Correct sensing, transmission and display of revolution per minute (rpm) speed of shafts is very important for smooth running and control of induction motors. Speed sensors sense shaft speed. Therefore, sensors are a critical component in a motor control system. When speed sensors are used in closed loop for feedback in a motor control system, it enables the designer to adjust the stator voltage/frequency relationship to realize the desired speed with minimal losses and improve the motor’s reliability by detecting fault conditions that may damage the motor. RPM sensors that can be used to feedback information to microcontroller include shaft encoders, proximity sensors, photoelectric sensors, sitrans WS300, quadrature encoder and Hall Effect tachometer. When choosing sensors, it is necessary to make sure the resolution of the sensor is appropriate for the speed of the shaft. Two factors that affect the quality of speed data (which are in form of pulses) are number of pulses per revolution (PPR) of the shaft and symmetry of the pulses.
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