Method and apparatus for monitoring unburned particulate accumulation in {HEAD ~ the exhaust duct} of {TAIL ~ a combustion system} 
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Method and apparatus for monitoring unburned particulate accumulation in { HEAD ~ the exhaust duct } of { TAIL ~ a combustion system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL