The 3-phase oscilloscope as an harmonic analyzer

The distinguishing feature of the 3-phase oscilloscope is its deflection system which provides deflections along three axes separated 120 degrees in space. When sinusoidal 3-phase currents flow in such a deflection system a rotating flux field of constant magnitude and constant angular velocity is produced as in a 3-phase induction motor. The flux field intensity is proportional to the maximum instantaneous current and the rate of revolution is equal to the frequency. This rotating magnetic field causes the beam spot of the cathode-ray tube to describe a circle having a diameter proportional to the current magnitude.