through which sodium flows, and a measuring wire 84 is directly connected to the outer surface of the pipe. The induction coil may have the same structure as the first induction coil of the above embodiment. In other words, the induction coil 82 has a structure in which induction wires are wound on the same circumference along the outer circumference of the pipe 80 so that the same current flows in the opposite directions, and an alternating current is supplied from the constant AC current source 84. Is done. An induction current flows through the piping and the conductive fluid by electromagnetic induction by an alternating current flowing through the induction coil 82. Since the current at a certain moment flowing through the induction coil 82 flows in the opposite directions along the two induction coils attached with the pipe 80 interposed therebetween, the current cannot make one round. For this reason, as shown by the arrow, the induced current flows along a route passing through sodium in the pipe from the middle. In FIG. 8, the induced current flows in the vertical direction in the sodium so that it is divided and merged at the lower part of the pipe and the upper part of the pipe. The measuring wire 84 is attached to the pipe surface at a position where the induction coil faces (a position corresponding to a branching / merging point of the induction current) by crimping or spot welding. An alternating current is supplied to the induction coil 82, the voltage between the measuring wires 84 is measured by the voltage measuring means 88, and is converted into a temperature. FIG. 9 shows an electrical equivalent circuit thereof.
[0025]
The relationship between the voltage appearing on the measuring wire and the resistance in the pipe is as follows.
[Equation 5]

In a few 5, E component E _NR resistor and phase of _N, it can be expressed as a function of the resistance R _N sodium in the pipe, it is possible to obtain the sodium temperature from that voltage. When measuring the sodium temperature in the stainless steel pipe, it is possible to obtain the sodium temperature t _N in a simplified manner as follows.
[Formula 6]

A and B in Equation 6 are constants and are undetermined coefficients of the least square method performed in calibration.
[0026]
As can be seen from the above, the induced potential difference type temperature measuring method has an advantage that the sodium temperature can be directly calculated from the measured value, and is a simpler temperature measuring method than the differential coil type described above. However, in the induction potential difference type temperature measurement method, since it is necessary to attach the measurement wire to the pipe by crimping or spot welding, the sodium temperature in the pipe cannot be measured without contact. However, since almost no current flows through the measuring wire, a thin wire can be used, and even if spot welding is used for connecting the measuring wire, the influence on the strength of the pipe is negligible.
[0027]
By the way, in this invention, since the measuring coil is a differential coil in the differential coil method, the influence between the induction coils is offset, but a slight influence can be considered on the current flowing in the pipe. For this reason, it is desirable that the distance between the first induction coil and the second induction coil in the axial direction is such that the electromagnetic influences of the coils are not affected. Although it is related to the accuracy of temperature measurement, as a practical guideline, the distance between the induction wires with respect to the distance between the induction coil and the pipe surface should be several tens of times or more. Further, when the induction coil is wound back, the electric wire passes through the air, but if it is too close to the pipe, the induction current caused by the induction electric wire wound directly around the pipe is canceled. Therefore, a separation distance that does not affect each other is also necessary. In the prototype, both have a separation distance equivalent to the pipe diameter. Note that there is no particular problem when the separation distance is large, but if there is a difference in the piping temperature at each coil position, it causes an error.
[0028]
The frequency of the alternating current supplied to the induction coil is limited by the skin effect of the alternating current in the pipe and the induced electromotive force. In order to pass a current near the center of the pipe, a low frequency with a small skin effect is more advantageous. On the other hand, it is advantageous that the electromotive force induced in the pipe by electromagnetic induction has a higher frequency. In the differential coil method, since it is necessary to generate a sufficient induced electromotive force in the measurement coil, it is necessary to set a slightly higher frequency. When the flow in the pipe is turbulent, the temperature in the pipe is relatively uniform, and the pipe is thin, it can be used up to a frequency of 1 kHz or more. Practically, a frequency of about several hundred Hz to 1 kHz is desirable. As a result of measuring the sodium temperature in a stainless steel pipe having an outer diameter of 76 mm and a wall thickness of 4.7 mm using a prototype, a voltage corresponding to the temperature change of sodium could be measured even at 1.3 kHz. In the case of the induced potential difference method, the voltage drop due to the electrical resistance in the pipe is directly measured by the measurement line, so that it can be used at a relatively low frequency (tens to hundreds of Hz).
[0029]
Any material that does not melt, oxidize, or deteriorate (such as significant resistance change) even when used in high-temperature air can be used for the induction coil, measurement coil, and measurement wire for measuring the sodium temperature in the pipe. Can be used. For example, a metal wire such as a nickel wire, a stainless steel wire, or a brass (brass) wire coated with ceramic long fibers or silica long fibers is useful.
[0030]
In the above embodiment, the induction coil is provided so as to follow the one-stroke route once. However, when it is necessary to obtain a large induced current with a small current, the induction coil is required to follow the same route multiple times. May be provided. There is no difference in use in them. In addition, for the measurement coil, the detection sensitivity can be increased by increasing the number of windings.
[0031]
The induction coil and the measurement coil do not need to be insulated from the pipe, but if there are two or more places connected to the pipe, a current path through the pipe can be created, resulting in a large measurement error. In the worst case, measurement is impossible. As long as the pipe, the electric wire, and the electric wire are completely insulated, no problem occurs. As the electric wire, it is preferable to use an insulated electric wire with a thin coating.
[0032]
In the above-described embodiment, the induction coil has an arrangement in which two electric wires are opposed to each other with a pipe interposed therebetween. In order to restrict the induction current path and increase the measurement accuracy, such a configuration is preferable, but only the coil along the measurement coil functions as a differential coil type temperature measurement method. In that case, the lengths of the first induction coil and the measurement coil may be arbitrarily changed according to the measurement target. Similarly, the induced potential difference type temperature measurement method can be made to function only on one side.
[0033]
The object whose temperature is measured according to the present invention is not limited to sodium, but may be any fluid having electrical conductivity and electrical resistance having temperature dependence. In principle, the present invention can be applied to a substance having conductivity and electric resistance having temperature dependence. However, a coil or a power supply device suitable for the measurement target is used.
[0034]
By the way, conventionally, non-destructive inspection inside a thick-walled pipe using an alternating current is difficult because the current concentrates on the surface of the sample due to the skin effect. When the induction coil is arranged so that the induced current crosses the sample as in the method of the present invention, nondestructive inspection is facilitated. Therefore, the method of causing an induced current to flow through the induction coil as in the present invention can be applied to nondestructive inspection.
[0035]
【The invention's effect】
As described above, the present invention is a method and apparatus for measuring the temperature of a conductive fluid in a pipe that causes a current to flow through the pipe and the inside conductive fluid by electromagnetic induction, so that a current electrode for supplying a large current is not necessary. Therefore, since there are no large-scale welded portions in the piping, stress concentrated portions are not generated in the piping, and safety and reliability in a high temperature environment are remarkably improved.
[0036]
The differential coil type can be non-contact inspection, so it can be attached and detached, and the measurement location can be moved easily and high-speed inspection is possible compared to the induction potential difference method, which requires the measurement wires to be connected to the piping. . Further, if an insulating material such as a coil is made heat resistant, it can be applied to inspection in a high temperature environment.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of a method for measuring the temperature of a conductive fluid in a pipe according to the present invention.
FIG. 2 is an explanatory diagram showing the flow of current.
FIG. 3 is an electrical equivalent circuit diagram thereof.
FIG. 4 is a block diagram showing an example of the device configuration.
FIG. 5 is an explanatory diagram showing the flow of signals and data.
FIG. 6 is a graph showing an example of the measurement result.
FIG. 7 is a perspective view showing a specific example of a temperature detection unit.
FIG. 8 is an explanatory diagram of another embodiment of the method for measuring the temperature of the conductive fluid in the pipe according to the present invention.
FIG. 9 is an electrical equivalent circuit diagram thereof.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Piping 12 Inductive coil 14 Measuring coil 16 AC constant current power supply 18 Voltage measuring means 20 1st induction coil 22 2nd induction coil

Claims (4)

In the method of measuring the temperature of the conductive fluid existing in the pipe using the temperature dependence of the electrical resistance of the conductive fluid,
On the same circumference along the outer circumference of the pipe, the induction wire is wound half a turn at a time, and the same current flows in the opposite direction to the first induction coil. An induced current flows through the fluid, and the same alternating current as that of the first induction coil is applied to the second induction coil that circulates the induction wire along the outer periphery of the pipe away from the first induction coil. Inducted current flows through piping by electromagnetic induction, and the difference in electromotive force induced in the measuring coil by both induced currents is measured, and the measured voltage is converted to temperature. A method for measuring the temperature of a conductive fluid. A first induction coil wound around the same circumference along the outer circumference of the pipe of the conductive fluid, and the same current flows in the opposite direction, and is continuous with the first induction coil and A second induction coil that circulates an induction wire along the outer periphery of the pipe away from the one induction coil, and a pipe and a conductive fluid by electromagnetic induction by supplying an alternating current to the first and second induction coils. An AC constant current power source for passing an induction current through the wire, a measurement wire arranged along one half-turn winding induction wire of the first induction coil, and a half-circumference induction wire arranged along the second induction coil A temperature measurement device for a conductive fluid in a pipe, comprising a differential measurement coil in which the measurement wires are continuous and a voltage measurement means provided between both ends of the measurement coil. In the method of measuring the temperature of the conductive fluid existing in the pipe using the temperature dependence of the electrical resistance of the conductive fluid,
Inductive current is generated in the conductive fluid by electromagnetic induction by supplying alternating current to an induction coil in which the same current flows in the opposite direction around the circumference of the pipe on the same circumference. A method for measuring a temperature of a conductive fluid in a pipe, wherein the voltage generated by the electrical resistance of the conductive fluid inside the pipe is measured and the measured voltage is converted into a temperature. Inductive coils are wound around the same circumference along the outer circumference of the conductive fluid pipe, and the same current flows in the opposite direction by winding the induction wires halfway, and electromagnetic induction by supplying alternating current to the induction coil An AC constant current power source that sends an induction current to the pipe and the conductive fluid by means of a measuring wire connected between the outer peripheral surface position of the piping corresponding to the branching point and the confluence of the induced current, and between the two measuring wires An apparatus for measuring a temperature of a conductive fluid in a pipe having voltage measuring means.

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