Patent ID: 8294410

Claim:
A method for failsafe monitoring of a motor ( 10 ) with a three-phase control comprising the steps: detecting current and voltage profiles, as provided to a motor ( 10 ) by drive electronics ( 12 ); determining a load speed (n L ) of the motor ( 10 ) using the delected current and voltage profiles; and failsafe switching off of the motor ( 10 ) when the determined load speed (n L ) does not correspond to a preset desired speed within a framework of preset tolerances; wherein determining the load speed (n L ) takes place by calculating an observer model with reference to the detected current profile (I mess , I eff ), to the detected voltage profile (U mess , U eff ), to a frequency (f FU , f sync ) preset by the three-phase control and characteristic data of the motor ( 10 ); wherein the motor is an asynchronous motor and determining the load speed takes place with reference to the formula: n =n syn (1− s ) wherein n sync is the synchronous speed and s is the slip; and wherein a tilting torque (M k ) and a tilting slip (s k )is calculated from characteristic data of the motor ( 10 ) and the load torque (M L ) is determined together with the slip (s) and the failsafe switching off takes place on exceeding a limit value.