| 摘要 |
PURPOSE:To enable operation to be kept without the generation of overcurrent interruption even at the time of overload operation, and improve the reliability of an equipment, by arranging a primary current sensor and a primary current estimating means, and by reducing frequency before the overcurrent interruption. CONSTITUTION:By a current differentiator 15, the change of the value of primary current from a current sensor 14 for detecting the primary current of a motor 13 is found. By a timer 16, the working time of the current differentiator 15 is controlled. By an upper limit current comparator 17 identifying whether or not an estimated current value from the current differentiator 15 is of upper limit current, the values are compared with each other, and the output of the output signal of its result is directed to an operation speed retainer 10. Then, before overcurrent interruption, frequency can be reduced, and so a constant current value can be set to be an upper limit current value or less, and without the generation of the overcurrent interruption, even at the time of overload operation, operation can be kept. |
