When the temperature is within {TAIL ~ a normal operating range} in which {HEAD ~ unburned particulates} accumulate on the duct, the digital pulses are accumulated in a first counter, the value of which count corresponds to the duration of time that the sensed temperature remains within the normal operating range 
in
When the temperature is within { TAIL ~ a normal operating range } in which { HEAD ~ unburned particulates } accumulate on the duct , the digital pulses are accumulated in a first counter , the value of which count corresponds to the duration of time that the sensed temperature remains within the normal operating range
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH