Patent ID: 6918307

Claim:
A device for on-line monitoring of flow quantities in a system comprising a flow-creating device such as a pump or a fan, comprising: means for obtaining a measure of a torque of said flow-creating device; means for obtaining a measure of a rotational speed of said flow-creating device; and means for determining a value of a flow rate through said flow-creating device, means for calculating a value of a mechanical input power of said flow-creating device, connected to said means for obtaining a measure of a torque and said means for obtaining a measure of a rotational speed; storage means for storage of data representing a predetermined relation between mechanical input power and flow rate through said flow-creating device; and whereby said means for determining a value of a flow rate is connected to said means for calculating a value of a mechanical input power and to said storage means; said means for obtaining a measure of a rotational speed in turn comprising: at least one current sensor for measuring an input current of an electric motor, said electric motor giving said torque to said flow-creating device at least one voltage sensor for measuring an input voltage over said electric motor; and means for determining a value of said rotational speed, connected to said current sensor, said voltage sensor and said storage means; said storage means being further arranged for storage of data representing a predetermined relation between input current and input voltage of said electric motor and rotational speed of said electric motor.