Validation of vortex flowmeters

A vortex-shedding flow meter produces an approximately sinewave signal whose average frequency is proportional to volumetric flow rate. The frequency of vortex shedding varies over a large range (up to 1:100), depending on the size of the flow meter. The conventional frequency-estimation method-a zero-crossing algorithm-fails at low flows, where the signal:noise ratio is poor. The paper describes a dual phase-locked loop structure that tracks the frequency over the flowmeter´s full range with improved accuracy. The lock indicators associated with each PLL provide the SEVA metrics.