A sensor is held in a substantially fixed position relative to {HEAD ~ the insulation} in {TAIL ~ the cavity} 
A sensor is held in a substantially fixed position relative to { HEAD ~ the insulation } in { TAIL ~ the cavity }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL