| 摘要 |
PURPOSE:To facilitate maintenance and eliminate a movable part to elongate the life of an AC motor, by monitoring the load of the motor by the motor itself utilizing it as a sensor. CONSTITUTION:The wave forms of an input voltage V and an input current I for an AC motor are shaped by filters 10A, 10B and are multiplied by a multiplier 11. The output of the multiplier V.I.cos phi is multiplied by an efficiency etaby an efficiency setter 12 and a shaft output 3<1/2>.V.l.cos phi.eta is obtained as the output 20 of the setter 12. This value is compared with the set value of a high-load setter 13 and a high-load output relay circuit 14 is operated. The voltage V and the current I are outputted as the numbers of pulse, proportional to a phase difference phi, by an AND logic 16 while the number of pulse is counted by a counter 17. The value of counting is compared with a light-load set value in a digital comparator 18 and is made to operate together with a light-load output relay 19. |
