LOAD LIMITER

The limiter is used for overload protection of devices driven by an electric motor and used in electric hoist, lift and elevator engineering, etc. It is not affected by the fluctuations of the mains voltage, has facilities for multistage and flexible tuning, is convenient for assembly and operation, it is also oscillation-stable and it increases sensitivity. The limiter consists of a current sensor (1) supplying a signal proportional to the current across the motor, and voltage sensor (2) supplying a signal proportional to the emf of the stator winding of the motor, the outputs of which are coupled to the inputs of a multiplier unit (3). The inputs of one or more filters (4) are coupled to the output of unit (3), in series or in parallel. The output of every filter is connected to the input of a respective comparison unit (5). When the filters and the comparison units are more than one, the outputs of the comparison units are connected into a common point. The limiter also has a correction unit (6), to the input of which voltage is fed, proportional to the mains voltage supplying the motor. The output of unit (6) is connected to an additional input of unit (3) or an additional input of each and every comparison unit (5). 5 claims, 5 figures