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UBC Theses and Dissertations

Measurement of induction motor speed from induced slip frequency signal Cai, Ji-Yuan


A method to detect the slip of a three-phase or single-phase induction motor and hence determine the motor speed is proposed. A pick-up coil is placed in close proximity to the motor and by suitable amplification and filtering of the weak slip frequency signal, the slip frequency signal component is isolated for the speed measurement. No device needs to be attached to the motor shaft. Experimental results from four test induction motors show that the proposed method of speed measurement is fully feasible and applies to normal loads, i.e., for slip less than 13% with considerable accuracy. Therefore, even the speed of sealed induction motor such as those used in refrigerators can be easily measured.

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