| 摘要 |
An indication that a motor has reached full speed operation is produced by generating an up to speed signal based upon measurement of the phase angle between the voltage applied to the motor and electric current flowing to the motor. A motor up to speed detector has; means for connecting an electric motor to an electric power source; means for measuring the time interval between the event of voltage applied to the motor crossing zero and the event of current flow to the motor reaching zero to obtain a measured value of current lag; and, means for comparing successive measured values of the current lag at predetermined time intervals after electric power is applied to the motor as the motor is started, and for generating a signal indicative that the motor has reached an up to speed condition in the event that successive measured values of the current lag increase. The up to speed signal is used to increase the voltage applied to the motor during a soft start in the event that the motor reaches full speed before the voltage applied to the motor reaches line voltage.
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