| 摘要 |
<p>The present invention relates to an apparatus and method for determining the speed of a motor, generator or alternator, more particularly for determining the speed of an alternating current (AC) induction motor. The invention overcomes problems associated with previous devices by providing a speed monitoring device that is readily retrofitted to an existing motor and comprises: a means for superimposing a test signal onto an input voltage, which voltage in use is applied to at least one winding of the stator of a motor (the test signal is at a frequency substantially equal to the rotor frequency); a means for varying the frequency of the test signal so that it varies from a minimum frequency to a maximum frequency; and a current monitor for monitoring a resultant current, in said at least one stator winding; and deriving from said resultant current a signal indicative of the rotor frequency.</p> |
