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In the case where variable RPM (more than two desired settings for RPM) are required for universal motors, the centrifugal mechanism of RPM control is used. This speed control method is used for universal motors in applications like home food and drink mixers. The setting of RPM is made by a centrifugal switch located inside the motor as shown in the diagram below. This centrifugal switch can be controlled or adjusted by means of an external lever. If the motor speed rises above that set by the lever, the centrifugal device or switch opens two contacts and inserts a resistance R in the power circuit to the motor, which causes the motor speed to decrease. If the motor runs too slowly, the centrifugal device will close the two contacts and short circuit the resistance so that the motor speed rises. This process is repeated so rapidly that variations in speed are not noticeable. A resistance is connected across the centrifugal switch or device to perform this function. A capacitor C is used across the contact points in order to reduce sparking produced due to the opening and closing of these points. Moreover, it prevents pitting the of contacts.
... TP.HCM, ngày… tháng 12 năm 2020 Giáo viên hướng dẫn Student: Cong Trung _ Chang Hee feee.hcmute.edu.v n FOREWORD... lecturing us and giving out valuable lessons and experiments Especially lecturer Nguyen Phan Thanh for helping us about Universal Motor and guiding us through Automatic Electric Drive project... for our project and once again we would like to express our gratitude to lecturer Nguyen Phan Thanh for giving us such a valuable lesson about Universal Motor Student: Cong Trung _ Chang Hee feee.hcmute.edu.v