Patent ID: 8310196

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 detected 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 the step of 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 determination takes place with reference to the formula: n L = 1 p * f FU * 60 ⁢ ⁢ s ⁢ / ⁢ min - I mess I n * f FU U mess * U N f N * ( n syn - n n ) and where I n nominal current, f N nominal frequency, U N nominal voltage, n syn synchronous speed, n n nominal speed, n L load speed, and p pole pair number are stored as the characteristic data of the motor ( 10 ).