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高精度液位測定装置に用いられる水晶振動型差圧センサの保守管理; 精度の維持及び故障時の兆候

The Way of maintenance to keep log-term accuracy and a sign of malfunction of digiquartz differential pressure transducer used for accurate level measurement system

向 泰宣; 小磯 勝也; 中村 仁宣; 細馬 隆  ; 吉元 勝起; 林 宏幸*

Mukai, Yasunobu; Koiso, Katsuya; Nakamura, Hironobu; Hosoma, Takashi; Yoshimoto, Katsunobu; Hayashi, Hiroyuki*

エレクトロマノメータ(ELTM)は、計量管理/保障措置及び運転管理の目的で、計量槽の液位/密度/液量を高精度で測定する装置である。JAEAでは、プルトニウム転換技術開発施設での槽の初期校正(1982)以来、水晶振動型差圧センサを用いたELTMを開発・実用化し、直近15年間の校正・測定結果として、基準圧力との差の$$sigma$$$$pm$$2Pa、測定密度と分析密度の差の$$sigma$$$$pm$$0.002g/cm$$^{3}$$の精度を維持している。しかしながら、これまでに経験したことのない測定値のドリフトを2008年に確認した。調査の結果、正常なセンサでは変化が認められないT$$_{0}$$値(差圧=0の振動周期)が、不具合を生じたセンサでは約7%変化していた。これは経年劣化によるものであることから、当該センサの交換時期を判断するうえで、T$$_{0}$$値の監視が有効であると言う重要な知見を得た。本報告では、実際に得られたELTMの長期的測定精度及び当該センサの交換を含めた保守管理方法について述べる。

Electro manometer (ELTM) is a device to measure accurately level, density and volume in an accountability tank for the purpose of nuclear materials accountancy, safeguards and operational control. JAEA have developed and put the ELTM using digiquartz differential pressure transducer into practical use at plutonium conversion development facility since initial tank calibration in 1982. As a result of calibrations and measurements in the last 15 years, the sustainable measurement accuracy is $$pm$$2 Pa as a sigma of difference from the standard pressure and $$pm$$ 0.002 g/cm$$^{3}$$ as a sigma of difference from the solution density analytically determined. However, a drift of data we have never experienced was found in 2008. After investigations, a characteristic value T$$_{0}$$ (period of vibration at zero pressure) which is stable in normal state had changed around 7% at the drift. This was the result of aging, so it was found that monitoring of T$$_{0}$$ value was the very effective information to know the timing of replacement of the transducer. We will present the long-term measurement accuracy of ELTM practically achieved and the way of maintenance including a replacement of the transducer.

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