| 摘要 |
PURPOSE:To simplify the detection of overload by setting an inverter at an output voltage with which only the torque less than a rated value is outputted with the low speed frequency and compulsorily operating the inverter at a low speed for a prescribed time in hoisting operation and detecting the existence of the revolution of an electric motor during this time. CONSTITUTION:Operation instruction is carried out by a two-stage motion type pushing button switch, and a slow speed pushing button switch is set ON at all times in the aspect of structure. The instruction is inputted in the form of the slow speed instruction and high speed instruction to an inverter through a control part. The inverter starts the frequency output by the instruction. Acceleration at a breath to a high speed is not carried out even for a high speed instruction, and the operation with a low speed set frequency is carried out for a prescribed time. When the revolution of an electric motor is detected during this time, the rated load or less is judged in case of revolution, while overload is judged in case of standstill. Accordingly, the function of the inverter can be utilized without adding special devices, and the detection of overload can be executed at a low cost. |
