If {HEAD ~ differential pressure} across the filter is to be measured and a clogging abnormality is to be detected based on the measurement value unlike the above described aspect of the present invention, a sensor for measuring {TAIL ~ the differential pressure} is necessary 
If { HEAD ~ differential pressure } across the filter is to be measured and a clogging abnormality is to be detected based on the measurement value unlike the above described aspect of the present invention , a sensor for measuring { TAIL ~ the differential pressure } is necessary
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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH