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