Uncertainty Evaluation Method of Rotating Element Current Meters

Abstract

The main expression of the calibration results of rotating element current meter is based on the approximate linear relationship between rotation rate and velocity, and the uncertainty evaluation method is not perfect. A technical scheme with hydraulic pitch as the result of calibration is studied, and the uncertainty can be devided to standard current velocity, rotation rate and hydraulic pitch. The measurement and uncertainty evaluation method of unit velocity and background velocity are studied based on the water velocity calibration platform. The calculation method of unit rotation rate for synchronous equidistant trigger speed measurement is proposed, and the uncertainty evaluation of unit rotation rate is realized through the self-developed standard rotation rate experimental platform. The uncertainty evaluation method for the laboratory calibration and onsite measurement results of current meter is proposed, based on the analysis of the calibration results of hydraulic screw pitch and the relationship between the calibration results and environmental factors. The results show that, the uncertainty of water flow velocity standard device is 0.04%v+2mm/s, the background velocity is the main uncertainty source in laboratory calibration results. After reasonable correcting the environmental impact of positive hydraulic pitch, the change of mechanical properties caused by long-term use is the main source of uncertainty.