After {HEAD ~ the head portion} 46 is sensed by {TAIL ~ the magnetic sensor} means 58, a signal is sent to an active controller 50 
is sensed by
After { HEAD ~ the head portion } 46 is sensed by { TAIL ~ the magnetic sensor } means 58 , a signal is sent to an active controller 50
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH