Patent ID: 7349814

Claim:
A method for measuring a flow in a pump system, in which a liquid flow is generated by means of a pump and the pump is actuated by an electric drive, in which the rotation speed of an alternating-current motor is controlled with a control unit, comprising: measuring ( 402 ) a pump power (P) in the pump system, measuring a rotation speed (v) of the pump, measuring ( 504 ) a static pressure (H s ), setting an estimate of a dynamic pressure (H d ) to a pre-estimated constant value, determining ( 506 ) an estimate of a total pressure (H) on the basis of the static pressure, a difference (Δh) of height between static pressure sensors, and the estimate of the dynamic pressure, determining a first estimate ( 410 , 416 ) of the liquid flow on the basis of the measured pump power (P) and rotation speed variables, determining a second estimate ( 514 , 516 ) of the liquid flow on the basis of the estimate of a total pressure (H) and rotation speed variables, determining a flow measurement result by a logical selection or any other predetermined function on said first estimate of the liquid flow and said second estimate of the liquid flow, determining ( 520 ) a new estimate of a dynamic pressure (H d ) on the basis of the flow measurement result, re-determining the estimate of a total pressure (H) on the basis of the static pressure, the difference (Δh) of height between the static pressure sensors, and the new estimate of the dynamic pressure, re-determining the second estimate of the liquid flow on the basis of the estimate of a total pressure (H) and rotation speed variables, and re-determining the flow measurement result by a logical selection or any other predetermined function on said first estimate of the liquid flow and said second estimate of the liquid flow.