Pump device and methods for operating a pump for liquids

The invention relates to methods for operating a liquid pump (6) having a rotor (6b, 6c, 34), in particular a blood pump, for conveying liquids, wherein the viscosity of the conveyed liquid, in particular blood, is determined while taking into account measured values of operating parameters of the pump, wherein the pump is operated in a predetermined region (26, 26') of a family of characteristiccurves (20, 21, 22), which family of characteristic curves links at least two operating parameters of the pump to each other, and wherein, in this region, at least three parameters of the pump are sensed and are taken into account in order to determine the viscosity. Because of the operation in a predetermined region of a family of characteristic curves, the viscosity of the conveyed liquid can bedetermined in addition to the volumetric flow rate through the pump and the pressure difference across the pump when an appropriate selection is made there from a sufficient number of sensed operating parameters. For this pur