means coupled with said generating means for producing an indication of when said electrical signal reaches a preselected value corresponding to {HEAD ~ a prescribed accumulation} of {TAIL ~ particulates} on said lining 
of
means coupled with said generating means for producing an indication of when said electrical signal reaches a preselected value corresponding to { HEAD ~ a prescribed accumulation } of { TAIL ~ particulates } on said lining
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH