A multiphase vortex flowmeter system determines the gas-to-liquid ratio (GLR) and flow rates from a well producing multiphase gas, oil and water by detecting the frequency and amplitude of vortices shed in a vortex flowmeter. In particular, the phase of the flow can be identified by detecting the change in the frequency of the vortices with respect to time, and the amplitude of the vortices. Based on the phase, the flow rates of liquid and gas can be calculated. As a feedback technique, these calculated values can be tuned by comparison with actual GLR and flow rates recorded for the well by a test separator.

The sensor comprises: a flat deformation element including first and second planar surfaces; a sensor lug extending starting from the first surface; a connection sleeve extending from the deformation element; a transducer element, which is arranged within the connection sleeve and contacts the first surface with a contact surface, for generating an electrical sensor signal representing temporally changing movements of the sensor lug and/or temporally changing deformations of the deformation element; and a fastener positioned within the connection sleeve and mechanically connected thereto, for fixing the transducer element in the connection sleeve, wherein the fastener includes a spring assembly with at least two stacked disk springs, which are elastically deformed by exerting a pressing force which holds the transducer element against the deformation element.