Individual sensors sense the magnitude of {HEAD ~ a variable power component} from each power source and provide {TAIL ~ a signal} proportional thereto 
Individual sensors sense the magnitude of { HEAD ~ a variable power component } from each power source and provide { TAIL ~ a signal } proportional thereto
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH