In Situ Calibration of a Permanent-Magnet Sodium Flowmeter Without a Bluff Body Based on Multi-Pair Electrode Signal Subtraction

The in situ calibration of a large-diameter permanent magnet sodium flowmeter (PMSF) without a bluff body relies on only turbulent pulsations, and the signal is weak and random, resulting in large repeatability errors of flow measurements. Moreover, the flow field is easily deformed by the Lorentz force, leading to a large nonlinearity error. In this article, a method of multi-pair electrode signal subtraction in the same direction (MPES-SSD) is proposed for eliminating the background noise and reducing the repeatability error. The low-frequency signal can be attenuated to make the cross correlation flow velocity closer to the standard flow velocity, so as to correct the nonlinearity error. A signal-to-noise ratio (SNR) based on the standard deviation of the amplitude of the cross-power spectral density is proposed to compare the signals before and after MPES-SSD. In situ calibration experiments with a DN150 PMSF without a bluff body were conducted to verify the effectiveness of the method. Combined with the low-frequency suppression method proposed previously by the present authors, the maximum relative error is reduced to no more than +/- 2.0%.