In-situ calibration of permanent magnet flow meters in PFBR using noise analysis technique

Abstract

In Fast Breeder Reactor sodium circuits, permanent magnet flow meters (PMFM) are extensively used to measure the liquid sodium flow rate. The performance of PMFM can degrade with respect to time due to various reasons. This degradation results in reduction in output voltage and affects flow meter stability. The distortion of the magnetic field in the large diameter flow meters makes its characteristics nonlinear. Further, the performance of the flow meter is also affected by vibrations, shocks, temperature and change of reluctance within the magnetic circuit. Hence, it is desirable to calibrate the PMFM at periodic time intervals for ensuring accuracy and stability. However, it is very difficult and almost impossible to calibrate large size flow meters once installed in the system under actual flow conditions in a sodium test loop. Therefore, it is necessary to calibrate the flow meter in-situ without disturbing its normal operating conditions.Experiments were carried out in different sodium loops in Fast Reactor Technology Group (FRTG) and Fast Breeder Test Reactor (FBTR) with permanent magnet flow meters of different sizes to develop an in-situ calibration procedure. Cross-correlation technique is studied and the flow rate is estimated from the transit time with a deviation of ±5.5%, which is comparable with that of calibration of the flow meter in actual sodium test loop. In this paper, in-situ calibration of PMFM is discussed with experimental details, data acquisition, cross-correlation technique and the results obtained.