Answer: B
Analysis: The number of rotor teeth of the three-phase reaction stepper motor is 50, and its pitch angle is 120° electric angle.
Stepper motor is a digital motor whose number of rotor teeth is related to the number of stator poles. In the three-phase reaction stepper motor, the common number of stator poles is 2, 3, 4, 5, 6, 8, 12, etc., of which the motor with a power of 2 poles has high torque and accuracy. Therefore, according to the number of rotor teeth of 50, the power of 2 poles of the stator can be calculated, that is, 8.
Since the number of stator poles is 8, the motor rotor needs to pass through 8 electrical angles per revolution, that is, 360° electric angle / 8=45° electric angle. The pitch angle refers to the electrical angle between the adjacent two rotor teeth, so the pitch angle is 45° electric angle / 50 teeth = 0.9° electric angle.
Therefore, the pitch angle of this stepper motor is 120° electric angle.