| 摘要 |
PURPOSE:To enable rotating speed to be switched, without changing open gain of speed control system, by providing plural frequency-detecting coils which are freely switched by a selecting step. CONSTITUTION:By providing plural speed detectors 1a, 1b and 1n which detect respectively different frequencies in proportion to revolution corresponding to the identical revolution of an electric motor 6, selection is made by switches s1, s2 and sn. An f-v converter 2 converts a selected speed detector's output frequency signal to a DC voltage signal, and a comparator 4 supplies a driving circuit 5 with a differential voltage between the DC voltage signal and a reference voltage. By switching plural speed detectors in this manner, it is possible to easily change revolving speed of the electric motor and also to prevent open gain on speed control system from being changed at the time of switching of the revolving speed, and therefore, stability of speed control system can be maintained. |
