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

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

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 2 Pa as a sigma of difference from the standard pressure and 0.002 g/cm 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 (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 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.