The Acceleration-Oscillogram Method of Motor-Torque Measurement

The need for an improved method of measuring starting torque of large induction starting synchronous motors as compared to the power input and dynamometer methods, has led to the use of the acceleration oscillogram. A low ripple, permanent magnet type d-c generator is driven by the motor, and traces a time-speed oscillogram, from which acceleration, and the torque producing it, may be calculated. Comparative torque tests, at full and reduced voltage, made by this and the other motor showed the definite advantage of the acceleration tests in combined convenience and accuracy. Interesting facts about synchronous motor starting torques, not accurately shown by previous tests, have been brought to light. The acceleration or deceleration oscillogram is also applied to the measurement of torques or losses of very small high-speed motors by using other methods of rotation indication, involving no loading of the motor.