| 摘要 |
This invention concerns a safety device which is used in particular for sliding doors in cold-rooms. The function of the safety device is based on measuring the dynamic input power to the operating motor. The safety device has a three-phase motor and a three-phase inverter bridge 7,9 for control of the motor. The safety unit according to the invention further comprises devices 10,11,12 for generating an analogue voltage in relation to the input power of the motor, an amplification and active low-pass filter unit 14, an analogue memory 15, a Zener diode 18 and a voltage comparator 23. The voltage comparator 23 is connected on the one hand to the analogue memory 15 and on the other hand to the Zener diode 18. This connection is implemented so that when the voltage after the unit 14 minus the voltage 18 of the Zener diode exceeds the voltage in the analogue memory 15 the voltage comparator 23 generates an output signal 32. <IMAGE> |
