During reversal {HEAD ~ the servo system} which is driven into saturation senses the occurrence of zero motion of the drive mechanism and reverses {TAIL ~ the direction} of energization of the electromagnetic drive 
reverses
During reversal { HEAD ~ the servo system } which is driven into saturation senses the occurrence of zero motion of the drive mechanism and reverses { TAIL ~ the direction } of energization of the electromagnetic drive
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH