Apparatus for monitoring {HEAD ~ the accumulation} of particulates on {TAIL ~ the lining} of an exhaust duct or the like for a combustion device, comprising: 
Apparatus for monitoring { HEAD ~ the accumulation } of particulates on { TAIL ~ the lining } of an exhaust duct or the like for a combustion device , comprising :
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH