| 摘要 |
A hall effect sensor (13) detects the passing of magnets (12) on the output shaft of the motor (1). The frequency of the sensor output is proportional to the rotation speed of the shaft . This signal is fed to a microprocessor (11) and the speed compared with the demanded speed input (Sg). The difference is used to control the duty cycle of a traic (8) which chops the current fed to the motor. A null-crossing detector (10) synchronizes the triac switching operation to the mains frequency.
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