{HEAD ~ One or more sensors} sense {TAIL ~ one or more welding conditions} before the weld is initiated 
sense
{ HEAD ~ One or more sensors } sense { TAIL ~ one or more welding conditions } before the weld is initiated
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH