
81
Turntables
Motors, synchronous/asynchronous In the asynchronous or
induction motor, current is induced into the rotor windings.
Speed is voltage and load-dependent which permits eddy-
current braking control but has poor speed stability. The
synchronous motor has a permanent magnet rotor that keeps
step with a rotating field generated by the stator, by copper-
ring shading or phase-splitting alternate poles. Speed depends
on pole number and mains frequency. A 4-pole motor runs at
1500 r.p.m. at 50 Hz; and so has a vibration/rotation frequency
of
25
Hz with harmonics at 50 Hz and 75 Hz.
Multi-pole motors Up to 24-pole motors have been
produced ...